Premium
Photoinduced electron transfer in porphyrin‐naphthyl pairs covalently and randomly bound to α‐helical poly( L ‐lysine)
Author(s) -
Pispisa Basilio,
Venanzi Mariano,
Palleschi Antonio,
D'Alagni Maria
Publication year - 1995
Publication title -
macromolecular chemistry and physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.57
H-Index - 112
eISSN - 1521-3935
pISSN - 1022-1352
DOI - 10.1002/macp.1995.021960908
Subject(s) - chemistry , electron transfer , chromophore , porphyrin , photochemistry , quenching (fluorescence) , photoinduced electron transfer , covalent bond , fluorescence , intramolecular force , excited state , time resolved spectroscopy , crystallography , reaction rate constant , kinetics , stereochemistry , organic chemistry , physics , quantum mechanics , nuclear physics
The photophysics of protoporphyrin‐naphthyl (P‐N) pairs covalently and randomly bound to the ε‐amino groups of the side‐chains of poly( L ‐lysine) (PL) were investigated by steady‐state and time‐resolved fluorescence measurements. The results indicate that quenching of excited naphthalene (λ ex = 280 nm) chiefly occurs by interconversion to the triplet state when the polymeric matrix is in random coil (pH ≈ 7) and by intramolecular electron transfer from ground‐state porphyrin, P → 1 N * , when the polypeptide is in α‐helical conformation (pH ≈ 11), the specific rate constant of the electron transfer being 3,1 · 10 7 s −1 (25°C). PNPL exhibits very little exciplex fluorescence, whatever the pH, suggesting both a reduced internal Brownian motion of the chromophores, owing to the amide bond in the substituted side‐chains, and a relatively large average interprobe separation distance. This agrees with polarized fluorescence data and with the results of a conformational statistics analysis on the fully ordered PNPL, indicating that the average interchromophoric distance for which the electron transfer has the highest probability to occur is around 12 Å. The computational results allowed us to reproduce the experimental fluorescence decay curves and estimate the parameters governing the electron transfer process. Implications of these findings on the relaxation time of the heli‐xcoil transition in PNPL are briefly discussed.