The molecular structure of [dimethyl(phenyl)silyl]tris(trimethylsilyl)methane

The structure of the crowded molecule (Me₃Si)₃C(SiMe₂Ph) has been determined by single crystal X-ray diffraction. The steric strain manifest itself mainly in lengthening of the Me₃SiC and Me₂PhSiC bonds (average length 1.920(6) $\text{,ac>A}\text{?}$) and closing up of the CSiC angles within the Me₃Si and Me₂PhSi groups (average 105.2(10)°), with correspondingly large C(1)SiC angles (113.5(13)°; C(1) is the central carbon atom).     

A small molecule with osteogenesis-inducing activity in multipotent mesenchymal progenitor cells

Purmorphamine, which is a 2,6,9-trisubstituted purine compound, was discovered through cell-based high-throughput screening from a heterocycle combinatorial library. It differentiates multipotent mesenchymal progenitor cells into an osteoblast lineage. It will serve as a unique chemical tool to study the molecular mechanisms of osteogenesis of stem cells and bone development.     

Microstructured cocultures of cardiac myocytes and fibroblasts: a two-dimensional in vitro model of cardiac tissue.

Cardiac myocytes and fibroblasts are essential elements of myocardial tissue structure and function. In vivo, myocytes constitute the majority of cardiac tissue volume, whereas fibroblasts dominate in numbers. In vitro, cardiac cell cultures are usually designed to exclude fibroblasts, which, because of their maintained proliferative potential, tend to overgrow the myocytes. Recent advances in microstructuring of cultures and cell growth on elastic membranes have greatly enhanced in vitro preservation of tissue properties and offer a novel platform technology for producing more in vivo-like models of myocardium. We used microfluidic techniques to grow two-dimensional structured cardiac tissue models, containing both myocytes and fibroblasts, and characterized cell morphology, distribution, and coupling using immunohistochemical techniques. In vitro findings were compared with in vivo ventricular cyto-architecture. Cardiac myocytes and fibroblasts, cultured on intersecting 30-microm-wide collagen tracks, acquire an in vivo-like phenotype. Their spatial arrangement closely resembles that observed in native tissue: Strands of highly aligned myocytes are surrounded by parallel threads of fibroblasts. In this in vitro system, fibroblasts form contacts with other fibroblasts and myocytes, which can support homogeneous and heterogeneous gap junctional coupling, as observed in vivo. We conclude that structured cocultures of cardiomyocytes and fibroblasts mimic in vivo ventricular tissue organization and provide a novel tool for in vitro research into cardiac electromechanical function.     

Reaction of the stable silylene Si[(NCH2But)2C6H4-1,2] with lithium amides

The thermally stable silylene Si[(NCH2But)2C6H4-1,2] 1 undergoes oxidative addition reactions with the lithium amides LiNRR'(R = SiMe3, R' = But; R = SiMe3, R' = C6H3Me2-2,6; R = R' = Me or R = R' = Pri) to afford the new lithium amides Li(THF)2[N(R)Si(SiMe3){(NCH2But)2C6H4-1,2}][R = But2 or R = C6H3Me2-2,6 (3a)] or the new tris(amino)functionalised silyllithiums Li(THF)x[Si{(NCH2But)2C6H4-1,2}NRR'][R = SiMe3, R' = C6H3Me2-2,6, x = 2 (3); R = R'= Me, x = 3 (4) or R = R' = Pri, x = 3 (5)]. Compounds 4 and 5 are stable at ambient temperature but compound 3 is thermally labile and converts into 3a upon heating. The pathway for the formation of 2 and 3 is discussed and the X-ray structures of 2-5 are presented.     

Synthesis of conjugated polyrotaxanes

A series of conjugated polyrotaxane insulated molecular wires are synthesised by aqueous Suzuki polymerisation, using hydrophobic binding to promote threading of the cyclodextrin units. These polyrotaxanes have conjugated polymer cores based on poly(para-phenylene), polyfluorene, and poly(diphenylene-vinylene), threaded through 0.9-1.6 cyclodextrins per repeat unit. Bulky naphthalene-3,6-disulfonate endgroups prevent the macrocycles from slipping off the conjugated polymer chains. Dialysis experiments show that the cyclodextrins become unthreaded only if smaller stoppers are used. MALDI TOF mass spectra detect oligomers with up to ten threaded cyclodextrins, and reveal the presence of some defects that result for oxidative homo-coupling of boronic acids. Weight-average molecular weights were determined by analytical ultracentrifugation, demonstrating that step-growth polymerisation is efficient enough to achieve degrees of polymerisation up to approximately 20 repeat units (84 para-phenylenes). The fluorescence spectra of these polyrotaxanes indicate that the presence of the threaded cyclodextrin macrocycles reduces the flexibility of the conjugated polymer pi-systems. Both the solution and the solid-state photoluminescence quantum yields are enhanced upon threading of the conjugated polyaromatic cores through alpha- or beta-cyclodextrins, and the emission spectra of the polyrotaxanes are blue-shifted compared to the corresponding unthreaded polymers. The greater weight of the 0-0 transition in the emission spectra, as well as the smaller Stokes shift, indicate that the polyrotaxanes are more rigid than the unthreaded polymers.     

Eine einfache chromatographische Methode zur Charakterisierung bitumin?ser Stoffe

Zusammenfassung Die Methode der Ringpapierchromatographie unter Anwendung von UV-Licht als einfachem Hilfsmittel zur Unterscheidung organischen Materials wurde hinsichtlich der Möglichkeit überprüft, zahlenmäßig greifbare Ergebnisse zu erhalten, die eine sichere Klassifizierung und Unterscheidung bituminöser Stoffe ermöglichen. Es wurde gefunden, daß für eine gute Reproduzierbarkeit der Ergebnisse die gleichmäßige Aufgabe der Lösung auf das Papier wesentlich ist. Ein äußerst gleichmäßiger Zufluß, der mit der Sauggeschwindigkeit des Papieres korrespondiert, konnte mit Hilfe eines Mikrodosiergerätes, das von einem Motor gleichmäßig angetrieben wurde, erzielt werden. Die erhaltenen Flächen für die verschiedenen Substanzgruppen stellen ein relatives, gut reproduzierbares Maß für die Zusammensetzung der untersuchten Proben dar.Herrn Prof. Dr. W. Fischer zum 60. Geburtstag gewidmet.     

Hyperfine fields in the 5sp series studied by the low temperature nuclear orientation of83Rb,83Sr,85Sr and85Ym in iron

The hyperfine fields B_hf (RbFe), B_hf (SrFe) and B_hf (YFe) have been determined by the low temperature nuclear orientation of dilute samples of⁸³Rb,^83,85Sr and⁸⁵Y^m in an iron lattice to be B_hf (RbFe)=+54 (10) kG, B_hf (SrFe)=(?)100 (30) kG and B_hf (YFe)=?226 (10) kG. These results are compared with recent calculations for these fields (1), (2).     

Stochastic linear maps and transition probability

Some aspects of the transition probability P(, ) between states , on unital ^*-algebras are discussed. It is shown that P increases under the action of any stochastic linear map T, i.e., P(T, T)P(, ). Some properties of P are derived in starting from a recently-proved characterization of the quantity in question.     

Organophosphines in PtP2Si2 derivatives – structural aspects

Abstract

In this review, the structural data of monomeric platinum(II) complexes with inner coordination spheres of Pt(η²-P₂L)(SiL)₂, Pt(η²-P₂L)(η²-Si₂L) and Pt(η²-P,SiL)₂ are classified and analyzed. These complexes crystallize in three crystal systems: monoclinic (8 examples), triclinic (4 examples) and orthorhombic (4 examples). Distorted square-planar environments about the Pt(II) atoms are built up by combination of homobi-P,P with two monodentate Si donor ligands; homobi-PP with homo-Si,Si donor ligands, or heterobi-P,Si donor ligands. The chelating ligands create metallacycles with the following angles: 65.0° (SiOSi) < 83.1° (SiC₂Si) < 85.2° (PC₂P) < 88.8° (SiSi₂Si)). The mean Pt-P and Pt-Si bond distances in Pt(η²-P₂L)·(SiL)₂ complexes are 2.319 and 2.365?Å; in Pt(η²-P₂L)(η²-Si₂L) the values are 2.316 and 2.360?Å. The complex [Pt{η²-Me₂P(C₂B₁₀H₁₀)SiMe₂}₂] exists in two isomeric forms, a monoclinic cis- and a triclinic trans-isomer. The structural data are compared and discussed with the complexes of inner coordination spheres: Pt(η²-P₂L)(XL)₂ (X?=?O, N, CN, BL, Cl, SL, SeL, Br, or I) and Pt(η²-P₂L)(η²-X₂L) (X?=?OL, NL, SL or SeL).     

An FT-IR study of adsorption of sulfur dioxide on alpha- and gamma-alumina

In the Claus process hydrogen sulfide reacts to elemental sulfur. Because the Claus reaction is thermodynamically limited, sulfur compounds are still present in Claus tailgas. To avoid air pollution, the tailgas has to be treated.Alfa- and gamma-alumina are being used either as a catalyst or as a support for an active component in the Claus process and some tailgas treatment processes. In order to elucidate the mechanism of the Claus reaction, the adsorption of sulfur dioxide on both of the above aluminas was investigated using Fourier transform infrared spectroscopy.Different adsorbed species displaying a different heat of adsorption were detected. A broad band near 3500 cm^–1 is associated with the basic hydroxyl groups. This band is assigned to a hydrogen bond between the surface of alumina and a bisulfite species. As bisulfite species are reactive towards hydrogen sulfide, we assume that bisulfite species are active intermediates on alumina in the Claus reaction.