Synthesis,Characterization And Antibacterial Activity Of Chitosan Oligosaccharide-O-Terpenol Derivatives

Chitosan oligosaccharide?COS?is the hydrolyzed product of chitin and chitosan.It is the only alkaline positively charged polysaccharide in the world with better solubility,biocompatibility,anti-microbial activity,degradability,biological nontoxic.COS can be easily absorbed.Meanwhile,it is considered as a potential novel food ingredient because of its authentic natural and safe character.However,the restricted antibacterial activity and the narrow bacteriostatic spectrum of COS limit its application in the aera of food,biology,pharmacy and so on.Nowadays,there is an increasing interest in the chemical modification of COS to enhance its antibacterial activity.Our study focued on the preparations of three kinds of COS derivatives through the substitution of hydroxyl groups on COS with acyclic terpenol?prenyl alcohol,geraniol,farnesol?.The chemical structures of COS derivatives were characterized by elemental analysis,UV-Vis absorption spectroscopy,Fourier transform infrared?FT-IR?,¹H nuclear magnetic resonance?NMR?,X-ray diffraction analysis?XRD?and thermogravimetric analysis?TGA?.The antibacterial activities of them againsted Staphylococcus aureus,Escherichia coli,Saccharomyces cerevisiae and Aspergillus niger and their antibacterial mechanism were also studied.The main results were listed as follows:1.Three acyclic terpenol including prenyl alcohol,geraniol and farnesol were replaced to the hydroxyl groups of COS in order to obtain COS derivatives,a three-step reaction was taken as follows:Firstly,the NH₂ groups on COS were protected by benzaldehyde.Secondly,terpenyl bromide was prepared by phosphorus tribromide.Third,the N-benzylidene COS was selectively grafted with terpenyl bromide in N,N-Dimethylformamide?DMF?,and then the COS derivatives were obtained by removing the benzylidene group.The structures of COS derivatives can be confirm by elemental analysis,UV-Vis,FT-IR,¹H NMR and XRD analyses.The physical properties of COS derivatives,including solubility and thermal stability,were determined.The TGA showed that the thermal stability of COS derivatives were better than COS.The XRD analyses suggested that crystallization was enhanced with the intensity of the peaks of X-ray diffraction.This was probably due to the change of intermolecular and intra-molecular hydrogen bonding.COS-O-Pre,COS-O-Ger and COS-O-Far exhibited a better solubility in aqueous and organic solvents.2.The antibacterial activity and bacteriostasis mechanism of COS-O-Pre,COS-O-Ger and COS-O-Far with similar degree of substitution?DS?were studied,according to the inhibition rate,MIC and membrane permeability.All the derivatives showed a stronger antibacterial effect than COS on Staphylococcus aureus,Escherichia coli,Saccharomyces cerevisiae and Aspergillus niger.The antibacterial activity increased with the increasing of DS.Under the same concentration,the inhibition rates of COS derivatives on microorganisms were higher than COS.The inhibitory action for Staphylococcus aureus was more remarkable than Escherichia coli,the inhibitory action for bacterial were more remarkable than that for fungi.COS and COS derivatives destroyed the cell membrane and then the intracellular substances released,which inhibited the growth of microorganism.These results suggested that the COS-O-Pre,COS-O-Ger and COS-O-Far had good solubility and antibacterial activity.Hence,they can be used as natural and effective antibacterial agent in the field of food,medicine,cosmetics domain and so on.