Effects of cyclodextrins on hydrolysis of malathion.

Cyclodextrins (CDs), with hydrophobic interior cavity and hydrophilic external surface, are capable of accelerating or inhibiting chemical degradation of organophosphorus pesticides through forming inclusion complexes between CDs and pesticides. This work evaluated the effects of CDs on hydrolysis of malathion in an attempt to assess their potential application in environmental approach. beta-CD and its two derivatives, randomly methylated beta-CD (RAMEB) and hydroxypropyl beta-CD (HP-beta-CD), were tested. It was found that RAMEB could inhibit the hydrolysis of malathion, and this was the function of pH and temperature, the inhibitory effects increase with increasing concentration of RAMEB and elevating temperature between 15 and 35 degrees C. On the other hand, beta-CD and HP-beta-CD have little or no stabilizing effects on malathion at all pH and temperature studied, except that the large concentration of beta-CD and HP-beta-CD can mildly reduce hydrolysis of malathion. Both 2 mol/L and 5 mol/L urea increase the inhibitory effects of RAMEB on hydrolysis of malathion at 25 degrees C, pH 9.0.