Marker experiments to determine diffusing species and diffusion path in medical Nitinol alloys

The out-diffusion of toxic Ni ions from NiTi (Nitinol), often used for biomedical applications, can be strongly reduced using oxygen plasma immersion ion implantation (PIII). Non-radioactive isotope markers, ⁶⁰Ni and ⁴⁶Ti, were implanted at 180 keV into NiTi prior to the oxygen implantation with fluences between 0.4 × 10¹⁶ and 4 × 10¹⁶ at./cm². Implanting oxygen ions by PIII in the temperature range of 400-550 °C leads to a surface oxide layer consisting of pure TiO₂. The results prove that Ni cations are the mobile species, while Ti is immobile during the oxygen insertion.     

Substituted Tetraaza‐ and Hexaazahexacenes and their N,N′‐Dihydro Derivatives: Syntheses,Properties, and Structures

The palladium‐catalyzed coupling of a substituted o‐diaminoanthracene and a substituted o‐diaminophenazine to substituted 2,3‐dichloroquinoxalines furnishes 10 differently substituted N,N′‐dihydrotetraaza‐ or ‐hexaazahexacenes with the quinoxaline group of the azaacenes carrying fluorine, chlorine, or nitro groups. The N,N′‐dihydrotetraazahexacenes with hydrogen, chlorine, and fluorine subtituents are oxidized to azaacenes, whereas only the parent N,N′‐dihydrohexaazahexacenes, with hydrogen substituents, are oxidized by MnO₂. The resultant azaacenes are characterized by their optical and spectroscopic data. In addition, single‐crystal X‐ray structures have been obtained for the parent tetraazahexacenes and their difluoro‐substituted derivatives. The di‐ and tetrachloro derivatives of the N,N′‐dihydrohexaazahexacene have also been structurally characterized.     

Towards a Sustainable Synthesis of Oxymethylene Dimethyl Ether by Homogeneous Catalysis and Uptake of Molecular Formaldehyde

Oxymethylene dimethyl ethers (OME_n; CH₃(‐OCH₂‐)_nO‐CH₃, n=3–5) are a novel class of sustainable synthetic fuels, which are of increasing interest due to their soot‐free combustion. Herein a novel anhydrous OME_n synthesis route is presented. Catalyzed by trimethyloxonium salts, dimethoxymethane takes up monomeric gaseous formaldehyde instantaneously and forms high purity OME_n at temperatures of 25–30 °C. This new anhydrous approach using molecular formaldehyde and catalytic amounts of highly active trimethyloxonium salts represents a promising new step towards a sustainable formation of OME_n emanating from CO₂ and H₂.     

Zur Reingewinnung von Substanzen durch Teilverflüssigung und Warmabsaugen

Zusammenfassung J. v. Braun, W. Gmelin undA. Schultheiß ⁵ geben an, ein zwischen 37 und 95° schmelzendes Gemisch von 2-Äthylcinchoninsäuremethylester (A) und 2,3-Dimethylcinchoninsäuremethylester (B) durch Absaugen des bei 40° geschmolzenen Anteils in einfacher Weise in die einheitlichen Komponenten A mit 38° und B mit 120 bis 121° Schmelzpunkt gespalten zu haben. Der Vorgang der Trennung ist mit der von mir ausgeführten und beschriebenen Methode der Reingewinnung von Substanzen durch Teilverflüssigung und Warmabsaugen fälschlich gleichgestellt und damit als rangältere Anwendung der gleichen Methode aufgefaßt worden. Es wird auf grundsätzliche Unterschiede in den zwei Arbeitsvorgängen hingewiesen und experimentell festgestellt, daß nach den Angaben der drei Autoren eben auf Grund dieser Abweichungen eine Zerlegung in die einheitlichen Bestandteile nicht zustande kommt. Die für das Gelingen der Trennung und Reinigung maßgebenden Umstände werden aufgezeigt. Über die Eigenart und Verwendbarkeit der eigenen Methode und ihre Beziehung zur Mikrochemie werden einige Angaben aufgestellt.Mit 1 Abbildung.     

Malondialdehyde tagging improves the analysis of arginine oligomers and arginine-containing dendrimers by HPLC-MS

The selective modification of arginine residues by malondialdehyde (MDA) was used to improve the mass spectrometric analysis of arginine oligomers (Arg(x), x = 4, 6, 7, 8, 9) and an arginine-containing dendrimeric peptide. MDA tagging significantly increased the hydrophobicity of the arginine side-chain and resulted in improved retention in RP HPLC of the oligoarginines using formic acid as mobile phase additive. This avoided the use of TFA to generate sufficient retention, as TFA was shown to lead to a dramatically reduced sensitivity (up to ten-fold for Arg(8) and Arg(9)) as a result of the strong signal suppression by ion pairing with multiple basic residues. MDA modification of Arg oligomers not only resulted in improved detection sensitivity for most of the peptides studied (e. g., more than six-fold for Arg(7)), but also greatly enhanced the quality of MS/MS spectra, in line with previous results for other peptides. Furthermore, MDA modification helped to identify major side products in a sample of a dendrimeric peptide, a class of peptides that is typically difficult to analyze by MS.     

Analysis of histones, histone variants, and their post-translationally modified forms

For many years, histones were considered passive structural components of eukaryotic chromatin. Meanwhile it has been proven that histones also participate in gene regulation and repression via post-translational modification. The multitude of these post-translational modifications and the existence of numerous histone variants require particular separation strategies for their analysis, a prerequisite for studying biological processes. The most widely utilized techniques for the separation of histones, namely PAGE, HPCE, RP-HPLC, and hydrophilic Interaction LC, are reviewed here. Problems inherent to the analysis of histones owing to their unique physical and chemical properties along with advantages and shortcomings of particular methods are discussed.     

Synthesis and characterization of dinuclear pyrazolato bridged platinum(IV) complexes

Reactions of [PtMe₃(OCMe₂)₃](BF₄) and [(PtMe₃I)₄] with pyrazole (pzH) afforded mononuclear pyrazole platinum(IV) complexes [PtMe₃(pzH)₃](BF₄) (1) and [PtMe₃I(pzH)₂] (2), respectively. The formation of dinuclear pyrazolato bridged platinum(IV) complexes (PPN)[(PtMe₃)₂(μ-pz)₃] (3), (PPN)[(PtMe₃)₂(μ-I)(μ-pz)₂] · 1/2Et₂O (4) and [K(18C6)][(PtMe₃)₂(μ-I)(μ-pz)₂] (5) was achieved by the reaction of each 1 and 2 with [PtMe₃(OCMe₂)₃](BF₄) in the presence of KOAc followed by reaction with (PPN)Cl (PPN⁺ = bis(triphenylphosphine)iminium cation) and 18C6, respectively. The reaction of complex 4 with AgO₂CCF₃ followed by addition of RSR′ (R/R′ = Me/Me, Me/Ph) resulted in the formation of complexes [(PtMe₃)₂(μ-pz)₂(μ-RSR′)] (R/R′ = Me/Me, 6; Me/Ph, 7). All complexes were characterized unambiguously by microanalysis and NMR (¹H, ¹³C) spectroscopic investigations. Additionally, crystal structures of complexes 3 and 4 as well as DFT calculation are presented. Furthermore, in vitro studies on the anti-proliferative activity of complexes 2 and 5 were carried out.     

Investigation of monovalent and bivalent enantioselective molecular recognition by electrospray ionization-mass spectrometry and tandem mass spectrometry

In this work is described the investigation of bivalent versus monovalent enantioselective molecular recognition in the context of enantioselective separations. Electrospray ionization-mass spectrometry (ESI-MS) and tandem mass spectrometry (MS/MS) are used for evaluating enantioselective systems through the measurement of (1) relative solution-phase binding constants via titration and (2) relative gas-phase binding via collision threshold dissociation. In HPLC, a cinchonane-type chiral stationary phase (CSP) based on tert.-butylcarbamoylquinine provides vastly increased retention and enantioselectivity for separation of bivalent versus monovalent alkoxy-benzoyl-N-blocked leucine enantiomers. The bivalent enantiomers are able to span and simultaneously interact with multiple interaction sites on the CSP surface, leading to enhanced separation. ESI-MS titration measurements also show an increased avidity for binding between bivalent selector and bivalent selectand, compared with the monovalent system. However, enhanced enantioselectivities measured in HPLC for the bivalent system cannot be reproduced by MS due to inherent mechanistic differences. Assumed discrepancies in relative response factors also give rise to systematic errors which are discussed. The results of MS/MS gas-phase experiments show that enantioselectivity is essentially lost in the absence of solvation, but that dissociation thresholds can provide a measure of relative dissociation energy in the bivalent interaction system compared to the monovalent counterpart. Such measurements may prove useful and efficient in better understanding multivalent interactions, in line with current theoretical considerations of effective concentrations and ion trap effects. This is the first application of mass spectrometric methods for assessing increased avidity of binding in multivalent enantioselective molecular recognition.     

Highly phosphorylated core oligosaccharide structures from cold-adapted Psychromonas arctica

Many cold habitats contain plenty of microorganisms that represent the most abundant cold-adapted life forms on earth. These organisms have developed a wide range of adaptations that involve the cell wall of the microorganism. In particular, bacteria enhance the synthesis of unsaturated fatty acids of membrane lipids to maintain the membrane fluidity, but very little is known about the adaptational changes in the structure of the lipopolysaccharides (LPSs), the main constituent of the outer leaflet of the outer membrane of Gram-negative bacteria. The aim of this study was to investigate the chemical structure of these LPSs for insight into the temperature-adaptation mechanism. For this objective, the cold-adapted Psychromonas arctica bacterium, which lives in the arctic sea-water near Spitzbergen (Svalbard islands, Arctic) was cultivated at 4 degrees C. The lipooligosaccharides (LOSs) were isolated and analysed by means of chemical analysis and electrospray ionisation high-resolution Fourier transform mass spectrometry. The LOS was then degraded either by mild hydrazinolysis (O-deacylation) or with hot 4 M KOH (N-deacylation). Both products were investigated in detail by using 1H and 13C NMR spectroscopy and mass spectrometry. The core consists of a mixture of species that differ because of the presence of nonstoichiometric D-fructose and/or D-galacturonic acid units.