Template-free one-step electrochemical formation of polypyrrole nanowire array

Oriented polypyrrole nanowire (nanorod) array readily forms using one-step pyrrole electropolymerization without using a template. These nanostructures having diameter in the range of 40–120 nm are obtained by electrogenerating polypyrrole in the presence of jointly non-acidic and weak-acidic anions. The latter are essential, their presence leads to the formation of an overoxidized polypyrrole thin layer that surrounds the polypyrrole nanostructure base. This simple and convenient method allows direct polymer nanowire array fabrication on various conductive substrates, the length of nanostructures being controlled by the polymerization time. Finally, a reaction mechanism involving oxidation of pyrrole and water and polypyrrole overoxidation is discussed.     

Phosphinoborane and Sulfidoborohydride as Chelating Ligands in Polyhydride Ruthenium Complexes: Agostic σ‐Borane versus Dihydroborate Coordination

A question of coordination mode : Two new borane compounds are prepared. They act as bifunctional ligands as illustrated by their reaction with ruthenium polyhydrides which leads to the formation of two complexes (see scheme) displaying either a δ‐agostic interaction of a η²‐B? H bond involving a trivalent boron atom or a dihydroborate ligation.

     

Activation of Hydrogen by Palladium(0): Formation of the Mononuclear Dihydride Complex trans‐[Pd(H)2(IPr)(PCy3)]

An even split : In sharp contrast with the general behavior of Pd⁰ complexes, [Pd(IPr)(PCy₃)] is able to activate the H? H bond. The resulting trans‐[Pd(H)₂(IPr)(PCy₃)] is the first isolated mononuclear dihydride palladium compound. Its formation is supported by multinuclear NMR spectroscopy, density functional calculations, and X‐ray diffraction studies. The stability and reactivity of this new species are examined.

     

Cover Picture: Photoprogrammable Organic Light‐Emitting Diodes (Angew. Chem. Int. Ed. 22/2009)

Programmable organic light‐emitting diodes: UV irradiation converts an oxetane‐functionalized dithienylethene derivative from its colorless open form into a dark blue closed form, while visible light reverses the reaction. In the Communication on page 4038 ff., K. Meerholz and co‐workers describe a reversibly switchable organic light‐emitting diode based on this principle.

     

CHO Cells Adhering to Nitrogen‐Rich Plasma‐Polymerised Ethylene Exhibit High Production of a Specific Recombinant Protein

In many industrial applications, inadequate cell attachment can be a limitation, especially when serum‐free media are used. Nitrogen‐rich plasma‐polymerised ethylene (PPE:N) exhibits high concentrations of polar groups that can help to promote the attachment of weakly adherent cell types. Tissue plasminogen activator‐producing Chinese hamster ovary (CHO) cells, adapted to suspension, were grown in the presence PPE:N flakes and were found to adhere to them. The growth rate was reduced, but cell viability was enhanced and their metabolism was more efficient, with generally higher recombinant protein productivity. Finally, cell adhesion on PPE:N surfaces was found to be independent of integrins, and was probably mediated by certain non‐specific interactions with the PPE:N surface.

     

Development and validation of a sensitive and selective method using GC/MS-MS for quantification of 5-fluorouracil in hospital wastewater

Pollution of the environment by pharmaceuticals is a subject of growing scientific and societal concern. However, few quantitative data have been reported concerning hospital wastewater contamination. Among the different molecules used at hospital, antineoplastic drugs appear to be of special interest, and 5-fluorouracil (5-FU) can be considered as a key compound of this therapeutic class. To monitor this pharmaceutical in hospital wastewater, a highly specific and selective method was developed using gas chromatography tandem mass spectrometry after solid-phase extraction. This sensitive method (limit of quantification = 40 ng L⁻¹) was then applied to assess sewage contamination of a middle-size hospital with oncology service located in Paris, France. Native 5-FU was detectable in 12 of the 14 analysed samples. In positive samples, concentration range was measured from 0.09 to 4.0 μg L⁻¹. Finally, a predicting model for the hospital wastewater concentrations is presented, and results of this model are discussed.     

“Half‐Bonds” in an Unusual Coordinated S42− Rectangle

Don′t be square! A rare S₄^2? rectangle bridging two M₂Cp₂(μ₂‐CH₂)₂ (M=Rh, Ir) fragments is found to contain two “half‐bonds” with S? S distances of 2.70 or 2.90 Å. Computational studies explore the connection between these “half‐bonds” and a Jahn–Teller distortion, as well as possible intermediates that form M₄S₄²⁺ clusters having the S₄^2? rectangle rotated by 90°.

     

The clone of operations preserving a cycle with loops

We consider all the binary relations on a k-element set which, when viewed as directed graphs, consist of a k-cycle and some loops. If k ≥ 3 and the relation has at least two loops, we show that it is only preserved by essentially unary operations. In all other cases, the relation is preserved by operations that depend on a greater number of variables. Received March 9, 2006; accepted in final form September 14, 2007.     

Translation between external representation systems in mathematics: All-or-none or skill conglomerate?

The study described herein represents an initial, exploratory attempt to understand what it means to translate between external representation systems. Researchers have traditionally considered translation as an all-or-none activity. We hypothesize that translation is comprised of both knowledge and skill components, and accordingly construe translation as an activity that our framework allows us to define as partial or complete. We examined the effects of part-whole knowledge in change unknown subtraction situations and the structure of three different external representations on first grade students’ ability to translate in a partitioning task. Based on three interviews conducted with each student, results from our mixed methods analysis showed that translation skill was affected by what students knew about subtraction and the structure of the ER. Further, whereas high knowledge students demonstrated greater difficulty with translating to the ERs, low knowledge students had difficulty translating from the problem statement as well as translating to the ERs.