Journal
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
Volume 107, Issue 27, Pages 12068-12073Publisher
NATL ACAD SCIENCES
DOI: 10.1073/pnas.0914885107
Keywords
ab initio molecular dynamics; hydrogen-bonding; solvation; infrared spectroscopy; vibrational modes
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Funding
- Studienstiftung des Deutschen Volkes
- Alexander von Humboldt Stiftung
- BMBF [05KS7PC2]
- Volkswagenstiftung
- Research Department Interfacial Systems Chemistry
- Fonds der Chemischen Industrie
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Solvation of molecules in water is at the heart of a myriad of molecular phenomena and of crucial importance to understanding such diverse issues as chemical reactivity or biomolecular function. Complementing well-established approaches, it has been shown that laser spectroscopy in the THz frequency domain offers new insights into hydration from small solutes to proteins. Upon introducing spatially-resolved analyses of the absorption cross section by simulations, the sensitivity of THz spectroscopy is traced back to characteristic distance-dependent modulations of absorption intensities for bulk water. The prominent peak at approximate to 200 cm(-1) is dominated by first-shell dynamics, whereas a concerted motion involving the second solvation shell contributes most significantly to the absorption at about 80 cm(-1) approximate to 2.4 THz. The latter can be understood in terms of an umbrella-like motion of two hydrogen-bonded tetrahedra along the connecting hydrogen bond axis. Thus, a modification of the hydrogen bond network, e. g., due to the presence of a solute, is expected to affect vibrational motion and THz absorption intensity at least on a length scale that corresponds to two layers of solvating water molecules. This result provides a molecular mechanism explaining the experimentally determined sensitivity of absorption changes in the THz domain in terms of distinct, solute-induced dynamical properties in solvation shells of (bio)molecules-even in the absence of well-defined resonances.
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