The isotherms were fit to a cubic spline function and isosteres
were created over the range of measured water mole fractions,
Xw = 0.00004–0.01 for genistein. An example isostere is given
in Figure 1b.
The water sorption isotherms for all of the compounds at
25◦C are given in Figure 2. Note that for PVP, the water
mole fraction is calculated using the vinylpyrrolidone molecular
weight, so that a mole fraction of 0.5 represents 1 mole of
water to 1 mole of monomer. In the isotherm for indomethacin,
there is a small step-like feature at 50% RH, the relevance of
which will be explained in the Discussion section. The isotherm