A new synthesis of trifluorinated compounds via 1,1-dichloro-1-alkenes in superacid

A two step process for converting ketone or aldehyde via 1,1-dichloro-1-alkenes to the corresponding 1,1,1-trifluoroderivatives is described, based on HF addition and chlorine-fluorine exchange under superacidic conditions.     

Dependence of the localized surface plasmon resonance of noble metal quasispherical nanoparticles on their crystallinity-related morphologies

The absorption spectra of 5 nm noble metal nanoparticles (Ag, Au, and Cu) with typical morphologies of multiply twinned particles (MTPs) and single crystals are calculated by using the discrete dipole approximation method. Among the considered morphologies, it is found that icosahedral, cuboctahedral and truncated octahedral particles behave like quasispherical particles whereas the optical response of the decahedral particles significantly differs from the others. This result, which originates from the shape anisotropy of the decahedron, points out the capacity to discriminate decahedral MTPs from a population of particles with mixed crystallinities and related quasispherical shapes.     

Optimization of the CHARMM additive force field for DNA: Improved treatment of the BI/BII conformational equilibrium

The B-form of DNA can populate two different backbone conformations: BI and BII, defined by the difference between the torsion angles ε and ζ (BI = ε-ζ < 0 and BII = ε-ζ > 0). BI is the most populated state, but the population of the BII state, which is sequence dependent, is significant and accumulating evidence shows that BII affects the overall structure of DNA, and thus influences protein-DNA recognition. This work presents a reparametrization of the CHARMM27 additive nucleic acid force field to increase the sampling of the BII form in MD simulations of DNA. In addition, minor modifications of sugar puckering were introduced to facilitate sampling of the A form of DNA under the appropriate environmental conditions. Parameter optimization was guided by quantum mechanical data on model compounds, followed by calculations on several DNA duplexes in the condensed phase. The selected optimized parameters were then validated against a number of DNA duplexes, with the most extensive tests performed on the EcoRI dodecamer, including comparative calculations using the Amber Parm99bsc0 force field. The new CHARMM model better reproduces experimentally observed sampling of the BII conformation, including sampling as a function of sequence. In addition, the model reproduces the A form of the 1ZF1 duplex in 75 % ethanol, and yields a stable Z-DNA conformation of duplex (GTACGTAC) in its crystal environment. The resulting model, in combination with a recent reoptimization of the CHARMM27 force field for RNA, will be referred to as CHARMM36.     

Microstructural and chemical characterization of nanostructured TiAlSiN coatings with nanoscale resolution

Nanoscale resolution electron microscopy analysis combined with ion beam assisted techniques are presented here, to give answers to full characterization of morphology, growth mode, phase formation, and compositional distribution in nanocomposite TiAlSiN coatings deposited under different energetic conditions. Samples were prepared by magnetron sputtering, and the effects of substrate temperature and bias were investigated. The nanocomposite microstructure was demonstrated by the formation of a face-centered cubic (Ti,Al)N phase, obtained by substitution of Al in the cubic titanium nitride (c-TiN) phase, and an amorphous matrix at the column boundary regions mainly composed of Si, N (and O for the samples with higher oxygen contents). Oxygen impurities, predicted as the principal responsible for the degradation of properties, were identified, particularly in nonbiased samples and confirmed to occupy preferentially nitrogen positions at the column boundaries, being mainly associated to silicon forming oxynitride phases. It has been found that the columnar growth mode is not the most adequate to improve mechanical properties. Only the combination of moderate bias and additional substrate heating was able to reduce the oxygen content and eliminate the columnar microstructure leading to the nanocomposite structure with higher hardness (>30 GPa).     

Zinc porphyrin sensitized redox processes in microemulsions

Photoinduced electron transfer from Zn tetraphenylporphyrin to acceptors solubilized either in the lipid interior or aqueous bulk of anionic oil-in-water microemulsions has been investigated by nanosecond laser photolysis. While intimate cosolubilization appears to decrease the efficiency of electron transfer in the former, enhanced charge separation of the redox products has been observed in the latter.     

Dérivés Alléniques du Phosphore. Influence de l'État de Coordination du Phosphore et de la Nature des Radicaux Liés au Phosphore sur les Signes de J(P?H)

The signs of the phosphorus-proton coupling constants in various allenic organophosphorus compounds have been determined by either analysis of the AB₂X spectra or double resonance. Probable absolute signs have been obtained by taking ³J(P? H) as positive. In allenic phosphine oxides, the following signs are obtained: ²J(P? H) +ve, ³J(P? H) +ve, ⁴J(P? H) ?ve, ⁵J(P? H) +ve and the ⁴J(P? H) coupling constant varies mostly with the inductive effect of the substituents bound to the phosphorus atom. In allenic phosphines, these sings are: ²J(P? H) +ve, ³J(P? H) +ve, ⁴J(P? H) ?ve and +ve and the ⁴J(P? H) coupling constant varies with both the inductive and resonance effects to the substituents. This coupling constant is negative except when the phosphorus atom is bound to groups which are electron-donating by resonance effects. These results are discussed in relation to the pπ? dπ bonding in phosphine.     

A hitchhiker's guide to G-quadruplex ligands

Over the past decade, nucleic acid chemists have seen the spectacular emergence of molecules designed to interact efficiently and selectively with a peculiar DNA structure named G-quadruplex. Initially derived from classical DNA intercalators, these G-quadruplex ligands progressively became the focal point of new excitement since they appear to inhibit selectively the growth of cancer cells thereby opening interesting perspectives towards the development of novel anti-cancer drugs. The present article aims to help researchers enter this exciting research field, and to highlight recent advances in the design of G-quadruplex ligands.     

FRET templated by G-quadruplex DNA: a specific ternary interaction using an original pair of donor/acceptor partners

G-quadruplex represents a suitable scaffold for FRET (fluorescence resonance energy transfer) since its two external quartets offer two well-defined binding sites for concomitant trapping of donor/acceptor partners. Combining selective G-quadruplex binders (macrocyclic bis(quinacridine) BOQ(1) or monomeric quinacridine MMQ(1), donor) with a highly fluorescent DNA probe (thiazole orange, acceptor), we designed a structure-specific FRET-system based on an unprecedented noncovalent ternary complex. This system could be potentially usable as a signature for quadruplex-DNA conformation in solution, but also might offer a unique means for observing cation and ligand binding influence on quadruplex topology.