Table 1. Binding, physical, and activity data for barbiturates.

	Thiopental	Pentobarbital	Phenobarbital
Dissociation constant K d for apoferritin binding (µM)	11.0±0.9	64.3±5.5	672±27
Enthalpy of binding to apoferritin (kcal/mol)a	−7.3±0.4	−4.4±0.7	—
apoferritin cavity volume (Å3)	388.6	407.6	—
Ligand volume (Å3)	223.9	210.5	211.3
Packing density	0.58	0.52	—
EC50 for anesthesia (µM)	25b	50b	590c
EC50 for GABA potentiation (µM)	20d	30–60d , e , f	300–900e , f
logPg	2.9	2.1	1.5

^aBecause of the low affinity of phenobarbital for apoferritin, it was not possible to obtain a satisfactory estimate of the molar binding enthalpy.

^b [16].

^c [41].

^d [42].

^e [43].

^f [44].

^gCalculated using XLOGP3 [45].