Hydrodynamic, optical and spectroscopic studies of some organic-aqueous binary systems

• Published in: Journal of molecular liquids Vol. 79; no. 1; pp. 45 - 58
• Main Authors: Arêas, Elizabeth P.G, Menezes, Helga H.A, Santos, Paulo S, Arêas, JoséA.G
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 1999
• Subjects: NMR; protein folding; Raman scattering; refractometry; rheology; self-association; solvent microstructure; self-association; NMR; rheology; Raman scattering; refractometry; solvent microstructure; protein folding
• ISSN: 0167-7322; 1873-3166
• DOI: 10.1016/S0167-7322(98)00101-9

The peculiar occurrence of pseudoplastic behaviour of protein solutions in certain organic-aqueous media has been subject of previous studies [Arêas et al., J. Coll. Interface Sci., 180 (1996), 578]. The role of the solvent in these events has been shown to be determinant, suggesting that particular configurations of the solvent/water microstructure are able to induce an extensive change in the folding of proteins such as lysozyme and cytochrome c, experimentally observed. In this work, we present a study on the rheology, refractivity and spectroscopic (Raman scattering and 1H and 13C nuclear magnetic resonance) behaviour of some of such binary organic-aqueous systems, as a function of the organic component mass fraction in water. Results obtained are consistent with the occurrence of a solution configurational transition at characteristic critical concentrations of the binary mixtures. The transition is apparent through several physico-chemical parameters monitored, including Raman frequency, 1H and 13C spin-lattice relaxation times, refractive index and viscosity. The effect has been observed for a few binary systems where protein was found to form stable solutions, including certain amides and urea derivatives, such as tetramethylurea, hexamethylphosphotriamide and dimethylformamide, some alcohols and for dimethylsulfoxide. All systems presenting the effect were found to contain coexistent polar/apolar molecular domains in their organic component. The effect is not observed for systems where the organic solvent molecule lacks a significative apolar moiety, such as formamide. Results were consistent with the view of a discontinuous liquid structure for those organic/aqueous binary mixtures.