Direct versus conjugate addition to a terphenyl substituted alkynyl difluoro silane

Alkynyl difluoro silanes can react with nucleophiles either directly at the silane unit by displacing the fluorine atoms (direct addition) or, in contrast, the nucleophile can attack the β -carbon of the adjacent alkynyl group (conjugate addition). By using this type of conjugate addition a number of fascinating unsaturated silicon and germanium compounds have been prepared in the past using alkyl substituted phenyl groups as substituents. Therefore we wanted to investigate which regioselectivity isobserved in the case of such an alkynyl difluoro silane shielded by a terphenyl substituent (Mes₂C₆H₃-, Mes =2,4,6-trimethylphenyl). Surprisingly, the reaction with phenyl lithium leads exclusively to direct displacement rather than conjugate addition, which we could prove by X-ray crystallography of 5. Moreover, the synthesis, spectroscopic data and crystal structures of important intermediates to the starting alkynyl difluoro terphenyl silane 2 are presented.     

Neuronal expression of muskelin in the rodent central nervous system

Background  

The kelch repeat protein muskelin mediates cytoskeletal responses to the extracellular matrix protein thrombospondin 1, (TSP1), that is known to promote synaptogenesis in the central nervous system (CNS). Muskelin displays intracellular localization and affects cytoskeletal organization in adherent cells. Muskelin is expressed in adult brain and has been reported to bind the Cdk5 activator p39, which also facilitates the formation of functional synapses. Since little is known about muskelin in neuronal tissues, we here analysed the tissue distribution of muskelin in rodent brain and analysed its subcellular localization using cultured neurons from multiple life stages.     

Copolymerization of methacrylic acid with methyl methacrylate by SET‐LRP

Single‐electron transfer living radical polymerization (SET‐LRP) has developed as a reliable, robust and straight forward method for the construction well‐defined polymers. To span an even larger variety of functional monomers, we investigated the copolymerization of methyl methacrylate with methacrylic acid by SET‐LRP. Copolymerizations were catalyzed by Cu(0)/Me₆‐TREN and performed in MeOH/H₂O mixtures at 50 °C. The SET‐LRP copolymerizations of varying methacrylic acid content were evaluated by kinetic experiments. At low (2.5%) and moderate (10%) MAA loadings, the copolymerizations obeyed perfect first order kinetics (k_p^app = 0.008 min^?1 and k_p^app = 0.006 min^?1) and exhibited a linear increase in molecular weights with conversion providing narrow molecular weight distributions. The SET‐LRP of MMA/25%‐MAA was found to be significantly slower (k_p^app = 0.0035 min^?1). However, a reasonable first‐order kinetics in monomer consumption was maintained, and the control of the polymerization process was preserved since the molecular weight increased linearly with conversion and could therefore be adjusted. This work demonstrates that the copolymerization of methacrylic acid by SET‐LRP is feasible and the design of well‐defined macromolecules comprising acidic functionality can be achieved. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010     

Investigation of the interaction mechanism of the recombinant human antibody MDJ8 and its fragments with chromatographic apatite phases

The chromatographic behaviour of a recombinant human antibody (IgG₁-subtype, κ-light chain, MW: 149.5 kD, pI: 9.3) was investigated as a function of the buffer pH and buffer type (HEPES, phosphate, borate) on fluoroapatite and hydroxyapatite stationary phases. HEPES buffer was used at pH 7.0, phosphate buffer at pH 8.2 and borate buffer between pH 8.5 and 11. Elution was by a double gradient method of first a salt gradient from 0 to 1 M NaCl in the corresponding buffer, followed by a step gradient to 0.4 M sodium phosphate. Regardless of the pH and buffer type, the antibody eluted in the NaCl gradient; capacity factors decreased with increasing pH. At pH 11 the antibody eluted in the flow-through. Retention was thus dominated by electrostatic interaction throughout the investigated pH-range. Investigation of antibody fragments obtained by papain digestion (fc- and fab-fragments) and deglycosylated fc-fragments showed that the sugar structures had no influence on the chromatographic behaviour. Instead the chromatographic behaviour was dominated by that of the fab-fragment. ζ-Potential measurements verified that the apatite surface bore a negative surface charge in the investigated pH range, while the antibody net surface charge switched from positive to negative as the pH increased. The corresponding isoionic point was a function of both the buffer concentration and the buffer species. However, above a pH of 8.3 the ζ-potential of the antibody generally was negative. Simulations of the molecular electrostatic potential of the antibody and the two fragments revealed the presence of a positively charged patch within the fab-fragment, which only disappeared above a pH of 10. Most likely this patch was responsible for the observed behaviour.     

Low‐temperature sol–gel transformation of methyl silicon precursors to silica‐based hybrid materials

Six new methyl silicon (IV) precursors of the type [MeSi{ON?C(R)Ar}₃] [when R = Me, Ar = 2‐C₅H₄N ( 1 ), 2‐C₄H₃O ( 2 ) or 2‐C₄H₃S ( 3 ); and when R = H, Ar = 2‐C₅H₄N ( 4 ), 2‐C₄H₃O ( 5 ) or 2‐C₄H₃S ( 6 )] were prepared and structurally characterized by various spectroscopic techniques. Molecular weight measurements and FAB (Fast Atomic Bombardment) mass spectral studies indicated their monomeric nature. ¹H and ¹³C{¹H} NMR spectral studies suggested the oximate ligands to be monodentate in solution, which was confirmed by ²⁹Si{¹H} NMR signals in the region expected for tetra‐coordinated methylsilicon (IV) derivatives. Thermogravimetric analysis of 1 revealed the complex to be thermally labile, decomposing to a hybrid material of definite composition. Two representative compounds ( 2 and 4 ) were studied as single source molecular precursor for low‐temperature transformation to silica‐based hybrid materials using sol–gel technique. Formation of homogenous methyl‐bonded silica materials (MeSiO_3/2) at low sintering temperature was observed. The thermogravimetric analysis of the methylsilica material indicated that silicon‐methyl bond is thermally stable up to a temperature of 400 °C. Reaction of 2 and Al(OPrⁱ)₃ in equimolar ratio in anhydrous toluene yielded a brown‐colored viscous liquid of the composition [MeSi{ON?C(CH₃)C₄H₃O}₃.Al(OPrⁱ)₃]. Spectroscopic techniques ¹H, ¹³C{¹H}, ²⁷Al{¹H} and ²⁹Si{¹H} NMR spectra of the viscous product indicated the presence of tetracoordination around both silicon and aluminum atoms. On hydrolysis it yielded methylated aluminosilicate material with high specific surface area (464 m²/g). Scanning electron micrography confirmed a regular porous structure with porosity in the nanometric range. Copyright © 2008 John Wiley & Sons, Ltd.