Formation of inclusion complexes and controlled release of atrazine using free or silica-anchored β-cyclodextrin

摘要

Immobilization of cyclodextrin on the surface of silica was performed using citric acid as the bonding agent. Inclusion complexes of atrazine with free (CD) or anchored (CDSI) β-cyclodextrin were prepared and then characterized using infrared spectroscopy, X-ray diffraction and differential scanning calorimetry. The complexa-tion reaction showed first order kinetics, with a rate constant (k) of 8.72 x 10~(-3) min~(-1). There was a rapid increase of absorbance in the first 40 min, followed by attainment of equilibrium after ~ 2 h. The stoichiometry of the reaction was 1:1, with both free and anchored β-cyclodextrin increasing the solubilization of atrazine in an aqueous medium (by around 1.5 and 3.4 times, respectively). The association constant (K_a) of the complex was 28.93 L mol~(-1) using CD and 130.68 L mol~(-1) using CDSI. In release tests, 62% of the atrazine complexed with CDSI or β-CD was released after 40 h, while 83% of free atrazine was released during the same period.