Nuclear spin relaxation and self-diffusion in the binary system, dimethylsulphoxide (DMSO)+ water

Abstract

Spin-lattice (T₁) and, where appropriate, tranverse (T₂) relaxation times are reported for the protons in DMSO + water mixtures over a range of temperature and composition. Self-diffusion coefficients are also measured. A minimum in T₁ for a d₆-DMSO + H₂O sample enables rotational correlation times for water molecules to be evaluated in mixtures with mol fractions of water, x(H₂O), ⩽0.7. The low temperature (170-250 K) behaviour of T₁ for DMSO + D₂O mixtures with x(D₂O)≃0.7 is interpreted in terms of end-over-end rotation of DMSO molecules and internal rotation of methyl groups. Under certain assumptions rotational correlation times for the DMSO molecules are obtained from the intramolecular contribution to T₁ derived from measurements on ternary mixtures of the type d₆-DMSO + DMSO + D₂O. These are found to be very similar to those for the water molecules at the same temperature and compositions suggesting that the DMSO and water molecules reorient together. All measurements indicate a minimum in molecular mobility, both rotational and translational, at around a mol fraction of water of 0.65.