Magnesium kinetic studies

While using 19 and 20 as catalysts, a linear relationship between M , conversion of monomer to polymer (%), and PDI (1.10-1.25) was recorded, which support a controlled polymerization of L-lactide. The kinetic studies revealed a first order polymerization of lactide and metal complex in CD2CI2 and CDCI3 solutions. The results indicated that magnesium complex 19 is more active than its Zn(II) analogs (6 days, [M]o/[I]o = 500, CH2CI2, 25 °C, 90% conversion) due to the expected higher polarity of the Mg-OR bond relative to that of the zinc complexes. 

Substituent effects on the rate of electrophilic amination of phenylmagnesium bromides, magnesium diphenylcuprates, and catalytic phenylzinc cyanocuprates with O-methylhydroxylamine in THF have been investigated in a competitive kinetic study.169 The mechanistic differences between these three reactions were discussed on the basis of the experimental results. 

Measurements of the specific surface area, SSA, of the products grown at various times indicate that the initial formation of a microcrystalline or amorphous precursor leads to a rapid increase in SSA. The development of these phases is also observed by scanning electron microscopy, and dissolution kinetic studies of the grown material have indicated the formation of OCP as a precursor phase ( , 7). The overall precipitation reaction appears to involve, therefore, not only the formation of different calcium phosphate phases, but also the concomitant dissolution of the thermodynamically unstable OCP formed rapidly in the initial stages of the reaction. In the presence of magnesium ion the overall rate of crystallization is reduced and lower Ca P ratios are observed for the first formed phases (51). 

Kinetic studies of NMP kinases, as well as many other enzymes having ATP or other nucleoside triphosphates as a substrate, reveal that these enzymes are essentially inactive in the absence of divalent metal ions such as magnesium (Mg2+) or manganese (Mn2+), but acquire activity on the addition of these ions. In contrast with the enzymes discussed so far, the metal is not a component of the active site. Rather, nucleotides such as ATP bind these ions, and it is the metal ion-nucleotide complex that is the true substrate for the enzymes. The dissociation constant for the ATP-Mg2+ complex is approximately 0.1 mM, and thus, given that intracellular Mg + concentrations are typically in the millimolar range, essentially all nucleoside triphosphates are present as NTP-Mg + complexes. 

Subsequently, kinetic studies reported by Whitesides and collaborators [81] provided further support for the view that the rate-determining step in formation of alkyl Grignard reagents involves electron transfer from the metal surface. The kinetics of the reaction of an organic halide RjX with magnesium were described by Eq. (3), in which S g accounted for the characteristics of magnesium surface that influence the rate, and an analogous... 

Kinetic studies were carried out in excess ketone. It was important to keep the Grignard concentration below 0.1 M so that associated species would not present a problem in the interpretation of the kinetic data. It was also important to prepare the Grignard reagent from unusually pure magnesium, since even parts per million of certain transition metal impurities in Grignard reagents cause the formation of by-products in significant amounts. 

In the active centers, the inner coordination shell of the magnesium atom must include the growing chain end and a halide atom. Kinetic studies are consistent with a mechanism... 

The first step in any kinetic study is to identify all the products and intermediates of the reaction. Dehydration often involves several distinct steps which may be very dependent upon reaction conditions, e,g, copper sulfate pentahydrate may yield trihydrate and/or monohydrate [29,30], Metastable intermediates may be formed, e,g, amorphous magnesium carbonate produced on dehydration undergoes [18] exothermic recrystallization at higher temperatures,... 

Tail, P.J.T. Zohuri, G.H. Kells, A.M. McKenzie, I.D. Kinetic studies in propene polymerization using magnesium dichloride supported 65. Ziegler-Natta catalysts. In Ziegler Catalysts. 

These data were interpreted to be compatible with and to confirm the presence of magnesium as an active, firmly bound moiety of the carboxy-peptidase molecule. The inhibitory actions of cyanide and sulfide were not explained (E. L. Smith, 1949b). Apparent inconsistencies in the data were attributed to the firmness of the bond between magnesium and the protein. These inhibition data, together with the anal5dical information discussed vide supra), served as the basis for kinetic studies, for a model for enzyme-substrate interaction, and for a possible mechanism of action of this enzyme (E. L. Smith and Hanson, 1949 E. L. Smith, 1949a, 1951a, b, c E. L. Smith and Lumry, 1949). 

Other kinetic studies of complexation using relaxation techniques can be found in Bridger et al. (1983) [hydroxo and chloro complexes of Fe(III)], Bridger et al. (1982) [complexation of Fe(III) by picolinic and dipicolinic acids], Strahm et al. (1979) (complexation of aqueous iron chloride), and Patel and Taylor (1973) (complexation of magnesium pyrophosphates). 

These compounds cause 50% inhibition of a partially purified reductase from Novikoff rat tumor at 10 8 to 10-7 M (150,151). Approximately the same degree of inhibition was observed with other mammalian reductases (152, 153), but the non-heme iron containing reductase from E. coli was not affected. The inhibition of the mammalian reductases is only partially reversible (154). Since these compounds are strong metal chelators complexation of iron is probably involved in the mechanism of inhibition however excess Fe2+ does not reverse the inhibition, and other evidence indicates that these compounds do not act solely by chelating free iron from solution thus depriving the enzyme of a cofactor (150, 151). Kinetic studies indicate no competition with respect to nucleoside diphosphate substrate, nucleotide effector, or magnesium ions, but partial competition for the dithiol substrate was observed. 

Mathieson AMcL, Walker GF (1954) Crystal stracture of magnesium vermiculite. Am Mineral 39 231-255 Mazzucato E, Artioli G, Gualtieri A (1999) High temperature dehydroxylation of muscovite-2Mi a kinetic study by in situ XRPD. Phys Chem Minerals 26 375-381 McCarty DK, Reynolds RC Jr (1995) Rotationally disordered illite/smectite in Paleozoic K-bentonites. Clays Clay Minerals 43 271-284... 

The rates of hydrocarbon adsorption on all oxidation catalysts (VA, Cu20, etc.) are so high as to make kinetic studies impossible. Characteristic equilibrium isotherms for ethylene sorption on magnesium chromite are shown in Fig. 1. This is a spurious equilibrium,... 

The transformation of the carboxylic acid substrate into acyl-CoA requires one ATP molecule and leads to the release of AMP and pyrophosphate. The reaction mechanism involves the formation of an acyl-AMP intermediate. Extensive and detailed kinetic studies provide details on the ordered addition of the substrate and ATP to the enzyme and the subsequent release of products (Fig. 31.34). The reaction proceeds via a Bi-Uni-Bi-Ping-Pong mechanism whereby ATP complexed to magnesium binds first, thus allowing the fixation of carboxylic acid to the enzyme. Acyl-AMP is thereafter formed and pyrophosphate released. Then... 

It is essential to clarify the crystallization kinetics of magnesium hydroxide and to investigate the influence of various factors on the reactive crystallization characteristics of magnesium hydroxide for better understanding of its crystallization process. The aims of this study are to discuss the followings ... 

A. L. Boskey and A. S. Posner, Magnesium Stabilization of Amorphous Calcium Phosphate A Kinetic Study, Mater. Res. Bull, 1974, 9, 907-916. 

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