We examined the antibacterial and hemolytic activities in a series of amphiphilic block and random copolymers of poly(vinyl ether) derivatives prepared by base-assisting living cationic polymerization. Block and random amphiphilic copolymers with similar monomer compositions showed the same level of activity against Escherichia coli . However, the block copolymers are much less hemolytic compared to the highly hemolytic random copolymers. These results indicate that the amphiphilic copolymer structure is a key determinant of activity. Furthermore, the block copolymers induced dye leakage from lipid vesicles consisting of E. coli -type lipids, but not mammalian lipids, while the random copolymers disrupted both types of vesicles. In addition, both copolymers displayed bactericidal and hemolytic activities at concentrations 1 or 2 orders of magnitude lower than their critical (intermolecular) aggregation concentrations (CACs), as determined by light scattering measurements. This suggests that polymer aggregation or macromolecular assembly is not a requisite for the antibacterial activity and selectivity against bacteria over human red blood cells (RBCs). We speculate that different single-chain conformations between the block and random copolymers play an important role in the antibacterial action and underlying antibacterial mechanisms.
When the fruitfly, Drosophila rtwlanogaster, was reared on media deficient in carotenoids and retinoids, the level of 3-hydroxyretinal (the chromophore of fly rhodopsin) in the retina decreased to < 1% compared with normal flies. The level of 3-hydroxyretinal increased markedly in flies that were given a diet supplemented with retinoids or carotenoids. The retinas of flies fed on all.tram retinoids and maintained in the dark predominantly contained the all-tram form of 3-hydroxyretinal, and showed no increase in the level of either the 11-c/s isomer or the visual pigment. Subsequent illumination of the flies converted substantial amounts of all-tram 3-hydroxyretinal to its 11-c/s isomer. The action spectrum of the conversion by illumination showed the optimum wavelength to be ~420 nm, which is significantly greater than the absorption maximum of free, all-tram 3-hydrox),retinal. Flies that were fed on carotenoids showed a rapid increase of the levels of 11-c/s 3-hydroxyretinal and of visual pigment in the absence of light.
For the precision synthesis of primary amino functional polymers, cationic polymerization of a phthalimidecontaining vinyl ether monomer precursor, 2-vinyloxyethyl phthalimide (PIVE), was examined using a base-assisting initiating system. Living polymerization of PIVE in CH 2 Cl 2 in the presence of 1,4-dioxane as an added base yielded nearly monodispersed polymers (M w /M n < 1.1) and higher molecular weight polymers, which have never been obtained using other initiating systems. Furthermore, block copolymers with hydrophobic or hydrophilic groups could be prepared. The deprotec-tion of the pendant phthalimide groups gave well-defined pHresponsive polymers with pendant primary amino groups. Dual-stimuli-responsive block copolymers having a pH-responsive polyamine segment and a thermosensitive segment selfassembled in water in response to both pH and temperature.
The nature of the polymer-water interface in the poly(methyl 2-propenyl ether) (PMPE)-water model system is investigated by sum-frequency generation spectroscopy, which at the moment gives the best depth resolution among available techniques. PMPE, synthesized via living cationic polymerization, is structurally similar to poly(methyl methacrylate) (PMMA) except for lacking a carbonyl group. We here probe the polymer local conformation as well as the aggregation states of water at the interface. Comparing the results of our measurements to the PMMA-water system, the effect of a carbonyl group on the water structure at the interface is discussed. This knowledge should be crucial to the design and construction of highly functionalized polymer interfaces for bioapplications.
Silica nanospheres (SNSs) of ca. 15 nm in diameter assemble into nanoring structures with the aid of amphiphilic block copolymers containing the oxyethylene side chains poly[(2-ethoxyethyl vinyl ether)-block-(2-methoxyethyl vinyl ether)] [poly(EOVEb-MOVE)]. Cryo-transmission electron microscope observation confirms that the ring assembly of SNSs occurs in the liquid phase. The SNSs favorably assemble into ring-like nanostructures in the presence of 1-2 wt% EOVE 100 -b-MOVE 310 at pH~7.8 and 45°C. Irregular aggregates of SNSs form at 60°C, most likely because of the hydrophobic collapse of the thermoresponsive block copolymer. A series of poly(EOVE-b-MOVE) with varying block lengths successfully induce the ring assembly of SNSs, whereas a random copolymer fails, indicating that the polymer's molecular structure critically affects the assembly mode of SNSs. Interestingly, SNSs of a larger size (ca. 30 nm) assemble one-dimensionally into chain-like nanostructures in the presence of EOVE 100 -b-MOVE 310 .
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