. 1999 Sep 28;96(20):11145–11150. doi: 10.1073/pnas.96.20.11145

Table 1.

Vacuum to water transfer free energies for small-molecule side-chain analogues

Residue	Small molecule	ΔG^exp	ΔG^DelPhi	ΔG^MTK	ΔG^error
Arg⁺	N-propyl guanidinium	–	−66.07	−64.49	–
Lys⁺	N-butyl ammonium	−69.24	−69.44	−69.11	0.13
His⁺	Methyl imidazolium	−64.13	−64.36	−64.81	−0.68
His⁰	Methyl imidazole	−10.25	−10.22	−9.32	0.93
Asp⁻	Acetate	−80.65	−80.44	−79.05	1.60
Asp⁰	Acetic acid	−6.70	−6.63	−5.57	1.13
Asn	Acetamide	−9.72	−9.76	−8.85	0.87
Glu⁻	Propionate	−79.12	−79.21	−77.53	1.59
Glu⁰	Propionic acid	−6.47	−6.41	−5.25	1.22
Gln	Propionamide	−9.42	−9.42	−8.55	0.87
Cys⁻	Methylthiol ion	−76.79	−76.66	−75.85	0.94
Cys⁰	Methylthiol	−1.24	−1.35	−1.08	0.16
Tyr⁻	p-cresol ion	−75.01	−74.88	−71.90	3.11
Tyr⁰	p-cresol	−6.13	−6.11	−4.74	1.39
Ser	Methanol	−5.08	−5.44	−4.83	0.25
Thr	Ethanol	−4.90	−5.02	−4.55	0.35
Met	Methylethyl sulfide	−1.49	−1.46	−1.07	0.42
Trp	Methyl indole	−5.91	−5.84	−4.76	1.15
Phe	Toluene	−0.76	−0.77	−0.37	0.39
BB	N-methyl acetamide	−10.08	−10.00	−9.53	0.55

Shown are experimental and calculated vacuum (ɛ_p = 2, ɛ_s = 1) to water (ɛ_p = 2, ɛ_s = 80) transfer free energies (kcal/mol) for small-molecule analogs of the amino-acid side chains. ΔG^exp indicates the experimental transfer free energy. ΔG^DelPhi indicates the transfer free energy reported by Sitkoff et al. (27) using the DelPhi program (29). ΔG^MTK and ΔG^error indicate the MTK transfer free energy and its error with respect to the experimentally measured value.