Syntheses of imidazolium-bridged cyclodextrin dimers and their catalytic properties in the hydrolytic cleavage of p-nitrophenyl alkanoates

Two imidazolium-bridged cyclodextrin dimers 3a and 3b were prepared by reacting 6-deoxy-6-N-imidazolyl-β-CD (2) with bis(bromomethyl)benzene. The catalytic properties of 2, 3a and 3b in the hydrolytic cleavage of p-nitrophenyl alkanoates, in the form of acetate (PNPA) , butanoate (PNPB) , hexanoate (PNPH) and octanoate (PNPO), were examined. CD dimeis showed middling rate enhancements around neutrality. Catalytic rate constants ( kc) in the presence of 3a or 3b did not vary much with chain length of esters. In contrast, dissociation constants ( Kd) and selectivity factors (kc/Kd) for "long-chain" esters were much smaller and significantly larger than those for short-chain ones respectively, indicating CD dimers 3a and 3b have good dimensional recognition ability and substrate selectivity in the hydrolytic cleavage of p-nitrophenyl alkanoates . Their kinetic consequences are briefly interpreted.     

噻酮对离体乳猪皮肤光透明效果影响的实验研究

研究一种新型促渗剂——噻酮对皮肤组织光透明效果的影响。分别用单纯聚乙二醇400(PEG400)溶液以及PEG400与噻酮的混合溶液作用于含角质层及去角质层的离体乳猪皮肤,利用积分球系统动态检测样品对632．8 nm光的透射率变化,并对样品拍照获得直观图。结果表明:混合溶液作用于两种皮肤模型后,其光透明性均有不同程度的增加,即衰减系数降低;比较去角质层皮肤与含角质层皮肤的衰减系数的变化,前者比后者大19倍;单纯的PEG400仅对去角质皮肤有一定的光透明效果,并且所导致的皮肤衰减系数的降低仅为混合液作用后的2/3。因此,噻酮作为良好的促渗剂能与PEG400产生协同效应,有效提高皮肤光透明效果。