Highly functionalized bridged silsesquioxanes

The objective of this work was to synthesize functionalized mesoporous silsesquioxanes with high concentrations of amine groups. During typical sol–gel syntheses, these materials are obtained by co-condensation of organic precursors with suitable linkers, such as tetraethoxysilane, necessary to prevent the mesoporous structure from collapsing. Thus, concentrations of amine groups in organosilicas usually do not exceed 2.7–3.4 mmol g⁻¹. The use of bridged bis-trimethoxysilanes, however, allowed formation of mesoporous materials with no linker. Polycondensation of bis-trimethoxysilanes containing amine groups was conducted in acidic, neutral and basic media, resulting in high yields of solid bridged silsesquioxanes. Gelation occurred quickly if no acid or base was added to the reaction mixture. The hybrid organic/inorganic nature of obtained materials was confirmed by FT-IR and MAS CP NMR spectroscopy. Elemental analysis showed that amino group concentration in the products was 3.3–4.1 mmol g⁻¹. Measurement of particle size distribution confirmed that choice of reaction media significantly affects particle sizes and agglomeration degrees, with the largest agglomerates (up to 50 μm) formed in basic media. A morphology study, using small-angle X-Ray scattering, displayed two-level fractal structures composed of aggregated 6.5–10.5 nm particles. Reactions in the presence of a surfactant resulted in formation of mesoporous structures. Furthermore, the obtained bridged silsesquioxanes were thermally stable down to 260 °C, but could reversibly absorb water and CO₂ at temperatures below 120 °C. Thus, condensation of the bridged precursor without a linker resulted in formation of a highly functionalized mesoporous material.     

Dynamically Harmonized FT-ICR Cell with Specially Shaped Electrodes for Compensation of Inhomogeneity of the Magnetic Field. Computer Simulations of the Electric Field and Ion Motion Dynamics

The recently introduced ion trap for FT-ICR mass spectrometers with dynamic harmonization showed the highest resolving power ever achieved both for ions with moderate masses 500?C1000?Da (peptides) as well as ions with very high masses of up to 200?kDa (proteins). Such results were obtained for superconducting magnets of very high homogeneity of the magnetic field. For magnets with lower homogeneity, the time of transient duration would be smaller. In superconducting magnets used in FT-ICR mass spectrometry the inhomogeneity of the magnetic field in its axial direction prevails over the inhomogeneity in other directions and should be considered as the main factor influencing the synchronic motion of the ion cloud. The inhomogeneity leads to a dependence of the cyclotron frequency from the amplitude of axial oscillation in the potential well of the ion trap. As a consequence, ions in an ion cloud become dephased, which leads to signal attenuation and decrease in the resolving power. Ion cyclotron frequency is also affected by the radial component of the electric field. Hence, by appropriately adjusting the electric field one can compensate the inhomogeneity of the magnetic field and align the cyclotron frequency in the whole range of amplitudes of z-oscillations. A method of magnetic field inhomogeneity compensation in a dynamically harmonized FT-ICR cell is presented, based on adding of extra electrodes into the cell shaped in such a way that the averaged electric field created by these electrodes produces a counter force to the forces caused by the inhomogeneous magnetic field.     

On parameter estimation of threshold autoregressive models

This paper studies the threshold estimation of a TAR model when the underlying threshold parameter is a random variable. It is shown that the Bayesian estimator is consistent and its limit distribution is expressed in terms of a limit likelihood ratio. Furthermore, convergence of moments of the estimators is also established. The limit distribution can be computed via explicit simulations from which testing and inference for the threshold parameter can be conducted. The obtained results are illustrated with numerical simulations.     

Transition radiation from a relativistic electron obliquely incident on a thin metal plate of finite transverse dimensions

The problem of transition radiation generated by the oblique motion of a relativistic electron through a thin metal plate of finite transverse dimensions is considered. The expressions for the spectral and angular densities of radiation emitted forward and backward are obtained. It is shown that, in the millimeter and the submillimeter range, the spectra of both forward and backward radiation for targets of finite transverse dimensions can differ substantially from the corresponding spectra for an infinite plate.     

Polariton-assisted manipulation of energy relaxation pathways: donor–acceptor role reversal in a tuneable microcavity

Resonant interaction between excitonic transitions of molecules and localized electromagnetic field allows the formation of hybrid light–matter polaritonic states. This hybridization of the light and the matter states has been shown to significantly alter the intrinsic properties of molecular ensembles placed inside the optical cavity. Here, we have observed strong coupling of excitonic transition in a pair of closely located organic dye molecules demonstrating an efficient donor-to-acceptor resonance energy transfer with the mode of a tuneable open-access cavity. Analysing the dependence of the relaxation pathways between energy states in this system on the cavity detuning, we have demonstrated that predominant strong coupling of the cavity photon to the exciton transition in the donor dye molecule can lead not only to an increase in the donor–acceptor energy transfer, but also to an energy shift large enough to cause inversion between the energy states of the acceptor and the mainly donor lower polariton energy state. Furthermore, we have shown that the polariton-assisted donor–acceptor chromophores'' role reversal or “carnival effect” not only changes the relative energy levels of the donor–acceptor pair, but also makes it possible to manipulate the energy flow in the systems with resonant dipole–dipole interaction and direct energy transfer from the acceptor to the mainly donor lower polariton state. Our experimental data are the first confirmation of the theoretically predicted possibility of polariton-assisted energy transfer reversal in FRET systems, thus paving the way to new avenues in FRET-imaging, remote-controlled chemistry, and all-optical switching.

Polariton-assisted donor–acceptor role reversal in resonant energy transfer between organic dyes tagged with the terminus of the closed oligonucleotide-based molecular beacon strongly coupled to electromagnetic modes of a tuneable microcavity.     

Optimization of the cathode porosity via mechanochemical synthesis with carbon black

Journal of Solid State Electrochemistry - Nanostructured carbon–coated composite cathode materials LiFe0.5Mn0.5PO4/C (LFMP/C) are prepared by the mechanochemically assisted solid-state...     

Raman Scattering Enhancement Based on High-Pressure High-Temperature Diamonds†

Journal of Russian Laser Research - We discuss the use of high-pressure high-temperature (HPHT) diamonds for the determination of trace amounts of various Raman active substances. The amount of the...     

Two-step one-pot electrosynthesis and catalytic activity of xCoO–yCo(OH)2-supported silver nanoparticles

Journal of Solid State Electrochemistry - Efficient two-step electrosynthesis of xCoO–yCo(OH)2 (CoOxHy)-supported silver nanoparticles (AgNPs) is carried out in N,N-dimethylformamide (DMF)...     

Sulfonated octa‐substituted Co(II) phthalocyanines immobilized on silica matrix as catalyst for Thiuram E synthesis

Silica nanoparticles were obtained during the work according to two different sol–gel methods. In first one Schtrober's technique and series of cobalt phthalocyanine metal complexes varying in peripheral substituents were used. Second method was performed using the same complexes but differed in applying surface‐active substance (SAS) and two precursors – tetraethoxysilane (TEOS) and aminopropyltrimethoxysilane (APTMOS). All obtained hybrid materials were analyzed via SEM, the size of single particle was studied, which in all cases was about 200 nm. In order to investigate hybrid's characteristics laser diffraction and liquid nitrogen adsorption methods were applied. Distinction in pore's specific volume of differently‐obtained nanoparticles was found. Catalytic activity of all obtained materials were tested in conversion of N,N‐diethylcarbamodithiolate to thiuram E. Effect of peripherally substituted phthalocyanines and morphology of matrixes were manifested on catalytic activity of the hybrids.