Electric potential at the surface of a protien

[Oijl]

Homework Statement

Consider a protein sphere with a radius of 18Å, and charge Q = -10e, in an aqueous solution of c = 0.05M NaCl at 25 ˚C. We consider the small ions as point charges and use the linear approximation to the Poisson-Boltzmann equation.

What is the surface potential of the protein in units kT/e?

ALSO

What is the concentration of Na+ ions and of Cl- ions at the surface and at 3 Å from the surface of the protein?

Homework Equations

An expression for the potential at the surface of a charged sphere (in a salty solution):

V(R) = [1/(4π(epsilon naught)D)]*[Q/R]*[(lambda sub D)/(R+lambda sub D)]

And

lambda sub D = square root of [(D(espsilon naught)kT)/(2(z^2)(e^2)c)]

where lambda sub D is the Debye screening length.ALSO, for the second question,

c+ = ce^(-qV(r)/kT)
c- = ce^(qV(r)/kT)

where q is the charge of the ion.

The Attempt at a Solution

How can I solve for V in terms of kT/e? I'd like to go on with my question, but I have to leave now, so I'll put up this so far, which is my basic question. Thanks.

EDIT:

Attempting the second question, I still need to be able to obtain a numerical value for V, for which I need to be able to evaluate the Debye screening length. I don't know what z is in that, so I can't get a number. What is z? The valency? If so, it's the valency of the ions in the solution, right? So, here, the valency of... Na? Cl?

 

[Vladimir Matveev]

Dear Oijl,

The task ("Electric potential at the surface of a protien") you are trying to solve is very important for the physiology and biophysics of the living cell. Literature gives molten globules very important role in the cell, however, in order to melt globule need harsh physical conditions. In my last article ("Native aggregation..."), I suggest that such harsh conditions can occur in microvolumes (several protein molecules) of cytoplasm. Your idea of the potential on the surface of the protein may be important to understand the sources of energy needed to melt globules. Perhaps we could write a joint paper. :)
You can download my article from my web-site: http://vladimirmatveev.ru
In any case, it would be interesting to know your opinion.