The structure of vitamin B12 V. The structure of the air-dried crystals of vitamin B12

摘要: The refinement of the positions found in air-dried B 12 crystals Oxford and Princeton investigations has been carried out through four cycles structure factor electron density calculations, on basis data. Owing to disordered character dried crystal consequent limitations X-ray data, no high precision atom placing can be achieved; preferred parameters are listed for 93 atoms molecule 15 water molecules with an additional 7 less well-defined sites. Certain interesting features molecular geometry have appeared during refinement. two planes benziminazole ring inner corrin nucleus, around which is constructed, lie at angle 80° one another—the tilt seems required by close contact between nitrogen methyl group attached direct junction five-membered rings nucleus. projected position across nucleus also determined largely packing considerations within molecule; various small distortions occur increase otherwise too short contacts. latest difference maps somewhat strengthen identification as groups single substituents nucleus; they show peaks many possible hydrogen positions. Of 18 indicated density, major part definite positions, bonded another active surface, remainder drying probably stranded different unit cells, among sites listed.