SCIENCE/TECHNOLOGY CONCENTRATES • Techniques expedite glucose transport across lipid bilayers Glucose transport across lipid bilayers has been facilitated by two research groups using different mechanisms. Hydrophilic substances such as glucose can traverse cell mem branes only through the action of specific transport proteins. Artificial systems that aid transport of such substances could be of potential use for drug delivery and other applications. An initial step toward this goal has now been taken by Pam ela R. Westmark and Bradley D. Smith of the University of Notre Dame [/. Am. Chem. Soc, 116,9343 (1994)]. They find that various boronic acids can pass through the lipid bilayer of a liposome (lipid vesicle), form a complex with glucose molecules encapsulated in the liposome, and then transport them out through the membrane. They also find that boronic acids can transport ribonucleosides, arabinonucleosides, other sugars, and a-hydroxycarboxylic acids through lipid bilayers. A second group, Juan R. Granja and M. Reza Ghadiri of Scripps Research Institute, has designed, synthesized, and characterized the first artificial transmem brane pore structure that transports glucose across a lipid bilayer [/. Am. Chem. Soc, 116, 10785 (1994)]. The synthetic membrane-spanning channel is a tubular hydrogen-bonded structure of cyclic peptides composed of alternating hydro phobic D- and L-amino acids. When the channels are embed ded in liposome membranes, they allow glucose to pass through the lipid bilayer.
• Highly charged iodine, argon ions generated from clusters Irradiation of hydrogen iodide clusters with an intense fem tosecond laser beam produces iodine ions as highly charged as I17+. Similar irradiation of clusters of argon atoms with a single HI molecule produces argon atoms as highly charged as Ar8+. In both cases, the highly charged ions have tremen dous kinetic energy as measured in a time-of-flight mass spectrometer, on the order of several hundred to 1,000 eV [Chem. Phys. Lett., 229,333 (1994)]. A. Welford Castleman Jr., chemistry professor at Pennsylvania State University, Uni versity Park, and coworkers say that their startling results indicate that the brief, intense burst of laser light appears to generate highly charged iodine ions within a cluster, which is then ripped apart in a "coulomb explosion." They base this idea on a number of observations. One is that highly charged iodine ions aren't generated when single HI mole cules are exposed to the laser beam. Another is that when clusters containing only argon are irradiated, the chemists detect only singly charged argon ions. Thus, Castleman sug gests, some feature of the clusters allows the rapid absorp tion of many photons. And iodine in the mixed clusters ap pears to be the species that is ionized because it has to be present to produce the highly charged argon ions.
• Superconductivity seen in lanthanum nickel boronitrides In the past year, the discovery of superconductivity in qua ternary metal borocarbides at temperatures as high as 23 Κ has reinvigorated research on intermetallic superconductors. Now, one of the pioneering teams in this effort has found
that another family of intermetallics—boronitrides—also harbors superconductors. Robert J. Cava of AT&T Bell Lab oratories, Murray Hill, N.J., and coworkers there, in the Netherlands, and in Japan, report that lanthanum nickel boronitride ( I ^ N ^ i y s y can be prepared by melting a mix ture of lanthanum, nickel, and boron in an electric arc under a nitrogen atmosphere [Nature, 372,245 (1994)]. The materi al slips into superconductivity when cooled to about 12 K. The layers of Ni2B2 tetrahedra found in both the nickel bo ronitrides and borocarbides are important building blocks for intermetallic superconductors, much the same way as Cu0 2 layers are for the cuprate superconductors, the re searchers point out. Their work strongly suggests "that a large number of unusual superconducting intermetallic phases are yet to be found, based on materials more com plex than had previously been considered as candidates for superconductivity/'
• 'Molecules in a box'—a new application of dendrimers Researchers in the Netherlands have synthesized a cagelike structure made from dendrimers, which are highly branched macromolecules that emanate from a central core. When synthesized in the presence of guest molecules, these dendritic boxes can capture and hold the guests inside cav ities from which diffusion appears to be extremely slow. The advance may lead to controlled drug delivery systems or could be used as a new approach to study the photochemis try of isolated molecules in well-defined cages. E. W. Meijer of Eindhoven University of Technology's organic chemistry laboratory and colleagues synthesized the boxes based on the construction of a chiral shell of protected amino acids on poly(propyleneimine) dendrimers with 64 amine end groups [Science, 265,1226 (1994)]. The chemists elucidated the structure with *Η and 13C nuclear magnetic resonance spec troscopies, along with infrared, ultraviolet, and circular dichroism spectroscopies. The researchers encapsulated sever al types of dye molecules in the cages, including rose bengal with an average loading of one dye molecule per box.
• Single-enantiomer version of antiasthma drug patented A patent has been awarded to Sepracor, in Marlborough, Mass., for the use of (R)-albuterol to treat asthma. The patent (U.S. 5,362,755) is the seventh awarded to the com pany for a "racemic switch/' the term applied to the rede velopment of an established racemic drug as a single enantiomer. In the case of albuterol, the racemic form is al ready the best-selling antiasthma drug, with worldwide sales of $1.1 billion. In its racemic form, the drug is an offpatent p2-adrenergic stimulant marketed in the U.S. under the tradename Ventolin by the inventor, the Allen & Hanburys division of Glaxo, and as Proventil by Schering Corp. David S. Barlow, general manager of Sepracor's drug business, says, "Our preclinical and clinical studies have demonstrated that (R)-albuterol is solely responsible for the desired therapeutic effect of bronchodilation. Further, (S)-albuterol, previously thought to be inert, can produce bronchi al hyperreactivity, thereby increasing the severity of asthma attacks." NOVEMBER 21,1994 C&EN
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