Hi Hefin,

did you took into account that you have to transfer your sedimentation coefficient s into Svedbergs (wich is 1 Svedberg = 100fs) ?

Hi Hefin,

I ran into some problems with your definition of the sedimentation coefficient. When I confirmed my memory by a tectbook on Physical Chemistry, I found that the sedimentation coefficien is defined as

s = (vesicle mass - mass of the solvent volume displaced by the vesicle)

                  / (6π * viscosity * particle radius)

Is your "vesicle mass" such a difference or just the calculated mass. I ask because we had the problem of vesicle separation about twenty five years ago. The specific mass of the vesicle membrane was lower than that the electrolyte, and the vesicles would float up under centrifugation due to the buoyant force. Therefore, we had to prepare the vesicles in CsCl solution and spun them down in NaCl solution to get a sedimentation at all. Under this condition we found centrifugation times in the order of 300 min.

Thanks both for your answers! So my vesicle mass is just the absolute mass in pg of the vesicle.  I know that the vesicles do indeed pellet in my solvent, I would just like a theoretical estimation of pelleting times (in fluids with different viscosities and centrifuges with different K factors) and the the moment, the values I'm getting are completely nonsensical.  How might I estimate or find out the mass of solvent volume displaced by the vesicle?

Thanks!

Hefin