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.     

Glass transition temperature of glucose, sucrose, and trehalose: an experimental and in silico study

Isothermal-isobaric molecular dynamics simulations are used to calculate the specific volume of models of different amorphous carbohydrates (glucose, sucrose, and trehalose) as a function of temperature. Plots of specific volume vs temperature exhibit a characteristic change in slope when the amorphous systems change from the glassy to the rubbery state. The intersection of the regression lines of data below (glassy state) and above (rubbery state) the change in slope provides the glass transition temperature (T(g)). These predicted glass transition temperatures are compared to experimental T(g) values as obtained from differential scanning calorimetry measurements. As expected, the predicted values are systematically higher than the experimental ones (about 12-34 K) as the cooling rates of the modeling methods are about a factor of 10(12) faster. Nevertheless, the calculated trend of T(g) values agrees exactly with the experimental trend: T(g)(glucose) < T(g)(sucrose) < T(g)(trehalose). Furthermore, the relative differences between the glass transition temperatures were also computed precisely, implying that atomistic molecular dynamics simulations can reproduce trends of T(g) values in amorphous carbohydrates with high quality.     

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.

     

Experimental 3D Analysis of the Large Scale Behaviour of a Plane Turbulent Mixing Layer

A new structure education method is proposed for representing the three dimensional large scale structures from hot wires measurement data. Due to the limited number of hot wire probes that can be used simultaneously, we firstly have to optimise the spatial location of sensors in order to detect large scale coherent structures. For such a purpose a detailed analysis of the 3D space-time flow organisation is given with particular emphasis on the full two point correlation tensor of the velocity field. Secondly, several procedures are developed in order to reconstruct instantaneous 3D velocity field on any finer and larger mesh than the experimental one from the limited available experimental information. The particular case of a spatially developing turbulent plane mixing layer is investigated. We then show that Stochastic Estimation and Proper Orthogonal Decomposition lead to a satisfactory reconstruction preserving the 3D coherent character of the flow. Finally, this reconstructed velocity field provides a 3D space-time representation of the large scale structures in a streamwise section of the flow and can then be used as realistic turbulent inflow condition for Large Eddy Simulations.     

A series solution for the effective properties of incompressible viscoelastic media

This paper presents a series solution for the homogenization problem of a linear viscoelastic periodic incompressible composite. The method uses the Laplace transform and the correspondence principle which are combined with the classical expansion along Neumann series of the solution of the periodic elasticity problem in Fourier space. The terms of the Neumann series appear as decoupled, containing geometry dependent terms and viscoelastic properties dependent terms which are polynomial fractions whose inverse Laplace transforms are provided explicitly.