%0 Journal Article
%T Quaternary Salts of Chitosan: History, Antimicrobial Features, and Prospects
%A Douglas de Britto
%A Rejane Celi Goy
%A Sergio Paulo Campana Filho
%A Odilio B. G. Assis
%J International Journal of Carbohydrate Chemistry
%D 2011
%I Hindawi Publishing Corporation
%R 10.1155/2011/312539
%X Recently, increasing attention has been paid to water-soluble derivatives of chitosan at its applications. The chemical characteristics and the antimicrobial properties of these salts can play significant role in pharmacological and food areas mainly as carriers for drug delivery systems and as antimicrobial packaging materials. In the current paper, a historical sequence of the main preparative methods, physical chemistry aspects, and antimicrobial activity of chitosan quaternized derivatives are presented and briefly discussed. In general, the results indicated that the quaternary derivatives had better inhibitory effects than the unmodified chitosan. 1. Background One of the first reports about methylation process of chitosan was presented by Wolfrom et al. in their study on carboxyl-reduced heparin published in 1963 [1]. Despite employing a very methylant agent (dimethylsulfate), only a 3,6-O-methylated product was claimed by the authors. In the seventies, Nudga et al. studied a series of N-alkylated chitosans [2¨C4] and described the preparation of a derivative with a 78% of quaternary amino sites. Then, Muzzarelli and Tanfani, in 1985 [5], prepared N-trimethyl chitosan iodide in a controlled three-step reaction: (a) started by a preparation of an N-alkyl chitosan via reductive alkylation, in which the chitosan amino groups react with appropriated aldehyde, generating a Schiff¡¯s base; (b) this compound is treated with a reducing agent, to yield the corresponding N-alkyl chitosan (c) then an overmethylation with an alkyl halide is carried out, generating, finally, the quaternary salt. With these sequences Muzzarelli and Tanfani obtained N,N,N-trimethyl chitosan (TMC) by reacting N-permethylated chitosan, which was previously prepared by treating chitosan with formaldehyde followed by reduction with sodium borohydrade and trimethylation with methyl iodide. Although, according to the authors, the product 60% trimethylated was not water soluble and characterized only with 13C NMR and elemental analysis. This effort was made, aiming its application as antibiotic and ion exchange material. In the following year, Domard et al. [6], also reacting chitosan with methyl iodide, gave an important contribution mainly on the role of the reagents in the quaternization. They established that the combination of N-methyl-2-pyrrolidone (NMP) and NaOH favors the quaternization better than sole addition of organic bases, for example, triethylamine. In order to understand the chemical structure of the TMC, several papers were published, emphasizing the features and
%U http://www.hindawi.com/journals/ijcc/2011/312539/