Effect of fluorination on the stability of carbon nanofibres in organic solvents

Beneficial effects of fluorination on the stability of carbon nanofibre (CNF) dispersion in organic solvents as a function of time are evidenced. Because of their excellent friction properties, fluorinated CNFs (CF_0.85) can be used as nanoparticles of tribo-active phase in lubrication; however, they have to be added into a matrix. We have shown that mixtures of CF_0.85 are more stable than CNF solutions. Investigations by ultraviolet–visible spectroscopy have been carried out 2 h after sonication and after an ageing of 4 months. Hansen solubility theory was used, and after ageing, tribological and Raman spectroscopy experiments showed no significant modification of physicochemical properties of the CF_0.85.     

Template‐Assembled Synthetic G‐Quadruplex (TASQ): A Useful System for Investigating the Interactions of Ligands with Constrained Quadruplex Topologies

A new biomolecular device for investigating the interactions of ligands with constrained DNA quadruplex topologies, using surface plasmon resonance (SPR), is reported. Biomolecular systems containing an intermolecular‐like G‐quadruplex motif 1 (parallel G‐quadruplex conformation), an intramolecular G‐quadruplex 2 , and a duplex DNA 3 have been designed and developed. The method is based on the concept of template‐assembled synthetic G‐quadruplex (TASQ), whereby quadruplex DNA structures are assembled on a template that allows precise control of the parallel G‐quadruplex conformation. Various known G‐quadruplex ligands have been used to investigate the affinities of ligands for intermolecular 1 and intramolecular 2 DNA quadruplexes. As anticipated, ligands displaying a π‐stacking binding mode showed a higher binding affinity for intermolecular‐like G‐quadruplexes 1 , whereas ligands with other binding modes (groove and/or loop binding) showed no significant difference in their binding affinities for the two quadruplexes 1 or 2 . In addition, the present method has also provided information about the selectivity of ligands for G‐quadruplex DNA over the duplex DNA. A numerical parameter, termed the G‐quadruplex binding mode index (G4‐BMI), has been introduced to express the difference in the affinities of ligands for intermolecular G‐quadruplex 1 against intramolecular G‐quadruplex 2 . The G‐quadruplex binding mode index (G4‐BMI) of a ligand is defined as follows: G4‐BMI=K_D^intra/K_D^inter, where K_D^intra is the dissociation constant for intramolecular G‐quadruplex 2 and K_D^inter is the dissociation constant for intermolecular G‐quadruplex 1 . In summary, the present work has demonstrated that the use of parallel‐constrained quadruplex topology provides more precise information about the binding modes of ligands.     

Dynamical derivation of Eyring equation and the second‐order kinetic law

Elementary gas‐phase reactions of the bimolecular type A + B → Products are characterized by the second‐order kinetic law , where [A] and [B] are the concentrations of A and B species, t is the time, and k is the rate constant, usually estimated by means of Eyring equation. Here, we show that its dynamical derivation, as such, is not consistent with the second‐order law. This contradiction is however removed by introducing a correlation between what we call potentially reactive pairs. A new presentation of the dynamical derivation of Eyring equation is finally proposed on the basis of the previous findings. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem 110:2355–2359, 2010     

Classical photodissociation dynamics with Bohr quantization

The standard classical expression of the state-resolved photodissociation cross section is not consistent with an efficient Bohr quantization of product internal motions. A new and strictly equivalent expression not suffering from this drawback is proposed. This expression opens the way to more realistic classical simulations of direct polyatomic photodissociations in the quantum regime where only a few states are available to the products.     

Synthesis and Resolution of Planar–Chiral Ruthenium–Palladium Complexes with ECE′ Pincer Ligands

Feel the pinch! Planar–chiral, cationic, ruthenium–palladium complexes based on η⁶,η¹‐coordinated ECE′ pincer ligands are synthesized as racemic mixtures by reacting ECE′–palladium complexes and [Ru(C₅R₅)(MeCN)₃]⁺ arenophiles (R=H or Me). Chiral resolution of the cationic complexes was achieved by using the chiral counterion [Δ‐TRISPHAT]^?, and solving the X‐ray crystal structure of one diastereoisomer (shown here).

     

New scalings in nuclear fragmentation

Fragment partitions of fragmenting hot nuclei produced in central and semiperipheral collisions have been compared in the excitation energy region 4-10?MeV per nucleon where radial collective expansion takes place. It is shown that, for a given total excitation energy per nucleon, the amount of radial collective energy fixes the mean fragment multiplicity. It is also shown that, at a given total excitation energy per nucleon, the different properties of fragment partitions are completely determined by the reduced fragment multiplicity (i.e., normalized to the source size). Freeze-out volumes seem to play a role in the scalings observed.     

β‐Diketiminate‐supported magnesium alkyl: synthesis,structure and application as co‐catalyst for polymerizations mediated by a lanthanum half‐sandwich complex

Mg(n‐Bu){η²‐HC[C(Me)NMes]₂} ( 2 ) (Mes = mesityl, 2,4,6‐Me₃C₆H₂), a new β‐diketiminate‐supported magnesium alkyl, has been synthesized and structurally characterized. The X‐ray analysis of the lanthanum half‐sandwich complex Cp*La(BH₄)₂(THF)₂ ( 1 ) (Cp* = pentamethylcyclopentadienyl; THF = tetrahydrofuran) is also reported. Complex 2 has been assessed as both alkylating agent and chain transfer agent for the lanthanum‐catalysed polymerization and coordinative chain transfer polymerization of isoprene and styrene using 1 as the pre‐catalyst. The results are compared with those for n‐butylethylmagnesium (BEM) which is traditionally used for this purpose. The 1,4‐trans stereospecific polymerization of isoprene shows a more controlled character using 2 versus BEM, and higher activities are observed for the chain transfer polymerization of styrene when 2 is used as chain transfer agent. The activity is in turn lower than that observed using BEM when 1 equiv. of magnesium compound is used for the polymerization of styrene. The combination of 1 , 2 and Al(i‐Bu)₃ leads finally to a 1,4‐trans stereoselective coordinative chain transfer polymerization of isoprene, in a similar way to BEM. Copyright © 2015 John Wiley & Sons, Ltd.     

Iron‐Catalyzed Trifluoromethylation of Enamide

Herein the first example of the iron(II)‐catalyzed trifluoromethylation of enamide using mild and simple reaction conditions is reported. The method is cost‐effective and uses the easy‐to‐handle Togni’s reagent as the electrophilic CF₃ source. This transformation is totally regioselective at the C3 position of enamides and exhibits broad substrate scope, good functional group tolerance and thus demonstrates its useful application in a late‐stage fluorination strategy.     

Simultaneous Determination of Artesunate and Amodiaquine in Fixed-Dose Combination by a RP-HPLC Method with Double UV Detection: Implementation in Interlaboratory Study Involving Seven African National Quality Control Laboratories

The fixed-dose combination artesunate (AS)–amodiaquine (AQ) is one of the most widely used treatments for uncomplicated falciparum malaria. It is currently proposed to the inclusion in the model list of essential medicines of World Health Organization and has been recently prequalified. Until now, no satisfactory method for the simultaneous determination of the two active ingredients had been available. Thus, a reversed phase high performance liquid chromatography for the quantitative determination of AQ and AS was developed and validated. Chromatography was performed using an end-capped octadecylsilyl silica gel column (100 × 4.6 mm, 3 μm) with a binary gradient using aqueous phase containing potassium dihydrogen phosphate (10 mM) and acetonitrile. Taking into consideration the physico-chemical characteristics of the two compounds related to their ionization, the use of a counter ion was necessary to ensure the retention of AQ in a reversed phase system simultaneously to AS. Thus, aqueous mobile phase was adjusted to pH 3.0 and the chosen counter ion was sodium 1-octanesulfonate (100 mM). In these conditions, the retention times were about 4 min for AQ and 10 min for AS with UV detection at 300 and 210 nm, respectively. Method was then validated according to ICH guideline (specificity/linearity/accuracy/precision) and potential interferences with excipients and degradation products were checked. It has also been used for an interlaboratory study involving seven African National Quality Control Laboratories and Afssaps (Agence française de sécurité sanitaire des produits de santé) laboratory. The results demonstrate that this rapid and simple method can be easily used by official laboratories for routine control, market survey and for the detection of potential substandard medicines which are very frequent in African countries.