| Nicosulfuron is a highly effective sulfonylurea herbicide which is widely used to eliminate various annual gramineous weeds,broadleaf weeds and sedge weeds.However,nicosulfuron is poorly soluble,unstable and easily hydrolytic.In recent years,various weeds have been produced resistance.Commercially available nicosulfuron oil suspension exsits various disadvantages such as poor storage stability,easy delamination,agglomeration and poor dispersibility.In order to resolve above problems,cyclodextrin nanosponges were prepared as carriers to load nicosulfuron for improving the solubility,stability and pesticide effect of nicosulfuron.This study carried out the following works.(1)Three kinds of nanosponges were prepared by crosslinking ?-cyclodextrin(?-CD)using diphenyl carbonate(DPC),pyromellitic dianhydride(PMDA)and epichlorohydrin(EP)as crosslinkers.Nicosulfuron content was measured through UV method.In the saturation solubility experiment,the best crosslinking molar ratio(?-CD: crosslinker)was selected.It was concluded by phase solubility study that nicosulfuron and nanosponge were combined in a mass ratio of 1:1.Among three kinds of nanosponges,epichlorohydrin crosslinked nanosponge(EP-CDNS)highestly improved the solubility of nicosulfuron at a crosslinking ratio of 1:8.The solubility of nicosulfuron was increased by 6.13 fold when concentration of EP-CDNS was 1.2 mg/mL.(2)Three kinds of drug-loaded nanosponges of NSF-DPC-CDNS,NSF-PMDA-CDNS and NSF-EP-CDNS were prepared and their encapsulation efficiency,water absorption,average particle size,zeta potential,morphological characteristics were evaluated.The structure was characterized by infrared spectroscopy,differential scanning calorimetry,thermogravimetric analysis and X-ray diffraction analysis.These results showed,comparing to other drug loaded nanosponges,the encapsulation rate of NSF-EP-CDNS was the highest for 78.69%,the swelling ratio was the largest for 8.92 and the Zeta potential was the highest for-41.9 ± 1.79 mV.The particle sizes of three nanosponges were about 200 nm after drug loading,which were consistent to the results of transmission electron microscopy.The structure characterization revealed that ?-CD was crosslinked by crosslinkers to form nanosponges and nicosulfuron was successfully loaded into nanosponges.(3)NSF-EP-CDNS was evaluated for its release behavior and stability.The release behavior was determined by cumulative release of nicosulfuron in water within 48 h and the release curve was fitted.The stability experiment measured the content of nicosulfuron in water over a period of time.The release behavior revealed the cumulative release rate of NSF-EP-CDNS was 90.11% after 48 h and the release kinetic curve was more consistent with the Ritger-Peppas model.In comparison,the pure nicosulfuron was 18.57% and the nicosulfuron oil suspension was 31.02%.The results of stability revealed,comparing to the pure nicosulfuron and nicosulfuron oil suspension,the nicosulfuron in NSF-EP-CDNS was the least decomposed and most stable at 4 °C,25 °C and 54 °C,indicating that nanosponge can improve the stability of nicosulfuron.(4)The herbicidal activity of NSF-EP-CDNS was evaluated.The inhibitory effect of NSF-EP-CDNS on the activity of acetolactate synthase(ALS)and maize growth were studied.ALS activity inhibition revealed the inhibition rate of NSF-EP-CDNS was 46.00%,higher than pure nicosulfuron(39.41%)and nicosulfuron oil suspension(41.37%).The inhibition on maize growth revealed,comparing to pure nicosulfuron and nicosulfuron oil suspension,NSF-EP-CDNS both had the strongest growth inhibition effect on maize sprout and root.In conclusion,the herbicidal activity of nicosulfuron can be enhanced after being loaded in EP-CDNS. |
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