title: Spectroscopic detection of tetracationic porphyrin H-aggregation on polyanionic matrix of inorganic polyphosphate.
abstract: 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.
authors.affiliation: Department of Molecular Biophysics, B. Verkin Institute for Low Temperature Physics & Engineering of NAS of Ukraine, 47 Lenin ave., 61103 Kharkov, Ukraine. zozulya@ilt.kharkov.ua
authors.forename: Victor N
authors.initials: VN
authors.lastname: Zozulya
authors.forename: Olga A
authors.initials: OA
authors.lastname: Ryazanova
authors.forename: Igor M
authors.initials: IM
authors.lastname: Voloshin
authors.forename: Alexandr Yu
authors.initials: AY
authors.lastname: Glamazda
authors.forename: Victor A
authors.initials: VA
authors.lastname: Karachevtsev
mesh_terms: D005453:Fluorescence; D008968:Molecular Conformation; D000071228:Polyelectrolytes; D011108:Polymers; D011122:Polyphosphates / Q000737:chemistry*; D011166:Porphyrins / Q000737:chemistry*; D013057:Spectrum Analysis; D014867:Water / Q000737:chemistry
chemical_list: D000071228:Polyelectrolytes; D011108:Polymers; D011122:Polyphosphates; D011166:Porphyrins; D014867:Water; C021096:tetra(4-N-methylpyridyl)porphine