A Orientation of water molecules in the hydration layer

APPENDIX 8.A ORIENTATION OF WATER MOLECULES IN THE HYDRATION LAYER 

Classic clathrate-like hydration was evidenced around the Val8a residue, which belonged to the convex region. The classic clathrate-like stmcture of the water molecule was found around a hydrophobic surface. 

In contrast, the inverted hydration structure was found for the mehttin interface water molecules proximal to the residues belonging to the flat central region showed orientational fluctuations among a strongly elathrate-like distribution, a weak elathrate-like form, an inverted structure, and a mixed behavior. It was further found that the prevalence of any one stmctural type typically persists for approximately 10-20 ps. 

The hydration structure of the central hydrophobic region could not be characterized by either a classic, smaU-molecule, elathrate-like stmeture or an orientationally inverted structure characteristic of truly extended surfaces, but rather by a fluctuating distribution over both. 

To characterize the degree to which the structural fluctuations derive contributions from the water molecules, we can consider a quantity (the ratio of the number of proximal water molecules with any one of its HB vectors pointing radially inward towards the solute atom, divided by the total number of proximal water molecules of this solute atom) in each configuration. Simulations indicate a high probability of clathrate-hke structures (/in = 0) dominating near the convex surface patch of ValSa, and that the probability of encountering inverted structures ( 1 = 1) increases markedly near the relatively flat region. 

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