On the molecular basis of HO/DMSO eutectic mixtures by using phenol compounds as molecular sensors: a combined NMR and DFT study

• Published in: Physical chemistry chemical physics : PCCP 2021-07, Vol.23 (29), p.15645-15658
• Main Authors: Fatima, Sana, Varras, Panayiotis C, Atia-tul-Wahab, Choudhary, M. Iqbal, Siskos, Michael G, Gerothanassis, Ioannis P
• Format: Article
• ISSN: 1463-9076; 1463-9084
• DOI: 10.1039/d0cp05861k

NMR and DFT studies of phenol compounds as molecular sensors were carried out to investigate H 2 O/DMSO eutectic mixtures at a molecular level. The experimental 1 H NMR chemical shifts of the OH groups, δ exp (OH), of phenol, paracoumaric acid, and vanillic acid show maximum deshielding and, thus, hydrogen bond interactions in the range of mole fractions 0.20 < χ (DMSO) < 0.33. In the mole fractions χ (DMSO) < 0.2, a progressive decrease in δ exp (OH) was observed which demonstrates a decrease in hydrogen bond interactions at infinite dilution in H 2 O, despite the increase in the number of available hydrogen bond acceptor and donor sites. DFT calculated δ calc (OH) of minimum energy solvation clusters were shown to be in reasonable agreement with the pattern in experimental δ exp (OH) data. The chemical shift deshielding and, thus, increased hydrogen bond interactions in the natural product + DMSO + n H 2 O ( n = 2, 3) solvation clusters, relative to complexes in DMSO or H 2 O solutions, cannot be attributed to a single structural parameter of the cooperative interactions between H 2 O and DMSO molecules with the phenol OH groups of the natural products. The minimum energy conformers of phenol compounds + 2H 2 O + DMSO complexes are in excellent agreement with a recent low temperature neutron diffraction experiment of 3D 2 O + DMSO and demonstrate a general structural motif of solvation complexes. The combined use of 1 H NMR and DFT studies with emphasis on δ (OH) of phenol compounds, as molecular sensors, can provide an effective method for the study of solute-solvent interactions at the atomic level. 1 H NMR and DFT studies of phenol containing natural products can be used to investigate solute-solvent interactions at the atomic level in eutectic mixtures.