T. Aoki et al., ENANTIOSELECTIVE PERMEATION THROUGH MA-[3-(PENTAMETHYLDISILOXANYL)PROPYL]-L-GLUTAMATE) MEMBRANES, Journal of membrane science, 99(2), 1995, pp. 117-125
Poly(L-glutamic acid ester) with 3-(pentamethyldisiloxanyl) propyl gro
ups was prepared from poly(gamma-methyl-L-glutamate) (PMLG) by ester e
xchange reaction. This polymer had an alpha-helical structure in the m
embrane prepared from 1,2-dichloroethane solution. The membrane formin
g ability of the polymer was better than that of PMLG. Optical resolut
ion of (+/-)-tryptophan was achieved by pressure driven permeation thr
ough the membrane. The enantioselectivity was 16% enantiomeric excess
(%ee) and the permeation rate was high (10(-6) g m/m2 h). This enantio
selective permeation continued for more than 160 h. With an increase i
n the disiloxane side chain content, the permeation rate could be incr
eased while maintaining the selectivity. Since the enantioselectivity
for adsorption favoured the (+)-isomer and that for permeation favoure
d the (-)-isomer, enantioselective permeation was caused by suppressio
n of the (+)-isomer permeation. It was suggested that the permeation o
f dilute aqueous tryptophan solution occurred mainly in the region of
highly mobile disiloxane side chains, which had no asymmetric centers,
by measurements and analysis of the pervaporation of dilute aqueous e
thanol solution. Therefore it was believed that this siloxane region w
as small enough for the asymmetric centers in the main chain to recogn
ize enantioselectively the permeating solute.