SCIENCE & TECHNOLOGY CONCENTRATES
MICROBIAL DUO TURNS CELLULOSE INTO FUEL Fuels derived from biological processing of cellulose could serve as environmentally friendly gasoline replacements. But organisms that break the complex plant matter into sugars and convert them to fuels on a commercial scale have proved elusive. Now, Jeremy J. Minty of the University of Michigan, Ann Arbor, and coworkers report using not one but two microbes to make a cellulosic biofuel from inedible plant matter (Proc. Natl. Acad. Sci. USA 2013, DOI: 10.1073/pnas.1218447110). The fungus Trichoderma reesei hydrolyzes cellulose to sugars, and genetically engineered Escherichia coli in the same reaction vessel converts the sugars to isobutyl alcohol. When burned, the alcohol produces 82% as much energy per gallon as gasoline and slightly more than ethanol. Microbes given corn roughage that was pretreated to improve its microbial digestibility generated a product mixture containing isobutyl alcohol in high concentration and in yields reaching 62% of the theoretical maximum. Both organisms feed on the sugars, and competition can ensue. If one microbe dominates, conversion to isobutyl alcohol will cease. The researchers have found conditions, however, where both T. reesei and E. coli survive and convert the cellulose to isobutyl alcohol as desired. Now they aim to optimize the microbial system and assess its larger-scale performance. The concept could be adapted to make commodity chemicals, the team notes.—PK
REVERSIBLE BONDING IMPROVES CRYSTALLIZATION
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In an advance that may lead to new types of highly porous and conductive organic materials, researchers have developed a chemically flexible method to assemble organic building blocks into covalently bonded networks that form unusually large crystals (Nat. Chem. 2013, DOI: 10.1038/nchem.1730). Methods to string together molecular units into well-ordered extended networks have produced a large number of crystalline metal-organic frameworks (MOFs) and a smaller number of metal-free
CRYSTAL STRUCTURE OF A CUPRATE-CARBONYL π-COMPLEX Bonding between a copper ion and the π-orbitals of a double bond, C=O in this case, has been observed by X-ray crystallography for the first time. Such three-center bonds have been proposed as intermediates in a number of important copper-catalyzed reactions, including additions ● Cu ●O using Gilman reagents (R2CuLi). ●C ● Li The arrangement is unstable, and H not shown until recently, researchers have only been able to infer the intermediate’s existence. In June, Steven H. Bertz, Craig A. Ogle, and Richard A. Hardin of the University of North Carolina, Charlotte, reported that by using a tetrahydrofuran-based solvent system they could stabilize a series of cuprate-carbonyl π-complexes and record their NMR signatures (J. Am. Chem. Soc. 2013, DOI: 10.1021/ ja404105u). Now, the team has prepared one of the compounds at the The copper center of the cupratecarbonyl π-complex adopts a gram scale and grown crystals suitable for pseudo-square planar geometry. X-ray analysis (Angew. Chem. Int. Ed. 2013, DOI: 10.1002/anie.201303783). The structure (shown) confirms structural predictions previously made on the basis of NMR and theoretical calculations. Correlating the data obtained from the X-ray and NMR methods may help chemists leverage the instability of these intermediates to tune and customize catalytic reactions.—CB
variants, such as covalent organic frameworks (COFs). The extreme porosities and gas-uptake capacities of some of these materials are leading manufacturers to commercialize them for gas separation and storage. Unlike MOFs, COFs tend to selfassemble via irreversible covalent bonding, an “unforgiving” type of bonding that leads to powdered products because crystallization Large COF is difficult to control. crystals grown University of Montreal from monomers featuring nitroso chemists Daniel Beaugroups. doin, Thierry Maris, and James D. Wuest have now shown that covalently bonded networks can be prepared with improved control over crystallization by using a more forgiving type of bonding. Specifically, the team used reversible self-addition polymerizations to CEN.ACS.ORG
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form covalent bonds between monomers with four tetrahedrally oriented nitroso groups and thereby prepared macroscopic single crystals of azodioxy COFs.—MJ
ANTIGEN LEVELS SHOW PROSTATE CANCER’S AGGRESSIVENESS The level of prostate-specific antigen (PSA) in serum is often used to diagnose prostate cancer. Some patients with high PSA levels undergo invasive biopsies or surgery, which can cause side effects like incontinence and impotence. Some prostate cancers are slow to progress, and studies have shown that some patients do better if they watch and wait instead of having surgery. Michael J. Ahrens of the biotech firm Ohmx Corp. and coworkers, including chemist Thomas J. Meade of Northwestern University, have now tested what could turn out to be an improved diagnostic procedure, and initial results are promising (Prostate 2013, DOI:
SCIENCE & TECHNOLOGY CONCENTRATES
10.1002/pros.22714). The researchers propose that PSA enzymatic activity, instead of PSA concentration, be measured to assess prostate cancer’s aggressiveness. Their study of surgically treated patients finds that higher levels of PSA activity correspond with less aggressive types of prostate cancers. “Our results suggest that many—22% in our study population—of the diagnosed patients with nonaggressive prostate cancer could have averted or delayed radical prostatectomy,” the researchers note. Ohmx is continuing validation studies and developing a commercial test, which they have trademarked PPA (PSA Peptidase Activity).—SB
REDESIGNED STAPLED PEPTIDE TARGETS p53 Peptides play many important roles in the human body. They don’t always translate smoothly, however, into drugs that control human physiology. One promising strategy to convert peptides into therapies is “stapling”— O H N LTF O
A cheap, lightweight material could one day help survivors of natural disasters get clean water fast. A porous gel embedded with silver nanoparticles absorbs contaminated water, kills bacteria in seconds, and releases drinkable water with a squeeze (Environ. Sci. Technol. 2013, DOI: 10.1021/ es401219s). Xiao (Matthew) Hu, a materials scientist at Nanyang Technological University, in Singapore, and his colleagues synthesized the gel and used it to sop up water laced with two troublesome bacterial species, Escherichia coli and Bacillus subtilis. After 15 seconds, the amount of bacteria in the water squeezed out of the gel was 0.1% that of the original levels. When the A porous gel decorated with team increased silver nanoparticles the soak time to disinfects water and five minutes, the releases it with a amount of bactesqueeze. ria in the treated water was about one-millionth that of the tainted water. The team reports that a thin, 4-g cylinder of the material can soak up and purify a half-liter of water with one squeeze. The gel can be reused more than 20 times without degrading or losing its bactericidal powers.—JNC
ENVIRON. SCI. TECHNOL.
GEL DISINFECTS WATER WITH A SQUEEZE
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reinforcing floppy N helical motifs with a H hydrocarbon brace. A biotech company that specializes in stapled peptides now reports an improved lead for cancer therapies (Proc. Natl. Acad. Sci. USA 2013, DOI: 10.1073/pnas.1303002110). The peptide, ATSP-7041(shown), stifles tumor growth in rodents by restoring the activity of vital tumor suppressor p53. Tomi K. Sawyer and his team at Aileron Therapeutics took inspiration from SAH-p53-8, a stapled peptide designed to prevent a protein called MDM2 from masking p53. That stapled peptide had limited activity in the company’s most stringent tests. To make improvements, Aileron teamed with Lyubomir T. Vassilev and colleagues at Roche, a firm that has brought to human clinical trials molecules targeting the p53MDM2 interaction. In tests on cells, the fruit of their collaboration, ATSP-7041, had a prolonged effect on p53 compared with RG7112, a Roche drug candidate in earlystage clinical trials.—CD
VANADIUM DIOXIDE DOES A SOLID TRIPLE POINT Phase diagrams show the conditions at which solid, liquid, and gas phases of a material may coexist or occur alone. Phase diagrams can also be drawn for solid-state materials to illustrate the intersections of different electronic, magnetic, or structural phases. By studying temperature- and stress-dependent transitions between metallic and insulating states in vanadium dioxide, a group led by David H. Cobden of the University of Washington, Seattle, has now identified the first triple point for a solid, at which three solid phases coexist: a coincidence of the metallic and two insulating states of VO2 at 65.0 °C and zero applied stress (Nature 2013, DOI: 10.1038/ CEN.ACS.ORG
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nature12425). The finding was made possible because the VO2 nanowires used in the study are relatively easy to work with, Cobden says. He notes that the triple point is near room temperature, the material is relatively stable, and his team was able to distinguish the three phases optically. The finding will help researchers understand and exploit the mechanisms of VO2 phase transitions, which are SAA NH2 of particular interest for N sensing and switching H O applications. It may also help explain the properties of other materials with metal-insulator transitions, such as hightemperature superconductors.—JK
PYROTECHNICS KEEP GETTING GREENER Fireworks are beautiful, but their colorburning components—often perchloratebased mixtures—are less than environmentally friendly. Scientists, including Jesse J. Sabatini of the Army’s Picatinny Arsenal, in New Jersey, have been working to develop less polluting compounds for pyrotechnics used by the military and for public display. For N N example, scientists N recently synthesized N H2N high-nitrogen nitriH minotetrazolate 5-Aminotetrazole salts, which served as perchlorate replacements in pyrotechnic mixtures. But the high-nitrogen salts were not commercially available. In addition, producing a specific firework color required synthesizing a custom salt: for example, a strontium compound for red and a barium compound for green. Now, Sabatini and colleague Jared D. Moretti have discovered that a readily available and cheap nitrogen-rich compound, anhydrous 5-aminotetrazole (5-ATZ), can be used as a perchlorate replacement in both red and green flares (Chem.—Eur. J. 2013, DOI: 10.1002/chem.201300779). Sabatini and Moretti prepared a number of 5-ATZcontaining mixtures, which included magnesium and barium or strontium nitrate. Two mixtures, one producing green flame and one producing red, performed as well as perchlorate-containing mixtures and showed “excellent stability,” the researchers write. They envision that 5-ATZ could serve as a foundation for cost-effective red and green light-emitting pyrotechnic devices.—EKW
