Determination of stoichiometry and equilibrium constants of complexes of tyrosine with cyclodextrins by time-resolved fluorescence spectroscopy and global analysis of fluorescence decays

Time-resolved fluorescence spectroscopy and global analysis of fluorescence decay times were applied to determine stoichiometry and equilibrium constants of complexes of tyrosine with α-, β- and γ-cyclodextrins (CDs). This study reveals from Global analysis of fluorescence decay curves of tyrosine with CDs in water the presence of only two fluorescence life-times of tyrosine: 3.35±0.10 ns for free tyrosine and 4.3±0.3 ns for the tyrosine–CD complex. The formation constants of tyrosine–CD complexes were determined from the pre-exponential factors as well as the fractional intensities and average fluorescence life-times. The cavity size of CD influenced the equilibrium constant but had no influence on the fluorescence life-time of the tyrosine–CD complex.