Fast LEED intensity measurements with a video camera and a video tape recorder

The measurement of LEED intensities with a TV camera-computer system, which has been published in an earlier paper, is reported to be improved with respect to the speed of data collection by a factor of about 10². Other properties such as sensitivity, reliability and handling facility have also been improved. The new measuring mode, which applies a video tape recorder, allows the simultaneous measurement of all appearing diffraction spots down to a beam current of 10⁻¹¹ A with a rate of 50 energy points/s. This pushes the total measuring time for LEED spectra to the order of seconds and makes possible to monitor non-stable surfaces. As an example intensity measurements for different adsorption stages of hydrogen on W(100) are presented.     

Exact solution of restricted cell model for hard parallel rectangles in a “brick-wall” configuration

The cell restrictions are defined, and it is shown that the model is essentially equivalent to a model presented in a previous paper.     

Synthesis and cannabinoid receptor activity of ketoalkenes from Echinacea pallida and nonnatural analogues

Despite its popularity and widespread use, the efficacy of Echinacea products remains unclear and controversial. Among the various compounds isolated from Echinacea, ketoalkenes and ketoalkenynes exclusively found in the pale purple coneflower (E. pallida) are major components of the extracts. In contrast to E. purpurea alkamides, these compounds have not been synthesized and studied for immunostimulatory effects. We present a practical and useful synthetic approach to the ketoalkenes using palladium-catalyzed cross-coupling reactions and the pharmaceutical results at the human cannabinoid receptors. The synthetic route developed provides overall good yields for the ketoalkenes and is applicable to other natural products with similar 1,4-diene motifs. No significant activity was observed at either receptor, indicating that the ketoalkenes from E. pallida are not responsible for immunomodulatory effects mediated via the cannabinergic system. However, newly synthesized non-natural analogues showed micro-molar potency at both cannabinoid receptors.     

The Genuine Bernstein–Durrmeyer Operators and Quasi-Interpolants

In this paper we consider the so-called genuine Bernstein–Durrmeyer operators and define corresponding quasi-interpolants of order ${r \in \mathbb{N}_0}$ in terms of certain differential operators. These quasi-interpolants preserve all polynomials of degree at most r?+?1. We analyse the eigenstructure of the differential operators and the quasi-interpolants and prove as main results an error estimate of Jackson–Favard type for sufficiently smooth functions and an upper bound for the error of approximation in the sup-norm in terms of an appropriate K-functional.     

Direct μ-flow injection isotope dilution ICP-MS for the determination of heavy metals in oil samples

The determination of trace elements in oil samples and their products is of high interest as their presence significantly affects refinery processes and the environment by possible impact of their combustion products. In this context, inductively coupled plasma mass spectrometry (ICP-MS) plays an important role due to its outstanding analytical properties in the quantification of trace elements. In this work, we present the accurate and precise determination of selected heavy metals in oil samples by making use of the combination of μ-flow direct injection and isotope dilution ICP-MS (ICP-IDMS). Spike solutions of ⁶²Ni, ⁹⁷Mo, ¹¹⁷Sn and ²⁰⁶Pb were prepared in an organic solvent, mixed directly with the diluted oil samples and tested to be fit for purpose for the intended ID approach. The analysis of real samples revealed strong matrix effects affecting the ICP-MS sensitivity, but not the isotope ratio measurements, so that accurate results are obtained by ICP-IDMS. Typical relative standard deviations were about 15% for peak area and peak height measurements, whereas the isotope ratios were not significantly affected (RSD < 2%). The developed method was validated by the analysis of a metallo-organic multi-element standard (SCP-21, typically applied as a calibration standard) and the standard reference material SRM1084a (wear metals in lubricating oil). The obtained results were in excellent agreement with the certified values (recoveries between 98% and 102%), so the proposed methodology of combining μ-flow direct injection and ICP-IDMS can be regarded as a new tool for the matrix-independent, multi-element and reliable determination of trace elements in oil and related organic liquids.     

Trapping and Reactivity of a Molecular Aluminium Oxide Ion

Aluminium oxides constitute an important class of inorganic compound that are widely exploited in the chemical industry as catalysts and catalyst supports. Due to the tendency for such systems to aggregate via Al‐O‐Al bridges, the synthesis of well‐defined, soluble, molecular models for these materials is challenging. Here we show that reactions of the potassium aluminyl complex K₂[( NON )Al]₂ ( NON =4,5‐bis(2,6‐diiso‐propylanilido)‐2,7‐di‐tert‐butyl‐9,9‐dimethylxanthene) with CO₂, PhNCO and N₂O all proceed via a common aluminium oxide intermediate. This highly reactive species can be trapped by coordination of a THF molecule as the anionic oxide complex [( NON )AlO(THF)]^?, which features discrete Al?O bonds and dimerizes in the solid state via weak O???K interactions. This species reacts with a range of small molecules including N₂O (to give a hyponitrite ([N₂O₂]^2?) complex) and H₂, the latter offering an unequivocal example of heterolytic E?H bond cleavage across a main group M?O bond.     

Further Prenylated Bi‐ and Tricyclic Phloroglucinol Derivatives from Hypericum papuanum

From the petroleum‐ether extract of the dried aerial parts of Hypericum papuanum, three new prenylated tricyclic and four new bicyclic acylphloroglucinol derivatives were isolated by bioactivity‐guided fractionation. The structures of the bicyclic compounds enaimeone A, B, and C ( 1 / 1a , 2 / 2a , and 3 / 3a , resp.) were elucidated as rel‐(1R,5R,6S)‐4‐hydroxy‐6‐(1‐hydroxy‐1‐methylethyl)‐5‐methyl‐1‐(3‐methylbut‐2‐enyl)‐3‐(2‐methylpropanoyl)‐bicyclo[3.2.1]oct‐3‐ene‐2,8‐dione ( 1 / 1a ), rel‐(1R,5R,6R)‐4‐hydroxy‐6‐(1‐hydroxy‐1‐methylethyl)‐5‐methyl‐1‐(3‐methylbut‐2‐enyl)‐3‐(2‐methylpropanoyl)bicyclo[3.2.1]oct‐3‐ene‐2,8‐dione ( 2 / 2a ), rel‐(1R,5R,6R)‐4‐hydroxy‐6‐(1‐hydroxy‐1‐methylethyl)‐5‐methyl‐3‐(2‐methylbutanoyl)‐1‐(3‐methylbut‐2‐enyl)bicyclo[3.2.1]oct‐3‐ene‐2,8‐dione ( 3 / 3a ). The tricyclic isolates 8‐hydroxy‐3β‐(1‐hydroxy‐1‐methylethyl)‐4,4,7‐trimethyl‐9‐(2‐methylpropanoyl)‐5βH‐tricyclo[5.3.1.0^1,5]undec‐8‐ene‐10,11‐dione ( 4 ), 8‐hydroxy‐3α‐(1‐hydroxy‐1‐methylethyl)‐4,4,7‐trimethyl‐9‐(2‐methylpropanoyl)‐5βH‐tricyclo[5.3.1.0^1,5]undec‐8‐ene‐10,11‐dione ( 5 ), and 8‐hydroxy‐3α‐(1‐hydroxy‐1‐methylethyl)‐4,4,7‐trimethyl‐9‐(2‐methylbutanoyl)‐5βH‐tricyclo[5.3.1.0^1,5]undec‐8‐ene‐10,11‐dione ( 6 ), and their corresponding tautomers 4a , 5a , and 6a , were named 1′‐hydroxyialibinones A, B, and D, respectively. Oxidative decomposition of furonewguinone A (=2,3,3a,5‐tetrahydro‐3a‐hydroxy‐2‐(1‐hydroxy‐1‐methylethyl)‐5‐methyl‐5‐(3‐methylbut‐2‐enyl)‐7‐(2‐methylpropanoyl)‐benzofuran‐4,6‐dione; 7 ) led to furonewguinone B (=3,3a,7,7a‐tetrahydro‐3a,6,7a‐trihydroxy‐2‐(1‐hydroxy‐1‐methylethyl)‐7‐methyl‐7‐(3‐methylbut‐2‐enyl)‐5‐(2‐methylpropanoyl)benzofuran‐4(2H)‐one; 8 / 8a ). Structure elucidation was based on extensive 1D and 2D NMR studies, as well as on data derived from mass spectrometry. Furthermore, the cytotoxicity towards KB nasopharyngeal carcinoma cells and the antibacterial activity were determined.     

An organophotocatalytic late-stage N–CH3 oxidation of trialkylamines to N-formamides with O2 in continuous flow

We report an organophotocatalytic, N–CH₃-selective oxidation of trialkylamines in continuous flow. Based on the 9,10-dicyanoanthracene (DCA) core, a new catalyst (DCAS) was designed with solubilizing groups for flow processing. This allowed O₂ to be harnessed as a sustainable oxidant for late-stage photocatalytic N–CH₃ oxidations of complex natural products and active pharmaceutical ingredients bearing functional groups not tolerated by previous methods. The organophotocatalytic gas–liquid flow process affords cleaner reactions than in batch mode, in short residence times of 13.5 min and productivities of up to 0.65 g per day. Spectroscopic and computational mechanistic studies showed that catalyst derivatization not only enhanced solubility of the new catalyst compared to poorly-soluble DCA, but profoundly diverted the photocatalytic mechanism from singlet electron transfer (SET) reductive quenching with amines toward energy transfer (E_nT) with O₂.

An N–CH₃-selective trialkylamine oxidation to N-formamides is reported in continuous flow using gaseous O₂. A novel, enhanced-solubility dicyanoanthracene organophotocatalyst switched the photochemical mechanism from electron to energy transfer.