Mannuronate monomers

Keywords Alginate, Depolymerization, Mannuronate monomers, OUgomannuro-nates. Surfactants... 

The controlled introduction of two lipophilic alkyl chains into mannuronate monomers represents a convenient way of producing double-tailed surfactants (Scheme 6). Indeed, the incorporation of longer hydrophobic alkyl chains than the two butyl groups brings a more amphiphilic character to the glycosides. 

Alginates are made up of long chains of two monomers guluronic acid and mannuronic acid. The chains can be made of all one monomer or mixtures of both. The stems of kelp are made of chains with more guluronic acid, and the leaves (fronds) have more mannuronic acid. Guluronic chains bind tightly to calcium in mannuronic chains the calcium is more easily replaced by sodium, allowing the fibers to swell easily. 

Figure 5 Mannuronic (A) and gluronic acid (B) components of alginate monomers...

A variety of organic adhesives which are capable of forming strong bonds between a polymeric (acrylate) restoration and the hydrophilic tooth material have recently been developed. A number of these monomers, which possess a pendent ionizable group, are polymerized in the mouth to form an adhesive layer. Alginates, which are used as impression materials, are formed by the reaction of the sodium salt of anhydro-beta-d-mannuronic acid with calcium sulfate. Calcium ions crosslink the linear polymer to form a gel. This reaction is carried out inside the mouth, and the gel formed retains the shape of the oral cavity. 

The monomers of alginate are mannuronic (M 1) and guluronic(G 2) acids, the polymers being composed of three types of sequence homo-... 

Scheme 4 Chemical transformation of unsaturated oligomannuronates of DP 2-4 into monomer 4 and dimer 5 mannuronates. (i) MSA, BuOH, 50-55°C, 5 days, 4 35% 5 25%...

Alginates are composed of (1—>4)-linked (3-D-mannuronic acid (M units) and a-L-guluronic acid (G units) monomers (Figure 16.9), with different sequential distribution along the polymer chain [142]. The composition, sequence, and molecular weight generally determine the physical properties of alginate [143]. 

Alginic acid is a linear copolymer with homopolymeric blocks of (l-4)-linked p-D-mannuronate (M) and its C-5 epi-mer a-L-glucuronate (G) residues, respectively, covalently linked together in different sequences or blocks. The different forms of alginic acid are represented in Figure 1.29. The monomers can appear in homopolymeric blocks of consecutive G-residues (G-blocks), consecutive M-residues (M-blocks), or alternating M- and G-residues (MG-blocks). 

Alginic acids isolated from different sources can differ in the ratio of mannuronic and guluronic acids (M/G) and in the distribution of the monomers along the polymeric chain. The size and distribution of individual blocks strongly afifect the properties of alginic acids and alginates [1]. 

Alginic acid is a linear multiblock copolymer from blocks of jS-(l->4)-D-mannuronic acid and a-(1 4)-L-guluronic acid, as well as alternating copolymers from these two monomer units. In natural products, the molecular weights reach about 150,000 and with regenerated products 30,000-60,000. Alginates are the salts of alginic acid. 

AiginicAcids.— The secondary and tertiary structures of alginic acid, carrageenans, and agarose have been discussed. Natural-abundance C n.m.r. spectroscopy has been used for the first time to determine the C-1 doublet and C-5 triplet frequencies in alginates which contain an unbranched chain composed of blocks of (1 - 4)-linked )S-D-mannuronate and -i guluronate residues. The triplet frequencies provide information on the monomer sequences in alginates. 

Alginates are polysaccharides that are linear copolymers of (3-D-mannuronic acid and a-L-guluronic acid residues with (1 4) linkages, as shown in Figure 14.13 [24]. The molecular chain is formed by homopolymeric blocks or heteropolymeric blocks of the two monomers, (3-D-mannuronic acid or a-L-guluronic acid. Alginates exhibit molecular weights between 20 and 600 kDa [3]. 

Monomer(s) structure - p-D-mannuronic acid and a-L-guluronic acid ... 

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