7-Selenabicyclo[2.2.1]heptane

Thermolysis of a benzene solution of N-[4-(p-(methoxybenzyl)seleno)cyclohexanoyl]-N,S-dimethyldithiocarbonate affords the hitherto unknown 7-selenabicyclo[2.2.1]heptane in 48% conversion and in 20% yield after chromatography. G3(MP2)-RAD calculations predict a rate constant of 5 × 10(4) s(-1) at 80 °C (3.8 × 10(6) s(-1) at 200 °C) for the intramolecular homolytic substitution process involved in this cyclization.     

Assignment of Relative Configuration of Desoxypropionates by 1H NMR Spectroscopy: Method Development,Proof of Principle by Asymmetric Total Synthesis of Xylarinic Acid A and Applications

The determination of the relative configuration of 1,3‐dimethyl‐substituted alkyl chains is possible by interpretation of ¹H NMR shift differences. Additionally, assignments are feasible in a variety of deuterated solvents, because the corresponding shift differences are not significantly influenced by the solvent. The trends for Δδ values depending on functional groups adjacent to the stereogenic centers are shown. Based on a thorough comparison with literature data, the relative configuration of natural products can be predicted. For this purpose, we derived an empirical rule for the ranges in which Δδ values usually occur. Furthermore, we were able to proof the validity of our method by the successful prediction of the relative configuration for the polyketide natural product xylarinic acid A, which was confirmed by the asymmetric total synthesis of its enantiomer. Based on the proposed simple analysis of published ¹H NMR data and the determination of the relevant chemical‐shift differences, we predicted the relative configurations of several previously unassigned natural products.     

Expression and Function of Macrophage Migration Inhibitory Factor in the Pathogenesis of UV-Induced Cutaneous Nonmelanoma Skin Cancer(†)

Chronic skin exposure to ultraviolet light stimulates the production of cytokines known to be involved in the initiation of skin cancer. Recent studies in mouse models suggested a role for macrophage migration inhibitory factor (MIF) in the UVB‐induced pathogenesis of nonmelanoma skin cancer (NMSC). Our studies aimed at defining the pathophysiological function of MIF in cutaneous inflammatory reactions and in the development and progression of NMSC. Immunohistochemical analysis revealed a moderate expression of MIF in normal human skin samples but an enhanced expression of this cytokine in lesional skin of patients with actinic keratosis or cutaneous SCC. Enzyme‐linked immunosorbent assay studies showed a time‐dependent increase in MIF secretion after a moderate single‐dose UVB irradiation in NHEKs and SCC tumor cells. MIF is known to interact with CXCR2, CXCR4 and CD74. These receptors are not constitutively expressed in keratinocytes and HaCaT cells and their expression is not induced by UVB irradiation either. However, stimulation with IFNγ upregulated CD74 surface expression in these cells. Affymetrix^® Gene Chip analysis revealed that only keratinocytes prestimulated with IFNγ are responsive to MIF. These findings indicate that MIF may be an important factor in the pathogenesis of NMSC tumorigenesis and progression in an inflammatory environment.     

The Solvent-Like Nature of Silica Particles in Organic Solvents

 Kamlet-Taft’s α (hydrogen bond donor acidity) and π^* (dipolarity/polarizability) values of various silica batches measured in various solvents are presented. The α and π^* parameters for the various solid acids are analyzed by means of Fe(phen)₂(CN)₂ (cis-dicyano-bis-(1,10)-phenanthroline-iron(II), 1), Michler’s ketone (4,4′-bis-(dimethylamino)-benzophenone, 2), and two hydrophilic derivatives of 2, (4-(dimethylamino)-4′-(di-2-hydroxyethyl)-amino-benzophenone (3a) and 4,4′-bis-(di-(2-hydroxyethyl)-amino)-benzophenone (3b) as well as coumarin 153 (4) as solvatochromic surface polarity indicators. Apparent β (hydrogen bond acceptor basicity) parameters for bare silica have been evaluated by means of an aminobenzodifuranone dye (5) as solvatochromic probe. The chemical interpretation of the α and π^* parameters and the nature of the solvent/surface interaction which they reflect are discussed. It can be shown that an increase of the HBA (hydrogen bond accepting) capacity of the solvent significantly decreases the HBD (hydrogen bond donating) capacity of the surface environment, whereas the dipolarity/polarizability value of the silica/solvent interface is a composite of many effects. The classification of the polarity of silica particles in organic solvents compared to pure liquids is outlined.     

ABS-Modified Epoxy Resins – Curing Kinetics,Polymerization Induced Phase Separation,and Resulting Morphologies

Summary : A commercial diglycidylether of bisphenol A (DGEBA) was modified with an acrylonitrile-butadiene-styrene-copolymer (ABS) and cured with the diamine hardener 4,4′-diaminodiphenylsulfone (DDS). The curing kinetics was followed by DSC- and PVT-measurements. The polymerization induced phase separation (PIPS) was studied using light microscopy and electron microscopy. While the cloud point analyzed by light microscopy is independent of the ABS content, the curing is accelerated by the presence of ABS. The non-linear dependency of the curing rate on the ABS content must have its origin in the different morphologies developed due to PIPS.     

Controlled,one-pot synthesis of recyclable poly(1,3-diene)-polyester block copolymers,catalyzed by yttrium β-diketiminate complexes

The one-pot synthesis of well-defined block copolymers of olefins/1,3-dienes and polar monomers, such as cyclic esters and acrylates has long been the focus of intense research. Cationic alkyl rare earth metal catalysts, activated by organoborates, have shown to be promising for the polymerization of isoprene or styrene and ε-caprolactone. In this study, we synthesize a series of yttrium bis(alkyl) complexes supported by simple β-diketiminate ancillary ligands. Subtle changes have been made to the β-diketiminate ligand framework to elucidate the effect of ligand structure on the rate and selectivity of olefin/1,3-diene and cyclic ester polymerization, with small ligand changes having a large impact on the resulting polymerizations. Generation of the active cationic species was easily streamlined by identification of appropriate catalyst : organoborate ratios, allowing for high catalyst efficiencies. Notably, we demonstrate the first cationic rare earth metal alkyl-initiated polymerization of δ-valerolactone and ε-decalactone as well as introduced five new block copolymer morphologies. In addition, selective degradation of the ester block in poly(isoprene-b-caprolactone) enabled recovery of the polyisoprene block with identical spectroscopic and thermal properties. Significantly, recopolymerization of the recovered poly(1,3-diene) with fresh ε-caprolactone reproduced the desired diblocks with nearly identical thermal and physical properties to those of virgin copolymer, illustrating a plausible recycling scheme for these materials.

Ligand features that promote one-pot block copolymerization of 1,3-dienes and cyclic esters were realized with yttrium β-diketiminate complexes. Depolymerization and repolymerization of the polyester block introduced a plausible recycling strategy.     

Quantification of astaxanthin in salmons by chemiluminescence and absorption after TLC separation

Astaxanthin is a keto-carotenoid, belongs to the chemical class of terpenes and is a yellow lipid soluble compound. The compound is present in marine animals like salmons and crustacean. Its colour is due to conjugated double bonds and these double bonds are responsible for its antioxidant effect. Its antioxidant activity is ten times stronger than other carotenoids and nearly 500 fold stronger than vitamin-E. We present a new thin layer chromatography (TLC) method to measure astaxanthin on TLC-plates (Merck, 1.05554) in the visible absorption range as well as by using chemiluminescence. For separation a solvent mixture of cyclohexane and acetone (10?+?2.4, v/v) was used. The RF-value of astaxanthin is 0.14.The limit of detection in vis-absorption is 64?ng / band and the limit of quantification is 92?ng/band. In chemiluminescence the values are 90?ng / band and 115?ng/band. The method offers two independently working measurement modes on a single plate which increase the accuracy of the quantification.     

Influence of the Template Removal Method on the Mechanical Stability of SBA-15

Removing the template from the pores after the polycondensation of the silica precursor is a necessary step in the synthesis of mesoporous silica materials. In our previous work, we developed a method for the efficient and spatially controlled functionalization of SBA-15. First, the silanol groups on the particle surface and in the pore entrances were passivated. After extraction of the template, a pretreatment step in N₂ converted the silanol groups to the single and geminal state. Afterwards, an azide functionality was introduced exclusively into the mesopores. This ensured that the catalyst could afterwards be immobilized unambiguously in the mesopores. The mechanical stability of a material functionalized in such a spatially controlled manner is studied and compared to other template removal methods. Even though several studies investigated the influence of the calcination temperature, the presence or the absence of oxygen during the template removal, the specific conditions used during the herein reported selective functionalization procedure have not been covered yet.     

Atomic-Scale Mapping of Impurities in Partially Reduced Hollow TiO2 Nanowires

The incorporation of impurities during the chemical synthesis of nanomaterials is usually uncontrolled and rarely reported because of the formidable challenge in measuring trace amounts of often light elements with sub-nanometer spatial resolution. And yet, these foreign elements (introduced by doping, for example) influence functional properties. We demonstrate how the hydrothermal growth and a partial reduction reaction on hollow TiO₂ nanowires leads to the introduction of parts per millions of boron, sodium, and nitrogen. This doping explains the presence of oxygen vacancies and reduced Ti states at the surface, which enhance the functional properties of TiO₂. Our results were obtained on model metal oxide nanomaterials and they shed light on a general process that leads to the uncontrolled incorporation of trace impurities in TiO₂, thereby, having a strong effect on applications in energy-harvesting.     

Temporary threshold shift in human subject exposed to noise

Using an audiometer,the effect of the noise level upon temporarythreshold shift(TTS)for five trained normal subjects(left ear only)was studied.The measurements were carried out after 6 min exposure(in third octave band)for different sound pressure levels ranging between 75-105 dB at three test fre-quencies 2,3,and 4 kHz.The results indicated that at exposure to noise of soundpressure level(SPL)above 85 dB,TTS increases linearly with ths SPL for all thetest frequencies.The work had extended to study the recovery curves for the sameears.The results indicated that the reduction in TTS on doubling the recoverytimes,for the two sound pressure levels 95 dB and 105 dB,occurs at a rate of near-ly 3 dB.The comparison of the recovery curve at 3 kHz with that calculated usingWard's general equation for recovery was made.Finally,to study the values ofTTS produced by exposure to certain noise at different test frequencies,distribu-tion curves for two recovery times were plotted representing TTS values,for anexposure