- #1
Oijl
- 113
- 0
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?
Last edited: