Scaling of some chemical properties of tetrahedral and octahedral molecules plus almost spherical C and B cages

It is shown that for tetrahedral and octahedral molecules the quantity a R _e /N ^1/3 is quadratic in the ratio z/N, where R _e is the equilibrium bond length, ze is the central charge and N is the total number of electrons. Some scaling properties for the ‘breathing’ force constant k are proposed for a series of 5 tetrachlorides.     

Curing induced structural reorganization and enhanced reactivity of amino-terminated organic thin films on solid substrates: observations of two types of chemically and structurally unique amino groups on the surface

Infrared-visible sum frequency generation vibrational spectroscopy (SFG) was used to characterize the structure of 3-aminopropyltriethoxysilane (APTES) films deposited on solid substrates under controlled experimental conditions for the first time. Our SFG spectra in combination with complementary analytical data showed that APTES films undergo structural changes when cured at an elevated temperature. Before the films are cured, well-ordered hydrophobic ethoxy groups are dominantly present on the surface. A majority of hydrophilic surface amino groups are protonated, and they are either buried or randomly oriented at the interface. After the films are cured, chemically and structurally different neutral amino groups are detected on the surface. Unlike the protonated amino groups, a new class of neutral amino groups is ordered at the interface and shows enhanced reactivity.     

Teflon-coated silicon microreactors: impact on segmented liquid-liquid multiphase flows

We describe fluoropolymer modification of silicon microreactors for control of wetting properties in chemical synthesis applications and characterize the impact of the coating on liquid-liquid multiphase flows of solvents and water. Annular flow of nitrogen gas and a Teflon AF (DuPont) dispersion enable controlled evaporation of fluoropolymer solvent, which in turn brings about three-dimensional polymer deposition on microchannel walls. Consequently, the wetting behavior is switched from hydrophilic to hydrophobic. Analysis of microreactors reveals that the polymer layer thickness increases down the length of the reactor from ～1 to ～13 μm with an average thickness of ～7 μm. Similarly, we show that microreactor surfaces can be modified with poly(tetrafluoroethylene) (PTFE). These PTFE-coated microreactors are further characterized by measuring residence time distributions in segmented liquid-liquid multiphase flows, which display reduced axial dispersion for the coated microreactors. Applying particle image velocimetry, changes in segment shape and velocity fluctuations are observed resulting in reduced axial dispersion. Furthermore, the segment size distribution is narrowed for the hydrophobic microreactors, enabling further control of residence distributions for synthesis and screening applications.     

Formation of aromatic structures from chain hydrocarbons in electrical discharges: absorption and fluorescence study of C11H9(+) and C11H9(•) isomers in neon matrices

A set of arenes (phenylacetylene, indene, and naphthalene cations and C(11)H(9)(+) isomers) was produced from 2,4-hexadiyne diluted in helium in a hot-cathode discharge source. The mass-selected ions were codeposited with neon at 6 K and investigated by electronic absorption spectroscopy. This reveals that fused-ring species are readily formed from an acyclic precursor in such a source. After photobleaching of matrices containing C(11)H(9)(+), neutral C(11)H(9)(?) radicals were also characterized. Assignment of the observed transitions to different m/z = 141 cationic and corresponding neutral isomers is given and supported by experiments using other precursors, fluorescence measurements, and time-dependent density functional and second-order approximate coupled cluster calculations.     

Determination of osteocalcin in meat and bone meal of bovine and porcine origin using matrix-assisted laser desorption ionization/time-of-flight mass spectrometry and high-resolution hybrid mass spectrometry

A method has been developed for determining the origin of meat and bone meal (MBM) by detecting species-specific osteocalcin (OC) using matrix-assisted laser desorption ionization/time-of-flight (MALDI/TOF) and high-resolution hybrid mass spectrometry (HR-Q/TOF MS). The analysis is based on the detection of typical species-specific OC and its tryptic peptide fragments which differ in mass due to differences in the amino-acid sequences between species. After dissolving the MBM samples in EDTA buffer, purification after ultrafiltration was performed using two methods: solid-phase extraction using Zip-Tip C(18) or size exclusion coupled with reverse-phase chromatography. Fractions containing partially purified intact OC were analyzed using LC-Q/TOF and MALDI/TOF mass spectrometry. Species-specific OC was detected at the typical protonated and doubly protonated molecular ions. Furthermore, typical porcine- and bovine-derived tryptic fragments from MBM were detected after enzymatic digestion. In order to determine the underlying amino-acid sequences and to confirm the assignment to OC-derived peptides, MS/MS analysis was carried out. In conclusion, we were able to detect OC in bovine and porcine MBM with high sensitivity and the MS-based method described here by which total OC mass and marker peptides of digested OC are recorded can be used as an alternative approach to detect genus-specific differences in MBM and can be applied as a confirmatory method to mainly immunological osteocalcin screening methods.     

Semiclassical fully differential ionization cross sections of helium with negatively charged fast projectiles

Fully differential cross sections are calculated for the ionization of helium by negatively charged fast projectiles using a semiclassical model developed previously for the ionization of atoms by positive projectiles. The method is tested in the case of 1 keV electron and 500 keV antiproton projectiles. The semiclassical results show reasonable agreement with the experiments and other theories. The origin of the obtained structures has been investigated by a partial wave analysis.     

Simultaneous end-on/side-on coordination modes of a diphosphorus tetrahedral complex imposed by pre-organization of oligometallic Cu(I) acceptors

The reaction of the [{CpMo(CO)(2)}(2)(μ,η(2):η(2)-P(2))] (Cp=cyclopentadienyl) metallo-ligand 2 with pre-organized Cu(I) bi- and trimetallic precursors afforded new coordination complexes with unprecedented coordination modes for a Mo(2)P(2) complex. Variable-temperature solution and solid-state (31)P NMR spectroscopy measurements were performed and X-ray diffraction studies revealed an η(2):η(1) coordination mode for the Mo(2)P(2) unit of 2 in the Cu(I) bimetallic complexes 3 and 4. DFT calculations were carried out to highlight the bonding situation of this unprecedented coordination mode in the Cu(I) bimetallic compound 3. It is built up from a side-on coordination of the P-P σ bond to one copper ion and from the interaction of the lone pair of one phosphorus atom with the second copper ion. The remaining available lone pair of the second phosphorus atom can be involved as well to interact with an additional metal centre, as evidenced in the Cu(I) trimetallic compound 5 in which an η(2):η(1):η(1) coordination mode of the ligand 2 is observed. Derivative 3 can be used as a molecular clip to obtain discrete π-stacked dimers through a ligand exchange reaction between acetonitrile ligands and cyano-capped π-conjugated systems, indicating the stability of the new η(2):η(1) coordination mode.     

Jordanian deformation of the open sℓ(2) Gaudin model

We derive a deformed s?(2) Gaudin model with integrable boundaries. Starting from the Jordanian deformation of the SL(2)-invariant Yang R-matrix and generic solutions of the associated reflection equation and the dual reflection equation, we obtain the corresponding inhomogeneous spin-1/2 XXX chain. The semiclassical expansion of the transfer matrix yields the deformed s?(2) Gaudin Hamiltonians with boundary terms.     

Rotational image deblurring with sparse matrices

We describe iterative deblurring algorithms that can handle blur caused by a rotation along an arbitrary axis (including the common case of pure rotation). Our algorithms use a sparse-matrix representation of the blurring operation, which allows us to easily handle several different boundary conditions. We also include robust stopping rules for the iterations. The performance of our algorithms is illustrated with examples.     

Voltammetric concentration measurements in diffusion-hindered media

In voltammetric analysis the signal—in most cases—depends on transport processes. When getting concentration values of analytes from voltammetric calibrating curves, it is expected that the mass transport characteristics in sample solutions and in calibrating standards are identical. Standard addition methods are used in analytical practice when making calibrating standard with transport properties matching that of the samples would be difficult. Voltammetric measurements can also be carried out in soil—in sediment—or in gel samples. The mass transport conditions in these media, however, can considerably differ from those existing in aqueous solutions. The application of standard addition technique, however, is not an option there. In this work, a glassy carbon electrode was applied with a built-in diffusion layer on its measuring surface and chronoamperometric measurements were carried out. The current–time transients taken in aqueous solution and in tortuous, diffusion-hindered media were compared. Ascorbic acid and iodine as analytes as well as silica sand sediments and green pepper pulps as tortuous matrices were used. It was proved that if the modified electrode is used for analysis, then short time chronoamperometric transients taken in tortuous media can be evaluated by calibration data taken in aqueous standard solutions.