Modification of polysaccharides

A practical method of modification of polysaccharides by clean oxidation using H2O2 as oxidant and cheap iron phthalocyanine as catalyst has been developed. Since no acids, bases or buffers and no chlorinated compounds were used, a pure product can be recovered without additional treatment. Importantly, this flexible method provides materials with a wide range of DScho and DScooh just by an appropriate choice of the reaction conditions. Oxidized polysaccharides thus obtained possess various, tailormade hydrophihc/hydrophobic properties which have been tested successfully in cosmetic and other apphcations. 

Recently Carraher, Naoshima and coworkers effected the modification of polysaccharides employing organostannanes and bis(cyclopenta-dienyl)titanium dichloride, BCTD (20-25). Here we report the modification of dextran employing the interfacial condensation technique using various phase transfer agents utilizing BCTD and dibutyltin dichloride, DBTD. 

Bacterial, plant, and fungal enzymes for degradation/modification of polysaccharides left-hand-twisted /8-solenoid with L-type cross section... 

Polysaccharides are chemically less stable than most other supports presented in this chapter. Chemical modification of polysaccharides can increase the solubility or... 

Irreversible inactivation of Ta bacteriophage also occurred when the phage was incubated with periodate-oxidized polyglucose 11 at pH 8.5-10.0 in the presence of 0.1 M borate buffer. Interpretation of the data is difficult, in view of the known lability and modification of polysaccharide polyaldehydes in alkaline media, 14 especially since phage inactivation occurs only at elevated pH values in the presence of polyaldehyde and 0.1 M borate buffer. 

Prepare the protein or macromolecule to be thiolated in a non-amine-containing buffer at pH 8.0. For the modification of ribosomal proteins (often cited in the literature) use 50 mM triethanolamine hydrochloride, 1 mM MgCl2, 50 mM KC1, pH 8. The magnesium and potassium salts are for stabilization of some ribosomal proteins. If other proteins are to be thiolated, the same buffer may be used without added salts for stabilization. Alternatively, 50 mM sodium phosphate, 0.15 M NaCl, pH 8, or 0.1 M sodium borate, pH 8.0 may be used. For the modification of polysaccharides, use 20 mM sodium borax, pH 10, to produce reactivity toward carbohydrate hydroxyl residues. Dissolve the protein to be modified at a concentration of 10 mg/ml in the reaction buffer of choice. Lower concentrations also may be used with a proportional scaling back of added 2-iminothiolane. 

The conversion of dextran with 1,2-epoxy-3-phenoxypropane, epoxyoctane or epoxydodecane may be exploited for the preparation of amphiphilic dextran derivatives. Polymeric surfactants prepared by hydrophobic modification of polysaccharides have been widely studied, starting with the pioneering work of Landoll [261]. Neutral water-soluble polymeric surfactants can be obtained by reaction of dextran with 1,2-epoxy-3-phenoxypropane in 1 M aqueous NaOH at ambient temperature (Fig. 35, [229,233]). The number n of hydrophobic groups per 100 Glcp units varies between 7 and 22 depending on the reaction conditions. 2-Hydroxy-3-phenoxy propyl dextran ethers (DexP) behave like classical associative polymers in aqueous solution. In dilute solution, the intrinsic viscosity decreases significantly whereas... 

Ball, D. H., Cimecioglu, A. L., Kaplan, D. L., and Huang, S. H. (1994). Site-selective modification of polysaccharides under homogeneous conditions. New anhydro and cationic polymers derived from amylose and pullulan. 208th Annual Meeting, Am. Chem. Soc., Div. Cellulose, Paper and Textiles, August 21-26, Washington, DC. 

Chemical Modification of Polysaccharides without Attempted Depolymerization... 

Dolence, Eric K. Hu, Chen-Ze Tsang, Ray Sanders, Clifton G. Osaki, Shigemasa. Electrophilic polyethylene oxides for the modification of polysaccharides, polypeptides (proteins) and polymer surfaces. (Surface Engineering Technologies, Division of Innerdyne, Inc., USA). US patent 55650234 1997. 

Pramendra Kumar is an Assistant Professor in the Chemistry Department at M.J.P. Rohilkhand University, Bareilly. He obtained his Master of Science from C.C.S. University, Meerut and Master of Engineering from Delhi College of Engineering. His research interests include modification of polysaccharides, synthesis of multifunctional nano materials and synthesis of nano bio-composites for their various applications e.g. water remediation, enzyme immobilization and other adsorbent applications. 

Modification of polysaccharides comprises polymerisation, depolymerisation (formation of oligosaccharides) and tailoring (selective adjustment of primary structure) (1). Polysaccharides can be modified chemically or with enzymes. Chemical modification is usually easy and cheap but not very specific. In addition, consumers increasingly dissent from chemically processed food additives. Enzymatic modification is more specific and natural . 

It is to be expected that chemical modification of polysaccharides will become of even higher importance in the near future. In addition to the limitations of petroleum-based alternatives and the requirement of sustainability, one reason is the wide... 

Modification of Polysaccharides and Oligosaccharides, and Uses of Modified Polysaccharides and Oligosaccharides... 

Tomasik, P.A. Chemical modifications of polysaccharides. In Chemical and Functional Properties of Food Saccharides-, CRC Press New York, 2003 pp. 217-229. 

Modification of polysaccharides through controlled/living radical polymerization grafting—towards the generation of high performance hybrids, 31,1751-1772. 

Kierulff, J.V. Modification of polysaccharides by means of phenol oxidizing enzyme. PCT world patent ( plication WO 99/32652. 

This method of extraction is cost-effective and simple. However, the method is time consuming and requires high extraction temperatures that may lead to degradation and structural modification of polysaccharides [71]. Relative advantages and limitatimis of hot water extraction procedure in comparison with other extraction methods are summarized in Table 1. 

It is evident from the literature that microwave-assisted extraction (MAE) method is much faster, consumes less solvent, and efficient in terms of yield than traditional reflux extraction of polysaccharides (Table 1) [86,87]. However, caution should be exercised to limit the microwave irradiation power as higher power can potentially cause structural modification of polysaccharides [81]. 

Scheme 1.19 Modification of polysaccharides using hydrazines, with subsequent reduction with sodium cyanoborohydride.

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