Synthesis, characterization and biological activity of Schiff bases based on chitosan and arylpyrazole moiety

 
 
 
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1. Introduction 
Chitosan (
β
-(1–4)-linked-d-glucosamine) is obtained by the deacetylation of chitin (
β
-(1–4)-linked 
N-acetyl-d-glucosamine), one of the most abundant natural polysaccharide in nature [1, 2]. Its 
structure is basically constituted of D-glucosamine units, with contents of N-acetyl-D-glucosamine 
in the range of 0–50% [3]. This polysaccharide displays interesting properties, such as abundant 
resources, nontoxicity, biodegradability, biocompatibility, and antibacterial properties. Therefore, it 
has prospective applications in many fields such as agriculture, pharmaceuticals, cosmetics, food 
industries, environmental protection, and biotechnology [4-10]. Antibacterial activity is one of the 
most important bioactivities of chitosan. It has been shown to be an effective agent against an array 
of common bacteria (Gram-positive as well as Gram-negative) and fungi [11]. Moreover, chitosan 
has several advantages over other types of antimicrobial agents because it possesses a higher 
antibacterial activity, a broader spectrum of activity, a higher killing rate, and a lower toxicity 
toward mammalian cells [12]. 
The reactive amino and hydroxyl groups of chitosan can be used to chemically alter its 
properties under mild reaction conditions [13
-16
]. The derivation is intended to improve its 
processability, solubility, antimicrobial activity and its ability to interact with other substances [
17-
21]. 
One of the most important modifications is related to Schiff bases, which are formed from the 
condensation of amino groups on the chitosan with the added aldehyde or ketone [22-26].
These 
materials are economically feasible and widely used in the field of biocides [21, 27] and in 
coordination chemistry [28- 31]. For instance, such Schiff bases can be chelated with various metal 
ions and be used as heterogeneous catalysts [32-34].
On the other hand, pyrazoles are of interest as potent bioactive molecules in pharmaceutical 
development and possess a wide range of biological activities [35, 36]. Besides being biologically 
active, they are also used as useful synthons in organic synthesis [37]. 
Based on the above consideration, the modification of chitosan with pyrazoles as substituent 
may improve some of the physical properties and antimicrobial activity of chitosan. Therefore, the 
aim of the present study is to develop new chitosan Schiff bases with arylpyrazole moiety. These 
compounds 
will be 
characterized by various methods, such as FT-IR, XRD, elemental and thermal 
analyses. The antimicrobial assays of 
the
prepared chitosan derivatives against Streptococcus 
pneumoniae (S. pneumonia, RCMB 010010) and Bacillis subtilis (B. subtilis, RCMB 010067) as 
Gram positive bacteria, and against Escherichia coli (E. coli, RCMB 010052) as Gram negative 
bacteria and against Aspergillus fumigatus (A. fumigatus, RCMB 02568), Geotricum candidum (G. 

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candidum, RCMB 05097) and Syncephalastrum recemosum (S. recemosum, RCMB 05922) fungi 
will be 
evaluated by the diffusion agar technique.