Self-assemblies of tricationic porphyrin on inorganic polyphosphate.

Self-assemblies formed by the new synthesized tricationic porphyrin derivative (TMPyP(3+)) on the polyanionic inorganic polyphosphate (PPS) in aqueous solution were studied using different spectroscopic techniques and DFT calculation method. From the fluorescence quenching of the bound TMPyP(3+) molecules and their Raman spectra we conclude that porphyrin chromophores form the stable π-π stacking-assemblies onto PPS polyanions. The transformation of the Soret band in absorption spectra at different PPS/TMPyP(3+)concentration ratios evidences that the assemblies are mixtures of J- and H-aggregates. Molecular modeling performed shows that the flexibility of PPS strand allows a realization of spiral or "face-to-face" one-dimensional structures formed by porphyrin molecules arranged in parallel and antiparallel modes. The peculiarity of PPS structure allows a formation of two porphyrin stacks on opposite sides of polymer strands that result in the appearance of higher-order aggregates. Their size was estimated from the light scattering data. Distinctions between TMPyP(3+) and TMPyP4 aggregation on PPS template are discussed.

Effect of Ni2+ and Cd2+ ions on thermally induced conformational transitions in poly(dA)-poly(dT) system.

Effects of Ni(2+) and Cd(2+) ions on thermally induced conformational transitions in the poly(dA)·poly(dT) polynucleotide duplex and poly(dA)·2poly(dT) triplex under near physiological ionic conditions were studied by measurement of UV absorption melting curves and static light scattering intensity. The diagrams of conformational transitions in poly(dA)-poly(dT)-Me(2+) systems were plotted. An aggregation in these polynucleotide systems arises at certain values of the metal ions concentration and the temperature after the polymer dissociation into single strands. The phenomenon is conditioned by the aggregation of poly(dA) via the interstrand cross-linking by the dication bridges. Unlike Ni(2+), Cd(2+) induces formation of very stable aggregates which did not disintegrate even upon cooling up to room temperature.

Spectroscopic detection of tetracationic porphyrin H-aggregation on polyanionic matrix of inorganic polyphosphate.

Self-assembly of tetracationic porphyrin TMPyP(4+) onto polyanionic matrix of inorganic polyphosphate (PPS) in aqueous solutions has been studied in a wide range of molar phosphate-to-dye ratios using techniques of polarized fluorescence, absorption, resonance Raman spectroscopy and static light scattering. The binding of TMPyP(4+) to PPS is characterized by the binding constant of 3 x 10(5) M(-1) and the cooperativity parameter of about 150. The fluorescence quenching of the bound TMPyP(4+) evidences the stacking of the porphyrine chromophores. Under the stoichiometric binding ratio TMPyP(4+) forms extended continuous face-to-face aggregates (so-called H-aggregates) which manifest themselves by a blue shift (12 nm) and a large hypochromisity (51%) of the Soret absorption band. Each face-to-face TMPyP(4+) stack is formed with participation of four PPS chains. Formation of such columnar aggregates is promoted by the ability of PPS chains to take a helix conformation where negative charges are arranged along two oppositely situated rows with intercharge distance of 0.36 nm which corresponds to the thickness of the porphyrin pi-electronic system. The ability of each PPS strand to be template for formation of two porphyrin stacks results in the integration of the adjacent stacks into higher-order aggregates which dimension was estimated from the fluorescence polarization data.