Novel ligands for a purine riboswitch discovered by RNA-ligand docking

The increasing number of RNA crystal structures enables a structure-based approach to the discovery of new RNA-binding ligands. To develop the poorly explored area of RNA-ligand docking, we have conducted a virtual screening exercise for a purine riboswitch to probe the strengths and weaknesses of RNA-ligand docking. Using a standard protein-ligand docking program with only minor modifications, four new ligands with binding affinities in the micromolar range were identified, including two compounds based on molecular scaffolds not resembling known ligands. RNA-ligand docking performed comparably to protein-ligand docking indicating that this approach is a promising option to explore the wealth of RNA structures for structure-based ligand design.     

Rare earth fluoride nanoparticles obtained using charge transfer complexes: a versatile and efficient route toward colloidal suspensions and monolithic transparent xerogels

Crystalline rare earth fluoride nanoparticles were synthesized by reacting rare earth ions with charge-transfer complexes, in solution, under mild conditions. An infrared study showed that these intermediate complexes are made up of solvent molecules (amide: N,N-dimethylformamide, 1-methyl-2-pyrrolidinone, etc.) and fluoride ions coming from hydrofluoric acid. The size and shape of the particles can be controlled through the process parameters. The complete study of the particles obtained through this process is carried out in this document, especially for the YbF(3) system. However, the process can easily be extended to the whole series of rare earth elements. We also show the ability of these objects to be transferred from an aqueous medium to an organic phase thanks to their surface modification. Finally, transparent monolithic xerogels of rare earth fluoride have been developed starting from the prepared colloidal solutions.     

Highly efficient bifacial transparent organic solar cells with power conversion efficiency greater than 3% and transparency of 50%

In this work, we present vacuum-deposited bifacial transparent organic solar cells on indium-tin-oxide-coated glass substrates. Good performances and high transparencies are achieved simultaneously by employing the planar-mixed heterojunction of the organic donor 2-{[7-(5-N,N-ditolylaminothiophen-2-yl)-2,1,3-benzothiadiazol-4-yl]methylene}malononitrile (DTDCTB) and fullerenes with carefully designed resonance top electrodes. Comprehensive optical simulation is exploited to investigate the effect of the top-electrode configuration on the cell transparency and efficiency. Cells with structures designed for high transparencies were fabricated and tested. The DTDCTB:C₆₀ device yields a high transmission of up to 66.4% at 530 nm and a power conversion efficiency (PCE) of 2.11%. Moreover, the DTDCTB:C₇₀ device demonstrates an exceptional PCE as high as 3.24% with a balanced transmission of ≈50% in the visible spectrum. Enhanced PCE values of transparent solar cells are also revealed with the use of external reflectors. Efficiency enhancements of ≈15% and ≈65% are achieved by simply attaching a reflection mirror at the cathode or anode side, respectively.     

Supramolecular electron transfer by anion binding

Anion binding has emerged as an attractive strategy to construct supramolecular electron donor-acceptor complexes. In recent years, the level of sophistication in the design of these systems has advanced to the point where it is possible to create ensembles that mimic key aspects of the photoinduced electron-transfer events operative in the photosynthetic reaction centre. Although anion binding is a reversible process, kinetic studies on anion binding and dissociation processes, as well as photoinduced electron-transfer and back electron-transfer reactions in supramolecular electron donor-acceptor complexes formed by anion binding, have revealed that photoinduced electron transfer and back electron transfer occur at time scales much faster than those associated with anion binding and dissociation. This difference in rates ensures that the linkage between electron donor and acceptor moieties is maintained over the course of most forward and back electron-transfer processes. A particular example of this principle is illustrated by electron-transfer ensembles based on tetrathiafulvalene calix[4]pyrroles (TTF-C4Ps). In these ensembles, the TTF-C4Ps act as donors, transferring electrons to various electron acceptors after anion binding. Competition with non-redox active substrates is also observed. Anion binding to the pyrrole amine groups of an oxoporphyrinogen unit within various supramolecular complexes formed with fullerenes also results in acceleration of the photoinduced electron-transfer process but deceleration of the back electron transfer; again, this is ascribed to favourable structural and electronic changes. Anion binding also plays a role in stabilizing supramolecular complexes between sulphonated tetraphenylporphyrin anions ([MTPPS](4-): M = H(2) and Zn) and a lithium ion encapsulated C(60) (Li(+)@C(60)); the resulting ensemble produces long-lived charge-separated states upon photoexcitation of the porphyrins.     

Effect of Penicillin on Nitrite-Oxidizing Bacteria in Activated Sludge

The effects of penicillin G on the number and activity of nitrite-oxidizing bacteria were investigated in laboratory-scale reactors and batch tests. At a concentration of 100 mg L⁻¹, addition of penicillin G for short periods did not significantly affect nitrite oxidation, while addition for more than 2 months suppressed nitrite oxidation. Fluorescence in situ hybridization with 16S ribosomal RNA-targeted probes revealed a slight decrease in the abundance of Nitrospira, while Nitrobacter was not affected by addition of penicillin G for more than 39 days. The resistance of nitrite-oxidizing bacteria to penicillin appeared to be positively affected by intermittent aeration only when accompanied by denitrification; otherwise, the aeration mode (continuous or intermittent aeration) did not significantly affect the abundance of Nitrobacter and Nitrospira.     

2,1,3-Benzothiadiazole-containing donor–acceptor–acceptor dyes for dye-sensitized solar cells

A series of organic dyes with a donor–acceptor–acceptor (D–A–A) configuration, in which various diarylthienylamine donors and a cyanoacrylic acid acceptor are bridged by a low-band-gap 2,1,3-benzothiadiazole acceptor, have been synthesized, characterized, and employed as photosensitizers for dye-sensitized solar cells (DSSCs). The adoption of 2,1,3-benzothiadiazole as the bridging acceptor endowed these tailor-made dyes with superior light-harvesting capabilities in comparison to their previously reported pyrimidine-based analogs. After fine-tuning the fabrication conditions, DSSCs based on these dyes showed solar spectral responses extending to the near-IR region and achieved power conversion efficiencies (PCEs) of up to 3.16% (OHexDPTB) under simulated AM 1.5G irradiation (100 mW cm^?2).     

Comparison of amorphous iridium water-oxidation electrocatalysts prepared from soluble precursors

Electrodeposition of iridium oxide layers from soluble precursors provides a route to active thin-layer electrocatalysts for use on water-oxidizing anodes. Certain organometallic half-sandwich aqua complexes of iridium form stable and highly active oxide films upon electrochemical oxidation in aqueous solution. The catalyst films appear as blue layers on the anode when sufficiently thick, and most closely resemble hydrous iridium(III,IV) oxide by voltammetry. The deposition rate and cyclic voltammetric response of the electrodeposited material depend on whether the precursor complex contains a pentamethylcyclopentadieneyl (Cp*) or cyclopentadienyl ligand (Cp), and do not match, in either case, iridium oxide anodes prepared from non-organometallic precursors. Here, we survey our organometallic precursors, iridium hydroxide, and pre-formed iridium oxide nanoparticles. From electrochemical quartz crystal nanobalance (EQCN) studies, we find differences in the rate of electrodeposition of catalyst layers from the two half-sandwich precursors; however, the resulting layers operate as water-oxidizing anodes with indistinguishable overpotentials and H/D isotope effects. Furthermore, using the mass data collected by EQCN and not otherwise available, we show that the electrodeposited materials are excellent catalysts for the water-oxidation reaction, showing maximum turnover frequencies greater than 0.5 mol O(2) (mol iridium)(-1) s(-1) and quantitative conversion of current to product dioxygen. Importantly, these anodes maintain their high activity and robustness at very low iridium loadings. Our organometallic precursors contrast with pre-formed iridium oxide nanoparticles, which form an unstable electrodeposited material that is not stably adherent to the anode surface at even moderately oxidizing potentials.     

Hydrothermal synthesis, crystal structure and properties of Ni(II)-4f complexes based on 1H-benzimidazole-5,6-dicarboxylic acid

Nine novel heterometallic coordination polymers [Ln(2)Ni(Hbidc)(2)(SO(4))(2)(H(2)O)(8)](n) (Ln = Pr (1), Sm (2), Eu (3), Gd (4), Tb (5), Dy (6), Ho (7), Er (8), Yb (9), H(3)bidc = 1H-benzimidazole-5,6-dicarboxylic acid) have been synthesized under hydrothermal conditions and characterized by elemental analysis, FT-IR, TG analysis and single crystal X-ray diffraction. X-ray analysis revealed that all complexes present almost identical three-dimensional (3D) structures with PtS-type topology. Complexes 1-7 are all isomorphous, and the structure variation of polymers 8 and 9 is induced by the lanthanide contraction effect. In additional, the luminescence properties of complexes 2, 3 and 5-7, and the magnetic properties of complexes 4 and 6-8 were investigated.     

Microwave spectrum and structure of carbonyl gold iodide,OCAuI – ARTICLE WITHDRAWN

WITHDRAWN TO APPEAR IN SPECIAL ISSUE IN 2007