Synthesis And Application Of Aminothiourea And Amino Modified Chitosan Derivatives

As one of the most important and abundant natural polysaccharide next to cellulose andstarch, chitosan (CS) has advantages of non-toxic, biocompatible and biodegradable. CS andits derivatives have broad prospect in application and practical value in many fields such asagriculture, food, biological medicine and environment engineering. CS is such an attractivematerial that many scientists have devoted themselves to search new structure modificationmethods of CS derivatives that possess good application abilities.This study aims to explore new methods for the simple synthesis of CS derivatives. Thisresearch also intended to find the application mechanisms of synthetic materials, which wouldprovide powerful theoretic support for the exploration and development of new applicationsof CS biopolymers. Based on the principle of “superposition of active groups”, aminothioureacross-linked chitosan,2-mercapto-5-amino-1,3,4-thiadiazole modified CS, amino groupmodified chitosan and chitosan-graft-P(MMA-co-GMA) electrostatic spinning film wereprepared efficiently. These products were characterized and confirmed using Fouriertransform infrared spectroscopy, elemental analysis, thermal gravity analysis, differentialscanning calorimetry, X-ray powder diffraction and scanning electron microscopy methods.The application studies of antimicrobials, anticorrosion and heavy metal ions adsorptionshowed that these products presented good application capabilities. The adsorption andanticorrosion mechanisms were also explored. The major findings and results were listed asfollows:1. Based on a simple “one-pot” strategy, the two new CS derivatives TS CS and TC CSwere prepared by introducing functional group Thiosemicarbazide (TS) andThiocarbohydrazide (TC) onto CS structure. The swelling tests revealed that these CSderivatives could form pH dependent gels and showed favorable water-absorbing property.Electrochemical test results revealed that the product TCFCS could act as mixed type metalcorrosion inhibitors, and restrained the metal corrosion by the adsorption of inhibitors on thesurface of metal; its inhibition efficiency for304steel and Cu sheets was92%and88%,respectively. The adsorption studies on a metal ion mixture aqueous solution showed thatthese two samples could adsorb heavy metal ions efficiently, especially to As (V), Cd (II) andPb (II). The removal of the metal ions was around66.4%to99.9%for the two adsorbents. The adsorption properties and capacities studies of adsorbent TSFCS to Cd (II) and Pb (II)showed that the adsorption process followed a pseudo-second-order rate equation and betterfitted Langmuir monolayer adsorption. In comparison with the results reported by literatures,the prepared adsorbent showed fast kinetic, high adsorption capacities (Cd157.2mg/g; Pb245.2mg/g). This adsorbent could regenerate easily, showing up to80%recovery after fivecycles. In vitro antibacterial activity of them against two Gram-positive bacteria (S. aureusand B. subtilis) and two Gram-negative bacteria (E. coli and P. aeruginosa) was evaluated byinhibition zone. The result showed that the antibacterial activity of compounds TSFCS andTCFCS were lower than raw CS.2. In this section, the twice cross-linked CS was synthesized and its applied propertieswere studied. Firstly, epoxy group was introduced onto the2-amino protected CS structure.Then, Hydrazine hydrate was used to prepare a cross-linked product (HECS) byhydrazine-epoxy ring opening reaction. By using formaldehyde as linkage, new cross-linkedCS derivative (TCHECS) containing TC group was synthesized smoothly based on HECS.The short-term electrochemical tests results revealed that the two products could act as mixedtype metal corrosion inhibitors in some extent; using Cu sheet as WE, the anticorrosion abilityof cross-linked product TCHECS was more efficient than the product HECS without TCgroup. The inhibition efficiency of TCHECS is88%. The adsorption studies on a metal ionmixture aqueous solution at various pH range showed that TCHECS could adsorb metal ionsmore efficiently. The removal of the As (V), Ni (II), Cu (II), Cd (II) and Pb (II) were around55.6%to99.9%. The results mentioned above revealed the introduction of TC group hadimproved the adsorption and anticorrosion abilities of the product TCHECS. In vitroantibacterial activity tests showed the antibacterial activity of HECS and TCHECS werelower than raw CS.3. This research intended to employ new synthetic methods and introduce a new aminogroup or new functional group containing amido onto6-site of CS instead of the hydroxylgroup. On the one hand, functional groups cysteamine (CT) and2-mercapto-5-amino-1,3,4-thiadiazole (AMT) were introduced on2-amino protected CS structure to get productsCYECS and AMECS through the thiol-epoxy “click” chemistry. On the other hand, a newstrategy for the preparing of6-deoxy-6-amino-chitosan was developed. The short-termelectrochemical tests revealed that the product AMECS could act as mixted type metalcorrosion inhibitors; its inhibition efficiency was93%by using Cu sheet as WE. This meantthe introduction of functional group AMT enhanced the anticorrosion ability of CS. In vitroantibacterial activity tests showed that compounds AMECS, CYECS and AMCS had variousantibacterial activities. The result that CYECS and AMCS were more effective than raw CS indicated the introduction of active amino group had enhanced the antimicrobial abilities ofCS. Moreover, in this research, the electro spun fibrous of P (MMA-co-GMA) was prepared,and the preparing method of CS-g-P (MMA-co-GMA) electro spun fibrous was studied. Theobtained fibrous was studied by FT-IR and SEM methods.In conclusion, the novel synthesis methods developed in this study are of greatsignificance to the synthesis of functional materials based on CS biopolymer. After beingmodified with aminothiourea or5-amino-1,3,4-thiadiazole group, the obtained CS derivativeshave greatly improved their application abilities of metal ions adsorption and anticorrosion,and can be used as corrosion inhibitors and heavy metal ions adsorbents. Amino groupmodified CS have improved their antibacterial abilities. The proposed method for preparing ofCS-g-P (MMS-co-GMA) provide an idea in structure modification of the other syntheticpolymer fibrous using CS. This research is very important to the intensive study andexploitation of CS.