TABLE 5.

Transfer of steroid hormones across biomembranes

Molecule	ΔGsol* (kcal/mol )	Kcalc† (cm/s)	Kexp‡ (cm/s)
Progesterone	−3.2	2.4 × 10−5	2.4 × 10−5
Testosterone	−0.9	3.7 × 10−5	2.5 × 10−5
Estradiol	0.3	3.0 × 10−5	1.7 × 10−5

^*The water-to-hexane transfer free energy of the hormones (Eq. 1).

^†The calculated transfer rate across a membrane of width of 30 Å.

^‡Experimental transfer rates, measured across Caco-2 cells (Faassen et al., 2003).