Nernst equation artificial

When a series of dihydronicotinamides with variable substituents R is oxidized either by flavin or by the le"-only nitroxide radical, the Nernst equation can be verified using the forward rate as well as the equilibrium constants, since the back reaction rate is independent of the nature of R. In the case of the flavin acceptor, the Nernst number n turns out to be 2, as required for 2e"-transfer. Hence, the transformase cofactor flavin will react with nicotinamide in the 2e"-mode, showing that the latter is—for the biological acceptor—a 2e"-only agent and requires a very potent le"-only oxidant such as nitroxide for artificial le"-behavior. 

A more practical version of this equation can be given by assuming that the concentration gradient near the surface is linear. This is not an accurate assumption, but it is blessed by history and is always used. In fact, the model here, which was originated by the famous German physical chemist Nernst, is artificial in the sense that it linearizes the current density. 

Complex membrane transport phenomena are relevant to several areas in medicine, such as ion transport through neurons, ion exchange, and electrodialysis [50,51]. The Nernst-Planck equation is often the starting point for the interpretation of transport through both artificial and biological membranes [50,51]. Strictly speaking, the Nernst-Planck equation requires the... 

According to the Levich equation (4.105) the limiting current density for a rotating disk electrode is proportional to Cg. On the other hand, the Nernst model (equation 4.81) indicates that the limiting current is proportional to the product Cb Db- By combining these two equations we find that 5has a Db dependence. This result reveals the artificial character of the Nernst diffusion layer model. Every dissolved species that reacts in an electrochemical system has its own speeifie Nernst diffusion layer. 

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