Sodium Alginate Samples Research Articles

Comparison of different methods for determination of molecular weight and molecular weight distribution of alginates

The scope of the present work was to assess and compare different methods to determine molecular weight (MW) averages and molecular weight distributions (MWD) of two samples of sodium alginate of different composition. Weight average ( M w ) and number average ( M n ) molecular weights were determined by totally integrated laser light scattering (LLS), both at wide angles (WA) and at a low angle (LA), and membrane osmometry, respectively. The two alginates were fractionated by preparative and analytical size exclusion chromatography. Absolute molecular weight distribution curves were obtained from SEC, using an on-line LA-LLS detector coupled with an RI concentration detector. Relative MWD curves were determined from ‘universal’ calibration of the SEC data. M w , M v , and M n were calculated from the ‘universal’ calibration curve and [η] j values of the fractions. Good correlation between molecular weight averages obtained from the different methods was observed. Mark-Houwink-Sakurada parameters, a and K, for the two different alginate samples have been determined.

Effect of formaldehyde pre-treatment on the intrinsic viscosity of alginate from various brown seaweeds

Sodium alginate samples were extracted from brown seaweeds by various methods and the effect of the extraction procedure on the intrinsic viscosity and, by implication, the molecular weight were studied. Pre-treating the weeds with formaldehyde and ethanol prior to extraction with sodium carbonate or extracting the weeds under neutral conditions with selected calcium ion sequestrants resulted in alginates with enhanced intrinsic viscosities. The intrinsic viscosity of alginate samples during extraction decreases significantly with increasing pH due to the presence of phenolic compounds. By isolating the phenolic compounds with formaldehyde or extracting them with ethanol, degradation processes can be inhibited.

Effect of periodate oxidation upon the stiffness of the alginate molecule in solution

Samples of sodium alginate from Laminaria digitata were oxidised in aqueous solution to different extents by the addition of calculated amounts of sodium metaperiodate. An empirical measure of the molecular stiffness of the products, both before and after reduction with sodium borohydride, was obtained by studying the sensitivity of their intrinsic viscosities to changes in the ionic strength of the solution. The results showed that, whereas the stiffness decreased very sharply with increasing degree of oxidation, it changed very little upon subsequent reduction of the products. From this, and the known structures of the inter-residue hemiacetals in the unreduced products, it was inferred that the increase in flexibility brought about by oxidation is specifically associated with rotation about the three bonds adjoining C-4, C-5, the original ring-oxygen atom, and C-1 of the oxidised hexuronic-acid residues. This rotation was considerably less-hindered than the rotation around the glycosidic linkage in both the intact alginate and in the partially oxidised and reduced products. The conversion of only a small percentage of the stiff pyranoid rings into these centres of high, local flexibility had a marked effect on the overall flexibility of the chains, showing that the possible presence of such centres should be taken into account in any discussion of the solution properties of heteropolysaccharides or of polysaccharides that may have suffered slight chemical modification.

Hydrodynamic properties of polyelectrolytes. Part III. Sodium alginate

AbstractThe viscosity and streaming birefringence of fractionated and unfractionated samples of sodium alginate have been measured at various concentrations, and rates of shear, and in the presence and absence of added salt. The viscosity data show the concave upward curve typical of polyelectrolytes at low concentrations, but pass through a minimum at higher concentrations. The influence of shear is least at this minimum. The initial slope of the orientation angle versus velocity gradient curves increases with concentration, but Δn/c is independent of concentration. The semiempirical theory of Peterlin for concentrated solutions is obeyed by the data for Δn, but not by that for the orientation angle. Molecular weights have been calculated from the hydrodynamic parameters. The viscosity behavior is interpreted in terms of the rigidity of the molecule.

MOLECULAR WEIGHT AND HYDRODYNAMIC PROPERTIES OF SODIUM ALGINATE

Sedimentation, diffusion, and viscosity measurements were made on five unfractionated samples of sodium alginate ranging in intrinsic viscosity from 3.1 to 17.5. Diffusion coefficients were subject to large errors and are believed to be overestimated.Though the molecular weights obtained from sedimentation–diffusion (Svedberg equation) and sedimentation – intrinsic viscosity (Perrin–Simha equations) showed good agreement and yielded values of 3 to 21 × 104, higher values (4.6 to 37 × 104) from sedimentation–viscosity (Mandelkern–Flory equation) appear to be the better estimates. A linear relation between intrinsic viscosity and molecular weight was found with a slope (Mandelkern–Flory equation values) equivalent to Km = 13.9 × 10−3. The results indicate that sodium alginate has a relatively high extension ratio.

MOLECULAR WEIGHT AND HYDRODYNAMIC PROPERTIES OF SODIUM ALGINATE

Sedimentation, diffusion, and viscosity measurements were made on five unfractionated samples of sodium alginate ranging in intrinsic viscosity from 3.1 to 17.5. Diffusion coefficients were subject to large errors and are believed to be overestimated.Though the molecular weights obtained from sedimentation–diffusion (Svedberg equation) and sedimentation – intrinsic viscosity (Perrin–Simha equations) showed good agreement and yielded values of 3 to 21 × 104, higher values (4.6 to 37 × 104) from sedimentation–viscosity (Mandelkern–Flory equation) appear to be the better estimates. A linear relation between intrinsic viscosity and molecular weight was found with a slope (Mandelkern–Flory equation values) equivalent to Km = 13.9 × 10−3. The results indicate that sodium alginate has a relatively high extension ratio.