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MAO

Distribution by Scientific Domains

Polymers and Materials Science	57%
Chemistry	24%
Medical Sciences	6%
Life Sciences	5%
4 Other Domains	8%

Terms modified by MAO

mao inhibitor

Selected Abstracts

High molar mass ethene/1-olefin copolymers synthesized with acenaphthyl substituted metallocene catalysts

JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 1 2008
Erkki Aitola
Abstract The influence of ligand structure on copolymerization properties of metallocene catalysts was elucidated with three C1 -symmetric methylalumoxane (MAO) activated zirconocene dichlorides, ethylene(1-(7, 9)-diphenylcyclopenta-[a]-acenaphthadienyl-2-phenyl-2-cyclopentadienyl)ZrCl2 (1), ethylene(1-(7, 9)-diphenylcyclopenta-[a]-acenaphthadienyl-2-phenyl-2-fluorenyl)ZrCl2 (2), and ethylene(1-(9)-fluorenyl-(R)1-phenyl-2-(1-indenyl)ZrCl2 (3). Polyethenes produced with 1/MAO had considerable, ca. 10% amount of trans -vinylene end groups, resulting from the chain end isomerization prior to the chain termination. When ethene was copolymerized with 1-hexene or 1-hexadecene using 1/MAO, molar mass of the copolymers varied from high to moderate (531,116 kg/mol) depending on the comonomer feed. At 50% comonomer feed, ethene/1-olefin copolymers with high hexene or hexadecene content (around 10%) were achievable. In the series of catalysts, polyethenes with highest molar mass, up to 985 kg/mol, were obtained with sterically most crowded 2/MAO, but the catalyst was only moderately active to copolymerize higher olefins. Catalyst 3/MAO produced polyethenes with extremely small amounts of trans -vinylene end groups and relatively low molar mass 1-hexene copolymers (from 157 to 38 kg/mol) with similar comonomer content as 1. These results indicate that the catalyst structure, which favors chain end isomerization, is also capable to produce high molar mass 1-olefin copolymers with high comonomer content. In addition, an exceptionally strong synergetic effect of the comonomer on the polymerization activity was observed with catalyst 3/MAO. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 373,382, 2008 [source]

Synthetic Explorations Towards Sterically Crowded 1,2,3-Substituted Bis(indenyl)zirconium(IV) Dichlorides

EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 9 2005
Andreas C. Möller
Abstract The systematic synthesis of 1,3-dialkyl-substituted 2-silylindenes and their suitability as zirconocene ligands is discussed. Unexpected reactivities rendered a number of substitution patterns unfeasible, especially for alkyl groups other than methyl in 2-(trimethylsilyl)indene derivatives, and essentially for all derivatives of 2-(dimethylsilyl)indene. The syntheses of rac/meso -bis[1-methyl-2-(trimethylsilyl)indenyl]zirconium(IV) dichloride (12) and bis[1,3-dimethyl-2-(trimethylsilyl)indenyl]zirconium(IV) dichloride (13b) are described. The solid-state structure of the latter displays strong deformations within the ligand framework and an unusually large Cpcentroid -Zr,Cpcentroid angle. Both, 12/MAO and 13b/MAO, displayed ethene and ethene-co-1-hexene polymerization activity. Curiously, 13b/MAO shows an extraordinary monomer selectivity, which can be rationalized by means of DFT calculations on the active site. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source]

High molar mass ethene/1-olefin copolymers synthesized with acenaphthyl substituted metallocene catalysts

Preparation of ethylene/1-octene copolymers from ethylene stock with tandem catalytic system

JOURNAL OF APPLIED POLYMER SCIENCE, Issue 5 2008
Tao Jiang
Abstract Tandem catalysis offers a novel synthetic route to the production of linear low-density polyethylene. This article reports the use of homogeneous tandem catalytic systems for the synthesis of ethylene/1-octene copolymers from ethylene stock as the sole monomer. The reported catalytic systems involving a highly selective, bis(diphenylphosphino)cyclohexylamine/Cr(acac)3/methylaluminoxane (MAO) catalytic systems for the synthesis of 1-hexene and 1-octene, and a copolymerization metallocene catalyst, rac -Et(Ind)2ZrCl2/MAO for the synthesis of ethylene/1-octene copolymer. Analysis by means of DSC, GPC, and 13C-NMR suggests that copolymers of 1-hexene and ethylene and copolymers of 1-octene and ethylene are produced with significant selectivity towards 1-hexene and 1-octene as comonomers incorporated into the polymer backbone respectively. We have demonstrated that, by the simple manipulation of the catalyst molar ratio and polymerization conditions, a series of branched polyethylenes with melting temperatures of 101.1,134.1°C and density of 0.922,0.950 g cm,3 can be efficiently produced. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source]

Borane chain transfer reaction in olefin polymerization using trialkylboranes as chain transfer agents

JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 16 2010
Wentian Lin
Abstract This article discusses a new borane chain transfer reaction in olefin polymerization that uses trialkylboranes as a chain transfer agent and thus can be realized in conventional single site polymerization processes under mild conditions. Commercially available triethylborane (TEB) and synthesized methyl-B-9-borabicyclononane (Me-B-9-BBN) were engaged in metallocene/MAO [depleted of trimethylaluminum (TMA)]-catalyzed ethylene (Cp2ZrCl2 and rac -Me2Si(2-Me-4-Ph)2ZrCl2 as a catalyst) and styrene (Cp*Ti(OMe)3 as catalyst) polymerizations. The two trialkylboranes were found,in most cases,able to initiate an effective chain transfer reaction, which resulted in hydroxyl (OH)-terminated PE and s -PS polymers after an oxidative workup process, suggesting the formation of the B-polymer bond at the polymer chain end. However, chain transfer efficiencies were influenced substantially by the steric hindrances of both the substituent on the trialkylborane and that on the catalyst ligand. TEB was more effective than TMA in ethylene polymerization with Cp2ZrCl2/MAO, whereas it became less effective when the catalyst changed to rac -Me2Si(2-Me-4-Ph)2ZrCl2. Both TEB and Me-B-9-BBN caused an efficient chain transfer in the Cp2ZrCl2/MAO-catalyzed ethylene polymerization; nevertheless, Me-B-9-BBN failed in vain with rac -Me2Si(2-Me-4-Ph)2ZrCl2/MAO. In the case of styrene polymerization with Cp*Ti(OMe)3/MAO, thanks to the large steric openness of the catalyst, TEB exhibited a high efficiency of chain transfer. Overall, trialkylboranes as chain transfer agents perform as well as BH-bearing borane derivatives, and are additionally advantaged by a much milder reaction condition, which further boosts their applicability in the preparation of borane-terminated polyolefins. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3534,3541, 2010 [source]

High molar mass ethene/1-olefin copolymers synthesized with acenaphthyl substituted metallocene catalysts

Propylene polymerization with nickel,diimine complexes containing pseudohalides

JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 1 2006
Marcos L. Dias
Abstract DADNiX2 nickel,diimine complexes [DAD = 2,6- iPr2C6H3NC(Me)C(Me)N2,6- iPr2C6H3] containing nonchelating pseudohalide ligands [X = isothiocyanate (NCS) for complex 1 and isoselenocyanate (NCSe) for complex 2] were synthesized, and the propylene polymerization with these complexes and also with the Br ligand (X = Br for complex 3) activated by methylaluminoxane (MAO) were investigated (systems 1, 2, and 3/MAO). The polypropylenes obtained with systems 1, 2, and 3 were amorphous polymers and had high molecular weights and narrow molecular weight distributions. Catalyst system 1 showed a relatively high activity even at a low Al/Ni ratio and reached the maximum activity at the molar ratio of Al/Ni = 500, unlike system 3. Increases in the reaction temperature and propylene pressure favored an increase in the catalytic activity. The spectra of polypropylenes looked like those of propylene,ethylene copolymers containing syndiotactic propylene and ethylene sequences. At the same temperature and pressure, system 2 presented the highest number of propylene sequences, and system 3 presented the lowest. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 458,466, 2006 [source]

Syndiospecific polymerization of styrene with BzCpTiCl3 and methylaluminoxane as cocatalysts

JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 16 2001
Constantin Schwecke
Abstract Benzyl cyclopentadienyl titanium trichloride (BzCpTiCl3) was synthesized from benzyl bromide, cyclopentadienyl lithium, and titanium tetrachloride and used in combination with methylaluminoxane (MAO) for the syndiospecific polymerization of styrene. Kinetic measurements of the polymerization were carried out at different temperatures. The polymerization with BzCpTiCl3/MAO differs from the polymerization with cyclopentadienyl titanium trichloride in its behavior toward the Al/Ti ratio. In addition, high activities are observed at high Al/Ti ratios. By analyzing the polymerization runs and the physical properties of the polymers with differential scanning calorimetry, 13C NMR spectroscopy, wide-angle X-ray scattering measurements, and gel permeation chromatography, we found that the phenyl ring coordinates to the titanium atom during polymerization. Other known substitutions of the cyclopentadienyl ring (V. Scholz, Dissertation, University of Hamburg, 1998) in principle influence the polymerization activity. The physical properties of the polymers produced by the catalysts already known are nearly identical. BzCpTiCl3 is the first catalyst that leads to polystyrene obviously different from the polystyrene produced by other highly active catalysts. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 2805,2812, 2001 [source]

Borane chain transfer reaction in olefin polymerization using trialkylboranes as chain transfer agents

FTIR, 13C NMR, and GPC analysis of high-propylene content co- and terpolymers with ethylene and higher ,-olefins synthesized with EtInd2ZrCl2/MAO

JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 12 2001
M. L. Ferreira
Abstract This article reports the results of propylene/,-olefin copolymerization and propylene/ethylene/,-olefin terpolymerization using low concentrations (less than 5 mol %) of long ,-olefins such as 1-octene, 1-decene, and 1-dodecene. Kinetics data are presented and discussed. The highest activity was found with the longest ,-olefin studied (1-dodecene). A possible explanation is proposed for this and other characteristics of the polymers obtained. The effect of low-ethylene contents (4 mol % in the gas phase) on the copolymerization of propylene/,-olefins was also examined. The polymers synthesized were characterized by 13C NMR, gel permeation chromatography, DSC, Fourier transform infrared spectroscopy, and wide-angle X-ray scattering. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 2005,2018, 2001 [source]

Conservation Strategies for Endemic Fish Species Threatened by the Three Gorges Dam

CONSERVATION BIOLOGY, Issue 6 2003
YOUNG-SEUK PARK
diseño de reserva; especies endémicas; modelo de comunidad; peces; presa Three Gorges Abstract: The largest damming project to date, the Three Gorges Dam has been built along the Yangtze River (China), the most species-rich river in the Palearctic region. Among 162 species of fish inhabiting the main channel of the upper Yangtze, 44 are endemic and are therefore under serious threat of global extinction from the dam. Accordingly, it is urgently necessary to develop strategies to minimize the impacts of the drastic environmental changes associated with the dam. We sought to identify potential reserves for the endemic species among the 17 tributaries in the upper Yangtze, based on presence/absence data for the 44 endemic species. Potential reserves for the endemic species were identified by characterizing the distribution patterns of endemic species with an adaptive learning algorithm called a "self-organizing map" (SOM). Using this method, we also predicted occurrence probabilities of species in potential reserves based on the distribution patterns of communities. Considering both SOM model results and actual knowledge of the biology of the considered species, our results suggested that 24 species may survive in the tributaries, 14 have an uncertain future, and 6 have a high probability of becoming extinct after dam filling. Resumen: El proyecto de represa más grande a la fecha, la Presa Three Gorges fue construida en el Río Yangtze (China), el río con mayor riqueza de especies en la región Paleártica. Entre las 162 especies de peces que habitan el canal principal del alto Yangtze, 44 son endémicas y por tanto están seriamente amenazadas de extinción global por la presa. Consecuentemente, es urgente desarrollar estrategias para minimizar los impactos de los cambios ambientales drásticos asociados con la presa. Tratamos de identificar las reservas potenciales para las especies endémicas entre los 17 afluentes en el alto Yangtze, en base a datos de presencia y ausencia de las 44 especies endémicas. Se identificaron las reservas potenciales para la especies endémicas caracterizando los patrones de distribución de especies endémicas con un algoritmo de aprendizaje adaptivo denominado "mapa auto-organizante" (MAO). Con este método, también predijimos las probabilidades de ocurrencia de especies en reservas potenciales en base a los patrones de distribución de las comunidades. Tomando en cuenta tanto los resultados del modelo MAO como el conocimiento actual de la biología de especies en consideración, nuestros resultados sugieren que 24 especies pueden sobrevivir en los afluentes, 14 tienen un futuro incierto y 6 tienen una alta probabilidad de extinguirse después del llenado de la presa. [source]

An Emerging Market's Reaction to Initial Modified Audit Opinions: Evidence from the Shanghai Stock Exchange,

CONTEMPORARY ACCOUNTING RESEARCH, Issue 3 2000
CHARLES J. P. CHEN
Abstract This study investigates the valuation effect of modified audit opinions (MAOs) on the emerging Chinese stock market. Here, the term MAO refers to both qualified opinions and unqualified opinions with explanatory notes. The latter can be considered an alternative form of a qualified opinion in China. The institutional setting in China enables us to find compelling evidence in support of the monitoring role of independent auditing as an institution. First, we find a significantly negative association between MAOs and cumulative abnormal returns after controlling for effects of other concurrent announcements. Further, results from a by-year analysis suggest that investors did not reach negative consensus about MAOs' valuation effect until the second year, exhibiting the learning process of a market without prior exposure to MAOs. Second, we do not observe significant differences between market reaction to non-GAAP- and GAAP-violation-related MAOs. Third, no significant difference is found between market reaction to qualified opinions and market reaction to unqualified opinions with explanatory notes. [source]

Ethene Polymerization Behavior of MAO-Activated Dichloridotitanium Complexes Bearing Bi- and Tetradentate Salicylaldimine Derivatives

EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 2 2010
Antti Pärssinen
Abstract New chiral bridged tetradentate (N2O2)TiIVCl2 -type complexes bearing dimethylbiphenyl (1-Ti,3-Ti) and previously published binaphthyl-bridged (4-Ti) complex were synthesized with high yields. This was achieved by treating the corresponding Schiff-base ligand (H2L) precursors with Ti(NMe2)4, followed by conversion of these diamido complexes to LTiCl2 derivatives by the addition of excess of Me3SiCl. A series of unbridged titanium complexes 5-Ti,8-Ti with similar substituents at the phenoxy group were studied and their polymerization properties, after methylaluminoxane (MAO) activation, compared with the above bridged complexes. It was found that the catalysts bearing chiral tetradentate biaryl-bridged salicylaldimine ligands produce multimodal polyethylene (PE) with low activity [below 10 kgPE/(molTi,h,bar)] while their unbridged analogues provide activities that are 10,1000 times greater under similar reaction conditions. The reasons for this dramatic difference in polymerization activities are discussed based on the stabilities of the different cationic species configurations. [source]

Nickel Complexes and Cobalt Coordination Polymers with Organochalcogen (S, Se) Ligands Bearing an N -Methylimidazole Moiety: Syntheses, Structures, and Properties,

EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 26 2008
Wei-Guo Jia
Abstract The organochalcogen ligands (S, Se) derived from 3-methylimidazole-2-thione/selone groups mbit (2a), mbis (2b), ebit (2c), and ebis (2d) [mbit = 1,1,-methylenebis(1,3-dihydro-3-methyl-2H -imidazole-2-thione), mbis = 1,1,-methylenebis(1,3-dihydro-3-methyl-2H -imidazole-2-selone), ebit = 1,1,-(1,2-ethanediyl)bis(1,3-dihydro-3-methyl-1H -imidazole-2-thione), ebis = 1,1,-(1,2-ethanediyl)bis(1,3-dihydro-3-methyl-1H -imidazole-2-selone)] were synthesized and characterized. Mononuclear NiII complexes NiBr2mbit (3a), NiBr2mbis (3b), NiBr2ebit (3c), and NiBr2ebis (3d) were obtained by the reactions of Ni(PPh3)2Br2 with 2a, 2b, 2c, and 2d, respectively. However, when the corresponding ligands 2a, 2b, 2c, and 2d were treated with CoCl2 in thf solution CoII 1D coordination polymers (CoCl2mbit)n (4a), (CoCl2mbis)n (4b), (CoCl2ebit)n (4c), and (CoCl2ebis)n (4d) were obtained. All compounds were fully characterized by IR spectroscopy and elemental analysis. The crystal structures of 2c, 3a, 3b, 3c, 4a, 4b, and 4c were determined by X-ray crystallography. The local geometry around the nickel atom in complexes 3a,c was distorted tetrahedron with coordinated S(Se) and two Br atoms, and the organochalcogen ligands form an eight- or a nine-membered ring with the nickel atom included. The cobalt atom coordination polymers 4a and 4b coexist as left-handed and right-handed helical chains, but 4c formed a zigzag chain with a CH3CN solvent molecule taken up in the channel structure. After activation with methylaluminoxane (MAO), the nickel complexes exhibited high activities for addition polymerization of norbornene (1.42,×,108 g,PNBmol,1,Nih,1 for 3a). The effects of the Al/Ni ratio, reaction temperature, and reaction time to norbornene polymerization were also investigated.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source]

Pyridine Carboxylate Complexes of MoII as Active Catalysts in Homogeneous and Heterogeneous Polymerization

EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 18 2007
Maria Vasconcellos-Dias
Abstract New lamellar materials intercalated with molybdenum(II) complexes with potential catalytic properties were prepared by a stepwise procedure. The lamellar material was first calcined at 823 K for four hours to eliminate all the carbonate ions; the layered structure was reconstructed after treatment with a solution of either pycH (pyridine-2-carboxylic acid) or pydcH2 (pyridine-2,6-dicarboxylic acid) in a KOH solution of dmf at 343 K. Impregnation with a solution of the organometallic precursor [Mo(CO)3I2(NCCH3)2] led to substitution of the nitrile groups by two pyridine ligands. All the materials were characterized by powder X-ray diffraction, FTIR, and 13C CP MAS and 27Al MAS solid-state NMR spectroscopy. Similar MoII complexes were also prepared by using pycH or pydcH2 and characterized by elemental analysis as well as FTIR and 1H and 13C solution NMR spectroscopy. These new materials and the complexes of pyc or pydc ligands containing 4.54 wt.-% and 6.33 wt.-% of Mo respectively, catalyze the ring-opening-metathesis polymerization of norbornene and the polymerization of styrene at 333 K, their performance increasing upon the addition of methylalumoxane (MAO) as cocatalyst.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source]

Cobalt and Nickel Complexes Bearing Pyrazolyliminophosphorane Ligands: Synthesis, Characterisation and Catalytic Ethylene Oligomerisation Behaviour

EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 23 2006
Cheng Zhang
Abstract Treatment of 1-(2,-azidophenyl)-3,5-dimethylpyrazole (1) with Ph2PR (R = Ph, Me) and (Ph2P)2CH2, respectively, affords the pyrazolyliminophosphoranes 2, 3 and 4. Reaction of 2 or 3 with [NiCl2(dme)] or NiBr2 yields the N,N-chelate nickel complexes 5,8, and with CoCl2 complexes 9 and 10. Reaction of 4 with [NiCl2(dme)], NiBr2 and CoCl2, respectively, affords the N,N,P-chelate complexes 11,13. Compounds 2,4 were characterised by 1H, 13C, 31P NMR and IR spectroscopy and elemental analysis, while complexes 5,13 were characterised by IR spectroscopy and elemental analysis. The structures of complexes 5, 9 and 12 were further characterised by single-crystal X-ray diffraction techniques. Complexes 5,13 are active catalysts for ethylene oligomerisation upon activation with alkylaluminium derivatives(Et2AlCl, MAO or MMAO). These complexes exhibit good to high catalytic activities (up to 3.54,×,106 g,mol,1,h,atm for the nickel complexes and 5.48,×,105 g,mol,1,h,atm for the cobalt complexes). The effects of varying ethylene pressure, temperature and aluminium co-catalyst/Ni or Co ratios with complexes 5, 9, 11 and 12 are reported. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source]

Carbosilane Dendrons Functionalized at Their Focal Point

EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 18 2005
Román Andrés
Abstract The Si,Ph bond of PhSi[(CH2)3SiMe2Bz]3 (5) is cleaved with triflic acid to give TfOSi[(CH2)3SiMe2Bz]3, which, in turn, reacts with triethylammonium chloride or potassium cyclopentadienide to give, respectively, ClSi[(CH2)3SiMe2Bz]3 (8) and (C5H5)Si[(CH2)3SiMe2Bz]3 (10). This strategy can be applied to the post-growth incorporation of nucleophiles to the focal point of carbosilane dendritic wedges. In this way, cyclopentadiene-functionalized dendritic wedges of second and third generation C5H5 -Gn -[(CH2)3SiMe2Bz]x (n = 2, x = 9, 11; n = 3, x = 27, 12) have been obtained starting from Ph-Gn -[(CH2)3SiMe2Bz]x (6, 7). The metallocenes [{(BzMe2SiCH2CH2CH2)3SiC5H4}2MCl2] (M = Ti, 14; Zr, 15) have also been obtained from 10 and their catalytic behavior in ethylene and propylene polymerization, using MAO as a cocatalyst, has been studied and compared to that of related non-dendritic complexes. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source]

Studies of the Nature of the Catalytic Species in the ,-Olefin Polymerisation Processes Generated by the Reaction of Diamido(cyclopentadienyl)titanium Complexes with Aluminium Reagents as Cocatalysts

EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 2 2005
Vanessa Tabernero
Abstract The reaction of the diamido(chloro)cyclopentadienyltitanium compounds TiCpRx[1,2-C6H4(NR,)2]Cl [CpRx = ,5 -C5H5, ,5 -C5(CH3)5, ,5 -C5H4(SiMe3); R, = CH2tBu, Pr] with the Grignard reagent MgClR (R = Me, CH2Ph) affords the monomethyl and monobenzyl derivatives TiCpRx[1,2-C6H4(NR,)2]R. Upon addition of methylaluminoxane (MAO), the chloro- and alkyltitanium complexes show low activity towards the polymerisation of ethylene and styrene. However, no methylation was observed during the treatment of trimethylaluminium with the chloro compounds TiCpRx[1,2-C6H4(NR,)2]Cl. Instead, these reactions give the dinuclear aluminium complexes Al2[1,2-C6H4(NR,)2]Me4 (R, = CH2tBu, Pr) through transmetallation of the diamido ligand, suggesting a deactivation process of the catalysts in the olefin polymerisation reactions. In an additional effort to model the catalytic species, stoichiometric reactions between the methyl derivatives TiCpRx[1,2-C6H4(NR,)2]Me and solid methylaluminoxane (MAO) were studied by NMR spectroscopy. Monitoring of these reactions revealed the formation of zwitterionic species depending on the nature of the solvent. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source]

Monoamine oxidase A rather than monoamine oxidase B inhibition increases nicotine reinforcement in rats

EUROPEAN JOURNAL OF NEUROSCIENCE, Issue 12 2006
Karine Guillem
Abstract Although nicotine is considered to be responsible for the addictive properties of tobacco, growing evidence underlines the importance of non-nicotine components in smoking reinforcement. It has been shown that tobacco smoke contains monoamine oxidase (MAO) A and B inhibitors and decreases MAO-A and MAO-B activity in smokers. Here, we investigated the effects of clorgyline hydrochloride (irreversible MAO-A inhibitor; 2 mg/kg/day), selegiline (irreversible MAO-B inhibitor; 4 mg/kg) and the beta-carboline norharmane hydrochloride (reversible MAO-B inhibitor; 5 mg/kg/day) treatments on nicotine self-administration (30 µg/kg/infusion, free base) in rats. Independent of the responsiveness to novelty and locomotor activity stimulation, only clorgyline hydrochloride treatment increased the intake of nicotine in a fixed-ratio schedule (FR5) of reinforcement. When a progressive-ratio schedule was implemented, both clorgyline hydrochloride and norharmane hydrochloride treatments potentiated the reinforcing effects of nicotine, whereas selegiline had no effect. Taken together, these results indicate that MAO-A inhibition interacts with nicotine to enhance its rewarding effects in rats and suggest that other compounds present in tobacco, such as beta-carboline, may also play an important role in sustaining smoking behavior in humans. [source]

The Extraordinary Cocatalytic Action of Polymethylaluminoxane (MAO) in the Polymerization of Terminal Olefins by Metallocenes: Chemical Change in the Group 4 Metallocene Dimethyl Derivatives Induced by MAO,

EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 20 2005
John J. Eisch
Abstract In the polymerization of olefins with Group 4 metallocene dichlorides or dimethyl derivatives as procatalysts the use of polymethylaluminoxane (MAO) as the cocatalyst, especially in extreme excess (102,103 times the metallocene equivalent), has been shown to have an extraordinary accelerating effect on the rate of olefin polymerization, when compared with the cocatalytic action of alkylaluminum halides. In attempts at explaining the greatly superior catalytic activity of MAO in olefin polymerization (the MAO conundrum), hypotheses have generally paralleled the steps involved in the cocatalytic action of RnAlCl3,n, namely the alkylation of Cp2MtCl2, ionization of Cp2Mt(R)Cl into the metallocenium cation, [Cp2Mt,R]+, and anion, [Rn,1AlCl4,n], and subsequent ion-pair separation. In order to understand any differences in catalytic action between such cocatalysts, we have studied the individual action of MAO (100 equiv.) and of MeAlCl2 (1,2 equiv.) on each of the Group 4 metallocene derivatives, Cp2TiCl2, Cp2ZrCl2, Cp2Ti(CH3)2 and Cp2Zr(CH3)2. With MeAlCl2 each of the metallocene derivatives appeared to form the cation, [Cp2Mt,CH3]+, with greater (Ti) or lesser (Zr) ease, because an alkyne such as diphenylacetylene was then found to insert into the Mt,CH3 bond stereoselectively. In striking contrast, treatment of each metallocene with MAO gave two reactions very different from MeAlCl2, namely a steady evolution of methane gas upon mixing and a finding upon hydrolytic workup that the diphenylacetylene present had undergone no insertion into the Mt,CH3 bond but instead had been reductively dimerized completely to (E,E)-1,2,3,4-tetraphenyl-1,3-butadiene. To account for this astonishing difference in chemical behavior between MAO and MeAlCl2 in their cocatalytic activation of Group 4 metallocenes to olefin polymerization, it is necessary to postulate a novel, unique sequence of reaction steps occurring between MAO and the metallocene. If one starts with the metallocene dichloride, then the free TMA present in the MAO would generate the Cp2Mt(CH3)2. This metallocene dimethyl derivative, complexed with an oligomeric MAO unit, would undergo a transfer-epimetallation with added olefin or acetylene to form a metallacyclopropane or metallacyclopropene, respectively. With added diphenylacetylene the resulting 2,3-diphenylmetallacyclopropene would be expected rapidly to insert a second alkyne to form the 2,3,4,5-tetraphenyl-1-metallacyclopentadiene. Simple hydrolysis of the latter intermediate would generate (E,E)-1,2,3,4-tetraphenyl-1,3-butadiene while alternative workup with D2O would give the 1,4-dideuterio derivative of this butadiene. Both such expectations were confirmed by experiment. In the case of added olefin, similar metallacyclopropane and metallacyclopentane intermediates should be produced until ring opening of the latter five-membered ring leads to an open-chain zwitterion, a process having ample precedent in the research of Gerhard Erker. The solution to the MAO conundrum then, namely the extraordinary cocatalytic activity of MAO in olefin polymerization by metallocenes, lies in the unique catalytic activation of the Group 4 metallocene dimethyl derivative, which occurs by transfer-epimetallation of the olefin monomer by the Cp2Mt(CH3)2,MAO complex. The most advantageous Lewis acidic sites in the MAO,oligomeric mixture for such metallocene,MAO complexation are suggested to be terminal Me2Al,O,AlMe, segments of an open-chain oligomer. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source]

Biotransformation of xenobiotics by amine oxidases

FUNDAMENTAL & CLINICAL PHARMACOLOGY, Issue 2 2001
Margherita Strolin Benedetti
Although the cytochrome P450 (CYP) system ranks first in terms of catalytic versatility and the wide range of xenobiotics it detoxifies or activates to reactive intermediates, the contribution of amine oxidases and in particular of monoamine oxidases (MAOs) to the metabolism of xenobiotics is far from negligible but has been largely neglected. In this review on the involvement of amine oxidases in the metabolism of xenobiotics, the major characteristics reported for the CYP system (protein, reaction, tissue distribution, subcellular localisation, substrates, inhibitors, inducers, genetic polymorphism, impact of different physiopathological conditions on the activity, turnover) will be compared, whenever possible, with the corresponding characteristics of amine oxidases (MAOs in particular). The knowledge of the involvement of MAO-A, -B or both in the metabolism of a drug allows us to predict interactions with selective or non-selective MAO inhibitors (e.g. the metabolism of a drug deaminated by both forms of MAO is not necessarily inhibited in vivo by a selective MAO-A or -B inhibitor). If a drug is metabolized by MAOs, competitive interactions can occur with other drugs that are MAO substrates, e.g. with ,-adrenoceptor agonists and antagonists, prodrugs of dopamine, serotonin 5-HT1 -receptor agonists as well as with primaquine, flurazepam and citalopram. Moreover, the knowledge of the involvement of MAOs in the metabolism of a drug may suggest possible, although not obligatory, interactions with tyramine-containing food or drink, with over the counter medicines sold to relieve the symptoms of coughs and colds (generally containing the indirectly-acting sympathomimetic amine phenylpropanolamine) or with phenylephrine-containing preparations. Finally, biotransformation by amine oxidases, as by CYP, does not always lead to detoxication but can produce toxic compounds. [source]

Association of 5-HTT gene polymorphism, platelet MAO activity, and drive for thinness in a population-based sample of adolescent girls

INTERNATIONAL JOURNAL OF EATING DISORDERS, Issue 5 2008
Kirsti Akkermann MSc
Abstract Objective: Several lines of evidence suggest that alterations in serotonergic activity contribute to the pathophysiology of abnormal eating behaviors. Since platelet monoamine oxidase (MAO) activity and the 5-HT transporter gene promoter polymorphism (5-HTTLPR) have been associated with eating disorders, the knowledge from a population-based sample may provide useful information which changes in 5-HT function observed in eating disorders represent trait vs. state effects. Method: The sample was based on both cohorts of the Estonian Children Personality, Behavior and Health Study (ECPBHS). The current study was conducted during the second follow-up where altogether 82% from the original sample was recruited. EDI-2 subscales,Drive for Thinness and Bulimia,were used to determine eating attitudes and behaviors. Platelet MAO activity was measured and the participants were genotyped for the 5-HTTLPR. Results: Allelic variation of 5-HTTLPR or platelet MAO activity were not independently associated with drive for thinness or binge eating, but girls homozygous for the 5-HTTLPR long allele and with high platelet MAO activity, both considered indicators of a higher capacity 5-HT system, exhibited higher scores of drive for thinness. Conclusion: The results suggest that drive for thinness is the highest in girls with the presence of two markers of higher serotonergic capacity. © 2008 by Wiley Periodicals, Inc. Int J Eat Disord 2008 [source]

Polystyrene-Supported 2-Arylindenyl Zirconocene Catalysts for Propylene Polymerization

ISRAEL JOURNAL OF CHEMISTRY, Issue 4 2002
Stephen C. Diehl
Mono- and bis 2-arylindenyl zirconocene/methylalumoxane (MAO) catalysts are prepared on a crosslinked polystyrene resin using gel-phase organic reactions. The 2-arylindene ligands are bonded to the polystyrene backbone through a disiloxane linkage, and the zirconocene is prepared directly on the support in high yield. These supported 2-arylindenylzirconocenes in the presence of MAO show high activity and yield polypropylenes with microstructures similar to those produced by the analogous solution-phase catalysts. [source]

Preparation of ethylene/1-octene copolymers from ethylene stock with tandem catalytic system

Monoamine oxidase activity in kidney and heart of Piaractus mesopotamicus (Holmberg)

JOURNAL OF FISH BIOLOGY, Issue 6 2007
C. M. C. Salles
The values of Michaelis,Menten constant (KM) and maximum velocity (VMAX) for kidney and heart monoamine oxidase (MAO) from pacu Piaractus mesopotamicus were determined. The mean ±s.e. KM values were 17·28 ± 2·27 ,M for kidney and 15·38 ± 1·86 ,M for heart. MAO activities were 111·60 ± 3·25 and 15·12 ± 0·30 nmols min,1 g,1 of wet tissue for kidney and heart, respectively. In addition, MAO inhibitory studies in these two tissues indicate that this enzyme may be a different isoform of MAO. [source]

Efficient synthesis and formulation of (R)-(,)-[11C]Deprenyl, a selective radioligand for the quantification of MAO-B activity using PET

JOURNAL OF LABELLED COMPOUNDS AND RADIOPHARMACEUTICALS, Issue 10 2002
Frédéric Dolle
Abstract Carbon-11 labeled (R)-(,)-Deprenyl is the tracer of reference for the quantification of monoamine oxidase (MAO)-B activity with PET. In this paper, its radiosynthesis is re-investigated and oriented towards the preparation of multi-milliCuries of radiotracer. Typically, using no-carrier-added [11C]methyl triflate as the alkylating agent, 140,190 mCi (5.1,7.0 GBq) of (R)-(,)-[11C]Deprenyl was obtained within 30 min of radiosynthesis (including HPLC purification and formulation) with specific radioactivities ranging from 0.8 to 1.2 Ci/,mol (29.6,44.4 GBq/,mol). The high efficiency of these radiosyntheses allows for multi-injection protocols and kinetic approaches for absolute quantification of the tracer. Copyright © 2002 John Wiley & Sons, Ltd. [source]

Synthesis of a 13C labeled N -cyclopropylamine tetrahydropyridine derivative

JOURNAL OF LABELLED COMPOUNDS AND RADIOPHARMACEUTICALS, Issue 10 2002
Simon Kuttab
Abstract The synthesis of 1-(2- 13C)-cyclopropyl-4-phenyl-1,2,3,6-tetrahydropyridine (8) is reported. Attempts were first made to prepare labeled cyclopropylamine via a cyclopropanation/Curtius rearrangement sequence, but the yields were too modest to be suitable for the synthesis of a labeled compound. The preparation of 8 was achieved via cyclopropanation of the N -formyl tetrahydropyridine derivative 21 using the Grignard reagent of ethyl bromide and Ti(O- iPr)4 as a catalyst. The synthesis proceeded in high yield (82%). The method has a wide potential for the synthesis of other cyclopropyl ring labeled and substituted cyclopropyl ring labeled tetrahydropyridine dervatives which can be used in Monoamine Oxidase (MAO) and Cyt P450 enzymes mechanistic studies. Copyright © 2002 John Wiley & Sons, Ltd. [source]

Protection from MPTP-induced neurotoxicity in differentiating mouse N2a neuroblastoma cells

JOURNAL OF NEUROCHEMISTRY, Issue 3 2001
Luigi A. De Girolamo
We have shown previously that subcytotoxic concentrations of MPTP (1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine) inhibit axon outgrowth and are associated with increased neurofilament heavy chain (NF-H) phosphorylation in differentiating mouse N2a neuroblastoma cells while higher doses (>,100 µm) cause cell death. In this work we assessed the ability of potential neuroprotective agents to alleviate both MPTP-induced cell death (cytotoxicity) and MPTP-induced NF-H phosphorylation/reduction in axon outgrowth (neurotoxicity) in N2a cells induced to differentiate by dbcAMP. The neurotoxic effects of MPTP occurred in the absence of significant alterations in energy status or mitochondrial membrane potential. The hormone oestradiol (100 µm) reduced the cytotoxic effect of MPTP, but blocked di-butyryl cyclic AMP (dbcAMP)-induced differentiation, i.e. axon outgrowth. Both the cytotoxic and neurotoxic effects of MPTP were reduced by the monoamine osidase (MAO) inhibitors deprenyl and, to a lesser extent, clorgyline. Alleviation of both neurotoxicity and cytotoxicity was also achieved by conditioned medium derived from rat C6 glioma cells. In contrast, whilst the p38 MAP kinase inhibitor, SB202190, protected cells against MPTP-induced neurotoxicity, it could not maintain cell viability at high MPTP exposures. In each case neuroprotection involved maintenance of the differentiating phenotype linked with attenuation of NF-H hyper-phosphorylation; the latter may represent a mechanism by which neuronal cells can moderate MPTP-induced neurotoxicity. The use of a simplified neuronal cell model, which expresses subtle biochemical changes following neurotoxic insult, could therefore provide a valuable tool for the identification of potential neuroprotective agents. [source]

Identification of Kaempferol as a Monoamine Oxidase Inhibitor and Potential Neuroprotectant in Extracts of Ginkgo Biloba Leaves

JOURNAL OF PHARMACY AND PHARMACOLOGY: AN INTERNATI ONAL JOURNAL OF PHARMACEUTICAL SCIENCE, Issue 4 2000
B. D. SLOLEY
The effects of Ginkgo biloba leaf extract on rat brain or livermonoamine oxidase (MAO)-A and -B activity, biogenic amine concentration in nervous tissue, N -methyl- d -aspartate (NMDA)- and N -(2-chloroethyl)- N -ethyl-2-bromobenzylamine (DSP-4)-induced neurotoxicity and antioxidant activity was investigated to determine the effects of the extract on monoamine catabolism and neuroprotection. Ginkgo biloba leaf extract was shown to produce in-vitro inhibition of rat brain MAO-A and -B. The Ginkgo biloba extract was chromatographed on a reverse-phase HPLC system and two of the components isolated were shown to be MAO inhibitors (MAOIs). These MAOIs were identified by high-resolution mass spectrometry as kaempferol and isorhamnetin. Pure kaempferol and a number of related flavonoids were examined as MAOIs in-vitro. Kaempferol, apigenin and chrysin proved to be potent MAOIs, but produced more pronounced inhibition of MAO-A than MAO-B. IC50 (50% inhibition concentration) values for the ability of these three flavones to inhibit MAO-A were 7 times 10,7, 1 times 10,6 and 2 times 10,6m, respectively. Ginkgo biloba leaf extract and kaempferol were found to have no effect ex-vivo on rat or mouse brain MAO or on concentrations of dopamine, noradrenaline, 5-hydroxytryptamine and 5-hydroxyindoleacetic acid. Kaempferol was shown to protect against NMDA-induced neuronal toxicity in-vitro in rat cortical cultures, but did not prevent DSP-4-induced noradrenergic neurotoxicity in an in-vivo model. Both Ginkgo biloba extract and kaempferol were demonstrated to be antioxidants in a lipid-peroxidation assay. This data indicates that the MAO-inhibiting activity of Ginkgo biloba extract is primarily due to the presence of kaempferol. Ginkgo biloba extract has properties indicative of potential neuroprotective ability. [source]

Catalytic synthesis of styryl-capped isotactic polypropylenes

JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 17 2010
Huahua Huang
Abstract Bis-styrenic molecules, 1,4-divinylbenzene (DVB) and 1,2-bis(4-vinylphenyl)ethane (BVPE), were successfully combined with hydrogen (H2) to form consecutive chain transfer complexes in propylene polymerization mediated by an isospecific metallocene catalyst (i.e., rac -dimethylsilylbis(2-methyl-4-phenylindenyl)zirconium dichloride, I) activated with methylaluminoxane (MAO), rendering a catalytic access to styryl-capped isotactic polypropylenes (i -PP). The chain transfer reaction took place in a unique way where prior to the ultimate chain transfer DVB/H2 or BVPE/H2 caused a copolymerization-like reaction leading to the formation of main chain benzene rings. A preemptive polymer chain reinsertion was deduced after the consecutive actions of DVB/H2 or BVPE/H2, which gave the styryl-terminated polymer chain alongside a metal-hydride active species. It was confirmed that the chain reinsertion occurred in a regio-irregular 1,2-fashion, which contrasted with a normal 2,1-insertion of styrene monomer and ensured subsequent continuous propylene insertions, directing the polymerization to repeated DVB or BVPE incorporations inside polymer chain. Only as a competitive reaction, the insertion of propylene into metal-hydride site broke the chain propagation resumption process while completed the chain transfer process by releasing the styryl-terminated polymer chain. BVPE was found with much higher chain transfer efficiency than DVB, which was attributed to its non-conjugated structure with much divided styrene moieties resulting in higher polymerization reactivity but lower chain reinsertion tendency. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3709,3713, 2010 [source]