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Intermediate Complex (intermediate + complex)
Selected AbstractsKinetics and mechanism of decomposition of intermediate complex during oxidation of pectate polysaccharide by potassium permanganate in alkaline solutionsINTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 2 2003Khalid S. Khairou The kinetics of decomposition of an [Pect·MnVIO42,] intermediate complex have been investigated spectrophotometrically at various temperatures of 15,30°C and a constant ionic strength of 0.1 mol dm,3. The decomposition reaction was found to be first-order in the intermediate concentration. The results showed that the rate of reaction was base-catalyzed. The kinetic parameters have been evaluated and found to be ,S, = , 190.06 ± 9.84 J mol,1 K,1, ,H, = 19.75 ± 0.57 kJ mol,1, and ,G, = 76.39 ± 3.50 kJ mol,1, respectively. A reaction mechanism consistent with the results is discussed. © 2002 Wiley Periodicals, Inc. Int J Chem Kinet 35: 67,72, 2003 [source] Kinetic study of the ruthenium(VI)-catalyzed oxidation of benzyl alcohol by alkaline hexacyanoferrate(III)INTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 7 2002A. E. Mucientes The kinetics of the Ru(VI)-catalyzed oxidation of benzyl alcohol by hexacyanoferrate(III), in an alkaline medium, has been studied using a spectrophotometric technique. The initial rates method was used for the kinetic analysis. The reaction is first order in [Ru(VI)], while the order changes from one to zero for both hexacyanoferrate(III) and benzyl alcohol upon increasing their concentrations. The rate data suggest a reaction mechanism based on a catalytic cycle in which ruthenate oxidizes the substrate through formation of an intermediate complex. This complex decomposes in a reversible step to produce ruthenium(IV), which is reoxidized by hexacyanoferrate(III) in a slow step. The theoretical rate law obtained is in complete agreement with all the experimental observations. © 2002 Wiley Periodicals, Inc. Int J Chem Kinet 34: 421,429, 2002 [source] Extended Hartree,Fock theory of chemical reactions.INTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 15 2008VIII. Abstract We have investigated the reaction pathways for the primary hydroxylation reaction of trimethylmethane by a high-valent Fe(IV)O porphyrin ,-cation radical species known as compound I at the B3LYP/CEP-31G level. The isoelectronic analogy of the Fe(IV)O core of compound I to a molecular oxygen (O2) has been successfully used to clarify the important roles of the singlet excited state of the Fe(IV)O core in the alkane hydroxylation, which has hitherto been neglected. The reaction is initiated by the rate-determining hydrogen-atom abstraction from the substrate to give a discrete radical intermediate complex, in accordance with the conventional radical rebound mechanism. Similar to the chemistry of O2, however, one of the singlet excited states, i.e., the diradical component of the 1, state of the Fe(IV)O core intercepts the triplet ground state (the 3, state) in the region of the transition state for the hydrogen abstraction. Our findings strongly indicate that the exchange polarization or intersystem crossing for the nonradiative transition to the locally singlet state is highly important to enhance the reactivity of compound I. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2008 [source] Alternating copolymerization of propylene oxide with carbon monoxide catalyzed by Co complex and Co/Ru complexesJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 24 2002Daisuke Takeuchi Abstract Co2(CO)8 catalyzes the ring-opening copolymerization of propylene oxide with CO to afford the polyester in the presence of various amine cocatalysts. The 1H and 13C{1H} NMR spectra of the polyester, obtained by the Co2(CO)8,3-hydroxypyridine catalyst, show the following structure [CH2CH(CH3)OCO]n. The Co2(CO)8,phenol catalyst gives the polyester, which contains the partial structural unit formed through the ring-opening copolymerization of tetrahydrofuran with CO. The bidentate amines, such as bipyridine and N,N,N,,N,-tetramethylethylenediamine, enhance the Co complex-catalyzed copolymerization, which produces the polyester with a regulated structure. Acylcobalt complexes, (RCO)Co(CO)n (R = Me or CH2Ph), prepared in situ, do not catalyze the copolymerization even in the presence of pyridine. This suggests that the chain growth involves the intermolecular nucleophilic addition of the OH group of the intermediate complex to the acyl,cobalt bond, forming an ester bond rather than the insertion of propylene oxide into the acyl,cobalt bond. Co2(CO)8Ru3(CO)12 mixtures also bring about the copolymerization of propylene oxide with CO. The molar ratio of Ru to Co affects the yield, molecular weight, and structure of the produced copolymer. The catalysis is ascribed to the RuCo mixed-metal cluster formed in the reaction mixture. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 4530,4537, 2002 [source] Design your own elastomeric or stereoregular polymer,POLYMERS FOR ADVANCED TECHNOLOGIES, Issue 10-12 2002Michal Shmulinson Abstract This study reports the synthesis and activity as precatalysts for the polymerization of propylene of five racemic group 4 complexes, cis-[p-R,C6H4C(NR)2]2MX2 (R,,=,CH3, R,=,SiMe3, M,=,Ti, X,=,Cl (1); R,,=,CH3, R,=,SiMe3, M,=,Zr, X,=,Cl (2); R,,=,H, R,=,i-pr, M,=,Zr, X,=,Cl (3); R,,=,CH3, R,=,SiMe3, M,=,Zr, X,=,CH3 (4)) and (acac)2MCl2 (M,=,Ti (5), M,=,Zr (6)) (acac,=,acetylacetone). The hydrocarbyl complex 4 was prepared by the alkylation of the corresponding complex 2 with MeLi·LiBr. Reaction of complex 4 with B(C6F5)3 or all complexes with MAO (MAO,=,methylalumoxane) results in the formation of a "cationic" intermediate complex which rapidly reacts with the incoming monomer. Some of the complexes catalyze the stereoregular polymerization of propylene only under pressure in either toluene or CH2Cl2, producing polypropylene with very large isotacticities (mmmm %,=,,95,98), high melting points (140,154,°C) and similar molecular weights as compared with cyclopentadienyl complexes, whereas complex 5 is active for the polymerization of elastomeric polypropylene. Copyright © 2003 John Wiley & Sons, Ltd. [source] Mycobacterium tuberculosis pantothenate kinase: possible changes in location of ligands during enzyme actionACTA CRYSTALLOGRAPHICA SECTION D, Issue 4 2009Bhaskar Chetnani The crystal structures of complexes of Mycobacterium tuberculosis pantothenate kinase with the following ligands have been determined: (i) citrate; (ii) the nonhydrolysable ATP analogue AMPPCP and pantothenate (the initiation complex); (iii) ADP and phosphopantothenate resulting from phosphorylation of pantothenate by ATP in the crystal (the end complex); (iv) ATP and ADP, each with half occupancy, resulting from a quick soak of crystals in ATP (the intermediate complex); (v) CoA; (vi) ADP prepared by soaking and cocrystallization, which turned out to have identical structures, and (vii) ADP and pantothenate. Solution studies on CoA binding and catalytic activity have also been carried out. Unlike in the case of the homologous Escherichia coli enzyme, AMPPCP and ADP occupy different, though overlapping, locations in the respective complexes; the same is true of pantothenate in the initiation complex and phosphopantothenate in the end complex. The binding site of MtPanK is substantially preformed, while that of EcPanK exhibits considerable plasticity. The difference in the behaviour of the E. coli and M. tuberculosis enzymes could be explained in terms of changes in local structure resulting from substitutions. It is unusual for two homologous enzymes to exhibit such striking differences in action. Therefore, the results have to be treated with caution. However, the changes in the locations of ligands exhibited by M. tuberculosis pantothenate kinase are remarkable and novel. [source] Utp25p, a nucleolar Saccharomyces cerevisiae protein, interacts with U3 snoRNP subunits and affects processing of the 35S pre-rRNAFEBS JOURNAL, Issue 13 2010Mauricio B. Goldfeder In eukaryotes, pre-rRNA processing depends on a large number of nonribosomal trans -acting factors that form intriguingly organized complexes. Two intermediate complexes, pre-40S and pre-60S, are formed at the early stages of 35S pre-rRNA processing and give rise to the mature ribosome subunits. Each of these complexes contains specific pre-rRNAs, some ribosomal proteins and processing factors. The novel yeast protein Utp25p has previously been identified in the nucleolus, an indication that this protein could be involved in ribosome biogenesis. Here we show that Utp25p interacts with the SSU processome proteins Sas10p and Mpp10p, and affects 18S rRNA maturation. Depletion of Utp25p leads to accumulation of the pre-rRNA 35S and the aberrant rRNA 23S, and to a severe reduction in 40S ribosomal subunit levels. Our results indicate that Utp25p is a novel SSU processome subunit involved in pre-40S maturation. Structured digital abstract ,,MINT-7889901: SAS10 (uniprotkb:Q12136) physically interacts (MI:0915) with Utp25p (uniprotkb:P40498) by pull down (MI:0096) ,,MINT-7889915: NIP7 (uniprotkb:Q08962) physically interacts (MI:0915) with RRP43 (uniprotkb:P25359) by two hybrid (MI:0018) ,,MINT-7889852: Utp25p (uniprotkb:P40498) physically interacts (MI:0915) with MPP10 (uniprotkb:P47083) by two hybrid (MI:0018) ,,MINT-7890065: NOP1 (uniprotkb:P15646) and Utp25p (uniprotkb:P40498) colocalize (MI:0403) by fluorescence microscopy (MI:0416) ,,MINT-7889865: Utp25p (uniprotkb:P40498) physically interacts (MI:0915) with SAS10 (uniprotkb:Q12136) by two hybrid (MI:0018) [source] Mathematical model of the rate-limiting steps for retrovirus-mediated gene transfer into mammalian cellsBIOTECHNOLOGY & BIOENGINEERING, Issue 1 2010Venkata S. Tayi Abstract A quantitative understanding of the process of retrovirus-mediated gene transfer into mammalian cells should assist the design and optimization of transduction protocols. We present a mathematical model of the process that incorporates the essential rate-limiting transduction steps including diffusion, convection and decay of viral vectors, their binding at the cell surface and entry into the cell cytoplasm, reverse transcription of uncoated RNA to form DNA intermediates, transport of the latter through the cytosol to the cell nucleus and, finally, nuclear import and integration of the delivered DNA into the target cell genome. Cell and virus population balances are used to account for the kinetics of multiple vector infections which influence the transduction efficiency and govern the integrated copy number. The mathematical model is validated using gibbon ape leukemia virus envelope pseudotyped retroviral vectors and K562 target cells. Viral intermediate complexes derived from the internalized retroviral vectors are found to remain stable inside the K562 cells and the cytoplasmic trafficking time is consistent with the time scale for retrovirus uncoating, reverse transcription and transport to the cell nucleus. The model predictions of transduction efficiency and integrated copy number agree well with experimental data for both static (i.e., standard gravity) and centrifugation-based gene transfer protocols. The formulation of the model can also be applied to transduction protocols involving lenti- or foamy-viruses and so should prove to be useful for the optimization of several types of gene transfer processes. Biotechnol. Bioeng. 2010;105: 195,209. © 2009 Wiley Periodicals, Inc. [source] | |||||||||||||