Multiple evidences for molecular level heterogeneity in a non-ionic biocatalytic deep eutectic solvent

Deep eutectic solvents (DESs) are new-generation solvents with exquisite and tuneable properties. Molecular-level heterogeneity has been identified as an intriguing feature of such solvents. Herein, we examined the spatio-temporal heterogeneity of a potential non-ionic biocatalytic DES, acetamide/urea/sorbitol (0.5Ac/0.3Ur/0.2Sor), and compared the result with corresponding binary acetamide/urea (0.6Ac/0.4Ur) DES, and another related non-ionic ternary DES (0.55Ac/0.36Ur/0.09PEG). The effect of the addition of a third component on the spatio-temporal heterogeneity of a DES was investigated. The excitation wavelength-dependent emission measurement suggests an induction of spatial heterogeneity in acetamide/urea/sorbitol compared to spatially homogenous acetamide/urea and acetamide/urea/PEG. The dynamic heterogeneity measurements in terms of solvation dynamics, dielectric relaxation, and rotational/translational diffusion indicate a length and timescale dependency. Overall, acetamide/urea/sorbitol is found to be dynamically more heterogenous than the other two related DESs.