Determination of the deprotonation constants of seleno-DL-cystine and seleno-DL-methionine and implication to their separation by HPLC

✍ Scribed by Marcos Rivail da Silva; Riansares Muños Olivas; O. F. X. Donard; Michel Lamotte

• Book ID: 101280212
• Publisher: John Wiley and Sons
• Year: 1997
• Tongue: English
• Weight: 131 KB
• Volume: 11
• Category: Article
• ISSN: 0268-2605
• DOI: 10.1002/(sici)1099-0739(199701)11:1<21::aid-aoc537>3.0.co;2-k

✦ Synopsis

We have determined the deprotonation constants (pK 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 pK 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 pK a values for the carboxylic groups was found to be much smaller for seleno-DL-cystine than for DLcystine. 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.