Host-guest-like thiamine-anion complexation in thiaminium bis(tetrafluoroborate).

In the title compound, 3-[(4-amino-2-methyl-5-pyrimidin-1-io)methyl]-5-(2-hydroxyethyl)-4-methylthiazolium(2+) bis(tetrafluoroborate), C(12)H(18)N(4)OS(2+).2BF(4)(-), the divalent thiamine cation (in the F conformation) is associated with BF(4)(-) anions via two characteristic bridging interactions between the thiazolium and pyrimidinium rings, i.e. C-H...BF(4)(-)...pyrimidinium and N-H...BF(4)(-)...thiazolium interactions. Thiamine molecules are linked by N-H...O hydrogen bonds to form a helical chain structure.

Estimation of individual phases from the four-phase structure invariants in the single isomorphous replacement case.

The probability distribution of the four-phase invariants in the case of single isomorphous replacement has been developed to estimate some individual phases. An example of its application to obtain the phases having special values of 0, pi or +/-pi/2 is given for a known protein structure in space group P2(1)2(1)2(1). The phasing procedure includes the determination of starting phases and an iterative calculation. The initial values of starting phases, which are required by the formula, can be obtained from the estimate of one-phase seminvariants and by specifying the origin and enantiomorph. In addition, the calculations lead to two sets of possible phases for each type of reflection by assigning arbitrarily an initial phase value. The present method provides a possibility for the multisolution technique to increase greatly the number of known phases while keeping the number of the trials quite small.

Oxythiamine hexafluorophosphate monohydrate, a thiamine antagonist with the same conformation as thiamine.

In the title compound, 3-[(3,4-dihydro-2-methyl-4-oxopyrimidin-5-yl) methyl]-5-(2-hydroxyethyl)-4-methylthiazolium hexafluorophosphate monohydrate,C(12)H(16)N(3)O(2)S(+).PF(6)(-).H(2)O, oxythiamine is a monovalent cation with a neutral oxopyrimidine ring. The molecule assumes the F conformation, which is a common form for thiamine but which is substantially different from the unusual V conformation found in the chloride and hydrochloride salts of oxythiamine. The anion-bridging interaction, C-H...anion...pyrimidine, is emphasized as being important for stabilization of the F conformation.