Interactions of cationic porphyrins with double-stranded oligodeoxynucleotides: a study by electrospray ionisation mass spectrometry

Electrospray ionisation mass spectrometry (ESI‐MS), electrospray ionisation tandem mass spectrometry (ESI‐MS/MS) and Ultraviolet‐visible (UV–vis) spectroscopy were used to investigate the non‐covalent interactions between small oligonucleotide duplexes with the GC motif and a group of cationic meso(N‐methylpyridynium‐4‐yl)porphyrins (four free bases with one to four positive charges, and the zinc complex of the tetracationic free base). The results obtained point to outside binding of the porphyrins, with the binding strength increasing with the number of positive charges. Fragmentations involving losses from both chains were observed for the porphyrins with N‐methylpyridinium‐4‐yl groups in opposite meso positions. Copyright © 2005 John Wiley & Sons, Ltd.