ISSN:
1076-5174
Keywords:
Chemistry
;
Analytical Chemistry and Spectroscopy
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
,
Physics
Notes:
The kinetics of gas-phase H—D exchange reactions of a series of protonated amino acids and peptides with deuterium-substituted alcohols (D2O, CH3OD, C2H5OD and 1-C4H9OD) were studied in an external source Fourier transform mass spectrometer. The number of exchanges observed on the time-scale of these experiments ranged from one to the total number of ‘labile’ substrate hydrogens, depending on the amino acid and the deuterating reagent. Exchange efficiencies, k/kADO, varied from 〈0.001 to 0.3. Within the series ROD, the reactivity increased with increasing size of the R group. For the amino acids with alkyl side-chains, a roughly linear correlation of log(k/kADO) with proton affinity difference (ΔPA = PA of unprotonated substrate - PA of reagent) was observed. The amino acids lysine and histidine and the dipeptides alanylglycine and diglycine showed higher reactivity and greater tendency for multiple exchange, with a weaker dependence on ΔPA. The ability of a peptide and an alcohol to exchange efficiently even when ΔPA is larger is attributed to the occurrence of exchange within a cyclic hydrogen-bonded complex, in which the deuterating agent forms a bridge between the site of protonation and a basic site on the substrate.
Additional Material:
3 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/jms.1190300807
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