| | 2 | Author
| 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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| default:Reihe_B/30/ZNB-1975-30b-0409.pdf | | | | Identifier
| ZNB-1975-30b-0409 | | | | Volume
| 30 | |
| 3 | Author
| CrI. Simionescu, S. Dumitriu, V. I. Popa | Requires 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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| default:Reihe_B/31/ZNB-1976-31b-0466.pdf | | | | Identifier
| ZNB-1976-31b-0466 | | | | Volume
| 31 | |
| 4 | Author
| C. Kerst, P. Potzinger, H. Gg, Wagner | Requires 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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| default:Reihe_A/51/ZNA-1996-51a-0105.pdf | | | | Identifier
| ZNA-1996-51a-0105 | | | | Volume
| 51 | |
| 5 | Author
| Susanna Kerschl, Bernd Wrackmeyer | Requires 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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| default:Reihe_B/39/ZNB-1984-39b-1037.pdf | | | | Identifier
| ZNB-1984-39b-1037 | | | | Volume
| 39 | |
| 6 | Author
| ErwinW. Becker | Requires 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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| default:Reihe_C/47/ZNC-1992-47c-0628.pdf | | | | Identifier
| ZNC-1992-47c-0628 | | | | Volume
| 47 | |
| 7 | Author
| N. G. Faleev3, S. N. Spirina3, V. S. Ivoilov3, T. V. Dem, R. S. Phillips0 | Requires 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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| default:Reihe_C/51/ZNC-1996-51c-0363.pdf | | | | Identifier
| ZNC-1996-51c-0363 | | | | Volume
| 51 | |
| 8 | Author
| Ekkehard Lindner, Günter Von Au | Requires 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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| default:Reihe_B/35/ZNB-1980-35b-1104.pdf | | | | Identifier
| ZNB-1980-35b-1104 | | | | Volume
| 35 | |
|
