Protonation Equilibria of Biologically Active Ligands in Mixed Aqueous Organic Solvents
Table 6
Protonation constants of α-amino acid esters in water-ethanol mixtures Temp. = 25°C and mol·dm−3 NaCla.
Esters
Water
30% E—70% W
50% E—50% W
70% E—30% W
CysOMe
9.17
6.38
9.23
6.09
9.34
5.88
10.82
6.24
CysOEt
9.36
6.54
9.37
6.17
9.48
5.97
11.13
6.28
TyrOMe
9.73
7.04
10.10
6.73
10.49
6.42
10.62
6.17
TyrOEt
9.71
7.05
10.13
6.75
10.52
6.45
10.63
6.19
TrpOMe
10.66
7.10
11.27
6.78
11.56
6.51
11.39
6.29
TrpOEt
10.79
7.10
11.28
6.98
11.70
6.80
11.77
6.45
LysOMe
9.99
6.98
9.80
6.90
9.52
6.63
9.12
6.46
LysOEt
10.32
7.18
9.70
6.81
9.45
6.60
9.00
6.35
HisOMe
7.10
4.96
6.72
4.78
6.54
4.61
6.34
4.39
Note. E = ethanol; W = water; adata taken from reference [56]. corresponds to 11 species (i.e., L− + H+ LH); corresponds to 12 species (i.e., LH + H+). The % is expressed as (volume/Volume).
