Interaction equilibrium dialysis method

In spite of much information available for the interactions of various metal ions with small oxoanions of phosphorus, relatively little information has been obtained for the complex formation of long-chain polyphosphate ion. This may be due to the fact that the conventional methods useful for the study of the complex formation of a relatively small ligand are not always applicable to the polyanion complex formation system. Since a gel chromatographic method based on the same principle as the equilibrium dialysis method has been proved to be applicable in the field of inorganic complex chemistry (1), this method has been applied to the study of the binding of long-chain polyphosphate ions to magnesium ion. 

Other methods to determine the interactions between aroma compounds and wine matrix components do not involve gas phase measurements. For example, the equilibrium dialysis method has been applied for determining interactions between yeast macromolecules and some wine aroma compounds (Lubbers et al. 1994a) and more recently to study the interaction of aroma compounds and catequins in aqueous solution (Jung and Ebeler 2003). While this method can be set up in different ways, a simple approach is to fill a dialysis cell (two chambers separated by a semiper-meable membrane) with an aromatized liquid. A non-volatile component of wine can be added to one chamber of the cell and then the system allowed to come to equilibrium. If the added non-volatile component binds the aroma compound, the other chamber will be depleted by this binding. Quantification of this change in concentration permits calculating the quantity that is bound to the added substrate. 

Effect of Ethanol on Conformational state of protein. To understand the effect of ethanol and pH in flavour-protein interactions the binding of y-decalactone to bovine serum albumin was investigated using the equilibrium dialysis method (20). Without ethanol, a decrease in pH (from 5.3 to3.5) reduces by one-half the y-decalactone binding onto protein. In the presence of ethanol, changing pH do not have any appreciable effect (Table VI). 

Equilibrium dialysis methods can be used to measure binding interactions directly. 

It is possible to measure the different single ion interaction coefficients directly by equilibrium dialysis (Bai et al., 2007 Strauss et al., 1967). An alternative method for measuring T2+ takes advantage of a fluorescent dye that chelates Mg2+ (Grilley et al., 2006). In essence, the method uses the dye to sense differences in the Mg2+ activity in the presence or absence of an RNA. Detailed theoretical justification, titration protocols, and data analysis for the method have been presented elsewhere (Grilley et al., 2009). For the A-riboswitch, titrations carried out in the presence or absence of ligand measure T2+ for the folded or unfolded state of the RNA, respectively... 

In a study of interaction between a small molecule and a macromolecule, equilibrium dialysis is a fundamentally important method and it has been applied to many studies. But in the case of surfactant ligands, it has a drawback as much as a week may be required to attain an equilibrium.5>33 Gel chromatography provides another technique for obtaining binding isotherm, but has been used mostly to determine an amount of binding saturation. It is supposed that absorption of surfactants into the gel phase may obstruct reaching equilibrium at lower surfactant concentrations. 

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