Raman Spectroscopic and Quantum Chemical Investigation of the Effects of Tri-Methylamine N-Oxide (TMAO) On Hydrated Urea, Hydrated Guanidinium, and Hydrogen Bonded Networks

Abstract

Trimethylamine N-Oxide (TMAO), guanidinium, and urea are three important osmolytes with their main significance to the biophysical field being in how they uniquely interact with proteins. TMAO is known to stabilize and counteract the destabilizing effects of both urea and guanidinium. The exact mechanisms by which TMAO stabilizes and both guanidinium and urea destabilize folded proteins continue to be debated in the literature. Some studies suggest that solvent interactions do not play a large role in TMAO’s stabilizing effects and therefore advocate direct stabilization, whereas others suggest that TMAO counteracts denaturation primarily through an indirect effect of strong solvent interactions. Herein, we use Raman spectroscopy to elucidate the physical interactions between the osmolytes of interest in aqueous solutions to better understand how they interact with each other and affect adjacent hydrogen-bonding networks of water. Comparing experiment to theory yields good agreement, and it was determined that adding TMAO into both an aqueous solution of guanidinium and an aqueous solution of urea induces a blue shift (shift to higher energy) in both urea and guanidinium’s H-N-H bending modes, which is indicative of direct interactions between the osmolytes