The effect of glucose on the relaxation process of water at picosecond time scales has beeninvestigated by depolarized Rayleigh scattering DRS experiments. The process is assigned to the fast hydrogen bonding dynamics of the water network. In DRS spectra this contribution can besafely separated from the slower relaxation process due to the sugar. The detected relaxation time is studied at different glucose concentrations and modeled considering bulk and hydrating water contributions. As a result, it is found that in diluted conditions the hydrogen bond lifetime ofproximal water molecules becomes about three times slower than that of the bulk. The effect of thesugar on the hydrogen bond water structure is investigated by analyzing the low-frequency Raman (LFR) spectrum sensitive to intermolecular modes. The addition of glucose strongly reduces theintensity of the band at 170 cm−1 assigned to a collective stretching mode of water moleculesarranged in cooperative tetrahedral domains. These findings indicate that proximal water moleculespartially lose the tetrahedral ordering typical of the bulk leading to the formation of high density environments around the sugar. Thus the glucose imposes a new local order among water molecules localized in its hydration shell in which the hydrogen bond breaking dynamics is sensitively retarded. This work provides new experimental evidences that support recent molecular dynamics simulation and thermodynamics results.
Hydrogen bond dynamics and water structure in glucose-water solutions by depolarized Rayleigh scattering and low-frequency Raman spectroscopy
PAOLANTONI, Marco;SASSI, Paola;MORRESI, Assunta;SANTINI, Sergio
2007
Abstract
The effect of glucose on the relaxation process of water at picosecond time scales has beeninvestigated by depolarized Rayleigh scattering DRS experiments. The process is assigned to the fast hydrogen bonding dynamics of the water network. In DRS spectra this contribution can besafely separated from the slower relaxation process due to the sugar. The detected relaxation time is studied at different glucose concentrations and modeled considering bulk and hydrating water contributions. As a result, it is found that in diluted conditions the hydrogen bond lifetime ofproximal water molecules becomes about three times slower than that of the bulk. The effect of thesugar on the hydrogen bond water structure is investigated by analyzing the low-frequency Raman (LFR) spectrum sensitive to intermolecular modes. The addition of glucose strongly reduces theintensity of the band at 170 cm−1 assigned to a collective stretching mode of water moleculesarranged in cooperative tetrahedral domains. These findings indicate that proximal water moleculespartially lose the tetrahedral ordering typical of the bulk leading to the formation of high density environments around the sugar. Thus the glucose imposes a new local order among water molecules localized in its hydration shell in which the hydrogen bond breaking dynamics is sensitively retarded. This work provides new experimental evidences that support recent molecular dynamics simulation and thermodynamics results.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
