UV-induced isomerization of β-alanine isolated in argon matrices

Stepan G. Stepanian, Alexander Yu Ivanov, Daryna A. Smyrnova, Ludwik Adamowicz

Research output: Contribution to journalArticle

16 Citations (Scopus)

Abstract

We have employed low-temperature matrix-isolation FTIR spectroscopy, the density functional theory and ab initio calculations at the MP2 and CCSD(T) levels of theory to determine the conformational composition of the simplest β-amino acid, β-alanine. UV irradiation and thermal annealing of the samples together with the FTIR spectra of deuterated β-alanine were used to separate bands of different conformers. A detailed study of the potential energy surface of β-alanine obtained at the MP2/aug-cc-pVDZ level of theory reveals twenty β-alanine conformers, but only five of them may exist in matrices due to their sufficiently high relative stabilities and low energy barriers separating them from each other. An analysis of the FTIR spectra allows us to confirm the presence of four β-alanine conformers in argon matrices with certainty. Two of them, conformers I and II, have an NH⋯O intramolecular H-bond, the third, conformer V, has an N⋯HO H-bond, and the fourth, conformer IV, has no intramolecular H-bonds. The relative populations of the conformers determined using the relative Gibbs free energies calculated at the CCSD(T)/CBS level of theory at 420 K are 48.1%, 23.7%, 16.8% and 3.2% for the conformers I, II, IV, and V, respectively. Some trace amount of conformer VII was also detected.

Original languageEnglish (US)
Pages (from-to)6-19
Number of pages14
JournalJournal of Molecular Structure
Volume1025
DOIs
StatePublished - Oct 10 2012

Fingerprint

Argon
Isomerization
Alanine
Potential energy surfaces
Energy barriers
Gibbs free energy
Density functional theory
Irradiation
Spectroscopy
Annealing
Amino Acids
Chemical analysis
Temperature

Keywords

  • β-Alanine
  • Ab initio calculations
  • Conformer
  • Gibbs free energies
  • IR spectroscopy
  • Matrix isolation

ASJC Scopus subject areas

  • Spectroscopy
  • Analytical Chemistry
  • Inorganic Chemistry
  • Organic Chemistry

Cite this

UV-induced isomerization of β-alanine isolated in argon matrices. / Stepanian, Stepan G.; Ivanov, Alexander Yu; Smyrnova, Daryna A.; Adamowicz, Ludwik.

In: Journal of Molecular Structure, Vol. 1025, 10.10.2012, p. 6-19.

Research output: Contribution to journalArticle

Stepanian, Stepan G. ; Ivanov, Alexander Yu ; Smyrnova, Daryna A. ; Adamowicz, Ludwik. / UV-induced isomerization of β-alanine isolated in argon matrices. In: Journal of Molecular Structure. 2012 ; Vol. 1025. pp. 6-19.
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AB - We have employed low-temperature matrix-isolation FTIR spectroscopy, the density functional theory and ab initio calculations at the MP2 and CCSD(T) levels of theory to determine the conformational composition of the simplest β-amino acid, β-alanine. UV irradiation and thermal annealing of the samples together with the FTIR spectra of deuterated β-alanine were used to separate bands of different conformers. A detailed study of the potential energy surface of β-alanine obtained at the MP2/aug-cc-pVDZ level of theory reveals twenty β-alanine conformers, but only five of them may exist in matrices due to their sufficiently high relative stabilities and low energy barriers separating them from each other. An analysis of the FTIR spectra allows us to confirm the presence of four β-alanine conformers in argon matrices with certainty. Two of them, conformers I and II, have an NH⋯O intramolecular H-bond, the third, conformer V, has an N⋯HO H-bond, and the fourth, conformer IV, has no intramolecular H-bonds. The relative populations of the conformers determined using the relative Gibbs free energies calculated at the CCSD(T)/CBS level of theory at 420 K are 48.1%, 23.7%, 16.8% and 3.2% for the conformers I, II, IV, and V, respectively. Some trace amount of conformer VII was also detected.

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