Chitosan Catalyst Research Articles

Chitosan as an active support for assembly of metal nanoparticles and application of the resultant bioconjugates in catalysis

Metal nanoparticle–chitosan (NPs–chitosan) bioconjugates were formed by exposure of chitosan to an aqueous solution of metal salts under thermal treatment. The metal nanoparticles that are formed strongly bound to chitosan, which encouraged us to investigate their catalytic performance. It was demonstrated that the metal NPs–chitosan bioconjugates functioned as effective catalysts for the reduction of 4-nitrophenol in the presence of NaBH 4, which was monitored by means of spectrophotometry as a function of reaction time. The silver NPs–chitosan bioconjugates exhibited excellent catalytic activity and were reusable for up to seven cycles. In contrast, the gold NPs–chitosan catalyst displayed poor catalytic activity, even in the second cycle. A highlight of our approach is that chitosan simultaneously acts as an active support for the synthesis and assembly of nanoparticles, and the resultant bioconjugates bear the advantage of easy separation from the reaction medium.

Synthesis of Novel Spiro Cyclic 2-Oxindole Derivatives of 6-Amino-4H-Pyridazine via [3+3] Atom Combination Utilizing Chitosan as a Catalyst

Azaenamines were reacted with 3-cyanomethylidene-2-oxindoles using chitosan catalyst to yield spirocyclic 2-oxindole derivatives of 6-amino-4H-pyridazine and fused pyridazinoquinazolines.

Copper Complexes Stabilized by Chitosans: Peculiarities of the Structure, Redox, and Catalytic Properties

Peculiarities of the structure and physicochemical properties of copper–chitosan complexes prepared by different methods were studied by IR, UV-visible, ESR spectroscopy, and electron microscopy. The catalytic activity of redox copper centers stabilized by the chitosan matrix in the reactions of oxidation of o- and p-dihydroxybenzenes in an aqueous medium was determined. Quantitative ESR measurements provide evidence for the localization of virtually all copper ions introduced in the initial heterogeneous chitosan samples with copper contents below 1.5 wt % in the form of isolated Cu2+ ions in square planar coordination. The chitosan matrix was shown to strongly bind copper ions under conditions of redox transformations in the catalytic tests or upon prolonged heating in boiling water. Reoxidation of the samples with H2O2 results in quantitative restoration of the initial ESR signal of Cu(II). Heterogenized copper–chitosan samples exhibited high activity and stability in the catalytic oxidation of dihydroxybenzenes into quinones, whereas the homogeneous system was characterized by irreversible poisoning due to formation of copper–hydroquinone complexes. Preparation of the binary composite system with a thin heterogeneous copper–chitosan film supported on a macroporous silica allows one to dramatically enhance the specific catalytic activity and the efficiency of the active component. Such an approach may turn out to be useful in the synthesis of supported chitosan catalyst with a low noble metal content.