The direct photo-oxidative decarboxylation of α-oxo-carboxylic acids

α-Oxo-carboxylic acids undergo photo-oxidative decarboxylation from both C-1 and C-2 positions, and reaction does not involve singlet oxygen: a mechanism involving an electron transfer reaction is postulated.     

Crystal structure of (4α,4aα,8aα)-(±)-octahydro-2-(phenylmethyl)-2H-1,2-benzoxazin-4-ol, 4-methylbenzenesulfonate(ester)

The title compound, a bicyclic tetrahydro-1,2-oxazine, crystallizes in a monoclinic lattice, space group P2₁/c, with a = 12.9809(18)Å, b = 12.920(2)Å, c = 13.631(2)Å, = 110.713(12)°, and Z = 4. The structure found in the solid state for this conformationally mobile molecule shows the tosyl group in an axial position and a benzyl group in an equatorial position of the bicyclic system.     

Unusual spin transition behavior in 2,6-bis((pyrazol-3-yl)-pyridine) iron(II)-bis-oxalato-platinate(II)

[Fe(bpp)2][Pt(ox)2].H2O (with bpp=2,6-bis(pyrazol-3-yl)-pyridine and ox=oxalate) was prepared, and its spin crossover behavior was characterized. The two-step spin transition behavior changes over several cycles. The original behavior is restored when the sample is allowed to relax for a week. Furthermore, the ST exhibits a strong dependence on the heating and cooling rate. Heating the compound at 1 K/min leads to a spin transition with a third step and a second plateau at gammaHS approximately 0.8. Quenching the sample to 77 K also affects the spin transition behavior. The kinetic relaxation is followed after quenching and after light-induced excited spin state trapping experiments.     

… zur Forschung in der Didaktik: 7 Thesen …

Goals and contents of chemical education research are presented as a list of seven statements in order to be discussed.     

Studies on the preparation and characterization of monodisperse polystyrene latices V.: The preparation of cationic latices

Summary Methods are described for the preparation of monodisperse polystyrene latices using as initiators, 2-azo-bis-(2-methylpropamidinium) dichloride and 2-azo-bis-(2-isopropyliminazolium) dichloride. The preparations were carried out in the absence of any added surface active agents. The effect on particle size of varying initiator concentration, monomer concentration, temperature and ionic strength was examined and the conditions defined for preparing monodisperse latices, with particles in the size range 0.2 to 1m. Electrophoretic measurements confirmed that the latex particles were cationic. The evidence obtained suggested that the charged sites on the particle surface were amidinium groupings. The latices were not stable at pH values greater than 11 and prolonged heating at 90° also caused coagulation.

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Zusammenfassung Es wurden Methoden zur Darstellung monodisperser Polystyrol-Latices unter Verwendung von 2-azo-bis-(2-methylpropamidinium)-dichlorid und 2-azo-bis-(2-isopropyliminazolium)-dichlorid als Initiator beschrieben. Die Darstellung erfolgte in Abwesenheit von grenzflächenaktiven Verbindungen. Der Einfluß unterschiedlicher Initiator- und Monomerkonzentrationen, der Temperatur und der lonenstärke auf die Teilchengröße wurde untersucht und die Bedingungen festgelegt, unter denen monodisperse Latices mit Teilchen im Größenbereich von 0,2-1m erhalten werden. Elektrophoretische Messungen bestätigten, daß die Latexteilchen kationisch sind. Die Ladungen auf der Teilchenoberfläche sind Amidiniumgruppen. Die Latices waren bei pH-Werten über 11 nicht stabil; längeres Erhitzen auf 90° führte ebenfalls zur Koagulation.

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With 6 figures and 9 tables     

A possible replacement of single crystal by melt-textured material in the study of YBa2Cu3O7−y

Improved superconducting properties were observed in melt-textured YBa₂Cu₃O_7-y ceramic material. The inductive current density has a small field dependence up to 5.5 T over a wide temperature range. The field and temperature dependences of the magnetic properties are similar to the behavior found in single crystals. Values of the intragrain critical current density in melt-texture samples have the same order of magnitude as in single crystals. The reduced porosity and improved grain alignment help to probe intrinsic physical properties that depend on crystallographic orientation. Thus experiments similar to those involving single crystals are possible. The modified Bean critical state model applied to single crystals can also be used in these melt-textured samples. Thus, it is possible to use melt-textured samples in some basic research which originally required the use of single crystals.     

SYNTHESIS AND SPECTROSCOPIC DIFFERENTIATION OF 2- AND 4-ALKOXYTHIOTETRONIC ACIDS

O-Alkylation of thiotetronic acids gives a mixture of 2- and 4-position enol ether products. Comparison of the physical data revealed that UV spectroscopy was the most reliable method of distinguishing between these related ethers. We have determined that 4-position ethers have a distinct absorption between 235-240 nm, while 2-position ethers have two absorbance peaks, one between 205-220 nm and the other between 305-310 nm. This report describes the synthesis and unambiguous characterization of 2- and 4-methoxy-3,5-dimethylthiotetronic acids. The UV absorption properties of several other pairs of thiotetronic acid ethers confirm that these differences are general features that provide a simple method for distinguishing between 2- and 4-substituted isomers.     

Liquid Extraction Surface Analysis (LESA) Electron-Induced Dissociation and Collision-Induced Dissociation Mass Spectrometry of Small Molecule Drug Compounds

Here, we present liquid extraction surface analysis (LESA) coupled with electron-induced dissociation (EID) mass spectrometry in a Fourier-transform ion cyclotron resonance mass spectrometer for the analysis of small organic pharmaceutical compounds directly from dosed tissue. First, the direct infusion electrospray ionisation EID and collision-induced dissociation (CID) behaviour of erlotinib, moxifloxacin, clozapine and olanzapine standards were compared. EID mass spectra were also compared with experimental or reference electron impact ionisation mass spectra. The results show that (with the exception of erlotinib) EID and CID result in complementary fragment ions. Subsequently, we performed LESA EID MS/MS and LESA CID MS/MS on singly charged ions of moxifloxacin and erlotinib extracted from a thin tissue section of rat kidney from a cassette-dosed animal. Both techniques provided structural information, with the majority of peaks observed for the drug standards also observed for the tissue-extracted species. Overall, these results demonstrate the feasibility of LESA EID MS/MS of drug compounds from dosed tissue and extend the number of molecular structures for which EID behaviour has been determined.

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On-site monitoring of trace levels of free manganese in sea water via sonoelectroanalysis using a boron-doped diamond electrode

Cathodic stripping voltammetry at a boron-doped diamond electrode utilising an insonated accumulation protocol is shown to be possible for the on-site trace detection of free manganese in seawater samples. No sample pre-treatment is required with the application of ultrasound providing a sensitive and selective protocol for the analysis of manganese. The protocol is used in the evaluation of manganese in seawater samples taken near the site of a former ferromanganese factory in the town Šibenik, Croatia.     

The influence of the amount of stationary phase and nature of solid support on retention indices

Summary It is shown that the retention indices of polar solutes are affected by the amount of stationary phase in the column. The retention indices increase with decreasing stationary phase loadings. The reasons for this behavior are most likely due to the existence of mixed retention mechanisms. At low amounts of stationary phases, adsorption on the support or column walls can take place. Studies were made using four supports, two of which were Chromosorb W and the other two Chromosorb P. The effects of changing the liquid phase loadings are more pronounced when using Chromosorb P.