Functional modification of agarose: A facile synthesis of a fluorescent agarose–guanine derivative
Introduction
Fluorescence phenomenon was harnessed to study agarose gelling system by Hayashi, Kinoshita, and Yasueda (1980). Polysaccharide conjugates were prepared with fluorescein to distinguish underivatized polysaccharides as well as for localizing and quantifying cell surface proteins in cell biology research (Glabe, Harty, & Rosen, 1983). Other fluorescent polysaccharides and their conjugates were prepared with an eye to identifying biomolecules, sensing pH as well as preparing cellulose based organic light emitting diode (Karakawa et al., 2007, Kobayashi et al., 1990, Qiu et al., 2005, Schulz et al., 2009, Suizhou et al., 2003). Urreaga and De la Orden (2007), have reported modification of cellulose with amino compounds and their fluorescence properties. Synthesis and fluorescent properties of pyrene-lableled guanine base was reported for studying the secondary structures of G-rich DNA (Okamoto, Kanatani, Ochi, Saitob, & Saito, 2004). There exist numerous reports in the literature on the modification of polysaccharides employing various strategies, e.g. grafting, cross linking, etc.
In an ongoing program of our laboratory on modification of seaweed polysaccharides for preparing new materials with improved functional properties (Meena et al., 2006a, Meena et al., 2006b, Meena et al., 2007a, Meena et al., 2008, Prasad et al., 2005a, Prasad et al., 2005b, Prasad et al., 2006a, Prasad, Meena, & Siddhanta, 2006), we report herein functional modification of agarose (Fig. 1) by grafting guanine (Fig. 1) on to agarose by a water based method. This guanine modified agarose exhibited exceptionally strong fluorescent properties. Guanine is 2-amino-6-hydroxypurine, which is one of the four nitrogenous bases found in nucleic acids (Finar, 2004). Agarose is a hydrophilic polymer and is widely used in biomedical applications and bioengineering. The basic disaccharide repeating units of agarose consists of (1,3) linked β-d-galactose (G) and (1,4) linked α-l-3,6-anhydrogalactose (A) (Fig. 1) (Rochas & Lahaye, 1989). To our knowledge, this agarose derivative and its effects are being reported for the first time.
Section snippets
Materials
Agarose used in this study was extracted from the seaweed Gracilaria dura as described in our previous work (Meena, Siddhanta, et al., 2007). Other chemicals used in this study (e.g. sodium hydroxide, potassium persulphate (KPS) and guanine, LR grade) were purchased from S.D. Fine Chemicals Ltd., Mumbai (India).
Synthesis of agarose-graft-guanine
A known weight of agarose (100 mg) was dissolved in 20 ml of hot water, to which 10.0 mg (0.738 mM) of KPS was added and mixed well. In a beaker, a known weight (50 mg) of guanine was
Yield and grafting pattern
Yield of the product was 90% which was calculated on the basis of the nitrogen content of the product (Kjeldahl's estimation) with respect to the total quantities of agarose and guanine that were used in the synthesis. Grafting percent (G%) in the product was 135%, whereas its total conversion (C%) value was 70% (cf. Meena et al., 2008).
FT-IR spectroscopy
Strong bands at 1642 for agarose (bonded H–O–H; Christiaen and Bodard, 1983, Prasad et al., 2006a) and 1673 and 1697 cm−1 for guanine for amide carbonyl (
Conclusion
A facile water based synthesis and characterization of agarose–guanine derivative has been described. This derivative exhibited substantially enhanced fluorescence emission, e.g. 105% greater than guanine at 5 × 10−5 M concentration. The remarkable fluorescent activity of the agarose–guanine derivative predisposes it for its potential uses as sensors in various applications including biomedical ones (cf. Donati, Gamini, Vetere, Campa, & Paoletti, 2002).
Acknowledgements
Ministry of Earth Sciences, New Delhi (MoES/9-DS/6/2007-PC-IV) is gratefully acknowledged for an award of a fellowship to MDO. Sincere thanks are accorded to the Discipline of Analytical Sciences for the spectral and SEM analyses.
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