Journal
JOURNAL OF CHEMICAL PHYSICS
Volume 136, Issue 7, Pages -Publisher
AMER INST PHYSICS
DOI: 10.1063/1.3684893
Keywords
hydrogen bonds; hydrophobicity; molecular dynamics method; organic compounds; positive ions; solvation; solvent effects; X-ray absorption spectra; X-ray scattering
Funding
- National Science Foundation [CHE-0431425, CHE-0809324]
- Swedish Research Council
- Office of Science, Office of Basic Energy Sciences, U.S. Department of Energy
- SSRL Structural Molecular Biology group by the National Institutes of Health, National Center for Research Resources
- U.S. Department of Energy, Office of Biological and Environmental Research
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We report small angle x-ray scattering data demonstrating the direct experimental microscopic observation of the small-to-large crossover behavior of hydrophobic effects in hydrophobic solvation. By increasing the side chain length of amphiphilic tetraalkyl-ammonium (CnH2n+1)(4)N+ (R4N+) cations in aqueous solution we observe diffraction peaks indicating association between cations at a solute size between 4.4 and 5 angstrom, which show temperature dependence dominated by hydrophobic attraction. Using O K-edge x-ray absorption we show that small solutes affect hydrogen bonding in water similar to a temperature decrease, while large solutes affect water similar to a temperature increase. Molecular dynamics simulations support, and provide further insight into, the origin of the experimental observations. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.3684893]
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