Structure-facilitated hydrophobic effects

The tendency for hydrocarbon chains to become remote from the polar solvent, water, is known as the hydrophobic effect (Chap. 4). Hydrocarbons form no hydrogen bonds with water, and a hydrocarbon surrounded by water facilitates the formation of hydrogen bonds between the water molecules themselves. The bulk water is more structured than it is in the absence of the hydrocarbon i.e., it has lost entropy (Chap. 10) and is thus in a thermodynamically less favorable state. This state is obviated by the hydrocarbon being organized so that it is remote from water, thus rendering the water molecules near to it less ordered. Thus the hydrophobic effect is said to be entropically driven. 

One of the most attractive roles of liquid liquid interfaces that we found in solvent extraction kinetics of metal ions is a catalytic effect. Shaking or stirring of the solvent extraction system generates a wide interfacial area or a large specific interfacial area defined as the interfacial area divided by a bulk phase volume. Metal extractants have a molecular structure which has both hydrophilic and hydrophobic groups. Therefore, they have a property of interfacial adsorptivity much like surfactant molecules. Adsorption of extractant at the liquid liquid interface can dramatically facilitate the interfacial com-plexation which has been exploited from our research. 

The importance of hydrophobic binding interactions in facilitating catalysis in enzyme reactions is well known. The impact of this phenomenon in the action of synthetic polymer catalysts for reactions such as described above is significant. A full investigation of a variety of monomeric and polymeric catalysts with nucleophilic sites is currently underway. They are being used to study the effect of polymer structure and morphology on catalytic activity in transacylation and other reactions. 

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