CAPILLARY ELECTROPHORETIC SEPARATION OF CATIONIC PORPHYRINS

Cationic porphyrins have a wide variety of uses including those as nuc leic acid binding and cleaving agents, as potential pharmacological ag ents, as electron donor/accepters in intramolecular electron transfer processes and as analytical reagents. Herein, we report the separation of cationic porphyrins by capillary electrophoresis on fused silica i n phosphate buffer at pH 2-5. The porphyrins studied in this work were synthesized from alkylation of the parent tetrapyridylporphyrin (TPyP ) to give various pyridinium porphyrins. For example, methylation of T PyP gives a mixture of the mono-, cis-di-, trans-di-, tri- and tetrame thylated porphyrins [e.g., trakis(N-methyl-4-pyridiniumyl)-21H,23H-por phyrin, TMPyP(4)]. Capillary electrophoresis on a synthetic mixture sh owed separation of four of these compounds. Mixtures after alkylation with iodopropionic acid and bromopropylamine were also separated. The cis-di-and trimethylated TMPyP derivatives were separated on a small p reparative scale by centrifugal partition chromatography. Capillary el ectrophoresis was also used to separate metallo TMPyP(4) complexes inc luding those of cobalt, copper, iron, manganese, palladium, tin, vanad ium and zinc. The conformational isomers (atropisomers) of 5,10, traki s(N-methyl-2-pyridiniumyl)-21H,23H-porphyrin, TMPyP(2), were also sepa rated. Net charge, molecular mass and molecular shape all contribute t o the differential retention of cationic porphyrins under capillary el ectrophoresis conditions. Additional factors affecting the separations , including aggregation and protonation of the porphyrins, were probed by evaluating the separation of TMPyP(4) and its butyl and octyl anal ogs as a function of solution conditions. Cationic porphyrins are diff icult to separate using traditional chromatographic methods: capillary electrophoresis and centrifugal partition chromatography provide exce llent new techniques for separation of this class of compounds. (C) 19 98 Elsevier Science B.V.