CHIRALITY OF INTERMEDIATES IN THIAMIN CATALYSIS - STRUCTURE OF (+)-2-(1-HYDROXYETHYL)-3,4-DIMETHYL-5-(2-HYDROXYETHYL)THIAZOLIUM IODIDE, THE ABSOLUTE STEREOCHEMISTRY OF THE ENANTIOMERS OF 2-(1-HYDROXYETHYL)THIAMIN, AND ENZYMATIC-REACTION OF THE DIPHOSPHATES