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1Author    M. Iv E, A.F M, F. D.Requires cookie*
 Title    Thiol Ester Aminolysis in Acetonitrile  
 Abstract    The kinetics of the reactions of p-nitro -phenyl thiolacetate with several amines in acetonitrile was studied. Hydrazine exhibits considerably greater nucleophilicity than expected from its pKa value. Common mech­ anism is suggested for the aminolysis of the thiol ester and its oxygen analogue. 
  Reference    (Z. Naturforsch. 30b, 138 [1975]; received September 30 1974) 
  Published    1975 
  Keywords    Thiol Ester, Aminolysis, Kinetics, Mechanism, Alpha Effect 
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 TEI-XML for    default:Reihe_B/30/ZNB-1975-30b-0138_n.pdf 
 Identifier    ZNB-1975-30b-0138_n 
 Volume    30 
2Author    S.Requires cookie*
 Title    Kinetics and Possible Mechanisms o f the Ce(IY) Oxidation of EDTA, CDTA, DTPA and NTA in Perchloric Acid Media  
 Abstract    a m ir B. H a n n a , W i l l i a m R . C a r r o l l , S a l e m A. A t t i g a , a n d W i l l i a m H . W e b b The rates of oxidation of four chelating agents with Ce(IV) in HC104 solutions, have been studied by the stopped-flow technique. The rates first increase with increasing acidity, reach maxima which are characteristic of the chelating agent and the medium, then progressively decrease with further increasing acid concentration. A t their maximum reactivities, the tendencies for oxidation decrease in the following order: 2rans-l,2-dia-minocyclohexane tetraacetic acid (CDTA) > ethylenedinitrilotetraacetic acid (EDTA) > diethylenetriaminepentaacetic acid (DTPA) > nitrilotriacetic acid (NTA). A mech­ anism for the oxidation of EDTA, involving Ce4+ and Ce(OH)3+ and both unprotonated and monoprotonated chelating agent, is proposed. 
  Reference    (Z. Naturforsch. 30b, 409—415 [1975]; received December 27 1974) 
  Published    1975 
  Keywords    Oxidation, Amino Acids, Kinetics, Mechanisms, Cerium(IY) 
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 TEI-XML for    default:Reihe_B/30/ZNB-1975-30b-0409.pdf 
 Identifier    ZNB-1975-30b-0409 
 Volume    30 
3Author    CrI. Simionescu, S. Dumitriu, V. I. PopaRequires cookie*
 Title    im kalten Plasma The Mechanism and Kinetics of Methane-Water Mixture Decomposition in Cold Plasma  
 Abstract    In the present paper the mechanism and kinetics of methane-water mixtures decompo-sition in cold plasma are discussed. It was found that nature and composition of the products depend on reaction time, ratio of the two components, and how long the products are in contact after the decomposition was performed. Reactions in the decomposition system generally follow two mechanisms: corresponding to the discharge phase and to postreaction one. The highest yield of formaldehyde was obtained for the ratio methane water of 0.6-1 and two minutes of discharge. Die Bildung von Formaldehyd aus den hypothe-tischen Bestandteilen der Uratmosphäre wurde von LÖB 1 noch im Jahre 1906 in den dmch elektrische Entladungen in einer Mischung von Kohlendioxyd und Wasser entstandenen Produkten nachgewiesen. Später erwähnt derselbe Verfasser die Erzeugung von Glycin über Formaldehyd in einem aus Kohlen-mon-oder -dioxyd, Ammoniak und Wasser beste-henden System. Die Verwendung anderer Systeme (CO + H2; 
  Reference    (Z. Naturforsch. 31b, 466—471 [1976]; eingegangen am 5. November 1975) 
  Published    1976 
  Keywords    Methane-Water, Decomposition, Formaldehyde, Mechanism, Kinetics 
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 TEI-XML for    default:Reihe_B/31/ZNB-1976-31b-0466.pdf 
 Identifier    ZNB-1976-31b-0466 
 Volume    31 
4Author    C. Kerst, P. Potzinger, H. Gg, WagnerRequires cookie*
 Title    The Mercury-Sensitized Photolysis of Pentamethyldisilane  
 Abstract    Two primary processes were observed in the Hg-sensitized photolysis of Me 5 Si 2 H: (I) hydrogen abstraction from the Si-H bond with a quantum yield of 0(1) = 0.85, (V) Si-Si bond breaking with 0(V) = 0.04. The hydrogen atoms formed in (/) undergo an H atom abstraction reaction (k(3)), as well as substitution reactions at the Si centers resulting in the formation of dimethylsilane and trimethylsilyl radical (k(4)) or trimethylsilane and dimethylsilyl radical (k(5)). The following branching ratios have been determined: M = 0.87. M 0.096, M = 0.034. k(3) + k(4) + k(5) k(3) + k(4) + k(5) k(3) + k(4) + k(5) The ratio of disproportionation (A: (2)) to combination (£(1)) for the pentamethyldisilyl radical has been determined with MeOH as the scavenger for 1-methyl-l-trimethylsilylsilene, 0.046 < k(2)/ A: C1) < 0.071. A mechanism with pertinent rate constants has been proposed which accounts for the results. 
  Reference    Z. Naturforsch. 51a, 105—115 (1996); received October 28 1995 
  Published    1996 
  Keywords    Hg-sensitized photolysis, pentamethyldisilane, mechanism, substitution reaction, silyl rad-ical disproportionation 
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 TEI-XML for    default:Reihe_A/51/ZNA-1996-51a-0105.pdf 
 Identifier    ZNA-1996-51a-0105 
 Volume    51 
5Author    Susanna Kerschl, Bernd WrackmeyerRequires cookie*
 Title    Organoborierung von Alkinylstannanen, XIV [1]  
 Abstract    Organoborierung von Bis(alkinyl)stannanen: Mechanismus und Anwendung der 119Sn—NMR-Spektroskopie O rganoboration of Alkynylstannanes, XIV [1] O rganoboration of Bis(alkynyl)stannanes: M echanism and Application of 119Sn NM R Spectroscopy Dimethylbis(phenylethynyl)stannane (1) reacts with trialkylboranes, BR3 (2), to give bis(al-kenyl stannanes (5) (R = C2H5), l-bora-4-stanna-2,5-cyclohexadienes (6) (R = C2H5, C3H7'), 1-stanna-2,4-cyclopentadienes (7) (R = C2H5) and l-stanna-3-cyclopentenes (8) (R = CH3, C2H5). I3C and uySn NMR data prove the structure of the reaction products (5 to 8). 119Sn NMR is useful (i) for following the course of the reaction (mechanism!) and (ii) for quantitative analysis of the product distribution. Deorganoboration reactions play an important role in the formation of the various heterocyclic systems. 
  Reference    Z. Naturforsch. 39b, 1037—1041 (1984); eingegangen am 24. Februar 1984 
  Published    1984 
  Keywords    et Alkynylstannanes, Organoboration, Mechanism, 1, ySn NMR Spectra, 13C NMR Spectra 
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 TEI-XML for    default:Reihe_B/39/ZNB-1984-39b-1037.pdf 
 Identifier    ZNB-1984-39b-1037 
 Volume    39 
6Author    ErwinW. BeckerRequires cookie*
 Title    Dynamics and Kinetics of Enzymes Kinetic Equilibrium of Forces in Biochemistry  
 Abstract    To explain the high specificity, high reaction rate, and high thermodynamic efficiency in enzymatic processes, cooperation of the enzyme with a molecular transfer unit is assumed. A "kinetic equilibrium of forces" is suggested, which enables high reaction rates to occur under equilibrium conditions and a thorough examination of the substrate to be made without con­ sumption of free energy. In case o f ATPases, ion-binding proteins are the most probable trans­ fer units. By analyzing the elementary effect in muscle contraction it is shown that the new theorem may be of substantial value in elucidating biochemical processes. 
  Reference    Z. Naturforsch. 47c, 628—633 (1992); received May 18 1992 
  Published    1992 
  Keywords    Enzyme, Mechanism, Free Energy Transfer, ATPase, Calmodulin, Muscle Contraction 
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 TEI-XML for    default:Reihe_C/47/ZNC-1992-47c-0628.pdf 
 Identifier    ZNC-1992-47c-0628 
 Volume    47 
7Author    N. G. Faleev3, S. N. Spirina3, V. S. Ivoilov3, T. V. Dem, R. S. Phillips0Requires cookie*
 Title    The Catalytic Mechanism of Tyrosine Phenol-Lyase from Erwinia herbicola: The Effect of Substrate Structure on pH-Dependence of Kinetic Parameters in the Reactions with Ring-Substituted Tyrosines  
 Abstract    Apparently hom ogeneous tyrosine phenol-lyase (TPL) from Erwinia herbicola has been prepared by a new method. The pH -dependencies o f the main kinetic parameters for the reactions of Erwinia TPL with tyrosine, 2-fluorotyrosine, 3-fluorotyrosine, 2-chlorotyrosine, and 3.4-dihydroxyphenylalanine (D O P A) have been studied. The pattern of pH-dependence ° f V^max depends on the nature of the substituent in the aromatic ring. For the substrates bearing small substituents (H, 2-F, 3-F) Kmax values were found to be pH-independent. For 2-chlorotyrosine and DO PA Vmax decreased at lower pH, the effect being described by equa­ tion with one pKa. Generally two bases are reflected in the pH dependence of Vmax/K m. The first base, probably is responsible for the abstraction of a-proton, while the second one, interacts with the phenolic hydroxyl at the stage of binding. The reaction of TPL with DOPA differs from the reactions with other tyrosines by the requirement of an additional base which is reflected in the pH-profiles of both and VmaJ K m. For the reaction of TPL from Citrobacter intermedins with DO PA only Vma J K m values could be determined. The activity of Citrobacter enzyme towards DO PA is considerably less than that of E. herbicola enzyme, and its maximal value is attained at higher pH. 
  Reference    Z. Naturforsch. 51c, 363 (1996); received N ovem ber 22 1995/February 27 1996 
  Published    1996 
  Keywords    Tyrosine Phenol-Lyase, Mechanism, Kinetics, Substrate Structure, pH -Dependence 
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 TEI-XML for    default:Reihe_C/51/ZNC-1996-51c-0363.pdf 
 Identifier    ZNC-1996-51c-0363 
 Volume    51 
8Author    Ekkehard Lindner, Günter Von AuRequires cookie*
 Title    Darstellung und Eigenschaften von und Reaktionen mit metallhaltigen Heterocyclen, VII [1] Heterolytische Spaltung der Re-Re-Bindung in den Zweikern-Anionen [(OC)4ReP(R2 )0] 2 2 ~ mit Elektrophilen - ein Weg zu Heterocyclen mit Re-C-o-Bindung Preparation and Properties of, and Reactions with, Metal-Containing Heterocycles, VII [1] Heterolytic Cleavage of the Re-Re Bond in the Binuclear Anions [(0C)4ReP(R2)0]2 2_ with Electrophiles -a Pathway to Heterocycles with Re-C a Bonds  
 Abstract    The preparation of the six-membered rhenacyclohexanes (OC)4ReP(R2)OCH2C(CH3)2CH2 (la, b) [R = CH3 (a), C6H5 (b)J is accomplished by heterolytic cleavage of the Re-Re bond in the binuclear anions [(0C)4ReP(R2)0]2 2 -with strong electrophiles like the alkane-diylbis(triflate) (CH3)2C(CH2Y)2 (Y= OSO2CF3), followed by an attack of the a>-positioned carbenium-like C atom on the phosphinite oxygen of the anion. 1 a, b insert SO2 under ring I I 
  Reference    Z. Naturforsch. 35b, 1104—1110 (1980); eingegangen am 9. Mai 1980 
  Published    1980 
  Keywords    Rhenacyclohexanes, Mechanism, S02-Insertio", X-ray, IR spectra, NMR spectra : 
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 TEI-XML for    default:Reihe_B/35/ZNB-1980-35b-1104.pdf 
 Identifier    ZNB-1980-35b-1104 
 Volume    35