Effect of urea and glycine betaine on the hydration sphere of model molecules for the surface features of proteins

Abstract Water properties may significantly affect protein stability. Osmolytes are compounds that intrinsically affect water in many different ways and thus can influence proteins with this type of indirect mechanism. In this study, we characterize water properties in ternary solutions: model–water–osmolyte, with two model molecules: N-methylacetamide (NMA) and dimethyl sulfoxide (DMSO) and two osmolytes: glycine betaine (TMG) and urea. We focus primarily on the water affected simultaneously by two solutes and propose a new FTIR-based experimental approach to study their properties. Our findings, supported by DFT and AIMD calculations, indicate that TMG promotes hydration cage enhancement around both model molecules. However, direct model–TMG interactions are rare. Simultaneously, urea interacts with them directly, displacing water molecules and weakening the hydrogen bonds in overlapped hydration spheres. The latter behavior results from the cooperativity loss between hydrophobic and hydrophilic-type hydration exhibited by the model molecules in the absence of urea. Relating the obtained results to protein systems, in the case of both osmolytes, the potential mechanism of stabilization–destabilization of these biomolecules is enthalpy-driven.