Fluorescence enhancement of a Meisenheimer complex of adenosine by gamma-cyclodextrin: a thermodynamic and kinetic investigation.
The fluorescent properties of a trinitrophenylated Meisenheimer complex of adenosine (TNP-Ado) in water were examined in the presence of alpha-, beta-, and gamma-cyclodextrins (CDs). The TNP-Ado complex exhibits minimal fluorescence in water, whereas addition of 10 mM alpha-CD, beta-CD, and gamma-CD enhances fluorescence by factors of 2, 7, and 110, respectively. The large enhancement by gamma-CD is attributed to its larger hydrophobic cavity, which is able to accommodate the TNP moiety of TNP-Ado. (1)H NMR spectra demonstrate 1:1 stoichiometry of the complex, which undergoes slow exchange on the NMR time scale. (1)H NMR and 2D ROESY spectra reveal substantial interaction of the TNP hydrogens with gamma-CD. Equilibrium constants were determined by fluorimetry from 10 to 20 degrees C by nonlinear curve fitting. Fluorescence is temperature dependent, with maximum fluorescence increasing with decreasing temperature. Complexation is exothermic with large negative entropy, consistent with formation of a tight complex between TNP-Ado and gamma-CD. Rate constants and activation parameters for both complexation and dissociation were determined by a combination of fluorimetry and 2D NMR exchange spectroscopy (EXSY).
Green
Thomas K
TK
Department of Chemistry & Biochemistry, Institute of Arctic Biology, University of Alaska Fairbanks, Fairbanks, Alaska 99775, USA. tkgreen@alaska.edu
Denoroy
Luc
L
Parrot
Sandrine
S
D000241:Adenosine / Q000031:analogs & derivatives / Q000737:chemistry*; D005453:Fluorescence; D007700:Kinetics; D009682:Magnetic Resonance Spectroscopy; D008958:Models, Molecular; D015394:Molecular Structure; D013816:Thermodynamics; D047408:gamma-Cyclodextrins / Q000737:chemistry*
D047408:gamma-Cyclodextrins; C036743:(2',3')O-(2,4,6-trinitrocyclohexadienylidine)adenosine; D000241:Adenosine