Structures of cationized proline analogues: Evidence for the zwitterionic form

Andrew S. Lemoff, Matthew F. Bush, Evan R. Williams

Research output: Contribution to journalArticle

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Abstract

The structures of lithiated and sodiated α-methyl-proline (α-Me-Pro) and structural isomers, both with and without a water molecule, are investigated using blackbody infrared radiative dissociation (BIRD) and density functional theory. From the BIRD kinetic data measured as a function of temperature, combined with master equation modeling of these data, threshold dissociation energies for the loss of a water molecule from these clusters are obtained. These energies are 77.5 ± 0.5 and 53 ± 1 kJ/mol for lithiated and sodiated α-Me-Pro, respectively. For the nonzwitterionic isomer, proline methyl ester, these values are 3.0-4.5 kJ/mol higher. These results provide compelling experimental evidence that α-Me-Pro is zwitterionic in these clusters. Theory at the temperature corrected B3LYP/6-311++G**//B3LYP/6-31++G** level indicates that the salt-bridge or zwitterionic forms of lithiated and sodiated α-Me-Pro are between 17 and 23 kJ/mol lower in energy than the nonzwitterionic or charge-solvated forms and that attachment of a single water molecule does not significantly change the structure or the relative energies of these clusters. The proton affinity of proline is 8 kJ/mol higher than that of α-Me-Pro, indicating that lithiated and sodiated singly hydrated proline should also be zwitterionic.

Original languageEnglish (US)
Pages (from-to)1903-1910
Number of pages8
JournalJournal of Physical Chemistry A
Volume109
Issue number9
DOIs
StatePublished - Mar 10 2005

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Proline
analogs
dissociation
Isomers
Molecules
Water
isomers
water
Infrared radiation
molecules
energy
attachment
Density functional theory
affinity
Protons
esters
Esters
Salts
density functional theory
salts

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry

Cite this

Structures of cationized proline analogues : Evidence for the zwitterionic form. / Lemoff, Andrew S.; Bush, Matthew F.; Williams, Evan R.

In: Journal of Physical Chemistry A, Vol. 109, No. 9, 10.03.2005, p. 1903-1910.

Research output: Contribution to journalArticle

Lemoff, Andrew S. ; Bush, Matthew F. ; Williams, Evan R. / Structures of cationized proline analogues : Evidence for the zwitterionic form. In: Journal of Physical Chemistry A. 2005 ; Vol. 109, No. 9. pp. 1903-1910.
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