Search results for "Ethylene"
showing 10 items of 2589 documents
Penetration enhancer containing vesicles as carriers for dermal delivery of tretinoin.
2011
The ability of a recently developed novel class of liposomes to promote dermal delivery of tretinoin (TRA) was evaluated. New penetration enhancer-containing vesicles (PEVs) were prepared adding to conventional phosphatidylcholine vesicles (control liposomes) different hydrophilic penetration enhancers: Oramix® NS10 (OrNS10), Labrasol® (Lab), Transcutol® P (Trc), and propylene glycol (PG). Vesicles were characterized by morphology, size distribution, zeta potential, incorporation efficiency, stability, rheological behaviour, and deformability. Small, negatively charged, non-deformable, multilamellar vesicles were obtained. Rheological studies showed that PEVs had fluidity higher than conven…
CoIILnIII dinuclear complexes (LnIII = Gd, Tb, Dy, Ho and Er) as platforms for 1,5-dicyanamide-bridged tetranuclear CoII2LnIII2 complexes: A magneto-…
2012
Five acetate-diphenoxo triply-bridged Co-II-Ln(III) complexes (Ln(I) = Gd, Tb, Dy, Ho, Er) of formula [Co(mu-L)(mu-Ac)Ln(NO3)(2)] and two diphenoxo doubly-bridged Co-II-Ln(III) complexes (Ln(III) = Gd, Tb) of formula [Co(H2O)(mu-L)Ln(NO3)(3)]center dot S (S = H2O or MeOH), were prepared in one pot reaction from the compartmental ligand N,N',N ''-trimethyl-N,N ''-bis(2-hydroxy3-methoxy-5-methylbenzyl)diethylene triamine (H2L). The diphenoxo doubly-bridged Co-II-Ln(III) complexes were used as platforms to obtain 1,5-dicyanamide-bridged tetranuclear Co-II-Ln(III) complexes (Ln(III) = Gd, Tb, Dy, Ho, Er). All exhibit ferromagnetic interactions between the Co-II and Ln(III) ions and in the case …
Theoretical Study on the Structures and Electronic Spectra of TCNE2−
2006
Investigations into the charge-separated states and electron-transfer transitions in tetracyanoethylene (TCNE) compiles have recently generated much interest. In this work we present theoretical calculations showing that the most stable structure of the dianion TCNE 2- has D 2d symmetry in vacuum as well as in the solvents dichloromethane and cicetonitrile. By means of the coupled cluster linear response, we compute the vertical electronic spectrum in both the gas phase and solution. The theoreitcal results, are compared to the experimental data and good agreement is achieved.
Separation of chelating agents as copper complexes by capillary zone electrophoresis using quaternary ammonium bromides as additives in N-methylforma…
2006
This study presents the use of quaternary ammonium bromides as additives in N-methylformamide (NMF) for the separation and quantification of chelating agents as copper complexes by capillary zone electrophoresis (CZE). The new quaternary ammonium bromides were synthesized in our laboratory and used for the first time for CZE applications performed in NMF media. The methods were developed and optimized for determination of six chelating agents (trans-1,2-diaminocyclohexane-N,N,N',N'-tetraacetic acid (CDTA), diethylenetriaminepentaacetic acid (DTPA), ethylenediaminetetraacetic acid (EDTA), N-(2-hydroxyethyl)ethylenediamine-N,N',N'-triacetic acid (HEDTA), nitrilotriacetic acid (NTA) and trieth…
On the synthesis and characterization of layered antimony(III) phosphate and its interaction with moist ammonia and amines
1998
Samples of antimony(III) phosphate, a layered material, were prepared at room temperature, using the two allotropic forms of Sb2O3, layered valentinite and cubic senarmontite. The compounds were characterized by infrared spectroscopy, X-ray diffraction, and thermogravimetric–differential thermal analysis. Solids exposed to ammonia, ethylenediamine, or hydrazine vapors also were studied. The interaction between SbPO4 and the bases always led to the formation of stoichiometric amounts of Sb2O3 and hydrogen phosphate(–2) salts of the bases. With ammonia, the SbPO4 raw materials gave rise to valentinite or senarmontite, depending on which Sb2O3 allotropic form was used to prepare antimony phosp…
A DFT study of the mechanism of Brønsted acid catalysed Povarov reactions
2015
Abstract The molecular mechanism of the Bronsted acid (BA) catalysed Povarov reaction of N -phenyl- C -methoxycarbonyl imine with a methylenecyclopropane (MCP) has been investigated using DFT methods at the MPWB1K/6-31G(d) level. This BA catalysed Povarov reaction is a domino process initialised by the formation of a cationic intermediate which experiences a quick intramolecular Friedel–Crafts reaction yielding the final tetrahydroquinoline. Protonation of the imine nitrogen atom notably increases the electrophilicity of the corresponding species, accelerating the reaction through ionic processes. Analysis of the Parr functions in the initial nucleophilic attack of MCP to the protonated imi…
Nanoreactors for the multi-functionalization of poly-histidine fragments
2019
Water-soluble MBHA derivatives were found to self-assemble in a water environment to generate aggregates showing core–shell architectures. The aggregates appeared to be capable of working as nanoreactors performing a multi-functionalization of poly-histidine fragments, which after an initial interaction with the solvated oligo(ethylene glycol) shell reach the reactive core.
Direct Evidence of the Amino Acid Side Chain and Backbone Contributions to Protein Anharmonicity
2010
Elastic incoherent neutron scattering has been used to study the temperature dependence of the mean-square displacements of nonexchangeable hydrogen atoms in powders of a series of homomeric polypeptides (polyglycine, polyalanine, polyphenylalanine and polyisoleucine) in comparison with myoglobin at the same hydration level (h = 0.2). The aim of the work was to measure the dynamic behavior of different amino acid residues separately and assess the contribution of each type of side chain to the anharmonic dynamics of proteins. The results provide direct experimental evidence that the first anharmonic activation, at approximately 150 K, is largely due to methyl group rotations entering the ti…
Metal ion complexation by tetraester derivatives of bridged calix [4] arenes
1992
A series of bridged calix [4] arenes (5–10 methylene groups in the bridge) were synthesized and transformed into their tetraester derivatives by reaction with ethyl bromoacetate. The stability constants for complexes of the tetraester derivatives with sodium, potassium and silver cations, determined in methanol by spectroscopic or potentiometric techniques, show a drastic decrease (more than 105 for Na +) for the shorter methylene chains. 1H NMR studies demonstrate a conformational rearrangement of the calixarene part to fourfold symmetry to be necessary for the complexation of a cation, which is prevented by the shorter chains. This is further confirmed by the X-ray structure of a tetraest…
The chloro‐substituent enhances performance of 2,4‐bis (imino)pyridylchromium catalysts yielding highly linear polyethylene
2020
The five unsymmetrical 2‐[1‐(2,4‐dibenzhydryl‐6‐chlorophenylimino)ethyl]‐6‐[1‐(arylimino)ethyl]pyridine compounds (aryl: 2,6‐Me2Ph L1 , 2,6‐Et2Ph L2 , 2,6‐i Pr2Ph L3 , 2,4,6‐Me3Ph L4 and 2,6‐Et2–4‐MePh L5 ) were prepared and characterized with FT‐IR and 1H/13C NMR spectroscopy as well as elemental analysis. The treatment of L1 – L5 with CrCl3·3THF affords the corresponding chromium chloride complexes (Cr1 – Cr5 ) in excellent yields. The molecular structures of Cr2 and Cr3 characterized by X‐ray diffraction show a distorted octahedral geometry with three nitrogen atoms and three chlorine atoms around the metal center. On activation with either MAO or MMAO, Cr1 – Cr5 collectively display hig…