Table 1. The physicochemical properties of hydrophobic amino acids.

	glycine (gly)	alanine (ala)	valine (val)	leucine (leu)	isoleucine (ile)
Molecular structure
Side chain	-H	-CH3	-CH(CH3)2	-CH2CH(CH3)	-CH(CH3)C2H5
pKa1 (-COOH) at 273.15 K	2.41	2.39	2.33	2.39	2.38
Degree of ionization (-COOH) at pH 3.29	88.3%	88.7%	90.2%	88.9%	89.0%
pKa2 (-NH2) at 273.15 K	10.32	10.43	10.34	10.33	10.41
Degree of ionization (-NH2) at pH 3.29	100.0%	100.0%	100.0%	100.0%	100.0%
Hydrophobicity	−0.4	1.8	4.2	3.8	4.5

Acid dissociation constants at 273.15 K were calculated from the values listed in Table S1 using the van't Hoff equation. Hydrophobicity values were taken from the literature⁶⁰.