title: The photoprotector mechanism of mycosporine-like amino acids. Excited-state properties and photostability of porphyra-334 in aqueous solution.
abstract: The photostability and photophysical parameters of an aqueous solution of the mycosporine-like amino acid (MAA) porphyra-334 have been determined. The excited-singlet state lifetime, measured by time-correlated single photon counting, was 0.4 ns. Laser flash photolysis experiments at 355 nm did not show any transient species. The triplet state of porphyra-334 was sensitized by triplet-triplet energy transfer. The T-T absorption spectrum was determined and the maximal absorption coefficient at 440 nm was estimated to be 1 x 10(4) M(-1) cm(-1). In this way an upper limit for the intersystem crossing quantum yield was determined. The very low quantum yield of fluorescence (phiF = 0.0016) and triplet formation (phiT < 0.05) together with a photodecomposition quantum yield of 2-4 x 10(-4), in the absence and the presence of oxygen respectively, can be explained by a very fast internal conversion process. These results support the photoprotective role assigned to this MAA in living systems.
authors.affiliation: Departamento de Química, FCEyN, Universidad Nacional de Mar del Plata, Argentina. ferconde@mdp.edu.ar
authors.forename: F R
authors.initials: FR
authors.lastname: Conde
authors.forename: M S
authors.initials: MS
authors.lastname: Churio
authors.forename: C M
authors.initials: CM
authors.lastname: Previtali
mesh_terms: D003512:Cyclohexanones / Q000737:chemistry* / Q000302:isolation & purification; D004355:Drug Stability; D005998:Glycine / Q000031:analogs & derivatives; D015394:Molecular Structure; D010782:Photolysis; D011789:Quantum Theory; D011837:Radiation-Protective Agents / Q000737:chemistry*; D000461:Rhodophyta / Q000737:chemistry; D012996:Solutions; D013050:Spectrometry, Fluorescence; D013053:Spectrophotometry
chemical_list: D003512:Cyclohexanones; D011837:Radiation-Protective Agents; D012996:Solutions; C421025:porphyra-334; D005998:Glycine