Ab initio quantum chemical study of microhydration of xylopyranose sugar

Complexes of xylopyranose with water molecules (n = 2 to 10) have been investigated by using Moller Plesset second order perturbation theory (MP) with aug-cc-pvdz as a basis set. Complete basis set limit for the xylopyranose-water clusters were calculate at MP2 level of theory. The change in vibrational frequency, free energy change and enthalpy change was calculated with increase in the number of water molecules. The addition of water molecule incorporates the series of intra/inter molecular H-bonding cooperativity in the six membered ring. The six membered xylose sugar does not change its structural configuration after addition of water molecules. The high magnitude of interaction energy for incoming water, lowering of Delta G and high vibrational frequency for OH group and high magnitude of cooperative energy in case of n = 7 and n = 10 hydrates of xylopyranose suggests that these clusters have special stability.