Synthesis of Water-Soluble Quaternary Ammonium Chitosan Derivatives and Their Potential Applications as Biocides.
Date of Award
Doctor of Philosophy (PhD)
William H. Daly
Chitosan is a polysaccharide obtained by deacetylating chitin, the major constituent of the exoskeleton of crustaceans. The driving force in the development of new applications for chitosan is not only is it naturally abundant, but it is non-toxic and biodegradable. It can be used as a chelating agent, coagulating agent, and flocculant. It has also been used to reduce blood cholesterol and as a dietary supplement. Chitosan derivatives have been synthesized for cosmetic applications and have been reported to exhibit antimicrobial activity. Further investigation of this potential activity is warranted due to increased antibiotic resistance. The focus of this work is the synthesis and characterization of water-soluble quaternary ammonium chitosan derivatives as potential biocides. Chitosan quat-188 exhibits excellent biocidal activity against E. coli and S. aureus. The adjuvant activity of chitosan quat-188 with the antibiotic rifampin has been demonstrated against Mycobacterium tuberculosis, showing an MIC of 4 mug/mL. We have developed a facile method for the production of acetylated and butyrylated chitosan quat-188 derivatives that also show antimicrobial activity. N-carboxymethyl chitosan is a water soluble derivative that can be either monocarboxylated or dicarboxylated. Varying the amount of reagents and the solvent conditions lead to different ratios of mono vs. disubstitution, ranging from 55/45 of mono/di to 17/83 of mono/di. The solid state 15N NMR spectra of chitin, chitosan and chitosan derivatives were measured. The chemical shifts relative to an ammonium nitrate reference were observed as follows: amide group of chitin, 157.6 ppm; the 2-amino group of 57.7 ppm; the quaternary ammonium group and the substituted 2-amino group in chitosan quat-188 were 84.3 and 63.5 ppm, respectively. The N-carboxylated derivatives exhibited a broad band from 40--100 ppm and centered around 64 ppm. The amide nitrogen in the aminoalkylcarbamoyl chitosan appeared at 149 ppm while the 2-amino group and the tertiary amine appeared as a broad band around 60.9 ppm.
Logan, Dewayne, "Synthesis of Water-Soluble Quaternary Ammonium Chitosan Derivatives and Their Potential Applications as Biocides." (2001). LSU Historical Dissertations and Theses. 381.