Is the determination of the association constant of cyclodextrin inclusion complexes dependent on the technique

Abstract

Differences in association constants values of cyclodextrin inclusion complexes can be found in the literature. Most of the times, different experimental conditions have been used leading to different results. This paper reports the association constants (Ka) values of two different cyclodextrins (CD), namely native beta-CD (βCD) and hydroxypropyl-βCD (HP-βCD) with bentazon (BTZ, herbicide used in control of broadleaf weeds and sedges in many crops). These constants were determined by spectrophotometric and fluorescence measurements carried out under the same experimental conditions, and they were compared with those previously obtained by electrochemical techniques. The association constant values for the BTZ/HP-βCD inclusion complex obtained by fluorescence measurements were lower than those expected taking into account the values obtained from the other techniques. Differences in the complexation of the guest with CD in the excited and basal state could explain these results.