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Fundamental Thermochemical Properties of Amino Acids: Gas-Phase and Aqueous Acidities and Gas-Phase Heats of Formation.
MedLine Citation:
PMID:  22277062     Owner:  NLM     Status:  Publisher    
Abstract/OtherAbstract:
The gas-phase acidities of the 20 L-amino acids have been predicted at the composite G3(MP2) level. A broad range of structures of the neutral and anion were studied to determine the lowest energy conformer. Excellent agreement is found with the available experimental gas-phase deprotonation enthalpies, and the calculated values are within experimental error. We predict that tyrosine is deprotonated at the CO2H site. Cysteine is predicted to be deprotonated at the SH but the proton on the CO2H is shared with the S- site. Self-consistent reaction field (SCRF) calculations with the COSMO parameterization were used to predict the pKa's in aqueous solution. The differences in the pKa values were used to estimate the free energy difference between the zwitterion and non-zwitterion forms in solution. The heats of formation of the neutral compounds were calculated from atomization energies and isodesmic reactions to provide the first reliable set of these values in the gas phase. Further calculations were performed on 5 rare amino acids to predict their heats of formation, acidities, and pKa values.
Authors:
Michele L Stover; Virgil E Jackson; Myrna H Matus; Margaret A Adams; Carolyn Jeane Cassady; David A Dixon
Publication Detail:
Type:  JOURNAL ARTICLE     Date:  2012-1-25
Journal Detail:
Title:  The journal of physical chemistry. B     Volume:  -     ISSN:  1520-5207     ISO Abbreviation:  -     Publication Date:  2012 Jan 
Date Detail:
Created Date:  2012-1-26     Completed Date:  -     Revised Date:  -    
Medline Journal Info:
Nlm Unique ID:  101157530     Medline TA:  J Phys Chem B     Country:  -    
Other Details:
Languages:  ENG     Pagination:  -     Citation Subset:  -    
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