Self-immobilized titanium and zirconium catalysts with phenoxy-imine ligands for ethylene polymerization. X-ray crystal structure of bis(N-(3-tert-butylsalicylidene)-4 '-allyloxyanilinato) zirconium(IV) dichloride

Four self-immobilized FI catalysts with allyl substituted phenoxy-imine ligands [{4-(CH2=CHCH2O)C6H5N=CH-C6H3(3-tert-C4H9)O}(2) MCl2] (1: M = Ti: 2: M = Zr), [{3-(CH2=CHCH2O)C6H5N=CH-C6H3(3-tert-C4H9)O}(2)MCl2] (3: M = Zr), [{4-(CH2=CHCH2-2,6-(iso-C3H7)(2))C6H5N=CH-C6H3(3,5-(NO2)(2))O}(2)MCl2] (4: M = Zr) have been synthesized and characterized. The molecular structure of 2 has been determined by X-ray crystallographic analysis. The results of ethylene polymerization showed that the self-immobilized titanium (IV) and zirconium (IV) catalysts 1-3 kept high activity for ethylene polymerization and 4 showed no activity. SEM showed the immobilization effect could greatly improve the morphology of polymer particles to afford micron-granula polyolefin as supported catalysts.

New neutral nickel(II) complexes bearing pyrrole-imine chelate ligands: synthesis, structure and norbornene polymerization behavior

New neutral nickel(II) complexes bearing nonsymmetric bidentate pyrrole-imine chelate ligands (4a-d), [2-(ArNCH)C4H3N]Ni(PPh3)Ph [Ar=2,6-diisopropylphenyl (a), 2-methyl-6-isopropylphenyl (b), 2,6-diethylphenyl (c), 2-tert-butylphenyl (d)], have been prepared in good yields from the sodium salts of the corresponding ligands and trans-Ni(PPh3)(2)(Ph)Cl, and the structure of complex 4a has been confirmed by X-ray crystallographic analysis. These neutral Ni(II) complexes were investigated as catalysts for the vinylic polymerization of norbornene. Using modified methylaluminoxane (MMAO) as a cocatalyst, these complexes display very high activities and produce great mass polymers. Catalyst activity of up to 4.2 x 10(7) g (mol Ni h)(-1) and the viscosity-average molecular weight of polymer of up to 9.2 x 10(5) g mol(-1) were observed. Catalyst activity, polymer yield, and polymer molecular weight can be controlled over a wide range by the variation of reaction parameters such as Al-Ni ratio, norbornene-catalyst ratio, monomer concentration, polymerization reaction temperature and time.

Ferrocenylphosphine-imine ligands for Pd-catalyzed asymmetric allylic alkylation

Ferrocenylphosphine-imine ligands 6 derived front (R,S)-PPFNH2-R 5 and a variety of benzaldehydes were applied in the Pd-catalyzed asymmetric allylic alkylation of 1,3-diphenylprop-2-en-1-yl acetate 7a or pivalate 7b with dimethyl malonate. The substituent effects on the catalytic reaction were investigated, and 96% e.e. with 99% yield was achieved when the m-nitro substituted ligand 6k was used. (C) 2002 Elsevier Science Ltd. All rights reserved.

Nickel(II) complexes of terdentate or symmetrical tetradentate Schiff bases: Evidence of the influence of the counter anions in the hydrolysis of the imine bond in Schiff base complexes

Two sets of ligands, set-1 and set-2, have been prepared by mixing 1,3-diaminopentane and carbonyl compounds (2-acetylpyridine or pyridine-2-carboxaldehyde) in 1:1 and 1:2 ratios, respectively, and employed for the synthesis of complexes with Ni(II) perchlorate, Ni(II) thiocyanate and Ni(II) chloride. Ni(II) perchlorate yields the complexes having general formula [NiL2](ClO4)(2)(L = L-1 [N-3-(1-pyridin-2-yl-ethylidene)-pentane-1,3-diamine] for complex 1 or L-2[N-3-pyridin-2-ylmethylene-pentane-1,3-diamine] for complex 2) in which the Schiff bases are monocondensed terdentate, whereas Ni(II) thiocyanate results in the formation of tetradentate Schiff base complexes, [NiL(SCN)(2)] (L = L-3[N,N'-bis-(1-pyridin-2- yl-ethylidine)-pentane-1,3-diamine] for complex 3 or L-4 [N,N'-bis(pyridin-2-ylmethyline)-pentane-1,3- diamine] for complex 4) irrespective of the sets of ligands used. Complexes 5 {[NiL3(N-3)(2)]} and 6 {[NiL4(N-3)(2)]} are prepared by adding sodium azide to the methanol solution of complexes 1 and 2. Addition of Ni(II) chloride to the set-1 or set-2 ligands produces [Ni(pn)(2)]Cl-2, 7, as the major product, where pn = 1,3-diaminopentane. Formation of the complexes has been explained by the activation of the imine bond by the counter anion and thereby favouring the hydrolysis of the Schiff base. All the complexes have been characterized by elemental analyses and spectral data. Single crystal X-ray diffraction studies con. firm the structures of three representative members, 1, 4 and 7; all of them have distorted octahedral geometry around Ni(II). The bis-complex of terdentate ligands, 1, is the mer isomer, and complexes 4 and 7 possess trans geometry. (C) 2008 Elsevier B. V. All rights reserved.

Cycloadditions of chiral carbonyl ylides with imine dipolarophiles as a route to enantiomerically pure alpha-amino-beta-hydroxy acids

The preparation of enantiomerically pure threo-beta-amino-alpha-hydroxy acids via 1,3-dipolar cycloadditions of imine dipolarophiles with the chiral isomunchnone derived from (5R)-5-phenylmorpholin-3-one 1 is described. The cycloadducts were obtained with excellent diastereofacial- and exo-selectivity. Subsequent hydrolysis and chemoselective exocyclic amide cleavage afforded the threo-beta-amino-alpha-hydroxy acids with recovery of the initial chiral auxiliary. (C) 2009 Published by Elsevier Ltd.

Effect of media polarity on the photoisomerisation of substituted stilbene, azobenzene and imine chromophores

The influence of substituents and media polarity on the photoinducedE→Z geometrical isomerisation of the stilbene, azobenzene and N-benzylideneaniline chromophores has been compared and assessed. The efficiency of the process in all three systems is markedly dependent on the presence and characteristics of electron-donor and electron-acceptor substituents at the 4- and 4′-positions. The results are discussed in terms of relaxation of the E-excited singlet state. In the absence of a nitro substituent, relaxation to the S1 orthogonal state competes effectively with non-productive intramolecular electron transfer; in the presence of a nitro substituent, the T1 orthogonal state is formed from inter-system crossing. For systems with a 4-nitro and a 4′-electron-donor substituent, access to the triplet state is inhibited by polar solvents promoting formation of the inactive charge-transfer state from the S1 state, and no isomerisation is observed. Similar effects are observed in both solution and polymer films. Such variations in behaviour have important implications for the utilisation of the chromophores in nonlinear optical phenomena including photorefractivity.

Immobilization of Poly(propylene imine) Dendrimer/Nickel Phtalocyanine as Nanostructured Multilayer Films To Be Used as Gate Membranes for SEGFET pH Sensors

We describe the assembly of layer-by-layer films based on the poly(propylene imine) dendrimer (PPID) generation 3 and nickel tetrasulfonated phthalocyanine (NiTsPc) for application as chemically sensitive membranes in sepal alive extended-gate field effect transistor (SEGFET) pH sensors PPID/NiTsPc films wet e adsorbed on quartz, glass. indium tin oxide. or gold (Au)-covered glass substrates Multilayer formation was monitored via UV-vis absorption upon following the increment in the Q-band intensity (615 nm) of NiTsPc The nanostructured membranes were very stable in a pH range of 4-10 and displayed a good sensitivity toward H(+), ca 30 mV/pH for PPID/N(1)TsPc films deposited on Au-covered substrates For films deposited on ITO, the sensitivity was ca 52 4 mV/pH. close to the expected theoretical value for ton-sensitive membranes. The use of chemically stable PPID/NiTsPc films as gate membranes in SEGFETs, as introduced here, may represent an alternative for the fabrication of nanostructured, porous platforms for enzyme immobilization to be used in enzymatic biosensors.

mer-[RuCl3(P-P)H2O] (P-P=dppb or diop) as a starting material for the synthesis of binuclear complexes. Crystallographic structures of [(dppb)ClRu-mu(Cl)(3)-RuCl(dppb)] and [(eta(6)-C6H6)Ru-mu(Cl)(3)-RuCl(dppb)]. Imine hydrogenation using mono- and binuclear ruthenium complexes

The reactivity of the mer-[RuCl3(dppb)H2O] complex (1) with di-hydrogen shows that the products formed depend on the conditions of the reaction, i.e., solvents and presence or absence of a base. The new mixed-valence complexes [(diop)ClRu-(h-Cl)(3)-RuCl(dppb)] (3), [(binap)CIRu-(p-Cl)(3)-RuCl(dppb)] (4), [(PPh3)(2)ClRu-(mu-Cl)(3)-RuCl(dppb)] (6), [(dppn)ClRu-(mu-Cl)(3)-RuCl(dppb)] (7), [(P-ptol(3))(2)ClRu-(mu-Cl)(3)-RuCl(dppb)] (8), [(SbPh3)(2)ClRu-(mu-Cl)(3)-RuCl(dppb)] (9), [(eta(6)-C6H6)Ru-(mu-Cl)(3)-RuCl(dppb)] (11) and the known mixed-valence [(dppb)CIRu-(mu-Cl)(3)-RuCl(dppb)] (5) and [(diop)ClRu-(mu-Cl)(3)-RuCl(diop)] (10) were synthesized from complexes (1) or (2) using a methodology developed in our research group. The known complexes [(dppb)ClRu-(mu-Cl)(2)-RuCl(dppb)] (12), [(dppb)(CO)Ru-(mu-Cl)(3)-RuCl(dppb)] (13) and [H2NEt2][(dppb)ClRu-(mu-Cl)(3)-RuCl(dppb)] (14) were synthesized by changing the reaction conditions between mer-[RuCl3(dppb)H2O] (1) and dihydrogen. The crystal structures of (5) and (11) were determined by single-crystal X-ray diffraction. Some of the complexes described here are effective pre-catalysts for the hydrogenation of imines. Preliminary results on the homogeneous hydrogenation of the imines Ph-CH2-N=CH-Ph and Ph-N=CH-Ph are presented. (C) 2004 Elsevier Ltd. All rights reserved.

A Chloro-Bridged Linear Chain Imine-Copper(II) Complex and Its Application as an Enzyme-Free Amperometric Biosensor for Hydrogen Peroxide

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Synthesis and preliminary characterization of Poly(Propylene)Imine hexadecylamine dendrimer (DAB-Am-16) modified with methyl acrylate

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

1,2-Additionen deprotonierter Alpha-Aminonitrile: Umgepolte Imine als vielseitige Synthesebausteine

Von aromatischen Aldehyden abgeleitete α-Aminonitrile können ohne die Anwendung von Schutzgruppen in α-Position deprotoniert werden, wenn keine lithiumhaltigen Basen verwendet werden. Ziel der vorliegenden Arbeit war es, die Reaktionen deprotonierter α-Aminonitrile mit Elektrophilen zu untersuchen. Die Addition von α-Aminocarbanionen an Imine führt unter intramolekularer Eliminierung von HCN zu Endiaminen, die sich in einer Eintopfsynthese abhängig von der Aufarbeitung in 1,2-Diamine oder 1,2-Diimine umwandeln lassen. Die nach Oxidation durch Luftsauerstoff erhaltenen Diimine können mit dem Reduktionsmittel BH3·THF diastereoselektiv reduziert werden. Es hat sich hier gezeigt, dass durch Zugabe einer katalytischen Menge an NaBH4 hauptsächlich die syn-Diamine erhalten werden, der Zusatz von Phthalsäure wiederum liefert bevorzugt die anti-Produkte. In beiden Fällen wird das Produkt in quantitativer Ausbeute erhalten. So konnte also eine effektive diastereoselektive Reduktionsmethode entwickelt werden, die eine freie Wahl der syn- oder anti-Konfiguration ermöglicht. Um enantiomerenreine 1,2-Diamine zu erhalten, wurden verschiedene Methoden getestet. Sowohl auxiliargesteuerte Synthesen mit einem N-Glycosyl-Aminonitril oder mit chiralen Sulfinyliminen als auch die Reduktion durch chirale Borverbindungen (CBS-Katalysatoren, Triacyloxyborhydrid oder Diisopinocamphenylboran), Transferhydrierungen mit chiralen Difluortitanocen-, Noyori- oder Organophosphat-Katalysatoren sowie enantioselektive Hydrierungen mit chiralen Übergangsmetall-katalysatoren waren jedoch nicht erfolgreich. Die Umsetzung der 1,2-Diimine mit Chlormethylethern oder -estern liefert die entsprechenden unsymmetrischen Imidazoliumsalze. Diese konnten zu N-heterocyclischen Carbenen deprotoniert und erfolgreich als Liganden in Suzuki- und Heck-Reaktionen eingesetzt werden. Durch die 1,2-Addition α-deprotonierter Streckerprodukte und anschließende Reduktion im Eintopfverfahren konnten 1,2-Aminoalkohole in mäßigen bis guten Ausbeuten dargestellt werden. Die Umsetzung von α-Aminocarbanionen mit N-Acyliminen erlaubt zudem die Synthese tetrasubstituierter Imidazole und trisubstituierter Oxazole in drei beziehungsweise vier Stufen: Die zunächst gebildeten α-Amino-α-acylaminopropionitrile können isoliert und in Gegenwart von Base einer Retro-Strecker-Reaktion unterworfen werden. Abhängig vom Substitutionsmuster schließt sich in manchen Fällen nach der Eliminierung von HCN direkt die Cyclisierung zum Imidazol an. Nicht cyclisierte Intermediate lassen sich durch Dehydratisierung mit PCl5 zu Imidazolen umsetzen, aber auch unter sauren Bedingungen zu α-Acylaminoketonen hydrolysieren, welche wiederum durch Einwirkung von PCl5 in Oxazole überführt werden können. Auf diese Weise wurden Imidazole und Oxazole in moderaten bis hohen Gesamtausbeuten hergestellt.

Imine von Formyl-[2.2]paracyclophanen und ihre Anwendung in der enantioselektiven Katalyse

Kohlenhydrate wurden bislang nur selten zur Darstellung chiraler Liganden verwendet. Sie gelten als zu polyfunktionell und konformativ zu flexibel, um daraus mit vertretbarem Aufwand Liganden zu synthetisieren, die die Anforderungen an ein leistungsfähiges Katalysatorsystem - die spezifische Komplexierung des Metalls in einer konformativ möglichst rigiden Umgebung - erfüllen.rnDas Element der planaren Chiralität erwies sich in vielen asymmetrischen, katalytischen Prozessen als entscheidend für die Erzielung hoher Enantioselektivitäten.rnDie vorliegende Arbeit baut auf den Kohlenhydratliganden-Synthesen mit Glycosylaminen auf, die über geeignete komplexierende Zentren verfügen, um damit andere als die bisher mit Kohlenhydraten bekannten enantioselektiven Katalysen durchführen zu können. Zur Synthese stickstoffhaltiger chiraler Verbindungen haben sich besonders perpivaloylierte Glycosylamine vom Typ des 2,3,4,6-Tetra-O-pivaloyl-β-D-galactopyranosylamins bewährt. Im Rahmen dieser Dissertation wurden Schiff-Basen aus pivaloyliertem Galactosylamin bzw. verschiedenen anderen Galactosylamin-Bausteinen als chiralem Rückgrat, und einem Aldehyd auf der Basis von planar chiralem [2.2]Paracyclophan dargestellt. Die neuen N-Galactosylimine wurden außerdem in asymmetrischen Ugi-Reaktionen und in Tandem Mannich-Michael-Reaktionen zu N-Galactosyl-dehydropiperidinonen untersucht. Bei der Spaltung der dargestellten N-Galactosylimine von Paracyclophan-aldehyden unter mineralsauren Bedingungen sollten die entsprechenden mono- und di-substituierten Formyl- [2.2]paracyclophane in enantiomerenreiner Form erhalten werden. Die erhaltenen Verbindungen wurden als potentielle N,O-Liganden in der asymmetrischen Strecker Reaktion, in die enantioselektiven Epoxidierungen und in der Addition von Diethylzink an aromatische und aliphatische Aldehyde untersucht.rn

Novel magnetic iron oxide nanoparticles coated with poly(ethylene imine)-g-poly(ethylene glycol) for potential biomedical application: synthesis, stability, cytotoxicity and MR imaging

Magnetic iron oxide nanoparticles have found application as contrast agents for magnetic resonance imaging (MRI) and as switchable drug delivery vehicles. Their stabilization as colloidal carriers remains a challenge. The potential of poly(ethylene imine)-g-poly(ethylene glycol) (PEGPEI) as stabilizer for iron oxide (γ-Fe₂O₃) nanoparticles was studied in comparison to branched poly(ethylene imine) (PEI). Carrier systems consisting of γ-Fe₂O₃-PEI and γ-Fe₂O₃-PEGPEI were prepared and characterized regarding their physicochemical properties including magnetic resonance relaxometry. Colloidal stability of the formulations was tested in several media and cytotoxic effects in adenocarcinomic epithelial cells were investigated. Synthesized γ-Fe₂O₃ cores showed superparamagnetism and high degree of crystallinity. Diameters of polymer-coated nanoparticles γ-Fe₂O₃-PEI and γ-Fe₂O₃-PEGPEI were found to be 38.7 ± 1.0 nm and 40.4 ± 1.6 nm, respectively. No aggregation tendency was observable for γ-Fe₂O₃-PEGPEI over 12 h even in high ionic strength media. Furthermore, IC₅₀ values were significantly increased by more than 10-fold when compared to γ-Fe₂O₃-PEI. Formulations exhibited r₂ relaxivities of high numerical value, namely around 160 mM⁻¹ s⁻¹. In summary, novel carrier systems composed of γ-Fe₂O₃-PEGPEI meet key quality requirements rendering them promising for biomedical applications, e.g. as MRI contrast agents.

Photoclickable surfaces for profluorescent covalent polymer coatings

The nitrile imine-mediated tetrazole-ene cycloaddition reaction (NITEC) is introduced as a powerful and versatile conjugation tool to covalently ligate macromolecules onto variable (bio)surfaces. The NITEC approach is initiated by UV irradiation and proceeds rapidly at ambient temperature yielding a highly fluorescent linkage. Initially, the formation of block copolymers by the NITEC methodology is studied to evidence its efficacy as a macromolecular conjugation tool. The grafting of polymers onto inorganic (silicon) and bioorganic (cellulose) surfaces is subsequently carried out employing the optimized reaction conditions obtained from the macromolecular ligation experiments and evidenced by surface characterization techniques, including X-ray photoelectron spectroscopy and FT-IR microscopy. In addition, the patterned immobilization of variable polymer chains onto profluorescent cellulose is achieved through a simple masking process during the irradiation. Photoinduced nitrile imine-alkene 1,3-dipolar cycloaddition (NITEC) is employed to covalently bind well-defined polymers onto silicon oxide or cellulose. A diaryl tetrazole-functionalized molecule is grafted via silanization or amidification, respectively. Under UV light, a reactive nitrile imine rapidly forms and reacts with maleimide-functionalized polymers yielding a fluorescent linkage. Via a masking method, polymeric fluorescent patterns are achieved.

The molecular basis for selective inhibition of unconventional mRNA splicing by an IRE1-binding small molecule

IRE1 couples endoplasmic reticulum unfolded protein load to RNA cleavage events that culminate in the sequence-specific splicing of the Xbp1 mRNA and in the regulated degradation of diverse membrane-bound mRNAs. We report on the identification of a small molecule inhibitor that attains its selectivity by forming an unusually stable Schiff base with lysine 907 in the IRE1 endonuclease domain, explained by solvent inaccessibility of the imine bond in the enzyme-inhibitor complex. The inhibitor (abbreviated 4μ8C) blocks substrate access to the active site of IRE1 and selectively inactivates both Xbp1 splicing and IRE1-mediated mRNA degradation. Surprisingly, inhibition of IRE1 endonuclease activity does not sensitize cells to the consequences of acute endoplasmic reticulum stress, but rather interferes with the expansion of secretory capacity. Thus, the chemical reactivity and sterics of a unique residue in the endonuclease active site of IRE1 can be exploited by selective inhibitors to interfere with protein secretion in pathological settings.