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Catalytically Active Form (catalytically + active_form)
Selected AbstractsThe 1,3-Diaminobenzene-Derived Aminophosphine Palladium Pincer Complex {C6H3[NHP(piperidinyl)2]2Pd(Cl)} , A Highly Active Suzuki,Miyaura Catalyst with Excellent Functional Group ToleranceADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 6 2010Jeanne Abstract The rapidly prepared 1,3-diaminobenzene-derived aminophosphine pincer complex {C6H3[NHP(piperidinyl)2]2Pd(Cl)} (1) is an effective Suzuki catalyst with excellent functional group tolerance. Side-product formations, such as homocoupling, debromation or protodeboration have only rarely been detected and if so, were in all cases below the 5% level. The presented reaction protocol is universally applicable. Experimental observations indicate that palladium nanoparticles are the catalytically active form of 1. [source] Highly Convenient, Clean, Fast, and Reliable Sonogashira Coupling Reactions Promoted by Aminophosphine-Based Pincer Complexes of Palladium Performed under Additive- and Amine-Free Reaction ConditionsADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 6 2009Jeanne Abstract Sequential addition of 1,1,,1,,-phosphinetriyltripiperidine and 1,3-diaminobenzene or resorcinol to toluene solutions of (cyclooctadiene)palladium dichloride [Pd(cod)(Cl)2] under nitrogen in "one pot" almost quantitatively yielded the aminophosphine-based pincer complexes {[C6H3 -2,6-(XP{piperidinyl}2)2]Pd(Cl)} (X=NH 1; X=O 2). Complex 1 (and to a minor extent 2) proved to be efficient Sonogashira catalysts, which allow the quantitative coupling of various electronically deactivated and/or sterically hindered and functionalized aryl iodides and aryl bromides with several alkynes as coupling partners within very short reaction times and low catalyst loadings. Importantly, in contrast to most of the Sonogashira catalysts, which either are both air- and moisture-sensitive and/or require the addition of co-catalysts, such as copper(I) iodide [CuI], for example, or a large excess of an amine, the coupling reactions were carried out without the use of amines, co-catalysts or other aditives and without exclusion of air and moisture. Moreover, the desired products were exclusively formed (no side-products were detected) without employing an excess of one of the substrates. Ethylene glycol and potassium phosphate (K3PO4) were found to be the ideal solvent and base for this transformation. Experimental observations strongly indicate that palladium nanoparticles are not the catalytically active form of 1 and 2. On the other hand, their transformation into another homogeneous catalytically active species cannot be excluded. [source] Structure of the isoaspartyl peptidase with l -asparaginase activity from Escherichia coliACTA CRYSTALLOGRAPHICA SECTION D, Issue 6 2004Adam Prahl The crystal structure of the Escherichia coli enzyme (EcAIII) with isoaspartyl dipeptidase and l -asparaginase activity has been solved and refined to a resolution of 1.65,Å, with crystallographic R -factor and Rfree values of 0.178 and 0.209, respectively. EcAIII belongs to the family of N-terminal hydrolases. The amino-acid sequence of EcAIII is homologous to those of putative asparaginases from plants. The structure of EcAIII is similar to the structures of glycosylasparaginases. The mature and catalytically active form of EcAIII is a heterotetramer consisting of two ,-subunits and two ,-subunits. Both of the equivalent active sites present in the EcAIII tetramer is assisted by a metal-binding site. The metal cations, modelled here as Na+, have not previously been observed in glycosylasparaginases. This reported structure helps to explain the inability of EcAIII and other plant-type asparaginases to hydrolyze N4 -(,- N -acetylglucosaminyl)- l -asparagine, the substrate of glycosylasparaginases. [source] A conserved mechanism of autoinhibition for the AMPK kinase domain: ATP-binding site and catalytic loop refolding as a means of regulationACTA CRYSTALLOGRAPHICA SECTION F (ELECTRONIC), Issue 2 2010Dene R. Littler The AMP-activated protein kinase (AMPK) is a highly conserved trimeric protein complex that is responsible for energy homeostasis in eukaryotic cells. Here, a 1.9,Å resolution crystal structure of the isolated kinase domain from the ,2 subunit of human AMPK, the first from a multicellular organism, is presented. This human form adopts a catalytically inactive state with distorted ATP-binding and substrate-binding sites. The ATP site is affected by changes in the base of the activation loop, which has moved into an inhibited DFG-out conformation. The substrate-binding site is disturbed by changes within the AMPK,2 catalytic loop that further distort the enzyme from a catalytically active form. Similar structural rearrangements have been observed in a yeast AMPK homologue in response to the binding of its auto-inhibitory domain; restructuring of the kinase catalytic loop is therefore a conserved feature of the AMPK protein family and is likely to represent an inhibitory mechanism that is utilized during function. [source] Characterization of the G-quadruplex structure of a catalytic DNA with peroxidase activityBIOPOLYMERS, Issue 5 2009De-Ming Kong Abstract It has been reported that the complexes formed by hemin and some G-quadruplexes can be developed as a new class of DNAzyme with peroxidase activity. This kind of DNAzyme has received a great deal of attention. But to date, the actual G-quadruplex structure that can provide hemin with enhanced peroxidase activity is in doubt. Herein, the G-quadruplex structure of CatG4, a 21-nucleotide DNA oligomer which was previously reported to bind hemin and the resulting complex exhibiting enhanced peroxidase activity, was characterized by fluorescence and circular dichroism measurements. The results suggest that the catalytically active form of CatG4 may be a unimolecular parallel quadruplex rather than a unimolecular chair-type antiparallel quadruplex or a multistranded parallel quadruplex. In addition, the fluorescence analysis of labeled oligonucleotides may be developed as a supplementary tool for the study of DNA conformations. © 2009 Wiley Periodicals, Inc. Biopolymers 91: 331,339, 2009. This article was originally published online as an accepted preprint. The "Published Online" date corresponds to the preprint version. You can request a copy of the preprint by emailing the Biopolymers editorial office at biopolymers@wiley.com [source] Characterization of an unusual folding pattern in a catalytically active guanine quadruplex structureBIOPOLYMERS, Issue 6 2006Pinaki R. Majhi Abstract In the presence of certain metal ions, DNA and RNA can form guanine quadruplex structures, which have been proposed to play a functional role in a variety of biological processes. An 18-nucleotide DNA oligomer, PS2.M, d(GTG3TAG3CG3T2G2), was previously reported to bind hemin and the resulting complex exhibited peroxidase activity. It was proposed that PS2.M folds unimolecularly into an antiparallel quadruplex with unusual, single-base loops and terminal guanines positioned in adjacent quartets. Here we describe structural and stability properties of PS2.M alone in different buffers and metal ions, using gel electrophoresis, circular dichroism (CD), ultraviolet (UV)-visible spectroscopies, and one-dimensional 1H nuclear magnetic resonance (NMR). Native gel behavior of PS2.M in the presence of either Na+ or Pb2+ suggests the formation of unimolecular structures but, in the presence of K+, both unimolecular and multistranded structures are observed. In the presence of Pb2+ ions, PS2.M forms a unimolecular quadruplex containing three guanine quartets. CD titrations reveal that binding of Pb2+ ions to PS2.M is stoichiometric, and a single lead cation suffices to fully fold PS2.M. The PS2.M,Na+ system also forms a similar unimolecular quadruplex. In the presence of K+, the PS2.M,K+ system forms mixed species. With increasing time and PS2.M concentration, the contribution of unimolecular species decreases while that of multimolecular species increases, and this behavior is independent of buffer media. These results suggest that the catalytically active form, studied in the presence of K+, may be a parallel, multistranded quadruplex rather than an antiparallel, unimolecular quadruplex. © 2006 Wiley Periodicals, Inc. Biopolymers 82:558,569, 2006 This article was originally published online as an accepted preprint. The "Published Online" date corresponds to the preprint version. You can request a copy of the preprint by emailing the Biopolymers editorial office at biopolymers@wiley.com [source] | ||||||||||