Correlation between the NMR Chemical Shifts and Thiolate Protonation Constants of Cysteamine, Homocysteine, and Penicillamine

Table 2

The species-specific chemical shifts (on the ppm scale) determined for cystamine, homocystine, and penicillamine disulfide microspecies (the thiolate protonation constants were determined previously in [21]).

Logk		1H
		α	β	γ	CH3
Cystamine
CysA2^a	9.67	2.928	2.807
CysA2^d	8.37	3.409	3.025
Δδ NN′		0.480	0.219
Homocystine
hCys2a	9.94	3.347	2.052	1.942	2.783
hCys2f	8.99	3.860	2.315	2.247	2.826
hCys2k	9.35	3.727	2.075	2.123	2.859
hCys2p	8.4	4.240	2.338	2.428	2.902
Δδ NN′		0.512	0.263	0.305	0.043
Δδ OO′		0.380	0.023	0.181	0.076
Panicillamine disulfide
Pen2a	9.34	3.691		1.296	1.321
Pen2f	8.09	3.982		1.454	1.398
Pen2k	8.24	3.989		1.340	1.416
Pen2p	6.99	4.280		1.498	1.493
Δδ NN′		0.291		0.158	0.077
Δδ OO′		0.298		0.044	0.095

Δδ (Delta delta) shows how the protonation shift observed on a nucleus, caused by the protonation of the various basic moieties can be quantified in ppm. Note that Δδ is nucleus-dependent; its value is different and distinctive not only for all types of nuclei but also for every atom in the molecule.