Figure 23.4.3.2 

Distribution of atomic hydration values. To determine which atoms are similar or distinct with respect to water binding, we plotted the number of atom types (e.g. Ala amide nitrogen, Ala Cα, …) at each hydration per occurrence value. Each atom type contributed one vertical unit to the graph. Oxygen atoms were the most hydrated (top graph), with negatively charged oxygen (black bars) slightly less hydrated on average than neutral oxygen (grey bars). Nitrogens (middle graph) were the next most hydrated, overlapping the oxygen distribution, and positively charged nitrogens (black bars) were somewhat more hydrated than neutral nitrogens (grey bars). Proline's amide nitrogen, with no hydrogen-bonding capacity, had the lowest nitrogen hydration value (leftmost bar). Carbon and sulfur atoms (bottom graph; note change of y-axis scale) were the least hydrated, with sulfur values at 0.05 and 0.15 hydrations per occurrence. Reproduced from Kuhn et al. (1995). Copyright (1995) Wiley-Liss, Inc. Reprinted by permission of Wiley-Liss, Inc., a division of John Wiley & Sons, Inc.