Polysaccharides dissociation

A good example of this interaction in catalysis is the hydrolysis of the bacterial cell wall polysaccharide by lysozyme. This enzyme contains two carboxylic gronps at its active site and, in active enzyme one must be in dissociated—COO, the other in the undissociated—COOH form. Therefore, the pK s of the two carboxylic groups ate different. This difference in dissociation constant is a consequence of the neighbouring amino acid residues and of the interactions between the functional groups in the microenvironment. 

Barker and coworkers have applied gel chromatography in studies of pneumococcal polysaccharides.121 Purification of the type-specific polysaccharide of Pneumococcus Type II was effected by chromatography on Sephadex G-200 in M sodium chloride in this way, the ribonucleic acid, a persistent impurity in preparations of this polysaccharide, was almost completely removed. The complex formed between the polysaccharide and the nucleic acid is largely dissociated in M sodium chloride, so that the two are free in this solvent and may be separated on the basis of their differing molecular size. 

The expected greater size of protein-polysaccharide complexes can reduce the diffusion rate of the adsorbing species towards the interface. This effect is especially important for small monomeric proteins. In addition, Ganzevles and co-workers (2006) have suggested that the diffusion of protein in the complexes may not solely be responsible for the slow surface tension decay. Rather, the gradual dissociation (and subsequent adsorption) of protein from complexes, when they are in close proximity to the interface, could also contribute to the behaviour. 

Infrared spectra of glycosaminoglycans in D20 and DC1 were used165 for quantitative evaluation of the uronic acid and acetamido groups in this class of polysaccharide. The results showed that i.r. spectroscopy of compounds in D20 solution provides a simple, quantitative basis for examination of ras(COJ) and amide I bands in heparin and chondroitin 4-sulfate. In DC1, analysis was based on p(C02H) and amide I bands which were well resolved. The apparent acid-dissociation constants of the studied polysaccharides were estimated from the absorbance of p(C02) or p(C02H) bands, or both, at different pH (pD) values. 

It can precipitate as potassium hydrogen tartrate (KHT) or as calcium tartrate (CaT), the latter being practically insoluble in aqueous solutions. Their equilibrium solubility varies with temperature, pH, and alcohol content, while the presence of a few wine components, such as polysaccharides and mannoproteins, may hinder spontaneous nucleation even if the solution is supersaturated. From Figure 14 that shows the equilibrium tartaric acid-dissociated fractions versus pH and ethanol volumetric fraction (Berta, 1993 Usseglio-Tomasset and Bosia, 1978), it can be seen that in the typical pH range (3 4) of wines KHT is predominant. As temperature is reduced from 20 to 0°C, KHT solubility in water or in a 12% (v/v) hydro-alcoholic solution reduces from 5.11 to 2.45 kg/m3 or from 2.75 to 1.1 kg/m3, respectively (Berta, 1993). Each of these data also varies with pH and reaches a minimum at the pH value associated with the maximum concentration of the hydrogen tartrate anions. For the above-mentioned solutions, the solubility minimum shifts from pH 3.57 to pH 3.73 as the ethanol content increases from 0 to 12% (v/v) (Berta, 1993). 

Polysaccharide-based CSPs also exhibit a chiral recognition for alcohols and a large number of resolutions have been reported. Chiral alcohols can usually be directly resolved with hexane containing a small amount of an alcohol as the eluent. For aliphatic alcohols, which cannot be directly resolved, their resolution is often efficiently attained as phenylcarbamate or benzoate derivatives on OD (Figure 17).85 For example, 2-butanol and 2-pentanol are completely resolved with a very high selectivity on OD as their phenylcarbamates. The derivatization of alcohols to phenylcarbamates and benzoates can be easily achieved by the reaction with phenyl isocyanates and benzoyl chlorides, respectively. In most cases, the phenylcarbamates are better resolved than the benzoates. For chiral compounds bearing phenolic hydroxy groups, the addition of a small amount of an acid to an eluent is recommended to depress its dissociation. 

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. 

Mucopolysaccharides are generally found to have a small but significant proportion of associated protein material. The results of structural determinations in this field have been reviewed recently.98 In most instances, rather drastic methods, including the use of alkali, are needed to remove the contaminating protein and so obtain a soluble product. Degradation may possibly accompany such isolation procedures, and dissociation of the protein-polysaccharide complex may also completely alter the physical properties of the product. 

Diphosphothymidine, I, 242 Diplococcua pneumoniae, polysaccharides formed by, II, 221 Disaocharides, III, 130 enzymatic syntheses of, V, 29-48 oxidation of, III, 132, 145 Dismutation, the term, IV, 101 Disproportionation, IV, 102 Dissociation constants, of hypobromous, hypochlorous and hypoiodous acids,... 

Acid-base titration studies measuring the concentrations and acid dissociation properties of functional groups on lichen cell walls, extracellular polysaccharides and lichen acids. 

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