EFFECTS OF EXCITED-STATE PROTON TRANSFER ON THE PHOSPHORESCENCE OF TYROSINE-PHOSPHATE COMPLEXES

Abstract Phosphate anions quench the fluorescence of tyrosine at room temperature as a result of an excited-state proton transfer. At 77 K in frozen solutions the fluorescence of tyrosine is still quenched by phosphate anions but the phosphorescence emission is enhanced. No tyrosinate phosphorescence is detected. A mechanism is proposed to explain these results: excited-state proton transfer from tyrosine to phosphates is followed by intersystem crossing in tyrosinate anions with subsequent back-transfer of the proton in the triplet state.