Science Concentrates

Thienoacenes now have up to seven fused rings

Oligothiophenes--multiple thiophene rings joined by single bonds--are a leading class of organic semiconducting materials used to fabricate electronic devices. Chemists have been interested in making fused-ring analogs with the idea that a more rigid structure will reduce defects and thus improve conjugation for better charge-carrier mobility. So far, molecules consisting of as many as five fused rings (pentathienoacene) have been made, but the synthetic route has been considered inefficient. An improved synthesis of pentathienoacene and extension of the series to make heptathienoacene (seven fused rings, shown) have been reported by Xinnan Zhang, Adrien P. Côté, and Adam J. Matzger of the University of Michigan, Ann Arbor (J. Am. Chem. Soc. 2005, 127, 10502).The team made the compounds by coupling two brominated thienothiophenes (two fused rings) or two dithienothiophenes (three fused rings), respectively, via a sulfide bridge, followed by a ring-closing reaction at the sulfide bridge to form the central fused ring. The oligothienoacenes have more efficient molecular packing than oligothiophenes, as expected. The researchers are in the process of exploring the semiconducting properties of the materials in organic field-effect transistors.

Method finds phosphorylation sites

Many cellular processes are regulated by protein phosphorylation at serine, threonine, or tyrosine residues. Identifying the specific sites of phosphorylation can be difficult because of the low abundance of the phosphorylated peptides. Ruedi Aebersold and coworkers at the Swiss Federal Institute of Technology, in Zurich, and the Institute for Systems Biology, in Seattle, use dendrimers to enrich phosphoproteins in complex mixtures (Nat. Methods 2005, 2, 591). In this new method, phosphorylated peptides are covalently coupled to the dendrimers, allowing the phosphopeptides to be separated from other peptides by size-selective methods. After the separation, the phosphopeptides are released and analyzed by mass spectrometry. Using human T cells as a model system, the team identified all known phosphorylation sites and some previously unknown ones on a total of 97 tyrosine phosphoproteins and interacting partners. Other methods often must focus on one type of phosphorylation site. In contrast, this method was able to identify serine, threonine, and tyrosine phosphorylation sites concurrently.

Orthogonal mRNA programs cells

One of the goals of synthetic biology is the introduction of new, well-defined functions into cells. Jason W. Chin and Oliver Rackham at the Medical Research Council Laboratory of Molecular Biology, in Cambridge, England, use "orthogonal" ribosome and messenger RNA pairs to program cells (Nat. Chem. Biol. 2005, 1, 159). These noninterfering ribosomes and mRNAs work together to process information, but the ribosomes can't read--and the mRNAs can't be read by--their natural counterparts because sequences on the messenger and ribosomal RNA responsible for initiating translation have been changed. Chin and Rackham found successful orthogonal pairs through a series of selection experiments designed to identify mRNA and ribosomes that work together without cross-talk from their naturally occurring counterparts. The researchers then used the ribosome-mRNA pairs to design a Boolean logic "AND" gate based on the synthesis of two fragments of the enzyme b-galactosidase, one fragment synthesized by an orthogonal pair and the other synthesized by a wild-type pair. Output from this AND gate requires that both pairs be present and functioning.

Drug discovery journal to debut

A new journal about drug discovery will be launched in January 2006 by Wiley-VCH and the Italian and German chemical societies. ChemMedChem will cover topics including drug design and discovery, drug development and delivery, molecular modeling, combinatorial chemistry, target validation, and lead generation. The publishing partners describe the monthly publication as "the new interdisciplinary journal for the fields of medicinal chemistry and pharmaceutical sciences," adding that it will describe "research at the interface of chemistry, biology, and medicine." ChemMedChem will offer peer-reviewed full papers, short communications, reviews, and highlights. Peter Gölitz--editor-in-chief of Angewandte Chemie, which is published by Wiley and the German Chemical Society--will serve as ChemMedChem's founding editor. The new publication joins several other journals that Wiley publishes with European chemical societies, including Chemistry--A European Journal, ChemBioChem, and ChemPhysChem.

W­Sb triple bond produced

Hunters of inorganic triple bonds continue to pursue their quarry, and their latest catch is the first isolable complex containing an antimony-tungsten triple bond (Angew. Chem. Int. Ed., published online July 6, dx.doi.org/10.1002/anie.200500781). The molecule (shown) was synthesized and characterized by chemistry professor Manfred Scheer of the University of Regensburg, in Germany, and colleagues Gábor Balázs and Marek Sierka. They prepared it by treating (N₃N)WCl [where N₃N is a silylated tris(2-aminoethyl)amine ligand] with a lithiated stibane of the type LiSb(H)R. The terminal WSb bond of the product is 2.5255 Å long and is the shortest W-Sb bond reported to date, consistent with its representation as a triple bond, according to the researchers. Calculations strongly support their conclusion that they have made a W-Sb triple bond with a weakly polarized character, they add.