http://www.nature.com/jid/journal/v54/n5/pdf/5618185a.pdf
Closely related compounds showed great differences in penetration. Benzoic acid was absorbed at 200 times the amount of its glycine conjugate—hippuric acid. Nicotinic acid barely penetrated; 10% of its amide, nicotinamide, penetrated. This suggests that molecules may be tailored to decrease or increase penetration as needed for the most suitable biological function.
Closely related compounds showed great differences in penetration. Benzoic acid was absorbed at 200 times the amount of its glycine conjugate—hippuric acid. Nicotinic acid barely penetrated; 10% of its amide, nicotinamide, penetrated. This suggests that molecules may be tailored to decrease or increase penetration as needed for the most suitable biological function.
