Several solute-solvent site radial distribution functions (RDFs) were calculated to investigate dilute aqueous TMAO/TBA solutions (Figure and Table ). The coordination numbers of the top sites of solutes were evaluated by integrating the RDFs for O The hydrogen-bond correlation function (p HB (t)) (Eq. 2) was calculated to clarify the effect of the N + O -, OH, and CH 3 -groups of each solute on the kinetics of the water molecules in the dilute aqueous TMAO/TBA solutions (Figure ).