Preparation,Structure-Activity Relationship And Properties Of Phenolic Aromatic Aldehyde Bio Based Antibacterial Agents

Plastic is one of the most widely used packaging materials at present,but it inadvertently becomes the carrier of microorganisms in production,storage,circulation,transportation and use.Pathogenic microorganisms pose a threat to human life and health and can cause serious public environmental problems.Adding antibacterial agent is the main means to improve the antibacterial performance of plastics,and it often only needs a very small amount to achieve the effect of broad-spectrum bacteriostasis.In recent years,green environmental protection,synergy of various mechanisms and optimization of synthetic process have become the main development direction of antibacterial agents.This subject takes the preparation of efficient,environmental friendly and simple antibacterial agents as the research content.Based on the synergy of various mechanisms of antibacterial agents,a new type of biological Schiff base ligands are designed and synthesized with eight green biological bases as raw materials.Then,a new type of biological Schiff base metal complex antibacterial agent is prepared by cooperating with metals.Its antibacterial structure-activity relationship is explored through in vitro antibacterial activity detection and quantum chemical calculation,The corresponding modified PLA films were prepared and their properties were studied.It provides new ideas for the molecular design,synthesis and application of new bio based antibacterial agents,which has important theoretical reference value and practical application significance.The main research contents and results are as follows:(1)Synthesis and characterization of ligands and complexes:the corresponding ligands L1～L8 were prepared by Schiff base reaction of eight biological aldehydes with p-aminodiphenylamine.The characterization of FTIR and ~1H-NMR showed that the synthetic products were consistent with the target structure,high purity and successful synthesis.After the successful synthesis of ligands L1～L8,thirty-two Schiff alkali metal complexes were prepared by one pot reaction with copper(Ⅱ),cobalt(Ⅱ),zinc(Ⅱ)and nickel(Ⅱ)ions.The successful preparation of Schiff alkali metal complexes was proved by FTIR and XPS.The thermal decomposition properties of Schiff alkali metal complexes were tested.The results showed that the thermal stability of Schiff alkali copper(Ⅱ)ion complexes was the best.The initial degradation temperature of all Schiff alkali metal complexes was about200℃,which met the processing requirements of most materials.(2)Study on the structure-activity relationship of antibacterial properties of complexes:the antibacterial properties of this series of Schiff alkali metal complexes are closely related to their structures through in vitro antibacterial activity detection and quantum chemical calculation.The stronger the electron donor ability,the smoother the molecular geometry,the smaller the molecular volume,the smaller the molecular orbital energy difference,the smaller the molecular single point energy,and the shorter the C=Nbond,the stronger the antibacterial properties of the complexes.The antibacterial ability of all Schiff alkali metal complexes against Gram-negative bacteria was stronger than that of Gram-positive bacteria.At the same time,it is inferred that this series of Schiff alkali metal complexes include redox mechanism,contact release mechanism and cell content denaturation mechanism.A variety of antibacterial mechanisms are combined and coordinated,and the antibacterial efficiency is high.(3)Preparation and properties of antibacterial films:through the compatibility test of 32 Schiff alkali metal complexes,it is found that in 1μAt the concentration of g/ml,32 Schiff alkali metal complexes have good biocompatibility.Schiff base cobalt ion and zinc ion complexes were successfully prepared by solution method.PLA/ln CO and PLA/ln Zn modified PLA films were successfully prepared by adding polylactic acid(PLA).The mass fraction was 1 wt%.The mechanical properties,optical properties,moisture permeability and fresh-keeping properties of the 16 films were tested.The mechanical properties test shows that the mechanical properties of most of the films added with antibacterial agents have been improved to a certain extent,and all meet the use needs.The optical performance test shows that compared with the PLA film without Schiff alkali metal complexes,the modified PLA film can reduce the excessive light transmittance of the PLA film,reduce the influence of light on the packaging contents,and improve the fresh-keeping performance of the PLA film.The moisture permeability test shows that the polarity of the modified PLA film is increased and the moisture permeability is improved,so as to effectively prevent condensation and increase the antibacterial and fresh-keeping properties of the packaging.Through the fresh-keeping performance test,it can be concluded that compared with PLA films without Schiff alkali metal complexes,PLA/L1-Co,PLA/L4-Co,PLA/L1-Zn and PLA/L4-Zn films can delay the time of microbial colony formation for 6 days,and PLA/L8-CO and PLA/L8-Zn films can delay the time of microbial colony formation for 8days.The other composite films grew aseptically within 21 days.Considering the water loss caused by the respiration of the virgin fruit under natural conditions,all the modified films extended the shelf life of the virgin fruit by 4～7 days.