The structure of Vitamin B12 VI. The structure of crystals of vitamin B12 grown from and immersed in water

Vitamin B12 crystals have been grown from water and photographed in their mother liquor by means of copper Kα X-radiation. The crystal unit cell dimensions are a = 25·33 Å, b = 22·32 Å and c = 15·92 Å, space group P212121 and the formula for the asymmetric unit probably C63H88O14N14PCo.22H2O. From the intensities of some 2900 X-ray reflexions visually measured in 1949, calculations have been made of the electron density in the crystal through a series of approximations. The calculations lead to positions of all the atoms in the B12 molecule, not counting hydrogen atoms; these positions agree closely with those derived for the air-dried crystals except over certain of the amide side chains which differ in conformational details. In the wet crystals the molecules make contact with one another through hydrogen bonds between the amide groups. Between them is a region occupied by water molecules. Some eight or nine of these have definite positions in the crystal; the remainder appear considerably disordered probably as a result of movement in the crystal. The disordered positions lie in or near channels which run between the B12 molecules continuously throughout the crystal and through which it seems likely that water passes out on drying.