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Determination of the deprotonation constants of seleno‐ DL ‐cystine and seleno‐ DL ‐methionine and implication to their separation by HPLC
Author(s) -
Rivail da Silva Marcos,
Muños Olivas Riansares,
Donard O. F. X.,
Lamotte Michel
Publication year - 1997
Publication title -
applied organometallic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.53
H-Index - 71
eISSN - 1099-0739
pISSN - 0268-2605
DOI - 10.1002/(sici)1099-0739(199701)11:1<21::aid-aoc537>3.0.co;2-k
Subject(s) - chemistry , cystine , protonation , deprotonation , methionine , selenium , potentiometric titration , amino acid , high performance liquid chromatography , chromatography , stereochemistry , medicinal chemistry , organic chemistry , cysteine , ion , biochemistry , enzyme
We have determined the deprotonation constants (p K a ) of seleno‐ DL ‐cystine and seleno‐ DL ‐methionine together with those of DL ‐cystine and DL ‐methionine for comparison, by potentiometric measurements. In the case of seleno‐ DL ‐cystine, the difference between the p K a values for the two amino groups was found to be only slightly lower than that observed for DL ‐cystine itself. In contrast, the difference between the two p K a values for the carboxylic groups was found to be much smaller for seleno‐ DL ‐cystine than for DL ‐cystine. In both seleno‐amino‐acids, the zwitterionic species appear to be dominant in the pH range between 4 and 7, while positively charged protonated species are found to be present at pH values lower than 4. Based on a knowledge of the ionic species distributions as a function of pH, we have proposed an interpretation for the chromatographic separation of selenocystine and selenomethionine by HPLC. © 1997 by John Wiley & Sons, Ltd.