Solvation of Methyl Lactate in Water: Molecular Dynamics Studies

Methyl lactate (ML), a chiral α-hydroxy ester, has been probed widely to understand the competition between two types of intramolecular H-bonds in solvents of different polarities. Recent experimental and high-level quantum chemical studies have revealed the predominant existence of ML-water insertion complexes over addition complexes in aqueous solution. Although the stability of monohydrate insertion conformer was studied accurately, ab initio quantum chemical calculations failed to predict the most stable dihydrate conformer in analogy with the experimental spectroscopic search. Atomistic molecular dynamics simulations of aqueous solution of methyl lactate predict that the population and lifetime of different H-bonded ML-water addition complexes are dictated by their interaction energies. Although the population of dihydrate insertion complexes is higher than that of the monohydrate complexes, the lifetime of the former is smaller than the latter, which is in good agreement with the experimental result. The nature of intramolecular H-bonds within a methyl lactate molecule in aqueous solution is opposite to that in the gas phase due to the solvation process in water by intermolecular H-bonding interactions.