Elsevier

Carbohydrate Polymers

Volume 89, Issue 2, 20 June 2012, Pages 354-361
Carbohydrate Polymers

Synthesis of the ketimine of chitosan and 4,6-diacetylresorcinol, and study of the catalase-like activity of its copper chelate

https://doi.org/10.1016/j.carbpol.2012.03.013Get rights and content

Abstract

In this study, a new chitosan derivative (ketimine) was synthesized by condensation of chitosan with 4,6-diacetylresorcinol (DAR) at heterogeneous medium. The ketimine derivative of chitosan (DAR-chitosan) was characterized by elemental (C, H, N), spectral (DR-UV–vis and FT-IR spectroscopy), structural (powder XRD), and morphological (SEM) analyses. The degree of substitution (DS) of DAR-chitosan was evaluated by elemental analysis and 13C CP-MAS NMR spectroscopy and found to be around 12%. The copper (II) metal complex of DAR-chitosan was prepared and characterized by FT-IR, DR-UV–vis and inductively coupled plasma-atomic emission spectroscopy (ICP-AES). Thermal behaviors of the synthesized compounds were investigated by DSC and TG-DTG-DTA analysis. The catalytic activity of copper (II) complex of chitosan derivative (DAR-chitosan-Cu) was investigated on hydrogen peroxide decomposition. The copper chelate showed high efficiency (over 80%) towards the decomposition of hydrogen peroxide as heterogeneous catalyst.

Highlights

► 4,6-Diacetylresorcinol derivative of chitosan was synthesized at heterogeneous medium. ► CSDAR-Cu has a higher thermal stability than CSDAR. ► Cu(II) complex displayed a good catalytic activity towards the decomposition of H2O2.

Introduction

Chitosan is a natural, cationic amino polysaccharide co-polymer of glucosamine and N-acetylglucasamine, obtained by the alkaline, partial N-deacetylation of chitin (Muzzarelli, 1977). Chitosan has been considered as a non-toxic, biodegradable, biocompatible and environmentally friendly material with many superior properties (Jigar and Sinha, 2007, Muzzarelli and Ilari, 1994). This biopolymer has applications ranging from artificial skin, photography, cosmetics, food and nutrition, ophthalmology and wastewater treatment (Ravi Kumar, Muzzarelli, Muzzarelli, Sashiwa, & Domb, 2004). In addition, chitosan has received significant interest for removal of heavy metal ions due to its good metal-binding capacities and easy reuse, as well as its relatively low cost compared with activated carbon and its possible biodegradability after usage (Muzzarelli, 2011, No and Meyers, 2000).

In the last years there have been many studies interested in chemical modification of chitosan and its derivatives to enhance their properties and consequently expand their potential applications (Heras et al., 2001, Terada et al., 1999, Yalçınkaya et al., 2010). Hence, functionalization of chitosan provided catalysts for oxidation of alkyl benzene (Chang, Wang, & Su, 2002), cyclopropanation of olefins (Sun, Xia, & Wang, 2002), Suzuki and Heck reactions (Hardy, Hubert, Macquarrie, & Wilson, 2004).

The presence of primary amine in the polymeric chain of chitosan leads to the possibility of a several chemical modifications, including the preparation of Schiff bases (Moore and Roberts, 1981, Muzzarelli et al., 1988). It is well known that, the diketone; 4,6-diacetylresorcinol (DAR) serves as a starting material for the generation of multidentate symmetrical Schiff bases (Shebl, 2009). In this sense the modification of chitosan with aldehydes and ketones to produce Schiff bases may result in a potentially complexing material for metallic species with potential analytical and environmental applications (Hardy et al., 2004, Wang et al., 2003).

It is well known that, chitosan can be chemically modified at very high degrees of substitution by homogenous reactions but at low levels by heterogeneous reactions (typically up to DS > 0.3). Although very high DS can be achieved when chitosan is dissolved in acidic solutions, many studies show that functionalization, even under mild conditions, dramatically reduces the molecular weight of the chitosan (Macquarrie & Hardy, 2005).

It has been known for about a century that the decomposition of H2O2 to H2O and O2 is considerably accelerated by many metal ions (Haber and Weiss, 1934, Kremer, 1985). The decomposition of hydrogen peroxide has been used as a model reaction for the investigation of the catalytic activity of various metal complexes and has also been studied as a catalase model. The catalase like properties of copper (II) complexes has also been investigated, but reports on this activity of copper (II)-containing systems reported are relatively scarce (Gao, Martell, & Reibenspies, 2003). The difference in reactivity of Cu(II) complexes towards H2O2 is due to the change in the redox potential of Cu(II) ions as a result of ligation with different ligands (Ozawa, Hanaki, Onodera, Kasai, & Matsushima, 1991).

The development of heterogeneous catalysts has become a major area of research recently, as the potential advantages like easy of separation, recovery, and reuse of catalysts, and the clean separation of product from the reaction mixture (Macquarrie & Hardy, 2005).

This study is aimed to synthesize of ketimine derivative of chitosan by condensation with 4,6-diacetylresorcinol (DAR) under heterogeneous reaction medium. Also, is aimed to prepare the metal complex (Cu2+) of chitosan derivative and to investigate the catalytic activity of the chelate towards to hydrogen peroxide decomposition reaction.

Section snippets

Instrumentation

Infrared (IR) spectra were recorded on a Perkin Elmer RX-1 FT-IR spectrophotometer using KBr pellets (4400–400 cm−1). Room temperature diffuse reflectance spectra in the ultra- violet and visible region (DR-UV–vis) were recorded on a Varian Cary 100 model UV-Vis spectrophotometer. Elemental analyses were carried out with LECO-CHNS-932. The surface morphology of chitosan and derivatives were examined by scanning electron microscope (SEM). The samples observed by using a JEOL JSM 5500LV Scanning

Solubility

Solubility of chitosan is related to the ionic concentration, pH, the distribution of acetyl groups along the chain, the intra-chain H bonds involving the hydroxyl groups and the molecular weight. It is well known that, solubilization of chitosan occurs by protonation of the single bondNH2 group on the C-2 position of the d-glucosamine repeat unit, whereby the polysaccharide is converted to a polyelectrolyte in acidic media (Rinaudo, 2006).

The synthesized crosslinked-chitosan derivative (DAR-chitosan) was

Conclusions

The new chitosan derivative (DAR-chitosan) was prepared by condensation of chitosan (CS) with 4,6-diacetylresorcinol (DAR) as crosslinking agent at heterogeneous medium. The result suggests that, the value of metal content of metal complex can be in a satisfaction range (6% Cu). In addition, the results of the thermal studies are shown that DAR-chitosan-Cu has a higher thermal stability than DAR-chitosan. Furthermore, the synthesized Cu(II) complex displayed a good catalytic activity towards

Acknowledgements

The author is grateful to Dr. Mahir Timur (Mustafa Kemal University) for help of preparation of 4,6-diacetylresorcinol. Also thanks the METU-Central Laboratory for CP–MAS 13C NMR analysis.

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