Interaction of porphyrin-containing macrotetracyclic receptor molecule with single-stranded and double-stranded...

Photophysical methods have been used to study the interaction with nucleic acids of a macrotetracyclic cryptand molecule, Pbiph, containing a porphyrin groups, two macrocycles, and a biphenyl bridge. Pbiph binds with a higher affinity to single-stranded polynucleotides than to double-stranded ones. This selectivity, observed by binding and competition studies, using absorption and fluorescence spectroscopy, is pH dependent. Pbiph does not intercalate into double helices and is suggested to bind into the major groove. These features, selective single-strand binding and nonintercalation, are attributed to steric effects of the bulky Pbiph molecule, resulting from the macropolyclic cryptand cage structure.