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On the basis of the molecular understanding that DMSO has a trigonal pyramidal geometry with one highly polarized sulfinyl group and two hydrophobic methyl groups, we used NMR technology to rationalize why DMSO can act as antifreeze for aqueous solutions. A series of DMSO-water, DMSO-methanol, and acetone-water binary solutions with various molar ratios were tested in specified low temperature conditions. The freezing test results indicated that only DMSO-water solutions with the DMSO-water molar ratio (nDMSO) in a specific range can form apparent ultralow freezing temperature solutions. Among all DMSO-water solutions, the apparent freezing temperature lower than -130 °C was obtained for nDMSO values of 0.25, 0.30, and 0.35, respectively. Multinuclear NMR chemical shifts, 1H diffusion experiment results, and viscosity measurements suggested that molecular rearrangement resulted in the formation of the water-core DMSO-shell aggregation unit in DMSO-water solutions. The weak methyl-methyl London dispersion forces among water-core DMSO-shell aggregation units can explain the apparent ultralow freezing temperatures of these DMSO-water solutions.
Wen et al. (Mon,) studied this question.