Novel derivatives of chitosan and their antifungal activities in vitro
Introduction
As one of the most abundant naturally occurring compounds, chitosan has attracted people’s attention on account of its unique physiochemical characteristics and its bioactivities.1, 2, 3, 4 However, because of its poor solubility in water, the use of chitosan is limited in many fields. In order to improve its aqueous solubility, many derivatives of chitosan have been synthesized, and carboxymethyl chitosan (CMCTS) is the most important one. Generally, CMCTS is synthesized by the reaction of chitosan and chloroacetic acid in 2-propanol in the presence of KOH. CMCTS can easily dissolve in water, which enlarges the scope of the use of chitosan.5, 6 However, there seems to be little further study on the modification of CMCTS. In the CMCTS molecule, the NH2 groups have a degree of substitution (DS) of 0.1–0.2,7 so there are also enough NH2 groups to take part in other reactions for CMCTS that is obtained from highly deacetylated chitosan.
Antifungal activity is one of the most important bioactivities of chitosan, and earlier studies have reported that chitosan can reduce the growth of phytopathogenic fungi, which are harmful to field crops, fruit, and vegetables.8, 9, 10, 11, 12, 13, 14 In studies on the antifungal activity of chitosan, researchers have focused most of their attention on the molecular weight and the degree of deacetylation of chitosan, which affect its activities. But, little work has been reported on the antifungal activities of the derivatives of chitosan.
In this paper, three kinds of Schiff bases of CMCTS are reported, as well as their antifungal activities against Valsa mali (V. mali), Alternaria solani (A. solani), and Fusarium oxysporium f. sp. vasinfectum (F. oxysporium f. sp. vasinfectum) from a study that employed the method of Jasso de Rodríguez and co-workers.15
Section snippets
Materials
Chitosan was purchased from Qingdao Baicheng Biochemical Corp. (China). Its degree of deacetylation was 97%, and the viscosity average-molecular weight was 2.0 × 105. Salicylaldehyde was purchased from Fluka Chemical Co. The IR spectrum was measured by a Nicolet Magne-Avatar 360 instrument using KBr disks. The elemental analyses (C, H, N) were performed on a Carlo–Erba 1106 elemental analyzer. The other reagents were of analytical grade and used without further purification. Three
Structure and physicochemical characteristics of the derivatives of chitosan
The results of the elemental analyses and the color of the Schiff bases are listed in Table 1, and the IR spectra of chitosan, CMCTS, and the Schiff bases are shown in Figure 1. As shown in Figure 1, the IR spectra of chitosan shows peaks assigned to the saccharide structure at 897.85 and 1154.98 cm−1 and characteristic amino peak at 1600.03 cm−1. CMCTS is confirmed by the absorption bands at 1600.57 [νsym(CO2)] and 1416.06 cm−1 [νas(CO2)].19 The elemental analyses results indicate that the
Conclusions
Antifungal activity is one of the most important bioactivities of chitosan and it will be improved in some of the derivatives, which is determined by the groups grafted to chitosan. CMCTS dissolves in water easily and water solubility remains after appropriate modification. Some of the derivatives of CMCTS have good bioactivities, and from our experiments, two kinds of Schiff bases of CMCTS have better antifungal activities than those of chitosan and CMCTS against V. mali, A. solani and F.
Acknowledgements
This work was financially supported by the Innovational Foundation of Chinese Academy of Science (KZCX3-SW-215). The authors are grateful to Professor Xiangli Dong of the Laiyang Agricultural College, for their technical assistance.
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