Semiempirical Calculations on the Electronic Structure and Preferred Conformation of Thiamine (Vitamin B1) and Thiamine Pyrophosphate (Cocarboxylase)

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Abstract

Extended Hückel and CNDO/2 molecular orbital calculations were performed on the title compounds in their various states of ionization. The electronic structures are discussed. The charges then were used to define the regions of preferred conformations in these molecules via the sum of a Lennard-Jones and a Coulombic potential. The conformational energy maps for thiamine hydrochloride with unperturbed and ylide (C-2 deprotonated) thiazolium rings are fairly similar. It appears that full 360° rotation around either of the bonds connecting the two aromatic rings (C-C and C-N bond) is subject to substantial barrier of at least 15-18 kcal/mol. The energetically most favored conformational regions apparently can interconvert readily at room temperature. A suggestion is made for possible conformational changes occurring in the coenzyme upon binding of substrates and enzyme.

Original languageEnglish (US)
Pages (from-to)3623-3630
Number of pages8
JournalJournal of the American Chemical Society
Volume96
Issue number11
DOIs
StatePublished - May 1 1974

All Science Journal Classification (ASJC) codes

  • Chemistry(all)
  • Biochemistry
  • Catalysis
  • Colloid and Surface Chemistry

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