Ionic forces, charge transfer systems

Elevated pressures can induce functional and structural alterations of proteins. The effects of pressure are governed by Le Chatelier s principle. According to this principle, an increase in pressure favours processes which reduce the overall volume of the system, and conversely increases in pressure inhibit processes which increase the volume. The effects of pressure on proteins depend on the relative contribution of the intramolecular forces which determine their stability and functions. Ionic interactions and hydrophobic interactions are disrupted by pressure. On the other hand, stacking interactions between aromatic rings and charge-transfer interactions are reinforced by pressure. Hydrogen bonds are almost insensitive to pressure. Thus, pressure acts on the secondary, tertiary, and quaternary structure of proteins. The extent and the reversibility, or irreversibility, of pressure effects depend on the pressure range, the rate of compression, and the duration of exposure to increased pressures. These effects are also influenced by other environmental parameters, such as the temperature, the pH, the solvent, and the composition of the medium. 

It follows that diffusion control is more frequently operative in polymeric systems than that in ordinary solution reactions, because and k are more likely to be comparable due to the low D values [9-16], If the election exchange reaction occurs between ionic species (charged polymer sites), the coulombic forces may reduce or enhance both the probability of the ions encoimtering each other and the rate of electron transfer. For the activation-controlled case, kg can be obtained as follows [17] ... 

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