Interactions between expanded porphyrins and nucleic acids

Two types of interaction of expanded porphyrins and nucleic acids are discussed. The first involves the specific chelation of the anionic phosphate diester backbone of DNA by the monoprotonated form of the water soluble sapphyrin 2. Support for the proposed binding mode derives from a variety of spectroscopic and biochemical studies, including visible absorption spectroscopy, circular dichroism spectroscopy, and supercoiled DNA unwinding experiments. The second interaction described is that of the water soluble europium texaphyrin complex Eu(T2B2 txph)(NO3)2 and RNA. This complex acts as a hydrolytic cleaving agent for uridyl uridine monophosphate, UpU, with a pseudo-fust order rate constant of 0.057 f 2 h-1 at 37O C and pH = 7.0 with 0.49 mM UpU and 0.3 mM Eu(T2B2 txph)(N03)2. Under identical conditions a 0.26 mM solution of Eu(N03)3 hydrolyses UpU with a rate constant of 0.007 f 3 h-1.