Fluorescence and the structure of proteins VI. Non-fluorescent phenol-amide complexes

Abstract

Abstract Tyrosine derivatives as well as other phenols form non-fluorescent complexes with amides in non-polar solvents. For example, the association constant for the 1:1 complex of phenol and N , N -dimethylacetamide in n -hexane is 285 l/mole at 25°, ΔF ° = −3.34 kcal/mole and ΔH = −4.45 kcal/mole. Formation of the complex leads to loss of fluorescence and a characteristic red shift in the absorption spectrum of phenol; other phenolic compounds with unsubstituted and sterically unobstructed hydroxyl groups show analogous behavior. The loss of fluorescence arises from internal energy degradation within the complex. In more polar solvents, association is weaker and at higher amide concentrations (0.1–0.2 M) in the latter solvents intermolecular collisional quenching also could be observed.