AutoCAD 2014

Hydration of hydrophobic solutes

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The  hydrophobic interaction is responsible for several important biological and chemical processes: aggregation of amphiphilic molecules and micelles, protein folding, aggregation of protein subunits into multi-subunit quaternary structure[P. Ball, Chem. Rev. 108, 74–108 (2008)]. Experimental results show that hydration structure changes with shape and size of  solute. In presence of  small  hydrophobic solutes the possible configuration of water hydrogen bonds can be restricted, but the overall number of  hydrogen bonds is the same. For large hydrophobic solutes, as surface, water molecules cannot maintain unchanged and this energetic effect drives segregation between water and hydrophobic solutes [D. Chandler, Nature 437, 640-647 (2005)]. Interaction between water molecules and hydrophobic solute affects also structural, dynamic and vibrational properties of water [M. Sharma, D. Donadio, E. Schwegler and G. Galli, Nano Let. 130, No 9, 2959-2962 (2008)].

In the present work we study the structural, dynamical and spectroscopic properties of water around a methane molecule using Car-Parrinello molecular dynamics. The infrared spectra, obtained by the Fourier transform of the dipole autocorrelation function, has been decomposed into the contribution due to the first-shell and to the bulk. The analysis revealed significant differences between the bulk and the first-shell signal in several regions of the spectra. Our findings suggest the presence of previously undetected spectroscopic fingerprints of liquid water at the interface with small hydrophobic solutes.



(Fig1. A methane in a box of 63 water molecules)






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