| Comments |
p.5878 right column top paragraph:” Based on Tables 3 and 4, Table 6 shows the changes in the components of and total SF entropy (eq 21). Water binding to the hydrophobic site in barnase loses effectively no entropy. What it loses in orientational entropy, it gains in vibrational and librational entropy. Binding to the more hydrophilic site of BPTI [bovine pancreatic trypsin inhibitor], it loses 12.1 J K^−1 mol^−1. All other ligands lose the same cratic entropy of 33.4 J K^−1 mol^−1 on binding, whereas the rotational entropy loss depends logarithmically on volume through the number of orientations. These values are modulated only slightly by the changes in vibrational and librational entropies because of the differing strengths of the interactions. Benzene loses the smaller value of 49.9 J K^−1 mol^−1 entropy because its high symmetry and weak interactions mean that it loses no rotational entropy about its z axis. The total entropy losses of BUT [4-hydroxy-2-butanone], benzamidine, and IPMP [2-methoxy-3-isopropylpyrazine] are all very close in the range from −71.3 to −74.4 J K^−1 mol^−1, which corresponds to TΔSL ≈ −22 kJ mol^−1." p.5879 right column bottom paragraph:"A real difficulty facing SF models has been how to estimate the configurational volume, Vtr, of the ligand in solution in the confinement of the solvent. For binding problems, the simplest approach is to ignore it and assume that it does not change upon binding. How good an assumption this is can be determined only by testing it. (Table 6 shows it to be a good approximation.)" |