Fluorescent Studies on Cooperative Binding of Cationic Pheophorbide‐a Derivative to Polyphosphate

Abstract

The cooperative binding of a novel water-soluble cationic derivative of pheophorbide-a (CatPheo-a) to inorganic polyphosphate (PPS) in buffered aqueous solutions was studied by means of polarized fluorescence spectroscopy in a wide range of molar phosphate-to-dye ratios (P/D). Under low P/D values, CatPheo-a forms extended stacking associates on the PPS matrix, while under high P/D the dye binds to PPS in the dimer form. The CatPheo-a self-association is accompanied by 40-fold dye fluorescence quenching and a substantial increase in the fluorescence polarization degree. The fluorescent titration data were used for determination of cooperative binding parameters by Schwarz's method.

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

“…As for the Zn TMPyP 3+ moiety of the conjugate, its emission quenches at the first poly(A)⋅poly(U) addition to 0.34 from initial, and it remains on this level in the P/D range from Table 1) was registered for complex of Zn(II)TMPyP 3+ -ImPzn with poly(A)⋅poly(U) (for its complex with poly(G) this value was equal to 3.1). Enhancement of the porphyrin emission under its binding to poly(G) at high polymer content was observed also for non-metallated TMPyP 3+ (Table 1, unpublished data), and earlier for Pheophorbide-a derivatives [50,51].…”

Spectroscopic study on binding of cationic Pheophorbide-ato antiparallel quadruplex Tel22

“…oligonucleotide measured in aqueous solution at near-physiological ionic conditions are presented in figure 2. Absorption spectrum of the free dye consists of the intense Soret band (B-band) located at 380 nm (ε 380 = 34200 M -1 cm -1 ) and four Q-bands [8] among which the most intensive peak is longwave one with maximum at 682 nm is (ε 682 = 16200 M -1 cm -1 ), that is typical for all chlorine derivatives [1,2]. These bands correspond to → * transitions polarized within the plane of conjugated macrocycle.…”

“…The CatPheo-a was synthesized from Pheophorbide-a (Frontier Scientific Inc., Logan, Utah) according the procedure previously described in [8] The 2 mM phosphate buffer (pH6.9) containing 0.5 mM EDTA and 0.1 M NaCl prepared from deionized water was used as solvent.…”

“…It contains a carboxylic group, which anionic character complicates binding of the dye to negatively charged nucleic acids. To correct this disadvantage a novel cationic derivative of this dye containing a trimethylammonium group (CatPheo-a, figure 1) was synthesized by us [8]. We supposed that transformation of Pheo-a into cationic compound would improve its DNA binding ability.…”

“…Spectroscopic properties of CatPheo-a, as well as the ways of its binding to model synthetic biopolymers of different secondary structures (single-strand inorganic polyphosphate, double-stranded poly(A)·poly(U), poly(G)·poly(C) polynucleotides and four-stranded poly(G) polynucleotides) were studied earlier at near-physiological ionic conditions using various spectroscopic techniques [8,9]. It was shown that CatPheo-a binds to all these polymers, but especially effective binding was observed in the case of quadruplex poly(G), evidently due to the structural features of the dye core which is appropriate for interaction with the G-tetrads through π -π stacking interactions.…”