Langmuir : the ACS journal of surfaces and colloids

Low-frequency vibrational spectrum of water around cyclodextrin and its methyl-substituted derivatives.

PMID 20704347


Atomistic molecular dynamics (MD) simulations have been carried out to study the low-frequency intermolecular vibrational spectrum of water present in the surrounding hydration layers and inside the cavities of beta-cyclodextrin (BCD) and its di- and trimethyl substituted derivatives, namely, heptakis(2,6-di-O-methyl)-beta-cyclodextrin (DIMEB) and heptakis(2,3,6-tri-O-methyl)-beta-cyclodextrin (TRIMEB) in aqueous solutions. Attempts have been made to explore the effects of confinement in and around these cyclic macromolecules and the formation of hydrogen bonds between water and the glucopyranose rings on the distribution of the intermolecular vibrational density of states of water. The calculations revealed that compared to bulk water these bands are blue-shifted for water in proximity to these molecules, the extents of the shifts being more pronounced for the cavity water molecules. It is further noticed that the relatively more restricted local motions of water bound to the cyclodextrins by hydrogen bonds result in larger blue shifts of these bands. These results can be verified by suitable experiments.