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 consta nts of complexes of tyrosine with alpha-, beta- and gamma -cyclodextrins (C Ds). This study reveals from Global analysis of fluorescence decay curves o f tyrosine with CDs in water the presence of only two fluorescence life-tim es of tyrosine: 3.35 +/- 0.10 ns for free tyrosine and 4.3 +/- 0.3 ns for t he tyrosine-CD complex. The formation constants of tyrosine-CD complexes we re determined from the pre-exponential factors as well as the fractional in tensities and average fluorescence life-times. The cavity size of CD influe nced the equilibrium constant but had no influence on the fluorescence life -time of the tyrosine-CD complex. (C) 2001 Elsevier Science B.V. All rights .