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Hydration water mapping around alcohol chains by THz‐calorimetry reveal local changes in heat capacity and free energy upon solvation

Using THz spectroscopy we were able to probe changes that occur in the hydrogen bond network dynamics upon solvation of alcohol chains. The THz spectra can be decomposed into the spectrum of bulk water, tetrahedral hydration water, and more disordered (or interstitial) hydration water. The tetrahedrally‐ordered hydration water exhibits a band at 195 cm‐1 and is localized around the hydrophobic moiety. The interstitial component yields a band at 164 cm‐1 and is associated with hydration water in the first hydration shell. Temperature dependent changes in the low frequency spectrum of solvated alcohol chains can be correlated with changes of heat capacity, entropy, and free energy upon solvation. Surprisingly, not the tetrahedrally‐ordered component but the interstitial hydration water is found to be mainly responsible for the temperature‐dependent change in ΔCp and ΔG. The solute specific offset in free energy is attributed to void formation and scales linearly with the chain length.

Authors:   Martina Havenith-Newen, Gerhard Schwaab, Fabian Böhm
Journal:   Angewandte Chemie International Edition
Year:   2017
Pages:   n/a
DOI:   10.1002/anie.201612162
Publication date:   08-May-2017
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