Binding properties of 2-acetylnaphthalene with hydroxypropyl cyclodextrins from fluorescence quenching experiments.
The quenching of 2-acetylnaphthalene (2-AN) fluorescence by hydroxypropyl cyclodextrins (HP-CD) has been analyzed using modified Stern-Volmer plots to obtain binding constants as a function of temperature for 2-AN:HP-CD complexes. The HP-CDs were commercially available and contained 4-7 HP groups per CD molecule for alpha-CD, beta-CD, and gamma-CD. HP substitution causes a 12 to over 40% increase in binding constant (K(ave)) for 2-AN compared to that for unsubstituted CDs, although the K(ave) value is not strongly dependent on the extent of HP substitution for beta-CD. No evidence of formation of a 2:2 complex, such as that observed with 2-AN and gamma-CD, is observed with 2-AN and HP-gamma-CD. Thermodynamic parameters (DeltaH degrees and DeltaS degrees ) suggest that the increase in K(ave) with HP substitution is due to an enlarged binding site for the HP-CDs that allows greater motional freedom for 2-AN. Comparison is made to the binding of 2-methylnaphthoate (2-MN) to CDs and HP-CDs, and the larger K(ave) values for 2-MN over 2-AN are attributed to greater dispersion forces for 2-MN complex formation.
Seel
Maximilian
M
Department of Chemistry, Union College, Schenectady, New York 12308, USA.
Werner
T C
TC
D001665:Binding Sites; D003505:Cyclodextrins / Q000032:analysis* / Q000737:chemistry*; D046911:Macromolecular Substances / Q000032:analysis / Q000737:chemistry; D009281:Naphthalenes / Q000032:analysis* / Q000737:chemistry*; D013050:Spectrometry, Fluorescence / Q000379:methods*
D003505:Cyclodextrins; D046911:Macromolecular Substances; D009281:Naphthalenes; C503376:2-acetylnaphthalene