Skin Microbiome Compositional Changes in Atopic Dermatitis Accompany Dead Sea Climatotherapy

Dead Sea climatotherapy (DSC) is a well‐established therapeutic modality for the treatment of several diseases, including atopic dermatitis. Skin microbiome studies have shown that skin microbiome diversity is anticorrelated with both atopic dermatitis severity and concurrent Staphylococcus aureus overgrowth. This study aimed to determine whether DSC induces skin microbiome changes concurrent with clinical improvements in atopic dermatitis. We sampled 35 atopic dermatitis patients and ten healthy controls on both the antecubital and popliteal fossa. High‐resolution microbial community profiling was attained by sequencing multiple regions of the 16S rRNA gene. Dysbiosis was observed in both lesional and nonlesional sites, which was partially attenuated following treatment. Severe AD skin underwent the most significant community shifts, and Staphylococcus epidermidis, Streptococcus mitis and Micrococcus luteus relative abundance were significantly affected by Dead Sea climatotherapy. Our study highlights the temporal shifts of the AD skin microbiome induced by Dead Sea climatotherapy and offers potential explanations for the success of climatotherapy on a variety of skin diseases, including AD.     

Determination of low levels of fluorine in concentrated phosphoric acid by use of the fluoride electrode

Summary The determination of both high and low fluorine concentrations in concentrated phosphoric acid is complicated by the reaction of hydrofluoric acid with phosphoric acid to form monofluorophosphoric acid (MFP), the formation being favoured at high concentrations of phosphoric acid. Neutralization to pH 6–8, a condition suitable for the determination of fluoride with the fluoride electrode, gives low recoveries, since only free hydrogen fluoride is converted into fluoride ion, while MFP is not. The rates of formation and dissociation of MFP were studied and thermodynamic and kinetic parameters were determined. MFP formed in concentrated phosphoric acid can be hydrolysed completely by treatment of the sample with dilute hydrochloric acid and boiling briefly under reflux. EDTA is added to mask any potentially interfering metal ions. The results obtained for concentrated phosphoric acid, after dilution and prehydrolysis, were satisfactory for all the fluorine levels examined.

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Bestimmung geringer Fluorgehalte in konzentrierter Phosphorsäure mit Hilfe der Fluorid-Elektrode

Zusammenfassung Die Bestimmung hoher und niedriger Fluorkonzentrationen in konz. Phosphorsäure wird durch die Reaktion der Flußsäure mit der Phosphorsäure zu Monofluorphosphorsäure (MPF) behindert, die in konz. Phosphorsäure begünstigt wird. Neutralisierung zu pH 6–8, die für die Bestimmung von Fluorid mit der Fluoridelektrode förderlich ist, gibt zu niedrige Resultate, da nur freier Fluorwasserstoff zu Fluoridion dissoziiert, nicht aber MFP. Die Anteile der Bildung und Dissoziation von MFP wurden untersucht, die thermischen und kinetischen Parameter bestimmt. In konz. Phosphorsäure gebildete MFP kann durch Behandlung der Probe mit verdünnter Salzsäure und kurzes Kochen unter Rückfluß vollständig hydrolysiert werden. Um störende Metallionen zu maskieren wird EDTA zugesetzt. Die nach Verdünnen und Hydrolyse der konz. Phosphorsäure erhaltenen Ergebnisse waren für alle untersuchten Größenordnungen von Fluor befriedigend.

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Presented at the 8th International Microchemical Symposium, Graz, August 25–30, 1980.     

Selective 3,3-Rearrangement of Azobenzenes upon Complexation by a Frustrated Lewis Pair

The reaction of the oxygen-bridged frustrated Lewis pairs (FLPs) tBu₂P−O−Si(C₂F₅)₃ ( 1 ) and tBu₂P−O−AlBis₂ ( 2 ) with azobenzene, promoted by UV irradiation, led to a selective complexation of the cis-isomer. The addition product of 2 is stable, while the adduct of 1 isomerizes in solution in an ortho-benzidine-like [3,3]-rearrangement by cleavage of the N−N bond, saturation of the nitrogen atoms with hydrogen atoms and formation of a new bond between two phenyl ortho-carbon atoms. Similar rearrangements take place with different para-substituted azobenzenes (R=Me, OMe, Cl) and di(2-naphthyl)diazene, while ortho-methylated azo compounds do not form adducts with 1 . All adducts were characterized by multinuclear NMR spectroscopy and elemental analyses and the mechanism of the rearrangement was explored by quantum-chemical calculations.     

Mechanism and characterization of alkylene‐ and p‐ethylenebenzylene‐spaced polycarbosilanes ceramic precursor synthesized by electropolymerization

An electropolymerization of haloalkylhalosilanes (Cl? R? SiCH₃Cl₂) that possess two types of electroactive sites, that is, the C? Cl and Si? Cl bond is described. The one‐pot synthesis method is shown to yield branched polycarbosilanes having a regular carbon block‐spaced silicon backbone structure. A series of branched polycarbosilanes, [? R? SiCH₃? ]_n with R being ? CH₂? , ? C₂H₄? , ? C₃H₆? , and ? CH₂? C₆H₄? C₂H₄? , have been successfully electropolymerized with M_n up to 42,600 Dalton. Experimental and simulation cyclic voltammetry of these monomers and the computational examination of their LUMOs are applied to study the electropolymerization mechanism. The results suggest that polymerization proceeds by iterating steps involving (1) electroreduction of a C? Cl bond to a carbanion, which is catalyzed by silylanion radical [Cl SiCl(CH₃)RCl] and/or Ni(0)/TDA‐1; and (2) nucleophilic attack of carbanions to Si? Cl bonds of a second monomer or oligomer to extend the polymer chain. The investigation reveals that the R spacer has a considerable impact on the polymerizability of the corresponding monomer. Such interfacial polymerization resembles a template polymerization, leading to unique microstructures that were preserved even after converted to silicon carbide ceramics at high temperatures. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 7677–7689, 2008     

Deeper insight into the mechanism of the reaction of photogenerated metallaketenes and imines

The reaction mechanism between Fischer carbene complexes and imines to produce beta-lactams has been studied by a combination of computational (DFT) and experimental methodologies. After the photogeneration of metalla-cyclopropanone species, the reaction initiates by 1,3-migration of the metal fragment from the former carbene carbon atom to the oxygen in the S o hypersurface. In spite of the endothermic nature of this rearrangement, it is biased by the more favorable HOMO(imine)-LUMO+1 interaction in the oxygen-coordinated ketene. This species reacts with the imine to yield metalla-zwitterions, which form the final products through a four electron conrotatory ring closure. The presence of the metal moiety during the whole reaction coordinate is demonstrated by the use of a chiral chromium(0) alkoxycarbene complex, which produces low but significant ee in the reaction with imines. The cis-trans stereoselection derives from the nucleophilic addition of the nitrogen atom of the imine to the oxygen-coordinated ketene, since there are no significant differences between the classical and the metallated processes in the electrocyclation step leading to the final 2-azetidinones.