Microscopic Heterogeneity Driven by Molecular Aggregation and Water Dynamics in Aqueous Osmolyte Solutions

Area of Science:

• Physical Chemistry
• Biophysical Chemistry
• Computational Chemistry

Background:

• Osmolytes modulate protein stability through direct interactions or by altering water structure and dynamics.
• Understanding these mechanisms is crucial for fields ranging from biochemistry to drug development.

Purpose of the Study:

• To investigate the water dynamics in binary osmolyte-water mixtures.
• To elucidate the role of molecular aggregation and solution heterogeneity in osmolyte function.
• To differentiate the mechanisms of action between protective osmolytes (like TMAO) and denaturant osmolytes (like TMU).

Main Methods:

• Molecular Dynamics (MD) simulations were employed to study binary osmolyte-water mixtures.
• Graph theoretical analysis and spatial inhomogeneity measurements (h-values) were used to quantify solution structure.
• Analysis of hydrogen bond lifetimes between osmolytes and water molecules.

Main Results:

• Trimethylurea (TMU) readily forms aggregates, leading to microscopic heterogeneity in TMU-water mixtures.
• TMAO molecules disperse evenly, resulting in homogeneous TMAO-water mixtures.
• Water molecules in heterogeneous TMU-water mixtures exhibit less hindered translational and rotational motion compared to homogeneous TMAO-water mixtures.
• TMU exhibits weaker osmolyte-water interactions than TMAO, facilitating TMU-TMU and TMU-protein interactions.

Conclusions:

• Osmolyte action on protein stability involves both direct osmolyte-protein interactions and indirect modulation of water structure and dynamics.
• The aggregation behavior and resulting solution heterogeneity are key factors in determining water dynamics and osmolyte efficacy.
• TMU's denaturing effect is linked to its aggregation and weaker water interactions, while TMAO's protective effect may relate to its homogeneous distribution and stronger water interactions.