SCIENCE & TECHNOLOGY CONCENTRATES

METHANE TO METHANOL DIRECTLY

With computational tools, chemists have designed a protein that selfassembles in three dimensions to produce protein crystals with the symmetry properties of their choice (Proc. Natl. Acad. Sci. USA, DOI: 10.1073/ pnas.1112595109). This achievement could someday have applications in designing nanoscale materials and might also help structural biologists decide which sections of a protein to modify for coaxing crystal formation. Jeffery G. Saven at the University of Pennsylvania; William F. DeGrado of the University of California, San Francisco; and coworkers set out to design a crystal with the honeycomb-like symmetry of the P6 space group, which occurs in just 0.1% of protein crystal structures. Starting with a three-helix bundle protein, they estimated the energetic consequences Saven’s team sought honeycomb-like crystal symmetry of varying each amino acid (artist’s rendition, left) in computer modeling of protein structures (middle). They found a protein that that might be involved crystallized just as predicted (right). with protein-protein contacts in a crystal. From those myriad possibilities, they picked five protein sequences that were predicted to form stable crystals in the lab. One of the five, a protein called P6-d, crystallized into a structure consistent with the P6 space group. The team plans to test the technique on more complex proteins soon.—CD

GUOJUN LIU

COATING FOR COTTON REPELS OIL AND WATER Cotton clothes marred with wet patches and stubborn oily stains could soon be a thing of the past, thanks to a coating that makes oily and aqueous liquids bead up and roll away rather than penetrate the fabric (Langmuir, DOI: 10.1021/la300634v). The superamphiphobic cotton was developed by Guojun Liu and Dean Xiong of Queen’s University, in Ontario, along with E. J. Scott Duncan of Defence R&D Canada, in Alberta. It’s made of a diblock copolymer, PIPSMA-b-PFOEMA, which is short for poly[3(triisopropyloxysilyl)propyl methacrylate]block-poly[2-(perfluorooctyl)ethyl methacrylate]. The PIPSMA portion condenses with the hydroxyl groups A drop of dyed water and a drop of cooking oil bead up on a coated cotton surface.

on the cotton surface, covalently grafting and cross-linking the polymer around the cotton fibers. The fluorinated PFOEMA part of the polymer gives the cotton fibers the ability to repel both oil and water. Droplets of pump oil, for example, remained in beads on the surface of the coated cotton for months without being absorbed or drawn into the interfiber spaces. When immersed in water, the coated fabric draws a layer of air around itself, which can also stay put for months. Liu tells C&EN that the mechanical properties and breathability of the coated cotton were barely changed from the uncoated fabric, and the coating is extremely stable to laundering.—BH

TOWARD A PREDICTIVE MODEL FOR NANOPARTICLE TOXICITY Researchers report the first model to predict nanoparticle toxicity based on the materials’ water solubility and electronic properties WWW.CEN-ONLINE.ORG

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APRIL 30, 2012

(ACS Nano, DOI: 10.1021/nn3010087). Metal oxide nanoparticles are semiconducting materials that drive oxidation and reduction reactions in devices such as fuel cells and electronics. Andre E. Nel of the University of California, Los Angeles, wondered whether these particles’ toxicity could be linked to their band gaps, the energy gaps between occupied and unoccupied electron energy levels. He thought that if the magnitude of the band gap matched the energies required to drive oxidation and reduction reactions in human cells, the materials could disrupt these well-regulated cellular reactions, leading to cellular damage and inflammation. To test the hypothesis, Nel and his team studied 24 metal oxide nanomaterials and predicted that six would be toxic: TiO2, Ni2O3, CoO, Cr2O3, Co3O4, and Mn2O3. When applied to human and mouse cells, five of the six predicted metal oxides—all but TiO2— caused toxic effects, including reducing cell survival by as much as 80%. Two materials not predicted by their band gaps, CuO and ZnO, were also toxic. Nel says these metal

CHRISTOPHER M. MACDERMAID

A metal-doped zeolite facilitates direct conversion of methane to methanol in aqueous media, according to a group led by chemists at Cardiff University, in Wales (Angew. Chem. Int. Ed., DOI: 10.1002/ anie.201108706). Methane, the main component of natural gas, is relatively plentiful in many parts of the world, but it is often found in remote locations lacking transportation infrastructure. Researchers would like to be able to convert the gas directly to shippable liquid fuels and chemicals such as methanol, but direct and commercially viable conversion methods remain elusive. Currently, methane is converted to methanol via an energy-intensive two-step process involving synthesis gas (CO and hydrogen). Cardiff’s Ceri Hammond and Graham J. Hutchings, together with coworkers in academia and at Dow Chemical, report that aqueous H2O2 oxidizes methane to methanol with greater than 90% selectivity in the presence of zeolite ZSM-5 doped with copper and iron, a stable and reusable catalyst. The iron centers convert H2O2 to a species that activates C–H bonds, and copper inhibits overoxidation of methanol to formic acid and CO2, the team says.—MJ

MADE-TO-MEASURE PROTEIN CRYSTALS