Selenium-77 nuclear magnetic resonance studies of selenols, diselenides, and selenenyl sulfides

Abstract

KHOON-SIN TAN, ALAN P. ARNOLD, and DALLAS L. RABENSTEIN. Can. J. Chem. 66, 54 (1988).77Se and 'H nuclear magnetic resonance spectra have been measured for selenols (RSeH), diselenides (RSeSeR), and selenenyl sulfides (RSeSR'), including selenenyl sulfides formed by reaction of glutathione and penicillamine with selenocystine and related diselenides. Exchange processes strongly affect the 77Se and 'H nuclear magnetic resonance spectra of all three classes of compounds. Sharp, exchange-averaged resonances are observed in the 'H nuclear magnetic resonance spectra of selenols; however, selenol proton exchange causes the 77Se resonances to be extremely broad over the pH range where the selenol group is titrated. Selenol/diselenide exchange he^ + RSeSeR K S~S~R + RSeH) also results in exchange-averaged 'H resonances for solutions containing RSeH and RSeSeR; however, the 77Se resonances were too broad to detect. Exchange reactions have similar effects on nuclear magnetic resonance spectra of solutions containing selenols and seleneny l sulfides. The results indicate selenol/diselenide exchange is much faster than thiol/disulfide exchange. The 77Se chemical shift depends on the chemical state of the selenium, e.g., titration of the selenol group of selenocysteamine causes the 77Se resonance to be shielded by 164 ppm, oxidation of.th+e selenol to form the diselfnide selenocystamine causes a deshielding of 333 ppm, and oxidation to form the selenenyl sulfide H3NCH2CH2SeSCH2CH2NH3 results in a deshielding of 404 ppm. 77Se chemical shifts were found to be in the range -240 to -270 ppm (relative to (CH3)2Se) for selenolates, approximately -80 ppm for selenols, 230-360 ppm for diselenides, and 250-340 ppm for selenenyl sulfides. The 77Se chemical shift is also affected by titration of neighboring carboxylic acid and ammonium groups, and their pKA values can be calculated from 77Se chemical shift data. On a dCterminC les spectres en resonance magnCtique nuclkaire du 7 7~e et du 'H de sClCnols (RSeH), de disClCnures (RSeSeR) et de disulfures de sClCnCnyles (RSeSR'), y compris des sulfures de sClCnCnyles qui se foment au cours de la reaction du glutathion et de la pCnicillamine avec la sClCnocystCine et des disClCnures apparentks. Les processus d'kchange affectent beaucoup les spectres en resonance magnCtique nuclCaire du 77Se et du 'H de ces trois classes de composCs. Avec les sCICnols, les spectres en resonance magnCtique nucleaire du 'H prCsentent des raies bien dCfinies qui rCsultent de moyennes; toutefois, 1'Cchange du proton du sClCnol fait que les rCsonances du 77Se sont extremement larges 1 tous les pH oC1 le groupement sClCnol peut Stre titrC. Dans le cas des solutions qui contiennent du RSeH et du RSeSeR, 1'Cchange sC1Cnol/disC1Cnure (R*SeH + RSeSeR R*SeSeR + RSeH) conduit aussi 1 des rksonances du 'H qui resultent de moyennes; toutefois, les rCsonances du 77Se sont trop Clargies pour &tre dCtectCes. Les rCactions d'Cchange ont des effets semblables sur les spectres en resonance magnktique nucl~airede solutions contena...

Selenocysteine‐Mediated Native Chemical Ligation

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