Chitosan-metal Complexes Research Articles

Applications of Chitosan Based Schiff bases and its Complexes – A Review

Chitosan, a natural polysaccharides biopolymer is a versatile and promising biomaterial. Chitosan metal complexes stand out in their applicability in different research fields due to their biocompatibility and biodegradability properties. Presence of primary aliphatic amino group along the polymer chain allows for a variety of chemical modifications, of which the most significant is imine functionalization. The ability to easily perform complexation between chitosan Schiff bases and metal ions results in metal complexes, enhancing its application, resulting in further innovation in various fields. The most recent advances of chitosan Schiff base complexes in various fields, including biomedical, catalysis, environmental, and adsorption are summarised in this review.

Synthesis of C-coordinated O-carboxymethyl chitosan metal complexes and evaluation of their antifungal activity

Based on a condensation reaction, a chitosan-derivative-bearing amino pyridine group was prepared and subsequently followed by coordination with cupric ions, zinc ions and nickel ions to synthesize chitosan metal complexes. The calculations using the density functional theory (DFT) show that the copper ions and nickel ions underwent dsp2 hybridization, the zinc ions underwent sp3 hybridization, and they all formed a coordination bond with the carbon atom in the p-π conjugate group. The antifungal properties of O-CSPX-M against Phytophthora capsici (P. capsici), Verticillium alboatrum (V. alboatrum), Botrytis cinerea (B. cinerea) and Rhizoctonia solani (R. solani) were also assayed. Apparently, chitosan metal complexes showed enhanced antifungal activity against four fungi at the tested concentrations compared to that of chitosan. It was shown that Cu complexes can inhibit the growth of P. capsici 100%, and Ni complexes can inhibit the growth of B. cinerea 77.1% at a concentration of 0.4 mg/mL and 0.2 mg/mL, respectively. The pot experiment also verified the result. In addition, the phytotoxicity experiment showed that O-CSPX-M had no obvious toxicity on wheat leaves. This kind of complexes may represent as an attractive direction for chemical modifications of metal fungicides.

Tuning the adsorption behaviour of β-structure chitosan by metal binding

Environmental contextChitosan is an abundant natural component of marine life with potential applications as an adsorbant material for pollutants. We investigate the binding behaviour of chitosan, and show that the β-type structure readily chelates metal ions leading to enhanced adsorption of anionic pollutants in the chitosan-metal complex. The results are highly relevant to the removal of anionic organic pollutants from water. AbstractChitosan, which is commonly extracted from squid pens of the Loligo genus, has a β-type structure. Chitosan has potential application to the adsorption of pollutants but has received little study. We investigate the adsorption ability of β-structure chitosan as well as FeIII and AlIII chitosan-metal complexes. Pristine β-chitosan shows lower adsorption abilities for dye, CrVI and fluoride ions compared with those for α-chitosan, mainly owing to having fewer –NH3+ groups on its surface. However, the anionic pollutant adsorption efficiency of β-chitosan is clearly enhanced when chelated with metal ions. A β-structure chitosan-Fe-Al complex displayed adsorption capacities of 621.45 mg g−1 and 144.53 mg g−1 for Acid Red 73 dye and fluoride ions, respectively, according to the fitted Langmuir–Freundlich model; and of more than 173.03 mg g−1 for CrVI, according to the Freundlich model. These values are much higher than those observed for α-structure chitosan-metal complexes. This enhancement effect on the sorptive behaviour of β-chitosan can be attributed to its loose structure. The polymer chains of β-chitosan are arranged in parallel with relatively weak intermolecular forces, which allows them to easily chelate metal ions. Anionic pollutants can then be efficiently adsorbed by the chelated metal ions in the chitosan-metal complex if the electrostatic attraction of the –NH3+ groups is weak. This investigation provides a better understanding of β-chitosan-based adsorbents for application to anionic pollutant adsorption and removal.

C-coordinated O-carboxymethyl chitosan metal complexes: Synthesis, characterization and antifungal efficacy

A novel type of O-carboxymethyl chitosan Schiff bases (O-CSPX) was synthesized via a condensation reaction. After the coordination reaction of cupric ions, zinc ions and nickel ions, metal complexes (O-CSPX-M) were achieved. The theoretical structure of O-CSPX-M calculated by Gaussian 09 reveals that the copper ions and nickel ions underwent dsp2 hybridization, the zinc ions underwent sp3 hybridization, and they all coordinated by the carbon atom in the p-π conjugate group. Then, the structures were confirmed by FT-IR, 1H NMR, CP-MAS 13C NMR, elemental analysis, DSC and XRD. The antifungal properties of O-CSPX-M against Phytophthora capsici (P. capsici), Gibberella zeae (G. zeae), Fusarium oxysporum (F. oxysporum) and Botrytis cinerea (B. cinerea) were evaluated at concentrations ranging from 0.05mg/mL to 0.40mg/mL. The experiments indicated that the derivatives have significantly enhanced antifungal activity after metal ions complexation compared with the original chitosan. Moreover, it was shown that 0.20mg/mL of O-CSPX-Cu can 100% inhibit the growth of P. capsici and 0.20mg/mL of O-CSPX-Ni can 87.5% inhibit the growth of B. cinerea. In addition, the phytotoxicity assay and cell viability assay were also evaluated. The experimental results may provide a novel direction for the development of metal fungicides.

Preparation and properties of chitosan–metal complex: Some factors influencing the adsorption capacity for dyes in aqueous solution

Chitosan–metal complexes have been widely studied in wastewater treatment, but there are still various factors in complex preparation which are collectively responsible for improving the adsorption capacity need to be further studied. Thus, this study investigates the factors affecting the adsorption ability of chitosan–metal complex adsorbents, including various kinds of metal centers, different metal salts and crosslinking degree. The results show that the chitosan–Fe(III) complex prepared by sulfate salts exhibited the best adsorption efficiency (100%) for various dyes in very short time duration (10min), and its maximum adsorption capacity achieved 349.22mg/g. The anion of the metal salt which was used in preparation played an important role to enhance the adsorption ability of chitosan–metal complex. SO42− ions not only had the effect of crosslinking through electrostatic interaction with amine group of chitosan polymer, but also could facilitate the chelation of metal ions with chitosan polymer during the synthesis process. Additionally, the pH sensitivity and the sensitivity of ionic environment for chitosan–metal complex were analyzed. We hope that these factors affecting the adsorption of the chitosan–metal complex can help not only in optimizing its use but also in designing new chitosan–metal based complexes.

Thermal and morphological study of chitosan metal complexes

The synthesis of chitosan Schiff bases, N-benzylidene chitosan (CTB), 4-dimethylamino-benzylidene chitosan (CTDB) and 4-nitro-benzylidene chitosan (CTNB), and their interaction with Cu2+, Zn2+ and Ni2+ were studied. The content of metal ions was determined by atomic absorption spectrometry, and the results showed that chitosan exhibited higher chelating capacity for the metal ions. Morphological changes of Schiff bases and complexes were demonstrated by SEM images. The presence of crystals attributed to copper sulfate adsorbed on the polymers surface was also observed, which indicates that part of the metal content is in the salt adsorbed and might influence in their further application studies. X-ray diffraction patterns showed that the formation of complexes resulted in the decrease in crystallinity. The thermal behavior of derivative and metal complexes were studied by thermogravimetric analysis, differential thermogravimetric analysis and differential scanning calorimetry. The results showed that the presence of new groups and metal ions bonded to chitosan affected their thermal stability.

Enhanced catalytic ability of chitosan–Cu–Fe bimetal complex for the removal of dyes in aqueous solution

In this study, despite the high adsorption ability, efficient catalytic activity of a chitosan–metal complex has been developed through the chelation of chitosan polymer with bimetals Cu(ii) and Fe(iii).

Synthesis, characterization and in vitro evaluation of cytotoxicity and antimicrobial activity of chitosan–metal nanocomposites

AbstractBACKGROUNDThe present study explores the synthesis of chitosan–metal nanocomposites in view of their increasing application as antimicrobial material.RESULTSChitosan nanoparticles were prepared by ionic gelation between chitosan and sodium tripolyphosphate. Copper sulphate hydrate (CuSO4.5H2O) and zinc acetate (Zn (O2CCH3)2) were used as precursors for synthesis of chitosan–copper nanocomposites (Cu/Ch) and chitosan–zinc nanocomposites (Zn/Ch), respectively. Synthesis of nanocomposites was confirmed by transmission electron microscopy (TEM), Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy with energy dispersive X‐ray microanalyses (SEM‐EDX) and differential scanning calorimetry (DSC). Cytotoxicity of nanoformulations was studied by Resazurin assay on Vero cell line (African green monkey kidney cell line). Their antibacterial activities were assessed by the zone of inhibition method and time dependent growth curve against Micrococcus luteus MTCC 1809, Pseudomonas aeruginosa MTCC 424 and Salmonella enterica MTCC 1253 in vitro. Antifungal activity was also studied against Alternaria alterneta, Rhizoctonia solani and Aspergillus flavus in vitro by the mycelium inhibition method.CONCLUSIONSIt was observed that all nanoformulations show high antimicrobial activity against all test microorganisms. So chitosan–metal complexes could be promising candidates for novel antimicrobial agents in cosmetic, food and textile industries. © 2014 Society of Chemical Industry

Depolymerization of chitosan–metal complexes via a solution plasma technique

Chitosan–metal complexes were depolymerized under acidic conditions using a solution plasma system. Four different types of metal ions, including Ag+, Zn2+, Cu2+, and Fe3+ ions, were added to the chitosan solution at a metal-to-chitosan molar ratio of 1:8. The depolymerization rate was affected by the types of metal ions that form complexes with chitosan. The complexation of chitosan with Cu2+ or Fe3+ ions strongly promoted the depolymerization rate of chitosan using a solution plasma treatment. However, chitosan–Ag+ and chitosan–Zn2+ complexes exhibited no change in the depolymerization rate compared to chitosan. After plasma treatment of the chitosan–metal complexes, the depolymerized chitosan products were separated into water-insoluble and water-soluble fractions. The water-soluble fraction containing low-molecular-weight chitosan was obtained in a yield of less than 57% for the depolymerization of chitosan–Fe3+ complex with the plasma treatment time of 180min.

Study on synthesis and adsorption characterization of hydroxypropyl chitosan metal complex

The studies on the modification of chitosan and the properties of its derivatives using physical fields (ultrasonic field) for raising the reaction speed and reaction yield have been carried out. The basic investigative data were provided for the development on the highly efficient, new water treatment agent. O-(hydroxyl isopropy1) chitosan-Fe(II) was synthesized via 1,2-epoxypropane derived reaction of Fe2+ with chitosan. The structure of the product was identified by its transform Fourier infrared spectrum, UV spectrum, and X-ray diffraction. The adsorptive properties of hydroxypropyl chitosan-Fe(II) complex (HPCTS-Fe2+) for heavy metal ions were researched. The experiments showed that the removal efficiencies were 99.8% and 78.8%, respectively, using 1% (g/mL) of the HPCTS-Fe2+, pH5, initial concentration 1 mg/L Cu2+, 0.1 mg/L Pb2+, respectively, equilibration for 30 min. It showed that HPCTS-Fe2+ might be used as a new highly efficient water treatment agent for adsorbing heavy metal ions.

Study on the thermal degradation of chitosan-Cu/Ni/Mn complexes

AbstractThe thermal degradation of chitosan-Cu/ Ni/ Mn complexes at different heating rates in nitrogen was studied by thermogravimetric analysis (TGA) in the temperature range 30-500 °C. Fourier transform-infrared (FTIR) was utilized to determine the microstructure of chitosan-metal complexes. The results of FTIR show that there are coordinating bonds between chitosan and cupric, manganese, nickel ions. The results of thermal analysis indicate that the thermal degradation of chitosan-Cu/ Mn/Ni complexes is a two-step reaction, which is related to water loss from the material, the deacetylation of the main chain and the cleavage of glycosidic linkages of chitosan, respectively. Characteristic temperature increases with the increment of heating rate and the impact of coordination of metal ion on the thermal degradation of chitosan is very significant. The kinetic parameters were determined by using Flynn-Wall-Ozawa method. The results show that the activation energy of the complexes is different but the variable tendency is similar

Insecticidal activity of chitosans of different molecular weights and chitosan-metal complexes against cotton leafworm Spodoptera littoralis and oleander aphid Aphis nerii

As an alternative to synthetic pesticides, chitosan has received much attention as a biopolymer active against some agricultural pests. The, insecticidal activity of chitosans of four molecular weights (2.27 × 10<sup>5</sup>,3.60 × 10<sup>5</sup>,5.97 × 10<sup>5</sup>,and9.47 × 10<sup>5 </sup>g/mol) was investigated against two species of arthropod pests: oleander aphid Aphis nerii and cotton leafworm Spodoptera littoralis. In addition, the most active chitosan of 2.27 × 10<sup>5 </sup>g/mol was chemically modified with metals of Ag(I), Cu(II), Ni(II), and Hg(II) to give corresponding chitosan-metal complexes. Larval mortality, growth inhibition, and antifeedant activities for third instar larvae of S. littoralis were evaluated at 4 g (a.i.) chitosan/kg diet. Chitosan of 2.27 × 10<sup>5 </sup>g/mol and its complexes with Ni and Hg were the most active compounds. The results against A. nerii indicated that chitosans of 3.60 × 10<sup>5</sup> and 5.97 × 10<sup>5 </sup>g/mol showed high activity among the different molecular weights in leaf-dip bioassay after 24 h of treatment with 48 and 49% mortalities, respectively, at 1000 mg/l. All compounds had a systemic effect against A. nerii. Chitosans of 2.27 × 10<sup>5</sup>,3.60 × 10<sup>5</sup>,and5.97 × 10<sup>5 </sup>g/mol showed the highest efficacy at all concentrations tested; however, chitosan-Cu was significantly the most active among the complexes.

Preparation of some chitosan heavy metal complexes and study of its properties

The chitosan was prepared and mixed with some metal salts (FeCl3, Co(OAc)2 and NiCl2) by different concentrations to form chitosan-metal complexes. The metal ions which strongly complexed to the amino groups of chitosan like Fe showed a smooth surface product, amorphous phase, thermally more stable and high electrical conductivity than other complexes, while the Co ions which the weakly complexed with chitosan showed a rough surface product, crystalline phase, thermally less stable and low electrical conductivity. The chitosan-metal complexes have a higher electrical conductivity than chitosan pure at room temperature.

Chitosan Metal Complex: An Artificial Metalloprotease Hydrolyzing Trypsin Inhibitor from Soybean

Most popular agents for protein cleavage are proteolytic enzymes, but they require more rigorous hydrolytic conditions, and it is very difficulty to separate them from the productions. In this paper, an new artificial metalloprotease, Cu(II) complex of cyclen (Cu(II)Cyc) using chitosan as supporter, was designed and synthesized successfully. The hydrolytic efficient under different conditions was measured and confirmed with HPLC, SDS-PAGE, further more. Some reaction conditions, such as pH, temperature, were researched, and the results show that the optimum reaction time was 48 h, temperature was 60 °C respectively, The observed rate constants for trypsase inhibitor cleavage was 1.006×10-2 h-1 under above conditions, and the observed rate constants was 2.120×10-2 h-1 when the pH was 9.0. This paper suggested that the chitosan metal complexes could efficiently accelerate the hydrolysis reaction.

MORPHOLOGICAL, THERMAL AND ELECTRICAL STUDIES ON CHITOSAN HEAVY METAL COMPLEXES

The chitosan was prepared and mixed with some metal salts (FeCl3, Co(CH3COO)2 and NiCl2) with different concentrations to form chitosan-metal complexes. The characterizations of these complexes were carried out by FTIR and their morphological studies were carried out by scanning electron microscope (SEM) and wide angle X-ray diffraction apparatus. The thermo gravimetric analysis (TGA) and differential scanning calorimetric (DSC) also were carried out. The metal ions which strongly complexed to the amino groups of chitosan like Fe+++ showed a smooth surface product, amorphous phase and thermally more stable than other complexes. The chitosan-metal complexes have a higher electrical conductivity than chitosan compounds at room temperature.

Development of antimicrobial jute packaging using chitosan and chitosan–metal complex

Scoured jute fabrics were treated with chitosan (pre-dissolved in 1% acetic acid) under a variety of conditions. The latter were included chitosan concentration, fixation temperature and time. The chitosan-treated jute fabrics were subjected to five washing cycles after each cycle the fabrics were monitored for antimicrobial activity and nitrogen content. The antimicrobial activity was evaluated using two kinds of microorganisms, namely, Staphylococcus aureus ( S. aureus) and Candida albicans ( C. albicans). Results obtained show that, although scoured jute fabrics contain residual nitrogen content amount 0.22% it did not shows any antimicrobial activity towards S. aureus or C. albicans. Treatment of jute fabrics with chitosan improves only the antibacterial properties towards S. aureus whereas, antifungal properties remain intact. A similar study was carried out using chitosan–metal complex aiming to impart the jute fabric antimicrobial properties. In this regards, Ag 1+, Zn 2+ and Zr 2+ ions were allowed separately to form a complex with chitosan. It has been found that, jute fabrics treated with chitosan–metal complex show better antimicrobial properties than those fabrics treated with either chitosan or metal salt separately. Moreover, the jute fabrics treated with chitosan–Zn complex have higher antimicrobial properties compared with those samples treated with chitosan–Zr or chitosan–Ag complexes.

CHITOSAN METAL COMPLEXES AND CHITOSAN- Cu ESR STUDIES

Properties of the polymer metal complexes can be explained up to certain extent by the molecular structure of the complexes, but this area has not been well studied in the case of the chitosan metal complexes. In this work, we are proposing that chitosan is bonded through the 4 nitrogen to copper by means of square planar geometry. The polymer requires some structural modifications in order to be arranged in that geometry. Two sites in the chitin were detected, one similar to chitosan and the other in a square planar tetrahedrically distorted arrangement, with three atoms of nitrogen and one of oxygen or two atoms of nitrogen and two of oxygen. ESR studies of the copper complexes by means of chlorine and nitrate as ion counter were carried out. Nitrate exhibits one type of retention site and, on the other hand, chlorine presents two types of retention sites.

Removal of Mn(II) and Zn(II) ions from flue gas desulfurization wastewater with water-soluble chitosan

Heavy metals are the most important pollutants in wastewater from dual-alkali flue gas desulfurization (FGD) system. Mn(II) and Zn(II) could predominate in the catalyzed oxidation of sulfite. So the feasibility of precipitation of heavy metal ion (Mn(II) and Zn(II)) by water-soluble chitosan was studied in a lab scale experiment. The association between chitosan and metal ions was verified through FT-IR. The pH investigation revealed that at the pH ranged from 5 to 9, there were three stages for different actions: chelation of chitosan for metal ion, precipitation of metal hydroxide and coprecipitation of metal hydroxide and chitosan–metal complex. The selective chelation of chitosan for Mn(II) and Zn(II) mixture solution was also studied. The results showed that the chelation of chitosan for Mn(II) was prior to Zn(II) in multiple component solution. Compared with the settling of metal hydroxide, the chitosan–metal complex had better separating performance. Application of chitosan solution for chelation could remove Mn(II) and Zn(II) efficiently and make it easily to separate sediment from dual-alkali FGD wastewater. On the other hand co-precipitation of the complicate heavy metal in the FGD wastewater enhanced the heavy metal removal of chitosan chelation.

Chitosan- metal complexes as antimicrobial agent: Synthesis, characterization and Structure-activity study

Chitosan (CS) metal complexes with bivalent metal ions, including Cu(II), Zn(II), Fe(II) were prepared, and characterized by FT-IR, XRD, AAS and elemental analysis. The crystalline and structural properties of chitosan-metal complexes were different from those of chitosan, and the -NH2, -OH groups in chitosan molecule were considered as the dominating reactive sites. In vitro antimicrobial activities of the obtained chitosan-metal complexes, which were found to be much better than free chitosan and metal salts, were examined against two gram-positive bacteria (S. aureus and S. epidermidis), two gram-negative bacteria (E. coli and P. aeruginosa) and two fungi (C. albicans and C. parapsilosis). Results indicatd that the inhibitory effects of chitosan-metal complexes were dependent on the property of metal ions, the molecular weight and degree of deacetylation of chitosan and environmental pH values. Electro microscopy confirmed that the exposure of S. auresus to the chitosan-Cu(II) complex resulted in the disruption of cell envelop. Based on the discussion upon the antimicrobial mechanism of chitosan-metal complexes and their molecular structures, the structure-activity correlation for the antimicrobial activities was elucidated. All the results show that chitosan-metal complexes are a promising candidate for novel antimicrobial agents that can be used in cosmetic, food, textile et al.

Ground water treatment by enhanced ultrafiltration

The efficiency of heavy metal removal from simulated ground water containing humic substances has been investigated by means of enhanced ultrafiltration (UF) with chitosan. The rejection coefficient of Cu (II), Pb (II), Ni (II) and Co (II) in the presence of humic, fulvic acids and polysaccharide biopolymer chitosan was studied for singlemetal and multi-component systems. The different experimental parameters such as time contact, initial concentration of metal ions, background electrolyte concentration, pH solutions, and diverse cellulose acetate UF membranes of different molecular weight cut-off on the extraction kinetic were investigated. Humic substances rejection increased with pH due to conformational transformation of ionizable molecules. The interactions of humic substances with multi-charged metals do not practically affect the retention of organic matter. Involvement of heavy metal ions into complexation with chitosan and humic substances provides effective removal of trace metals from solutions as a result of complex retention. In conformity with this principle, the degree of heavy metal rejection improved with an increase in the ratio between chitosan or humic substances and metal due to an increase in completeness of metal binding. This ratio is also responsible for the phase-dispersion state of the solution initiating a transition of intra-molecular complexes to inter-molecular ones at higher concentrations of metal ions with respect to a higher molecular weight of complex formation substances. This leads to an aggregation of humic acids-metal complexes and a decrease in the transmembrane flux. Fulvic acids do not tend to form intermolecular aggregates, and chitosan-metal complexes allow metal ions to be rejected without any substantial reduction of membrane productivity.