Preparation,Characterization And Performance Studies Of Chitosan-curcumin Derivatives

Curcumin(Cur)is a natural hydrophobic polyphenol in the rhizome of the perennial herb turmeric.Studies have shown that Cur has various physiological functions such as antioxidant,antibacterial,anti-inflammatory,and anticancer.Although Cur has a wide range of potential benefits,the practical application of Cur is limited due to its low water solubility,poor stability,and low bioavailability caused by rapid metabolism.Chitosan(CS)is a water-soluble chain polysaccharide obtained by the deacetylation of chitin,which has the advantages of biodegradability,non-toxicity,and good biocompatibility.In addition,the molecular chains of CS contain abundant amino and hydroxyl groups,which can be used as binding sites for chemical modifications.Therefore,chemical grafting based on CS is an effective method to improve the water solubility and stability of Cur,thereby enhancing its bioavailability.In this paper,three novel CS-grafted Cur derivatives were prepared,the characterization and performance of three derivatives were studied.The main research contents were as follows:(1)CS-Cur was prepared by directly grafting Cur with CS,using free radical oxidation grafting reaction.The successful synthesis of CS-Cur was demonstrated by using ultraviolet-visible(UV-vis)absorption spectroscopy,fluorescence spectroscopy,Fourier transform infrared(FT-IR)spectroscopy,and nuclear magnetic resonance(~1H NMR)spectroscopy.The grafting rate of CS and Cur was 0.8%.The water solubility test showed that the water solubility of CS-Cur was 10.73±1.12 g/L,and the average Cur content per 100 mg of CS-Cur was about 0.33±0.11 mg.Compared with free Cur,the water solubility of grafted Cur was improved;the stability test showed that CS-Cur had good photothermal stability compared to Cur;the antioxidant test showed that CS-Cur had good antioxidant activity;the antibacterial test showed that CS-Cur had better photodynamic antibacterial activity after 450 nm LED light irradiation,and the antibacterial effect of CS-Cur on Staphylococcus aureus(S.aureus)was better than Escherichia coli(E.coli).The better bacteriostatic effect was mainly due to the production of reactive oxygen species(ROS);The cytotoxicity tests showed that CS-Cur had good biological safety.(2)Due to the low solubility of CS and the low reaction efficiency of free radical oxidation grafting reaction,the C-6 hydroxyl group of CS was carboxylated through 2,2,6,6-tetramethyl-1-piperdinyloxy(TEMPO)mediated catalytic reaction to prepare carboxylated chitosan(COCS)with good water solubility.COCS was coupled with Cur through esterification reaction to prepare COCS-Cur.The prepared COCS-Cur had higher Cur grafting rate and water solubility compared to CS-Cur.The grafting rate of Cur on COCS was 6.9%.The water solubility of COCS-Cur was 13.33±0.91 g/L,and the average Cur content per 100 mg of COCS-Cur was about 1.33±0.28 mg.The results exhibited that COCS-Cur can spontaneously form nano micelles when dispersed in water,due to the presence of both hydrophilic chain COCS and hydrophobic segment Cur in COCS-Cur.Transmission electron microscopy(TEM)showed that the micelles were approximately spherical,with a particle size of 40.97±4.46 nm.After grafting Cur with COCS,COCS-Cur derivatives exhibited good photothermal stability,antioxidant activity,photodynamic antibacterial activity,and in-vitro biosafety.(3)The TEMPO-mediated catalytic reaction will degrade CS,resulting in low yield and waste.Therefore,chloroacetic acid was used to replace the C-6 hydroxyl group of CS to prepare carboxymethyl chitosan(CMCS),which could effectively improve the problem of low yield in the synthesis process of COCS.Subsequently,CMCS-Cur was prepared by coupling CMCS with Cur through esterification reaction.The grafting rate of Cur on CMCS was 10.3%.The water solubility of CMCS-Cur was significantly improved compared to Cur,reaching 15.67±0.76 g/L,and the average Cur content per 100 mg of CMCS-Cur was about 1.45±0.94 mg.CMCS-Cur could self-assemble into nano micelles in an aqueous solution.TEM showed that the micelles exhibited a necklace-shaped spherical connection,with a particle size of 50.43±11.46 nm.Through determination,CMCS-Cur had good photothermal stability,antioxidant properties,photodynamic antibacterial activity,and in-vitro biosafety.In summary,the CS-Cur,COCS-Cur,and CMCS-Cur derivatives prepared in this paper significantly improved the water solubility and stability of Cur,and retained the original properties of Cur such as antioxidant and photodynamic antibacterial activities.This expands the practical application range of Cur in water systems and also provides ideas for the design and synthesis of novel high water-soluble Cur derivatives.