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Polysaccharides as Nanomaterials for Therapeutics
Published in Dan Peer, Handbook of Harnessing Biomaterials in Nanomedicine, 2021
Heparin is a linear glycosaminoglycan (GAG) composed of repeating disaccharide units of 1,4-linked uronic acid (d-glucuronic (GlcAor l-iduronic acid (IdoA) and d-glucosamine (GlcN) (Figure 5.1). The uronic acid usually comprises 90 percent l-idopyranosyluronic acid (l-iduronic acid, IdoA) and 10 percent d-glucopyranosyluronic acid (d-glucuronic acid, GlcA). In addition, there are structural variations at the disaccharide level [46]. Due to high content of sulfo and carboxyl groups, heparin has the highest negative charge density of any known biological molecule [46]. The Mw of heparin varies between 5–40 kDa and it is extracted mainly from mucosal tissues of porcine and bovine [46]. Clinically, heparin has been used as an anticoagulant since the 1930s [46]. The anticoagulant activity of heparin requires direct interaction with the serine protease inhibitor antithrombin III, which causes a conformational change that allows antithrombin III to inhibit thrombin and other serine proteases within the coagulation cascade [47]. Heparin is produced exclusively by mast cells (as opposed to the structurally related GAG heparan sulphate) [23]. Beyond its anticoagulant activity, heparin has been shown to have antiviral activity and ability to inhibit complement activation, tumor growth and angiogenesis [47].
Ocean-based sorbents for decontamination of metal-bearing wastewaters: a review
Published in Environmental Technology Reviews, 2018
R. Senthilkumar, D.M. Reddy Prasad, Govindarajan Lakshmanarao, Saravanakumar Krishnan, B.S. Naveen Prasad
Only limited studies were focussed on exploring green seaweed as biosorbent for metal ions (Table 1). Of these, Ulva species was identified as effective biosorbent for variety of metal ions. Ulva is a very common green algal type often found on rocks and on other algae around various parts of World Ocean. On dry weight basis, Ulva species generally comprises of 38% to 54% of cell wall polysaccharides with a majority of water soluble ulvan [56]. Ulvan basically comprise of glucuronic acid, sulfated rhamnose, xylose, sulfated xylose and iduronic acid [70]. Hence, ulvan behaves as an anionic polyelectrolyte as it comprises of sulphonic and carboxylic groups inside its structure; and therefore exhibits strong affinity towards various heavy metal ions. Zeroual et al. [58] examined the potential of Ulva lactuca biomass to sorb Hg(II) from aqueous solution. The batch equilibrium trial experimental results indicated that pH strongly influenced biosorption performance of U. lactuca biomass with maximum Hg(II) uptake capacities observed as 27.2, 84.7 and 149.3 mg/g at pH 3.5, 5.5 and 7, respectively, according to the Langmuir model. The authors reported major removal mechanism as ion-exchange, in which negatively charged binding sites (such as carboxylic) of the green seaweed biomass attracts and subsequently binds the positively charged Hg(II) ions. Vijayaraghavan [71] investigated the potential of Ulva reticulata to specifically biosorb nickel ions from synthetic and electroplating industrial wastewaters. Based on the preliminary batch experimental results, the author implied that highest nickel uptake was observed at optimum pH 4.5 and the results of isotherm trials at pH 4.5 indicated that U. reticulata exhibited as high as 62.3 mg/g nickel uptake capacity from wastewaters. The study also indicated that desorption was practical and effective with 0.1 M CaCl2 at pH 2.5 adjusted using HCl and the biosorbent was regenerated and reused for three sorption-desorption cycles. Vijayaraghavan and Joshi [56] examined the ability of Ulva sp. to sorb Mn(II) and Cr(III) from aqueous solutions. The pH edge experiments indicated that equilibrium pH strongly influenced sorption capacity with pH 4.5 was found to be optimum. Through the Langmuir model, the authors determined maximum biosorption capacities as 58.8 and 150.3 and mg/g for Mn(II) and Cr(III), respectively.