Table 2. Representative Calculated Average Occupancies of Solvent Shells^a.

peptide	HFIP	HFIP	HFIP	H2O	H2O	H2O	H2O/HFIP
hydrogen	shell 1	shell 2	shell 3	shell 1	shell 2	shell 3	shell 1	shell 2	shell 3
1AspHA	1.54	42.64	148.89	10.98	101.76	290.45	7.1	2.4	2.0
6TrpH	0.94	50.35	163.80	3.65	64.95	302.35	3.9	1.3	1.8
6TrpHA	0.46	50.87	168.09	3.25	61.16	302.69	7.1	1.2	1.8
6TrpHD1	1.00	54.95	164.34	3.04	61.59	301.77	3.0	1.1	1.8
6TrpHE1	2.62	61.22	157.36	2.20	64.67	299.08	0.8	1.1	1.9
6TrpHZ2	7.26	61.77	151.90	2.09	66.91	299.21	0.3	1.1	2.0
6TrpHH2	11.20	60.38	147.65	2.79	69.16	298.23	0.2	1.1	2.0
6TrpHZ3	10.64	60.78	146.63	2.56	65.98	300.97	0.2	1.1	2.1
6TrpHE3	5.43	60.90	152.19	2.18	56.70	308.87	0.4	0.9	2.0
8LysH	3.17	51.87	156.76	1.67	72.80	298.53	0.5	1.4	1.9
12ProHA	5.83	62.36	154.89	3.90	72.78	296.10	0.7	1.2	1.9
17ProQG	9.25	56.04	141.80	8.32	86.54	295.97	0.9	1.5	2.1
20SerH	2.32	47.21	150.92	12.51	93.50	281.81	5.4	2.0	1.9

^aShell 1 is the solvent layer from 0 to 0.556 nm from the center of a peptide hydrogen atom. Shell 2 is the solvent layer from 0.556 to 1.112 nm, while Shell 3 includes the solvent layer from 1.112 to 1.657 nm. A rapidly rotating HFIP molecule is represented by a sphere 0.556 in diameter.²⁶ The columns labeled HFIP provide the calculated average number of solvent fluorine atoms in a given shell. These atoms may or may not be on the same HFIP molecules. Mean deviations from the average varied but were of the order ±20% for Shell 1 and ±2% for Shells 2 and 3. A water-to-HFIP ratio greater than 2.56 corresponds to the local solvent mixture being enriched in water.