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Sea slug's strange halogenated sesquiterpenoid
A halogenated sesquiterpenoid with an unusual carbon skeleton has been isolated from the sea slug Aplysia dactylomela. Consisting of three six-membered rings and two fused four-membered rings, the unique compound (shown) has been named aplydactone by chemist Valentin A. Stonik of the Pacific Institute of Bioorganic Chemistry of the Far-Eastern Division of the Russian Academy of Sciences, Vladivostok, and coworkers [J. Am. Chem. Soc., 123, 504 (2001)]. The four-membered rings may be biosynthesized, the researchers suggest, through an intramolecular enzymatic [2 + 2] cycloaddition in an isomeric spirocyclic compound that they previously isolated from the same sea creature. Several of the carbon-carbon bonds in aplydactone's four-membered rings are significantly longer than those found in cyclobutane. The dihedral angles are also unusual. "It was hard to imagine before [its isolation] that such compounds could be stable enough to exist in nature," the authors write.
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Lipid bilayers stack up
Lipid bilayers stack one on top of another in the presence of Cu2+ to form long columnlike structures of uniform width [J. Am. Chem. Soc., 123, 496 (2001)]. Materials scientist Darryl Y. Sasaki and coworkers at Sandia National Laboratories fashion the bilayers from lipids they previously used in developing metal-ion sensors—distearylphosphatidylcholine and a synthetic receptor lipid functionalized with iminodiacetic acid. Addition of Cu2+ to the bilayer solution induces vesicle aggregation, evident from an increase in solution turbidity. The team images the bilayers with transmission electron microscopy before and after addition of Cu2+. In the presence of Cu2+, roughly a fifth of the bilayers self-assemble into stacks. The researchers hypothesize that Cu2+ is chelated by iminodiacetic acid on adjacent bilayers. The first two bilayers that interact determine the width of the stack that forms, they suggest. Their work may have applications in building nanoscaffolds or developing new optical materials, they say.
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'Lost-wax' method forms nanoparticles
To prepare solid and hollow nanoparticles of polymers, semiconductors, metals, and metal oxides, chemists at Rice University employ an approach similar to the lost-wax technique used by ancient Greeks to create molds for bronze statues [Science, 291, 453 (2001)]. Vicki L. Colvin and coworkers prepare a macroporous polymer template from a silica colloidal crystal by polymerizing monomers in the crystal voids. After etching out the silica, the Rice team fills the voids of the polymer template with materials such as titanium dioxide, polypyrrole, cadmium sulfide, and nickel. The host polymer is removed with a solvent or by heating, leaving behind a monodisperse colloidal array of the guest material. "We replicate the size and shape of the starting sacrificial particle into many other materials, shapes, and forms," Colvin explains. The team also generates particles with nonspherical shapes by compressing or stretching the plastic mold. "We are now aiming to form hollow and core-shell sphere polymers specifically designed for drug delivery," Colvin tells C&EN.
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Left-handed polyalanine helix
Polyalanines can fold into a previously unknown left-handed helix depending on the charge of the terminal ends, according to Kwang S. Kim and coworkers at Pohang University of Science & Technology, South Korea. This new folding motif, named l-helix, has five residues per turn. It is adopted by polyalanines in which both terminal ends are charged: NH3+-(alanine)n-COO- (at left in figure). Polyalanines with neutral terminal ends [CH3-(alanine)n-NH2, right] fold into the well-known right-handed a-helix [J. Am. Chem. Soc., 123, 514 (2001)]. The results are based on calculations and simulations of polyalanines with different terminal charge conditions in the gas phase. They do not take into account solvent effects. The researchers suggest that manipulating the terminal ends can be used to control the handedness of a protein fold.
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SCIENCE & TECHNOLOGY ROUNDUP
- Ionic liquid forms of DNA, containing duplex DNA as the anion and a poly(ethylene glycol)-transition-metal complex as the cation, have been prepared by chemists at the University of North Carolina, Chapel Hill [J. Am. Chem. Soc., 123, 218 (2001)]. The chemists probe the ionic liquids electrochemically.
- Schizophrenia, which may be related to an excess of dopamine receptors in brain cells, currently can be diagnosed only through psychiatric and behavioral tests. Researchers at the Weizmann Institute of Science in Israel report that white blood cells of schizophrenics also have extra dopamine receptors and could thus be used in a blood test to diagnose the disease [Proc. Natl. Acad. Sci. USA, 98, 625 (2001)].
- When the oil component of a water-in-oil microemulsion is replaced with an anisotropic nematic liquid crystal, the liquid-crystal molecules exhibit directional coupling with the surfactant that's stabilizing the water microdroplets in the emulsion, according to researchers in Japan. The bulk material formed is essentially isotropic and thus transparent [Nature, 409, 321 (2001)].
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