Dissociation, ionic polysaccharides

The identicalness of the ionization sites in a linear polyelectrolyte (Tanford, 1961) stimulated the interest of Walter and Jacon (1994) in a possible relationship between Kz and M of ionic polysaccharides displaying the characteristic titration curve of a weak, monobasic acid. Without any theoretical assumption, Eq. (S.4) was derived from simple algebra by combining elementary principles of the dissociation theory of weak acids with polymer segment theory ... 

Cesaro, A., and Villegas, M. (1996). Proton dissociation of ionic polysaccharides can the molecular weight be approximated by pH determinations Food Hydrocoil. 10 45-50. 

Since ionic polysaccharides are stiffer than most synthetic polyelectrolytes, they were thought to be appropriate experimental models to test theories based on cylindrical symmetry. Systematic determinations of co interion and coion diffusion coefficioits and activity coefficients have been made in the presence of ionic polysaccharides these measurements pertain to the interaction of small ions in the ionic atmosphere with the polyelectrolyte. Here, resiilts are presented for estimating the fraction of ions dissociated from the ionic polysaccharide in simple salts solutions. 

Fucan is a sulfated polysaccharide, naturally present in algae such as Fucus vesiculosus or Ascophyllum nodosum. Fucan is a general name for a mixture of three polysaccharides, and among them, fucoidan (or homofucan) can be theoretically considered as an homopolymer of a-1,2 L-fucose-4-sulfate and has been studied as a ligand in the same way as fucan himself. Their interaction with two proteins implicated in the coagulation process (thrombin and antithrombin) has been studied and is at least partially ionic. However, the dissociation of the complex fucan-antithrombin seems to include a slower step which could be attributed to a conformation change of the fucan [18]. 

Ionic polymers (polyelectrolytes and polyampholytes) constitute an important class of water-soluble maaomole-cules. ° Their monomer units are capable of ionization in polar solvents, for example, in water. The ionization occurs via either dissociation of hydrogen ions H from the acidic groups or dissociation of water molecules and protonation of the basic groups on the polymer chain. The solubility of polyelectrolytes in polar solvents is determined first of all by a huge gain in translational entropy of the counterions. The majority of bio-maaomolecules (proteins, nucleic acids, and polysaccharides) operating in aqueous environment carry ionizable groups (carboxyl, sulfate, amine, etc.) and are included in this class of polymers. 

Electrostatic forces between ions occur in the interactions of ions formed by dissociation of inorganic salts and in ionic interactions of ionised functional groups of organic substances such as ionised protein functional groups, for example ionised carboxyl groups (-COO ), ionised amino groups (-NH3+) and ionised functional groups of some polysaccharides (-COO , OSOj"). 

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