title: The effect of the antioxidant spermine on the photophysical reactions of tryptophan in aqueous solution at 77 K.
abstract: Fluorescence, phosphorescence and electron paramagnetic resonance techniques were used to investigate the effect of the antioxidant spermine on the initial photophysical reactions of tryptophan (Trp) in aqueous salt solutions at 77 K. At low concentrations of Trp (3.5 X 10(-5) M) a ground state complex was formed between one Trp and two spermine molecules (a 1:2 complex). Complexed Trp was photodegraded at a rate 65% lower than the free molecule due to a change in the charge-transfer character of the excited 1La state. At high concentrations of Trp (3.5 X 10(-3) M) the phosphorescence was almost completely quenched due to hydrogen-bond formation between two neighbouring Trp molecules. A strong complex was formed between this Trp dimer and one spermine molecule on addition of spermine (a 2:1 complex). Spermine enhanced intersystem crossing in one of the two Trp molecules in the 2:1 complex and phosphorescence was observed. From this triplet state the tryptophyl radical was formed with high efficiency by hydrogen-atom transfer. The yield of radical formation from the triplet state in the 2:1 complex was much larger than from the excited singlet state in the 1:2 complex.
authors.affiliation: Institute of Physics, AVH University of Trondheim, Norway.
authors.forename: G S
authors.initials: GS
authors.lastname: Mahmoud
authors.forename: T B
authors.initials: TB
authors.lastname: Melø
mesh_terms: D000975:Antioxidants; D004578:Electron Spin Resonance Spectroscopy; D005615:Freezing; D008163:Luminescent Measurements; D010777:Photochemistry; D010782:Photolysis; D013050:Spectrometry, Fluorescence; D013096:Spermine; D014364:Tryptophan
chemical_list: D000975:Antioxidants; D013096:Spermine; D014364:Tryptophan