Research On Enantioselective Interactions Of Herbicide Dichlorprop With Chitosan And Lipase

This paper mainly studied the chiral interactons of chitosan and chiral Aryloxycarboxylic herbicide dichorprop (DCPP), and the toxicity and degradation changes of DCPP with chitosan moleculars(CS) and chitosan nanoparticles(NP) in three freshwater green algae, preliminarily revealing the chiral recognition and environmental effects of CS and NP on DCPP. In addition, we researched the chiral interactions of lipase and DCPP, showing the chiral recognition and mechanisms between them. This paper can be mainly devided into four parts:(1) The enantioselective interactions of fluorescence labeled chitosan moleculars (FCS) and fluorescence labeled chitosan nanoparticles(FNP) with DCPP were studied. The results showed chitosan and DCPP can form one binding site, and the chiral selectivity was existed with interaction orders of (S)-DCPP> (RS)- DCPP>(R)- DCPP. And also, the interactions of FNP was stronger than FCS with DCPP. Furthermore, the main force between them was the hydrophobic force, and the electrostatic force was also existed.(2) The enantioselective ecotoxicity of (R)-, (S)- (RS)-DCPP with CS and NP in three algae was investigated. We can conclude that CS and NP showed chiral recognition on DCPP in three freshwater green algae, and the chiral recognition was different with different algae. For Chlorella vulgaris the orders of inhibition rates were (R)-DCPP-CS > (S)-DCPP-CS > (RS)-DCPP-CS and (R)-DCPP-NP > (S)-DCPP-NP > (RS)-DCPP-NP; for Scenedesmus obliquus the orders were (S)-DCPP-CS > (RS)-DCPP-CS > (R)-DCPP-CS and (S)-DCPP-NP > (RS)-DCPP-NP> (R)-DCPP-NP; and for Chlorella pyrenoidosa the orders were (RS)-DCPP-CS > (S)-DCPP-CS > (R)- DCPP-CS and (RS)-DCPP-NP > (S)-DCPP-NP > (R)-DCPP-NP.CS and NP had different inhibition rates on different kinds of algae, and the order was Chlorella pyrenoidosa > Chlorella vulgaris > Scenedesmus obliquus. What's more, the same kind of algae showed different responses with CS and NP. The inbihition of CS on Chlorella vulgaris was weaker than NP in the initial 72h and stronger than NP after 96h. For Scenedesmus obliquus, CS showed weaker inhibition than NP, but for Chlorella pyrenoidosa CS showed stronger inhibition than NP.CS and NP with DCPP can promote the growth of Chlorella vulgaris at low concentrations, while inhibite at high concentrations. And the inhibition was different with the order of NP> CS> (R)-DCPP-NP > (R)-DCPP-CS >> (R)-DCPP. Furthermore, the inhibition was increased with the increasing incubation time, but decreased at the time of 96 h.(3) The enantioselective degradation of (R)-, (S)-, (RS)-DCPP with CS in Chlorella pyrenoidosa was investigated. The results showed that the residual ratios of DCPP with CS compared with DCPP itself were increased in Chlorella pyrenoidosa. That's to say, the degradation rates of herbicide were reduced with CS. Moreover, the chiral selectivity of CS on DCPP and its enantiomers dose esist in Chlorella pyrenoidosa, with the degradation sequence of (R)-DCPP-CS > (S) DCPP-CS > (RS)-DCPP-CS. And the degradation order of the herbicide itself was (RS)-DCPP < (R)-DCPP < (S)-DCPP, which was different from the sequence of DCPP with CS.Chiral herbicide DCPP in algae had different half-life time with the order of (S)-DCPP < (R)-DCPP < (RS)-DCPP, while the order was changed with CS and it's (R)-DCPP-CS < (S)-DCPP-CS < (RS)-DCPP-CS. So CS can chang the degradation sequence of DCPP and the degradation enantioselectivity does exist.(4) We researched the chiral recognition of lipase on DCPP, and mechanisms were also investigated. The interaction differences between the chiral herbicide DCPP and lipase were studied using UV differential spectrophotometry and fluorescence spectrophotometry. Enantioselectivity was clearly observed in the presence of 50 mM, pH 8 phosphate buffer solution. (R)-DCPP was the most reactive towards lipase as measured by UV absorption and fluorescence spectra, followed by (RS)-DCPP and (S)-DCPP. It can be concluded that one binding site was formed between DCPP and lipase, and the lipase was enantioselective towards chiral DCPP. The hydrophobic force, which was maybe the main force effecting enantioselectivity, played an important role in the interactions of lipase and DCPP. And the results of synchronous fluorescence spectrometry expressed that the combined site was closer to tryptophan compared with tyrosine in protein molecules, which maybe make a contribution to the chiral selectivity. The lipase-catalyzed kinetic experiments showed that the effect of DCPP on the lipase-catalyzed hydrolysis of FDA was enantioselective. Lipase was most reactive towards (RS)-DCPP at high concentrations, but (R)-DCPP at low concentrations was the strongest inhibitor.