Calyx and dimorphic neurons of mouse Scarpa's ganglion express histamine H3 receptors

Background  

Histamine-related drugs are commonly used in the treatment of vertigo and related vestibular disorders. The site of action of these drugs however has not been elucidated yet. Recent works on amphibians showed that histamine H3 receptor antagonists, e.g. betahistine, inhibit the afferent discharge recorded from the vestibular nerve. To assess the expression of H3 histamine receptors in vestibular neurons, we performed mRNA RT-PCR and immunofluorescence experiments in mouse Scarpa's ganglia.     

Ethylene‐norbornene copolymers prepared with metallocene‐ based catalysts: new sequence assignments by 13C NMR

A series of ethylene‐norbornene copolymers were synthesized in the presence of zirconocenes with different symmetries and ligand patterns and at different norbornene (N)/ethylene (E) mole ratios. Copolymers were characterized by ¹³C NMR spectroscopy; Inadequate NMR sequences were used also. The comparison of ¹³C NMR spectra of copolymers prepared with different norbornene content and the correlation between ¹³C NMR chemical shifts and conformational structures of the chain on the basis of molecular mechanics calculations were performed. Preliminary assignments were revised and new comonomer sequences such as ENNE which contain meso and racemo NN dyads were assigned.     

Ethylene–Norbornene Copolymerization by Rare-Earth Metal Complexes and by Carbon Nanotube-Supported Metallocene Catalysis

E–N copolymerization with a number of half-sandwich rare-earth metal compounds [M(η5-C₅Me₄SiMe₂R)(η1-CH₂SiMe₃)₂(L)] (M = Sc, Y, Lu) has been achieved. Mainly atactic alternating E N copolymers are obtained with all catalytic systems. Interestingly, copolymers arising from [Sc(η5-C₅Me₄SiMe₂C₆F₅)(η¹-CH₂SiMe₃)₂(THF)]/[/[Ph₃C][B(C₆F₅)₄] possess narrower molar mass distributions than those from [Sc(η⁵-C₅Me₄SiMe₃)(η¹-CH₂SiMe₃)₂(THF)] / [Ph₃C][B(C₆F₅)₄]. In addition, homogeneous surface coating of multi-walled carbon nanotubes is accomplished for the first time by in situ E–N copolymerization as catalyzed by rac-Et(Ind)₂ZrCl₂/MMAO-3A anchored onto the carbon nanotube surface. The copolymerization reaction allows for the destructuration of the native nanotube bundles. The relative quantity of E N copolymer can be tuned up as well as the norbornene content in the formed copolymers and accordingly their glass transition temperature. By melt blending with an ethylene-vinyl-co-acetate copolymer (27 wt.-% vinyl acetate comonomer) matrix, high performance polyolefinic nanocomposites are obtained.     

Long‐lived layered silicates‐immobilized 2,6‐bis(imino)pyridyl iron (II) catalysts for hybrid polyethylene nanocomposites by in situ polymerization: Effect of aryl ligand and silicate modification

Heterogeneous‐layered silicate‐immobilized 2,6‐bis(imino)pyridyl iron (II) dichloride/MMAO catalysts, in which the active polymerization species are intercalated within sodium‐ and organomodified‐layered silicate galleries, were prepared for producing hybrid exfoliated polyethylene (PE) nanocomposites by means of in situ polymerization. The inorganic filler was first treated with modified‐methylaluminoxane (MMAO) to produce a supported cocatalyst: MMAO reacts with silicates replacing most of the organic surfactant, thus modifying the original crystallographic clay order. MMAO anchored to the nanoclay was able to activate polymerization iron complexes initiating the polymer growth directly from the filler lamellae interlayer. The polymerization mechanism taking place in between the montmorillonite lamellae separates the layers, thus promoting deagglomeration and effective clay dispersion. Transmission electron microscopy revealed that in situ polymerization by catalytically active iron complexes intercalated within the lower organomodified clay led to fine dispersion and high exfoliation extent. The intercalated clay catalysts displayed a longer polymerization life‐time and brought about ethylene polymerization more efficiently than analogous homogeneous systems. PEs having higher molecular masses were obtained. These benefits resulted to be dependent more on the filler nature than on the ligand environment around the iron metal center and the experimental synthetic route. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 548–564, 2009     

Thermal behavior and pyrolysis products of modified organo-layered silicates as intermediates for in situ polymerization

A systematic study on organo-layered silicate intermediates used for preparing in situ polyethylene nanocomposites was performed by pyrolysis–gas chromatography/mass spectrometry and thermogravimetric analysis. The type and composition of the pyrolysis products gave useful information about mechanism of thermal degradation. The combination of pyrolysis and thermal decomposition data allowed us to describe the evolution of the organoclay structure after the reactive pretreatment steps with alkylaluminoxane cocatalyst and zirconocene or bis(imino)pyridine iron precatalyst, respectively. A proof of the formation of heterogeneous organoclay-immobilized catalyst was obtained.     

In situ polymerization of ethylene using metallocene catalysts: Effect of clay pretreatment on the properties of highly filled polyethylene nanocomposites

Highly filled polyethylene (PE)‐based nanocomposites were obtained by insitu polymerization technique. An organically modified montmorillonite, Cloisite® 15A (C15A), was previously treated with methylaluminoxane (MAO) to form a supported cocatalyst (C15A/MAO) before being contacted with a zirconocene catalyst. The main features of C15A/MAO intermediates were studied by elemental analysis, TGA, TGA‐FTIR, WAXD, and TEM. MAO reacts with the clay, replaces most of the organic surfactant within the clay galleries and destroys the typical crystrallographic order of the nanoclay. The catalytic activity in the presence of C15A/MAO is higher than in ethylene polymerization without any inorganic filler and increases with MAO supportation time. This indicates that part of the polymer chains grows within the clay galleries, separates them, and makes it possible to tune the final morphology of the composites. The polymerization results and the influence of C15A pretreatment and polymerization conditions on thermal and morphological properties of the hybrid PE/C15A nanocomposites are presented. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 5390–5403, 2008     

Polynomial approximation with an exponential weight on the real semiaxis

We consider the polynomial approximation on (0,+∞), with the weight $u(x)= x^{\gamma}e^{-x^{-\alpha}-x^{\beta}}$ , α>0, β>1 and γ≧0. We introduce new moduli of smoothness and related K-functionals for functions defined on the real semiaxis, which can grow exponentially both at 0 and at +∞. Then we prove the Jackson theorem, also in its weaker form, and the Stechkin inequality. Moreover, we study the behavior of the derivatives of polynomials of best approximation.     

Facing unexpected reactivity paths with Zr(IV)-pyridylamido polymerization catalysts

This work provides original insights to the better understanding of the complex structure-activity relationship of Zr(IV)-pyridylamido-based olefin polymerization catalysts and highlights the importance of the metal-precursor choice (Zr(NMe(2))(4) vs. Zr(Bn)(4)) to prepare precatalysts of unambiguous identity. A temperature-controlled and reversible σ-bond metathesis/protonolysis reaction is found to take place on the Zr(IV)-amido complexes in the 298-383 K temperature range, changing the metal coordination sphere dramatically (from a five-coordinated tris-amido species stabilized by bidentate monoanionic {N,N(-)} ligands to a six-coordinated bis-amido-mono-amino complexes featured by tridentate dianionic {N(-),N,C(-)} ligands). Well-defined neutral Zr(IV)-pyridylamido complexes have been prepared from Zr(Bn)(4) as metal source. Their cationic derivatives [Zr(IV) N(-),N,C(-)}Bn](+)[B(C(6)F(5))(4)](-) have been successfully applied to the room-temperature polymerization of 1-hexene with productivities up to one order of magnitude higher than those reported for the related Hf(IV) state-of-the-art systems. Most importantly, a linear increase of the poly(1-hexene) M(n) values (30-250 kg mol(-1)) has been observed upon catalyst aging. According to that, the major active species (responsible for the increased M(n) polymer values) in the aged catalyst solution, has been identified.     

On the ethylene-norbornene copolymerization mechanism

Results of our studies on polymerization kinetics and tests of copolymerization statistical models of ethylene-norbornene (E-N) copolymers obtained on the basis of microstructures determined by ¹³C NMR analysis are reported. Ethylene-norbornene (E-N) copolymers were synthesized by catalytic systems composed of racemic isospecific metallocenes, i-Pr[(3Prⁱ-Cp)(Flu)]ZrCl₂ or a constrained geometry catalyst (CGC) and methylaluminoxane. Polymerization kinetics revealed that E-N copolymerization is quasi living under standard polymerization conditions. Calculations of the number of active sites and of chain propagation and chain transfer turnover frequencies indicate that the metal is mainly in the Mt-N* state, while the Mt-E* state contributes more to transfer and propagation rates. The first-order and the second-order Markov statistics have been tested by using the complete tetrad distribution obtained from ¹³C NMR analysis of copolymer microstructures. The root-mean-square deviations between experimental and calculated tetrads demonstrate that penultimate (second-order Markov) effects play a decisive role in E-N copolymerizations. Results show clues for more complex effects depending on the catalyst geometry in copolymers obtained at high N/E feed ratios. Comonomer concentration was shown to have a strong influence on copolymer microstructure and copolymer properties. The copolymer microstructure of alternating isotactic copolymers obtained with i-Pr[(3Prⁱ-Cp)(Flu)]ZrCl₂ have been described at pentad level. Second-order Markov statistics better describes also the microstrucure of these copolymers.