Reaktionen von aminofluorosilanen zu vier- bis siebengliedrigen ringsystemen

The reaction of N,N′-dimethylurea, N,N′-dimethylethylenediamine and t-butylamine with fluorosilyl-substituted disilazanes leads after primary lithiation with butyllithium to the formation of the six, seven- and four-membered rings I–III. The five- and seven-membered rings IV and V were prepared in a comparable reaction with the disodium salt of ethyleneglycol.     

First-principles statistical mechanics study of the stability of a subnanometer thin surface oxide in reactive environments: CO oxidation at Pd(100)

We employ a multiscale modeling approach to study the surface structure and composition of a Pd(100) model catalyst in reactive environments. Under gas phase conditions representative of technological CO oxidation (approximately 1 atm, 300-600 K) we find the system on the verge of either stabilizing subnanometer thin oxide structures or CO adlayers at the surface. Under steady-state operation this suggests the presence or continuous formation and reduction of oxidic patches at the surface, which could be key to understand the observable catalytic function.     

α-Funktionelle 2-Methylphenylphosphane, 2-(HE?CH2)?C6H4?PH2 (E = O,NR, PH). II. Komplexbildungsverhalten mit den Metallcarbonylen des Cr,Mo, W

α-Functionalized 2-Methyl Phenylphosphines, 2-(HE? CH₂)? C₆H₄? PH₂ (E = O, NR, PH) II. Coordination Behaviour with Metal Carbonyles of Cr, Mo, W The preparation of different carbonyl substituted coordination compounds (M: Cr, Mo, W) of the phosphines 2-(HE? CH₂)C₆H₄? PH₂ (E = O, NPh, PH) is described. In one case, after deprotonation of a PH₂ group a phosphine/phosphide migration of a W(CO)₅ fragment is detected.     

N‐Methyl‐2, 2'‐Dipicolylamine Complexes as Potential Models for Metal‐Mediated Base Pairs

Metal‐mediated base pairs can be used to insert metal ions into nucleic acids at precisely defined positions. As structural data on the resulting metal‐modified DNA are scarce, appropriate model complexes need to be synthesized and structurally characterized. Accordingly, the molecular structures of nine transition metal complexes of N‐methyl‐2, 2'‐dipicolylamine (dipic) are reported. In combination with an azole‐containing artificial nucleoside, this tridentate ligand had recently been used to generate metal‐mediated base pairs (Chem. Commun. 2011 , 47, 11041–11043). The Pd^II and Pt^II complexes reported here confirm that the formation of planar complexes (as required for a metal‐mediated base pair) comprising N‐methyl‐2, 2'‐dipicolylamine is possible. Two Hg^II complexes with differing stoichiometry indicate that a planar structure might also be formed with this metal ion, even though it is not favored. In the complex [Ag₂(dipic)₂](ClO₄)₂, the two Ag^I ions are located close to one another with an Ag ··· Ag distance of 2.9152(3) Å, suggesting the presence of a strong argentophilic interaction.     

Photostability of sunscreens

Sunscreens were originally designed to include mainly UVB-filters. Because of the deeper penetration of UVA light, causing photoaging and DNA damage, there has been a shift towards broad spectrum sunscreens. These broad spectrum sunscreens now include both UVA- and UVB-filters and other ingredients which possess antioxidant activity. Although sunscreens are regulated in most countries, photostability testing is not mandatory. Because of the ability of sunscreen ingredients to absorb UV-light and the complexity of most of these formulations, which may include more than one UV-filter, antioxidants and other formulation excipients, it is important that their photostability in combination is determined.     

Mass and energy flow management in the sector of surface treatment

Vehicle refinishing body shops are concerned by the environmental policy against photochemical air pollution caused by VOC emissions. For supporting these small enterprises the mass and energy flow model IMPROVE has been developed. Based on an LCA-approach, the process steps of vehicle refinishing are modelled. The model IMPROVE helps to disseminate the consequences of product substitution in comparison to so far used products and techniques in the body shop. For the dissemination of experiences practical guidelines have been developed. Moreover, a comprehensible tool for the Solvent Balance is being offered. Thus, various means are available for consulting and also for strategic production planning for the SME in the sector.     

Performance of two different types of passive samplers for the GC/ECD-FID determination of environmental VOC levels in air

Two types of passive samplers differing in their geometry (OVM 3500 by 3M, ORSA 5 by Dr?ger) were compared with respect to their suitability for typical environmental indoor and outdoor VOC concentrations. Benzene, toluene, o-, m-, p-xylene, ethylbenzene, tetrachloroethene, trichloroethene, nonane and ethyl acetate were representatively analyzed by dual-column capillary gas chromatography with tandem ECD-FID detection. There was a good correlation between the results obtained with OVM 3500 and ORSA 5 monitors indicating that both monitors can be used for this kind of application. The ratio between the results for indoor air sampling with OVM 3500 and ORSA 5 monitors was between 0.89 and 1.14 showing no systematic variation. For outdoor air sampling the ratio was between 1.06 and 1.26 indicating that the results obtained with OVM 3500 monitors were slightly higher. Reproducibility was slightly better when using ORSA 5 monitors. But, due to the higher sampling rates which are a result of the larger cross-sectional area, signal-to-noise ratios obtained with OVM 3500 monitors were between six to nine times higher than those of ORSA 5 samplers. Blank values of the unexposed samplers were comparable for both sampler types. As a consequence, detection limits were by a factor of 1.5 to 4 better for OVM 3500 monitors. Received: 18 August 1998 / Revised: 6 October 1998 / Accepted: 15 October 1998     

Synthetic peptide arrays and peptide combinatorial libraries for the exploration of protein-ligand interactions and the design of protein inhibitors

Synthetic peptides have a long tradition as molecular tools in biomedical research and drug discovery. The introduction of high-throughput synthesis and screening technologies for synthetic peptides, such as arrays and combinatorial libraries, enabled the large-scale and detailed exploration of protein-ligand interactions, as well as the discovery of novel biologically active peptides. This review summarizes currently available synthetic peptide array and library technologies, in particular mixture-based peptide libraries, which are illustrated by numerous applications in various fields of biomedical research.     

Umsetzungen von Dilithio-nitroalkanen und -allylnitroderivaten mit Carbonylverbindungen

Reactions of dilithio-nitroalkanes and dilithio-allynitroalkanes with carbonyl compounds Primary nitro compounds can by acylated via dilithium derivatives 5 with carbonic-acid derivatives to give α-nitro esters 6a – i and with carboxylic-acid esters and anhydrides to give α-nitroketones 6j – q . In the reaction of 1-nitro-1-buten with two mol-equiv. of butyllithium, the dilithium compound 10 is formed by successive Michael-addition and nitronate deprotonation. Dilithium derivatives 5 also react with ketones and benzaldehyde (→ 18a – g ); the nitro aldols 25 and 26 are likewise formed by addition of doubly deprotonated allylic nitro compounds. Some of the products have been further transformed by reduction or by Nef-reactions to the hydrochloride of the α-amino-acid 26 , to 2-amino-alcohols 28a and 28b , to α-hydroxyamino-acid esters 27a – c , to α-hydroxyimino esters 35 and 36 , to α-hydroxyimino ketones 31 and 33 , to the α-diketone 34 , and to the α-keto ester 37 .     

Benzoylphosphonate-Based Photoactive Phosphopeptide Mimetics for Modulation of Protein Tyrosine Phosphatases and Highly Specific Labeling of SH2 Domains

A light switch for phosphotyrosine- recognizing proteins: Irradiation of the bioisosteric benzoylphosphonate suffices to "turn off" the activity of target proteins and to label them covalently. Photoactive bioisosters may find applications in functional cell biology, bioanalytics, and proteome research.