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Surface studies of keratin fibers and related model compounds using ESCA . I—intermediate oxidation products of the model compound 1‐cystine and their hydrolytical behaviour
Author(s) -
Setiawan L. D.,
Baumann H.,
Gribbin D.
Publication year - 1985
Publication title -
surface and interface analysis
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.52
H-Index - 90
eISSN - 1096-9918
pISSN - 0142-2421
DOI - 10.1002/sia.740070406
Subject(s) - chemistry , cysteic acid , cystine , protonation , inorganic chemistry , cysteine , sulfinic acid , organic chemistry , medicinal chemistry , ion , enzyme
The intermediate oxidation products of 1‐cystine, namely cystine S‐monoxide, cystine S,S‐dioxide and cysteine sulphinic acid have been synthesized according to the procedures of other workers. Attempts to prepare cystine trioxide and cystine tetroxide have also been carried out. The stability of cystine S‐monoxide, cystine S,S‐dioxide and cysteine sulphinic acid in aqueous solutions both under mild hydrolytical conditions (2 h, 25 °C) at different pH values and under the conditions of acid hydrolysis (6 N HCl, 105 °C, 1–20 h, 24 h) have been studied. Cystine, its oxidation products and the disproportionation products are identified by ESCA (C 1s, O 1s, N 1s, S 2p). Both cysteine sulphinic acid and cysteic acid exist mainly as Zwitterions due to the fact that in the carbon spectra of each of them an additional peak shifted to about 1.4 eV (relative to the hydrocarbon peak) has been observed, which is attributed to carbon bond to protonated nitrogen. In addition, only in the cases of cysteine sulphinic acid and cysteic acid an increasing of the nitrogen binding energy of about 1 eV compared with those of cystine and its corresponding oxides has been found indicating of protonated nitrogen. Both the monoxide and the dioxide are relatively unstable in aqueous solutions (2 h, 25 °C, pH 1–10). However the monoxide is more stable than the dioxide under these conditions. Cysteine sulphinic acid is stable under this mild hydrolytical condition. Even in 6 N HCl at 105 °C for 1–20 h in vacuo cysteine sulphinic acid is moderately stable. After 24 h it cannot be detected at all. The results achieved from these studies are discussed in detail in conjunction with previous results reported by other investigators concerning the hydrolytical behaviour of cystine intermediate oxidation products.