Synthesis, cyclic voltammetry, and photophysical properties of a bridged o-phenylenediamine-C(60) dyad

The synthesis, complete spectroscopic characterization, cyclic voltammetry, and photophysical measurements of a new o-phenylenediamine-C(60) dyad are described. By using a tether strategy, only a single regioisomer was obtained. Cyclic voltammetry measurements indicate that the two electroactive groups do not interact in their singlet ground states. Photophysical investigations reveal a rapid photoinduced electron transfer between the singlet excited state of the fullerene acceptor and the o-phenylenediamine donor, yielding a charge-separated radical pair.     

Vergleichende Untersuchungen zur Struktur von 4‐Dimethylaminopyridin‐Addukten

Comparative Structural Studies on 4‐Dimethylaminopyridine‐Adducts Lewis acid‐base adducts of the type dmap—MMe₃ (M = Al 1 , Ga 2 , In 3 , Tl 4 ) as well as dmap—AlCl₃ ( 6 ) and dmap—Al(t‐Bu)₃ ( 7 ) were synthesized by reaction of MR₃ with 4‐dimethylamino‐pyridine (dmap) whereas dmap—AlH₃ ( 5 ) was obtained from AlH₃·Et₂O. 1 — 7 were characterized by means of NMR (¹H, ¹³C{¹H}) and mass spectrometry and elemental analysis. In addition, their solid state structures were determined by single crystal X‐ray diffraction studies. A comparison of the structural parameters reveales the influence of both electronic (Lewis acidity of the group 13 atom) and steric interactions on the structure and stability of as prepared Lewis acid‐base adducts.     

Extraction inductively coupled plasma-optical emission spectrometry (ICP-OES) determination of traces of phosphorus in tungsten

A method for the separation and preconcentration of traces of phosphorus from tungsten was developed. Solid phase extraction of the phosphovanadomolybdate complex performed on a micro-column was applied. Phosphorus was determined by optical emission spectroscopy (OES) with inductively coupled plasma (ICP) excitation. A limit of detection of 0.4 g/g P with respect to the solid phase is obtained. By directly coupling the extraction/elution step to the ICP instrument a detection limit of 0.06 g/g P in W was achieved. Besides, the complexity of spectral evaluation in ICP-OES determinations of traces in spectralline-rich matrices is discussed.Presented in part at the 1989 European Winter Conference on Plasma Spectrochemistry, Reutte, Austria     

Open-tubular liquid chromatography under turbulent and secondary flow conditions

Summary Liquid chromatography in open tubes at flow rates around 0.1 cm · s^–1 and less can generate an enormous number of theoretical plates but suffers from long analysis times. The Golay and van Deemter equations are also obeyed with high accuracy.If straight tubes of circular cross section and very smooth inner surface are used, secondary flow effects can be neglected. Thus the plate height should depend only on the flow velocity and the number of theoretical plates should decrease with increase in linear flow, whereas the number of plates per unit time should be constant.Under turbulent conditions, however, the plate height seems to be more or less independent of linear flow over a wide range. Increasing the flow to several hundred cm · s^–1 causes, for example, 0.2 mm ID capillaries to show the reverse effect and a slight decrease in plate height is found. Alkali treated and silanized capillaries below 100 m i. d. deviate from the Golay prediction before turbulence occurs and a relative decrease in the plate height and thus higher efficiency is found possibly caused be secondary flow effects in the coiled tube or the roughness of the inner walls. These effects allow an increase in the efficiency of given open-tubular systems simply by increasing the solvent velocity drastically. Although plate heights are in the range mm to cm, efficiencies, in theoretical plates per second, similar to classic HPLC, are found. Therefore the quite interesting possibility of overcoming the well-known restrictions of classical HPLC to achieve high efficiency liquid chromatograms exists.Presented at the 17th International Symposium on Chromatography, September 25–30, 1988, Vienna, Austria.     

Asymmetric Diels-Alder Reaction of 1-Methoxybuta-1,3-diene with (2R)-N-Glyoxyloylbornane-10,2-sultam

Starting from sultam 1 , the chiral dienophile (2R)-N-glyoxyloylbornane-10,2-sultam ( 4 ) was readily prepared. Non-catalyzed atmospheric- and high-pressure as well as [Eu(fod)₃]-promoted [4 + 2] cycloadditions of 1-methoxy-buta-1,3-diene ( 5 ) to chiral dienophile 4 , leading with high asymmetric induction to 6-methoxy-3,6-dihydro-2H-pyran-2-yl derivatives 6 – 9 , are described. The extent and direction of asymmetric induction in these reactions were established by ¹H-NMR analysis and chemical correlation, respectively. Stereochemical models for both non-catalyzed and [Eu(fod)₃]-promoted reactions are proposed.     

Studies on the metabolism of mitragynine,the main alkaloid of the herbal drug Kratom,in rat and human urine using liquid chromatography‐linear ion trap mass spectrometry

Mitragynine (MG) is an indole alkaloid of the Thai medicinal plant Mitragyna speciosa (Kratom in Thai) and reported to have opioid agonistic properties. Because of its stimulant and euphoric effects, Kratom is used as a herbal drug of abuse. The aim of the presented study is to identify the phase I and II metabolites of MG in rat and human urine after solid‐phase extraction (SPE) using liquid chromatography‐linear ion trap mass spectrometry providing detailed structure information in the MSⁿ mode particularly with high resolution. The seven identified phase I metabolites indicated that MG was metabolized by hydrolysis of the methylester in position 16, O‐demethylation of the 9‐methoxy group and of the 17‐methoxy group, followed, via the intermediate aldehydes, by oxidation to carboxylic acids or reduction to alcohols and combinations of some steps. In rats, four metabolites were additionally conjugated to glucuronides and one to sulfate, but in humans, three metabolites to glucuronides and three to sulfates. Copyright © 2009 John Wiley & Sons, Ltd.     

Temperature and pressure dependent rate coefficients for the reaction of Hg with Br and the reaction of Br with Br: a pulsed laser photolysis-pulsed laser induced fluorescence study

A pulsed laser photolysis-pulsed laser induced fluorescence technique has been employed to study the recombination of mercury and bromine atoms, Hg + Br + M --> HgBr + M (1) and the self-reaction of bromine atoms, Br + Br + M --> Br2 + M (2). Rate coefficients were determined as a function of pressure (200-600 Torr) and temperature (243-293 K) in nitrogen buffer gas and as a function of pressure (200-600 Torr) in helium buffer gas at room temperature. For reaction 1, kinetic measurements were performed under conditions in which bromine atoms were the reactant in excess concentration while simultaneously monitoring the concentration of both mercury and bromine. A temperature dependent expression of (1.46 +/- 0.34) x 10(-32) x (T/298)(-(1.86+/-1.49)) cm6 molecule(-2) s(-1) was determined for the third-order recombination rate coefficient in nitrogen buffer gas. The effective second-order rate coefficient for reaction 1 under atmospheric conditions is a factor of 9 smaller than previously determined in a recently published relative rate study. For reaction 2 we obtain a temperature dependent expression of (4.31 +/- 0.21) x 10(-33) x (T/298)(-(2.77+/-0.30)) cm6 molecule(-2) s(-1) for the third-order recombination rate coefficient in nitrogen buffer gas. The rate coefficients are reported with a 2sigma error of precision only; however, due to the uncertainty in the determination of absolute bromine atom concentrations and other unidentified systematic errors we conservatively estimate an uncertainty of +/-50% in the rate coefficients. For both reactions the observed pressure, temperature and buffer gas dependencies are consistent with the expected behavior for three-body recombination.     

A supramolecular fluorescence probe for caffeine

[structure: see text] Supramolecular sensing is rather limited to charged analytes. This report describes a practicable assay for caffeine, which employs a competitive "indicator-displacement" approach and allows detection by fluorescence. A simple analytical protocol is described that allows quantitation of caffeine in beverages.     

Electron spin resonance study of radicals generated in cellulose/N-methylmorpholine solutions after flash photolysis at 77 K

The processes of radical formation in N-methylmorpholine-N-oxide monohydrate (NMMO) and cellulose/NMMO solutions were studied by ESR at 77 K under high-power UV (lambda = 248 nm) excimer laser flash photolysis. Radicals mainly generated were attributed to the nitroxide type radicals -CH2-NO*-CH2- and -CH2-NO*-CH3 at the first step and methyl *CH3 and formyl *CHO radicals at the second step of the photoreaction. Kinetic studies of these radicals revealed that formation and recombination rates of the radicals depend on the cellulose concentration in cellulose/NMMO solutions and the concentration of additional ingredients, e.g. Fe(II) and propyl gallate. Even at frozen state temperature, acceleration or quenching of radical reaction processes was found. The proposed scheme of UV light-induced NMMO degradation during irradiation based on ESR data correlates well with independently obtained results based on high-performance liquid chromatography (HPLC). The analysis of degradation products by HPLC, e.g. aminoethanol and acetaldehyde, supports the assumption concerning a radical-initiated ring opening of NMMO.