Synthesis of acyl thiourea derivatives of chitosan and their antimicrobial activities in vitro

Three different acyl thiourea derivatives of chitosan (CS) were synthesized and their structures were characterized by FT-IR spectroscopy and elemental analysis. The antimicrobial behaviors of CS and its derivatives against four species of bacteria (Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus, and Sarcina) and four crop-threatening pathogenic fungi (Alternaria solani, Fusarium oxysporum f. sp. vasinfectum, Colletotrichum gloeosporioides (Penz.) Saec, and Phyllisticta zingiberi) were investigated. The results indicated that the antimicrobial activities of the acyl thiourea derivatives are much better than that of the parent CS. The minimum value of MIC and MBC of the derivatives against E. coli was 15.62 and 62.49 microg/mL, respectively. All of the acyl thiourea derivatives had a significant inhibitory effect on the fungi in concentrations of 50-500 microg/mL; the maximum inhibitory index was 66.67%. The antifungal activities of the chloracetyl thiourea derivatives of CS are noticeably higher than the acetyl and benzoyl thiourea derivatives. The degree of grafting of the acyl thiourea group in the derivatives was related to antifungal activity; higher substitution resulted in stronger antifungal activity.     

Degradation behavior of chitosan chains in the 'green' synthesis of gold nanoparticles

The degradation behavior of chitosan chains in the synthesis of Au nanoparticles by a 'green' method was investigated in this paper for the first time. UV-vis absorption spectra suggested the formation of Au nanoparticles and TEM images showed that their sizes were between 10 and 50nm. During the process of synthesis, the intrinsic viscosity [eta] of chitosan was observed to decrease gradually, implying that the chitosan chains degraded under the reaction conditions. Further studies showed that the degree of degradation of the chitosan chains was changed with different reaction temperatures, reactant ratios, and the molecular weights of chitosan.     

Comparative study of electrokinetic potentials and binding affinity of lipopolysaccharides-chitosan complexes

Electrokinetic properties of complexes of chitosan (Ch) with lipopolysaccharides (LPSs) from Escherichia coli O55:B5, Yersinia pseudotuberculosis 1B 598, and Proteus vulgaris O25 (48/57) and their size distribution were investigated using zeta-potential distribution assay and quasi-elastic light scattering. The interaction of LPS from different microorganisms with chitosan at the same w/w ratio of components (1:1) resulted in the formation of complexes in which the negative charge of LPS was neutralized (LPS from E. coli) or overcompensated (Y. pseudotuberculosis and P. vulgaris). The changing in size of the endotoxin aggregates during binding with chitosan was observed. The binding constants of chitosan with LPSs were determined by a method with using the anionic dye Orange II. The LPS from E. coli possess higher affinity to chitosan in comparison with the two others samples of endotoxin.     

Kinetics of ultrasonic degradation and polymerisation degree distribution of sonochemically degraded chitosans

The process of physical degradation by means of the ultrasonic action towards chitosans with mole fraction of 2-acetamido-2-deoxy-β- -glucopyranose units (the degree of N-acetylation, F_A) in the range of 0.10≤F_A≤0.28, and the weight average polymerisation degree in the range of has been investigated. The decrease of as well as changes in the distribution of the degree of polymerisation (P) has been determined as a function of time, F_A, temperature, concentration of chitosan solution and concentration of acetic acid in the solution. The use of low-power ultrasound emitter allowed to establish that in the case of chitosan (binary heteropolysaccharide) the general rate parameter (k) increased with F_A. This can be explained by the relatively stronger aggregation of macromolecules with higher F_A, which results in size increase of macromolecular individuals and hence in their higher susceptibility to ultrasonic action. It was also observed that k decreased with chitosan concentration and temperature. The value of limiting degree of polimerisation (x_e) was found to be influenced by structural parameters of chitosan chains (F_A, aggregation). The increase of acetic acid concentration caused the increase in the k value, what indicated accelerating effect of ultrasound towards acidic hydrolysis of chitosan. The shape of the P curve of sonochemically degraded chitosans are in good correlation with the mid-point breakage concept of degradation accepted in sonochemical degradation of polymers.     

Preparation and physico-chemical characterization of chitin and chitosan from the pens of the squid species, Loligo lessoniana and Loligo formosana

β-chitin and its chitosan from the pens of Loligo lessoniana and Loligo formosana has been isolated, prepared, and physico-chemically characterized to demonstrate a potential chitin source. Without deminerization due to negligible ash content, only deproteinization was used in the chitin isolation with an yield of 35–38%, without significant difference either between the two species or the collection seasons. Reducing step not only saves production cost but also obviates acid pollutant. Mild alkaline deacetylation with various time periods was employed in the chitosan preparation. Optical rotation and thermal transition of chitin from both species suggested the weak intermolecular forces compared with shrimp chitin. The results of nitrogen contents indicate the effectiveness of the deproteinization method used. The samples were categorized as a Class III: moderate hygroscopicity. Traces of elements presented in pens markedly decreases but are incapable to be got rid of within the step of chitin–chitosan preparation. In addition, a small amount of cadmium, as the contamination, was detected in the samples from L. formosana.     

Anti-inflammatory effect of chemically modified chitin

Anti-inflammatory effects of the three types of chitin derivatives namely phosphated chitin (P-chitin), phosphated–sulfated chitin (PS-chitin), and sulfated chitin (S-chitin) were investigated using a canine model of chitosan-induced pneumonia. After simultaneous administration of chitosan with or without each chitin derivative (chitosan alone: n=6, chitosan and P-chitin: n=6, chitosan and PS-chitin: n=1, and chitosan and S-chitin: n=3), hematological examination and X-ray image processing were performed for up to 24 h. Then the lungs were recovered and were evaluated by softex imaging after inflation and fixation. The hematological findings showed that PS-chitin and S-chitin did not prevent the decrease in white blood cell (WBC) count as seen in dogs administered chitosan, while P-chitin prevented such decrease in WBC count. The surface of the inflated and fixed lung specimens was hemorrhagic in the PS- and S-chitin groups as well as in the chitosan group, while the lung looked like normal in the P-chitin group. The pulmonary blood vessels of the chitosan group showed severe change while the P-chitin group showed no changes with softex findings. Furthermore, the pattern of histogram density obtained with image processing of thoracic X-ray in P-chitin group did not change among pre and post administration while chitosan group showed rightward movement and significant changes on parameters. The cause of which is attribured to an attenuation of X-ray permeability by angiectasis of the lung.     

A new linear potentiometric titration method for the determination of deacetylation degree of chitosan

The degree of deacetylation (DD) is one of the most important properties of chitosan. Therefore, a simple, rapid and reliable method for the determination of DD of chitosan is essential. In this report, two new potentiometric titration functions are derived for the determination of DD of chitosan. The effects of the precipitation and the errors induced in pH measurement are discussed in detail. To make this method more simple and reliable, two universal pH regions for the accurate plotting of different DD chitosan samples are proposed for the new potentiometric titration functions. The DD values of three chitosan samples obtained with this new method show good agreement with those yielded from elemental analysis and ¹H-NMR.     

Flocculation of algae using chitosan

Flocculation of three freshwater algae, Spirulina,Oscillatoria and Chlorella, and onebrackish alga, Synechocystis, using chitosan was studiedinthe pH range 4 to 9, and chlorophyll-a concentrations inthe range 80 to 800 mg m^–3, which produces aturbidity of 10 to 100 nephelometric turbidity units (NTU) in water. Chitosanreduced the algal content effectively by flocculation and settling. Theflocculation efficiency is very sensitive to pH, and reached a maximum at pH7.0for the freshwater species, but lower for the marine species. The optimalchitosan concentration that is required to effect maximum flocculation dependedon the concentration of alga. Flocculation and settling were faster whenconcentrations of chitosan higher than optimal are used. The settled algalcellsare intact and live, but will not be redispersed by mechanical agitation. Thede-algated water may be reused to produce fresh cultures of algae.     

Inhibition of chitosan-immobilized urease by slow-binding inhibitors: Ni, F and acetohydroxamic acid

The inhibitions by Ni²⁺ and F⁻ ions and by acetohydroxamic acid of jack bean urease covalently immobilized on chitosan membrane was studied (pH 7.0, 25°C) and compared with those of the native enzyme. The reaction progress curves of the immobilized urease-catalyzed hydrolysis of urea were recorded in the absence and presence of the inhibitors. They revealed that the inhibitions are of the competitive slow-binding type similar to those of native urease. The immobilization weakened the inhibitory effect of the inhibitors on urease as measured by the inhibition constants K_i^*. The increase in their values: 17.9-fold for Ni²⁺, 26.5-fold for F⁻ and 1.7-fold for acetohydroxamic acid, was accounted for by environmental effects generated by heterogeneity of the urease–chitosan system: (1) mass transfer limitations imposed on substrate and reaction product in the external solution, and (2) the increase in local pH on the membrane produced by both the enzymatic reaction and the electric charge of the support. By relating the K_M/K_i^* ratio to the electrostatic potential of chitosan it was found that while the reduced Ni²⁺ inhibition is mainly brought about by the potential, inhibition by acetohydroxamic acid is independent of the potential, and the acid inhibits urease in its non-ionic form. The reduction in F⁻ inhibition was ascribed to the increased pH in the local environment of the immobilized enzyme.