TABLE 3.

Macroscopic constants for each equilibrium ( $K_{a }$ – $K_d$ ) denoted in Figure 6 for L-cysteine and L-cysteine ethyl ester.

Biothiol	$pKa$	$pKb$	$pKc$	$pKd$
L-Cysteine	8.53	8.86	10.36	10.03
L-Cysteine ethyl ester	7.45	6.77	8.41	9.09