Trimethylamine N-oxide (TMAO) and urea are both osmolytes found in many marine animals, yet they show opposite effects in (de-)stabilizing proteins. Gaining molecular-level insights into the TMAO-urea interaction in aqueous solution is a key step in elucidating their biological roles. Here, combined ab initio molecular dynamics simulations, polarization-resolved femtosecond infrared pump-probe spectroscopy, and nuclear magnetic resonance spectroscopy reveal that the hydrophobic interaction between TMAO and urea is favorable in comparison with the hydrogen-bonding interaction. The association of the hydrophobic methyl group of TMAO with urea is driven by the large mismatch between the strong TMAO-water hydrogen bond and the weak urea-water hydrogen bond. Our observations provide a rationale for the counteraction of osmotic pressure resulting from urea by TMAO. Trimethylamine N-oxide (TMAO) and urea, which are small organic molecules solvated in water, co-exist in cells of marine animals to control the osmotic pressure. TMAO stabilizes protein structure, whereas urea destabilizes it. But, the mechanism of cancellation of the effects due to TMAO and urea is not clear. In this work, we have identified how TMAO and urea interact in water by combining ab initio molecular dynamics simulation, time-resolved infrared spectroscopy, and nuclear magnetic resonance spectroscopy. We show that the interaction between both osmolytes is favored by hydrophobic association. The hydrophobic TMAO-urea interaction is predicted by ab initio free energy calculations, explained by hydrogen-bond mismatch between TMAO and urea, and evidenced by pump-probe infrared and nuclear magnetic resonance spectroscopy.
All Science Journal Classification (ASJC) codes
- Environmental Chemistry
- Chemical Engineering(all)
- Biochemistry, medical
- Materials Chemistry