Cu-Glycine Complex

Figure 3.4. TJV-vis absorption spectra of 3.10c in water and in water containing 3.0 mM of Cu (glycine) complex, 3.0 mM of Cu(N-methyl-Ftyrosine) and 3.0 mM of Cu(L-abrine).

By using a Zn/ Cu generator for the production of the short-lived positron-emitting radionuchde, Cu[Cu(S2CNR2)2l (R = Me, Et), have been prepared and their biodistribution in mice has been studied. They showed a higher take up in the brain than that of a Cu-glycine complex, which may be due to their stable namre and lipophilic character (1783). 

Cu" amino-acid complexes Cu"-N-salicylidene-glycine complex CuCl3(guanine)H20]2 Cu(N-Pr"salen)2]... 

The deamination by H02 or H2O2 cannot be the result of a reduction of Cu(II) as the corresponding Cu(I) complexes of ethylenediamine or glycine, which are unstable (57), undergo disproportionation to Cu° and Cu(II) without affecting the ligand (52) moreover, reagents which do reduce Cu+2 to Cu+ did not induce deamination. 

A similar reaction is observed with the Cu+2 complex. No reaction occurs with glycine esters. A similar reaction occurs when cobalt (III) complexes are prepared from solutions of hydroxyethylethylenediamine and similar ligands (24, 25). The chelate ring-forming portion of the complex remains intact however, the products derived from the oxidized hydroxyethyl group appear complicated. 

Chiral salen-Cu(II) complex 39c also promoted selective monoalkylation of glycine derivative 20 to produce the corresponding a-amino acids (R)-42 with enantiomeric excesses in the range of 70 to 80% (Scheme 7.10) [32], The enantiomeric excess was... 

Based on a positive non-linear effect observed for the alkylation of alanine and glycine substrates 40 and 20, active species involved in these transformation are predicted to be comprising of more than one salen-Cu(II) complex 39c [32]. Furthermore, enantioselectivity was affected by catalyst concentration, which suggested that a catalytically active dimeric form of the catalyst existed in equilibrium with catalytically inactive oligomeric and monomeric forms of the complex [36]. 

An ion-pair derived from the substrate and solid NaOH forms a cation-assisted dimeric hydrophobic complex with catalyst 39c, and the deprotonated substrate occupies the apical coordination site of one of the Cu(II) ions of the complexes. Alkylation proceeds preferentially on the re-face of the enolate to produce amino acid derivatives with high enantioselectivity. However, amino ester enolates derived from amino acids other than glycine and alanine with R1 side chains are likely to hinder the re-face of enolate, resulting in a diminishing reaction rate and enantioselectivity (Table 7.5). The salen-Cu(II) complex helps to transfer the ion-pair in organic solvents, and at the same time fixes the orientation of the coordinated carbanion in the transition state which, on alkylation, releases the catalyst to continue the cycle. 

Organic molecules can be stabilized with respect to hydrolysis and oxidation by coordinating them with metal ions. Thus, hydrolysis of salicylaldehyde-glycine Schiff base occurs with relative ease compared with the low rate of hydrolysis of the Cu(II) complex (Figure 1, III). The resistance to chemical attack has been attributed to stabilization... 

Two types of glycine complexation experiments were performed In our study. Work at 0.70 M Ionic strength was performed at moderate complexation Intensities within the pH range 4.6 to 2.5. Cu(II) glycine complexation constants were determined by non-llnear least squares fits using the equation ... 

Under proper conditions, Cu(Il) Ion selective electrodes are well suited to extreme complexation conditions. Our glycine complexation experiments at low pH and at high pH produced very similar results In spite of extremely different extents of Cu(II) complexation between the two types of experiments. 

The CD band II extrema near 650 nm for 1 1 Cu(II) complexes of dipeptides and tripeptides with ionized amide hydrogen composed of L-amino acids can be calculated with reasonable accuracy from values for glycine-containing dipeptides. The signs of the Cotton effects near 650 nm are negative, except for the LAla-LAla complexes, which have a positive sign (Tsangaris and Martin, 1970, and references therein). 

Plots of the heat changes against atomic number of the transition metal have been made by a number of workers (e.g.8). The exothermicity of the reaction with ethylenediamine increases from Mn(II) to Cu(II) and then falls at Zn(II) paralleling the trend observed in the heats of hydration of these metal cations (7). With the glycinate complexes crystal-field effects will account for the considerable increase in exothermicity in going from Mn(II) to Ni(II). 

High-precision and high-accuracy determination of amino acids is difficult. Let us examine the possibilities of an indirect approach through dissolving a metal ion compound followed by the highly accurate EDTA (or other) metal ion methods. An iodide-Cu(II) method was proposed in 1950. Likely candidates are Cu(II) and Hg(II), which form very stable complexes with amino acids. The glycinate complexes have the stability constants shown in Table 11-3. The objective is to get quantitative dissolving of a low solubility metal ion compound when excess of it is stirred with a measured... 

Figure 1.1 Stability constants of Cu(ll)-glycine complexes obtained at different ionic strength with nitrate [9] and perchlorate [10] as background electrolytes.

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