An experimental and kinetic modeling study on the oxidation of 1,3-dioxolane

The modern catalytic or enzymatic advances allow the production of novel biofuel. Among them, 1,3-dioxolane can be produced from formaldehyde and ethylene glycol, both can be obtained from biomass. In this study, the oxidation of 1,3-dioxolane is studied at stoichiometric conditions. The ignition delay times of 1,3-dioxolane/O₂/inert mixtures were measured in a shock tube and in a rapid compression machine at pressures of 20 to 40 bar and temperatures ranging from 630 to 1300 K. The pressure profiles recorded in the rapid compression machine show a first stage of ignition enlightening the influence of the low temperature chemistry of combustion. Furthermore, mole fraction profiles of the stable intermediates produced during the oxidation of 1,3-dioxolane were measured in a jet-stirred reactor at 10 bar. Following these observations, a detailed kinetic model was developed with reaction rate coefficients and thermochemical data calculated by theoretical calculations or estimated by analogies to suitable molecules. In order to get an insight into the most important reaction pathways brute force sensitivity analysis and reaction pathway analysis were performed with the proposed model and discussed. It became clear that in the fuel-in-air case for the alkylhydroperoxide of 1,3-dioxolane the ring opening beta-scission pathway is favored against the further alkane-like second addition to molecular oxygen, which leads to a limited negative temperature coefficient.     

Insights into the oxidation of propylene oxide through the analysis of experiments and kinetic modeling

Cyclic ethers are important intermediates in the oxidation of hydrocarbons and biofuels. Studying the oxidation and pyrolysis of cyclic ethers will help in improving our understanding of this functional group and provide consistency to the base mechanism where they play an important role. In this aspect, propylene oxide has been investigated in this study by obtaining ignition delay time measurements in the rapid compression machine and shock tube. The experiments were performed in a range of pressures varying from 10 to 40 bar at different equivalence ratios (0.5–2.0) and dilution percentages. Additionally, speciation measurements in the shock tube at pyrolysis conditions have been performed at a pressure of 40 bar to explore the isomerization pathways. A detailed kinetic mechanism was developed to describe both the oxidation and pyrolysis chemistry of propylene oxide. The mechanism is not only able to predict the data obtained from this study but also reproduces the data from the literature in a consistent trend. For a better understanding of the oxidation and pyrolysis chemistry of propylene oxide, the kinetic analyses were performed using the developed mechanism to comprehend the important reaction pathways and sensitive reactions. At the investigated regime, the consumption of propylene oxide through its isomerization channels is the critical pathway that controls the reactivity of the fuel.     

Synthesis and characterization of A4[Re6Q8L6]@SiO2 red-emitting silica nanoparticles based on Re6 metal atom clusters (A = Cs or K, Q = S or Se, and L = OH or CN)

Metal atom clusters constitute very promising candidates as luminophores for applications in biotechnology because they are nanosized entities offering robust luminescence in the near-infrared field (NIR). However, they cannot be used as prepared for biological applications because of potential toxic effects and quenching of the clusters' luminescence in aqueous media, and they therefore need to be dispersed in a biocompatible matrix. We describe herein the encapsulation of octahedral rhenium clusters, denoted as A(4)[Re(6)Q(8)L(6)] (A = Cs or K, Q = S or Se, and L = OH or CN), in silica nanoparticles by a water-in-oil microemulsion process, paying particular attention to the clusters' stability. The obtained A(4)[Re(6)Q(8)L(6)]@SiO(2) nanoparticles are 30 nm in size with good monodispersity and a perfectly spherical shape, as shown by scanning electron microscopy (SEM). The presence of cluster units inside the silica matrix was evidenced by scanning transmission electron microscopy in annular dark-field mode (ADF-STEM). From the point of view of their optical properties, the A(4)[Re(6)Q(8)L(6)]@SiO(2) nanoparticles show red and NIR emission under UV excitation, even when dispersed in water. The evolution of the structural and luminescence properties of clusters before and after encapsulation was followed by Raman and photoluminescence spectroscopy.     

Tetrathiafulvalene‐amido‐2‐pyridine‐N‐oxide as Efficient Charge‐Transfer Antenna Ligand for the Sensitization of YbIII Luminescence in a Series of Lanthanide Paramagnetic Coordination Complexes

The tetrathiafulvalene‐amido‐2‐pyridine‐N‐oxide ( L ) ligand has been employed to coordinate 4f elements. The architecture of the complexes mainly depends on the ionic radii of the lanthanides. Thus, the reaction of L in the same experimental protocol leads to three different molecular structure series. Binuclear [Ln₂(hfac)₅(O₂CPhCl)( L )₃] ? 2 H₂O (hfac^?=1,1,1,5,5,5‐hexafluoroacetylacetonate anion, O₂CPhCl^?=3‐chlorobenzoate anion) and mononuclear [Ln(hfac)₃( L )₂] complexes were obtained by using rare‐earth ions with either large (Ln^III=Pr, Gd) or small (Ln^III=Y, Yb) ionic radius, respectively, whereas the use of Tb^III that possesses an intermediate ionic radius led to the formation of a binuclear complex of formula [Tb₂(hfac)₄(O₂CPhCl)₂( L )₂]. Antiferromagnetic interactions have been observed in the three dinuclear compounds by using an extended empirical method. Photophysical properties of the coordination complexes have been studied by solid‐state absorption spectroscopy, whereas time‐dependent density functional theory (TD‐DFT) calculations have been carried out on the diamagnetic Y^III derivative to build a molecular orbital diagram and to reproduce the absorption spectrum. For the [Yb(hfac)₃( L )₂] complex, the excitation at 19 600 cm^?1 of the HOMO→LUMO+1/LUMO+2 charge‐transfer transition induces both line‐shape emissions in the near‐IR spectral range assigned to the ²F_5/2→²F_7/2 (9860 cm^?1) ytterbium‐centered transition and a residual charge‐transfer emission around 13 150 cm^?1. An efficient antenna effect that proceeds through energy transfer from the singlet excited state of the tetrathiafulvalene‐amido‐2‐pyridine‐N‐oxide chromophore is evidence of the Yb^III sensitization.     

Photoinduced electron transfer in Zn(II)porphyrin-bridge-Pt(II)acetylide complexes: variation in rate with anchoring group and position of the bridge

The synthesis and photophysical characterization of two sets of zinc porphyrin platinum acetylide complexes are reported. The two sets of molecules differ in the way the bridging phenyl-ethynyl unit is attached to the porphyrin ring. One set is attached via an ethynyl unit on the β position, while the other set is attached via a phenyl unit on the meso position of the porphyrin. These were compared with previously studied complexes where attachment was made via an ethynyl unit on the meso position. Femtosecond transient absorption measurements showed in all systems a rapid quenching of the porphyrin singlet state. Electron transfer is suggested as the quenching mechanism, followed by an even faster recombination to form both the porphyrin ground and triplet excited states. This is supported by the variation in quenching rate and porphyrin triplet yield with solvent polarity, and the observation of an intermediate state in the meso-phenyl linked systems. The different linking motifs between the dyads resulted in significant variations in electron transfer rates.     

A simplified [11C]phosgene synthesis

A new flow-through system for the production of [¹¹C]phosgene, a versatile labelling agent in radiochemistry for PET, is described. Cyclotron-produced [¹¹C]CH₄ is mixed with Cl₂ and converted into [¹¹C]CCl₄ by passing the mixture through an empty quartz tube at 510 °C. The outflow is directed through a Sb-filled guard that takes out Cl₂ and then, without intentional O₂ addition, through a second empty quartz tube at 750 °C, giving rise to [¹¹C]phosgene in 30–35% radiochemical yield.     

Inverse problem approaches for stationary Fourier transform spectrometers

A design of a miniaturized stationary Fourier transform IR spectrometer has been developed that produces a two-dimensional interferogram. The latter is disturbed by effects like parasitic interferences or disparities in the cutoff wavelength of the pixels. Thus, a simple Fourier transform cannot be used to estimate the spectrum of the scene. However, as these defects are deterministic, they can be measured and taken into account by inversion methods. A regularization term can also be added. The first experimental results prove the efficiency of this processing methodology.     

ATLAS discovery potential for a heavy charged Higgs boson

The sensitivity of the ATLAS detector to the discovery of a heavy charged Higgs boson is presented. Assuming a heavy SUSY spectrum, the most promising channels above the top quark mass are H^± → tb and H^± → τ^±ν_τ which provide coverage in the low and high tanβ regions up to ∼ 600 GeV. The achievable precisions on the charged Higgs mass and tanβ determination are also discussed. The H^± → W^± h⁰ channel, though restricted to a small MSSM parameter space, shows a viable signal in NMSSM where the parameter space is less constrained. The observation of the channel H⁻ → τ⁻_L ν_τ + c.c. may constitute a distinctive evidence for models with singlet neutrinos in large extra dimensions.