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Same Reaction Conditions (same + reaction_condition)
Selected AbstractsSyntheses and Crystal Structures of Tetrakis(arylamidine)nickel(II) Chloride and Bis[2,4-dipyridyl-1,3,5-triazapentadienato]nickel(II)EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 2 2004Jianping Guo Abstract The reaction of LiN(SiMe3)2 with arylnitrile, followed by the addition of anhydrous NiCl2 gives ionic complexes of the general formula [Ni{H2NC(Ar)=NH}4]Cl2 (Ar = Ph 1, p -tolyl 2). When the above reaction is carried out with cyanopyridine instead of arylnitrile under the same reaction conditions, neutral complexes of the general formula [{HN=C(Py)N=C(Py)NH}2Ni] (Py = 4-pyridyl, 3; 3-pyridyl, 4] are obtained. Compound 1 undergoes a metathesis reaction with sodium benzoate to give the neutral complex [(PhCO2)2Ni {H2NC(Ph)=NH}4] (5). Magnetic susceptibility measurements show that 1,4 are diamagnetic and that 5 is paramagnetic with two unpaired electrons. These results suggest that 1,4 are d8 square-planar complexes and 5 is an octahedral complex. The solid state structures of compounds 1,5 were determined by X-ray crystallography. Structural analyses reveal that 1 and 2 form a one-dimensional network through charge-assisted hydrogen bonds; whereas 5 forms a one-dimensional network through hydrogen bonds only. In complexes 3 and 4, the 2,4-dipyridyl-1,3,5-triazapentadienyl ligand behaves as a bidentate ligand forming a six-membered ring with the metal ion. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004) [source] LIPOXYGENASE ACTIVITY IN PRICKLY PEAR FRUIT (OPUNTIA FICUS INDICA [L.] MILL.JOURNAL OF FOOD BIOCHEMISTRY, Issue 2 2010CACTACEAE) ABSTRACT Prickly pear LOX activity was detected in the membrane fractions of the fruit extracts at various stages of ripening. LOX specific activity was very low in the fruit of wild plants at the green stage (0.49 ± 0.04) and increased with fruit ripening, more than doubling in the ripened fruit (1.22 ± 0.06). Moreover, it was not influenced by the cultivar, whereas it was considerably increased (13.3 ± 1.4) by agronomic processes to which prickly pear plants are submitted to improve the organoleptic properties of fruits. The apparent molecular mass of the enzyme was estimated to be 96 kDa. The enzyme had an optimum pH value of 5.5 and a clear specificity for linolenic acid, which was oxidized at a rate one and a half times that of linoleic acid, under the same reaction conditions. The involvement of prickly pear LOX in the flavor biosynthesis of the fruit is supposed. PRACTICAL APPLICATIONS Over the last decade in particular, prickly pear fruits have been widely used as food, not only the whole fruit but also processed to make juices, jams and liquors popular the world over. Prickly pear production has therefore risen considerably and consequently both the labor force employed and revenues generated have increased. For those engaged in this sector it is therefore a prime objective to maximise the profile and thereby profitability of the fruit. It is here that our research into lipoxygenase activity can play a part, as it is known that this enzyme is responsible for the organoleptic properties of fruits and vegetables. The results are presented below. The relationship between lipoxygenase specific activity and specific agronomic processes utilized to improve the fruit quality is also addressed. [source] Fully automated high yield synthesis of (R)- and (S)-[11C]verapamil for measuring P-glycoprotein function with positron emission tomographyJOURNAL OF LABELLED COMPOUNDS AND RADIOPHARMACEUTICALS, Issue 14 2002Gert Luurtsema Abstract Racemic (±) verapamil is a well characterized substrate for P-glycoprotein (P-gp). However, the in vivo pharmacokinetics and pharmacodynamics of both enantiomers are reported to be different. In the preparation of evaluation studies of both enantiomers in animals and humans, the purpose of the present study was to optimize and automate the synthesis of (R)- and (S)-[11C]verapamil. (R)- and (S)-[11C]verapamil were prepared from (R)- and (S)-desmethyl-verapamil, respectively, by methylation with no-carrier added [11C]methyliodide or [11C]methyltriflate. Different conditions of the methylation reaction were studied: reaction time, temperature, base and solvent, and chemical form of the precursor using either the hydrochloric acid salt or the free base of the starting material. After optimization, the synthesis was fully automated using home-made modules and performed according to GMP guidelines. Optimal yields of 60,70% for the methylation reaction were obtained using 1.5 mg of the free base of (R)- or (S)-desmethyl-verapamil in 0.5 ml of acetonitrile at 50°C for 5 min with [11C]methyltriflate as methylating agent. Under the same reaction conditions, but with a reaction temperature of 100°C, the radiochemical yield starting with [11C]methyliodide as methylation reagent was 40%. The specific activity of (R)- and (S)-[11C]verapamil was >20 GBq/,mol and the radiochemical purity was >99% for both methods. The total synthesis time was 45 min. The automated high yield synthesis of (R)- and (S)-[11C]verapamil provides the means for evaluating both enantiomers as in vivo tracers of P-gp function. Copyright © 2002 John Wiley & Sons, Ltd. [source] Specific acid catalysis and Lewis acid catalysis of Diels,Alder reactions in aqueous mediaJOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 3 2004Egid B. Mubofu Abstract A comparative study of specific acid catalysis and Lewis acid catalysis of Diels,Alder reactions between dienophiles (1, 4 and 6) and cyclopentadiene (2) in water and mixed aqueous media is reported. The reactions were performed in water with copper(II) nitrate as the Lewis acid catalyst whereas hydrochloric acid was employed for specific acid catalysis. At equimolar amounts of copper(II) nitrate and hydrochloric acid (0.01,M, for example) and under the same reaction conditions, the reaction rate for 1a with 2 is about 40 times faster with copper catalysis than with specific acid catalysis. Moreover, at 32°C and 0.01,M HCl, the reaction of 1b with 2 is about 21 times faster than the same uncatalyzed reaction in pure water under the same reaction conditions. The inverse solvent kinetic isotope effect shows that these Diels,Alder reactions undergo specific acid catalysis. Copyright © 2004 John Wiley & Sons, Ltd. [source] Computational study of base-induced skeletal conversion via a spirocyclic intermediate in dibenzodithiocinium derivatives by ab initio MO calculationsJOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 5 2003Keiji Okada Abstract Reaction of 6-methyl-12-oxo-5H,7H -dibenzo[b,g][1,5]dithiocinium salt (1-SO) with methanolic KOH afforded a mixture of dibenzothiepin derivatives 2-SO. In order to clarify the intermediates of the rearrangement, ab initio MO calculations with the HF/6,31G* basis set were performed on the reaction intermediates, the transition states and related compounds. The rearrangement was explained in terms of the usual [2,3]-sigmatropic shift via a spirocyclic intermediate, followed by a 1,3-shift of the sulfonyl group. However, a different type of rearrangement was observed in 6-methyl-5H,7H -dibenzo[b,g][1,5]dithiocinium salt (1-S), giving an unexpected dibenzothiepin derivative 3-S along with a small amount of a ring-opening product 8 under the same reaction conditions. The formation of 3-S and 8 was understandable by the assumption of a cationic intermediate resulting from heterolytic cleavage at the benzyl position. Copyright © 2003 John Wiley & Sons, Ltd. [source] Immobilization of ,-Galactosidase on Fibrous Matrix by Polyethyleneimine for Production of Galacto-Oligosaccharides from LactoseBIOTECHNOLOGY PROGRESS, Issue 2 2002Nedim Albayrak The production of galacto-oligosaccharides (GOS) from lactose by Aspergillus oryzae ,-galactosidase immobilized on cotton cloth was studied. A novel method of enzyme immobilization involving PEI,enzyme aggregate formation and growth of aggregates on individual fibrils of cotton cloth leading to multilayer immobilization of the enzyme was developed. A large amount of enzyme was immobilized (250 mg/g support) with about 90,95% efficiency. A maximum GOS production of 25,26% (w/w) was achieved at near 50% lactose conversion from 400 g/L of lactose at pH 4.5 and 40 °C. Tri- and tetrasaccharides were the major types of GOS formed, accounting for about 70% and 25% of the total GOS produced in the reactions, respectively. Temperature and pH affected not only the reaction rate but also GOS yield to some extend. A reaction pH of 6.0 increased GOS yield by as much as 10% compared with that of pH 4.5 while decreased the reaction rate of immobilized enzyme. The cotton cloth as the support matrix for enzyme immobilization did not affect the GOS formation characteristics of the enzyme under the same reaction conditions, suggesting diffusion limitation was negligible in the packed bed reactor and the enzyme carrier. Increase in the thermal stability of PEI-immobilized enzyme was also observed. The half-life for the immobilized enzyme on cotton cloth was close to 1 year at 40 °C and 21 days at 50 °C. Stable, continuous operation in a plug-flow reactor was demonstrated for about 3 days without any apparent problem. A maximum GOS production of 26% (w/w) of total sugars was attained at 50% lactose conversion with a feed containing 400 g/L of lactose at pH 4.5 and 40 °C. The corresponding reactor productivity was 6 kg/L/h, which is several-hundred-fold higher than those previously reported. [source] Diastereoselective Synthesis of Five- and Seven-Membered Rings by [2+2+1], [3+2], [3+2+2], and [4+3] Carbocyclization Reactions of ,-Substituted (Alkenyl)(methoxy)carbene Complexes with Methyl Ketone Lithium EnolatesCHEMISTRY - A EUROPEAN JOURNAL, Issue 17 2005José Barluenga Prof. Dr. Abstract ,-Substituted alkenylcarbene complexes react with methyl ketone lithium enolates to give different carbocyclization products depending on the structure of the lithium enolate, on the metal of the carbene complex, and on the reaction media. Thus, the reactions of aryl and alkyl methyl ketone lithium enolates with ,-substituted alkenyl chromium and tungsten carbene complexes in diethyl ether afford 1,3-cyclopentanediol derivatives derived from a formal [2+2+1] carbocyclization reaction. However, the lithium enolates of acetone and tungsten complexes furnish formal [3+2+2] carbocyclization products. In the case of alkynyl methyl ketone lithium enolates, competitive formal [2+2+1] and [3+2] carbocyclization reactions occur and 1,3-cyclopentanediol and 3-cyclopentenol derivatives are formed. Conversely, alkenyl methyl ketone lithium enolates react with alkenylcarbene complexes under the same reaction conditions to form 2-cycloheptenone derivatives by a formal [4+3] carbocyclization reaction. Finally, when the reaction was performed in the presence of a coordinating medium, the [3+2] carbocyclization pattern was observed independently of the nature of the methyl ketone lithium enolate used. Los complejos alquenilcarbeno , -sustituidos reaccionan con enolatos de litio de metil cetonas para dar diferentes productos de carbociclación dependiendo de la estructura del enolato de litio, del metal del complejo carbeno y del medio de reacción. Así, la reacción de enolatos de litio de aril y alquil metil cetonas con complejos alquenilcarbeno de cromo y wolframio , -sustituidos en dietil eter origina derivados de 1,3-ciclopentanodiol, derivados de una reacción de carbociclación formal [2+2+1]. Sin embargo, el enolato de litio de la acetona y complejos de wolframio dan lugar a productos de carbociclación formal [3+2+2]. En el caso de enolatos de litio de alquinil metil cetonas, se observa la formación de una mezcla de derivados de 1,3-ciclopentanodiol y 3-ciclopentenol derivados de reacciones de carbociclación formal [2+2+1] y [3+2] competitivas. Por el contrario, los enolatos de litio de alquenil metil cetonas reaccionan con complejos alquenilcarbeno en las mismas condiciones de reacción para generar derivados de 2-cicloheptenona a través de una reacción de carbociclación formal [4+3] Finalmente, cuando la reacción se lleva a cabo en presencia de PMDTA, un medio coordinante, se observa el modelo de carbociclación formal [3+2], independientemente de la naturaleza del enolato de litio utilizado. [source] Synthesis and Characterization of a Series of New Asymmetric Salphen Mono- and Binuclear Metal ComplexesCHINESE JOURNAL OF CHEMISTRY, Issue 6 2010Jiayuan Li Abstract Two novel asymmetric salen ligands H2L1 [N -phenyl- N -(2-hydroxy-5-methylphenyl)- N, -(2-hydroxy-3-meth- oxylphenyl)- o -phenyldiamine] and H2L2 [N -phenyl- N -(2-hydroxy-5-chlorophenyl)- N, -(2-hydroxy-3-methoxyl- phenyl)- o -phenyldiamine] and their metal complexes MLn (M=Zn, Co, Ni, Cu; n=1, 2) have been prepared and characterized by elemental analyses, 1H NMR, ESI-MS, FT-IR and UV-Vis spectra. In particular, the complex ZnL1, the binuclear monosalphen complex, was synthesized and studied in detail using 1H NMR and ESI-MS techniques. For other metal complexes under the same reaction conditions, only mononuclear complexes were obtained. The results are relevant to both the metal ions and the structure of ligands. [source] Coupling reaction of carbonyl compounds mediated by gallium metal in aqueous mediaCHINESE JOURNAL OF CHEMISTRY, Issue 9 2003Zhi-Yong Wang Abstract A simple and effective pinacol coupling of various aromatic aldehydes mediated by gallium in good yields has been carried out. The reaction is highly effective in water in the presence of KOH or HCl and was strongly affected by the steric environment surrounding the carbonyl group. Aliphatic aldehydes, ketones and aromatic ketones appear inert under the same reaction conditions. [source] Readily available sulfamide,amine alcohols for enantioselective phenylacetylene addition to aldehydes in the absence of Ti(OiPr)4CHIRALITY, Issue 5 2005Jincheng Mao Abstract Ephedrine-derived sulfamide,amine alcohol 3 was found to be an effective catalyst for the asymmetric phenylacetylene addition to aldehydes at room temperature without using Ti(OiPr)4 and Zn(OTf)2. It afforded the propargylic alcohols in high yields (up to 99%) and good enantioselectivities (up to 84% ee), which were much higher than that based on N -methylephedrine under the same reaction conditions. Its weakly coordinative sulfonamide moiety of the ligand plays an important role for further acceleration and stereocontrol in the alkynylation. Chirality 17:245,249, 2005. © 2005 Wiley-Liss, Inc. [source] | ||||||||||