Esters metal complexes, hydrolysis

Acetic add, frons-cyclohexanediaminetetra-metal complexes, 554 Acetic add, ethylenediaminetetra-in analysis, 522 masking, 558 metal complexes, 554 Acetic acid, iminodi-metal complexes, 554 Acetic acid, nitrilotri-metal complexes titrimetry, 554 Acetoacetic add ethyl ester bromination, 419 Acetone, acetyl-deprotonation metal complexes, 419 metal complexes reactions, 422 Acetone, selenoyl-liquid-liquid extraction, 544 Acetone, thenoyltrifluoro-liquid-liquid extraction, 544 Acetone, trifluorothenoyl-in analysis, 523 Acetonitrile electrochemistry in, 493 exchange reactions, 286 metal complexes hydrolysis, 428 Acetylacetone complexes, 22 liquid-liquid extraction, 543 Acetylacetone, hexafiuorothio-metal complexes gas chromatography, 560 Acetylactone, trifluorothio-metal complexes gas chromatography, 560 Acetylation metal complexes, 421 Acetylenedicarboxylic add dimethyl ester cycloaddition reactions, 458 Acid alizarin black SN metallochromic indicator, 556 Actinoids... 

For the hydrolysis of phosphate esters under mild conditions, metal ions and metal complexes are the most efficient nonenzymatic reagents currently available. However, they do not reach the catalytic efficiency of enzymes, and higher reactivities are desirable in view of applications. To mimic enzymatic dinuclear sites is a strategy to generate more efficient artificial phosphoesterases. 

Asymmetric transformations of ot-amino acids promoted by optically active metal complexes have been reported by several groups 269). The control of the stereoselective hydrolysis reactions of racemic esters by chiral micellar compounds prepared from amino acids has been intensively investigated 270). 

In addition to the above-mentioned reactions, metal complexes catalyze decarboxylation of keto acids, hydrolysis of esters of amino acids, hydrolysis of peptides, hydrolysis of Schiff bases, formation of porphyrins, oxidation of thiols, and so on. However, polymer-metal complexes have not yet been applied to these reactions. 

This reaction process is depicted in general terms in equation (34), and includes the category generalized in equation (35). The earliest example of this type of reaction appears to be the ready transesterification of uncomplexed ester groups shown in Scheme 39,133,134 which intramolecular participation forms a new chelate ring in the transition state. Since this discovery, numerous studies have been made on the intramolecular catalysis of ester hydrolysis by metal-complexed hydroxide... 

The systems described in this chapter possess properties that define supramolecular reactivity and catalysis substrate recognition, reaction within the supermolecule, rate acceleration, inhibition by competitively bound species, structural and chiral selectivity, and catalytic turnover. Many other types of processes may be imagined. In particular, the transacylation reactions mentioned above operate on activated esters as substrates, but the hydrolysis of unactivated esters and especially of amides under biological conditions, presents a challenge [5.77] that chemistry has met in enzymes but not yet in abiotic supramolecular catalysts. However, metal complexes have been found to activate markedly amide hydrolysis [5.48, 5.58a]. Of great interest is the development of supramolecular catalysts performing synthetic... 

An interesting correlation has been observed53 between the formation constant XCuL of the metal complex and its catalytic activity in a mixed ligand with an amino acid ester. Large values of XCUL (equation 13) lead to lower base hydrolysis rates in the ternary complex. The Lewis... 

The metal ion-promoted hydrolysis of a number of bidentate esters such as methyl 2,3-diaminopropionate (8), methyl histidinate (9), methyl cysteinate (10) and the ethyl ester of ethylenediaminemonoacetate (11) have been studied. The first three esters give very thermodynamically stable metal complexes in solution with pendant ester functions.64"71 Typical kinetic data for these systems are given in Tables 9 and 10. 

Base (and water) hydrolysis of the 1 1 complex of the tetramethyl ester of EDTA with copper(II) ([Cu(Me4EDTA)]2+) has been investigated.82 In the complex probably two ester groups of the ligand are bonded to the metal ion in conjunction with the two nitrogen donors. Rate accelerations of the order of 10s were observed in base hydrolysis compared with the unprotonated ligand (Table 14). A variety of metal complexes of the ligand have also been isolated and characterized.83... 

Evidence for intramolecular hydrolysis of the methyl ester (62) by metal hydroxide has been provided.329 Molecular models of the metal complex (63) indicate that when complexation with the imidazole nitrogen and the phenolic hydroxyl group occurs, it is not possible for coordination of the ester carbonyl group to occur. This point, taken in conjunction with the observed pH rate profile which shows that ionization of the M—OH2 group is associated with catalysis, eliminates metal ion activation of the carbonyl bond to intermolecular attack by OH- as a contributing factor. For base hydrolysis of (62) kOH = 2.7 x 10-2 M-1 s-1 at 25 °C. The specific rate constants for intramolecular hydrolysis by the M—OH species are 0.245 s-1 and 2 x 10-2 s-1 for the Co11 and Ni11 complexes respectively. 

The phosphate esters (81) and (82) are also subject to catalysis by metal ions275,276 and possible reactive complexes are illustrated. Metal complexes of adenosinediphosphoric acid and adenosinemonophosphoric acids have been studied277 and the effect of divalent metal ions on the hydrolysis of ADP and ATP has been investigated.278,279... 

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