|Cameron, Randall - Randy|
Submitted to: Biomacromolecules
Publication Type: Peer reviewed journal
Publication Acceptance Date: 11/24/2011
Publication Date: 11/24/2011
Citation: Milokva, V., Kamburova, K., Cameron, R.G., Radeva, T. 2011. Complexation of ferric oxide particles with pectins of ordered and random distribution of charged units. Biomacromolecules. 13:138-145. Interpretive Summary: Differences in the distribution of charges within a pectin molecule have been shown to affect functionality. In this study we compared pectin populations with an equal population level of methylesterification but different distributions of those charges. One population contained an ordered distribution of negative charges associated with non-methylesterified carboxyl groups on galacturonic acid residues of the polymer and the other population had a random distribution of these charged groups. This difference resulted in a charge density difference of only 5% but this resulted in measurable differences in behavior between the charged groups and metal oxides. The interactions of these charged groups and their metal counter ion affected the thickness of the pectin layers formed. These differences demonstrate that the distribution of methyl esters and related electrical charges can influence the physical chemistry property of the molecules and subsequently its emergent properties.
Technical Abstract: Complexation between ferric oxide particles and pectins with degree of methylation 50%, but having blockwise (ordered) or random arrangement of free carboxyl groups, are 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 approximately 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 charged groups, 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 notably 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. Furthermore, the addition of small amounts of CaCl2 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 CaCl2, indicating more loose structure of this layer.