ABSTRACT:Living cationic copolymerization of isobutyl vinyl ether with p-methoxystyrene was effected by an equimolar mixture of hydrogen iodide and iodine (HIII2 initiator) at -l5°C in nonpolar solvents (carbon tetrachloride and toluene). Isobutyl vinyl ether reacted faster than pmethoxystyrene. The products were random copolymers with a nearly monodisperse molecular weight distribution (MWD) (MwiM.= 1.1-1.2). Their number-average molecular weight (M.) increased in proportion to total monomer conversion. The iodine-initiated copolymerization under similar conditions led to long-lived (but not perfectly living) copolymers with a narrow MWD (MwiM.= 1.2-1.3). In contrast, boron trifluoride etherate induced a conventional transferdominant copolymerization. TheM. of the copolymers obtained with the HIII2 initiator was almost independent of the monomer feed ratio, but in the BF30Et2-initiated non-living process, the polymer molecular weight decreased sharply with increasing isobutyl vinyl ether content in the feed. These findings show the living copolymerization by HIII2 to be free from the cross-transfer usually involved in the conventional cationic copolymerization of vinyl monomers.
Changes in membrane fluidity induced by lectin addition to 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) vesicles containing synthetic glycopeptides were measured by depolarization of the fluorescent probes 8-anilino-1-naphthalenesulfonate (ANS) and 1,6-diphenyl-1,3,5-hexatriene (DPH). In the present synthesized glycopeptides, N-acetylglucosamine (GlcNAc) and a tripeptide were connected by aliphatic chains of different lengths. A pyrenyl group, which is introduced to the peptide moiety, acted as a probe to characterize the distribution of glycopeptides in the membrane on the basis of its excimer formation. The glycopeptide was shown to be distributed to DPPC vesicles with the peptide moiety buried in the hydrophobic core of the lipid bilayer and the glyco moiety exposed to the outside of the membrane. By the addition of wheat germ agglutinin (WGA) to the vesicles containing the glycopeptides, intravesicular cross-linking of glycopeptides in the membrane and aggregation of vesicles were observed. The intravesicular cross-linking was antagonized by GlcNAc above the phase transition temperature. However, the dissociation of aggregation required the addition of a stronger antagonist, N,N'-diacetylchitobiose. The addition of the glycopeptide to DPPC vesicles above the phase transition temperature decreased the membrane fluidity. However, a succeeding addition of WGA caused a large increase of membrane fluidity at either the surface or the hydrophobic core of the lipid bilayer membrane. This increase of membrane fluidity was attributed to two factors by use of two kinds of antagonists having different potencies: one is a WGA-mediated cross-linking of glycopeptides in the membrane, and the other is a close contact of vesicles on aggregation.
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