Science Concentrates BIOBASED CHEMICALS
▸ Nickel turns waste lignin into valuable compounds To make fuels and chemicals from biomass, producers typically use the sugar-containing cellulose components. But first they must remove the surrounding lignin, a hardy phenolic biopolymer that helps support plant structure. Researchers have been looking for viable methods to crack apart the lignin into useful chemical intermediates, with some success coming from using precious-metal catalysts. A new study shows that an inexpensive nickel catalyst can transform 68% of lignin from the grass Miscanthus into aromatic compounds, while preserving
COATINGS
A shrinkly, wrinkly waterrepellent surface This SEM image reveals a Superhydrophobic coatings that make crinkled, water-repellent layer water droplets dance and roll off a of Teflon on top of a polyolefin. surface have been proposed for applications such as self-cleaning cars, buildings, and food-processing equipment. Chiara Neto of the University of Sydney and colleagues have devised a method for creating a more durable type of one of these coatings by combining slippery Teflon (polytetrafluoroethylene) and a heat-shrinkable plastic (ACS Appl. Mater. Interfaces 2016, DOI: 10.1021/acsami.5b12165). The scientists spin-coated a Teflon solution onto two types of shrinkable plastic: PolyShrink, a polystyrene material similar to that found in the children’s craft toy Shrinky Dinks, and a commercial polyolefin shrink-wrap. When heated, each type of polymer contracts, and the tightly bonded Teflon layer crinkles. The surface structure— decorated with nanometer-scale wrinkles on top of folds a few micrometers across—traps pockets of air and prevents the surface from getting wet. A combination of polyolefin coated with a 10-nm-thick layer of Teflon repelled water most effectively, inducing droplets to bead up to a measured contact angle of 172° so that they barely touch the surface. What’s more, the superhydrophobic coating retains its water repellency even when scratched.—KATHERINE
BOURZAC, special to C&EN
residual plant sugars for subsequent conversion to fuels and other chemicals (ACS Sustainable Chem. Eng. 2016, DOI: 10.1021/ acssuschemeng.5b01776). Mahdi M. AbuOmar of Purdue University and colleagues combine 1 g of milled Miscanthus with 45 mL of methanol in a reactor containing nickel dispersed on activated carbon. The researchers place the catalyst in a microporous stainless steel cage so that the nickel can contact phenolic oligomers that form as the lignin breaks apart under high pressure and temperature, while keeping the catalyst separate from the carbohydrate residue left behind by the reaction. The catalyst deoxygenates the oligomers, turning them into a range of compounds, including dihydroeugenol, propylsyringol, and ferulic acid methyl ester, which can be used to make vanillin, the principal component of vanilla flavoring. The team further treats the residue with an iron chloride catalyst to make furfural and levulinic
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C&EN | CEN.ACS.ORG | MARCH 14, 2016
acid—products that can be used to make biofuels or other chemicals.—DEIRDRE
LOCKWOOD, special to C&EN
TOTAL SYNTHESIS
▸ Making mannopeptimycins
sugars has been elusive. The biggest hurdle has been generating an N-glycosylated guanidine moiety in the molecule. No such chemical motif has ever been found in any other natural product. Chemists led by Gong Chen of Nankai University were able to add the sugar unit to the hindered guanidine nitrogen by using gold catalysis and incorporated this transformation into the first total syntheses of mannopeptimycins α and β (J. Am. Chem. Soc. 2016, DOI: 10.1021/jacs.6b01384). They hope the HO advance will enable exploration of
The bacteria-battling natural products OH known as mannopeptimycins have been known to go mano a mano against OH methicillin-resistant Staphylococcus OH O HO HO aureus and vancomycin-resistant O NH OH Enterococcus and win handily. The OH O mannopeptimycins have an unusuHN NH OH O al structure and a novel mode of HO O action, making them an interesting HN HO OH O N OH target for chemical synthesis beO HN cause analogs might improve their N HN H O antibacterial activity or reveal more NH details about how they work. But preparHN O ing the cyclic hexapeptides decorated HO NH HN with sugar groups has proven challengO ing. Chemists have made pieces of these O compounds, but until now, a total synthesis of the entire structure with its attached Mannopeptimycin α
CHIARA NETO (MICROGRAPH); SPONNER/SHUTTERSTOCK (GRASS)
Using a nickel catalyst, researchers converted lignin from Miscanthus grass into phenolic compounds, such as propylsyringol and ferulic acid methyl esters, that can be converted into valuable flavor and fragrance compounds.
previously inaccessible mannopeptimycin derivatives.—BETHANY HALFORD
DRUG DELIVERY
▸ Oligophosphoester transporters are better cargo ferries
PHYSICAL CHEMISTRY
Intrazeolitic molecules For the past several decades, Karl Seff of the University of Hawaii and his coworkers have been conducting intrazeolitic chemistry in which they use X-ray crystallography to watch what happens inside the tiny pores of zeolites as they are heated or chemically treated. Put another way, Seff says, “it’s doing chemistry in a 1-nm test tube.” The research has paid off with observations that could be helpful in understanding how the industrially important catalysts and sorbents work, as well as with the discovery of a few unexpected new molecules (J. Phys. Chem. C 2016, DOI: 10.1021/acs.jpcc.5b11490). The Seff team’s work has centered on the synthetic sodium aluminosilicates known as zeolites A and X + in which some sodium ions H H O are replaced by silver ions. In one observation, the re+O O+ searchers noticed that the crystallinity of the material H waxes and wanes depending on the dynamics of oxygen atoms in the zeolite frameWhen treated with methanol, a silverwork and the presence of containing zeolite generates the benzene O2. Furthermore, the team mimic C3H3O33+. When reduced to C3H3O32+, observed formation of quanthe molecule forms a dimer that neatly fits tum-dot-like silver halide into a zeolite pore (right). clusters and octahedral Ag6 clusters within the pores under various conditions. Seff notes that Ag6 is the smallest possible single crystal of silver that can form. When passing ammonia through the silver-exchanged zeolites, the researchers observed formation of unprecedented bent N3H5 and cyclic N3H3. And with methanol, they saw cyclic C3H3O33+—a new molecule that is electronically equivalent to benzene. Seff cautions that this menagerie of molecules may only be spotted within the pores of zeolites and be impossible to isolate outside those confines.—STEVE RITTER
A new class of molecular transporters— compounds that shepherd drugs and molecular probes such as imaging agents across biological barriers—enters cells more readily than some of the best-performing transporters developed previously. Nearly two decades ago, Paul A. Wender of Stanford University and coworkers discovered that proteins with properly spaced guanidinium surface groups enter cells more readily than other proteins. This led Wender’s group and others to develop many types of O cell-penetrating peptides and P Cargo O O O other molecular H O transporters n to ferry +NH compounds 2 N NH2 across bioH logical membranes for Oligophosphoester drug delivery molecular transporter and other applications. Wender, Robert M. Waymouth, and Colin J. McKinlay have now developed oligophosphoesters as molecular transporters (J. Am. Chem. Soc. 2016, DOI: 10.1021/ Li You of Shanghai Institute of Organic jacs.5b13452). Compared with oligocarbonChemistry have reported an asymmetric ates and oligoarginines, two of the best-per- twofold C–H oxidative cross-coupling forming types of molecular transporters, reaction of ferrocenes with heteroarenes oligophosphoesters move two and six times that takes place without having to first as much attached cargo, respectively, per prefunctionalize one or the other aryl couunit time. The researchers have filed a NR12 patent application on the technology and plan to investigate its use for delivering H R3 Taxol to cancer patients.—STU BORMAN
+
Fe J. PHYS. CHEM. C (MOLECULAR MODELS)
GREEN CHEMISTRY
▸ Dual C–H/C–H asymmetric crosscoupling unveiled Although chemists have turned modifying unreactive C–H bonds into a routine event in organic synthesis, now and again a new approach still turns up. In one of the latest examples, De-Wei Gao, Qing Gu, and Shu-
catalyst with a protected chiral amino acid ligand that proceeds in a twofold manner, first activating the ferrocene and then the heteroarene. The atom-economical reaction avoids the need for an aryl halide or aryl organometallic pre-
R3 X
Pd(CO2CH3)2
X
H
R2
Chiral ligand:
NR12
O
Fe OH
R2
NHR
R = various groups, X = O, N, S
Asymmetric double C–H activation pling partners, which is usually required in cross-coupling strategies (J. Am. Chem. Soc. 2016, DOI: 10.1021/jacs.6b00127). The new reaction is a greener, less expensive method for preparing planar chiral ferrocenes, which are useful as chiral ligands and as asymmetric catalysts, You says. The team’s strategy involves a palladium
cursor, proceeds using oxygen in the air as an oxidant instead of a metal oxidant, and doesn’t need a significant excess of either coupling partner. The team shows that the ferrocene derivatives can be developed as N,O and N,S and N,P bidentate planar chiral ligands and as chiral catalysts.—STEVE RITTER MARCH 14, 2016 | CEN.ACS.ORG | C&EN
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