Refine Search

New Search

Results in Journal Frontiers in Chemistry: 3,890

(searched for: journal_id:(162255))
Page of 78
Articles per Page
by
Show export options
  Select all
Arbab Ali, Tufail Shah, Rehmat Ullah, Pingfan Zhou, Manlin Guo, Muhammad Ovais, Zhiqiang Tan,
Published: 13 July 2021
Frontiers in Chemistry, Volume 9; doi:10.3389/fchem.2021.629054

Abstract:
Diverse applications of nanoparticles (NPs) have revolutionized various sectors in society. In the recent decade, particularly magnetic nanoparticles (MNPs) have gained enormous interest owing to their applications in specialized areas such as medicine, cancer theranostics, biosensing, catalysis, agriculture, and the environment. Controlled surface engineering for the design of multi-functional MNPs is vital for achieving desired application. The MNPs have demonstrated great efficacy as thermoelectric materials, imaging agents, drug delivery vehicles, and biosensors. In the present review, first we have briefly discussed main synthetic methods of MNPs, followed by their characterizations and composition. Then we have discussed the potential applications of MNPs in different with representative examples. At the end, we gave an overview on the current challenges and future prospects of MNPs. This comprehensive review not only provides the mechanistic insight into the synthesis, functionalization, and application of MNPs but also outlines the limits and potential prospects.
Santiago Ruiz, , María Sagrario Sánchez, María Cruz Ortiz
Published: 13 July 2021
Frontiers in Chemistry, Volume 9; doi:10.3389/fchem.2021.681958

Abstract:
In the context of binary class-modelling techniques, the paper presents the computation in the input space of linear boundaries of a class-model constructed with given values of sensitivity and specificity. This is done by inversion of a decision threshold, set with these values of sensitivity and specificity, in the probabilistic class-models computed by means of PLS-CM (Partial Least Squares for Class-Modelling). The characterization of the boundary hyperplanes, in the latent space (space spanned by the selected latent variables of the fitted PLS model) or in the input space, makes it possible to calculate directions that can be followed to move objects toward the class-model of interest. Different points computed along these directions will show how to modify the input variables (provided they can be manipulated) so that, eventually, a computed ‘object’ would be inside the class-model, in terms of the prediction with the PLS model. When the class of interest is that of “adequate” objects, as for example in some process control or product formulation, the proposed procedure helps in answering the question about how to modify the input variables so that a defective object would be inside the class-model of the adequate (non-defective) ones. This is the situation illustrated with some examples, taken from the literature when modelling the class of adequate objects.
, Wenjun Lan, Chenyan Wu, Qiang Fei
Published: 12 July 2021
Frontiers in Chemistry, Volume 9; doi:10.3389/fchem.2021.695628

Abstract:
In this study, 17 novel pyrimidine derivatives containing an amide moiety were synthesized. Then their in vitro antifungal activities against Botryosphaeria dothidea (B. dothidea), Phomopsis sp., and Botrytis cinereal (B. cinereal) were determined. A preliminary biological test showed that compounds 5-bromo-2-fluoro-N-(2-((2-methyl-6-(trifluoromethyl)pyrimidin-4-yl)oxy)phenyl)benzamide (5f) and 5-bromo-2-fluoro-N-(3-((2-methyl-6-(trifluoromethyl)pyrimidin-4-yl)oxy)phenyl)benzamide (5o) exhibited higher antifungal activity against Phomopsis sp., with an inhibition rate of 100% compared to that of Pyrimethanil at 85.1%. In particular, compound 5o exhibited excellent antifungal activity against Phompsis sp., with the EC50 value of 10.5 μg/ml, which was even better than that of Pyrimethanil (32.1 μg/ml). As far as we know, this is the first report on the antifungal activities against B. dothidea, Phomopsis sp., and B. cinereal of this series of pyrimidine derivatives containing an amide moiety.
Ping Li, Xiang-Ying Sun, Jiang-Shan Shen
Published: 12 July 2021
Frontiers in Chemistry, Volume 9; doi:10.3389/fchem.2021.713104

Abstract:
In this work, a facile one-pot hydrothermal route was employed to synthesize a series of fluorescent carbon dots (CDs) by using 20 natural amino acids, respectively, as the starting materials. It was found that the CDs synthesized using phenylalanine could possess the intrinsic peroxidase-like activity that could effectively catalyze a traditional peroxidase substrate like 3, 3’, 5, 5’- tetramethylbenzidine (TMB) in the presence of H2O2 to produce a blue solution; thereby, a catalytic sensing system for H2O2 has been developed. On the basis of this catalytic reaction, together with the fact that glucose oxidase (GOx) can catalyze the hydrolysis of glucose to generate H2O2, a sensitive catalytic sensing system for glucose could be further established. Furthermore, based on this catalytic reaction, taken together with the two enzymatic catalytic systems of acetylcholinesterase (AChE) and choline oxidase (CHO), a highly sensitive multi-catalytic sensing system could be successfully developed for organophosphorus (OPs) pesticides such as dimethoate, DDVP, and parathion-methyl. Limit of detections (LODs) of H2O2 and glucose were estimated to be 6.5 and 0.84 μM, respectively. The limit of detection of the sub-nM level could be obtained for tested dimethoate, DDVP, and parathion-methyl OPs pesticides. The established sensing systems can exhibit good practical application performance in serum and several fruit samples.
Wei Hu,
Published: 12 July 2021
Frontiers in Chemistry, Volume 9; doi:10.3389/fchem.2021.705762

Abstract:
Editorial on the Research Topic Advances in Density Functional Theory and Beyond for Computational Chemistry The rapid development of modern computational chemistry has led to a growing need to understand the microscopic mechanisms determining the properties of molecular and solid materials at an atomic level. The interactions between atoms and electrons are governed by the laws of quantum mechanics; hence, accurate and efficient computational methods for solving the quantum-mechanical equations are needed. The Kohn-Sham density functional theory (DFT) Hohenberg and Kohn (1964), Kohn and Sham (1965) marks a decisive breakthrough in these efforts, and in the past few decades DFT has made an unparalleled impact on a variety of interesting and challenging problems in computational chemistry. The real forte of DFT is its favourable price and performance ratio as compared with electron-correlated wave-function-based methods, such as the Møller–Plesset perturbation theory Binkley and Pople (1975) or coupled cluster theory Čížek (1966). Thus, large-scale molecular and solid systems can be studied by DFT with sufficient accuracy, thereby expanding the predictive power inherent in electronic structure theory. As a result, DFT is now by far the most widely used electronic structure method. Although 50 years have passed since the formulation of the Kohn-Sham DFT, many open questions remain, including the mathematical issues in solving the Kohn-Sham equations, the developments of more accurate and efficient density functionals, and applying the DFT calculations to solve more scientific problems. This research topic focuses on covering recent advances within the framework of DFT. Computational chemistry methods have become increasingly important in recent years, as manifested by their rapidly extending applications in a large number of diverse fields, such as computations of molecular structures and properties, the design of pharmaceutical drugs and novel materials, etc. In part as a result of this general trend, the size of the systems which can be computationally studied has also increased, generating even further needs for large-scale applications. This is because larger molecular systems show interesting phenomena and have important implications in modern biochemistry, biotechnology, and nanotechnology. Thus, it is of great importance to apply and further develop computational methods which provide physically sound models for large molecules at a reasonable computational cost. A representative approach is the linear scaling technique Goedecker (1999), which owns a computational cost that scales linearly O(N) with the size of the system. The linear-scaling DFT is an area of active research in computational chemistry, with the performances improve steadily over the years, especially on parallel high-performance machines. Historically, linear-scaling implementations were restricted to basic ground state energy and electron density calculations, but this has also improved in recent years with geometry optimizations and molecular dynamics (MD) becoming available. Moreover, recent developments of machine learning algorithms enable the large-scale MD simulations with ab initio accuracy, and has been applied to a variety of applications Jia et al. (2020). This research topic aims to report the state-of-the-art computational methods in several of the important questions related to the family of linear scaling methods. A deep understanding of the excitations in molecules and solids are of fundamentally importance in many technological applications. There is already a rich set of theoretical and simulation methods for excited-state calculations, such as the GW plus Bethe-Salpeter equation Hedin (1965), time-dependent density functional theory (TDDFT) Runge and Gross (1984) and many-body coupled cluster (CC) theory Čížek (1966). Unfortunately, these post-Hartree-Fock and excited state methods for electronic excitations are all subject to computational bottlenecks, which are far more severe than those affecting the standard calculations of the ground-state energy, not only because of the system size, but also because the large number of excited states that need to be considered. A major difficulty for treating excited complex systems arises from the different nature of the various competing excited electronic states. For example, the localized neutral and delocalized charge transfer excitons, as a result of the relatively large length scale. Therefore, this research topic also aims to cover developments of novel electronic structure algorithms and scalable computational methods for excited states of complex systems. The past several decades have witnessed tremendous strides in the capabilities of computational chemistry simulations, driven in large part by the extensive parallelism offered by powerful computer clusters and scalable programming methods on high performance computing (HPC) Hu et al. (2021), Kowalski et al. (2021). However, such massively parallel simulations increasingly require more advanced algorithms to achieve satisfactory performance across the vastly diverse ecosystem of modern heterogeneous computer systems. The design of efficient parallel codes proves to be difficult: the diversity of involved data structures and algorithms, as well as the frequently occurring inherent sequential control propose enormous challenges to efficiently use of a large number of processors. This research topic also focuses on the developments of more effective computational methods by use of high performance parallel computing. This editorial sums up the contents of our Research Topic “Advances in Density Functional Theory and Beyond for Computational Chemistry” and a total of nine original research contributions have been included in this article collection, involving linear-scaling density functional theory, multiple scattering theory, ab initio...
Thanh Chung Pham, Van-Nghia Nguyen, Yeonghwan Choi, Dongwon Kim, Ok-Sang Jung, Dong Joon Lee, Hak Jun Kim, Myung Won Lee, Juyoung Yoon, Hwan Myung Kim, et al.
Published: 12 July 2021
Frontiers in Chemistry, Volume 9; doi:10.3389/fchem.2021.713078

Abstract:
The ability to detect hypochlorite (HOCl/ClO−) in vivo is of great importance to identify and visualize infection. Here, we report the use of imidazoline-2-thione (R 1 SR 2 ) probes, which act to both sense ClO− and kill bacteria. The N2C=S moieties can recognize ClO− among various typical reactive oxygen species (ROS) and turn into imidazolium moieties (R 1 IR 2 ) via desulfurization. This was observed through UV–vis absorption and fluorescence emission spectroscopy, with a high fluorescence emission quantum yield (ՓF = 43–99%) and large Stokes shift (∆v∼115 nm). Furthermore, the DIM probe, which was prepared by treating the DSM probe with ClO−, also displayed antibacterial efficacy toward not only Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) but also methicillin-resistant Staphylococcus aureus (MRSA) and extended-spectrum ß-lactamase–producing Escherichia coli (ESBL-EC), that is, antibiotic-resistant bacteria. These results suggest that the DSM probe has great potential to carry out the dual roles of a fluorogenic probe and killer of bacteria.
Yifeng Shi, Xuyao Han, , Yuhao Wu, Yuhan Jiang, Jinghao Lin, Yihuang Chen,
Published: 9 July 2021
Frontiers in Chemistry, Volume 9; doi:10.3389/fchem.2021.724188

Abstract:
Recently, as our population increasingly ages with more pressure on bone and cartilage diseases, bone/cartilage tissue engineering (TE) have emerged as a potential alternative therapeutic technique accompanied by the rapid development of materials science and engineering. The key part to fulfill the goal of reconstructing impaired or damaged tissues lies in the rational design and synthesis of therapeutic agents in TE. Gold nanomaterials, especially gold nanoparticles (AuNPs), have shown the fascinating feasibility to treat a wide variety of diseases due to their excellent characteristics such as easy synthesis, controllable size, specific surface plasmon resonance and superior biocompatibility. Therefore, the comprehensive applications of gold nanomaterials in bone and cartilage TE have attracted enormous attention. This review will focus on the biomedical applications and molecular mechanism of gold nanomaterials in bone and cartilage TE. In addition, the types and cellular uptake process of gold nanomaterials are highlighted. Finally, the current challenges and future directions are indicated.
K. Vipin Raj, Pawan S. Dhote, ,
Published: 9 July 2021
Frontiers in Chemistry, Volume 9; doi:10.3389/fchem.2021.689780

Abstract:
Gold-catalysis, in this century, is one of the most emerging and promising new areas of research in organic synthesis. During the last two decades, a wide range of distinct synthetic methodologies have been unveiled employing homogeneous gold catalysis and aptly applied in the synthesis of numerous natural products and biologically active molecules. Among these, the reactions involving α-oxo gold carbene/α-imino gold carbene intermediates are of contemporary interest, in view of their synthetic potential and also due to the need to understand the bonding involved in these complexes. In this manuscript, we document the theoretical investigations on the regio-selectivity dependence of substitution on the gold-catalyzed cycloisomerization of o-nitroarylalkyne derivatives. We have also studied the relative stabilities of α-oxo gold carbene intermediates.
Yin Ma, Lijun Xiong, Yao Lu, Wenqiang Zhu, Haihong Zhao, Yahui Yang, Liqiu Mao, Lishan Yang
Published: 9 July 2021
Frontiers in Chemistry, Volume 9; doi:10.3389/fchem.2021.638216

Abstract:
Inorganic nitride nanomaterials have attracted widespread attention for applications in renewable energy due to novel electrochemical activities and high chemical stabilities. For different renewable energy applications, there are many possibilities and uncertainties about the optimal nitride phases and nanostructures, which further promotes the exploration of controllable preparation of nitride nanomaterials. Moreover, unlike conventional nitrides with bulk or ceramic structures, the synthesis of nitride nanomaterials needs more accurate control to guarantee the target nanostructure along with the phase purity, which make the whole synthesis still a challenge to achieve. In this mini review, we mainly summarize the synthesis methods for inorganic nitride nanomaterials, including chemistry vapor deposition, self-propagation high-temperature synthesis, solid state metathesis reactions, solvothermal synthesis, etc. From the perspective of nanostructure, several novel nitrides, with nanostructures like nanoporous, two-dimensional, defects, ternary structures, and quantum dots, are showing unique properties and getting extensive attentions, recently. Prospects of future research in design and synthesis of functional inorganic nitrides are also discussed.
Yuzhuang Fu, Fangfang Fan, Yuwei Zhang, , Zexing Cao
Published: 9 July 2021
Frontiers in Chemistry, Volume 9; doi:10.3389/fchem.2021.706959

Abstract:
The enzymatic hydration of CO2 into HCO3 − by carbonic anhydrase (CA) is highly efficient and environment-friendly measure for CO2 sequestration. Here extensive MM MD and QM/MM MD simulations were used to explore the whole enzymatic process, and a full picture of the enzymatic hydration of CO2 by CA was achieved. Prior to CO2 hydration, the proton transfer from the water molecule (WT1) to H64 is the rate-limiting step with the free energy barrier of 10.4 kcal/mol, which leads to the ready state with the Zn-bound OH−. The nucleophilic attack of OH− on CO2 produces HCO3 − with the free energy barrier of 4.4 kcal/mol and the free energy release of about 8.0 kcal/mol. Q92 as the key residue manipulates both CO2 transportation to the active site and release of HCO3 −. The unprotonated H64 in CA prefers in an inward orientation, while the outward conformation is favorable energetically for its protonated counterpart. The conformational transition of H64 between inward and outward correlates with its protonation state, which is mediated by the proton transfer and the product release. The whole enzymatic cycle has the free energy span of 10.4 kcal/mol for the initial proton transfer step and the free energy change of −6.5 kcal/mol. The mechanistic details provide a comprehensive understanding of the entire reversible conversion of CO2 into bicarbonate and roles of key residues in chemical and nonchemical steps for the enzymatic hydration of CO2.
Subhash Chander, Giriraj T. Kulkarni, Neerupma Dhiman,
Published: 9 July 2021
Frontiers in Chemistry, Volume 9; doi:10.3389/fchem.2021.573748

Abstract:
Hydrogels possess a unique three-dimensional, cross-linked network of polymers capable of absorbing large amounts of water and biological fluids without dissolving. Nanohydrogels (NGs) or nanogels are composed of diverse types of polymers of synthetic or natural origin. Their combination is bound by a chemical covalent bond or is physically cross-linked with non-covalent bonds like electrostatic interactions, hydrophobic interactions, and hydrogen bonding. Its remarkable ability to absorb water or other fluids is mainly attributed to hydrophilic groups like hydroxyl, amide, and sulphate, etc. Natural biomolecules such as protein- or peptide-based nanohydrogels are an important category of hydrogels which possess high biocompatibility and metabolic degradability. The preparation of protein nanohydrogels and the subsequent encapsulation process generally involve use of environment friendly solvents and can be fabricated using different proteins, such as fibroins, albumin, collagen, elastin, gelatin, and lipoprotein, etc. involving emulsion, electrospray, and desolvation methods to name a few. Nanohydrogels are excellent biomaterials with broad applications in the areas of regenerative medicine, tissue engineering, and drug delivery due to certain advantages like biodegradability, biocompatibility, tunable mechanical strength, molecular binding abilities, and customizable responses to certain stimuli like ionic concentration, pH, and temperature. The present review aims to provide an insightful analysis of protein/peptide nanohydrogels including their preparation, biophysiochemical aspects, and applications in diverse disciplines like in drug delivery, immunotherapy, intracellular delivery, nutraceutical delivery, cell adhesion, and wound dressing. Naturally occurring structural proteins that are being explored in protein nanohydrogels, along with their unique properties, are also discussed briefly. Further, the review also covers the advantages, limitations, overview of clinical potential, toxicity aspects, stability issues, and future perspectives of protein nanohydrogels.
, Shehnaz Akhter, Kashif Ali, Syed Tahir Raza Rizvi
Published: 9 July 2021
Frontiers in Chemistry, Volume 9; doi:10.3389/fchem.2021.693885

Abstract:
Topological invariants are the significant invariants that are used to study the physicochemical and thermodynamic characteristics of chemical compounds. Recently, a new bond additive invariant named the Mostar invariant has been introduced. For any connected graph , the edge Mostar invariant is described as Moe()=gxE()|m(g)m(x)|, where m(g)(or m(x)) is the number of edges of lying closer to vertex g (or x) than to vertex x (or g). A graph having at most one common vertex between any two cycles is called a cactus graph. In this study, we compute the greatest edge Mostar invariant for cacti graphs with a fixed number of cycles and n vertices. Moreover, we calculate the sharp upper bound of the edge Mostar invariant for cacti graphs in (n,s), where s is the number of cycles.
Published: 8 July 2021
by 10.3389
Frontiers in Chemistry, Volume 9; doi:10.3389/fchem.2021.730111

Abstract:
Editorial on the Research TopicDesign of Macrocyclic Compounds for Biomedical Applications The search for new biologically active compounds to tackle global health challenges is an important goal in organic synthesis, biochemistry, and medicine. The biological activity of macrocyclic structures is an actively developing area of science. Macrocyclic compounds have unique physicochemical properties, such as spatial preorganization, presence of a size-defined cavity, propensity of undergoing self-assembly, low pharmacologically active concentrations, low toxicity, antiallergenicity, etc. Macrocyclic compounds such as crown ethers, cyclodextrins, cucurbiturils, calixarenes, porphyrins, pillararenes and cyclic peptides have been used in various biomedical applications. In this Research Topic, we present a collection of original research and review articles that show the significant recent advances made in the synthesis of new macrocycles and their biomedical applications. One of the ways to overcome the antimicrobial resistance of microorganisms is the use of macrocycle-antibiotic hybrids, as reviewed by Surur et al.. This review article describes the synthesis and properties of the most well-known hybrids of macrocyclic compounds with antibiotics such as rifamycins, vancomycin, etc. It is known that the major limitation of the use of antibiotic hybrids is the increase in molecular weight. However, progresses and advances in this area show the possibility of improving the oral bioavailability of bulky molecules for systemic clinical use. Ibrahim et al. have developed novel Tröger’s base derivatives and studied their anticancer properties. The synthesized Tröger’s base phenhomazines derivatives were screened for anticancer activity, and 1,4,7,10-tetraoxa[10](2,8) trögerophane has shown a promising selectivity on a colon cell line with IC50 = 92.7 μg/ml. The obtained results open up prospects for the development of new promising anticancer agents. It is known that macrocyclic compounds can be used in targeted delivery systems as containers for drugs. It has been shown by Chandra et al. that cucurbit[7]uril is able to form a host-guest complex with the neurotransmitter serotonin. In this case, the binding affinity is pH-dependent. The results demonstrate promising biological applications in the delivery and pH-controlled release of serotonin. Saleh et al. described the use of cucurbit[7]uril as a liver protective agent and an adjuvant in toxicological pharmacology. The protective effects of cucurbit[7]uril were evaluated in the biochemical study of the extracted livers of mice following cyanobacterial crude extract treatment with or without cucurbit[7]uril. The addition of cucurbit[7]uril has been shown to significantly reduce the toxicity of cyanotoxin-induced hepatotoxicity (P < 0.05) in vivo. Supramolecular chemistry is useful in the controlled and/or local delivery of immunomodulatory drugs, as reviewed by Soni et al.. In their review, macrocycles such as cyclodextrins are highlighted for their drug solubilizing and stabilizing actions and the utility of polymer-based hydrogels and nanomaterials in local drug delivery is also described. Besides drug delivery, cyclodextrin-based supramolecular systems have found applications in other biomedically relevant areas such as the separation of biomolecules, enzymatic catalysis, sensing, diagnosis and therapy, as summarized by Luo et al. The chirality of cyclodextrins makes them suitable for the separation of biomolecules. According to the molecular mechanics simulation conducted by Alvira, even a very simple and affordable native cyclodextrin such as β-cyclodextrin is able to discriminate the enantiomeric forms of the amino acids alanine, valine, leucine, and isoleucine. The development of macrocyclic chemistry has contributed to the design of new materials with effective and selective catalytic properties. In a mini-review, Shang et al. have described recent advances in the use of macrocyclic compounds as building blocks for the design of bioinspired catalysts. The described materials, from single-molecule to metal-organic framework materials, have unique catalytic properties and binding affinity for biologically significant substrates. The authors agree that the materials obtained have a lower catalytic activity in comparison with natural enzymes at this stage of research. However, the trend in the development of synthetic catalysts may lead to future application. Facilitation of ion transport across lipid bilayers is an important supramolecular function with potential applications in biophysics research and the treatment of ion channel diseases. Macrocyclic ionophores are of particular interest for achieving high membrane transport selectivity as exemplified by the almost perfect K+ over Na+ selectivity exhibited by the natural product valinomycin. Zhao et al. have developed a cyclic azapeptide anionophore with a small binding cavity that facilitates selective transmembrane transport of fluoride ions. Remarkably, this anionophore shows negligible transport for larger anions including chloride and acetate. Overall, this article collection includes several excellent studies in the design and investigation of macrocyclic structures and covers various fields of chemistry, biology and medicine. As guest editors of this article collection, we thank all authors and reviewers for their valuable contributions. We hope that the publications presented in this collection will attract even greater interest in the chemistry of macrocyclic compounds and supramolecular chemistry. All authors listed have made a substantial, direct, and intellectual contribution to the work, and approved it for publication. PP acknowledges of the grant of the President of the Russian Federation for state support of young scientists and leading scientific schools of the Russian Federation (MK-12.2020.3, NSh-2499.2020.3) for financial support....
Francis Kwaku Asiam, Nguyen Huy Hao, Ashok Kumar Kaliamurthy, Hyeong Cheol Kang, Kicheon Yoo,
Published: 8 July 2021
by 10.3389
Frontiers in Chemistry, Volume 9; doi:10.3389/fchem.2021.701781

Abstract:
The steric shielding offered by sensitizers on semiconducting surfaces as a result of branching in the dyes used offers the less utilization of semiconducting substrate sites during device fabrication in dye-sensitized solar cells (DSSCs). This work proposes a strategy to increase the coverage through the utilization of small molecules which have the ability to penetrate into the sites. The small molecules play the dual role of vacancy filling and sensitization, which can be viewed as an alternative to co-sensitization also. Hence, we show for the first time ever that the co-adsorption of catechol with Z907 as a sensitizer enhances the electron density in the photo-anode by adsorbing on the vacant sites. Catechol was subsequently adsorbed on TiO2 after Z907 as it has a stronger interaction with TiO2 owing to its favorable thermodynamics. The reduced number of vacant sites, suppressed charge recombination, and enhanced spectral response are responsible for the improvement in the PCEs. Quantitatively, both organic and aqueous electrolytes were used and the co-sensitized DSSCs had PCE enhancements of 7.2 and 60%, respectively, compared to the control devices.
Adriana Ferreira Lopes Vilela, Vitor Eduardo Narciso dos Reis,
Published: 8 July 2021
by 10.3389
Frontiers in Chemistry, Volume 9; doi:10.3389/fchem.2021.708374

Abstract:
We have developed a dual enzymatic system assay involving liquid chromatography-mass spectrometry (LC–MS) to screen AChE and BACE1 ligands. A fused silica capillary (30 cm × 0.1 mm i.d. × 0.362 mm e.d.) was used as solid support. The co-immobilization procedure encompassed two steps and random immobilization. The resulting huAChE+BACE1-ICER/MS was characterized by using acetylcholine (ACh) and JMV2236 as substrates. The best conditions for the dual enzymatic system assay were evaluated and compared to the conditions of the individual enzymatic system assays. Analysis was performed in series for each enzyme. The kinetic parameters (KMapp) and inhibition assays were evaluated. To validate the system, galantamine and a β-secretase inhibitor were employed as standard inhibitors, which confirmed that the developed screening assay was able to identify reference ligands and to provide quantitative parameters. The combination of these two enzymes in a single on-line system allowed possible multi-target inhibitors to be screened and identified. The innovative huAChE+BACE1-ICER/MS dual enzymatic system reported herein proved to be a reliable tool to identify and to characterize hit ligands for AChE and BACE1 in an enzymatic competitive environment. This innovative system assay involved lower costs; measured the product from enzymatic hydrolysis directly by MS; enabled immediate recovery of the enzymatic activity; showed specificity, selectivity, and sensitivity; and mimicked the cellular process.
Chunhong Liu, Zhipeng Yu, Jiabin Yao, Jiecheng Ji, Ting Zhao, ,
Published: 7 July 2021
Frontiers in Chemistry, Volume 9; doi:10.3389/fchem.2021.713305

Abstract:
Several new chiral pillar[4]arene[1]quinone derivatives were synthesized by reacting pillar[4]arene[1]quinone (EtP4Q1), containing four 1,4-diethoxybenzene units and one benzoquinone unit, with various chiral amines via Michael addition. Due to the direct introduction of chiral substituents on the rim of pillar[n]arene and the close location of the chiral center to the rim of EtP4Q1, the newly prepared compounds showed unique chiroptical properties without complicated chiral resolution processes, and unprecedented high anisotropy factor of up to −0.018 at the charge transfer absorption band was observed. Intriguingly, the benzene sidearm attached pillar[4]arene[1]quinone derivative 1a showed solvent- and complexation-driven chirality inversion. This work provides a promising potential for absolute asymmetric synthesis of pillararene-based derivatives.
, Tomás Ramirez-Reina, Svetlana Ivanova, Anne-Cécile Roger, Miguel Ángel Centeno, José Antonio Odriozola
Published: 7 July 2021
by 10.3389
Frontiers in Chemistry, Volume 9; doi:10.3389/fchem.2021.694976

Abstract:
Designing an economically viable catalyst that maintains high catalytic activity and stability is the key to unlock dry reforming of methane (DRM) as a primary strategy for biogas valorization. Ni/Al2O3 catalysts have been widely used for this purpose; however, several modifications have been reported in the last years in order to prevent coke deposition and deactivation of the samples. Modification of the acidity of the support and the addition of noble metal promoters are between the most reported strategies. Nevertheless, in the task of designing an active and stable catalyst for DRM, the selection of an appropriate noble metal promoter is turning more challenging owing to the lack of homogeneity of the different studies. Therefore, this research aims to compare Ru (0.50 and 2.0%) and Re (0.50 and 2.0%) as noble metal promoters for a Ni/MgAl2O4 catalyst under the same synthesis and reaction conditions. Catalysts were characterized by XRF, BET, XRD, TPR, hydrogen chemisorption (H2-TPD), and dry reforming reaction tests. Results show that both promoters increase Ni reducibility and dispersion. However, Ru seems a better promoter for DRM since 0.50% of Ru increases the catalytic activity in 10% and leads to less coke deposition.
Nicolò Bisi, Lucia Feni, Kaliroi Peqini, Helena Pérez-Peña, Sandrine Ongeri, Stefano Pieraccini,
Published: 7 July 2021
by 10.3389
Frontiers in Chemistry, Volume 9; doi:10.3389/fchem.2021.666585

Abstract:
Alpha-synuclein (αSyn) is a highly expressed and conserved protein, typically found in the presynaptic terminals of neurons. The misfolding and aggregation of αSyn into amyloid fibrils is a pathogenic hallmark of several neurodegenerative diseases called synucleinopathies, such as Parkinson’s disease. Since αSyn is an Intrinsically Disordered Protein, the characterization of its structure remains very challenging. Moreover, the mechanisms by which the structural conversion of monomeric αSyn into oligomers and finally into fibrils takes place is still far to be completely understood. Over the years, various studies have provided insights into the possible pathways that αSyn could follow to misfold and acquire oligomeric and fibrillar forms. In addition, it has been observed that αSyn structure can be influenced by different parameters, such as mutations in its sequence, the biological environment (e.g., lipids, endogenous small molecules and proteins), the interaction with exogenous compounds (e.g., drugs, diet components, heavy metals). Herein, we review the structural features of αSyn (wild-type and disease-mutated) that have been elucidated up to present by both experimental and computational techniques in different environmental and biological conditions. We believe that this gathering of current knowledge will further facilitate studies on αSyn, helping the planning of future experiments on the interactions of this protein with targeting molecules especially taking into consideration the environmental conditions.
Xiaohu Mi, Tingting Zhang, Baobao Zhang, Min Ji, Bowen Kang, Chao Kang, Zhengkun Fu, Zhenglong Zhang, Hairong Zheng
Published: 7 July 2021
Frontiers in Chemistry, Volume 9; doi:10.3389/fchem.2021.699548

Abstract:
Plasmonic nanostructures with sharp tips are widely used for optical signal enhancement because of their strong light-confining abilities. These structures have a wide range of potential applications, for example, in sensing, bioimaging, and surface-enhanced Raman scattering. Au nanoparticles, which are important plasmonic materials with high photothermal conversion efficiencies in the visible to near-infrared region, have contributed greatly to the development of photothermal catalysis. However, the existing methods for synthesizing nanostructures with tips need the assistance of poly(vinylpyrrolidone), thiols, or biomolecules. This greatly hinders signal detection because of stubborn residues. Here, we propose an efficient binary surfactant–mediated method for controlling nanotip growth on Au nanoparticle surfaces. This avoids the effects of surfactants and can be used with other Au nanostructures. The Au architecture tip growth process can be controlled well by adjusting the ratio of hexadecyltrimethylammonium bromide to hexadecyltrimethylammonium chloride. This is due to the different levels of attraction between Br−/Cl− and Au3+ ions. The surface-enhanced Raman scattering and catalytic abilities of the synthesized nanoparticles with tips were evaluated by electromagnetic simulation and photothermal catalysis experiments (with 4-nitrothiophenol). The results show good potential for use in surface-enhanced Raman scattering applications. This method provides a new strategy for designing plasmonic photothermal nanostructures for chemical and biological applications.
Lynn S. Lisboa, Mie Riisom, Roan A. S. Vasdev, Stephen M. F. Jamieson, L. James Wright, Christian G. Hartinger,
Published: 7 July 2021
by 10.3389
Frontiers in Chemistry, Volume 9; doi:10.3389/fchem.2021.697684

Abstract:
Two new di(2,2′-bipyridine) ligands, 2,6-bis([2,2′-bipyridin]-5-ylethynyl)pyridine (L1) and bis(4-([2,2′-bipyridin]-5-ylethynyl)phenyl)methane (L2) were synthesized and used to generate two metallosupramolecular [Fe2(L)3](BF4)4 cylinders. The ligands and cylinders were characterized using elemental analysis, electrospray ionization mass spectrometry, UV-vis, 1H-, 13C and DOSY nuclear magnetic resonance (NMR) spectroscopies. The molecular structures of the [Fe2(L)3](BF4)4 cylinders were confirmed using X-ray crystallography. Both the [Fe2(L1)3](BF4)4 and [Fe2(L2)3](BF4)4 complexes crystallized as racemic (rac) mixtures of the ΔΔ (P) and ΛΛ (M) helicates. However, 1H NMR spectra showed that in solution the larger [Fe2(L2)3](BF4)4 was a mixture of the rac-ΔΔ/ΛΛ and meso-ΔΛ isomers. The host-guest chemistry of the helicates, which both feature a central cavity, was examined with several small drug molecules. However, none of the potential guests were found to bind within the helicates. In vitro cytotoxicity assays demonstrated that both helicates were active against four cancer cell lines. The smaller [Fe2(L1)3](BF4)4 system displayed low μM activity against the HCT116 (IC50 = 7.1 ± 0.5 μM) and NCI-H460 (IC50 = 4.9 ± 0.4 μM) cancer cells. While the antiproliferative effects against all the cell lines examined were less than the well-known anticancer drug cisplatin, their modes of action would be expected to be very different.
Menghao Wu, Changli Chen, Yizhou Zhao, , Yujing Li
Published: 6 July 2021
by 10.3389
Frontiers in Chemistry, Volume 9; doi:10.3389/fchem.2021.699861

Abstract:
With the increasing enthusiasm for the hydrogen economy and zero-emission fuel cell technologies, intensive efforts have been dedicated to the development of high-performance electrocatalytic materials for the cathodic oxygen reduction reaction (ORR). Some major fundamental breakthroughs have been made in the past few years. Therefore, reviewing the most recent development of platinum-group-metal (PGM) ORR electrocatalysts is of great significance to pushing it forward. It is known that the ORR on the fuel cell electrode is a heterogeneous reaction occurring at the solid/liquid interface, wherein the electron reduces the oxygen along with species in the electrolyte. Therefore, the ORR kinetic is in close correlation with the electronic density of states and wave function, which are dominated by the localized atomic structure including the atomic distance and coordination number (CN). In this review, the recent development in the regulation over the localized state on the catalyst surface is narrowed down to the following structural factors whereby the corresponding strategies include: the crystallographic facet engineering, phase engineering, strain engineering, and defect engineering. Although these strategies show distinctive features, they are not entirely independent, because they all correlate with the atomic local structure. This review will be mainly divided into four parts with critical analyses and comparisons of breakthroughs. Meanwhile, each part is described with some more specific techniques as a methodological guideline. It is hoped that the review will enhance an insightful understanding on PGM catalysts of ORR with a visionary outlook.
Ana C. Zanatta, Wagner Vilegas,
Published: 6 July 2021
by 10.3389
Frontiers in Chemistry, Volume 9; doi:10.3389/fchem.2021.710025

Abstract:
Seasonality is one of the major environmental factors that exert influence over the synthesis and accumulation of secondary metabolites in medicinal plants. The application of the metabolomics approach for quality control of plant extracts is essentially important because it helps one to establish a standard metabolite profile and to analyze factors that affect the effectiveness of the medicinal plants. The Brazilian Cerrado flora is characterized by a rich diversity of native plant species, and a number of these plant species have been found to have suitable medicinal properties. Some of these plant species include Byrsonima intermedia and Serjania marginata. To better understand the chemical composition of these plant species, we conducted a study using the state-of-the-art techniques including the HPLC system coupled to an Exactive-Orbitrap high resolution mass spectrometer with electrospray ionization interface UHPLC-(ESI)-HRMS and by NMR being performed 2D J-resolved and proton NMR spectroscopy. For the analysis, samples were harvested bimonthly during two consecutive years. UHPLC-(ESI)-HRMS data were preprocessed and the output data uploaded into an in-house Excel macro for peak dereplication. MS and NMR data were concatenated using the data fusion method and submitted to multivariate statistical analysis. The dereplication of LC-HRMS data helped in the annotation of the major compounds present in the extracts of the three plant species investigated allowing the annotation of 68 compounds in the extracts of B. intermedia (cinnamic acids, phenolic acids derived from galloyl quinic and shikimic acid, proanthocyanidins, glycosylated flavonoids, triterpenes and other phenols) and 81 compounds in the extracts of S. marginata (phenolic acids, saponins, proanthocyanidins, glycosylated flavonoids among other compounds). For a better assessment of the great number of responses, the significance of the chemical variables for the differentiation and correlation of the seasons was determined using the variable importance on projection (VIP) technique and through the application of the false discovery rate (FDR) estimation. The statistical data obtained showed that seasonal factors played an important role on the production of metabolites in each plant species. Temperature conditions, drought and solar radiation were found to be the main factors that affected the variability of phenolic compounds in each species.
Zakir Ullah, Kang Kim, Arramshetti Venkanna, Hye Su Kim, Moon Il Kim
Published: 6 July 2021
by 10.3389
Frontiers in Chemistry, Volume 9; doi:10.3389/fchem.2021.669515

Abstract:
As a non-covalent interaction of a chiral scaffold in catalysis, pnicogen bonding of epi-cinchonidine (epi-CD), a cinchona alkaloid, was simulated to consider whether the interaction can have the potential controlling enantiotopic face like hydrogen bonding. Among five reactive functional groups in epi-CD, two stable complexes of the hydroxyl group (X-epi-CD1) at C17 and of the quinoline ring (X-epi-CD2) at N16 with pnictide family analytes [X = substituted phosphine (PX), i.e., F, Br, Cl, CF3, CN, HO, NO2, and CH3, and pnictide family analytes, i.e., PBr3, BiI3, SbI3, and AsI3] were predicted with intermolecular interaction energies, charge transfer (QMulliken and QNBO), and band gap energies of HOMO–LUMO (Eg) at the B3LYP/6-31G(d,p) level of density functional theory. It was found that the dominant site of pnicogen bonding in epi-CD is the quinoline ring (N16 atom) rather than the hydroxyl group (O36 atom). In addition, the UV-Vis spectra of the complex were calculated by time-dependent density functional theory (TD-DFT) at the B3LYP/6-31+G(d,p) level and compared with experimental measurements. Through these calculations, two intermolecular interactions (H-bond vs. pnicogen bond) of epi-CD were compared.
Minghua Yuan, Yanan Chu,
Published: 5 July 2021
by 10.3389
Frontiers in Chemistry, Volume 9; doi:10.3389/fchem.2021.691093

Abstract:
The proteolysis targeting chimeras (PROTACs), which are composed of a target protein binding moiety, a linker, and an E3 ubiquitin ligase binder, have been a promising strategy for drug design and discovery. Given the advantages of potency, selectivity, and drug resistance over inhibitors, several PROTACs have been reported in literature, which mostly focus on noncovalent or irreversible covalent binding to the target proteins. However, it must be noted that noncovalent or irreversible PROTACs have several drawbacks such as weak binding affinity and unpredictable off-target effects. Reversible covalent PROTACs, with properties of enhanced potency, selectivity, and long duration of action, have attracted an increasing amount of attention. Here, we propose a comparison between these three patterns and highlight that reversible covalent PROTACs could pave the way for a wide variety of challenging target degradations.
Aleša Bricelj, Christian Steinebach, Robert Kuchta, Michael Gütschow,
Published: 5 July 2021
by 10.3389
Frontiers in Chemistry, Volume 9; doi:10.3389/fchem.2021.707317

Abstract:
Proteolysis-targeting chimeras (PROTACs) have received tremendous attention as a new and exciting class of therapeutic agents that promise to significantly impact drug discovery. These bifunctional molecules consist of a target binding unit, a linker, and an E3 ligase binding moiety. The chemically-induced formation of ternary complexes leads to ubiquitination and proteasomal degradation of target proteins. Among the plethora of E3 ligases, only a few have been utilized for the novel PROTAC technology. However, extensive knowledge on the preparation of E3 ligands and their utilization for PROTACs has already been acquired. This review provides an in-depth analysis of synthetic entries to functionalized ligands for the most relevant E3 ligase ligands, i.e. CRBN, VHL, IAP, and MDM2. Less commonly used E3 ligase and their ligands are also presented. We compare different preparative routes to E3 ligands with respect to feasibility and productivity. A particular focus was set on the chemistry of the linker attachment by discussing the synthetic opportunities to connect the E3 ligand at an appropriate exit vector with a linker to assemble the final PROTAC. This comprehensive review includes many facets involved in the synthesis of such complex molecules and is expected to serve as a compendium to support future synthetic attempts towards PROTACs.
C. Pérez-González, C. Salvo-Comino, F. Martin-Pedrosa, L. Dias, M. A. Rodriguez-Perez, C. Garcia-Cabezon, M. L. Rodriguez-Mendez
Published: 5 July 2021
by 10.3389
Frontiers in Chemistry, Volume 9; doi:10.3389/fchem.2021.706460

Abstract:
A portable potentiometric electronic tongue (PE-tongue) was developed and applied to evaluate the quality of milk with different fat content (skimmed, semi-skimmed, and whole) and with different nutritional content (classic, calcium-enriched, lactose-free, folic acid–enriched, and enriched in sterols of vegetal origin). The system consisted of a simplified array of five sensors based on PVC membranes, coupled to a data logger. The five sensors were selected from a larger set of 20 sensors by applying the genetic algorithm (GA) to the responses to compounds usually found in milk including salts (KCl, CaCl2, and NaCl), sugars (lactose, glucose, and galactose), and organic acids (citric acid and lactic acid). Principal component analysis (PCA) and support vector machine (SVM) results indicated that the PE-tongue consisting of a five-electrode array could successfully discriminate and classify milk samples according to their nutritional content. The PE-tongue provided similar discrimination capability to that of a more complex system formed by a 20-sensor array. SVM regression models were used to predict the physicochemical parameters classically used in milk quality control (acidity, density, %proteins, %lactose, and %fat). The prediction results were excellent and similar to those obtained with a much more complex array consisting of 20 sensors. Moreover, the SVM method confirmed that spoilage of unsealed milk could be correctly identified with the simplified system and the increase in acidity could be accurately predicted. The results obtained demonstrate the possibility of using the simplified PE-tongue to predict milk quality and provide information on the chemical composition of milk using a simple and portable system.
Sebastjan Kralj, Milan Hodošček, Barbara Podobnik, Tanja Kunej, Urban Bren, ,
Published: 2 July 2021
Frontiers in Chemistry, Volume 9; doi:10.3389/fchem.2021.705931

Abstract:
In a survey of novel interactions between an IgG1 antibody and different Fcγ receptors (FcγR), molecular dynamics simulations were performed of interactions of monoclonal antibody involved complexes with FcγRs. Free energy simulations were also performed of isolated wild-type and substituted Fc regions bound to FcγRs with the aim of assessing their relative binding affinities. Two different free energy calculation methods, Molecular Mechanical/Generalized Born Molecular Volume (MM/GBMV) and Bennett Acceptance Ratio (BAR), were used to evaluate the known effector substitution G236A that is known to selectively increase antibody dependent cellular phagocytosis. The obtained results for the MM/GBMV binding affinity between different FcγRs are in good agreement with previous experiments, and those obtained using the BAR method for the complete antibody and the Fc-FcγR simulations show increased affinity across all FcγRs when binding to the substituted antibody. The FcγRIIa, a key determinant of antibody agonistic efficacy, shows a 10-fold increase in binding affinity, which is also consistent with the published experimental results. Novel interactions between the Fab region of the antibody and the FcγRs were discovered with this in silico approach, and provide insights into the antibody-FcγR binding mechanism and show promise for future improvements of therapeutic antibodies for preclinical studies of biological drugs.
Xi-Han Zhao,
Published: 2 July 2021
Frontiers in Chemistry, Volume 9; doi:10.3389/fchem.2021.718000

Abstract:
In recent years, nano-impact electrochemistry (NIE) has attracted widespread attention as a new electroanalytical approach for the analysis and characterization of single nanoparticles in solution. The accurate analysis of the large volume of the experimental data is of great significance in improving the reliability of this method. Unfortunately, the commonly used data analysis approaches, mainly based on manual processing, are often time-consuming and subjective. Herein, we propose a spike detection algorithm for automatically processing the data from the direct oxidation of sliver nanoparticles (AgNPs) in NIE experiments, including baseline extraction, spike identification and spike area integration. The resulting size distribution of AgNPs is found to agree very well with that from transmission electron microscopy (TEM), showing that the current algorithm is promising for automated analysis of NIE data with high efficiency and accuracy.
Krishna K. Barakoti, Pradeep Subedi, Farzaneh Chalyavi, Salvador Gutierrez-Portocarrero, Matthew J. Tucker,
Published: 2 July 2021
Frontiers in Chemistry, Volume 9; doi:10.3389/fchem.2021.678112

Abstract:
We present the analysis of formaldehyde (HCHO) in anhydrous methanol (CH3OH) as a case study to quantify HCHO in non-aqueous samples. At higher concentrations (C > 0.07 M), we detect a product of HCHO, methoxy methanol (MM, CH3OCH2OH), by Fourier transform infrared spectroscopy, FTIR. Formaldehyde reacts with CH3OH, CD3OH, and CD3OD as shown by FTIR with a characteristic spectral feature around 1,195 cm−1 for CH3OH used for the qualitative detection of MM, a formaldehyde derivative in neat methanol. Ab initio calculations support this assignment. The extinction coefficient for 1,195 cm−1 is in the order of 1.4 × 102 M−1cm−1, which makes the detection limit by FTIR in the order of 0.07 M. For lower concentrations, we performed the quantitative analysis of non-aqueous samples by derivatization with dinitrophenylhydrazine (DNPH). The derivatization uses an aqueous H2SO4 solution to yield the formaldehyde derivatized hydrazone. Ba(OH)2 removes sulfate ions from the derivatized samples and a final extraction with isobutyl acetate to yield a 1:1 methanol: isobutyl acetate solvent for injection for electrospray ionization (ESI). The ESI analysis gave a linear calibration curve for concentrations from 10 to 200 µM with a time-of-flight analyzer (TOF). The detection and quantification limits are 7.8 and 26 μM, respectively, for a linear correlation with R 2 > 0.99. We propose that the formaldehyde in CH3OH is in equilibrium with the MM species, without evidence of HCHO in solution. In the presence of water, the peaks for MM become less resolved, as expected from the well-known equilibria of HCHO that favors the formation of methylene glycol and polymeric species. Our results show that HCHO, in methanol does not exist in the aldehyde form as the main chemical species. Still, HCHO is in equilibrium between the production of MM and the formation of hydrated species in the presence of water. We demonstrate the ESI-MS analysis of HCHO from a non-aqueous TiO2 suspension in methanol. Detection of HCHO after illumination of the colloid indicates that methanol photooxidation yields formaldehyde in equilibrium with the solvent.
, Gabriel Maia da Silva Salvador, Sílvia V. F. Castro, Nakédia M. F. Carvalho, Rodrigo A. A. Munoz
Published: 2 July 2021
Frontiers in Chemistry, Volume 9; doi:10.3389/fchem.2021.684256

Abstract:
3D printing is a type of additive manufacturing (AM), a technology that is on the rise and works by building parts in three dimensions by the deposit of raw material layer upon layer. In this review, we explore the use of 3D printers to prototype electrochemical cells and devices for various applications within chemistry. Recent publications reporting the use of Fused Deposition Modelling (fused deposition modeling®) technique will be mostly covered, besides papers about the application of other different types of 3D printing, highlighting the advances in the technology for promising applications in the near future. Different from the previous reviews in the area that focused on 3D printing for electrochemical applications, this review also aims to disseminate the benefits of using 3D printers for research at different levels as well as to guide researchers who want to start using this technology in their research laboratories. Moreover, we show the different designs already explored by different research groups illustrating the myriad of possibilities enabled by 3D printing.
Qinhai Xu, Xiaolin Liu, Yanglin Jiang, Peng Wang
Published: 2 July 2021
Frontiers in Chemistry, Volume 9; doi:10.3389/fchem.2021.658105

Abstract:
Herein, selenium and nitrogen co-doped carbon quantum dots (Se/N-CQDs) were hydrothermally synthesized by using citric acid, histidine, and sodium selenite, which had sp3 and sp2 hybridized carbon atoms and showed excitation-dependent fluorescence behavior. Furthermore, due to the redox reaction of ABTS•+ and Se/N-CQDs, Se/N-CQDs had the excellent antioxidant capacity that it was demonstrated by scavenging ABTS•+ with the fading of blue. Based on the synergistic effect of Se/N-CQDs and Mn(II) on ABTS•+, Se/N-CQDs and ABTS•+, as a stable, sensitive, selective, and reproducible colorimetric sensor, was applied to the detection of Mn(II) with a detection limit of 1.69 μM and a linear range of 0 to 142.90 μM. More importantly, the probe was successfully applied to detecting Mn(II) in tap water, illustrating that it could be a promising tool for Mn(II) detection in water environments.
Céline Montanari, Peter Olsén, Lars A. Berglund
Published: 1 July 2021
Frontiers in Chemistry, Volume 9; doi:10.3389/fchem.2021.682883

Abstract:
The development of large, multifunctional structures from sustainable wood nanomaterials is challenging. The need to improve mechanical performance, reduce moisture sensitivity, and add new functionalities, provides motivation for nanostructural tailoring. Although existing wood composites are commercially successful, materials development has not targeted nano-structural control of the wood cell wall, which could extend the property range. For sustainable development, non-toxic reactants, green chemistry and processing, lowered cumulative energy requirements, and lowered CO2-emissions are important targets. Here, modified wood substrates in the form of veneer are suggested as nanomaterial components for large, load-bearing structures. Examples include polymerization of bio-based monomers inside the cell wall, green chemistry wood modification, and addition of functional inorganic nanoparticles inside the cell wall. The perspective aims to describe bio-based polymers and green processing concepts for this purpose, along with wood nanoscience challenges.
Zhiyue Zhao, Zhiwei Jiang, Hong Xu,
Published: 1 July 2021
Frontiers in Chemistry, Volume 9; doi:10.3389/fchem.2021.700887

Abstract:
We report a sustainable strategy to cleanly address biomass waste with high-value utilization. Phenol-rich bio-oil is selectively produced by direct pyrolysis of biomass waste corn straw (CS) without use of any catalyst in a microwave device. The effects of temperature and power on the yield and composition of pyrolysis products are investigated in detail. Under microwave irradiation, a very fast pyrolysis rate and bio-oil yield as high as 46.7 wt.% were obtained, which were competitive with most of the previous results. GC-MS analysis showed that temperature and power (heating rate) had great influences on the yield of bio-oil and the selectivity of phenolic compounds. The optimal selectivity of phenols in bio-oil was 49.4 area% by adjusting the operating parameters. Besides, we have made detailed statistics on the change trend of some components and different phenols in bio-oil and given the law and reason of their change with temperature and power. The in situ formed highly active biochar from CS with high content of potassium (1.34 wt.%) is responsible for the improvement of phenol-rich oils. This study offers a sustainable way to fully utilize biomass waste and promote the achievement of carbon neutrality.
, Chongyu Zhu, Christopher V. Synatschke, Xiaoyong Zhang
Published: 1 July 2021
Frontiers in Chemistry, Volume 9; doi:10.3389/fchem.2021.681189

Abstract:
Editorial on the Research Topic Design, Synthesis and Biomedical Applications of Functional Polymers With the advancement of synthetic polymer chemistry, researchers are now able to readily prepare polymers with tailored composition, architecture, and functionality. This has greatly expanded the application of polymers in many areas. In particular, functional polymers as soft and biocompatible materials have been more and more involved in various biomedical applications. Facilitated by elegantly-designed functional polymers, tremendous progress has been achieved in the biomedical field including but not limited to the development of stimuli-responsive polymer materials, innovative drug delivery systems, and advanced theranostics. Chemical design and synthesis of polymers undoubtedly plays an important role in driving these achievements. On the other hand, for practical biomedical applications, polymers need to meet many requirements. Among those biocompatibility and biodegradability of polymers are profoundly necessary properties. Synthetic technologies leading to biocompatible and biodegradable polymers such as polyesters, polycarbonates and poly(amino acids) are therefore of great interest. The goal of this Research Topic is to highlight recent developments in synthetic polymer chemistry and functional polymers for biomedical applications. Below we highlight 5 papers included in this Research Topic on the synthesis and biomedical application of stimuli-responsive polymers and biocompatible/biodegradable polymers. Stimuli-responsive polymeric materials have attracted considerable interest due to their ability to respond to specific physical, chemical or biological triggers. This character is particularly useful for targeted drug delivery and imaging of pathological changes in diseased tissue. In the original research article, Zhao et al. reported the synthesis of poly(ethylene glycol) (PEG) with a single cinnamaldehyde acetal unit in the polymer chain. The incorporation of cinnamaldehyde acetal unit makes the polymer pH-responsive. In acidic environment, the acetal linkage would be hydrolyzed and the polymer can be degraded into PEG fragments and release cinnamaldehyde, a bioactive molecule. They further used this polymer to prepare a whole PEG-based hydrogel via thiol-ene reaction. The hydrogel can be completely degraded under low pH condition, demonstrating potential as a smart drug delivery system for therapeutic application. Intracellular delivery enables more efficient drug delivery and therapeutic efficacy but is a critical and challenging process. By utilizing functional polymers and polymer-associated nanoparticles, a number of effective approaches have been developed for intracellular delivery applications. In a mini-review, Wang summarized the design and application of pH-responsive amphiphilic carboxylate polymers as innovative drug delivery system to transport therapeutic payloads across cell membrane and release them in endosomes. The mini-review also provides mechanistic insights into the effect of different carboxylate polymers on their endosomal escape properties, and highlights the challenges and future opportunities for this kind of polymers for intracellular delivery applications. Polyesters and polycarbonates are important class of biocompatible and biodegradable polymers supporting a myriad of biomedical applications. Synthetic methodologies that are able to produce these polymers from readily-available chemical building blocks in an efficient and green manner are highly needed. In a review article, Liang et al. summarized recent developments in ring-opening copolymerization (ROCOP) of epoxides with carbon dioxide and cyclic anhydrides to prepare polyesters and polycarbonates. Specifically, they highlighted the advances in the catalysts used in ROCOP including organometallic complexes and metal-free Lewis pairs systems. They also reviewed the progress of using post-polymerization modification strategy to prepare polyesters and polycarbonates with functional groups such as hydroxyl and alkene groups that can be used as chemical handles for further functionalization. In addition to polyesters and polycarbonates, poly(amino acids) represent another important class of biocompatible and biodegradable polymers that demonstrate a broad range of biomedical applications. In a mini-review, Chen et al. summarized the development of the synthesis, modification and biomedical applications of epsilon-poly-L-lysine and L-lysine-based dendrimers. They reviewed the diverse applications of these lysine-based polymers as effective antimicrobial and antiviral agents, functional adjuvants, and innovative drug delivery systems. An effective approach leading to poly(amino acids) is ring opening polymerization of cyclic monomers of N-(thio)carboxyanhydrides (N(T)CA. Due to the lack of effective experimental tools, a clear understanding of the reaction mechanism and kinetics in ROP of N(T)CA remains challenging. This however can be realized by the assistance of advanced computational chemistry. In a mini-review, Bai et al. summarized the use of density functional theory (DFT) calculations to investigate the reaction details and overall kinetics of ROP of N(T)CA, and to optimize the structure of monomers, initiators and catalysts for the polymerization. This article will be very useful for synthetic polymer chemists to gain deeper insight into the reaction mechanism of ROP of N(T)CA at molecular level. CF wrote the editorial. CZ, CS, and XZ reviewed the editorial. All authors contributed to the article and approved the submitted version. The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest. Keywords: biomedical application, functional polymers, synthesis, design, stimuli-response materials, biodearadable polymer Citation: Fu C, Zhu C, Synatschke CV and Zhang X (2021)...
Brendan J. Kennedy, Timothy A. Ablott, Maxim Avdeev, Melody L. Carter, Linda Losurdo, Matilde Saura-Muzquiz, Kevin J. Thorogood, Jimmy Ting, Kia S. Wallwork, Zhaoming Zhang, et al.
Published: 1 July 2021
Frontiers in Chemistry, Volume 9; doi:10.3389/fchem.2021.706269

Abstract:
The structure of lead-technetium pyrochlore has been refined in space group Fd3¯m with a = 10.36584(2) Å using a combination of synchrotron X-ray and neutron powder diffraction data and confirmed via Electron Diffraction. The oxide is found to be oxygen deficient with a stoichiometry of Pb2Tc2O7-d. Displacive disorder of the Pb cations is evident from the refinements, as has been observed in Bi2Tc2O7-d. X-ray absorption spectroscopic measurements at the Tc K-edge demonstrate the valence of the Tc is greater than 4.0 as anticipated from the refined oxygen stoichiometry. Raman spectroscopy confirms the presence of disorder leading us to conclude that this pyrochlore is the first example of a valence V technetium oxide.
Xiuzhao Yin, Lu Liu,
Published: 1 July 2021
Frontiers in Chemistry, Volume 9; doi:10.3389/fchem.2021.683765

Abstract:
Photocatalysts have been paid great attention owing to their excellent performance in the degradation of dangerous organic pollutants. Herein, a novel longitudinally grown WO3 photocatalyst was prepared by using a hydrothermal process, which had strong ultraviolet, visible light absorption, and weak near-infrared (NIR) absorption. The WO3 photocatalyst exhibited excellent performance in the rapid degradation of methylene blue (MB) in industry. The photothermal effect is mainly responsible for the rapid degradation of MB under NIR laser irradiation. Besides, different morphologies and structures affect the degradation of MB. The longitudinally grown enlarged the contact area between photocatalyst and MB, and expanded the scope of the absorption wavelength of light, enhancing the stability of photocatalytic materials. So this unique transverse longitudinal structure exhibited a potential capability for degrading organic pollutants.
Yanhong Zhu, Zhongkui Li, Pengfei Wang, Qi–Ming Qiu, Hongwei Ma,
Published: 30 June 2021
Frontiers in Chemistry, Volume 9; doi:10.3389/fchem.2021.709777

Abstract:
A detailed understanding of the mismatched base-pairing interactions in DNA will help reveal genetic diseases and provide a theoretical basis for the development of targeted drugs. Here, we utilized mononucleotide fragment to simulate mismatch DNA interactions in a local hydrophobic microenvironment. The bipyridyl-type bridging ligands were employed as a mild stabilizer to stabilize the GG mismatch containing complexes, allowing mismatch to be visualized based on X-ray crystallography. Five single crystals of 2′-deoxyguanosine–5′–monophosphate (dGMP) metal complexes were designed and obtained via the process of self-assembly. Crystallographic studies clearly reveal the details of the supramolecular interaction between mononucleotides and guest intercalators. A novel guanine–guanine base mismatch pattern with unusual (high anti)–(high anti) type of arrangement around the glycosidic angle conformations was successfully constructed. The solution state 1H–NMR, ESI–MS spectrum studies, and UV titration experiments emphasize the robustness of this g–motif in solution. Additionally, we combined the methods of single-crystal and solution-, solid-state CD spectrum together to discuss the chirality of the complexes. The complexes containing the g–motif structure, which reduces the energy of the system, following the solid-state CD signals, generally move in the long-wave direction. These results provided a new mismatched base pairing, that is g–motif. The interaction mode and full characterizations of g–motif will contribute to the study of the mismatched DNA interaction.
Satya Kumar Avula, Majid Khan, Sobia Ahsan Halim, Ajmal Khan, Samia Ahmed Al-Riyami, Rene Csuk, Biswanath Das,
Published: 30 June 2021
Frontiers in Chemistry, Volume 9; doi:10.3389/fchem.2021.642614

Abstract:
A series of novel 1H-1,2,3-triazole analogs (9a–j) were synthesized via “Click” chemistry and Suzuki–Miyaura cross-coupling reaction in aqueous medium. The compounds were evaluated for their carbonic anhydrase-II enzyme inhibitory activity in vitro. The synthesis of triazole 7a was accomplished using (S)-(-) ethyl lactate as a starting material. This compound (7a) underwent Suzuki–Miyaura cross-coupling reaction with different arylboronic acids in aqueous medium to afford the target molecules, 9a–j in good yields. All newly synthesized compounds were characterized by 1H NMR, 13C NMR, FT-IR, HRMS, and where applicable 19F NMR spectroscopy (9b, 9e, 9h, and 9j). The new compounds have shown moderate inhibition potential against carbonic anhydrase-II enzyme. A preliminary structure-activity relationship suggested that the presence of polar group at the 1H-1,2,3-triazole substituted phenyl ring in these derivatives (9a–j) has contributed to the overall activity of these compounds. Furthermore, via molecular docking, it was deduced that the compounds exhibit inhibitory potential through direct binding with the active site residues of carbonic anhydrase-II enzyme. This study has unraveled a new series of triazole derivatives as good inhibitors against carbonic anhydrase-II.
Published: 30 June 2021
Frontiers in Chemistry, Volume 9; doi:10.3389/fchem.2021.718755

Abstract:
Editorial on the Research Topic Polymer Chemistry Editor’s Pick 2021 The section Polymer Chemistry of the journal Frontiers in Chemistry was born with the scope of witnessing, disseminating and fostering the advancements of the discipline of macromolecular science in its broadest significance. The opening of a specific section devoted entirely to this subject was justified by the profound impact this discipline and the outcomes of its research efforts have had and continue to have on our everyday life. As stated in the inaugural article (Musto) “Despite the astonishing achievements we have witnessed along the years, many exciting challenges remain to be faced, including green polymer chemistry, environmental pollution issues, polymers for energy storage and delivery, polymers for the human health.” Seven years after its launch, we may say that, so far, the section has accomplished the tasks it was created for. The readership is growing, as well as the community of editors and qualified authors. Many interesting papers have appeared, addressing the most relevant challenges currently open, with special emphasis on health related issues. It was therefore decided, according with the editorial office, that the time was mature to realize a Research Topic, assembling a collection of articles that could give to the reader an outlook of the section activity and a summary of its main achievements. The choice among the numerous high-quality contributions was not easy; it was driven by the limited number of articles to be included (thirteen), the readership acceptance as evaluated by the significant bibliometric figures made available by the journal platform and, of course, the personal taste of the Editor, of which he takes full responsibility. The work presented herein witnesses the broad range of activities covered by the section and demonstrates strong advances in theory, experiment and methodology applied to forefront research challenges. The first contribution Si et al. deals with the development of an innovative hydrogel to be used for selective removal of aromatic pollutants from wastewater. This stimuli-responsive, molecularly imprinted material was characterized by spectroscopic and electron microscopy means and was investigated in terms of adsorption and selective recognition of substituted phenols. It was demonstrated that the hydrogel has good selectivity, temperature switching properties, and is reusable, which makes it a good candidate for controlled separation and release of phenolic pollutants. In the second paper Ding et al. is described the synthesis of chitosan grafted by β-cyclodextrin. This functional material exhibited strong antimicrobial activity against E. coli and Staphylococcus xylosus, which was tuned by adjusting the amino content of the polysaccharide. The reported results may be relevant in the livestock industry as a means of reducing the dosage of antibiotics and the antibiotic residues in animal-derived foods. Next, Galizia and Bye present a detailed review on organic solvent nanofiltration, highlighting the relationship among this process and the underlying physical-chemistry and polymer chemistry. In the first part of the review are discussed the available theoretical models, along with some misleading conclusions commonly encountered in the literature. The following section describes the most conventional materials currently in use and identifies a number of alternative materials that may impact this technology in the near future. The work by Pizarro et al. is an excellent example of the application of precision synthetic routes, in particular, atom-transfer radical polymerization (ATRP), to finely control the surface properties of polymer films. It was demonstrated that parameters such as pore size, roughness, thickness, and wettability of a co-polymer film could be varied by changing the co-monomer structures. Moreover, thermal annealing was found to improve significantly the surface quality, thus providing a further means toward surface engineering. The review article by Yao et al. is an account of current research on polymer-based composites to be used as electrolytes in Lithium batteries. This is a relevant technological challenge, since substitution of the conventional liquid electrolytes currently in use with solid-state components may allow to overcome numerous weaknesses of Li-ion cells. The survey describes in detail the main classes of composites under consideration, with the relative conductivity mechanisms. The fundamental issues still unsolved are critically discussed. The research paper by Quigley et al. concerns a relevant health issue, namely the repairing of Volumetric Muscle Loss (VML) as a consequence of trauma (road/industrial accident, war injury) or disease (muscular dystrophy, muscle atrophy). The authors report an innovative biosynthetic material based on the “Trojan Horse” concept. It is an alginate/myoblast construct that was tested successfully as a scaffold for remodelling of diseased and/or damaged muscle. The work by Talebian et al. deals with electrically conductive hydrogels to be used as biofibers for in-vivo stimulation of electrically excitable cells. The biofibers were realized by electrospinning of an alginate/graphene nanocomposite. The graphene-additivated biofibers exhibited better mechanical, electrical and electrochemical properties in comparison to the pristine fibers. In the light of the results obtained, they were also proposed as 3D scaffolds for tissue engineering applications. Light-responsive materials, e.g., materials that exhibit on-off switching properties when irradiated at specific frequencies, are a hot-topic for an increasing number of high-tech applications. The paper by Pang et al. reports on the realization and the morphological/spectroscopic characterization of one of such systems based on the interaction between β-cyclodextrin and the azobenzene group. This...
Ruili Shi, Zhi Zhao, XiaoMing Huang, Pengju Wang, , Linwei Sai, Xiaoqing Liang, Haiyan Han, Jijun Zhao
Published: 30 June 2021
Frontiers in Chemistry, Volume 9; doi:10.3389/fchem.2021.637750

Abstract:
We searched the lowest-energy structures of hydrated calcium ion clusters Ca2+(H2O)n (n = 10–18) in the whole potential energy surface by the comprehensive genetic algorithm (CGA). The lowest-energy structures of Ca2+(H2O)10–12 clusters show that Ca2+ is always surrounded by six H2O molecules in the first shell. The number of first-shell water molecules changes from six to eight at n = 12. In the range of n = 12–18, the number of first-shell water molecules fluctuates between seven and eight, meaning that the cluster could pack the water molecules in the outer shell even though the inner shell is not full. Meanwhile, the number of water molecules in the second shell and the total hydrogen bonds increase with an increase in the cluster size. The distance between Ca2+ and the adjacent water molecules increases, while the average adjacent O-O distance decreases as the cluster size increases, indicating that the interaction between Ca2+ and the adjacent water molecules becomes weaker and the interaction between water molecules becomes stronger. The interaction energy and natural bond orbital results show that the interaction between Ca2+ and the water molecules is mainly derived from the interaction between Ca2+ and the adjacent water molecules. The charge transfer from the lone pair electron orbital of adjacent oxygen atoms to the empty orbital of Ca2+ plays a leading role in the interaction between Ca2+ and water molecules.
Fei Yu, Ming Cai, Liang Shao,
Published: 30 June 2021
Frontiers in Chemistry, Volume 9; doi:10.3389/fchem.2021.679120

Abstract:
Kinase dysregulation is greatly associated with cell proliferation, migration and survival, indicating the importance of kinases as therapeutic targets for anticancer drug development. However, traditional kinase inhibitors binding to catalytic or allosteric sites are associated with significant challenges. The emergence of resistance and targeting difficult-to-degrade and multi-domain proteins are significant limiting factors affecting the efficacy of targeted anticancer drugs. The next-generation treatment approaches seem to have overcome these concerns, and the use of proteolysis targeting chimera (PROTAC) technology is one such method. PROTACs bind to proteins of interest and recruit E3 ligase for degrading the whole target protein via the ubiquitin-proteasome pathway. This review provides a detailed summary of the most recent signs of progress in PROTACs targeting different kinases, primarily focusing on new chemical entities in medicinal chemistry.
Pierre Delfosse, Colin C. Seaton, Louise Male, ,
Published: 30 June 2021
Frontiers in Chemistry, Volume 9; doi:10.3389/fchem.2021.709161

Abstract:
The synthesis and characterization of three aromatic oligoamides, constructed from the same pyridyl carboxamide core but incorporating distinct end groups of acetyl (Ac) 1, tert-butyloxycarbonyl (Boc) 2 and amine 3 is reported. Single crystal X-ray diffraction analysis of 1–3 and a dimethylsulfoxide (DMSO) solvate of 2 (2-DMSO), has identified the presence of a range of intra- and intermolecular interactions including N-H⋯N, N-H⋯O=C and N-H⋯O=S(CH3)2 hydrogen-bonding interactions, C-H⋯π interactions and off-set, face-to-face stacking π-π interactions that support the variety of slipped stack, herringbone and cofacial crystal packing arrangements observed in 1–3. Additionally, the cytotoxicity of this series of aromatic oligoamides was assessed against two human ovarian (A2780 and A2780cisR), two human breast (MCF-7 and MDA-MB-231) cancerous cell lines and one non-malignant human epithelial cell line (PNT-2), to investigate the influence of the terminal functionality of these aromatic oligoamides on their biological activity. The chemosensitivity results highlight that modification of the terminal group from Ac to Boc in 1 and 2 leads to a 3-fold increase in antiproliferative activity against the cisplatin-sensitive ovarian carcinoma cell line, A2780. The presence of the amine termini in 3 gave the only member of the series to display activity against the cisplatin-resistance ovarian carcinoma cell line, A2780cisR. Compound 2 is the lead candidate of this series, displaying high selectivity towards A2780 cancer cells when compared to non-malignant PNT-2 cells, with a selectivity index value >4.2. Importantly, this compound is more selective towards A2780 (cf. PNT-2) than the clinical platinum drugs oxaliplatin by > 2.6-fold and carboplatin by > 1.6-fold.
Eliane Ribeiro Januario, Patrícia Ferreira Silvaino, Arthur Pignataro Machado, Jorge Moreira Vaz,
Published: 30 June 2021
Frontiers in Chemistry, Volume 9; doi:10.3389/fchem.2021.685073

Abstract:
The processes currently used in the chemical industry for methane conversion into fuels and chemicals operate under extreme conditions like high temperatures and pressures. In this sense, the search for methane conversion under mild conditions remains a great challenge. This review aims to summarize the use semiconductors and metal-semiconductors as heterogeneous photocatalysts for methane conversion under mild conditions into valuable products. First, a brief presentation of photochemical conversion of methane is provided and then the focus of this review on the use of heterogeneous photocatalysts for methane conversion are described. Finally, the main challenges and opportunities are discussed.
Udisha Singh, Vinod Morya, Bhaskar Datta, Chinmay Ghoroi,
Published: 30 June 2021
Frontiers in Chemistry, Volume 9; doi:10.3389/fchem.2021.704234

Abstract:
Of the multiple areas of applications of DNA nanotechnology, stimuli-responsive nanodevices have emerged as an elite branch of research owing to the advantages of molecular programmability of DNA structures and stimuli-responsiveness of motifs and DNA itself. These classes of devices present multiples areas to explore for basic and applied science using dynamic DNA nanotechnology. Herein, we take the stake in the recent progress of this fast-growing sub-area of DNA nanotechnology. We discuss different stimuli, motifs, scaffolds, and mechanisms of stimuli-responsive behaviours of DNA nanodevices with appropriate examples. Similarly, we present a multitude of biological applications that have been explored using DNA nanodevices, such as biosensing, in vivo pH-mapping, drug delivery, and therapy. We conclude by discussing the challenges and opportunities as well as future prospects of this emerging research area within DNA nanotechnology.
Kathleen A. Trychta, Bing Xie, Ravi Kumar Verma, Min Xu, ,
Published: 29 June 2021
Frontiers in Chemistry, Volume 9; doi:10.3389/fchem.2021.689608

Abstract:
The lumen of the endoplasmic reticulum (ER) has resident proteins that are critical to perform the various tasks of the ER such as protein maturation and lipid metabolism. These ER resident proteins typically have a carboxy-terminal ER retention/retrieval sequence (ERS). The canonical ERS that promotes ER retrieval is Lys-Asp-Glu-Leu (KDEL) and when an ER resident protein moves from the ER to the Golgi, KDEL receptors (KDELRs) in the Golgi recognize the ERS and return the protein to the ER lumen. Depletion of ER calcium leads to the mass departure of ER resident proteins in a process termed exodosis, which is regulated by KDELRs. Here, by combining computational prediction with machine learning-based models and experimental validation, we identify carboxy tail sequences of ER resident proteins divergent from the canonical “KDEL” ERS. Using molecular modeling and simulations, we demonstrated that two representative non-canonical ERS can stably bind to the KDELR. Collectively, we developed a method to predict whether a carboxy-terminal sequence acts as a putative ERS that would undergo secretion in response to ER calcium depletion and interacts with the KDELRs. The interaction between the ERS and the KDELR extends beyond the final four carboxy terminal residues of the ERS. Identification of proteins that undergo exodosis will further our understanding of changes in ER proteostasis under physiological and pathological conditions where ER calcium is depleted.
Michał Jakubczak,
Published: 29 June 2021
Frontiers in Chemistry, Volume 9; doi:10.3389/fchem.2021.685014

Abstract:
Graphene-based nanocomposites constitute an interesting and promising material for various applications. Intensive progress in the development of this group of materials offers an opportunity to create new systems useful for drinking water decontamination or other biotechnological applications. Nanohybrid structures of graphene-ceramic systems can be obtained using covalent graphene surface modification with nanoparticles (NPs) of ceramic and/or co-deposition of metals with selected morphology and chemistry. The present paper systematizes the associated bio-related knowledge and inspires future development of graphene/NPs systems. Emerging knowledge and unique research techniques are reviewed within designing the required nanocomposite structure and chemical composition, development and optimization of new methods of covalent surface modification of graphene with NPs as well as analysis of mechanisms governing the formation of covalent bonding. Further, innovative research tools and methodologies are presented regarding the adjustment of functionalities of materials used for the application in drinking water decontamination or biocidal composites. This study provides a comprehensive base for rational development of more complex, hybrid graphene-based nanomaterials with various bio-functionalities that can be further applied in industrial practice.
Tian-Xing Zhang, Juan-Juan Li, Hua-Bin Li, Dong-Sheng Guo
Published: 29 June 2021
Frontiers in Chemistry, Volume 9; doi:10.3389/fchem.2021.710808

Abstract:
Fullerene has attracted much attention in biomedical research due to its unique physical and chemical properties. However, the hydrophobic nature of fullerene is limited to deploy in the body, given that the biofluids are mainly water. In this study, a water-soluble supramolecular nanoformulation based on a deep cavitand calixarene (SAC4A) and fullerene is developed to overcome the hydrophobicity of fullerene and is used as a potential photodynamic agent. SAC4A solubilizes fullerene very well with a simple grinding method. The significantly increased water solubility of fullerene enables efficient activation of reactive oxygen species. The host–guest strategy to solubilize fullerene can not only provide a new method to achieve water solubility but also expand the biomedical applications of fullerene.
, Tatsiana Burankova, Mario Öeren, Kristina Juhhimenko, Jenni Ilmarinen, Kristjan Siilak, Kamini A. Mishra,
Published: 28 June 2021
Frontiers in Chemistry, Volume 9; doi:10.3389/fchem.2021.701028

Abstract:
Inherently chiral, barrel-shaped, macrocyclic hosts such as cyclohexanohemicucurbit[n]urils (cycHC[n]) bind zinc porphyrins and trifluoroacetic acid externally in halogenated solvents. In the current study, we tested a set of eighteen organic guests with various functional groups and polarity, namely, thiophenols, phenols, and carboxylic and sulfonic acids, to identify a preference toward hydrogen bond–donating molecules for homologous cycHC[6] and cycHC[8]. Guests were characterized by Hirshfeld partial charges on acidic hydrogens and their binding by 1H and 19F NMR titrations. Evaluation of association constants revealed the complexity of the system and indirectly proved an external binding with stoichiometry over 2:1 for both homologs. It was found that overall binding strength is influenced by the stoichiometry of the formed complexes, the partial atomic charge on the hydrogen atom of the hydrogen bond donor, and the bulkiness of the guest. Additionally, a study on the formation of complexes with halogen anions (Cl− and Br−) in methanol and chloroform, analyzed by 1H NMR, did not confirm complexation. The current study widens the scope of potential applications for host molecules by demonstrating the formation of hydrogen-bonded complexes with multisite hydrogen bond acceptors such as cycHC[6] and cycHC[8].
Yeting Guo, , Dongru Sun, Yumeng Zhang, Minyang Zheng, Ruiwen Ding, Yan Liu,
Published: 28 June 2021
Frontiers in Chemistry, Volume 9; doi:10.3389/fchem.2021.675821

Abstract:
Cyclic dipeptides (DKPs) are peptide precursors and chiral catalysts in the prebiotic process. This study reports proline-containing DKPs that were spontaneously obtained from linear dipeptides under an aqueous solution. Significantly, the yields of DKPs were affected by the sequence of linear dipeptides and whether the reaction contains trimetaphosphate. These findings provide the possibility that DKPs might play a key role in the origin of life.
Asmita Dey, Ujjal Haldar,
Published: 28 June 2021
Frontiers in Chemistry, Volume 9; doi:10.3389/fchem.2021.644547

Abstract:
The foremost limitation of block copolymer synthesis is to polymerize two or more different types of monomers with different reactivity profiles using a single polymerization technique. Controlled living polymerization techniques play a vital role in the preparation of wide range of block copolymers, thus are revolutionary techniques for polymer industry. Polymers with good control over molecular weight, molecular weight distribution, chain-end functionality and architectures can be prepared by these processes. In order to improve the existing applications and create new opportunities to design a new block copolymer system with improved physical and chemical properties, the combination of two different polymerization techniques have tremendous scope. Such kinds of macromolecules may be attended by combination of homopolymerization of different monomers by post-modification techniques using a macroinitiator or by using a dual initiator which allows the combination of two mechanistically distinct techniques. This review focuses on recent advances in synthesis of block copolymers by combination of living cationic polymerization with other polymerization techniques and click chemistry.
Page of 78
Articles per Page
by
Show export options
  Select all
Back to Top Top