Effect of pH on the Phosphorescence of Tryptophan, Tyrosine, and Proteins

摘要: Abstract Whereas the fluorescence of proteins has been extensively investigated, in particular by Weber and co-workers, phosphorescence little investigated. This paper reports studies a representative group aromatic amino acids. The previously discovered quenching tyrosine tryptophan acid alkaline pH is accompanied an enhancement phosphorescence. at neutral formate ion Interpretation these phenomena depends on series assumptions concerning excited states tyrosinate ion, which are shown Figs. 6 7. Basically, assumed to have π, π* lower energies than n, states. In 3n, state lie below first singlet state. facilitates triplet conversion (intersystem crossing) accounts for as compared tyrosine. An even more speculative assumption made explain fact that hydrogen-bonded bases both quenched. heme myoglobin hemoglobin, neither nor seen or pH. When separated, residual protein exhibits normal emission. solution emission quenched energy transfer from heme. solution, other hand, reasons given believing either acids singlets