Identification of degradation products of antioxidants in polyolefins by liquid chromatography combined with atmospheric pressure photoionisation mass spectrometry

Round robin tests have revealed the trend that the concentration of stabilizers in polyolefins is usually underestimated. However, it is still unclear whether this underestimation is due to systematic errors of the analysis procedures or to degradation of the stabilizers during the production of the round robin sample itself. Within the present work, the degradation pathways of six common antioxidants (ADK Stab AO-60, Everfos 168, Kinox 30, Irganox 3114, Irganox 1076, and Cyanox 1790) were investigated. Methods based on high-performance liquid chromatography with UV detection or hyphenated with mass spectrometry (employing either an ion trap or a quadrupole/time-of-flight instrument) were developed, whereby the suitability of atmospheric pressure photoionisation was studied and compared with the performance of more established ionisation techniques like electrospray ionisation and atmospheric pressure chemical ionisation. While ADK Stab, Kinox 30, Everfos 168, and Irganox 1076 turned out to be thermally stable at 115 °C, Irganox 3114 and Cyanox 1790 were partly degraded by oxidation. In the presence of talcum, which is a widely used inorganic filler for polyolefins, additional degradation reactions such as the cleavage of ester bonds and the loss of tert-butyl groups were observed at elevated temperature.     

Snx[BPO4]1−x composites as negative electrodes for lithium ion cells: Comparison with amorphous SnB0.6P0.4O2.9 and effect of composition

A comparative study of two Sn-based composite materials as negative electrode for Li-ion accumulators is presented. The former SnB_0.6P_0.4O_2.9 obtained by in-situ dispersion of SnO in an oxide matrix is shown to be an amorphous tin composite oxide (ATCO). The latter Sn_0.72[BPO₄]_0.28 obtained by ex-situ dispersion of Sn in a borophosphate matrix consists of Sn particles embedded in a crystalline BPO₄ matrix. The electrochemical responses of ATCO and Sn_0.72[BPO₄]_0.28 composite in galvanostatic mode show reversible capacities of about 450 and 530 mAh g⁻¹, respectively, with different irreversible capacities (60% and 29%). Analysis of these composite materials by ¹¹⁹Sn Mössbauer spectroscopy in transmission (TMS) and emission (CEMS) modes confirms that ATCO is an amorphous Sn^II composite oxide and shows that in the case of Sn_0.72[BPO₄]_0.28, the surface of the tin clusters is mainly formed by Sn^II in an amorphous interface whereas the bulk of the clusters is mainly formed by Sn⁰. The determination of the recoilless free fractions f (Lamb-Mössbauer factors) leads to the effective fraction of both Sn⁰ and Sn^II species in such composites. The influence of chemical composition and especially of the surface-to-bulk tin species ratio on the electrochemical behaviour has been analysed for several Sn_x[BPO₄]_1−x composite materials (0.17<x<0.91). The cell using the compound Sn_0.72[BPO₄]_0.28 as active material exhibits interesting electrochemical performances (reversible capacity of 500 mAh g⁻¹ at C/5 rate).     

Mannich products of kojic acid and N-heterocycles and their Ru(II)-arene complexes: Synthesis, characterization and stability

Ru(II)-η⁶-p-cymene compounds bearing pyrone-derived ligands, which were obtained by Mannich reaction with piperidine and related analogues, have been synthesized. The compounds were characterized by NMR spectroscopy, mass spectrometry, thermogravimetric analysis and in the case of 2-(2,6-dimethyl-morpholin-4-ylmethyl)-3-hydroxy-6-hydroxymethyl-pyran-4-one by X-ray diffraction analysis. The chlorido complexes are prone to aquation in aqueous solution which results in the formation of dimers. Dimer formation can be inhibited by in situ replacement of the chlorido ligand by imidazole yielding compounds which are significantly more stable in water, as demonstrated by ¹H NMR spectroscopy.     

A stochastic evolution model for residue Insertion-Deletion Independent from Substitution

We develop here a new class of stochastic models of gene evolution based on residue Insertion-Deletion Independent from Substitution (IDIS). Indeed, in contrast to all existing evolution models, insertions and deletions are modeled here by a concept in population dynamics. Therefore, they are not only independent from each other, but also independent from the substitution process. After a separate stochastic analysis of the substitution and the insertion-deletion processes, we obtain a matrix differential equation combining these two processes defining the IDIS model. By deriving a general solution, we give an analytical expression of the residue occurrence probability at evolution time t as a function of a substitution rate matrix, an insertion rate vector, a deletion rate and an initial residue probability vector. Various mathematical properties of the IDIS model in relation with time t are derived: time scale, time step, time inversion and sequence length. Particular expressions of the nucleotide occurrence probability at time t are given for classical substitution rate matrices in various biological contexts: equal insertion rate, insertion-deletion only and substitution only. All these expressions can be directly used for biological evolutionary applications. The IDIS model shows a strongly different stochastic behavior from the classical substitution only model when compared on a gene dataset. Indeed, by considering three processes of residue insertion, deletion and substitution independently from each other, it allows a more realistic representation of gene evolution and opens new directions and applications in this research field.     

Characterization of calixarene‐bonded stationary phases

Calixarene‐bonded stationary phases received growing interest in HPLC as stationary phases with special retention characteristics and selectivity. The commercially available unsubstituted and p‐tert‐butyl‐substituted Caltrex^® columns have been intensively studied and characterized in our workgroup. They can be used as reversed phases, yet they support additional interactions. Especially, their steric, polar and ionic properties differ from conventional alkyl‐bonded phases. However, also the hydrophobic interaction shows differences since adsorption and partition interactions on or in a bonded layer of calixarenes are not similar to those of alkyl‐bonded layers. The relative strength of the hydrophobic properties of the stationary phases has been found depending on the methanol concentration of the mobile phase. Generally, the dependencies of their interaction strengths on mobile‐phase conditions, e.g. the change of the intensity of the hydrogen‐bonding abilities with decreasing methanol content, are not similar from phase to phase either. This probably gives calixarene‐bonded stationary phases enhanced suitability for analyses at extreme compositions of the mobile phase. An overview about the synthesis, retention and selectivity properties of Caltrex^® columns is given here.     

Recent developments in the chemistry of donor-functionalized phosphinines

This review provides an overview of the most significant strategies developed in recent years for the preparation of donor-functionalized phosphinines and new developments in this field are highlighted. Selected synthetic procedures for the introduction of additional sulfur-, oxygen-, phosphorus-, and nitrogen-donor groups into the heterocyclic framework are presented. Examples of their coordination chemistry and potential applications in homogeneous catalysis and phosphorus containing molecular materials will be given.