Science Concentrates

New complex turns H₂O into O₂

Chemists have created a ruthenium complex that catalyzes the conversion of water to molecular oxygen--a reaction performed by plants and of great interest for developing renewable energy sources [J. Am. Chem. Soc., published online June 5, http://dx.doi.org/10.1021/ja0486824]. Researchers have sought to model this natural oxidation, which occurs via a manganese tetramer, but few examples exist. Now, a team led by Antoni Llobet, chemistry professor at the University of Girona, in Spain, has synthesized a promising compound containing two ruthenium atoms (shown, pink = ruthenium, red = oxygen, purple = nitrogen, and gray = carbon). The new complex turns H₂O into molecular O₂ at a much faster rate than other recently reported ruthenium-containing, water-oxidizing species. Those compounds contain rotating Ru–O–Ru groups, whereas the new complex, which does not, forms strategically oriented Ru=O groups, which likely help increase the complex's activity.

Small-molecule protein labeling with less labor

A general and efficient method for site-specifically labeling proteins with small synthetic molecules that's compatible with high-throughput protein microarray preparation and enzymatic screening has been developed by Christopher T. Walsh, Jun Yin, and coworkers at Harvard Medical School. Currently available methods for specific labeling of a target protein in a complex mixture of cellular proteins require attaching a bulky peptide tag to one end of the target protein. The tag directs the small-molecule label to the target protein. But these tags are bulky (200–400 amino acids) and don't work with all target proteins, Walsh says. Instead, his team tags the target protein with an 80-amino-acid component of a nonribosomal peptide synthetase. This tag can be enzymatically labeled with a small molecule such as biotin via a phosphopantetheinyl tether [J. Am. Chem. Soc., published online June 4, http://dx.doi.org/10.1021/ja047749k]. Biotin-labeled target proteins prepared this way can be directly immobilized on a streptavidin-coated surface for high-throughput enzymatic screening, the researchers say.

Diamino acids in meteorite

For the first time, diamino acids have been discovered in a meteorite. Using gas chromatography and mass spectrometry, a team led by Uwe J. Meierhenrich of the University of Bremen, in Germany, has identified seven diamino acids--including D- and L-2,3-diaminopropanoic acid, D- and L-2,4-diaminobutanoic acid, 3,3´-diaminoisobutanoic acid, 2,3-diaminobutanoic acid, and 4,4´-diaminoisopentanoic acid (shown)--in the Murchison chondritic meteorite [Proc. Natl. Acad. Sci. USA, 101, 9182 (2004)]. Previously, researchers found monoamino acids in the Murchison meteorite. Amino acids arriving on Earth through similar avenues are thought to have triggered life's beginnings. Diamino acids may also have played a role in the development of life on Earth. They are the backbone of peptide nucleic acid materials thought to have preceded both RNA and DNA in early life. This new work suggests that diamino acids had extraterrestrial origins and may have arrived on Earth via meteorites during prebiotic times.

Proteins that harvest light tapped for electronics

The remarkable light-harvesting ability of photosynthetic protein complexes in plants and certain bacteria can make the scientists who create photovoltaic devices turn green with envy. But using the complexes as photon-harvesting components in solid-state electronics has proven difficult: They aren't stable enough for practical use when removed from their native biological environs. Now, a group led by MIT electrical engineering professor Marc Baldo and Shuguang Zhang has developed a technique for integrating the light-harvesting complexes from Rhodobacter sphaeriodes and spinach's photosystem I into solid-state electronics [Nano Lett., 4, 1079 (2004)]. Using surfactant peptides, the team was able to stabilize the complexes so that their functionality wasn't diminished when incorporated into solid-state electronics. The researchers report that depositing an amorphous organic semiconductor between the photosynthetic complexes and the top metal contact was also crucial to successful integration. The technique preserves the complex's light-harvesting power for at least three weeks.

Silicon analogs of vinyllithium

An unexpected stable silicon analog of a vinyllithium compound has been isolated and characterized by chemistry professor Akira Sekiguchi and colleagues at the University of Tsukuba, in Japan [Organometallics, 23, 3088 (2004)]. The researchers prepared the sp²-type silyllithium by reaction of a tetrasila-1,3-butadiene with tert-butyllithium (shown). The crystal structure of the diene reveals a twisted silicon backbone, which opens the compound up to attack by reducing agents, the researchers report. The silyllithium is formed by cleavage of the central Si–Si bond of the diene. It retains the sp² bonding and geometry of the parent molecule, and the lithium atom is solvated with tetrahydrofuran molecules. The silyllithium is expected to be an important reagent to synthesize disilene compounds, the researchers note, which in turn could be used to prepare silicon-based polymers. Another silyllithium, with triisopropylphenyl substituents, has also just been reported by postdoctoral researcher David Scheschkewitz of ETH Zurich [Angew. Chem. Int. Ed., 43, 2965 (2004)].