Vitamin B12, also known as cobalamin, is a polycyclic compound containing trivalent cobalt, which can cause rash, itching, diarrhea and asthma. It promotes the growth of malignant tumors. Four reduced pyrrole rings are connected together to form a corrin macrocycle (similar to porphyrin), which is the only vitamin containing metal elements. Vitamin B12 is a red crystalline powder, odorless and tasteless, soluble in water, difficult to dissolve in ethanol, insoluble in acetone, chloroform and ether, and is most stable under weak acid conditions of pH 4.5-5.0. It decomposes in strong acid (pH <2) or alkaline solution, and can be damaged to a certain extent when heated. Higher animals and plants cannot produce vitamin B12. Vitamin B12 in nature is synthesized by microorganisms. Vitamin B12 is the only vitamin that requires a secretion of gastric parietal cells (intrinsic factor) to be absorbed. It participates in the production of bone marrow red blood cells, prevents pernicious anemia, and prevents damage to brain nerves.
