Pyruvic acid metal complexes

The Fe(III) complexes of the dianion of pyruvic acid thiosemicarbazone (thpu2- Fig. 7), (cation+)[Fe(thpu)2]-nH20, are very similar to those of the salicylaldehyde derivatives (Fig. 6) discussed above. The spin state properties are quite sensitive to changes in the counter-cation (typically an alkali-metal cation or a protonated nitrogenous base) and the lattice water content of the material. The parent compound, NH4[Fe(thpu)2], is low spin at room temperature [113]. Li[Fe(thpu)2]-3H20 is also low spin but K[Fe(thpu)2] 2-H20 shows almost complete spin crossover between 80 and 300 K [108]. 

N-Do/Jor Ligands. The full account of the preparation and properties of V[N(SiMc3)2]3 has been published. (Et4N)3[V(NCSe)e] has been prepared and its electronic spectrum reported in several solvents. The electronic spectra of fVL lfNCSij complexes (L = py, 3-picoline, 3,4-lutidine, or 3,5-lutidine) are consistent with tetrahedral microsymmetry about the V " atom, and the magnetic properties of V complexes with the thiosemicarbazones of salicylaldehyde and pyruvic acid have been interpreted in terms of a tetragonal environment about the metal. ... 

The reaction of [NiL] (H2L = 76a) with ammonium persulfate, pyruvic acid and AgN03 gives (76b) which acts as an N202 donor to a number of transition metals. The complexes [ZnL] (H2L = 76a or 76b) have been prepared, and their electronic spectra reported.533... 

In a series of reactions similar to those described for amino acid complexes, pyruvic acid undergoes metal-catalyzed condensation with aldehydes and also halogenation (Scheme 14). Again, the metal ion presumably functions by accelerating the formation of the methylene carbanion. 

When free (W /f. / 1 (-tartaric acid is healed above its melting point, amorphous anhydrides arc formed which, on boiling with water, regenerate the acid. Further heating causes simultaneous formation of pyruvic acid. CHiCOCOOII pyrotartaric acid. llOOrCH C HirH,lCT>OH and. linally. a black, charred residue. In common with other hydroxy organic acids, tartaric acid complexes many metal rons. 

Each of the reactions is catalyzed by a different type of proteinoid or metal-proteinoid complex. The reaction of pyruvic acid to alanine and the reverse reaction are hypothesized from the experimental results in the amination of a-ketoglutaric acid 241 and the deamination of glutamic acid 2S). 

Synthesis of the first water-soluble catalyst complexes was reported in 1973 [3] and was based on the use of sulfonated triphenylphosphine to replace TPP. The sulfonated derivative was found to stabilize the lower oxidation states of a number of transition metals such as Rh, Ru, Ir, Pt, Ni, and Cu in aqueous systems and these water-soluble catalysts facilitated hydrogenation of soluble substrates like pyruvic acid. 

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). 

Schiff base formation between pyridoxal (140) and amino acids leads to complexes of type (141) which are in tautomeric equilibrium with (142). This tautomeric equilibrium leads to transamination, thus the same metal complexes can be obtained when either pyridoxal and alanine or pyridoxamine and pyruvic acid are allowed to react together in the presence of a metal ion. Hopgood" has studied the rates of transamination of 15 amino acids in the presence of zinc(II) and pyridoxal 5-phosphate (143). On mixing the reagents zinc(II)-aldimine complexes are rapidly formed (ca. 5 min) and these species subsequently transaminate in a slow second step. Ai" and Zn" systems have been particularly well studied.The role of the metal ion seems to involve both stabilization or trapping of the Schiff base, and in addition it also ensures the planarity of the conjugated ir-system. In the case of the aldimine tautomer, extensive H NMR studies have shown that formation of the ternary complex results in activation at the amino acid 2-carbon. At room temperature the reaction occurs without incorporation of into the aldehyde methine position indicating that the primary mechanism is carbanion formation rather than tautomerism. 

Cobalt is well known for its ability to break an oxidatively destructive chain reaction catalysed by another metal (cf. Baur and Preis, 1936). This suggested to the Dutch workers that the iron and copper complexes of oxine, pyrithione, and dimethyldithiocarbamic acid were oxidatively destroying thioctic acid (dihydrolipoic acid) (2.28) which is the essential coenzyme for the oxidative decarboxylation of pyruvic acid. This was confirmed when they found pyruvic acid accumulating in the medium (Sijpesteijn and Janssen, 1959 also personal communications from these authors). The receptor in all three examples is the small molecule (2.28) although, at the time, it caused surprise to find one of such low molecular weight. 

Degradation of L-tryptophan takes place in some bacteria by the tryptophanase reaction in which the amino acid is converted to indole (35), pyruvic acid and ammonia. The reaction was first observed in 1903. Wood and his collaborators first prepared the enzyme tryptophanase which catalyses the change from Escherichia coli and showed that pyridoxal phosphate is the co-enzyme involved . Snell and his colleagues have proposed a mechanism for the reaction in which the required cleavage occurs via the intermediacy of a pyridoxal phosphate-tryptophan-metal complex... 

The development of aqueous phase hydrogenation reactions catalysed by water soluble transition metal sulfonated phosphine complexes began with the pioneering work of Joo and Beck in the Ru/tppms-catalysed hydrogenation of pyruvic acid to lactic acid in 1974 which coincides with the first application of water soluble RhH(CO)(tppts)3 catalysts in the biphasic propene hydroformylation. The success of Ru/tppms contrasted with the lack of activity observed using transition metal complexes modified with water soluble ligands such as the system 57 [Table 4, n=l] in hydrogenation reactions in aqueous media. ... 

Hydrazinium metal pyruvates [N2H5]2M[CH3COCOO]4, where M = Co or Ni, are prepared from aqueous solution containing a mixture of the respective salts, pyruvic acid, and hydrazine hydrate [11]. The magnetic moments and electronic spectra of the complexes suggest a high-spin... 

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