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The standard potentials of proteins are not commonly measured by the methods described

Physical Chemistry | 8th Edition | ISBN: 9780716787594 | Authors: Peter Atkins, Julio de Paula ISBN: 9780716787594 348

Solution for problem 7.33 Chapter 7

Physical Chemistry | 8th Edition

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Physical Chemistry | 8th Edition | ISBN: 9780716787594 | Authors: Peter Atkins, Julio de Paula

Physical Chemistry | 8th Edition

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Problem 7.33

The standard potentials of proteins are not commonly measured by the methods described in this chapter because proteins often lose their native structure and function when they react on the surfaces of electrodes. In an alternative method, the oxidized protein is allowed to react with an appropriate electron donor in solution. The standard potential of the protein is then determined from the Nernst equation, the equilibrium concentrations of all species in solution, and the known standard potential of the electron donor. We shall illustrate this method with the protein cytochrome c. The one-electron reaction between cytochrome c, cyt, and 2,6-dichloroindophenol, D, can be followed spectrophotometrically because each of the four species in solution has a distinct colour, or absorption spectrum. We write the reaction as cytox + Dred5cytred + Dox, where the subscripts ox and red refer to oxidized and reduced states, respectively. (a) Consider E 7 cyt and E7D to be the standard potentials of cytochrome c and D, respectively. Show that, at equilibrium (eq), a plot of ln([Dox]eq/[Dred]eq) versus ln([cytox]eq/[cytred]eq) is linear with slope of 1 and y-intercept F(E 7 cyt E7D )/RT, where equilibrium activities are replaced by the numerical values of equilibrium molar concentrations. (b) The following data were obtained for the reaction between oxidized cytochrome c and reduced D in a pH 6.5 buffer at 298 K. The ratios [Dox]eq/[Dred]eq and [cytox]eq/[cytred]eq were adjusted by titrating a solution containing oxidized cytochrome c and reduced D with a solution of sodium ascorbate, which is a strong reductant. From the data and the standard potential of D of 0.237 V, determine the standard potential cytochrome c at pH 6.5 and 298K. [Dox]eq/[Dred]eq 0.00279 0.00843 0.0257 0.0497 0.0748 0.238 0.534 [cytox]eq/[cytred]eq 0.0106 0.0230 0.0894 0.197 0.335 0.809 1.39

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2. The bonds are formed because the original atoms didn’t have the outermost energy level filled with electrons. 3. All of the chemical reactions in the body involve the making and breaking of these chemical bonds. 4. Chemical reactions are indicated by equations: Ionic...

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Chapter 7, Problem 7.33 is Solved
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Textbook: Physical Chemistry
Edition: 8
Author: Peter Atkins, Julio de Paula
ISBN: 9780716787594

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The standard potentials of proteins are not commonly measured by the methods described

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