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Scott Benz,
Beilstein Journal of Organic Chemistry, Volume 17, pp 2570-2584; https://doi.org/10.3762/bjoc.17.172

Abstract:
In the presence of a suitable acid or base, α-hydroxyaldehydes, ketones, and imines can undergo isomerization that features the 1,2-shift of an alkyl or aryl group. In the process, the hydroxy group is converted to a carbonyl and the aldehyde/ketone or imine is converted to an alcohol or amine. Such α-ketol/α-iminol rearrangements are used in a wide variety of synthetic applications including asymmetric synthesis, tandem reactions, and the total synthesis and biosynthesis of natural products. This review explores the use of α-ketol rearrangements in these contexts over the past two decades.
Luke O. Jones, Leah Williams, Tasmin Boam, Martin Kalmet, Chidubem Oguike,
Beilstein Journal of Organic Chemistry, Volume 17, pp 2553-2569; https://doi.org/10.3762/bjoc.17.171

Abstract:
Cryogels are macroporous polymeric structures formed from the cryogelation of monomers/polymers in a solvent below freezing temperature. Due to their inherent interconnected macroporosity, ease of preparation, and biocompatibility, they are increasingly being investigated for use in biomedical applications such as 3D-bioprinting, drug delivery, wound healing, and as injectable therapeutics. This review highlights the fundamentals of macroporous cryogel preparation, cryogel properties that can be useful in the highlighted biomedical applications, followed by a comprehensive review of recent studies in these areas. Research evaluated includes the use of cryogels to combat various types of cancer, for implantation without surgical incision, and use as highly effective wound dressings. Furthermore, conclusions and outlooks are discussed for the use of these promising and durable macroporous cryogels.
, , Vladimir A. Oleinikov
Published: 14 October 2021
Abstract:
Low-frequency hysteresis loops and specific absorption rate (SAR) of various assemblies of elongated spheroidal magnetite nanoparticles have been calculated for a range of particle semiaxis ratios a/b = 1.0 – 3.0. The SAR of a dilute randomly oriented assembly of magnetite nanoparticles in an alternating magnetic field of moderate frequency, f = 300 kHz, and amplitude H 0 = 100 - 200 Oe is shown to decrease significantly with an increase in the aspect ratio of nanoparticles. In addition, there is a narrowing and shift of the intervals of optimal particle diameters towards smaller particle sizes. However, the orientation of a dilute assembly of elongated nanoparticles in a magnetic field leads to an almost twofold increase in SAR at the same frequency and amplitude of the alternating magnetic field, the range of optimal particle diameters remaining unchanged. The effect of the magneto-dipole interaction on the SAR of an assembly of oriented clusters of elongated magnetite nanoparticles has also been investigated depending on the volume fraction of nanoparticles in a cluster. It has been found that the SAR of the assembly of oriented clusters decreases by approximately an order of magnitude with an increase in the volume fraction of nanoparticles in a cluster in the range 0.04 - 0.2.
, , Gennady Sushko, Andrey V. Solov’Yov
Beilstein Journal of Nanotechnology, Volume 12, pp 1151-1172; https://doi.org/10.3762/bjnano.12.86

Abstract:
This paper presents a detailed computational protocol for the atomistic simulation of formation and growth of metal-containing nanostructures during focused electron beam-induced deposition (FEBID). The protocol is based upon irradiation-driven molecular dynamics (IDMD), a novel and general methodology for computer simulations of irradiation-driven transformations of complex molecular systems by means of the advanced software packages MBN Explorer and MBN Studio. Atomistic simulations performed following the formulated protocol provide valuable insights into the fundamental mechanisms of electron-induced precursor fragmentation and the related mechanism of nanostructure formation and growth using FEBID, which are essential for the further advancement of FEBID-based nanofabrication. The developed computational methodology is general and applicable to different precursor molecules, substrate types, and irradiation regimes. The methodology can also be adjusted to simulate the nanostructure formation by other nanofabrication techniques using electron beams, such as direct electron beam lithography. In the present study, the methodology is applied to the IDMD simulation of the FEBID of Pt(PF3)4, a widely studied precursor molecule, on a SiO2 surface. The simulations reveal the processes driving the initial phase of nanostructure formation during FEBID, including the nucleation of Pt atoms and the formation of small metal clusters on the surface, followed by their aggregation and the formation of dendritic platinum nanostructures. The analysis of the simulation results provides spatially resolved relative metal content, height, and growth rate of the deposits, which represents valuable reference data for the experimental characterization of the nanostructures grown by FEBID.
Robin Klintworth, Garreth L. Morgans, Stefania M. Scalzullo, , ,
Beilstein Journal of Organic Chemistry, Volume 17, pp 2543-2552; https://doi.org/10.3762/bjoc.17.170

Abstract:
A wide range of N-(ethoxycarbonylmethyl)enaminones, prepared by the Eschenmoser sulfide contraction between N-(ethoxycarbonylmethyl)pyrrolidine-2-thione and various bromomethyl aryl and heteroaryl ketones, underwent cyclization in the presence of silica gel to give ethyl 6-(hetero)aryl-2,3-dihydro-1H-pyrrolizine-5-carboxylates within minutes upon microwave heating in xylene at 150 °C. Instead of functioning as a nucleophile, the enaminone acted as an electrophile at its carbonyl group during the cyclization. Yields of the bicyclic products were generally above 75%. The analogous microwave-assisted reaction to produce ethyl 2-aryl-5,6,7,8-tetrahydroindolizine-3-carboxylates from (E)-ethyl 2-[2-(2-oxo-2-arylethylidene)piperidin-1-yl]acetates failed in nonpolar solvents, but occurred in ethanol at lower temperature and microwave power, although requiring much longer time. A possible mechanism for the cyclization is presented, and further functionalization of the newly created pyrrole ring in the dihydropyrrolizine core is described.
Huan Ren, Lifang Wu, Lina Tan, Yanni Bao, Yuchen Ma, , Qianli Zou
Beilstein Journal of Nanotechnology, Volume 12, pp 1140-1150; https://doi.org/10.3762/bjnano.12.85

Abstract:
Biomolecules, such as proteins and peptides, can be self-assembled. They are widely distributed, easy to obtain, and biocompatible. However, the self-assembly of proteins and peptides has disadvantages, such as difficulty in obtaining high quantities of materials, high cost, polydispersity, and purification limitations. The difficulties in using proteins and peptides as functional materials make it more complicate to arrange assembled nanostructures at both microscopic and macroscopic scales. Amino acids, as the smallest constituent of proteins and the smallest constituent in the bottom-up approach, are the smallest building blocks that can be self-assembled. The self-assembly of single amino acids has the advantages of low synthesis cost, simple modeling, excellent biocompatibility and biodegradability in vivo. In addition, amino acids can be assembled with other components to meet multiple scientific needs. However, using these simple building blocks to design attractive materials remains a challenge due to the simplicity of the amino acids. Most of the review articles about self-assembly focus on large molecules, such as peptides and proteins. The preparation of complicated materials by self-assembly of amino acids has not yet been evaluated. Therefore, it is of great significance to systematically summarize the literature of amino acid self-assembly. This article reviews the recent advances in amino acid self-assembly regarding amino acid self-assembly, functional amino acid self-assembly, amino acid coordination self-assembly, and amino acid regulatory functional molecule self-assembly.
Yajing Zhang, Qian Wang, Zongsheng Yan, Donglai Ma, Yuguang Zheng
Beilstein Journal of Organic Chemistry, Volume 17, pp 2520-2542; https://doi.org/10.3762/bjoc.17.169

Abstract:
Photoredox catalysis has been applied to renewable energy and green chemistry for many years. Ruthenium and iridium, which can be used as photoredox catalysts, are expensive and scarce in nature. Thus, the further development of catalysts based on these transition metals is discouraged. Alternative photocatalysts based on copper complexes are widely investigated, because they are abundant and less expensive. This review discusses the scope and application of photoinduced copper-based catalysis along with recent progress in this field. The special features and mechanisms of copper photocatalysis and highlights of the applications of the copper complexes to photocatalysis are reported. Copper-photocatalyzed reactions, including alkene and alkyne functionalization, organic halide functionalization, and alkyl C–H functionalization that have been reported over the past 5 years, are included.
Karishma Berta Cotta, ,
Beilstein Journal of Nanotechnology, Volume 12, pp 1127-1139; https://doi.org/10.3762/bjnano.12.84

Abstract:
Nanoparticle deployment in drug delivery is contingent upon controlled drug loading and a desired release profile, with simultaneous biocompatibility and cellular targeting. Iron oxide nanoparticles (IONPs), being biocompatible, are used as drug carriers. However, to prevent aggregation of bare IONPs, they are coated with stabilizing agents. We hypothesize that, zwitterionic drugs like norfloxacin (NOR, a fluoroquinolone) can manifest dual functionality – nanoparticle stabilization and antibiotic activity, eliminating the need of a separate stabilizing agent. Since these drugs have different charges, depending on the surrounding pH, drug loading enhancement could be pH dependent. Hence, upon synthesizing IONPs, they were coated with NOR, either at pH 5 (predominantly as cationic, NOR+) or at pH 10 (predominantly as anionic, NOR−). We observed that, drug loading at pH 5 exceeded that at pH 10 by 4.7–5.7 times. Furthermore, only the former (pH 5 system) exhibited a desirable slower drug release profile, compared to the free drug. NOR-coated IONPs also enable a 22 times higher drug accumulation in macrophages, compared to identical extracellular concentrations of the free drug. Thus, lowering the drug coating pH to 5 imparts multiple benefits – improved IONP stability, enhanced drug coating, higher drug uptake in macrophages at reduced toxicity and slower drug release.
, Maria Chrzanowska, Wiktoria Adamska
Beilstein Journal of Organic Chemistry, Volume 17, pp 2511-2519; https://doi.org/10.3762/bjoc.17.168

Abstract:
A convenient and simple protocol has been developed for the synthesis of a series of new tetracyclic tetrahydroisoquinoline derivatives, 7,12-dihydro-6,12-methanodibenzo[c,f]-azocine-5-carboxylic acids by three component Petasis reaction with the use of aminoacetaldehyde acetals bearing substituted benzyl groups as the amine components followed by Pomeranz–Fritsch double cyclization reaction. By applying this method, several acids have been prepared in satisfactory yields. An unprecedented chemical behavior of a Petasis reaction product in diluted HCl solution leading to the formation of a phenylglycine derivative has been observed and the mechanism explaining such reactivity has been proposed.
, Pradeep Namboodiri
Beilstein Journal of Nanotechnology, Volume 12, pp 1115-1126; https://doi.org/10.3762/bjnano.12.83

Abstract:
The open-loop (OL) variant of Kelvin probe force microscopy (KPFM) provides access to the voltage response of the electrostatic interaction between a conductive atomic force microscopy (AFM) probe and the investigated sample. The measured response can be analyzed a posteriori, modeled, and interpreted to include various contributions from the probe geometry and imaged features of the sample. In contrast to this, the currently implemented closed-loop (CL) variants of KPFM, either amplitude-modulation (AM) or frequency-modulation (FM), solely report on their final product in terms of the tip–sample contact potential difference. In ambient atmosphere, both CL AM-KPFM and CL FM-KPFM work at their best during the lift part of a two-pass scanning mode to avoid the direct contact with the surface of the sample. In this work, a new OL AM-KPFM mode was implemented in the single-pass scan of the PeakForce Tapping (PFT) mode. The topographical and electrical components were combined in a single pass by applying the electrical modulation only in between the PFT tip–sample contacts, when the AFM probe separates from the sample. In this way, any contact and tunneling discharges are avoided and, yet, the location of the measured electrical tip–sample interaction is directly affixed to the topography rendered by the mechanical PFT modulation at each tap. Furthermore, because the detailed response of the cantilever to the bias stimulation was recorded, it was possible to analyze and separate an average contribution of the cantilever to the determined local contact potential difference between the AFM probe and the imaged sample. The removal of this unwanted contribution greatly improved the accuracy of the AM-KPFM measurements to the level of the FM-KPFM counterpart.
Beilstein Journal of Nanotechnology, Volume 12, pp 1101-1114; https://doi.org/10.3762/bjnano.12.82

Abstract:
Tin selenide (SnSe) has thermoelectric (TE) and photovoltaic (PV) applications due to its exceptional advantages, such as the remarkable figure of merit (ZT ≈ 2.6 at 923 K) and excellent optoelectronic properties. In addition, SnSe is nontoxic, inexpensive, and relatively abundant. These aspects make SnSe of great practical importance for the next generation of thermoelectric devices. Here, we report structural, optoelectronic, thermodynamic, and thermoelectric properties of the recently experimentally identified binary phase of tin monoselenide (π-SnSe) by using the density functional theory (DFT). Our DFT calculations reveal that π-SnSe features an optical bandgap of 1.41 eV and has an exceptionally large lattice constant (12.2 Å, P213). We report several thermodynamic, optical, and thermoelectric properties of this π-SnSe phase for the first time. Our finding shows that the π-SnSe alloy is exceptionally promising for the next generation of photovoltaic and thermoelectric devices at room and high temperatures.
, Jarosław Domaradzki, , Tomasz Kotwica, Danuta Kaczmarek
Published: 5 October 2021
Abstract:
The paper presents the results of the analysis of resistive switching properties observed in (Ti-Cu)-oxide thin film with gradient distribution of elements over the thin film thickness. Thin films were prepared using the multisource reactive magnetron co-sputtering process. Programmed profile of the pulse width modulation coefficient during sputtering of the Cu target allowed to obtain the designed gradient U-shape profile of Cu concentration in the deposited thin film. Electrical measurements of Au/(Ti-Cu)Ox/TiAlV structure showed the presence of nonpinched hysteresis loops in the voltage–current plane testifying the resistive switching behavior. Additionally, the initial forming process of conducting filaments has been observed as well. Optical, x-ray, and ultraviolet photoelectron spectroscopy measurements allowed to create the scheme of the bandgap alignment of the prepared thin films with respect to the Au and TiAlV electrical contacts. Detailed structure and elemental profile investigations allowed to conclude about the presence of conducting filaments of the observed resistive switching mechanism occurring in the prepared test structure. The obtained results showed that the prepared gradient (Ti-Cu)Ox thin film could be an interesting alternative to the conventional multilayer stack construction of resistive switching devices.
Mikhail M. Krasnov, Natalia D. Novikova, Roger Cattaneo, Alexey A. Kalenyuk,
Published: 1 October 2021
Abstract:
Impedance matching and heat management are important factors influencing performance of THz sources. In this work we analyze thermal and radiative properties of such devices based on mesa structures of a layered high-temperature superconductor Bi2Sr2CaCu2O8+δ. Two types of devices are considered, containing either a conventional large single crystal, or a whisker. We perform numerical simulations for various geometrical configurations and parameters and make a comparison with experimental data for the two types of devices. It is demonstrated that the structure and the geometry of both the superconductor and the electrodes are playing important roles. In crystal-based devices an overlap between the crystal and the electrode leads to appearance of a large parasitic capacitance, which shunts THz emission and prevents impedance matching with open space. The overlap is avoided in whisker-based devices. Furthermore, the whisker and the electrodes form a turnstile (crossed-dipole) antenna facilitating good impedance matching. This leads to more than an order of magnitude enhancement of the radiation power efficiency in whisker-based, compared to crystal-based devices. These results are in good agreement with presented experimental data.
Siyu Wang, , Shutao Wang, Shulin Ning, Zhuoqi Zhang,
Beilstein Journal of Organic Chemistry, Volume 17, pp 2505-2510; https://doi.org/10.3762/bjoc.17.167

Abstract:
A base- and catalyst-free C(sp3)–H allylic alkylation of 2-alkylpyridines with Morita–Baylis–Hillman (MBH) carbonates is described. A plausible mechanism of the reaction might involve a tandem SN2’ type nucleophilic substitution followed by an aza-Cope rearrangement. Various alkyl substituents on 2-alkylpyridines were tolerated in the reaction to give the allylation products in 26–91% yields. The developed method provides a straightforward and operational simple strategy for the allylic functionalization of 2-alkypyridine derivatives.
Beilstein Journal of Nanotechnology, Volume 12, pp 1093-1100; https://doi.org/10.3762/bjnano.12.81

Abstract:
Most of the technically important properties of nanomaterials, such as superparamagnetism or luminescence, depend on the particle size. During synthesis and handling of nanoparticles, agglomeration may occur. Agglomeration of nanoparticles may be controlled by different mechanisms. During synthesis one observes agglomeration controlled by the geometry and electrical charges of the particles. Additionally, one may find agglomeration controlled by thermodynamic interaction of the particles in the direction of a minimum of the free enthalpy. In this context, one may observe mechanisms leading to a reduction of the surface energy or controlled by the van der Waals interaction. Additionally, the ensemble may arrange in the direction of a maximum of the entropy. Simulations based on Monte Carlo methods teach that, in case of any energetic interaction of the particles, the influence of the entropy is minor or even negligible. Complementary to the simulations, the extremum of the entropy was determined using the Lagrange method. Both approaches yielded identical result for the particle size distribution of an agglomerated ensemble, that is, an exponential function characterized by two parameters. In this context, it is important to realize that one has to take care of fluctuations of the entropy.
Josefine Meurer, , Johannes Ahner, , , Stefan Zechel, Kalina Peneva,
Beilstein Journal of Organic Chemistry, Volume 17, pp 2496-2504; https://doi.org/10.3762/bjoc.17.166

Abstract:
The self-healing behavior of two supramolecular polymers based on π–π-interactions featuring different polymer backbones is presented. For this purpose, these polymers were synthesized utilizing a polycondensation of a perylene tetracarboxylic dianhydride with polyether-based diamines and the resulting materials were investigated using various analytical techniques. Thus, the molecular structure of the polymers could be correlated with the ability for self-healing. Moreover, the mechanical behavior was studied using rheology. The activation of the supramolecular interactions results in a breaking of these noncovalent bonds, which was investigated using IR spectroscopy, leading to a sufficient increase in mobility and, finally, a healing of the mechanical damage. This scratch-healing behavior was also quantified in detail using an indenter.
Jun-Xian Gou, Yang Luo, Xi-Nan Yang, Wei Zhang, Ji-Hong Lu, Zhu Tao,
Published: 29 September 2021
Abstract:
Three different complexes, TMeQ[6]-TBT, Q[7]-TBT and Q[8]-TBT, are constructed by three different cucurbiturils and synthesized guest melamine-cored Schiff base (TBT) through outer-surface interaction and host-guest interaction, where TBT and TMeQ[6] form complex TMeQ[6]-TBT through outer-surface interaction, while TBT and Q[7,8] form complexs Q[7]-TBT and Q[8]-TBT through host-guest interaction., and finally, Q[7]-TBT is selected as a UV detector for the detection of precious metal Ag+. This work makes full use of the characteristics of each cucurbiturils and combines that of Schiff bases to construct a series of complexes and apply them to metal detection.
Published: 29 September 2021
Abstract:
Background: Friction and wear of polymers at the nano scale is a challenging problem due to the complex viscoelastic properties and structure. Using molecular-dynamics simulations, we investigate how a graphene sheet on top of a semicrystalline polymer (PVA) affects the friction and wear. Results: Our setup is meant to resemble an AFM experiment with a silicon tip. We have used two different graphene sheets: an unstrained, flat sheet, and one that has been crumpled before being deposited on the polymer. Conclusion: The graphene protects the top layer of the polymer from wear and reduces the friction. The unstrained flat graphene is stiffer, and we find that it constrains the polymer chains and reduces the indentation depth.
Mohammad S. Ahmad,
Published: 27 September 2021
Abstract:
The effect of tensile stress on the electronic properties of pristine graphene mono-sheet was investigated. We applied different stress factors in order to investigate the mechanical and electronic properties of graphene monolayer. As a consequence of the applied tensile stress, different patterns of ripples were created. Whereas, different rippling levels were significantly tuned the electronic properties of the graphene monolayer. For instance, the band gap of graphene monolayer dramatically increased with increasing the tensile stress factor. Moreover, the combined effect of applying tensile stress as well as bending the sheet significantly modified the band gap. However, applying more tensile stress induced a reverse behavior. We highly believe that, controlling local curvatures of graphene monolayer opens up opportunities for strain assisted tuning of local electronic structure such as band gap engineered devices.
Keshav Nagpal, , Frédérique Ducroquet,
Beilstein Journal of Nanotechnology, Volume 12, pp 1078-1092; https://doi.org/10.3762/bjnano.12.80

Abstract:
Light-emitting diodes (LED) are widely employed in display applications and lighting systems. Further research on LED that incorporates carbon nanostructures and metal nanoparticles exhibiting surface plasmon resonance has demonstrated a significant improvement in device performance. These devices offer lower turn-on voltages, higher external quantum efficiencies, and luminance. De facto, plasmonic nanoparticles, such as Au and Ag have boosted the luminance of red, green, and blue emissions. When combined with carbon nanostructures they additionally offer new possibilities towards lightweight and flexible devices with better thermal management. This review surveys the diverse possibilities to combine various inorganic, organic, and carbon nanostructures along with plasmonic nanoparticles. Such combinations would allow an enhancement in the overall properties of LED.
, Fernanda N. Rodrigues, Nidyedja G.G. Gonçalves, Mateus T. Aerre, , Francisco F. Bezerra, Paulo A.S. Mourão, , Maria S.R. Bastos, , et al.
Published: 24 September 2021
Abstract:
Iron nanoparticles (FeNP) present excellent magnetic properties and chemical stability, and for this reason, they are often configured into materials for a variety of potential uses in medical, biotechnological, and other applications. In this work, iron oxide nanoparticles functionalized with galactomannan (FeNP/Gal) from Caesalpinia pulcherrima were synthesized and submitted to characterization and evaluation of the cytotoxic activity. The functionalized nanoparticles were synthesized by co-precipitation and subjected to a process of surface modification with galactomannan and epichlorohydrin. These nanomaterials were characterized using infrared spectroscopy, X-ray diffraction (XRD), thermogravimetric analysis (TGA), differential thermogravimetric analysis (DTA), and scanning electron microscopy (SEM). 1D and 2D nuclear magnetic resonance (NMR) spectroscopy were also used in the structural analysis of the galactomannan. In addition, in vitro study was carried out to evaluate the cytotoxic activity of the FeNP/Gal nanoparticles on human cells of the HEK-293 strain (ATCC® CRL-1573). The FeNP/Gal nanoparticles had an average diameter of 13 ± 2 nm as opposed to 11 ± 2 nm for unreacted FeNP. The infrared spectrum of the FeNP/Gal nanoparticles presents characteristic absorbance bands of their chemical constituents, confirming that the iron oxide nanoparticles were functionalized with galactomannan. The cytotoxicity assay for the FeNP/Gal nanoparticles did not show significant cytotoxicity against HEK 293-Human embryonic kidney cell lines below 800 µg/mL However, this study points out the possibility of using hemicellulose and other plant-based polysaccharides to produce nanostructured materials for ​​tissue engineering and other biomedical applications.
Jing He, Yueting Wei, Yijiao Feng, Chuntian Li, Bin Dai,
Published: 24 September 2021
Abstract:
A direct C-H halogenation of 3-aryl-1H-pyrazol-5-amines with NXS (X = Br, I, Cl) as cheap and safe halogenating reagents at room temperature has been developed. This transformation provides an effective metal-free protocol towards the synthesis of novel 4-halogenated pyrazole derivatives with moderate to excellent yields. The method represents simple and mild reaction conditions, broad substrate scope as well as gram-scale synthesis. The utility of this procedure is established by further transformations of the 4-halogenated products. Mechanism studies show that DMSO plays a dual role of catalyst and solvent.
Gurrala Thirupathi, Kamatam Govardhan,
Published: 23 September 2021
Abstract:
The magnetohydrodynamics (MHD) stagnation point Casson nanofluid flow towards stretching surface with velocity slip and convective boundary condition has been investigated in this article. Effects of thermal radiation, viscous dissipation, heat source and chemical reaction have also been incorporated. Using appropriate similarity transformation Partial Differential Equations (PDEs) are converted into Ordinary Differential Equations (ODEs) and shooting technique along with Adams–Moulton method of order four has been used to obtain the numerical results. Different physical parameters effects on velocity, temperature and concentration of nanofluid flow have been presented graphically and discussed in detail. Numerical values of the skin friction coefficient, Nusselt number and Sherwood number are also and discussed.
Berkin Uluutku, Enrique A. López-Guerra,
Beilstein Journal of Nanotechnology, Volume 12, pp 1063-1077; https://doi.org/10.3762/bjnano.12.79

Abstract:
Viscoelastic characterization of materials at the micro- and the nanoscale is commonly performed with the aid of force–distance relationships acquired using atomic force microscopy (AFM). The general strategy for existing methods is to fit the observed material behavior to specific viscoelastic models, such as generalized viscoelastic models or power-law rheology models, among others. Here we propose a new method to invert and obtain the viscoelastic properties of a material through the use of the Z-transform, without using a model. We present the rheological viscoelastic relations in their classical derivation and their z-domain correspondence. We illustrate the proposed technique on a model experiment involving a traditional ramp-shaped force–distance AFM curve, demonstrating good agreement between the viscoelastic characteristics extracted from the simulated experiment and the theoretical expectations. We also provide a path for calculating standard viscoelastic responses from the extracted material characteristics. The new technique based on the Z-transform is complementary to previous model-based viscoelastic analyses and can be advantageous with respect to Fourier techniques due to its generality. Additionally, it can handle the unbounded inputs traditionally used to acquire force–distance relationships in AFM, such as ramp functions, in which the cantilever position is displaced linearly with time for a finite period of time.
Azra Kocaarslan, Zafer Eroglu, ,
Beilstein Journal of Organic Chemistry, Volume 17, pp 2477-2487; https://doi.org/10.3762/bjoc.17.164

Abstract:
The development of long-wavelength photoinduced copper-catalyzed azide–alkyne click (CuAAC) reaction routes is attractive for organic and polymer chemistry. In this study, we present a novel synthetic methodology for the photoinduced CuAAC reaction utilizing exfoliated two-dimensional (2D) few-layer black phosphorus nanosheets (BPNs) as photocatalysts under white LED and near-IR (NIR) light irradiation. Upon irradiation, BPNs generated excited electrons and holes on its conduction (CB) and valence band (VB), respectively. The excited electrons thus formed were then transferred to the CuII ions to produce active CuI catalysts. The ability of BPNs to initiate the CuAAC reaction was investigated by studying the reaction between various low molar mass alkyne and azide derivatives under both white LED and NIR light irradiation. Due to its deeper penetration of NIR light, the possibility of synthesizing different macromolecular structures such as functional polymers, cross-linked networks and block copolymer has also been demonstrated. The structural and molecular properties of the intermediates and final products were evaluated by spectral and chromatographic analyses.
Yi Liu, , , Tianxin Hao, Xuan Liu, Qiuping Ding, Yiyuan Peng
Beilstein Journal of Organic Chemistry, Volume 17, pp 2462-2476; https://doi.org/10.3762/bjoc.17.163

Abstract:
Great progress has been made in the tandem annulation of enynes in the past few years. This review only presents the corresponding reactions of 1,3-enyne structural motifs to provide the functionalized pyridine and pyrrole derivatives. The functionalization reactions cover iodination, bromination, trifluoromethylation, azidation, carbonylation, arylation, alkylation, selenylation, sulfenylation, amidation, esterification, and hydroxylation. We also briefly introduce the applications of the products and the reaction mechanisms for the synthesis of corresponding N-heterocycles.
Najeh Tka, Mohamed Adnene Hadj Ayed, Mourad Ben Braiek, Mahjoub Jabli,
Beilstein Journal of Organic Chemistry, Volume 17, pp 2450-2461; https://doi.org/10.3762/bjoc.17.162

Abstract:
A facile synthesis of 2,4-diaryl-9-chloro-5,6,7,8-tetrahydroacridine derivatives is reported which is based on POCl3-mediated cyclodehydration followed by double Suzuki–Miyaura cross-coupling. The absorption and fluorescence properties of the obtained products were investigated and their HOMO/LUMO energy levels were estimated by cyclic voltammetry measurements. Besides, density functional theory calculations were carried out for further exploration of their electronic properties.
Anwei Hou,
Beilstein Journal of Organic Chemistry, Volume 17, pp 2441-2449; https://doi.org/10.3762/bjoc.17.161

Abstract:
The sesterterpene synthase SmTS1 from Streptomyces mobaraensis contains several unusual residues in positions that are otherwise highly conserved. Site-directed mutagenesis experiments for these residues are reported that showed different effects, resulting in some cases in an improved catalytic activity, but in other cases in a loss of enzyme function. For other enzyme variants a functional switch was observed, turning SmTS1 from a sesterterpene into a diterpene synthase. This article gives rational explanations for these findings that may generally allow for protein engineering of other terpene synthases to improve their catalytic efficiency or to change their functions.
Ren-Jie Fang, Chen Yan, , Ying Han,
Beilstein Journal of Organic Chemistry, Volume 17, pp 2425-2432; https://doi.org/10.3762/bjoc.17.159

Abstract:
The p-TsOH-catalyzed Diels–Alder reaction of 3-(indol-3-yl)maleimides with chalcone in toluene at 60 °C afforded two diastereoisomers of tetrahydropyrrolo[3,4-c]carbazoles, which can be dehydrogenated by DDQ oxidation in acetonitrile at room temperature to give the aromatized pyrrolo[3,4-c]carbazoles in high yields. On the other hand, the one-pot reaction of 3-(indol-3-yl)-1,3-diphenylpropan-1-ones with chalcones or benzylideneacetone in acetonitrile in the presence of p-TsOH and DDQ resulted in polyfunctionalized carbazoles in satisfactory yields. The reaction mechanism included the DDQ oxidative dehydrogenation of 3-(indol-3-yl)-1,3-diphenylpropan-1-ones to the corresponding 3-vinylindoles, their acid-catalyzed Diels–Alder reaction and sequential aromatization process.
Martin Kamlar, , Martin Nigríni, ,
Beilstein Journal of Organic Chemistry, Volume 17, pp 2433-2440; https://doi.org/10.3762/bjoc.17.160

Abstract:
Here we present an enantioselective aminalization of aldehydes catalyzed by Brønsted acids based on pentacarboxycyclopentadienes (PCCPs). The cyclization reaction using readily available anthranilamides as building blocks provides access to valuable 2,3-dihydroquinazolinones containing one stereogenic carbon center with good enantioselectivity (ee up to 80%) and excellent yields (up to 97%).
Haipin Zhou, Zihan Rui, Yiming Yang, Shengtao Xu, Yutian Shao, Long Liu
Published: 15 September 2021
Abstract:
Hoshinoamides A, B and C, linear lipopeptides, were isolated from the marine cyanobacterium Caldora penicillata, with potent antiplasmodial activity against chloroquine-sensitive Plasmodium falciparum. Herein, we describe the first total synthesis of Hoshinoamides A. Our synthetic strategy uses the combined methods of solution and solid phase peptide synthesis. Liquid phase synthesis is to improve the coupling yield of L-Val3 and N-Me-D-Phe2. Connecting other amino acids efficiency and convergence by solid state synthesis. This synthetic strategy has good purity and high yield.
Andrey I. Puzanov, , Anna S. Zalivatskaya, Dmitriy N. Zakusilo, Darya S. Mikson, Irina A. Boyarskaya,
Beilstein Journal of Organic Chemistry, Volume 17, pp 2417-2424; https://doi.org/10.3762/bjoc.17.158

Abstract:
Acetylene derivatives of 1,2,4-oxadiazoles, i.e., 5-(2-arylethynyl)-3-aryl-1,2,4-oxadiazoles, have been obtained, for the first time reported, from 5-(2-arylethenyl)-3-aryl-1,2,4-oxadiazoles by their bromination at the carbon–carbon double bond followed by di-dehydrobromination with NaNH2 in liquid NH3. The reaction of the acetylenyl-1,2,4-oxadiazoles with arenes in neat triflic acid TfOH (CF3SO3H) at room temperature for 1 h resulted in the formation of E/Z-5-(2,2-diarylethenyl)-3-aryl-1,2,4-oxadiazoles as products of regioselective hydroarylation of the acetylene bond. The addition of TfOH to the acetylene bond of these oxadiazoles quantitatively resulted in E/Z-vinyl triflates. The reactions of the cationic intermediates have been studied by DFT calculations and the reaction mechanisms are discussed.
, , , , , Carlos A. Velázquez Contreras, Ramón E. Robles-Zepeda, Mirtha Navarro-Hoyos,
Beilstein Journal of Nanotechnology, Volume 12, pp 1047-1062; https://doi.org/10.3762/bjnano.12.78

Abstract:
Curcumin (CUR) is a phenolic compound that is safe for human consumption. It exhibits chemopreventive, antiproliferative, antiangiogenic, and antimetastatic effects. However, these benefits can be hampered due to the lipophilic nature, rapid metabolism, low bioavailability, and fast elimination of the molecule. Considering this, the present work reviews the use of CUR-based nanosystems as anticancer agents, including conventional nanosystems (i.e., liposomes, nanoemulsions, nanocrystals, nanosuspensions, polymeric nanoparticles) and nanosystems that respond to external stimuli (i.e., magnetic nanoparticles and photodynamic therapy). Previous studies showed that the effects of CUR were improved when loaded into nanosystems as compared to the free compound, as well as synergist effects when it is co-administrated alongside with other molecules. In order to maximize the beneficial health effects of CUR, critical factors need to be strictly controlled, such as particle size, morphology, and interaction between the encapsulating material and CUR. In addition, there is an area of study to be explored in the development of CUR-based smart materials for nanomedical applications. Imaging-guided drug delivery of CUR-based nanosystems may also directly target specific cells, thereby increasing the therapeutic and chemopreventive efficacy of this versatile compound.
, A'liyatur Rosyidah
Beilstein Journal of Organic Chemistry, Volume 17, pp 2399-2416; https://doi.org/10.3762/bjoc.17.157

Abstract:
In recent years fifteen 5,6-dihydro-α-pyrone derivatives, bearing either a distinctive cyclopropane or furan ring and named brevipolides A–O (1–15), have been isolated from the invasive plant Hyptis brevipes Poit. Their fascinating structural features, and the potent biological activities, including cytotoxicity against an array of human cancer cell lines and inhibition of the chemokine receptor CCR5, make them attractive synthetic targets. This review article highlights the recent synthetic methodologies and briefly summarizes their biological activities.
, Olusoji O. Adebisi, , Kojo S. Acquah, Mercedes De La Cruz, Larry L. Mweetwa, Joy E. Rajakulendran, , Deng Hai, Rainer Ebel, et al.
Beilstein Journal of Organic Chemistry, Volume 17, pp 2390-2398; https://doi.org/10.3762/bjoc.17.156

Abstract:
Five new phenolic siderophores 1–5 were isolated from the organic extract of a culture broth in a modified SGG medium of Pseudomonas sp. UIAU-6B, obtained from sediments collected from the Oyun river in North Central Nigeria. The structure of the new compounds, pseudomonin A–C (1–3) and pseudomobactin A and B (4 and 5) isolated alongside two known compounds, pseudomonine (6) and salicylic acid (7), were elucidated based on high-resolution mass spectrometry, 1D and 2D NMR analyses. The absolute configuration of the threonine residue in compounds 1–5 was determined by Marfey analysis. The antimicrobial evaluation of compound 4 exhibited the most potent activity against vancomycin-sensitive Enterococcus faecium VS144754, followed by 3 and 5, with MIC values ranging from 8 to 32 µg/mL. Compounds 2 and 3 exhibited moderate activity against Mycobacterium tuberculosis H37Rv, with MIC values of 7.8 and 15.6 µg/mL, respectively. Plausible biosynthetic hypotheses toward the new compounds 1–5 were proposed.
Zahra Faraji Rad, , Graham J. Davies
Beilstein Journal of Nanotechnology, Volume 12, pp 1034-1046; https://doi.org/10.3762/bjnano.12.77

Abstract:
Microneedle-based microdevices promise to expand the scope for delivery of vaccines and therapeutic agents through the skin and withdrawing biofluids for point-of-care diagnostics – so-called theranostics. Unskilled and painless applications of microneedle patches for blood collection or drug delivery are two of the advantages of microneedle arrays over hypodermic needles. Developing the necessary microneedle fabrication processes has the potential to dramatically impact the health care delivery system by changing the landscape of fluid sampling and subcutaneous drug delivery. Microneedle designs which range from sub-micron to millimetre feature sizes are fabricated using the tools of the microelectronics industry from metals, silicon, and polymers. Various types of subtractive and additive manufacturing processes have been used to manufacture microneedles, but the development of microneedle-based systems using conventional subtractive methods has been constrained by the limitations and high cost of microfabrication technology. Additive manufacturing processes such as 3D printing and two-photon polymerization fabrication are promising transformative technologies developed in recent years. The present article provides an overview of microneedle systems applications, designs, material selection, and manufacturing methods.
Andrey I. Puzanov, , Anna S. Zalivatskaya, Dmitriy N. Zakusilo, Darya S. Mikson, Irina A. Boyarskaya,
Published: 30 June 2021
Abstract:
Acetylene derivatives of 1,2,4-oxadiazoles, 5-(2-arylethynyl)-3-aryl-1,2,4-oxadiazoles, have been obtained, for the first time, from 5-(2-arylethenyl)-3-aryl-1,2,4-oxadiazoles by their bromination at the carbon-carbon double bond followed by di-dehydrobromination with NaNH2 in liquid NH3. Reaction of the acetylene 1,2,4-oxadiazoles with arenes in neat triflic acid TfOH (CF3SO3H) at room temperature for 1 h result in the formation of E-/Z-5-(2,2-diarylethenyl)-3-aryl-1,2,4-oxadiazoles as products of regioselective hydroarylation of the acetylene bond. Addition of TfOH to acetylene bond of these oxadiazoles gives rise quantitatively to E-/Z-vinyl triflates. Reaction cationic intermediates have been studied by DFT calculations. The reaction mechanisms have been discussed.
Martin Kamlar, , Martin Nigríni, Ivana Císařová,
Published: 28 June 2021
Abstract:
Here we present an enantioselective aminalization of aldehydes catalyzed by Brønsted acids based on pentacarboxycyclopentadienes (PCCPs). Cyclization reaction using readily available anthranilamides as building-blocks provides an access to valuable 2,3-dihydroquinazolinones containing one stereogenic carbon center with high degree of enantioselectivities (ee up to 81 %) and excellent yields (up to 97%).
Berkin Uluutku, Enrique A. López-Guerra,
Published: 2 June 2021
Abstract:
Viscoelastic characterization of materials at the micro- and nanoscales is commonly performed with the aid of force-distance relationships acquired using atomic force microscopy (AFM). The general strategy for existing methods is to fit the observed material behavior to specific viscoelastic models, such as generalized viscoelastic models or power-law rheology models, among others. Here we propose a new method to invert and obtain the viscoelastic properties of a material through the use of the Z-transform, without using a model. We present the rheological viscoelastic relations in their classical derivation and their Z-domain correspondence. We illustrate the proposed technique on a model experiment involving a traditional ramp-shaped force-distance AFM curve, demonstrating good agreement between the viscoelastic characteristics extracted from the simulated experiment and the theoretical expectations. We also provide a path for calculating standard viscoelastic responses from the extracted material characteristics. The new technique based on the Z-transform is complementary to previous model-based viscoelastic analyses and can be advantageous with respect to Fourier techniques due to its generality. Additionally, it can handle the unbounded inputs traditionally used to acquire force-distance relationships in AFM, such as “ramp” functions, in which the cantilever position is displaced linearly with time for a finite period of time.
Suman Rani, Nisha Kamra, Sumit Thakral, , Ajeet Singh, Payare L Sangwan, Shashank K Singh
Published: 17 May 2021
Abstract:
Synthesis of a number of highly oxygenated furo[3,2-c]pyran-4-one (4, 5) and furo[3,2-c]chromen-4-one (8, 9) has been accomplished by a simple one pot reaction from easily available versatile starting materials - dehydroacetic acid and 3-acetyl-4-hydroxycoumarin. All the synthesized molecules were characterized utilizing various spectroscopic techniques and screened for anticancer activity (in vitro) against three Colon (HCT-116, SW-620, HT-24), Lung (A-549), Prostate-(PC-3), Breast-(MCF-7) cell lines. Compounds 5a, 9d, 9f showed good activity against breast MCF-7 cancer cell line having IC50 values 6.9, 2.8, 5.3 µM, respectively. Out of these compound 9d showed better activity against prostate PC-3 cell line with IC50 value 3.8 µM. The synthesized compounds were also studied for potential antibacterial activity (in vitro) using different strains of bacteria (Bacillus subtilis and Staphylococcus aureus -Gram-positive, and Escherichia coli- Gram negative) as well as fungal strains (Aspergillus niger and Candida albicans) using Norfloxacin and Fluconazole as antibacterial and antifungal standard drugs, respectively. The outcome of the antimicrobial screening study showed that compound 9f exhibited promising activity against S. aureus and B. subtilis while 5h showed excellent and 5i and 9b showed better activity against E. coli. The compounds 5c-5e displayed excellent activity against C. albicans and A. niger than Fluconazole.
David Martínez-López, Amirhossein Babalhavaeji, ,
Beilstein Journal of Organic Chemistry, Volume 15, pp 3000-3008; https://doi.org/10.3762/bjoc.15.296

Abstract:
Aminoazobenzene derivatives with four ortho substituents with respect to the N–N double bond are a relatively unexplored class of azo compounds that show promise for use as photoswitches in biology. Tetra-ortho-methoxy-substituted aminoazobenzene compounds in particular can form azonium ions under physiological conditions and exhibit red-light photoswitching. Here, we report the synthesis and characterization of two bis(4-amino-2-bromo-6-methoxy)azobenzene derivatives. These compounds form red-light-absorbing azonium ions, but only under very acidic conditions (pH < 1). While the low pK a makes the azonium form unsuitable, the neutral versions of these compounds undergo trans-to-cis photoisomerization with blue-green light and exhibit slow (τ1/2 ≈ 10 min) thermal reversion and so may find applications under physiological conditions.
Vito A. Fiore, Chiara Freisler,
Beilstein Journal of Organic Chemistry, Volume 15, pp 2603-2611; https://doi.org/10.3762/bjoc.15.253

Abstract:
N-Phenyl-N-(trifluoromethylsulfonyl)propiolamides react with triphenylphosphane in the presence of various active methylene compounds CH2XY in a 1:1:1 molar ratio to furnish 1-phosphonium-5-oxabetaines, Ph3P+–C(R)=CH–C(O–)=CXY. These betaines are formed preferentially, but not exclusively, as E-diastereoisomers with respect to the vinylic double bond. In some cases, separation of the two diastereoisomers was achieved by fractionating crystallization. Structure determination by X-ray diffraction analysis revealed marked conformational differences around the CH–C(O–) single bond of E and Z-isomers and extended charge delocalization in the anionic part.
Roland Löw, Talina Rusch, Tobias Moje, Fynn Röhricht, ,
Beilstein Journal of Organic Chemistry, Volume 15, pp 1815-1821; https://doi.org/10.3762/bjoc.15.175

Abstract:
Triazatriangulenium (TATA) and trioxatriangulenium (TOTA) ions are particularly suited systems to mount functional molecules onto atomically flat surfaces such as Au(111). The TATA and TOTA units serve as platforms that absorb onto the surface and form ordered monolayers, while the functional groups are protruding upright and freestanding from the central carbon atoms. Azobenzene derivatized TATA’s are known to exhibit extremely fast cis→trans isomerization on metal surfaces, via a peculiar non-adiabatic singlet→triplet→singlet mechanism. We now prepared norbornadienes (NBD) and quadricyclanes (QC) attached to TATA and TOTA platforms which can be used to check if these accelerated rates and the spin change mechanism also apply to [2 + 2] cycloreversions (QC→NBD).
Lara Martín-Sánchez, , Mariana Avalos, , ,
Beilstein Journal of Organic Chemistry, Volume 15, pp 1181-1193; https://doi.org/10.3762/bjoc.15.115

Abstract:
Terpene synthases are widely distributed among microorganisms and have been mainly studied in members of the genus Streptomyces. However, little is known about the distribution and evolution of the genes for terpene synthases. Here, we performed whole-genome based phylogenetic analysis of Streptomyces species, and compared the distribution of terpene synthase genes among them. Overall, our study revealed that ten major types of terpene synthases are present within the genus Streptomyces, namely those for geosmin, 2-methylisoborneol, epi-isozizaene, 7-epi-α-eudesmol, epi-cubenol, caryolan-1-ol, cyclooctat-9-en-7-ol, isoafricanol, pentalenene and α-amorphene. The Streptomyces species divide in three phylogenetic groups based on their whole genomes for which the distribution of the ten terpene synthases was analysed. Geosmin synthases were the most widely distributed and were found to be evolutionary positively selected. Other terpene synthases were found to be specific for one of the three clades or a subclade within the genus Streptomyces. A phylogenetic analysis of the most widely distributed classes of Streptomyces terpene synthases in comparison to the phylogenomic analysis of this genus is discussed.
Lukas J. Patalag,
Beilstein Journal of Organic Chemistry, Volume 12, pp 2739-2747; https://doi.org/10.3762/bjoc.12.270

Abstract:
Herein, we report on the synthesis and characterization of novel fluorescent fatty acids with large Stokes shifts. Three examples consisting of the same number of carbon atoms and thus of similar chain length are presented differing in their degree of unsaturation. As major fluorogenic contributor at the terminus benzo[c][1,2,5]thiadiazole was used. Respective syntheses based on Wittig reactions followed by iodine-mediated isomerization are presented. The absorption properties are modulated by the number of conjugated C=C double bonds of the oligoene chain ranging from one to three. Large Stokes shifts of about 4900–5700 cm−1 and fluorescence quantum yields of up to 0.44 were observed.
Mathias Lang, Alexandra Schade,
Beilstein Journal of Organic Chemistry, Volume 12, pp 2570-2576; https://doi.org/10.3762/bjoc.12.252

Abstract:
Herein we report the syntheses of two porous hyper-crosslinked polymers (HCPs) via thiol–yne reaction with rigid tetrahedral and pseudo-octahedral core structures. Sorption measurements with nitrogen gas at 77 K revealed BET-surface areas up to 650 m²/g. Those networks also showed a high thermal stability as well as insolubility in common organic solvents.
Andrew J. Counsell, Angus T. Jones, ,
Beilstein Journal of Organic Chemistry, Volume 12, pp 2457-2461; https://doi.org/10.3762/bjoc.12.239

Abstract:
An efficient protocol for the direct synthesis of N-tetraalkylated derivatives of the azamacrocycles cyclam and cyclen has been developed, using a partially miscible aqueous–organic solvent system with propargyl bromide, benzyl bromide, and related halides. The method works most effectively when the reaction mixture is shaken, not stirred. A crystal structure of the N-tetrapropargyl cyclam derivative 1,4,8,11-tetra(prop-2-yn-1-yl)-1,4,8,11-tetraazacyclotetradecane diperchlorate is reported.
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