Complexation of Ferric Oxide Particles with Pectins of Ordered and Random Distribution of Charged Units

Abstract

Complexation between ferric oxide particles and pectins with degree of methylation 50% but having ordered or random arrangement of free carboxyl groups is investigated by electric light scattering and electrophoresis. The influence of charge distribution in pectin chain on the electrical properties of oppositely charged oxide particles and stability of their suspensions is examined as a function of pectin concentration. Although the difference in charge density of pectin samples is ~5%, we found small but measurable difference in the behavior of both oxide/pectin complexes. This is attributed to condensation of counterions near the chains of pectin with ordered distribution of charges, leading to a decrease in the effective charge density and to a corresponding decrease in the contour length of the adsorbing pectin chains. Two parameters are sensitive to the conformation of the adsorbed chains in suspensions, stabilized by pectin adsorption (at particle charge reversal). The electro-optical effect is higher for the complex with less charged pectin, which is explained with larger amount of chains, adsorbed in more coiled conformation than the chains of pectin with random distribution of free carboxyl groups. The addition of small amounts of CaCl(2) has no significant influence on the thickness of the layer from the less charged pectin, in agreement with a more compact conformation of the chains in this adsorbed layer. In contrast, the thickness of the layer from pectin with random distribution of charged groups decreases with increasing concentration of CaCl(2), indicating a more loose structure of this layer.

Comparative Electrokinetic Study of Alginate-Coated Colloidal Particles

“…creases at higher salt concentrations. These observations are in line with previously reported studies on the behavior of alginate and pectin in the presence of divalent cations [29,31]. According to the electro-optic theory, when a direct current (ν = 0 Hz) is applied to the suspension with no spherical particles (with anisotropic electrical polarizability), all the charges of the particles are polarized (ions in the Stern layer, ions from the diffuse part In accordance with the theory, the effect from the suspension of the ellipsoidal particles resulting from the polarization of free counterions along the long particle axis and critical frequency of relaxation υ cr can be estimated by using [33]:…”

“…The experimental results indicate that the effect increases with the increasing concentration of CaCl 2 from up to 3 × 10 −5 M and decreases at higher salt concentrations. These observations are in line with previously reported studies on the behavior of alginate and pectin in the presence of divalent cations [29,31].…”

“…The results indicate that the experimental value of the relaxation frequency of the effect for the polymer-coated particles is lower compared to the bare particles-νcr (A082) ~5 kHz, νcr (A122) ~3 kHz, and νcr (A047) ~17 kHz. Previously, one possible explanation was shown for the similar decrease in νcr observed for particles covered by polymers: this is related to the influence of the charge density and contour length (or molecular weight) of the polymer chain [28,29]. It is known that the polyelectrolyte behavior of ALG molecules is governed by the presence of carboxylic groups of the mannuronic (pKa~3.38) and glucuronic residues (pKa~3.65), which renders the alginate molecule as a polyanion in the presence of inorganic acids [35].…”

Influence of charge density and calcium salt on stiffness of polysaccharides multilayer film

“…The explanation for the observed increase in the electrical polarizability on addition of divalent cations is that they cause larger charge fluctuations along the polyelectrolyte chain (in comparison to the monovalent cations) because of their larger valence [42]. Similar increase of the electro-optical effect on increasing concentration of CaCl 2 from 10 −5 to 4 × 10 −5 M has been found for PEC, adsorbed as a monolayer onto ␤-FeOOH particles [43].…”

Smart and green interfaces: From single bubbles/drops to industrial environmental and biomedical applications

“…Effect of ionic strength and molecular weight on the stability of adsorbed polyelectrolyte bi-layers was also demonstrated for oxide particles in stabilized suspensions [2]. The sensitivity of electro-optics to particle surface charge was used to clarify the role of charge distribution of pectin chains, adsorbing them on oppositely charged ferric oxide particles [3]. The electro-optical signal contains information also on the particle dimensions (through their rotational diffusion coefficients), which allows investigating colloid stability in presence of polyelectrolytes.…”