Tricationic porphyrin conjugates: evidence for chain-structure-dependent relaxation of excited singlet and triplet States.
Conjugates of 5-(4-carboxyphenyl)-10,15,20-tris(4-methylpyridinium-4-yl)porphyrin (P-H) are promising photoactive agents for medical applications. As their ultimate efficacy will depend on the behavior of initial excited states, photophysical parameters have been determined with conventional steady-state absorption and fluorescence as well as time-resolved femto- and nanosecond spectroscopies. The fluorescence quantum yield of P-H and P-H conjugated to uncharged groups increases from approximately 0.03 in pH 7 buffer to approximately 0.05 in Triton X100 micelles (TX100) and in ethanol and to 0.12 in sodium dodecyl sulfate (SDS) micelles. Corresponding (1)S(1) lifetimes are approximately 5-10 ns. In buffer, an equilibrium between P-H monomers and small-size aggregates is observed. Conjugation with poly-S-lysine (P-(Lys)(n)) results in fluorescence quenching in all solvents. Structural reorganization of conjugates bearing a Di-O-isopropylidene-alpha-d-galactopyranosyl or a alpha/beta-d-galactopyranosyl group occurs in ethanol (k approximately 0.15 ps(-1)) after (1)S(1) state solvation (approximately 700 fs). Relaxation of bulky P-(Lys)(n) polypeptide chains takes place on a longer time scale in all solvents (k <or= 0.01 ps(-1)) with enhanced internal conversion. Triplet state ((3)T(1)) transient spectra of all derivatives in PBS, SDS, TX100, and ethanol exhibit a strong absorbance with a broad maximum in the 460-475 nm region and minor maxima at approximately 540, 630, and 690 nm. In ethanol, energy transfer from the P-H (3)T(1) state to beta-carotene provides an estimate of epsilon approximately 40,000 M(-1) cm(-1) at 460 nm for the P-H (3)T(1) state. Using triplet meso-tetraphenylporphyrin as an actinometer, the P-H triplet quantum yield (Phi(T)) is estimated to be approximately 0.50 in all solvents. This high Phi(T) leads to effective singlet oxygen production in buffered solutions.
Faculdade de Medicina de Lisboa, Hospital de Santa Maria, Clinica Universitaria de Dermatologia, 1600 Lisboa, Portugal.
João Nuno
JN
Silva
Francisco
F
Bosca
João P C
JP
Tomé
Eduarda M P
EM
Silva
Maria G P M S
MG
Neves
José A S
JA
Cavaleiro
Larry K
LK
Patterson
Paulo
P
Filipe
Jean-Claude
JC
Mazière
René
R
Santus
Patrice
P
Morlière
D008823:Micelles; D017830:Octoxynol / Q000737:chemistry; D011107:Polylysine / Q000737:chemistry; D011166:Porphyrins / Q000737:chemistry*; D011726:Pyridinium Compounds / Q000737:chemistry*; D011789:Quantum Theory; D026082:Singlet Oxygen / Q000737:chemistry*; D012967:Sodium Dodecyl Sulfate / Q000737:chemistry; D013056:Spectrophotometry, Ultraviolet; D013997:Time Factors
C509722:5-(4-carboxyphenyl)-10,15,20-tris(4-methylpyridinium-4-yl)porphyrin; D008823:Micelles; D011166:Porphyrins; D011726:Pyridinium Compounds; D026082:Singlet Oxygen; D011107:Polylysine; D012967:Sodium Dodecyl Sulfate; D017830:Octoxynol