Protonation Equilibria of Biologically Active Ligands in Mixed Aqueous Organic Solvents
Table 8
Protonation constants of some α-amino acids in water and water-dioxane mixtures Temp. = 25°C and mol·dm−3 NaClO4a.
AA
Water
10% D—90% W
20% D—80% W
30% D—70% W
40% D—60% W
50% D—50% W
60% D—40% W
Gly
9.58
2.32
9.55
2.41
9.56
2.70
9.58
2.87
9.58
3.15
9.60
3.48
9.62
3.60
Ala
9.70
2.40
9.66
2.52
9.72
2.64
9.68
2.89
9.73
3.10
9.75
3.39
9.78
3.63
Val
9.61
2.38
9.56
2.53
9.60
2.68
9.58
2.86
9.60
3.08
9.62
3.43
9.66
3.65
Leu
9.75
2.50
9.59
2.64
9.64
2.80
9.66
2.99
9.70
3.31
9.72
3.55
9.75
3.75
Ile
9.76
2.47
9.72
2.58
9.63
2.74
9.67
2.97
9.65
3.26
9.70
3.55
9.71
3.74
Phe
9.20
2.43
9.15
2.57
9.10
2.64
9.12
2.81
9.15
3.10
9.16
3.36
9.15
3.50
Ser
9.15
2.42
9.07
2.57
9.10
2.62
9.13
2.82
9.16
3.04
9.20
3.17
9.17
3.35
Thr
9.04
2.45
9.02
2.53
9.06
2.60
9.05
2.75
9.07
2.96
9.10
3.18
9.17
3.40
Note. D = dioxane, W = water, Val = DL-valine, Ala = DL-alanine, Leu = L-leucine, Ile = L-isoleucine, Phe = DL-phenylalanine, Ser = L-serine, and Thr = L-threonine. aData taken from reference [61]. corresponds to 11 species (i.e., L− + H+ LH); corresponds to 12 species (i.e., LH + H+). The % is expressed as (volume/Volume).