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.
All Science Journal Classification (ASJC) codes
- Colloid and Surface Chemistry