Spectroscopic Studies on Binding of Porphyrin-Phenazine Conjugate to Four-Stranded Poly(G)

Abstract

Binding of a novel cationic porphyrin-imidazophenazine conjugate, TMPyP(3+)-ImPzn, to four-stranded poly(G) was investigated in aqueous solutions of neutral pH under near physiological ionic conditions using absorption, polarized fluorescent spectroscopy and fluorescence titration techniques. In absence of the polymer the conjugate folds into stable internal heterodimer with stacking between the porphyrin and phenazine chromophores. Binding of TMPyP(3+)-ImPzn to poly(G) is realized by two competing ways. At low polymer-to-dye ratio (P/D < 6) outside electrostatic binding of the cationic porphyrin moieties of the conjugate to anionic polynucleotide backbone with their self-stacking is predominant. It is accompanied by heterodimer dissociation and distancing of phenazine moieties from the polymer. This binding mode is characterized by strong quenching of the conjugate fluorescence. Increase of P/D results in the disintegration of the porphyrin stacks and redistribution of the bound conjugate molecules along the polymer chain. At P/D > 10 another binding mode becomes dominant, embedding of TMPyP(3+)-ImPzn heterodimers into poly(G) groove as a whole is occurred.

Binding of Metallated Porphyrin-Imidazophenazine Conjugate to Tetramolecular Quadruplex Formed by Poly(G): a Spectroscopic Investigation

“…In our case, metallization of porphyrin part of conjugate also leads to a change in the type of the conjugate binding to four-stranded poly(G) as compared with data described in Ref. [38] for non-metallated one.…”

“…4). The fluorescence titration curve is steeper than for non-metalize conjugate, where only I/I o =1.3 was reached at P/D=100 [38], and it is similar to that for the complex of individual TMPyP 3+ dye with poly(G) where I/I o =3.7 at the same P/D value (Fig. 5).…”

“…Initial part of the titration curve showing the changes in the fluorescence intensity of the porphyrin moiety (observation at 655 nm) somewhat differs from those observed earlier for binding of non-metallated conjugate and free porhyrins to oppositely charged polymers [38]. It is seen that the small initial polymer addition results in the 65 % fluorescence quenching.…”

“…Results were compared with those obtained earlier for the interaction of nonmetallated conjugate with the same polymer [38].…”

“…It was shown that metaloconjugates stabilize Tel22 quadruplex. Also, the binding of non-metallated TMPyP 3+ -ImPzn conjugate to poly(G)-based intermolecular quadruplex [8] was investigated [38]. It was found that this conjugate folds into stable intramolecular heterodimer which at high P/D incorporates into poly(G) quadruplex groove.…”