Synthesis and Properties of New Cationic-Periphery Porphyrins, Tetrakis(p-(aminomethyl)phenyl)porphyrin and N-Methyltetrakis(p-(aminomethyl)phenyl)porphyrin

Article abstract of DOI:10.1021/jo00074a029

Two new cationic periphery porphyrins, tetrakis(p-(aminomethyl)phenyl)porphyrin, TAMPP, and N-methyltetrakis(p-(aminomethyl)phenyl)porphyrin, N-MTAMPP, have been synthesized.These porphyrins are protonated in a pH range suitable for studies of binding with nucleic acids.The structure of the N-methylated analogue is significantly different, resulting in a phenomenon that has not been previously reported: the aryl rings at the methine bridge positions of the porphyrin ring undergo restricted rotational motion.The ability of the aryl rings to rotate may be crucial to allow intercalation of cationic periphery porphyrins.The acidity constants and associated pKa's for the porphyrins TAMPP and N-MTAMPP were determined by a combination of spectrophotometric and potentiometric methods.The acid-base properties of these new porphyrins are profoundly altered by N-methylation.The pyrroleninic nitrogen of the free base N-methylated analogue is significantly more basic (at an ionic strength of 0.12 M, the apparent pKa's for deprotonation of TAMPP with all four central nitrogen atoms protonated and the form with three protonated are the same, 8.8, while for N-MTAMPP, these pKa's are 2.4 and 8.1, respectively).As a result, the N-methylated species bears an additional positive charge in the neutral pH region where binding studies with nucleic acids are normally carried out.The peripheral amino groups of the N-methylated porphyrin are more basic as well, by 1.5 pH units at an ionic stength of 0.12 M.