| 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. | |
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MedLine Citation:
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PMID: 17419624 Owner: NLM Status: MEDLINE |
Abstract/OtherAbstract:
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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). |
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Authors:
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Zhixin Tian; Anna Pawlow; John C Poutsma; Steven R Kass |
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Publication Detail:
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Type: Journal Article; Research Support, U.S. Gov't, Non-P.H.S. Date: 2007-04-10 |
Journal Detail:
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Title: Journal of the American Chemical Society Volume: 129 ISSN: 0002-7863 ISO Abbreviation: J. Am. Chem. Soc. Publication Date: 2007 May |
Date Detail:
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Created Date: 2007-04-25 Completed Date: 2007-07-25 Revised Date: - |
Medline Journal Info:
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Nlm Unique ID: 7503056 Medline TA: J Am Chem Soc Country: United States |
Other Details:
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Languages: eng Pagination: 5403-7 Citation Subset: IM |
Affiliation:
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Department of Chemistry, The College of William and Mary, Williamsburg, Virginia 23187, USA. |
Export Citation:
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APA/MLA Format Download EndNote Download BibTex |
| MeSH Terms | |
Descriptor/Qualifier:
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Acids
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chemistry Amino Acids / chemistry* Benzyl Alcohol / chemistry Cysteine / chemistry* Deuterium / chemistry Fourier Analysis Gases Hydrogen / chemistry Hydrogen Bonding Mass Spectrometry Molecular Conformation Spectrometry, Mass, Electrospray Ionization Sulfhydryl Compounds / chemistry |
| Chemical | |
Reg. No./Substance:
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0/Acids; 0/Amino Acids; 0/Gases; 0/Sulfhydryl Compounds; 100-51-6/Benzyl Alcohol; 1333-74-0/Hydrogen; 52-90-4/Cysteine; 7782-39-0/Deuterium |
From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine
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