DYNAMIC ASPECTS IN HOST-GUEST INTERACTIONS - 5 - KINETICS OF THE METAL COMPLEXATION REACTIONS OF -PYRIDYLAZO)-5-(N-PROPYL-N-SULFOPROPYLAMINO)PHENOL ASSOCIATED WITH CYCLODEXTRIN INCLUSION REACTIONS

The kinetics of the 1:1 complex formation reactions of -pyridylazo)-5- (N-propyl-N-sulfopropylamino)phenol (5-Br-PAPS) with some metal ions i n the presence of alpha-, beta-, and gamma-cyclodextrin (alpha-, beta- , and gamma-CDx) have been investigated by the stopped-flow spectropho tometric method. The inclusion of 5-Br-PAPS by CDx causes a substantia l decrease in the second-order formation rate constants owing to the s teric hindrance to effective approach of metal ion to the specific ori entation of 5-Br-PAPS in the CDx cavity and/or to the slower release o f metal-coordinated water molecules in the apolar cavity. Binding of 5 -Br-PAPS with cyclodextrins is indicated by change in the W-vis absorp tion spectra and the H-1 NMR spectra. It is suggested that the reactio n rates are governed by the presence of the encapsulated 5-Br-PAPS, wh ich reacts more slowly with some metal ions in aqueous solution.