International Journal of Biological Macromolecules 51 (2012) 18–24 Contents lists available at SciVerse ScienceDirect International Journal of Biological Macromolecules jo u rn al hom epa ge: www.elsevier.com/locate/ijbiomac Modification and characterization of cellulosic cotton fibers for efficient immobilization of urease M. Monier ∗ , A.M.A. El-Sokkary Chemistry Department, Faculty of Science, Mansoura University, Mansoura, Egypt a r t i c l e i n f o Article history: Received 10 April 2012 Accepted 19 April 2012 Available online 26 April 2012 Keywords: Cotton Grafting Urease Acrylonitrile a b s t r a c t Cotton fibers were first grafted by polyacrylonitril in the presence of KMnO 4 and oxalic acid as a combined redox initiator. Moreover, modification of the grafted cotton fibers was done by changing the nitrile group ( CN) into hydrazidine group through the reaction with hydrazine hydrate, then the fibers were activated by glutaraldehyde to introduce free aldehyde groups which were able to react with amino groups of urease to form Schiff’s base, and result in cotton fibers immobilized urease. The efficiency of the immobilization was evaluated by examining the relative enzymatic activity of enzyme before and after the immobilization of urease. The results showed that the optimum temperature of immobilized urease was 35 ◦ C, which was higher than that of the free enzyme (30 ◦ C), and the immobilized urease exhibited a higher relative activity than that of free urease over 35 ◦ C. The optimal pH for immobilized urease was 6.5, which was lower than that of the free urease (pH 7.0), and the immobilization resulted in stabilization of enzyme over a wider pH range. The kinetic constant value (K m ) of immobilized urease was higher than that of the free urease. However, the thermal and operational stabilities of immobilized urease have been improved greatly. © 2012 Elsevier B.V. All rights reserved. 1. Introduction Cellulose is the most abundant natural, polysaccharide in the world. It has been used as a material for centuries in all types of practical uses. Social concerns for sustainable green products are encouraging the efficient exploitation of cellulose [1]. Cellulosic cotton fibers are generally strong, with high mechani- cal properties. In addition, they are also hydrophilic, but insoluble in water, stable to chemicals, non-toxic to living bodies, reproducible, recyclable and biocompatible. With these specific and promising characteristics of cotton, modification techniques to promote these original properties or to add new functionalities to cellulose have been studied. Chemical modifications have been positioned at the center of the field of cellulose modification [2,3]. Chemical treatment of cellulose materials using oxidizing agents is quite a frequent technique in cellulose chemistry aim- ing to functionalize cellulose with some active functional groups. During the oxidation of cellulose, aldehyde, ketone and carboxyl groups may be formed in the cellulose, depending on the nature of the oxidizing agent and the conditions of oxidation. Most oxidations proceed with low selectivity. Oxidations reactions of ∗ Corresponding author. Tel.: +20 10 03975988. E-mail address: monierchem@yahoo.com (M. Monier). cellulose with periodate were carried out with a high selectiv- ity [4–10]. This reaction takes place between C 2 –C 3 bond of the glucopyranoside ring and leads to the formation of two aldehyde groups at C 2 and C 3 positions; the resulting compound is the dialde- hyde cellulose (DAC). Another type of important chemical modification has been extensively studied many years ago which is grafting of different vinyl monomers onto polysaccharides with the aim of obtaining different functional products. Composite is a term given to the products of graft copolymerization reaction of polysaccharide and vinyl monomer in the presence of initiator [11–15]. These graft copolymerization reactions have been carried out by different initiation techniques such as gamma irradiation [16–19] and chemical initiation [20]. Modifications of cellulose and its derivatives through graft copolymerization of different vinyl monomers gives new materials for composite membranes [20,11] metal ion sorption and enzyme immobilization [12]. Urease which catalyzes the degradation of urea to ammonia and carbon dioxide, has been used in an immobilized form in kidney machines for blood detoxification. According to one report approx- imately half a million patients worldwide are being supported by hemodialysis [21]. Urease occupies a unique place in enzymology in that it has been the first enzyme to be crystallized. Its immobilized form has found broad applications, such as blood detoxification in 0141-8130/$ – see front matter © 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.ijbiomac.2012.04.019