| There are great differences between enantiomers for chiral pesticides in organisms and the ecological environment.Therefore,it is inaccurate for environmental risk assessment of chiral pesticides if considered as the same compound.It may cause huge losses for human health and the ecological environment.Epoxiconazole has the characteristics of broad-spectrum sterilization,high efficacy,low residue,systematic property and long-lasting effect as a chiral triazole fungicide.In this study,the chiral analysis method of epoxiconazole enantiomers was established,and the absolute configuration of epoxiconazole enantiomers was determined.The stereoselective behavior of epoxiconazole enantiomers in soil and rat liver microsomes was investigated.The main results were listed as followed:1.The separation of epoxiconazole enantiomers was achieved using a Lux Cellulose-1 chiral column under reversed-phase HPLC.The effect of different mobile phase composition on separation was investigated.Baseline separation of epoxiconazole enantiomers with acetonitrile/water(60:40,v/v)as mobile phase at flow rate of 0.6 mL/min at 30℃ and the detection wavelength was 220 nm.The optical rotation of the epoxiconazole enantiomers was determined by HPLC coupled with an CD detector.The absolute configuration of epoxiconazole enantiomer was determined through comparing with experimental and predicted ECD spectra.The eluted order on the Lux Cellulose-1 chiral column was confirmed to be(S,R)-(-)-epoxiconazole and the second peak is(R,S)-(+)-epoxiconazole.2.A residue analysis method for the determination of epoxiconazole enantiomers in fruits and vegetables samples was established.The method was systematically evaluated by the precision,accuracy,sensitivity and matrix effect of sample.Excellent linearity of enantiomers was observed with the concentration range of 0.1-10 mg/L and there was no matrix effect.The results of the addition recovery experiment showed that the average recovery of epoxiconazole enantiomers in the six matrices was 80.8%-96.7%,with 1.5%-6.1%inter-day relative standard deviation(RSD)and 1.1%-6.7%intra-day RSD.The limit of quantifications(LOQs)for two enantiomers in the six matrices were 0.05 mg/kg,whereas the limit of detections(LODs)were 0.10-0.15 ng.3.The stereoselective bioactivity of epoxiconazole enantiomers for Fusarium graminearum Schw,Gaeumanomyces graminis,Colletotrichum lagenarium,Alternaria solani,Botrytis cinerea,Sclerotinia sclerotiorum,Rhizoctonia solani,Gibberella fujikuroi,Phytophthora capsici leon was studied.The results showed that differences were observed in the fungicidal activities among the stereoisomers of epoxiconazole on the test fungi.And the fungicidal activity of(R,S)-(+)-epoxiconazole was 1.3-7.3 times that of(S,R)-(-)-epoxiconazole.4.The stereoselective behavior of epoxiconazole enantiomers in the soils(Jiangsu,Jiangxi,Jilin,and sterile Jilin soils)was investigated under aerobic and anaerobic conditions.Under aerobic conditions,there was enantioselectivity degradation for epoxiconazole enantiomers in Jiangxi,Jiangsu,and Jilin soils with(S,R)-(-)-epoxiconazole was preferentially degraded except sterile Jilin soils;and the half-lives of(S,R)-(-)-epoxiconazole in Jiangxi,Jiangsu,Jilin and sterile Jilin soils were 57.8,43.3,34.7,138.6 d,respectively,while the half-lives of(R,S)-(+)-epoxiconazole were 77.0,57.8,46.2,138.6d,respectively.In addition,the results of single enantiomers incubation suggested that there was no chiral conversion between the two enantiomers in the reaction process.Under anaerobic conditions,the results showed that the(S,R)-(-)-epoxiconazole was preferentially degraded;the half-lives of(S,R)-(-)-epoxiconazole and(S,R)-(+)-epoxiconazole were 63.0 d and 99.0 d,respectively.5.Stereoselective metabolism of epoxiconazole enantiomers in rat liver microsomes was investigated.The result showed the(S,R)-(-)-epoxiconazole was preferentially degraded with the EF value of 0.28 at 80 min,and there was no enantiomorphic transformation between the two enantiomers in the metabolic process.The enzyme kinetic constants showed that(S,R)-(-)-epoxiconazole was more rapidly degraded in rat liver microsomes.(R,S)-(+)-epoxiconazole has a greater degree of inhibition to(S,R)-(-)-epoxiconazole. |
