Int. J. Mol. Sci. 2015, 16, 9064-9077; doi:10.3390/ijms16059064
International Journal of
ISSN 1422-0067 www.mdpi.com/journal/ijms
Chitosan Derivatives as Important Biorefinery Intermediates.
Quaternary Tetraalkylammonium Chitosan Derivatives Utilized in Anion Exchange Chromatography for Perchlorate Removal
Shakeela Sayed and Anwar Jardine *
Department of Chemistry, University of Cape Town, Main Road Rondebosch, Cape Town 7700,
South Africa; E-Mail: email@example.com * Author to whom correspondence should be addressed; E-Mail: firstname.lastname@example.org;
Tel.: +272-1650-4010; Fax: +272-1650-5195.
Academic Editor: James H. Clark
Received: 30 March 2015 / Accepted: 16 April 2015 / Published: 23 April 2015
Abstract: There has recently been great interest in the valorization of biomass waste in the context of the biorefinery. The biopolymer chitosan, derived from chitin, is present in large quantities of crustacean waste. This biomass can be converted into value-added products with applications in energy, fuel, chemicals and materials manufacturing. The many reported applications of this polymer can be attributed to its unique properties, such as biocompatibility, chemical versatility, biodegradability and low toxicity. Cost effective water filters which decontaminate water by removal of specific impurities and microbes are in great demand. To address this need, the development of ion exchange resins using environmentally friendly, renewable materials such as biopolymers as solid supports was evaluated. The identification and remediation of perchlorate contaminated water using an easy, inexpensive method has come under the spotlight recently. Similarly, the use of a low cost perchlorate selective solid phase extraction (SPE) cartridge that can be rapidly employed in the field is desirable. Chitosan based SPE coupled with colorimetric analytical methods showed promise as a renewable anion exchange support for perchlorate analysis or removal. The polymers displayed perchlorate retention comparable to the commercial standard whereby the quaternized iron loaded polymer TMC-Fe(III) displayed the best activity.
Keywords: biorefinery; chitosan; water treatment; perchlorate; solid phase extraction; iron
Int. J. Mol. Sci. 2015, 16 9065 1. Introduction
Biomass offers an alternative source of environmentally friendly and sustainable materials. When investigating biomass and potential applications thereof, the concept of the biorefinery is raised. This concept deals with the translation of biomass into value-added products such as energy, fuel, chemicals and materials . It is important to note that the best biomass utilized is nonfood feedstocks such as food waste, agricultural residues, forestry wastes, industrial, sanitary and solid urban residues . Typical feedstocks which have been investigated for conversion into useful products includes lignocellulosic biomass (wood, straw and corn stover), cellulose, starch, chitin and chitosan, zein, vegetable oil, pectin and waxes to name a few . The majority of these come from agricultural waste however; there has been increasing interest in marine biomass. These aquatic biorefineries avoid problems faced by terrestrial biorefineries such as change in land usage . The major material obtained from marine biomass is the biopolymer chitin. Sources of chitin include the exoskeletons of arthropods such as crustaceans (crabs, lobster, shrimp), fungi, insects (ants), annelids, cephalopods (squid and octopus) etc. . It has been reported that more than 6 mega tons of crustacean shell waste is discarded per annum .
The utilization of chitin and its deacetylated form chitosan is therefore of great importance where the lobster itself can be seen as being part of a closed biorefinery. Figure 1 demonstrates the potential and current uses of the lobster and parts thereof.
Figure 1. The lobster biorefinery.
Modifications of chitosan can improve the polymers’ inherent properties which include biocompatibility, chemical versatility, biodegradability and low toxicity. These modifications can be tailored for a specific application . For example, quaternary derivatives of chitosan have been shown to possess improved properties with an increase in solubility attributed to the presence of the quaternized nitrogen. Two of the most common derivatives are 3-trimethylammonium-2-hydroxypropyl-N-chitosan chloride (CHI-Q188) and N,N,N-trimethyl chitosan chloride (TMC) (Figure 2) . CHI-Q188 was proven to have antimicrobial
Int. J. Mol. Sci. 2015, 16 9066 properties and could also act as a biocide with proven activity against Escherichia coli (E. coli),
Staphylococcus aureus (S. aureus) and Pseudomonas aeruginosa (P. aeruginosa) . This polymer has previously been applied as a flocculent in water treatment and minimization of biofouling due to its antimicrobial activity . The antimicrobial activity of TMC has been demonstrated by Jia et al. who showed better inhibition compared to chitosan against E. coli . Chitosan itself has been used in water remediation primarily as a flocculent and metal chelator . Due to the versatility of this polymer, chitosan derivatives have been utilized for the prevention of point of source and point of use contamination. In addition, chitosan has been used in the removal of microbial pathogens in drinking water due to the polymer’s inherent antimicrobial activity . For these reasons, the application of chitosan as a water purification resin is appealing.
Figure 2. The structures of chitosan (1), 3-trimethylammonium-2-hydroxypropyl-N-chitosan chloride (CHI-Q188) (2), N,N,N-trimethyl chitosan chloride (TMC) (3) and Amberlite IRA 400 Cl.
Recently, there has been increasing interest in water purification using sustainable natural resources . Potable water is key to sustainable livelihoods and an integral part of any biorefinery .
Food as well as water security is inseparable and under constant threat of pollution. In particular, inorganic contaminants that are passed on in the food chain such as perchlorate deserves special attention. Perchlorate salts are highly water soluble and can easily leach from soil into groundwater and potentially end up in the food chain. This ion competitively inhibits the uptake of iodide by the thyroid, which can result in decreased hormone production and diminished mental development . In 2008, the United States Environmental Protection Agency set an Interim Drinking Water Health Advisory level of 15 µg/L for perchlorate . Anion exchange where the perchlorate anion (ClOସି ) is swapped for less harmful anions such as chlorides (Cl−) or hydroxides (OH−) is a popular method of remediation .