Hydrogen-carbon,carbon-carbon double rearrangement induced by proximity effects. 1–formation of methoxybenzyl ions in the electron impact mass spectra of substituted 1,1-bis(dimethoxyphenyl)methanes

The 75 eV electron impact mass spectra of 1,1-bis(dimethoxyphenyl)methanes bearing o-methoxy groups are dominated by intense peaks corresponding, at least formally, to benzyl ions [(CH₃O)₂C₆H₃CH₂]⁺ (b). They arise from ions [((CH₃O)₂C₆H₃)₂CH]⁺ (a), which are in turn formed from molecular ions by loss of an alkyl radical through benzylic cleavage. The analysis of compounds labelled with ²H or ¹³C at methoxy groups led to the determination of the mechanism. Hydrogen migration, as hydride, followed by electrophilic substitution by the methylene carbon of the phenyl methylene ether cation through a six-centred transition state is responsible for the formation of benzylic ions b.     

EFFECT OF MID-UV RADIATION ON DNA-Cu2+ COMPLEX: ABSORPTION AND CIRCULAR DICHROISM STUDY

Abstract— When DNA is complexed with Cu²⁺ ions it becomes sensitized to mid-UV light. Irradiation of the complex at 310 ± 10 nm produces marked changes in absorption and circular dichroism spectra in addition to those in melting profiles of irradiated samples. These variations show conformational changes in DNA structure due to a photoreduction of some copper sites in the DNA-Cu²⁺ complex. In addition to this effect an irreversible damage in DNA structure could be invoked to explain the observed behaviour. These facts can be related to the presence in DNA-Cu²⁺ complex of a small absorption band extending up to mid-UV range while the absorption of DNA is negligible in this spectral range.     

An interlaboratory comparison on whole water samples

The European Water Framework Directive 2000/60/EC requires monitoring of organic priority pollutants in so-called whole water samples, i.e. in aqueous non-filtered samples that contain natural colloidal and suspended particulate matter. Colloids and suspended particles in the liquid phase constitute a challenge for sample homogeneity and stability. Within the joint research project ENV08 “Traceable measurements for monitoring critical pollutants under the European Water Framework Directive 2000/60/EC”, whole water test materials were developed by spiking defined amounts of aqueous slurries of ultra-finely milled contaminated soil or sediment and aqueous solutions of humic acid into a natural mineral water matrix. This paper presents the results of an European-wide interlaboratory comparison (ILC) using this type of test materials. Target analytes were tributyltin, polybrominated diphenyl ethers and polycyclic aromatic hydrocarbons in the ng/L concentration range. Results of the ILC indicate that the produced materials are sufficiently homogeneous and stable to serve as samples for, e.g. proficiency testing or method validation. To our knowledge, this is the first time that ready-to-use water materials with a defined amount of suspended particulate and colloidal matter have been applied as test samples in an interlaboratory exercise. These samples meet the requirements of the European Water Framework Directive. Previous proficiency testing schemes mainly employed filtered water samples fortified with a spike of the target analyte in a water-miscible organic solvent.     

Experience of the National Institute of Metrology (INM) in development and certification of reference materials used in the metrological assurance of clinical laboratory measurements

In order to provide quality assurance in the field of clinical chemistry, required by European Standards, the Romanian national metrological infrastructure has to be improved. The main objectives of this important activity are metrological assurance of concentration measurements, the assessment of the uncertainty, and the traceability of measurements. Within this framework, reference materials play an important role. The experience of INM in the preparation, certification and use of reference materials and in metrological assurance of clinical laboratory measurements (especially when absorption photometric devices are used) is described. The combined uncertainty associated with chemical preparation of these reference materials is estimated. Received: 25 April 1997 / Revised: 8 July 1997 / Accepted: 12 July 1997     

Palladium(II) and platinum(II)-C(3)-substituted 2,2′-bipyridines

Reaction of Pd(OAc)₂ with HL¹ and HL² (HL¹=6-iso-propyl-2,2-bipyridine; HL²=6-neo-pentyl-2,2-bipyridine), followed by treatment with LiCl or KI, gives [PdCl(L¹)]₂, (1), [PdCl(L²)]₂ (2), and [PdI(L²)]₂ (3), respectively. The chloride bridge in complexes1 and2 is split by PPh³ to give the mononuclear species PdCl(L¹)(PPh₃) (4) and PdCl(L²)(PPh₃) (5). Spectroscopic data provide evidence for coordination of the deprotonated ligands through a nitrogen and the C₍₃₎ atom of the 6-substituted pyridine. An analogous platinum complex PtCl(L³)(SMe₂) (6) (HL³=6-tert-butyl-2,2-bipyridine) was obtained from trans-PtClMe(SMe₂)₂ and HL³. The crystal structures of compounds1 and6 have been solved by X-ray diffraction analysis.Dipartimento di Chimica, Universita di Sassari, via Vienna 2, I-07100 Sassari, Italy; Dipartimento di Chimica Strutturale e Stereochimica Inorganica, Universita di Milano, Centro CNR, I-20133 Milano, Italy; Published in Khimiya Geterotsiklicheskikh Soedinenii, No. 8, pp. 1127–1137, August, 1999.     

Sample evaporation in conventional split/splitless GC injectors: Part 2: Use of perylene for visual observation of three different scenarios in empty injector inserts

Perylene is strongly fluorescent as long as it is in solution. This has enabled visual observation of non-evaporated sample material in a “transparent injector”, i.e. in a heated glass device imitating a conventional vaporizing injector. Three scenarios of sample evaporation are described. Some samples (solvents) are nebulized and “flash evaporated” in the gas phase between the needle exit and the column entrance (Scenario 1). With most solvents, the liquid leaves the syringe needle as a thin jet which rushes through both the empty vaporizing chamber and the split outlet at high velocity, often without substantial evaporation. It does not touch the surfaces of the insert and passes round the bend at the bottom of the device without any problem (Scenario 2). Some samples are splashed on to the insert wall, wet it, and evaporate rather slowly from this surface (Scenario 3).     

Studies in organic mass spectrometry. Part 9—mass spectra of 9,10-disubstituted 2,3,6,7-tetraalkoxy-9,10-dihydroanthracenes: A remarkable loss of radicals from even-electron ions

The electron impact-induced fragmentations of 23 9,10-disubstituted 2,3,6,7-tetraalkoxy-9,10-dihydroanthracenes, including six stereoisomeric pairs, were studied. The loss of the 9-(or 10-)substituent constitutes the main fragmentation route. The resulting ions give rise to a remarkable violation of the so-called ‘even-electron rule’ as they eject the second substituent at the 10-(or 9-)position as a radical. The latter aspect was particularly investigated with the aid of low-energy (nominal value 15 eV) and mass-analysed ion kinetic energy spectra.     

Approximation of some Feller semigroups associated with a modification of Szász–Mirakjan–Kantorovich operators

We deepen the study of a sequence (C _n ) _n≧1 of positive linear operators, first introduced in [4], that generalize the classical Szász–Mirakjan–Kantorovich operators. In particular, we present some qualitative properties and an asymptotic formula for such a sequence. Moreover, we prove that, under suitable assumptions, the C ₀-semigroups generated by the second order differential operator $$V_l(u)(x)=xu''(x)+\frac{l}{2} u'(x)\quad (x \geqq 0,\ l \in [0, 2]) $$ on suitable domains of continuous or integrable functions may be approximated by means of iterates of the C _n ’s.     

Seed oil triglyceride profiling of thirty-two hybrid grape varieties

Triglyceride profile of seed oil samples from 32 hybrid grape varieties not studied before was investigated. A new method for the analysis of triacylglycerols (TAGs) has been developed based on the direct infusion in the electrospray ionization (ESI) source and employing tetrahydrofuran/methanol/water (85:10:5 v|v|v) as solvent; the formation of [M?+?Na](+) ions in high yield has been observed. TAGs were identified by ESI-tandem mass spectrometry analysis, and the matrix-assisted-laser-desorption-ionization and time-of-flight profile of samples was determined. Six were the principal TAGs identified in seed oil: trilinolein (LLL) was the most abundant (43%), followed by dilinoleoyl-oleoylglycerol (LOL, 23%), and dilinoleoyl-palmitoylglycerol (LPL, 15%). Compounds present in lower concentration were LSL and LOO (11%), LOP (6%), and LSP (2%). Compared with seed oils produced from V. Vinifera grapes, some significant differences in the relative abundances of TAGs were found, in particular hybrid grape seed oils showed higher LOL and lower LPL content, respectively. Among the samples studied, a particularly high content of LLL (rich in unsaturated fatty acids) was found in seed oils from two red varieties. Copyright ? 2012 John Wiley & Sons, Ltd.