Are carboxyl groups the most acidic sites in amino acids? Gas-phase acidity, H/D exchange experiments, and computations on cysteine and its conjugate base

被引：0

作者：

Tian, Zhixin ^{[2
]}

Pawlow, Anna ^{[1
]}

Poutsma, John C. ^{[1
]}

Kass, Steven R. ^{[2
]}

机构：

[1] Department of Chemistry, College of William and Mary, Williamsburg, VA 23187, United States

[2] Department of Chemistry, University of Minnesota, Minneapolis, MN 55455, United States

来源：

Journal of the American Chemical Society | 2007年 / 129卷 / 17期

关键词：

Hydrogen-deuterium exchange experiments were carried out on the conjugate base of cysteine with four different deuterated alcohols. Three H/D exchanges are observed to take place in each case; and a relay mechanism which requires the SH and CO2H groups to have similar acidities and subsequently proceeds through a zwitterionic intermediate is proposed. Gas-phase acidity measurements also were carried out in a quadrupole ion trap using the extended kinetic method and in a Fourier transform mass spectrometer by an equilibrium determination. The results are in excellent accord with each other and high-level ab initio and density functional theory calculations and indicate that the side-chain thiol in cysteine is more acidic than the carboxyl group by 3.1 kcal mol-1. Deprotonated cysteine is thus predicted to be a thiolate ion. A zwitterionic species also was located on the potential energy surface; but it is energetically unfavorable (+10.1 kcal mol-1). © 2007 American Chemical Society;

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摘要：

Journal article (JA)

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页码：5403 / 5407