Repulsive force, polysaccharides

An increasing concentration of anionic surfactant can strengthen the electrostatic repulsive forces between the maltodextrin associates, as modified by the addition of the negatively charged head-groups of the surfactant to the neutral molecules of polysaccharide. The consequence of this effect is a reduction in the extent of maltodextrin association. In combination with the other effects, this leads to parameter dependency with a local maximum and minimum below the cmc of the surfactant (see Figures 6.10a and 6.10b). 

Already the ancient Egyptians knew that one can keep soot particles dispersed in water when they were incubated with gum arabicum, an exudate from the stems of acaia trees, or egg white. In this way ink was made. The reason for the stabilizing effect is the steric repulsive force cause by adsorbed polymers. In the first case these are a mixture of polysaccharide and plycoprotein, in the second case it is mainly the protein albumin. Steric stabilisation of dispersions is very important in many industrial applications. Direct quantitative measurements were... 

Water, occasionally modified by a small volume of ethanol and electrolytes, is the universal food solvent. In this medium, a polysaccharide polyanion s molar volume (vm) is maximum, because charge repulsion forces the molecules into the stiff (uncurled) conformation of a rigid rod that cannot be extended further, but can be oriented (Odell, 1989). vm is larger for extended, stiff conformations than for compact random-coil conformations (Berth, 1992). As solvent quality deteriorates, e.g., by addition of salt or... 

A pair of polysaccharide molecules approaching each other in water exerts an interaction potential ( ) that is the algebraic sum of the competing attractive and repulsive forces. integrated over all pairs of molecules, is . This principle is embodied in the Deijaguin-Verwey-Landau-Overbeek (DLVO) theory of colloidal stability (Ross and Morrison, 1988). The equilibrium distance between the molecules is related to c, the volume of the hydrated particles, ionic strength, cosolute, nonsolvent additions, temperature, and shearing. 

Emulsions are thermodynamically unstable structures given a degree of kinetic stability by an adsorbed interfacial layer of amphiphilic emulsifiers. The emulsifiers serve to lower the interfacial tension and provide some inter-droplet repulsive forces to stabilize the dispersions (e.g., steric and electrostatic). The interfacial layer is typically between about 1 and lOnm thick for food grade emulsifiers, such as surfactants, phospholipids, proteins, or polysaccharides, and the interfacial concentration is in the order of a few mg per square meter of surface (McClements, 2005 McClements and Decker, 2000). 

The solubility of proteins near their isoelectric point environments can be improved by complexation with charged polysaccharide such as pectin, mainly due to electrostatic interactions. It was found that at pH values between 4 and 5, near the isoelectric point of soy protein, the protein particles have a lower net charge, causing aggregation, having no electrostatic repulsion forces, hydrophobic interactions are dominant [32]. 

Fig. 4 Solubility of polysaccharides iu aqueous medium. (A) Hydration/possible H bonds for a sequence of o-Glcp P(l—>4)-D-Glcp (cellobiose). (B) Scheme for cahbration of equilibrium distances due to repulsive electrostatic and attractive van der Waals forces. (Chemistry MDL ISIS/draw. Graphics Macromedia Fireworks.) (View this art in color at www.dekker. com.)...

Forces between DNA Double Helices. The repulsion and attraction of DNA is the molecular interaction most studied to date. In simple salts, repulsion is again exponential with decay rates of 2.8 3.3 A (II). Unlike forces between polysaccharides, the coefficient of the force depends on the type of cationic counterion, even though electrostatic double layer repulsion is low enough to suggest that the helix is largely neutralized by ion association. 

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