Study on hydrolysis kinetics of azadirachtin and tructure analysis of hydrolysate

Objective  To study hydrolysis of azadirachtin in water systematically.

Method  Azadirachtin A from the 44.56% azadirachtin TC was isolated and purified by silica column chromatography and semi-preparative high performance liquid chromatography (HPLC). The chemical structure and content of isolated azadirachtin A were identified by nulear magnetic resonance (NMR) and HPLC. A method for determining azaditachtin residue in water by HPLC was established.

Result  The mass fractions of azadirachtin A were 90.37% and 91.82% detected by NMR and HPLC respectively. When azadirachtin was added with the concentrations of 0.1, 1.0 and 5.0 mg·kg^-1, the average recovery rates of azadirachtin from water samples ranged from 92.53% to 94.12%, the variation coefficients ranged from 0.35% to 0.84%, and the minimum detection limit was 0.012 mg·L^-1. Azadirachtin was stable in buffer solutions with pH varying from 4.0 to 6.0. When pH was above 8.0, hydrolysis of azadirachtin was accelerated, and the degradation half-life was 14.856 h at pH 8.0 and declined to 0.033 h at pH 10.0. The degration half-lives of azadirachtin in buffer solutions at pH 6.0 were 24.68, 13.69 and 2.36 d under 25, 35 and 45 ℃ temperature respectively, while were 9.35, 6.51 and 0.94 d at pH 7.0. A lactone derivative of azadirachtin was obtained by isolating and purifing hydrolysate in buffer solution at pH 2.0.

Conclusion  Azadirachtin is extremely unstable in alkaline environment while relatively stable in weak acid environment. Temperature has a great effect on the degradation of azadirachtin and the degradation accelerates as temperature increases.