Peptide models XXVII. An exploratory ab initio study on the 21st amino acid side-chain conformations of N-formyl-L-selenocysteinamide (For-L-Sec- NH2) and N-acetyl-L-selenocysteine-N-methylamide (Ac-L-Sec-NHMe) in their γ(L) backbone conformation

Judith C. Vank, Carlos P. Sosa, Andras Perczel, Imre G. Csizmadia

Research output: Contribution to journalArticle

25 Citations (Scopus)

Abstract

Selenocysteine is expected to have 9 x 9 = 81 conformations [3 x 3 = 9 backbone: ψ (g+,a,g-) x φ (g+,a,g-) and 3 x 3 = 9 side-chain: χ1 (g+,a,g-) x χ2(g+,a,g-)]. In the present study, all the torsional modes of the side-chain (χ1: rotation about the C(α)-C(β) and χ2: rotation about the C(β)-Se bonds) were investigated in the relaxed γ(L) backbone [(φ,ψ); (g-,g+)] conformation. Seven out of the nine expected minima were found at the RHF/3-21G level of theory for N-formyl-L-selenocysteinamide (For-L-Sec-NH2) and N-acetyl-L-selenocysteine-N-methylamide (Ac-L-Sec-NHMe). The stabilization energy exerted by the -CH2-SeH side-chain has been compared with that of -CH2-SH and -CH2-OH. Relative energies of the various conformers were also obtained via single point calculations at the B3LYP/6- 31G(d,p) level of theory. Topological analysis of the electron density has been performed by Bader's Atoms in Molecule (AIM) approach using the results. The structures were also optimized at the B3LYP/6-31+G(d,p) level of theory.

Original languageEnglish
Pages (from-to)395-408
Number of pages14
JournalCanadian Journal of Chemistry
Volume78
Issue number3
DOIs
Publication statusPublished - Jan 1 2000

Keywords

  • Ab initio MO study
  • Atoms in Molecules (AIM)
  • Bader's electron density analysis
  • Multidimensional Conformational Analysis (MDCA)
  • Selenocysteine side-chain conformations

ASJC Scopus subject areas

  • Catalysis
  • Chemistry(all)
  • Organic Chemistry

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