The transport of pharmaceuticals through silk fibroin membranes has be
en investigated. The membrane was prepared from Chinese cocoon. The pe
rmeability coefficients of five kinds of pharmaceutical, i.e. 5-fluoro
uracil (5FU), L-(+)-ascorbic acid (Vc), resorcinol (Res), sodium pheno
lsulfonate (SPS) and benzyltrimethylammonium chloride (BTAC), were mea
sured in the pH range from 3.0 to 9.0. The silk fibroin membrane was a
n amphoteric ion-exchange membrane composed of both weak acidic and we
ak basic groups. Membrane-potential measurements revealed that the iso
electric point of the membrane was about pH 4.5. The positively charge
d pharmaceutical, BTAC, was excluded from the membrane below the isoel
ectric point. On the other hand, the negatively charged one, SPS, had
a permeability that decreased as the pH increased. The neutral molecul
e, Res, however, penetrated through the membrane independently of pH v
alue over the measured pH range. In the case of 5FU and Vc, the permea
bility coefficients decreased steeply above pH 7 and pH 4, respectivel
y, because 5FU and Vc were negatively charged above pH 7 (pK(a) = 8.0)
and pH 4 (pK(a) = 4.25), respectively.