# Calculating Hydration from Asymmetry Estimates

Calculating Hydration from Asymmetry Estimates

Should the user supply an axial ratio (as major-axis/minor-axis), the corresponding values of the degree of hydration for both the prolate and oblate ellipsoid models will be calculated by Sednterp. To do this, the frictional coefficient ratios (prolate= and oblate=) corresponding to the user-supplied a/b may be calculated using the formulas of Perrin (Ref. 18):

[note that both of these equations are incorrect in Ref. 59]

Equation 27.

Equation 28.

These values then are used to calculate the corresponding degree of hydration:

Equation 29:

Equation 30:

where δ1,p is the predicted degree of hydration for the prolate model, δ1,o is that for the oblate model and vbar is the protein's partial specific volume. As before, f0 can be calculated using either equation 21 or 22 and Vp can replace vbar.