Assembly principles and relaxation processes in nanosized heterogeneous complexes: Multiporphyrin structures and CdSe/ZnS nanocrystals

Based on the extra-ligand addition effect, the principles of targeted self-assembly of nanosized multiporphyrin complexes of various types with controllable geometry and composition (up to 8 tetrapyrroles) and heterogeneous composites based on trioctylphosphine oxide-stabilized CdSe/ZnS semiconductor nanocrystals and organic compounds were developed. The dynamics and mechanisms of energy and charge transfer (including electron tunneling) in such systems were studied by continuous, picosecond fluorescence (Δ_1/2 ≈ 30 ps), and femtosecond transient (Δ_1/2 ≈ 120 fs) spectroscopy with varying the quantitative and qualitative constitution of the composites, the temperature, and the polarity of the medium.     

Applying a dynamic method to the measurement of ion mobility

A dynamic method is applied to measure the mobility of gas-phase ions in the dual ion funnel interface of the electrospray source of a quadrupole orthogonal time-of-flight mass spectrometer. In a new operational mode, a potential barrier was formed in the second ion funnel of the mass spectrometer and then progressively increased. In this region, a flow of gas drags the ions into the mass spectrometer while the electric force applied by the potential barrier decelerates them. Ions with lower mobility can be carried by the gas flow more easily than those with high mobility. Thus, electrical forces can block the more mobile ions more easily. Hence, the electric barrier formed in the ion funnel permits only ions below a certain mobility threshold to enter the mass spectrometer. When the barrier voltage is increased, this threshold moves from high to low mobilities. Ions with mobilities above the threshold cannot enter the mass spectrometer, and their signal decreases to zero. Thus, in a barrier voltage scan, mass spectrometric signals of ions sequentially disappear. Differentiation of these decreasing ion signal curves produces peaks from which an ion mobility spectrum can be reconstructed. Blocking voltages, i.e., the positions of the peaks on the barrier voltage scale are directly related to the mobility of these ions. An internal calibration using ions with known mobility values helps determine the unknown ion mobilities and allows calculation of ionic cross sections.     

Analysis of phenolic choline esters from seeds of Arabidopsis thaliana and Brassica napus by capillary liquid chromatography/electrospray‐ tandem mass spectrometry

Total phenolic choline ester fractions prepared from seeds of Arabidopsis thaliana and Brassica napus were analyzed by capillary LC/ESI‐QTOF‐MS and direct infusion ESI‐FTICR‐MS. In addition to the dominating sinapoylcholine, 30 phenolic choline esters could be identified based on accurate mass measurements, interpretation of collision‐induced dissociation (CID) mass spectra, and synthesis of selected representatives. The compounds identified so far include substituted hydroxycinnamoyl‐ and hydroxybenzoylcholines, respective monohexosides as well as oxidative coupling products of phenolic choline esters and monolignols. Phenolic choline esters are well separable by reversed‐phase liquid chromatography and sensitively detectable using electrospray ionization mass spectrometry in positive ion mode. CID mass spectra obtained from molecular ions facilitate the characterization of both the type and substitution pattern of such compounds. Therefore, LC/ESI‐MS/MS represents a valuable tool for comprehensive qualitative and quantitative analysis of this compound class. Copyright © 2008 John Wiley & Sons, Ltd.     

Inside Cover: Bifunctional Dendrimers: From Robust Synthesis and Accelerated One‐Pot Postfunctionalization Strategy to Potential Applications (Angew. Chem. Int. Ed. 12/2009)

By taking advantage of “click” chemistry's chemoselective nature, a new platform of bifunctional AB₂C dendrimers, having acetylene/azide groups anchored within the interior and hydroxy groups on the periphery, has been realized. In their Communication on page 2126 ff. M. Malkoch and co‐workers reveal a simple synthetic route for two sets of frameworks. To illustrate the utility of AB₂C dendrimers they were used in a one‐pot postfunctionalization protocol, in the development of dendritic nanoparticles, and in the formation of hydrogels.

     

The Hamiltonian of the amplified oscillator

The solution of the quantum stochastic differential equation for the amplified oscillator has been disccussed. An explicit operator has been established the matrix elements of which coincide with those of the Hamiltonian for a large class of functions. Meinem Lehrer Heinz K?nig zum 80. Geburtstag in Dankbarkeit gewidmet     

A general formula for the algebraic degree in semidefinite programming

In this article, we use a natural desingularization of the conormalvariety of (n x n)-symmetric matrices of rank at most r to finda general formula for the algebraic degree in semidefinite programming.     

Influence of dynamic brake pad properties on automotive disk brake squeal

Comparing different methods of characterizing dynamic properties of brake pad materials clearly shows, that those properties strongly depend on the boundary conditions as well as on amplitude and frequency in the excitation. Actually simulations of brake squeal suffer on the missing of correct material parameters identified under conditions relevant for squeal. The present paper gives inside into a method for the measurement and identification of linear and nonlinear brake pad material parameters identified under correct boundary conditions. (© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Effective elastic properties of 3D polypropylene microstructures of an injection moulded plate via different homogenization schemes

The mechanical properties of a polypropylene (PP) part depend on its morphology and degree of crystallinity. To evaluate its effective elastic behaviour two upscaling schemes are developed and compared. In the 1^st method the spherulites are assumed to be isotropic and vary linearly with the spherulite diameter. In the 2^nd one, the homogenization is performed successively on two scales. At the nanoscale, the bilamina of amorphous and crystalline phases is homogenized. Then, at the microscale, a 3D radial distribution of effective bilamina is homogenized. (© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Effect on kinetics by deuterium in the 1,5-hydrogen shift of a cisoid-locked 1,3(Z)-pentadiene, 2-methyl-10-methylenebicyclo[4.4.0]dec-1-ene: evidence for tunneling?

Prompted by extensive theoretical interest in the role of tunneling in the intramolecular 1,5-hydrogen shift in 1,3(Z)-pentadienes and the large uncertainty in the published values of the theoretically relevant kinetic deuterium-isotope effect and its dependence on temperature, we have examined a degenerate bicyclic version, 2-methyl-10-methylenebicyclo[4.4.0]dec-1-ene, which is locked into the rearrangement-competent cisoid conformation, in the hope of obtaining more precise and accurate values. From rate constants determined over a range of 33 degrees C from 167.7 to 201.6 degrees C, Arrhenius parameters, Ea = 32.8 +/- 0.4 kcal mol(-1) and log A = 11.1 +/- 0.2, were obtained. An average kinetic isotope effect of 4.2 +/- 0.5 obtained from all values for kH/kD and k-H/k-D may be compared with a value of 5.0 +/- 0.3, recalculated from data in the pioneering publication of Roth and K?nig. From a highly problematic extrapolation of the temperature dependence, a value of kH/kD of 16.6 (standard error between 6.5 and 43) is calculated for the kinetic isotope effect at 25 degrees C (Roth and K?nig: 12.2). With curvature in Arrhenius plots being one of the three types of experimental evidence considered indicative of tunneling, the kinetic study of the previously published rearrangement of 1-phenyl-5-p-tolyl-1,3(Z)-pentadiene has been extended over a period of 339 days to a range of 108 degrees C (77-185 degrees C) without discerning any deviation from a straight-line Arrhenius plot: Ea = 28.7 +/- 0.5 (kcal mol(-1)) and log A = 9.41 +/- 0.30.