Theoretical study on specific properties of water molecules around TMAO

Abstract

Trimethylamine N-oxide is well known as a representative osmolyte. However, the mechanism is not completely unraveled even now. In the mechanism of regulating osmotic pressure, it is considered that the influence of TMAO on surrounded water molecules is important. In this study, we perform QM/MM-MD simulation in which we treat a TMAO molecule as QM (HF/6-31G). The results show that the density of water molecules around the oxygen atom of TMAO is nearly twenty times larger than that of bulk water. This means that water molecules are hydrogen-bonded to the oxygen atom of TMAO specifically. The density of water molecules within 6Å from TMAO is 0.99g/cm³. It means that the density is almost same as that of bulk in spite of excluded volume of TMAO. The water molecules which are excluded by TMAO are bound to TMAO.