Oxaloacetic acid metal complexes

Catalytic decarboxylation processes occur in aliphatic keto acids in which the keto group is in an a-position to one carboxyl group and in a P-relationship to another. Thus, the normal decarboxylation of a p-keto acid is facilitated by metal coordination to the a-keto acid moiety. The most-studied example is oxaloacetic acid and it has been shown that its decarboxylation is catalyzed by many metals following the general order Ca2+ < Mn2+ < Co2+ < Zn2+ < Ni2+ < Cu2+ < Fe3+ < Al3"1".66 67 The overall rate constants can be correlated with the stability constants of 1 1 complexes of oxalic acid rather than oxaloacetic acid, as the uncoordinated carboxylate anion is essential for the decarboxylation. The generally accepted mechanism is shown in Scheme 15. Catalysis can be increased by the introduction of x-bonding ligands, which not only increase the... 

In most enzyme systems, enolate intermediates are stabilized by metal ion complexation. Although few good numbers are available, it appears that metal ion complexation of the oxygen of the keto and enol forms can increase the acidity of an adjacent carbon-hydrogen bond by four to six orders of magnitude. For example, complexation with lowers the ipK at C-3 of oxaloacetate from 13 to 9 (76), and a similar shift is seen with pyruvate (75). Enolates of a-keto acids can be effectively stabilized by metal complexation. For example, in the cases of pyruvic acid and oxaloacetic acid, both the keto oxygen and one of the carboxyl oxygens coordinate to the metal (Scheme 11). 

Osmium, quinuclidinetetraoxime-stereochemistry, 44 Osmium, tetrachloronitrido-tetraphenylarsenate stereochemistry, 44 Osmium, tris( 1,10-phenanthroline) -structure, 64 Osmium(II) complexes polymerization electrochemistry, 488 Osmium(III) complexes magnetic behavior, 273 Osmium(lV) complexes magnetic behavior, 272 Osmium(V) complexes magnetic behavior, 272 Osmium(VI) complexes magnetic behavior, 272 Oxaloacetic acid decarboxylation metal complexes, 427 Oxamidoxime in gravimetry, 533 Oxidation-reduction potentials non-aqueous solvents, 27 Oxidation state nomenclature, 120 Oxidative addition reactions, 282 Oxidative dehydrogenation coordinated imines, 455 Oximes... 

The metal ion promoted decarboxylation of oxaloacetic acid is somewhat more complicated, Scheme 7.3 due to the presence of the enolic complex MAe,K)iic (which does not decarboxylate) which is in equilibrium with the active ketonic complex. 

D-Lactate cytochrome c reductase is inhibited by p-mercuriphenyl sulfonate salts, metal chelators, and dicarboxylic acids such as oxalate and oxaloacetate (Table XVI) (312, 314, 315). According to Nygaard (314), salts (cations) inhibit at the acceptor site, and dicarboxylic acids at the substrate site. Cremona and Singer (315) have studied the inhibitions by metal chelators and by oxalate. They recognized two types of inhibition. One type of inhibition is that which is caused by EDTA or oxalate. This kind of inhibition is reversed immediately upon dilution of the enzyme-inhibitor mixture. The second is that which results from addition of o-phenanthroline. Enzyme preparations treated with o-phenanthroline bind 2 moles of the chelator per mole of Zn . This complex is stable and inactive, and does not result in the release of Zri . The inactive... 

To give a real example, have a closer look on main functions and cycle of magnesium in green plants. Control on autocatalysis depends on the principal functions of Mg, that is, on photosynthesis when substantial parts of Mg taken up by roots are allocated to chlorophyll and rubisco synthesis, less will be available for other metabolic pathways, reducing the turnovers there unless there are lots of Mg around like in marine plants. In addition, the tricarboxylate cycle (citrate cycle) requires Mg (besides Fe and Mn) to produce the enzymes hence some Mg (as well as Fe, Mn) must be invested to produce the citrate (malate, oxaloacetate (aspartate)) ions delivered by the roots to render Mg (and other metals) in turn bioavailable by means of complexation and resorption of almost neutral complex entities. Furthermore, the tricarboxylate cycle is coupled to biosynthesis of amino acids by redox transamination hence there will be both competition at the metal center(s) and possible extraction of metal ions from enzymes once NHj and electrons are... 

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