Science Concentrates THEORETICAL CHEMISTRY
▸ DFT method closes the gap on predicting band gaps
JACOBY
ART & ARTIFACTS
▸ Turning oil paint into a gel helped speed up art It used to be that artists working with oil paint needed to wait weeks—sometimes even months—for a paint layer to dry before they could apply strokes of a new color to the canvas. There’s a reason the saying “watching paint dry” became synonymous with
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C&EN | CEN.ACS.ORG | JANUARY 16, 2017
Polymer-modified Mg2Si nanoparticles break down to SiH4 in acidic environments. The SiH4 then reacts with O2 to produce clumps of SiO2.
NANOMEDICINES
Nanoparticles suffocate tumors To suffocate and slow the growth of cancer cells, researchers have designed magnesium silicide nanoparticles that deoxygenate acidic environments, such as those inside tumors (Nat. Nanotechnol. 2017, DOI: 10.1038/nnano.2016.280). The team, led by Wenbo Bu and Jianlin Shi of the Chinese Academy of Sciences’ State Key Laboratory of High Performance Ceramics & Superfine Microstructure, wanted to develop agents that could selectively remove oxygen in tumors but not in healthy tissue, and do so without the use of toxic materials. The agents they developed, 100-nm-diameter Mg2Si particles modified with poly(vinylpyrrolidone), scavenge for oxygen by first breaking down to magnesium ions and silane in acidic environments. The silane then reacts with oxygen to produce water and silicon dioxide. In sealed dialysis bags, the particles react with both dissolved oxygen and oxygen held in hemoglobin. The researchers tested the nanomaterials in mice that had two tumors grafted into their bodies. The scientists injected Mg2Si particles into one tumor and just saline into the other. After eight hours, blood oxygen saturation levels in the particle-treated tumors were about 75% lower than those injected with saline. Meanwhile, oxygen levels didn’t change significantly in normal tissue injected with the particles. But when the team delivered the particles intravenously, instead of directly into tumors, they observed only a slight reduction in tumor oxygen levels. Shi thinks this is because the particles haven’t been optimized to target tumors.—MICHAEL TORRICE
boredom. Then in the 19th century, artists such as J. M. W. Turner began following a “gumtion” recipe to formulate their paints. The change gave paint a jellylike viscosity that made it possible for artists to complete an oil artwork in only days. A team of researchers led by Laurence de Viguerie and Philippe Walter of the University of Pierre & Marie Curie have now taken advantage of modern spectroscopy
Turner’s 1841 painting “Dawn of Christianity” relied on a new “gumtion” gel paint formulation.
to uncover the chemistry behind the paint recipes that Turner and other artists used (Angew. Chem. Int. Ed. 2017, DOI: 10.1002/anie.201611136). The team recreated the gumtion formulation by adding lead acetate to a common oil paint base of mastic resin, linseed oil, and turpentine. They found that the paint gelled similarly to how traditional oil paint dries via an oxidative free-radical mechanism. But the presence of the lead
CREDIT: ADAPTED FROM NAT. NANOTECHNOL. (TUMOR DIAGRAM); PUBLIC DOMAIN/WIKIMEDIA COMMONS (PAINTING)
A popular quantum mechanical method for calculating the properties of molecules and solid materials has routinely underestimated the size of semiconductor band gaps. A new version of that computational method developed by University of Minnesota researchers is now showing marked improvement in calculating band gap values without sacrificing the method’s speed and simplicity (J. Phys. Chem. Lett. 2016, DOI: 10.1021/acs.jpclett.6b02757). Band gaps represent the energy difference between a material’s valence and conduction electron bands, with the magnitude making the difference between conductors, insulators, and semiconductors. Researchers have long used the Kohn-Sham form of density functional theory (KS-DFT) to investigate electron band structures, excitation energies, and other fundamental properties. One version of KS-DFT relies on so-called local functionals—mathematical descriptions of electron density—and is popular because its simplicity offers substantial computational cost savings relative to other quantum methods. But local functional programs tend to miss the mark on band gaps, forcing researchers to refine their work using computationally-intensive methods based on nonlocal functionals. Pragya Verma and Donald G. Truhlar developed a local functional, called HLE16, and tested it on 31 semiconductors. They find that it yields more accurate band-gap estimates than current local functionals and matches the low-error values of the most popular nonlocal functionals.—MITCH
acetate quickened the process. The metal ions didn’t just increase the rate of drying, they also integrated into the gel’s molecular architecture. The researchers say the technological advance revolutionized the ability of artists “to express sensations or feelings, capturing momentary effects of light” using more fluid, spontaneous, and loose brushwork.—SARAH EVERTS
BIOLOGICS
CREDIT: ANDREI LOMIZE/WIKIMEDIA COMMONS (RIBBON STRUCTURE)
▸ Predicting immune response to protein Tiny changes to a therapeutic protein can enhance its performance or initiate a dangerous immune reaction. Novo Nordisk knows that all too well after dropping a Phase III drug trial in 2012 for its engineered Factor VII blood-clotting protein designed to treat hemophilia. Using publicly available software, Novo Nordisk and Food & Drug Administration researchers began outlining methods to predict how immune cells chop up and display engineered proteins on their surface. Their model has shown that two out of three engineered changes in the Factor VII protein activate unwanted T cell immune responses in some people (Sci. Transl. Med. 2017, DOI: 10.1126/ scitranslmed. aag1286). One Factor VII protein determining factor for the response is a person’s unique HLA genes, which are involved in presenting foreign protein fragments to T cells. The researchers subsequently used the model with HLA testing to correctly identify patients from the failed clinical trial that did and didn’t develop antibodies to the engineered protein. HLA testing is already common for organ donations, prompting study leader Zuben E. Sauna of FDA to say that more studies like this may lead to HLA tests being applied in “precision medicine,” where drugs can be given to the majority of pa-
INORGANIC CHEMISTRY
Chromium complex has a long luminescent glow Ruthenium bipyridine and related precious-metal complexes are popular because they exhibit long-lived, redox-active excited states that are useful for making solar cells and light-emitting devices and as sensitizers for photocatalytic organic reactions. Researchers would like to replace the precious metals with more abundant first-row transition metals, such as iron, but they have been waylaid so far because the excited-state luminescence lifetimes are too short. A key to modulating the properties of the complexes to extend the lifetime is designing ligands that better stabilize the metal ions. To that end, Laura A. Büldt, N Oliver S. Wenger, and their coworkers at the University of Basel have designed a N N bulky chelating diisocyanide terphenyl Cr ligand that dramatically improves chromiN um(0)’s excited-state lifetime, surpassing N that of the best iron(II) complexes by N two orders of magnitude (J. Am. Chem. Soc. 2017, DOI: 10.1021/jacs.6b11803). The researchers say the electronic effects of their ligand and the cage structure it forms around the chromium(0) ion provides a room-temperature excited-state lifetime of 2.2 nanoseconds, which exceeds the 37 picoseconds of the previous iron(II) Tris(diisocyanide)chromium(0) complex record holder. In addition, they found that the chromium complex is a stronger photoreductant than ruthenium tris(bipyridine). Wenger’s group has tested the chromium complex and an analogous molybdenum complex in photoredox catalysis and is exploring grafting the chromium complex onto semiconductor surfaces to make dye-sensitized solar cells.—STEVE RITTER
tients they will help, and withheld from the few that they could harm.—RYAN CROSS
CATALYSIS
▸ Boron nitride catalyzes olefin hydrogenations For the second time in about a month, researchers report that boron nitride, which ranks as a well-known catalyst support, but not as a catalyst, catalyzes industrially important reactions. This time it’s olefin hydrogenation, a reaction used for making fuels and chemicals and for processing foods (ACS Omega 2016, DOI: 10.1021/ acsomega.6b00315). The advance may lead to lower-cost, metal-free industrial hydro-
genation catalysts. A few studies in recent years have reported that boron nitride, especially the hexagonal form, h-BN, can catalyze water-splitting and other processes. Last month, scientists upped BN’s catalysis status by showing that it can drive industrially important dehydrogenation reactions. Now, a team led by Richard G. Blair of the University of Central Florida has shown that defect-laden h-BN, made via a ball-milling process, can serve as an active catalyst for hydrogenating propene, cyclohexene, diphenylethylenes, and other alkenes. The team found that h-BN mediates hydrogenations under milder conditions than those used with nickel-based hydrogenation catalysts and is more active than metal-free frustrated Lewis pair catalysts. NMR analysis and binding-energy calculations show that nitrogen vacancies are most likely the catalytically active sites among the eight types of lattice defects examined.—MITCH JACOBY JANUARY 16, 2017 | CEN.ACS.ORG | C&EN
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