Molar absorption coefficients of porphyrin esters in chloroform determined by copper titration

Article abstract of DOI:10.1042/bj1610425

Chromatographically pure porphyrin esters free from metalloporphyrins were titrated with Cu²⁺ to determine the molar amount of porphyrin present. The end point of the titration was defined by a t.l.c. method detecting traces of metal free porphyrin ester in admixture to its copper complex. From spectrometic measurement at the Soret maximum and the molar amounts found by the titration, ε(M) was calculated for proto-, copro-, penta-, hexa- and hepta- carboxylic and uro porphyrin permethyl esters. The values for uroporphyrin showed perfect agreement with those of previous workers, whereas those for coproporphyrin were about 5% lower and those for protoporphyrin more than 20% lower. The implications of the findings are discussed. Determinations of ε(M) of some higher esters (ethyl to pentyl) and some partial methyl esters with one carboxyl group free are also presented.