Correlation between the NMR Chemical Shifts and Thiolate Protonation Constants of Cysteamine, Homocysteine, and Penicillamine
Table 1
The species-specific chemical shifts (on the ppm scale) determined for cysteamine, homocysteine, and penicillamine microspecies (the thiolate protonation constants were determined previously in [21]; the N, S, and O symbols represent the amino, thiolate, and carboxylate basic moieties, respectively).
Logk
1H
13C
α
β
γ
CH3
α
β
γ
CH3
Cysteamine
CysA a
9.67
2.646
2.506
48.83
30.57
CysA b
8.37
3.076
2.720
46.95
25.43
Δδ N
0.431
0.213
−1.88
−5.14
Δδ S
0.129
0.118
−2.08
−1.30
Homocysteine
hCys a
9.94
3.288
1.726
1.805
2.424
58.97
23.71
45.22
hCys b
8.99
3.807
2.020
2.068
2.503
55.68
23.40
43.58
hCys d
9.35
3.653
1.793
1.927
2.492
56.95
23.48
44.41
hCys f
8.4
4.172
2.087
2.190
2.571
51.18
23.05
42.85
Δδ N
0.519
0.294
0.263
0.079
−3.29
−0.31
−1.64
Δδ S
0.074
0.096
0.108
0.155
0.77
−0.81
−6.22
Δδ O
0.365
0.067
0.122
0.069
−2.02
−0.23
−0.81
Penicillamine
Pen a
9.34
3.049
1.191
1.437
71.83
49.42
30.91
37.10
Pen b
8.09
3.298
1.294
1.535
69.31
47.81
35.42
31.69
Pen d
8.24
3.464
1.250
1.470
69.94
49.16
30.85
36.66
Pen f
6.99
3.713
1.353
1.568
67.42
47.55
35.36
31.25
Δδ N
0.249
0.103
0.098
−2.52
−1.61
4.51
−5.41
Δδ S
0.404
0.187
0.031
−1.77
−1.07
−4.95
1.32
Δδ O
0.415
0.059
0.033
−1.89
−0.26
−0.06
−0.44
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.
