Copper ions amino acid hydrolysis

There are a few documented examples of studies of ligand effects on hydrolysis reactions. Angelici et al." investigated the effect of a number of multidentate ligands on the copper(II) ion-catalysed hydrolysis of coordinated amino acid esters. The equilibrium constant for binding of the ester and the rate constant for the hydrolysis of the resulting complex both decrease in the presence of ligands. Similar conclusions have been reached by Hay and Morris, who studied the effect of ethylenediamine... 

Metal-ion catalysis has been extensively reviewed (Martell, 1968 Bender, 1971). It appears that metal ions will not affect ester hydrolysis reactions unless there is a second co-ordination site in the molecule in addition to the carbonyl group. Hence, hydrolysis of the usual types of esters is not catadysed by metal ions, but hydrolysis of amino-acid esters is subject to catalysis, presumably by polarization of the carbonyl group (KroU, 1952). Cobalt (II), copper (II), and manganese (II) ions promote hydrolysis of glycine ethyl ester at pH 7-3-7-9 and 25°, conditions under which it is otherwise quite stable (Kroll, 1952). The rate constants have maximum values when the ratio of metal ion to ester concentration is unity. Consequently, the most active species is a 1 1 complex. The rate constant increases with the ability of the metal ion to complex with 2unines. The scheme of equation (30) was postulated. The rate of hydrolysis of glycine ethyl... 

It has been known for many years that the rate of hydrolysis of a-amino acid esters is enhanced by a variety of metal ions such as copper(II), nickel(II), magnesium(H), manganese(II), cobalt(II) and zinc(II).338 Early studies showed that glycine ester hydrolysis can be promoted by a tridentate copper(II) complex coupled by coordination of the amino group and hydrolysis by external hydroxide ion (Scheme 88).339 Also, bis(salicylaldehyde)copper(II) promotes terminal hydrolysis of the tripeptide glycylglycylglycine (equation 73).340 In this case the iV-terminal dipeptide fragment... 

The rates of hydrolysis of amino acid esters or amides are often accelerated a million times or so by the addition of simple metal salts. Salts of nickel(n), copper(n), zinc(n) and cobalt(m) have proved to be particularly effective for this. The last ion is non-labile and reactions are sufficiently slow to allow both detailed mechanistic studies and the isolation of intermediates, whereas in the case of the other ions ligand exchange processes are sufficiently rapid that numerous solution species are often present. Over the past thirty years the interactions of metal ions with amino acid derivatives have been investigated intensively, and the interested reader is referred to the suggestions for further reading at the end of the book for more comprehensive treatments of this interesting and important area. 

A kinetic investigation of the hydrolysis of 8-acetoxyquinoline in solutions of pH between 1 and 9, and in the presence and absence of copper(II) ions, yielded some interesting results (205). In the absence of copper(II), it was found that the rate of hydrolysis was first-order with respect to 8-acetoxyquinoline, but the rate equation that fitted the kinetic data was quite complex since the ester and the ester cation reacted with both the hydrogen and the hydroxide ion. In the presence of copper(II), the hydrolysis of the ester occurred more rapidly and the rate equation was found to be first-order with respect to 8-acetoxyquinoline copper(II) and hydroxide ion. Therefore, the reaction intermediate (structure XXXVII) is presumably a 1 1 chelate of copper(II) which is attacked by hydroxide ion, just as in the case of the amino acid ester. 

The hydrolysis of chelated amino acid esters, H2NCHRCO2R, is known to be accelerated by metal ions, most notably cobalt(III). Dramatic enhancements are also observed with copper(II). Mechanistic studies of the hydrolysis of amino acid esters with copper(II) complexes of glycyl-DL-valine and dien (H2HCH2CH2NHCH2CH2NH2) have been reported/ The hydrolysis of benzyl-penicillin (30) by copper(II) salts to give (31) has been further investigated, and it is proposed that the key step involves intramolecular attack by metal-coordinated hydroxide in an intermediate of type (32). 

The presence of copper ions seemed to help synthesize tetrj lycine [17]. Using a supercritical water flow reactor with temperature control inside the fluids, it is suggested that condensates of glycine, which yielded amino acids after hydrolysis, formed even in supercritical water at 400 °C, under 25 MPa pressure [18]. When an aqueous mixture of ten amino acids was heated at 200-400 °C, the acid hydrolysis of the products led to a higher content in glutamic acid and a-amino acids, such as a-aminobutyric acid, 5-aminovaleric acid and 6-aminohexanoic acid than in a-amino acids even over supercritical conditions of water su esting that a-amino acids could be chemical markers of abiotic hydrothermal systems [18]. Reviews report the various conditions of amino acid syntheses [19-21 and Ref therein]. 

Acylamino groups also are useful activating groups and have the advantage that the amino groups obtained after hydrolysis of the acyl function can be removed from an aromatic ring by reduction of the corresponding diazonium salt with hypophosphorous acid, preferably in the presence of copper(I) ions. 

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