Metal Selectivity of Sargassum spp. and Their Alginates in Relation to Their α-l-Guluronic Acid Content and Conformation

Abstract

The discovery of a consistent and unusual enrichment in homopolymeric alpha-L-guluronic acid G-blocks in alginates extracted from a suite of Sargassum brown algae is described in this study. 1H NMR spectroscopy was used to characterize these alginates which display homopolymeric guluronic acid block (G-block) frequency values (F(GG)) between 0.37 and 0.81. The presence of these G-blocks results in an enhanced selectivity for cadmium or calcium relative to monovalent ions such as sodium and the proton as well as smaller divalent ions such as magnesium. Results of competitive exchange experiments for the Cd-Ca-alginate system yield selectivity coefficient, K*(Cd)Ca, values between 0.43 +/- 0.10 and 1.32 +/- 0.02 for a range in F(GG) of 0.23 to 0.81. In contrast to the Cd-Ca-alginate system, the Mg-Ca-alginate and Mg-Cd-alginate systems yielded maximum values of K*(Mg)Ca (18.0 +/- 1.4) and K*(Mg)Cd (16.0 +/- 0.9) for the alginates extracted from Sargassum fluitans (F(GG) = 0.81; Cuba) and Sargassum thunbergii (F(GG) = 0.75; Korea), respectively. Selectivity studies with mixed-metal pair alginate systems highlight the importance of the specific macromolecular conformation of the alginate polymer in determining metal binding behavior in multiple-metal systems. Furthermore, they demonstrate the importance of the conformation of the alginate as it occurs within the tissue of Sargassum in determining the metal binding behavior of this algal biosorbent. The unique composition of the alginates present in species of Sargassum may represent a distinct advantage over other brown algal species when considering their implementation for the strategic removal of toxic heavy metals from contaminated and industrial wastewaters.

Microalgae (Scenedesmus obliquus) dewatering using forward osmosis membrane: Influence of draw solution chemistry

“…The lowest B value for CaCl 2 ( Table 2) indicates there are specific interactions between Ca 2+ and algal biomass. Once diffused through the membrane, Ca 2+ ions bind preferentially to oxygen atoms of carboxylate groups in a highly organized manner and form bridges between adjacent algal cells as well as their extracellular polysaccharides (EPSs) and soluble microbial products (SMPs), leading to the egg-box-shaped gel network [14,[34][35][36]. As a result, large microalgae flocs were formed in the feed tank (Fig.…”

Asymmetrical Flow Field Flow Fractionation - Multidetection System as a Tool for Studying Metal - Alginate Interactions

“…Alginates are 1-4 linked linear polysaccharides of β-mannuronic acid and α-guluronic acid monomers occurring as structural components in the cell walls of brown algae of the Sargassum family, Laminaria digitata, and Macrocystis pyrifera. [27,28] They are also widely found as capsular compounds in several bacteria such as Pseudomonas aeruginosa, Azotobacter vinelandii and Azotobacter crococcum. [28] Due to the fact that polysaccharides are produced by polymerase enzymes, these macromolecules are broadly distributed in size and composition, with some characteristics depending on the microorganism of origin.…”

“…[28] Due to the fact that polysaccharides are produced by polymerase enzymes, these macromolecules are broadly distributed in size and composition, with some characteristics depending on the microorganism of origin. [27,28] Acidic polysaccharides and natural colloids in general, however, are mostly found as very complex mixtures spanning over a wide molar mass and size range. Unless appropriate separation is previously performed, batch analysis cannot provide details of the role(s) of the differently sized components in the mixtures.…”

Quantifying Pb and Cd Complexation by Alginates and the Role of Metal Binding on Macromolecular Aggregation

“…For example, in algae, alginates have a structural function, whereas in bacteria, they generally adopt a more acetylated form that serves a protective function. 5 Because of their metal binding properties, alginates can be used to remove metals from wastewaters and industrial effluents 2,6 and as a matrix to immobilize Pb and Cd complexing particles, including ion-exchange resins 6 or microorganisms 7 in order to treat contaminated waters. The major difficulties in understanding the metal binding of most natural biopolymers, including alginates, results from their (i) polyelectrolytic properties -at circumneutral pH, the carboxylic sites of alginic acid are ionized, thereby creating an electric field which increases complex stability; (ii) polyfunctionality -a diversity in the chemical nature and the resulting electronic and steric environment of the coordinating sites; and (iii) capacity to change their threedimensional conformation.…”