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Table 2.

Physical properties of permeant and “impermeant” compounds

Compound MM Chemical formula pKa and pKb % neutral at pH 7.4 log Kocta Koct neutral Koct * % neutral/100 Pmeasuredb neutral Pcellc at pH 7.4 τd 16-µm diameter cell 
 D   %    µm/s µm/s  
Norepinephrine 169.2 C8H11NO3 8.6 −1.11 0.078 0.005 0.0003 5.1 h 
Epinephrine 183.2 C9H13NO3 8.6 −0.87 0.13 0.008 0.0006 2.9 h 
1,4-Butanediol 90.1 C4H10O2 >15 100 −0.70 0.20 0.20 3e 0.014 7.2 min 
Nitric oxide 30.0 NO −2.9 100 −0.35 0.45 0.45 0.031 3.2 min 
5-HT 276.2 C10H12N29.7 0.50 0.50 3.2 0.016 0.0011 1.5 h 
Butyric acid 88.1 C4H8O2 4.7 0.2 0.70 5.0 0.01 1,000e 0.3 17 s 
NAS 218.3 C12H14N2O2 10.1 99.8 0.68 4.8 4.8 0.3 18 s 
Nicotine 162.2 C10H14N2 8.0 20 1.10 12.6 2.5 0.2 34 s 
Codeine 299.4 C18H21NO3 9.7 0.50 1.24 17 0.09 1,400e 0.006 16 min 
Melatonin 232.3 C13H16N2O2 16.3 100 1.39 25 25 1.7f 1.7 3.5 s 
Indole-3-ethanolg 161.2 C10H11NO 15.2 100 1.62 42 42 2.3h 2.9 2.1 s 
Hexanoic acid 116.2 C6H12O2 4.8 100 1.71 51 51 11,000i 3.6 1.7 
Lidocaine 234.3 C14H22N27.9 24 2.15 141 33.9 2.4 2.5 s 
Compound MM Chemical formula pKa and pKb % neutral at pH 7.4 log Kocta Koct neutral Koct * % neutral/100 Pmeasuredb neutral Pcellc at pH 7.4 τd 16-µm diameter cell 
 D   %    µm/s µm/s  
Norepinephrine 169.2 C8H11NO3 8.6 −1.11 0.078 0.005 0.0003 5.1 h 
Epinephrine 183.2 C9H13NO3 8.6 −0.87 0.13 0.008 0.0006 2.9 h 
1,4-Butanediol 90.1 C4H10O2 >15 100 −0.70 0.20 0.20 3e 0.014 7.2 min 
Nitric oxide 30.0 NO −2.9 100 −0.35 0.45 0.45 0.031 3.2 min 
5-HT 276.2 C10H12N29.7 0.50 0.50 3.2 0.016 0.0011 1.5 h 
Butyric acid 88.1 C4H8O2 4.7 0.2 0.70 5.0 0.01 1,000e 0.3 17 s 
NAS 218.3 C12H14N2O2 10.1 99.8 0.68 4.8 4.8 0.3 18 s 
Nicotine 162.2 C10H14N2 8.0 20 1.10 12.6 2.5 0.2 34 s 
Codeine 299.4 C18H21NO3 9.7 0.50 1.24 17 0.09 1,400e 0.006 16 min 
Melatonin 232.3 C13H16N2O2 16.3 100 1.39 25 25 1.7f 1.7 3.5 s 
Indole-3-ethanolg 161.2 C10H11NO 15.2 100 1.62 42 42 2.3h 2.9 2.1 s 
Hexanoic acid 116.2 C6H12O2 4.8 100 1.71 51 51 11,000i 3.6 1.7 
Lidocaine 234.3 C14H22N27.9 24 2.15 141 33.9 2.4 2.5 s 

MM, molecular mass; pKa and pKb, acid or base equilibrium dissociation constant; log Koct, logarithm to base 10 of n-octanol/water partition coefficient of neutral form; Koct, partition coefficient of neutral form.

a

Each log Koct value is the mean of several calculated and experimental “logP” values reported in the DrugBank database (Law et al., 2014) and the SciFinder database of the American Chemical Society. Koct is computed from these mean values. See also discussion in Sangster (1989).

b

Pmeasured, experimental membrane permeabilities measured in planar lecithin bilayers or in tsA201 cells.

c

Pcell, predicted permeabilities for cell membranes at pH 7.4 calculated from Eq. 1b.

d

τ, predicted exponential equilibration time constant between inside of cell and bath at pH 7.4 calculated from Eq. 2 for a 16-µm diameter cell.

e

Three values of membrane permeability measured experimentally with egg lecithin/hexadecane painted planar lipid bilayers (Finkelstein, 1976; Orbach and Finkelstein, 1980).

f

Pm in tsA201 cells from this paper.

g

Also called tryptophol.

h

Membrane permeability measured experimentally with tocopherol/cholesterol/brain phospholipid/chloroform-methanol painted planar lipid bilayers (Bean et al., 1968).

i

Membrane permeability measured experimentally with egg phosphatidylcholine/decane painted planar lipid bilayers (Walter and Gutknecht, 1986).

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