Rotational and translational dynamic heterogeneities (DHs) of ambient aqueous solutions of trimethylamine-N-oxide (TMAO) and tetramethylurea (TMU) at several solute concentrations have been investigated and compared. Motional characteristics of water molecules at solute interfaces and in bulk solutionshave been thoroughly examined for the search of slow dynamics. Note, TMAO possesses zwitterionic structure and is a protein stabilizer whereas TMU is a neutral dipolar molecule and a strong denaturant. Results suggest that water-TMAO solutions possess stronger DH than water-TMU solutions with the solute concentration dependence being stronger for TMAO than for TMU. Diffusive dynamics slows down near the solute surface for both the solutes. Solvation structure shows TMAO-water interaction is stronger than TMU-waterinteraction, producing longer H-bond fluctuation timescale in TMAO solutions. In short, this paper presents, for the first time, a systematic and comparative study of motional features and inter-species interactions between aqueous solutions containing solutes that differ in their individual impacts on protein stability.
Volume 134, 2022
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