Issue Date: April 19, 2004
More than 8,300 papers were presented late last month at the American Chemical Society national meeting in Anaheim, Calif. Here's a potpourri of research results discussed there.
- Vaccinelike agent may prevent type 1 diabetes
- Ligand cleanup in a snap
- Ionizing radiation breaks down CFCs
- TIGER tracks down pathogens
- Enzyme gets protective coat
- Limestone chip removes arsenic
- From nature's packaging to store packaging
- Versatile fluorinations using BrF3
- Snake-inspired nanoscale films
A small molecule called ISO-1 (shown) has demonstrated promising activity as a vaccinelike agent that prevents the development of type 1 diabetes. In type 1 diabetes, the immune system attacks and kills pancreatic beta cells, shutting down pancreatic insulin production and causing hyperglycemia (excess blood sugar). Yousef Al-Abed of North Shore-Long Island Jewish Research Institute, Manhasset, N.Y., and coworkers now have found that mice given a compound that induces type 1 diabetes were completely protected from the disease by ISO-1, and that the drug also prevented the disease in 90% of mice genetically bred to develop it. Al-Abed believes that ISO-1 may work by inhibiting macrophage migration inhibitory factor--a protein he and his coworkers had earlier found to play a key role in the inflammatory cascade leading to beta cell destruction. ISO-1 is currently undergoing further animal tests for activity against type 1 diabetes as well as the type 2 form of the disease, in which the body either produces insufficient insulin or cells don't use it properly. A number of research groups also are studying other potential vaccinelike agents against diabetes.
To quickly and inexpensively remove unwanted phosphine ligands in reactions catalyzed by group 10 transition metals, reach for cuprous chloride. Add a small amount to the worked-up reaction mixture, and stir for 10 minutes. Or transfer the reaction mixture to a rotary evaporator flask, add a few crystals of cuprous chloride, and connect the flask to a rotary evaporator. Either way, according to chemistry professor Bruce H. Lipshutz and graduate student Bryan Frieman of the University of California, Santa Barbara, copper pulls the phosphines away from the catalyst and sequesters them in a complex that is easily separated by column chromatography. Many phosphines can be recovered by treating the complexes with the dilithium salt of a commercial dithiocatechol. The protocol is based on the copper-induced acceleration of the Stille coupling, which is catalyzed by palladium. Researchers in Spain have shown that the role of copper there is to pull phosphine away from palladium, according to Lipshutz. "As soon as I saw those results, I knew the answer to cleaning up phosphines."
Ionizing radiation breaks down CFCs
Low-energy electrons generated by ionizing radiation play a key role in decomposing chlorofluorocarbons and other organohalides in aqueous environments, according to a new study. Investigating the mechanisms of these decomposition reactions, Johns Hopkins University chemists Chris C. Perry and D. Howard Fairbrother, Rutgers University physicists Nadir Faradzhev and Theodore E. Madey, and their coworkers irradiated ice films containing CF2Cl2 and other organohalides with X-rays and probed the reaction products via vibrational and photoelectron spectroscopy. The group reported that the cascade of low-energy electrons generated by the X-rays leads to the formation of solvated Cl– ions and CF2Cl radicals. In dilute films, CF2Cl intermediates react with oxygen-containing molecules to produce stable carbonyl dihalides, they said. Continued exposure to X-rays converts the dihalides to CO2 and produces H3O+ and solvated F– ions. The study may lead to radiation-based cleanup procedures for halogen compounds and broadens understanding of stratospheric processes, according to the group.
Using a new strategy called TIGER--for triangulation-identification for the genetic evaluation of risk--which combines polymerase chain reaction (PCR) and mass spectrometry analysis of nucleic composition, Steven A. Hofstadler and coworkers at Ibis Therapeutics in Carlsbad, Calif., and SAIC in San Diego can identify bacteria and viruses in a wide variety of samples. Because it can be used with microbes that haven't been previously identified, such an approach could be helpful for identifying biological warfare agents or tracking emerging infectious diseases. Multiple pairs of PCR primers from different regions of the genome are used to amplify the DNA extracted from clinical or air-monitoring samples. The primers correspond to highly conserved regions in bacterial DNA or viral nucleic acids that flank highly variable regions. Using primers from regions throughout the genome allows a single set of PCR primers to identify any organism. Accurate mass measurements of the PCR products provide an unambiguous base composition. By combining the base compositions from the different primer pairs, researchers can obtain a signature for any organism. If more information is needed, more specific "drill-down" primers can be used to identify different strains of viruses or bacteria. By adding known numbers of DNA sequences that can act as standards, researchers can make the method quantitative rather than simply qualitative. The team has used TIGER to distinguish the severe acute respiratory syndrome virus from other corona viruses, to identify a Group A streptococcal pneumonia outbreak, and to monitor biowarfare agents in air samples.
By wrapping single-enzyme molecules in a protective polymer netting, scientists have extended the biocatalyst's shelf life. Using the enzyme chymotrypsin as a test case, Jay W. Grate and Jungbae Kim of Pacific Northwest National Laboratory attached vinyl groups to lysine residues on the enzyme's surface. The modified enzyme was then solubilized in hexane and mixed with silane monomers containing both vinyl groups and trimethoxysilyl groups. Following free-radical polymerization of the vinyl groups, the pendant trimethoxysilyl groups were hydrolyzed and condensed. Although the process surrounds each chymotrypsin molecule in a polymer netting several nanometers thick, the enzyme's catalytic activity and ability to bind a substrate are unaffected, the researchers reported. The soluble, encapsulated enzymes are remarkably stable and can be made into films or deposited onto other nanostructured substrates for applications in biosensing and environmental remediation, Kim said. He and Grate are optimistic that the method can be used to stabilize many other enzymes, too.
Chemists have discovered an inexpensive and effective method for extracting arsenic from drinking water. Cathleen J. Webb, a chemistry professor at Western Kentucky University, Bowling Green, and colleagues observed that the limestone bedrock in the Madison Aquifier in South Dakota retained arsenic. She then fabricated a simple limestone chalk filter and found that, at high pH, it removed more than 95% of the arsenic in a contaminated sample (from 100 ppb down to 5 ppb). The smaller the limestone grain, the more effectively arsenic was removed. Webb, chemistry student Chelsea Campbell, and coworkers experimented with a chip of Kentucky limestone and observed that mineral precipitates formed on the outer surface of the chip when it was dunked in highly concentrated arsenic solutions. They suspect that the precipitates contain calcium-arsenic oxides, perhaps hydrated. EPA's standard for arsenic in drinking water is less than 50 ppb, and in 2006, EPA will be adopting a more stringent standard of 10 ppb. The new standard, Webb said, will strain poor rural communities with arsenic-tainted water because current iron-based methods for arsenic removal are expensive. She hopes that this simple limestone filter will benefit rural communities in the U.S. as well as abroad.
From nature's packaging to store packaging
Swedish researchers have introduced a novel oxygen barrier film made from agricultural waste. Oxygen barrier films play an important role in food packaging. Often placed between an outer paper carton and an inner liquid barrier, they help stave off the spoiling of perishables by protecting food from oxygen's reactivity. Currently, oxygen barriers--for example, in an orange juice carton--usually consist of thin films of aluminum or ethyl vinyl alcohol (a polymer). These materials, however, are difficult to recycle. That's why Maria H. Gröndahl, a graduate student, and Paul Gatenholm, a professor of biopolymer technology at Chalmers University of Technology, Göteborg, Sweden, started investigating xylan, a group of hemicelluloses found in the walls of many plant cells, especially those of straw and husk. Xylan (backbone shown) is generally thrown away. But Gröndahl found that xylan has excellent oxygen barrier properties, similar to ethyl vinyl alcohol. She took xylan from aspen wood and added the plasticizers xylitol and sorbitol to make the material flexible. She has applied for a patent on this environmentally friendly oxygen barrier film.
Versatile fluorinations using BrF3
Bromine trifluoride has been known as a useful fluorinating reagent for a long time, yet most chemists have shied away from it because BrF3 can react violently with water and oxygen-containing organic solvents. In recent years, chemistry professor Shlomo Rozen and coworkers at Tel Aviv University, in Israel, have developed successful procedures using BrF3 to add fluorine to a variety of organic substrates used in pharmaceutical and agricultural applications. In Anaheim, Rozen reported that alkyl halides (RCH2Br) can be converted to , -difluoro esters (RCF2COOCH2CH3), and esters can be convert-ed to -trifluoromethyl esters (the product in the reaction sequence shown) and difluoroacrylates (F2C'CRCOOCH3). These compounds can be further hydrolyzed to carboxylic acids. The multistep reactions involve preparing sulfonated intermediates, where the sulfur is required for further reaction with BrF3 in CFCl3 solvent. In the example shown, an ester is reacted with lithium diisopropylamide, CS2, and CH3I to form a disulfide. Reaction with BrF3 followed by treatment with HOF·CH3CN oxidizing agent and tetrabutylammonium fluoride produces the ester in 70% yield [Chem. Commun., 2004, 594]. Because a general synthesis of -trifluoromethylcarboxylic acids has not been available, they have been "conspicuously lacking from the arsenal of fluorine-containing compounds, despite their enormous potential," Rozen said.
Snake-inspired nanoscale films
Receptor organs used by pythons, boas, pit vipers, and other snakes to detect heat from prey while hunting in complete darkness have inspired the design of nanocomposite films that are prospective candidates for thermal and acoustic microsensor arrays. The organs, located in the jaws of snakes, have membranes with built-in thermomechanical sensitivity, noted Vladimir V. Tsukruk, professor of materials science and engineering at Iowa State University. "Our first design is a nanocomposite membrane composed of a central layer of gold nanoparticles sandwiched between polyelectrolyte multilayers." The membranes are fabricated by spin-assisted layer-by-layer assembly [Adv. Mater., 16, 157 (2004)]. The polymer multilayers consist of poly(allylamine hydrochloride) and poly(sodium 4-styrenesulfonate). The membranes, which are about 50 nm thick and 100 µm in diameter, are robust and smooth, have lifetimes of several months, and show outstanding mechanical strength, Tsukruk noted. "They exhibit excellent elasticity and mechanical stability as well as superior sensitivity to thermal and pressure stimuli compared with conventional inorganic membranes," he said. His group is now investigating the properties of the films.
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