Study of the perturbed hydrogen-bonded water structure of the hydration shell of N-Methyl-Acetamide by Raman multivariate curve resolution spectroscopy

Abstract

In this work, Raman scattering measurement combined with multivariate curve resolution (Raman-MCR) technique has been used to obtain the solute correlated spectra (SC) of N-methyl-acetamide (NMA) in an aqueous medium. The SC spectra is composed of NMA intramolecular vibrations and NMA induced-perturbations of water OH stretch vibrations. The SC spectra obtained for different mole-fractions of NMA reveal that as the mole-fraction of NMA increases the perturbed water interacting with the amide group is retained whereas it gets depleted from the hydrophobic hydration shell of the methyl group of NMA. The high wavenumber region of the OH spectrum shows that the fraction of the weakly hydrogen-bonded population is higher in the bulk water compared to perturbed water. The Raman spectra of perturbed OH spectral features due to hydration of the hydrophobic methyl group of NMA have been extracted from SC spectra obtained at low mole-fraction of NMA by the MCR technique. Its spectral feature resembles the SC-OH spectra of hydrophobic hydration of the methyl group of methanol.