Determination of the preferred tautomeric form histamine by 13C nmr spectroscopy.

The pH-dependent 13C chemical shifts for histamine indicate an approximate 4: 1 preference for the N-H tautomer of the imidazole ring, similar to that previously deduced for L-histidine. It is concluded that the 13C chemical shift method is a complimentary technique to the method of determining tautomer preference from pK values. Factors determining the tautomer preference in histamine and L-histidine are discussed.