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Concomitant Formation (concomitant + formation)
Selected AbstractsSelective Palladium-Catalysed ipso Arylation of ,,,-Disubstituted Benzo[b]thien-2-ylmethanols with Aryl Bromides using PCy3 as LigandEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 8 2007A. Beatrix Bíró Abstract ,,,-Diphenylbenzo[b]thien-2-ylmethanol was treated with a series of aryl bromides in the presence of palladium(II) acetate and tricyclohexylphosphane to give the appropriate 2-aryl-benzo[b]thiophenes in good to excellent yield with concomitant formation of benzophenone. The reaction wassuccessfully extended to ,,,-diphenylbenzo[b]thien-3-ylmethanol, although in certain cases the transformation was biased by concurrent ortho arylation. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source] Nanocrystalline Electroplated Cu,Ni: Metallic Thin Films with Enhanced Mechanical Properties and Tunable Magnetic BehaviorADVANCED FUNCTIONAL MATERIALS, Issue 6 2010Eva Pellicer Abstract Nanocrystalline 3,µm thick Cu1,xNix (0.45,,,x,,,0.87) films are electrodeposited galvanostatically onto Cu/Ti/Si (100) substrates, from a citrate- and sulphate-based bath containing sodium lauryl sulphate and saccharine as additives. The films exhibit large values of reduced Young's modulus (173,<,Er,<,192,GPa) and hardness (6.4,<,H,<,8.2,GPa), both of which can be tailored by varying the alloy composition. The outstanding mechanical properties of these metallic films can be ascribed to their nanocrystalline nature,as evidenced by X-ray diffraction, transmission electron microscopy, and atomic force microscopy,along with the occurrence of stacking faults and the concomitant formation of intragranular nanotwins during film growth. Due to their nanocrystalline character, these films also show very low surface roughness (root mean square deviation of around 2,nm). Furthermore, tunable magnetic properties, including a transition from paramagnetic to ferromagnetic behavior, are observed when the Ni percentage is increased. This combination of properties, together with the simplicity of the fabrication method, makes this system attractive for widespread technological applications, including hard metallic coatings or magnetic micro/nano-electromechanical devices. [source] A Tandem, Nitroalkene Conjugate Addition/[3+2] Cycloaddition Approach to the Synthesis of the Pentacyclic Core of (±)-ScandineADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 16-17 2006Scott Abstract The complete pentacyclic core of the melodinus alkaloid scandine has been synthesized. The synthetic strategy features two key steps: (1) a tandem nitroalkene conjugate addition/[3+2] cycloaddition of the resulting silyl nitronate and (2) an intramolecular Heck reaction of an aryl iodide with a ,-disubstituted allylic alcohol which set a highly congested, quaternary stereogenic center with the concomitant formation of an aldehyde. Intramolecular reductive amination with this aldehyde completed the pentacyclic core. [source] Protein Hydrolysate of Salted Duck Egg White as a Substitute of Phosphate and Its Effect on Quality of Pacific White Shrimp (Litopenaeus Vannamei)JOURNAL OF FOOD SCIENCE, Issue 8 2009Thammarat Kaewmanee ABSTRACT:, Protein hydrolysate from salted egg white (PHSEW) with different degrees of hydrolysis (DH) (3%, 6%, and 9%) was produced using pepsin. Disappearance of proteins with molecular weight (MW) of 108 and 85 kDa with the concomitant formation of proteins with MW of 23, 20, 13, and 5 kDa was observed in PHSEW. The use of PHSEW for quality improvement of Pacific white shrimp (Litopenaeus vannamei) was investigated. Shrimp soaked in 4% NaCl containing 7% PHSEW and 2.5% mixed phosphates (0.625% sodium acid pyrophosphate [SAPP] and 1.875% tetrasodium pyrophosphate [TSPP]) had the highest cooking yield with the lowest cooking loss (P,< 0.05), compared with shrimps with other treatments. Nevertheless, no difference in weight gain was obtained in comparison with those treated with 4% NaCl containing 3.5% mixed phosphate (P,> 0.05). Cooked shrimp treated with 4% NaCl containing 7% PHSEW and 2.5% mixed phosphate or those treated with 4% NaCl containing 3.5% mixed phosphate had the higher score of appearance, texture, and overall likeness but less shear force, in comparison with the control (no treatment) (P,< 0.05). Microstructure study revealed that muscle fibers of cooked shrimp from both treatments had the swollen fibrils and gaps, while the control had the swollen compact structure. Therefore, use of PHSEW could reduce phosphate residue in shrimps without an adverse effect on sensory properties. [source] Scavenging effect of melatonin on hydroxyl radicals generated by alloxanJOURNAL OF PINEAL RESEARCH, Issue 4 2000H.J. Brömme Alloxan can act as a generator of reactive oxygen species (ROS) as long as sufficient suitable reducing agents (e.g. reduced glutathione) and oxygen are available. Using electron spin resonance-spectroscopy and the oxygen-centered spin trap DEPMPO, we demonstrate that hydroxyl radicals (OHzrad;) are formed in vitro by alloxan in the presence of glutathione (GSH) and chelated divalent iron. Furthermore, peroxidation of polyunsaturated fatty acids from phosphatidylcholine-containing liposomes with concomitant formation of malondialdehyde (MDA) was used as a further indicator for a preceding OHzrad; formation. Melatonin, the main secretory product of the pineal gland, is an effective scavenger of OHzrad;. The 50%-inhibitor concentration (IC50-value) for melatonin to scavenge OHzrad; generated from the alloxan/GSH-reaction in the presence of ferrous ions was 23 ,mol/L. In contrast to the ability to effectively scavenge OHzrad;, the potential of melatonin to prevent lipid peroxidation is considerably less pronounced. [source] Zirconia-Based Metastable Solid Solutions through Self-Propagating High-Temperature Synthesis: Synthesis, Characterization, and Mechanistic InvestigationsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 8 2000Filippo Maglia Cubic Zr1,xMexOy(Me = Fe, Co, Ni, Cu) metastable solid solutions with metal content significantly higher than equilibrium levels have been synthesized by the self-propagating high-temperature synthesis method based on a thermite reaction between metallic zirconium and the transition-metal oxides CoO, Fe2O3, CuO, and NiO. Through in situ XRD analysis, it was determined that when heated to 1100°C, the cubic solid solution transformed to the tetragonal phase with the concomitant formation of iron oxide. When cooled to lower temperatures, the tetragonal phase transformed to the monoclinic phase at or below 500°C. Results of auxiliary experiments strongly suggest that the formation of the solid solution takes place behind the combustion front by a reaction between zirconia and the metal. [source] Primary Photoprocesses in a Fluoroquinolone Antibiotic Sarafloxacin,PHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 4 2009Fernando Lorenzo The photophysical properties of the fluoroquinolone antibiotic sarafloxacin (SFX) were investigated in aqueous media. SFX in water, at pH 7.4, shows intense absorption with peaks at 272, 322 and 335 nm, (, = 36800 and 17000 dm3 mol,1 cm,1, respectively). Both the absorption and emission properties of SFX are pH-dependent; pKa values for the protonation equilibria of both the ground (5.8 and 9.1) and excited singlet states (5.7 and 9.0) of SFX were determined spectroscopically. SFX fluoresces weakly, the quantum yield for fluorescence emission being maximum (0.07) at pH 8. Laser flash photolysis and pulse radiolysis studies have been carried out in order to characterize the transient species of SFX in aqueous solution. Triplet,triplet absorption has a maximum at 610 nm with a molar absorption coefficient of 17,000 ± 1000 dm3 mol,1 cm,1. The quantum yield of triplet formation has been determined to be 0.35 ± 0.05. In the presence of oxygen, the triplet reacts to form excited singlet oxygen with quantum yield of 0.10. The initial triplet (3A*) was found to react with phosphate buffer to form triplet 3B* with lower energy and longer lifetime and having an absorption band centered at 700 nm. SFX triplet was also found to oxidize tryptophan to its radical with concomitant formation of the anion radical of SFX. Hence the photosensitivity of SFX could be initiated by the oxygen radicals and/or by SFX radicals acting as haptens. [source] Mouse hepatitis coronavirus replication induces host translational shutoff and mRNA decay, with concomitant formation of stress granules and processing bodiesCELLULAR MICROBIOLOGY, Issue 9 2007Matthijs Raaben Summary Many viruses, including coronaviruses, induce host translational shutoff, while maintaining synthesis of their own gene products. In this study we performed genome-wide microarray analyses of the expression patterns of mouse hepatitis coronavirus (MHV)-infected cells. At the time of MHV-induced host translational shutoff, downregulation of numerous mRNAs, many of which encode protein translation-related factors, was observed. This downregulation, which is reminiscent of a cellular stress response, was dependent on viral replication and caused by mRNA decay. Concomitantly, phosphorylation of the eukaryotic translation initiation factor 2, was increased in MHV-infected cells. In addition, stress granules and processing bodies appeared, which are sites for mRNA stalling and degradation respectively. We propose that MHV replication induces host translational shutoff by triggering an integrated stress response. However, MHV replication per se does not appear to benefit from the inhibition of host protein synthesis, at least in vitro, since viral replication was not negatively affected but rather enhanced in cells with impaired translational shutoff. [source] Mapping the Transformation [{RuII(CO)3Cl2}2],[RuI2(CO)4]2+: Implications in Binuclear Water,Gas Shift ChemistryCHEMISTRY - A EUROPEAN JOURNAL, Issue 8 2010Moumita Majumdar Abstract The complete sequence of reactions in the base-promoted reduction of [{RuII(CO)3Cl2}2] to [RuI2(CO)4]2+ has been unraveled. Several ,-OH, ,:,2 -CO2H-bridged diruthenium(II) complexes have been synthesized; they are the direct results of the nucleophilic activation of metal-coordinated carbonyls by hydroxides. The isolated compounds are [Ru2(CO)4(,:,2 - C,O -CO2H)2(,-OH)(NPF -Am)2][PF6] (1; NPF -Am=2-amino-5,7-trifluoromethyl-1,8-naphthyridine) and [Ru2(CO)4(,:,2 - C,O -CO2H)(,-OH)(NP-Me2)2][BF4]2 (2), secured by the applications of naphthyridine derivatives. In the absence of any capping ligand, a tetranuclear complex [Ru4(CO)8(H2O)2(,3 -OH)2(,:,2 - C,O -CO2H)4][CF3SO3]2 (3) is isolated. The bridging hydroxido ligand in 1 is readily replaced by a ,-donor chlorido ligand, which results in [Ru2(CO)4(,:,2 - C,O -CO2H)2(,-Cl)(NP-PhOMe)2][BF4] (4). The production of [Ru2(CO)4]2+ has been attributed to the thermally induced decarboxylation of a bis(hydroxycarbonyl),diruthenium(II) complex to a dihydrido,diruthenium(II) species, followed by dinuclear reductive elimination of molecular hydrogen with the concomitant formation of the RuIRuI single bond. This work was originally instituted to find a reliable synthetic protocol for the [Ru2(CO)4(CH3CN)6]2+ precursor. It is herein prescribed that at least four equivalents of base, complete removal of chlorido ligands by TlI salts, and heating at reflux in acetonitrile for a period of four hours are the conditions for the optimal conversion. Premature quenching of the reaction resulted in the isolation of a trinuclear RuI2RuII complex [{Ru(NP-Am)2(CO)}{Ru2(NP-Am)2(CO)2(,-CO)2}(,3:,3 - C,O,O, -CO2)][BF4]2 (6). These unprecedented diruthenium compounds are the dinuclear congeners of the water,gas shift (WGS) intermediates. The possibility of a dinuclear pathway eliminates the inherent contradiction of pH demands in the WGS catalytic cycle in an alkaline medium. A cooperative binuclear elimination could be a viable route for hydrogen production in WGS chemistry. [source] Photohydroxylation of 1,4-Benzoquinone in Aqueous Solution RevisitedCHEMISTRY - A EUROPEAN JOURNAL, Issue 2 2004Justus von Sonntag Dr. Abstract In water, photolysis of 1,4-benzoquinone, Q gives rise to equal amounts of 2-hydroxy-1,4-benzoquinone HOQ and hydroquinone QH2 which are formed with a quantum yield of ,=0.42, independent of pH and Q concentration. By contrast, the rate of decay of the triplet (,max=282 and ,410 nm) which is the precursor of these products increases nonlinearly (k=(2,3.8)×106 s,1) with increasing Q concentration ((0.2,10) mM). The free-radical yield detected by laser flash photolysis after the decay of the triplet also increases with increasing Q concentration but follows a different functional form. These observations are explained by a rapid equilibrium of a monomeric triplet Q* and an exciplex Q2* (K=5500±1000,M,1). While Q* adds water and subsequent enolizes into 1,2,4-trihydroxybenzene Ph(OH)3, Q2* decays by electron transfer and water addition yielding benzosemiquinone .QH and . OH adduct radicals .QOH. The latter enolizes to the 2-hydroxy-1,4-semiquinone radical .Q(OH)H within the time scale of the triplet decay and is subsequently rapidly (microsecond time scale) oxidized by Q to HOQ with the concomitant formation of .QH. On the post-millisecond time scale, that is, when .QH has decayed, Ph(OH)3 is oxidized by Q yielding HOQ and QH2 as followed by laser flash photolysis with diode array detection. The rate of this pH- and Q concentration-dependent reaction was independently determined by stopped-flow. This shows that there are two pathways to photohydroxylation; a free-radical pathway at high and a non-radical one at low Q concentration. In agreement with this, the yield of Ph(OH)3 is most pronounced at low Q concentration. In the presence of phosphate buffer, Q* reacts with H2PO4, giving rise to an adduct which is subsequently oxidized by Q to 2-phosphato-1,4-benzoquinone QP. The current view that . OH is an intermediate in the photohydroxylation of Q has been overturned. This view had been based on the observation of the . OH adduct of DMPO when Q is photolyzed in the presence of this spin trap. It is now shown that Q*/Q2* oxidizes DMPO (k ,1×108,M,1,s,1) to its radical cation which subsequently reacts with water. Q*/Q2* react with alcohols by H abstraction (rates in units of M,1,s,1): methanol (4.2×107), ethanol (6.7×107), 2-propanol (13×107) and tertiary butyl alcohol (,0.2×107). DMSO (2.7×109) and O2 (,2×109) act as physical quenchers. [source] Dithiolate-Bridged Fe-Ni-Fe Trinuclear Complexes Consisting of Fe(CO)3,n(CN)n (n=0, 1) Components Relevant to the Active Site of [NiFe] HydrogenaseCHEMISTRY - AN ASIAN JOURNAL, Issue 6 2009Satyanarayan Pal Dr. Abstract Step-by-step: A trinuclear Fe-Ni-Fe complex 1 was synthesized from the reaction of [Fe(CO)4I2] with Li2[Ni(norbornane- exo -2,3-dithiolate)2]. The CO ligands in 1 were transformed into CN, upon treatment with ,N(SiMe3)2, and the monocyanide complex 3 and the dicyanide complex 4 were obtained. Complexes 3 and 4 were found to react with protonic acids, whereas 1 is robust. A dithiolate-bridged Fe-Ni-Fe trinuclear carbonyl complex [(CO)3Fe(,-ndt)Ni(,-ndt)Fe(CO)3] (1, ndt=norbornane- exo -2,3-dithiolate) has been synthesized from the reaction of [Fe(CO)4I2] and Li2[Ni(ndt)2]. This reaction was found to occur with concomitant formation of a tetranuclear cluster [Ni3(,-ndt)4FeI] (2). Treatment of 1 with Na[N(SiMe3)2] transforms some of the CO ligands into CN,, and the monocyanide complex (PPh4)[(CO)2(CN)Fe(,-ndt)Ni(,-ndt)Fe(CO)3] (3) and the dicyanide complex (PPh4)2[(CO)2(CN)Fe(,-ndt)Ni(,-ndt)Fe(CO)2(CN)] (4) were isolated. X-ray structural analyses of the trinuclear complexes revealed a Fe-Ni-Fe array in which the metal centers are connected by the ndt sulfur bridges and direct FeNi bonds. Hydrogen bonding between the CN ligand in 3 and cocrystallized ethanol was found in the solid-state structure. The monocyanide complex 3 and dicyanide complex 4 reacted with acids such as HOTf or HCl generating insoluble materials, whereas complex 1 did not react. [source] Facile Oxidation of Leucomethylene Blue and Dihydroflavins by Artemisinins: Relationship with Flavoenzyme Function and Antimalarial Mechanism of ActionCHEMMEDCHEM, Issue 8 2010Richard Abstract The antimalarial drug methylene blue (MB) affects the redox behaviour of parasite flavin-dependent disulfide reductases such as glutathione reductase (GR) that control oxidative stress in the malaria parasite. The reduced flavin adenine dinucleotide cofactor FADH2 initiates reduction to leucomethylene blue (LMB), which is oxidised by oxygen to generate reactive oxygen species (ROS) and MB. MB then acts as a subversive substrate for NADPH normally required to regenerate FADH2 for enzyme function. The synergism between MB and the peroxidic antimalarial artemisinin derivative artesunate suggests that artemisinins have a complementary mode of action. We find that artemisinins are transformed by LMB generated from MB and ascorbic acid (AA) or N -benzyldihydronicotinamide (BNAH) in,situ in aqueous buffer at physiological pH into single electron transfer (SET) rearrangement products or two-electron reduction products, the latter of which dominates with BNAH. Neither AA nor BNAH alone affects the artemisinins. The AA,MB SET reactions are enhanced under aerobic conditions, and the major products obtained here are structurally closely related to one such product already reported to form in an intracellular medium. A ketyl arising via SET with the artemisinin is invoked to explain their formation. Dihydroflavins generated from riboflavin (RF) and FAD by pretreatment with sodium dithionite are rapidly oxidised by artemisinin to the parent flavins. When catalytic amounts of RF, FAD, and other flavins are reduced in,situ by excess BNAH or NAD(P)H in the presence of the artemisinins in the aqueous buffer, they are rapidly oxidised to the parent flavins with concomitant formation of two-electron reduction products from the artemisinins; regeneration of the reduced flavin by excess reductant maintains a catalytic cycle until the artemisinin is consumed. In preliminary experiments, we show that NADPH consumption in yeast GR with redox behaviour similar to that of parasite GR is enhanced by artemisinins, especially under aerobic conditions. Recombinant human GR is not affected. Artemisinins thus may act as antimalarial drugs by perturbing the redox balance within the malaria parasite, both by oxidising FADH2 in parasite GR or other parasite flavoenzymes, and by initiating autoxidation of the dihydroflavin by oxygen with generation of ROS. Reduction of the artemisinin is proposed to occur via hydride transfer from LMB or the dihydroflavin to O1 of the peroxide. This hitherto unrecorded reactivity profile conforms with known structure,activity relationships of artemisinins, is consistent with their known ability to generate ROS in,vivo, and explains the synergism between artemisinins and redox-active antimalarial drugs such as MB and doxorubicin. As the artemisinins appear to be relatively inert towards human GR, a putative model that accounts for the selective potency of artemisinins towards the malaria parasite also becomes apparent. Decisively, ferrous iron or carbon-centered free radicals cannot be involved, and the reactivity described herein reconciles disparate observations that are incompatible with the ferrous iron,carbon radical hypothesis for antimalarial mechanism of action. Finally, the urgent enquiry into the emerging resistance of the malaria parasite to artemisinins may now in one part address the possibilities either of structural changes taking place in parasite flavoenzymes that render the flavin cofactor less accessible to artemisinins or of an enhancement in the ability to use intra-erythrocytic human disulfide reductases required for maintenance of parasite redox balance. [source] | ||||||||||||||||||||||||||||