Science Concentrates

Probing protein folding

A method to probe the forces that control higher order structure in proteins under native conditions--that is, structure-promoting conditions for the protein--has been developed by chemists at the University of Wisconsin, Madison. To evaluate such forces, scientists typically use a spectroscopic method to monitor changes in structure when the protein is treated with heat or a chemical agent. But these procedures can give an incomplete picture. For examining protein folding under native conditions, the method developed by Matthew G. Woll and Samuel H. Gellman may be particularly useful [J. Am. Chem. Soc., published online Aug. 19, http://dx.doi.org/10.1021/ja046891i]. The method is based on replacing a backbone amide of a protein with a thioester linkage. When this modified protein is mixed with a thiol (red), a thiol/thioester exchange (shown) occurs rapidly. The process can be monitored by high-performance liquid chromatography, providing an equilibrium constant for the exchange reaction that can be used to estimate the protein's folding thermodynamics under native conditions, Gellman says.

Clear nanotube films in three simple steps

A three-step method for making high-quality films out of single-walled carbon nanotubes (SWNTs) has been developed by scientists at the University of Florida [Science, 305, 1273 (2004)]. Because they're conductive, transparent, ultrathin, and flexible, these SWNT films, made by physics professor Andrew G. Rinzler and colleagues, could have myriad uses in electronic devices such as video displays, solar cells, and communications gadgets. To make the films, Rinzler's group first vacuum filters a dilute, surfactant-based suspension of SWNTs through a membrane. This membrane serves as a template upon which the nanotube film grows. The researchers next wash the surfactant away with water and then use a solvent to dissolve the membrane, leaving behind a homogeneous film. According to Rinzler, the film has "excellent electrical conductivity, maximal mechanical strength, and uniform optical homogeneity on an unprecedented length scale."

New mini-NMR

Nuclear magnetic resonance spectroscopy is an indispensable analytical tool, yet its sensitivity and resolution are limited, and the necessary bulk of NMR machines hampers the technology's portability. Now, associate chemical physics professor Daniel P. Weitekamp and colleagues at California Institute of Technology have developed a new prototype NMR that could pave the way for portable NMR spectroscopy at the micrometer or smaller scale. Called BOOMERANG (better observation of magnetization, enhanced resolution, and no gradient), the method detects oscillations in the force between the sample and surrounding ferromagnets, rather than the radio signal variations that are the basis for conventional NMR [Proc. Natl. Acad. Sci. USA, 101, 12804 (2004)]. When miniaturized, this setup will be more sensitive than other NMR methods, the authors predict. They demonstrated that BOOMERANG can obtain ¹H and ¹⁹F NMR spectra of both solids and liquids.

New surfaces for bringing up stem cells

Human embryonic stem cell lines don't grow just anywhere. Many surfaces and growth conditions trigger the cells to differentiate, destroying their pluripotency--the power to grow into any type of cell. Now, postdoc Brendan P. Orner, graduate student Ratmir Derda, chemistry and biochemistry professor Laura L. Kiessling, and colleagues at the University of Wisconsin, Madison, are making use of arrays of synthetic surfaces that not only grow stem cells but also allow researchers to learn which molecules help stem cells maintain pluripotency [J. Am. Chem. Soc., 126, 10808 (2004)]. The scientists start with a self-assembled monolayer of perfluorinated alkanethiols (ATs) on gold, which is phobic to both cells and solvents. They next spot the surface by removing some ATs and fill the "holes" with ATs attached to ligands that bind cells and attract solvents. When they fill the holes with polyethyleneglycol acid-ATs (shown), the cells grow and remain undifferentiated for two days. Next, the group plans to create arrays with various ligands to find the molecules that best support undifferentiated stem cells.

Putting CO to a new use in fuel cells

Carbon monoxide is usually an unwanted by-product in fossil fuel reforming reactions to produce hydrogen for fuel cells because it can poison the typical fuel cell's platinum catalyst. A standard way to remove CO from gas streams is via the water-gas shift reaction in which CO reacts with water to produce CO₂ and additional H₂. But this separate reaction step is inconvenient. Postdoctoral researcher Won Bae Kim and chemical engineering professor James A. Dumesic at the University of Wisconsin, Madison, have now demonstrated a modified process for oxidizing CO that bypasses the shift reaction and generates additional electricity in the process [Science, 305, 1280 (2004)]. Dumesic's group has previously developed catalysts and reactors to produce H₂ for fuel cells from plant sugars, rather than fossil fuels. The new work involves reacting by-product CO, water, and an aqueous polyoxometalate (POM) oxidizing agent, H₃PMo₁₂O₄₀, in the presence of a gold catalyst at room temperature. The CO is converted to CO₂, and hydrogen ions--rather than H₂--are formed in solution as the POM is reduced. The reduced POM can subsequently be reversibly oxidized and supply electrons to a secondary fuel cell to generate electricity.