Preparation And Bioactivity Of Chitooligosaccharide And Its Chlorosalicylaldehyde Schiff Base Copper And Cerium Complexes

Chitooligosaccharide（COS）is the degradation product of chitosan and the only abundant basic amino oligosaccharide in natural polysaccharides.Chitooligosaccharide have excellent biological adaptability and stability.They are used in planting,breeding,medicine,food and other fields as antioxidants,drug carriers,food additives or feed additives.In order to make good use of the excellent biological activity of chitooligosaccharide,strengthen its antibacterial,antioxidant and anticancer functions,and then expand the application range of chitooligosaccharide,a series of Schiff base derivatives of chitooligosaccharide and their complexes were designed and synthesized.Two chitooligosaccharide metal complexes（COS-Cu,COS-Ce）and four chlorosalicylaldehyde chitooligosaccharide metal complexes（5-Cl-COS-Cu,3,5-Cl-COS-Cu,5-Cl-COS-Ce,3,5-Cl-COS-Ce）were synthesized by microwave solid state method in accordance with green chemistry idea.The complexes were characterized by EA,FT-IR,¹HNMR,ICP and SEM.Copper ion and cerium ion were coordinated with hydroxyl oxygen atom and amino nitrogen atom in chitooligosaccharide to form complexes.SEM image shows that chitooligosaccharide Schiff base complexes have more complex three-dimensional structure and morphology than ligands.This may be due to the influence of microwave radiation.Chlorosalicylaldehyde chitooligosaccharide copper complexes and cerium complexes showed better antibacterial effect than Schiff base ligand.Copper complexes showed better antibacterial activity against Gram-negative bacteria.The introduction of chlorine substituent in Schiff base improved the antibacterial properties of the ligand and showed the superposition effect of molecular structure.The high concentration of the Cu（II）complex showed good inhibitory effect on Staphylococcus aureus.In the production system of NBT/VB₂/methionine superoxide anion radical,Cu（II）complexes has better antioxidant activity than ligands when the concentration is greater than 0.4 mg/m L.The free radical scavenging rate reached 85%.Ce（III）complexes showed significantly improved antioxidant activity compared with the ligand when the concentration is greater than 0.3 mg/m L.In DPPH test,the scavenging rate of the complexes to free radical increased with the increase of the concentration.The results of cell activity test showed that Cu（II）complex had stronger inhibitory effect on Hep G2 cells than chitooligosaccharide and chlorosalicylaldehyde chitooligosaccharide Schiff base.Introduction concentration reaches 1000μg/m L of3,5-Cl-SCOS-Cu reduced the survival rate of Hep G2 human hepatoma cells cultured in vitro by more than 60%.The introduction concentration of Ce（III）complex reaches 1000μg/m L,the survival rate of Hep G2 cells decreased in a cliff like manner,and the survival rate was less than 35%.Hep G2 cells were observed by laser confocal microscope.3,5-Cl-SCOS-Cu mainly induced apoptosis and reduced cell survival rate.It also destroyed the cell membrane structure.The cell activity decreased gradually with the increase of introduction concentration.3,5-Cl-SCOS-Ce mainly inhibits the activity of Hep G2 cells by destroying the cell membrane structure.When the introduction concentration reaches 1000μg/m L,a large number of cells were necrotic,and the necrotic cells were evenly distributed in orange red bright spots under the image of laser confocal microscope.The test results showed that the chlorosalicylaldehyde chitooligosaccharide complexes had certain antioxidant activity and high antibacterial ability.The inhibitory effect on human liver cancer cells makes it have the potential to become related drugs.Through further research,it is expected to obtain a class of low toxic antioxidants,bacteriostatic agents or anticancer drugs.