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Gas-Phase Solvation of Protonated Amino Acids by Methanol.
MedLine Citation:
PMID:  25402819     Owner:  NLM     Status:  Publisher    
Abstract/OtherAbstract:
The enthalpy and entropy changes for the formation of the 1:1 complexes of methanol with various gaseous protonated amino acids have been measured using pulsed-ionization high pressure mass spectrometry. The enthalpy changes for formation of the clusters, Gly(MeOH)H+, Ala(MeOH)H+, Val(MeOH)H+, Leu(MeOH)H+, Ile(MeOH)H+ and Pro(MeOH)H+ have been determined to be -92.0, -83.3, -82.4, -79.5, -78.7 and -73.6 kJ mol-1, respectively. These values agree very well with the energetic values computed at the MP2(full)/6-311++G(2d,2p)//B3LYP/6-311+G(d,p) level of theory for the lowest energy adducts in each system. Both experimental observations and computational determinations of the potential energy surface for the glycine system suggest that a mixture of low lying isomers may be present for each of the cluster systems examined. The primary structural motif for these clusters is the coordination of the methanol molecule to the ammonium group of the protonated amino acid via a strong ionic hydrogen bond. For the amino acids studied here, computational results reveal that one methanol molecule does not sufficiently stabilize any zwitterionic structure such that no appreciable extent of proton transfer from the amino acid to methanol was observed.
Authors:
Kris Eldridge; Ronghu Wu; Jonathan K Martens; Terry Brian McMahon
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Publication Detail:
Type:  JOURNAL ARTICLE     Date:  2014-11-17
Journal Detail:
Title:  The journal of physical chemistry. A     Volume:  -     ISSN:  1520-5215     ISO Abbreviation:  J Phys Chem A     Publication Date:  2014 Nov 
Date Detail:
Created Date:  2014-11-17     Completed Date:  -     Revised Date:  2014-11-18    
Medline Journal Info:
Nlm Unique ID:  9890903     Medline TA:  J Phys Chem A     Country:  -    
Other Details:
Languages:  ENG     Pagination:  -     Citation Subset:  -    
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