Carbaryl insecticide conjugation onto chitosan via iodochitosan and chitosan carbonyl imidazolide precursors S. Chirachanchai * , A. Lertworasirikul, W. Tachaboonyakiat The Petroleum and Petrochemical College, Chulalongkorn University, Bangkok 10330, Thailand Accepted 7 July 2000 Abstract Chitosanconjugatedwith1-naphthylmethylcarbamateorcarbarylCBR),werepreparedbytwomoleculardesigns,i.e.withoutspacervia iodochitosan to obtain chitosan-carbaryl Type 1, CHI-CBR), and with spacer by using N,N 0 -carbonyldiimidazole CDI) to obtain chitosan acetate-carbonyl imidazolide-carbaryl Type 2, CA-CDI-CBR). The chitosan precursors of Types 1 and 2 were accomplished for 50±60% substitution as con®rmed by FT-IR, NMR, and elemental analysis. The conjugation of carbaryl onto iodochitosan Type I) was achieved via alkylationof N-substitutedamideusingNaHasacatalyst.Thecouplingreactionofcarbarylontochitosanacetatewassucceededbycarbonyl imidazolide which proceeded by nucleophilic substitution. The introduction of carbaryl was identi®ed from the ester peak at 1707 cm 21 by FT-IR curve ®tting technique. q 2001 Elsevier Science Ltd. All rights reserved. Keywords: Chitosan; Iodochitosan; Carbonyldiimidazole; Chitosan acetate; Carbaryl; Drug conjugation; Insecticide 1. Introduction Chitin±chitosan copolymer Scheme 1) is the second most abundant natural occurring polymer next to cellulose, found as the major constituent of the exoskeleton of crusta- ceans and insects as well as the cell wall of bacteria and mushrooms. Chitin±chitosan has received much attention due to its applications in value added products in various ®elds owing to its speci®c properties of biodegradability Xu, McCarthy, Gross, & Kaplan, 1996) and biocompatibil- ity Prudden, Miegel, Hanson, Friedlich, & Balassa, 1970), together with the possibility for physical Mi, Wong, Shyu, & Chang, 1999; Sawayanagi, Numbu, & Nagai, 1982; Somorin, Nishi, Tokura, & Noguchi, 1979) and chemical modi®cations Kurita, Ishii, Tomita, Nishimura, & Shimoda, 1994). Chitosan gives higher potential chemical modi®cations than chitin owing to an additional reactive aminogroupatC-2Fujii,Kumagai,&Noda,1980;Hirano, Ohe, & Ono, 1976; Yalpani & Hall, 1984; Nishimura, Kongo, & Kurita, 1991) besides the secondary hydroxyl at C-3 and primary hydroxyl at C-6 Nagasawa, Toshira, Inoue, & Tonoura, 1971; Kurita et al., 1992). In the past decades, chitin±chitosan derivatives received agreatinterestastheadvancedpolymericmaterialsfordrug delivery system DDS) Ohya, Nonomura, & Ouchi, 1995; Mietal.,1997;Onishi,Machida,&Nagai,1994)inmedical and pharmaceutical areas. The present work is, thus, oriented on the utilization of chitosan in agriculture Hirano &Nagao,1989)byintroducinginsecticideontochitosanvia chemical conjugation. 1-naphthyl methylcarbamate or carbaryl CBR) Scheme 1), the short application interval but widely used insecticide, was applied as a model drug. The present work is focused on the preparation of CBR conjugated chitosan by designing into two types Scheme 2), i.e. Type 1, to enhance the stability of carbaryl through chitosan polymer chains by connecting carbaryl directly on chitosan unit, and Type 2, to achieve the delivery system controlled by the stability of the spacer group attached between chitosan main chain and carbaryl. 2. Experimental 2.1. Materials Chitosan with a degree of deacetylation DD) 75.8% was provided by the Asian Institute of Technology, Bangkok, and DD 85.9% was the product from Wako Chemicals, Japan. N,N 0 -carbonyldiimidazole was produced by TCI, Japan. Chloroform, methanol and hydrochloric acid were purchased from J.T. Baker, USA. Acetic acid, N,N 0 - dimethylformamide, benzene, and sodium hydroxide were the products from UNIVAR, Australia. Sodium iodide and Carbohydrate Polymers 46 2001) 19±27 0144-8617/01/$ - see front matter q 2001 Elsevier Science Ltd. All rights reserved. PII:S0144-861700)00275-7 www.elsevier.com/locate/carbpol * Corresponding author. Fax: 166-2-215-4459. E-mail address: csuwabun@chula.ac.th S. Chirachanchai).