Metathesis of methyl 10-undecenoate

1984 ◽  
Vol 49 (8) ◽  
pp. 1736-1745 ◽  
Author(s):  
Hynek Balcar ◽  
Alena Dosedlová ◽  
Vladimír Hanuš ◽  
Lidmila Petrusová ◽  
Bohumír Matyska

The metathesis of methyl 10-undecenoate was studied using the WCl6 + (CH3)4Sn catalyst system. The rate of metathesis and the maximum degree of conversion are affected markedly by the reactions of the ester, and of the other oxygen compounds if present, with tungsten hexachloride. Introduction of an oxygen ligand to the central tungsten atom of the active centre increases the reactivity and stability of the latter, thus affecting positively the initial rate of the metathesis reaction. At the same time, however, the rate of the catalyst deactivation increasing concentration of the ester, whereupon the degree of the conversion decreases. As a result of competition of the two effects, a maximum appears in the dependence of the amount of the ester reacted on the ester-to-tungsten hexachloride ratio.

2019 ◽  
Vol 19 (04) ◽  
pp. 2050068
Author(s):  
Hezan Huang ◽  
Bo Zhou

The distance spectral radius of a connected graph is the largest eigenvalue of its distance matrix. For integers [Formula: see text] and [Formula: see text] with [Formula: see text], we prove that among the connected graphs on [Formula: see text] vertices of given maximum degree [Formula: see text] with at least one cycle, the graph [Formula: see text] uniquely maximizes the distance spectral radius, where [Formula: see text] is the graph obtained from the disjoint star on [Formula: see text] vertices and path on [Formula: see text] vertices by adding two edges, one connecting the star center with a path end, and the other being a chord of the star.


1973 ◽  
Vol 131 (1) ◽  
pp. 97-105 ◽  
Author(s):  
Paul C. Engel ◽  
William Ferdinand

1. Lineweaver–Burk plots for glutamate dehydrogenase, glucose 6-phosphate dehydrogenase and several other enzymes show one or more abrupt transitions between apparently linear sections. These transitions correspond to abrupt increases in the apparent Km and Vmax. with increasing concentration of the varied substrate. 2. The generalized reciprocal initial-rate equation for a multi-site enzyme requires several restrictions to be put on it in order to generate such plots. These mathematical conditions are explored. 3. It is shown that the effective omission of a term in the denominator of the reciprocal initial-rate equation represents a minimal requirement for generation of abrupt transitions. This corresponds in physical terms to negative co-operativity followed by positive co-operativity affecting the catalytic rate constant for the reaction. 4. Previous models for glutamate dehydrogenase cannot adequately account for the results. On the other hand, the model based on both negative and positive co-operativity gives a good fit to the experimental points. 5. The conclusions are discussed in relation to current knowledge of the structure and mechanism of glutamate dehydrogenase.


Author(s):  
J. K. Roberts ◽  
G. Bryce

The fact that the rate of production of atomic hydrogen at a tungsten surface at a given temperature is proportional to the square root of the hydrogen pressure means either that the important process is the evaporation of atoms from an adsorbed film which over the whole range of experimental conditions is sparsely occupied, or that the production of atoms is in the main due to a process in which a hydrogen molecule strikes a bare tungsten atom in the surface, one atom being adsorbed and the other evaporating and the surface being almost completely covered over the whole range of experimental conditions. Either process leads to a temperature variation in the rate of atom production in agreement with experiment. A definite decision between the two processes cannot yet be made.


Author(s):  
R. C. L. Bosworth

In a study of the properties of hydrogen on tungsten by the method of contact potentials the following points have been established:(1) The contact potential of a 92% covered surface of hydrogen on tungsten against bare tungsten is 1·04 V., and the Richardson constants for such a surface are, approximately,A = 30, b = 5·60 V.(2) A film of deuterium is 20 m V. positive relative to a similar hydrogen film.(3) Over the range of temperatures and pressures used by Bryce in a study of the production of atomic hydrogen the films are nearly saturated, so that the production of atomic hydrogen is primarily due to a molecule striking a bare tungsten atom, one atom being adsorbed and the other going into the gas phase.(4)The condensation coefficient for hydrogen molecules on cold tungsten is 0·01.(5) The effective dipole moment of each hydrogen atom on the surface is −0·42 Debye unit and is independent of the fraction of the surface covered.


1978 ◽  
Vol 176 (3) ◽  
pp. 733-737 ◽  
Author(s):  
H A Krebs ◽  
R Hems ◽  
P Lund ◽  
D Halliday ◽  
W W Read

The initial rate of incorporation of [15N]alanine into the 6-amino group of the adenine nucleotides in rat hepatocytes was about one-eighteenth of the rate of incorporation into urea. Thus the purine nucleotide cycle cannot provide most of the ammonia needed in urea synthesis for the carbamoyl phosphate synthase reaction (EC 2.7.2.5). On the other hand, contrary to the view expressed by McGivan & Chappell [(1975) FEBS Lett. 52, 1–7], the experiments support the view that hepatic glutamate dehydrogenase can supply the required ammonia.


Author(s):  
Joan Oliver Araujo

La tesis que acabamos de exponer y que consideramos acertada, esto es, que el Estado autonómico español debe transformarse en un Estado federal siguiendo el modelo alemán, quedaría, sin embargo, muy incompleta si no pusiéramos sobre la mesa el hecho de que los nacionalistas catalanes y vascos consideran totalmente insuficiente el modelo federal, que está lejos de dar satisfacción a sus deseos de autogobierno. Cataluña y el País Vasco, se quiera o no se quiera, guste o no guste, son Comunidades Autónomas (ahora el nombre es lo de menos) distintas a las otras quince. Son verdaderas naciones que, a diferencia de aquellas, quieren un grado de autonomía (siempre) mayor. Resulta evidente, en estos momentos, la manifiesta insuficiencia del modelo federal clásico para aquellos dos territorios, por una parte, y la necesidad de buscar con urgencia una fórmula realista de convivencia estable dentro del Estado español, por otra. Nuestra propuesta —a través de una reforma constitucional— se puede concretar en la fórmula del «federalismo asimétrico» o «federalismo dual», que implicaría el reconocimiento constitucional de un estatus jurídico específico a Cataluña y al País Vasco a modo de Estados-libres-asociados, que les otorgase a ambos el máximo autogobierno compatible con el Estado español. De este modo, el Estado Federal español estaría integrado, por una parte, por quince «Estados-miembros» o Estados-federados de régimen común y, por otra, por dos «Estados-libres-asociados».The aforementioned thesis is right, since the Spanish autonomic state should become a federal state, following the German model. Nonetheless, we cannot forget the fact that Catalan and Basque nationalists consider that, far from satisfying their self-government expectations, the federal model is utterly insufficient. Whether we like or not, Catalonia and the Basque Country are different from the other fifteen autonomous communities. Unlike the rest, they are true nations, which (always) aim at a higher degree of self-government. The inadequacy of the traditional federal model with regard to those two territories is quite evident, as well as the need to urgently find a realistic formula to ensure a stable coexistence within the Spanish state. Our proposal, which demands a constitutional reform, settles on the formula of «asymmetric federalism » or «dual federalism». This formula would imply the constitutional recognition of a specific legal status for Catalonia and the Basque Country as free associated states, granting the maximum degree of self-government compatible with the Spanish state. Thereby, the Spanish federal state would consist, for one thing, of fifteen «member states» or common federated states and, there again, two «free associated states».


1997 ◽  
Vol 272 (4) ◽  
pp. C1087-C1098 ◽  
Author(s):  
E. E. Burmeister Getz ◽  
S. L. Lehman

The models of the sarcoplasmic reticulum (SR) Ca pump used to simulate Ca kinetics in muscle fibers are simple but inconsistent with data on Ca binding or steady-state uptake. We develop a model of the SR pump that is consistent with data on transient and steady-state Ca removal and has rate constants identified under near-physiological conditions. We also develop models of the other main Ca-binding proteins in skeletal muscle: troponin C and parvalbumin. These models are used to simulate Ca transients in cut fibers during and after depolarizing pulses. Simulations using the full SR pump model are contrasted with simulations using a Michaelis-Menten (MM) approximation to SR pump kinetics. The MM pump underestimates the amount of Ca released during depolarization, underestimates the initial rate of Ca binding by the pump, and overestimates the later rate of Ca pumping. These errors are due to fast initial binding by the SR pump, which is neglected in the MM approximation.


1977 ◽  
Vol 161 (3) ◽  
pp. 569-581 ◽  
Author(s):  
C L McMinn ◽  
J H Ottaway

1. The kinetic properties of the 2-oxoglutarate dehydrogenase system were investigated. To this end, initial-velocity studies were carried out by the method of Fromm [(1967) Biochim. Biophys. Acta 139, 221-230]. Reciprocal plots of the results did not agree with those expected for the Hexa Uni Ping Pong mechanism previously proposed for the system. 2. The measured initial velocities were fitted to initial-rate equations corresponding to several possible mechanisms by using a computer optimization technique. Statistical analyses performed on the results of the optimization studies indicated that one mechanism was a significantly better fit to the experimental data than the other mechanisms tested. This mechanism is one in which there is a random order of binding of NAD+ and CoA and release of succinyl-CoA, although the binding of 2-oxoglutarate and release of CO2 is still given a Ping Pong mechanism, which precedes the binding of the other substrates. These conclusions were supported by NADH-inhibition studies. 3. The usefulness of the method of fitting initial-rate data to rate equations and the applicability of the proposed enzymic mechanism to the enzyme complex are discussed.


2013 ◽  
Vol 23 (1) ◽  
pp. 90-101 ◽  
Author(s):  
TOMÁŠ KAISER ◽  
ROSS J. KANG

We consider two graph colouring problems in which edges at distance at most t are given distinct colours, for some fixed positive integer t. We obtain two upper bounds for the distance-t chromatic index, the least number of colours necessary for such a colouring. One is a bound of (2-ε)Δt for graphs of maximum degree at most Δ, where ε is some absolute positive constant independent of t. The other is a bound of O(Δt/log Δ) (as Δ → ∞) for graphs of maximum degree at most Δ and girth at least 2t+1. The first bound is an analogue of Molloy and Reed's bound on the strong chromatic index. The second bound is tight up to a constant multiplicative factor, as certified by a class of graphs of girth at least g, for every fixed g ≥ 3, of arbitrarily large maximum degree Δ, with distance-t chromatic index at least Ω(Δt/log Δ).


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