Copper complexes amino acids

A chiral amino-acid/copper complex is bound to a silica- or polymeric stationary phase and copper ions are included in the mobile phase to ensure there is no loss of copper. Amino acids then may be separated by the formation of diastereomeric copper complexes. Water stabilizes the complex by coordinating in an axial position. Steric factors then determine which of the two complexes is more stable. One of the water molecules is usually sterically hindered from coordinating with the copper. i ... 

A remarkable increase in SOD-mimetic activity was found in a comparison of synovial fluid from rheumatoid arthritis and osteoarthritic patients with normal control values [613]. The increase in SOD-mimetic activity correlated with increased rheumatoid disease activity and increasing progression of disease severity. There was also a good correlation between SOD-mimetic activity and C-reactive protein in synovial fluid from patients with rheumatoid arthritis. This SOD-mimetic activity may be attributed to either an elaboration of ceruloplasmin by synovial cells [614] or the liver along with copper albumin and amino-acid copper complexes which, in part, accounts for the established increase in synovial fluid copper and ceruloplasmin in rheumatoid arthritis [30] and it is well known that ceruloplasmin [102, 489, 615] as well as amino-acid and other small-molecular-weight copper complexes have SOD-mimetic activity [287-295, 327]. 

As a-amino acids form well-defined copper complexes which catalyze the luminol chemiluminescence, assays have been developed on this basis [41]. This application can be difficult since amino acid copper complexes catalyse the luminol/ hydrogen peroxide reaction while amino acids themselves inhibit the luminol/ hydrogen peroxide/copper amine reaction [41]. 

This interpretation is supported by literature studies on copper(II) complexes containing two -amino-acid ligands. For N-unsubstituted -amino-acid ligands, deductions as to position of the cis -trans geometrical equilibrium in solution are difficult as illustrated by the fact that for some -amino acids solid complexes have been isolated of both the ds and trans geometry. In contrast it seems as if copper(II) complexes containing two N-alkylated -amino-acid ligands crystallise exclusively in the trans form ". ... 

The enthalpies of complexation of 3.8c to the copper(lf) - amino acid ligand complexes have been calculated from the values of at 20 C, 25 1C, 30 1C, 40 1C and 50 1C using the van t Hoff equation. Complexation entropies have been calculated from the corresponding Gibbs energies and enhalpies. 

In acidic solution, the degradation results in the formation of furfural, furfuryl alcohol, 2-furoic acid, 3-hydroxyfurfural, furoin, 2-methyl-3,8-dihydroxychroman, ethylglyoxal, and several condensation products (36). Many metals, especially copper, cataly2e the oxidation of L-ascorbic acid. Oxalic acid and copper form a chelate complex which prevents the ascorbic acid-copper-complex formation and therefore oxalic acid inhibits effectively the oxidation of L-ascorbic acid. L-Ascorbic acid can also be stabilized with metaphosphoric acid, amino acids, 8-hydroxyquinoline, glycols, sugars, and trichloracetic acid (38). Another catalytic reaction which accounts for loss of L-ascorbic acid occurs with enzymes, eg, L-ascorbic acid oxidase, a copper protein-containing enzyme. 

The methylene group of a-amino acid metal complexes such as the copper(II) glycinato complex is activated to some extent by the polarizing influence of the metal.46,47 Consequently, carban-ion-type reactions can be carried out at this position, while the amino and carboxyl groups are protected by coordination. These reactions cannot be performed on either the free ligand or the conjugate base. 

Gorantla VRK, Matijevic E, Babu SV. Amino acids as complexing agents in chemical-mechanical planarization of copper. Chem Mat 2005 17 2076-2080. 

Copper has a marked tendency to form complexes with organic substances, especially proteins, polypeptides, and amino acids. In complexed form, copper may not react with reagents or may not be extracted quantitatively. Special care must therefore be taken to free copper from these bonds quantitatively before its determination. This often cannot be achieved without dry or wet ashing. 

Underivatized amino acids form complexes with copper(II). A variety of copper(II)-trapped phases have been developed for the enantiosepara-tion of amino acids. N-Salicylidene-(J )-2-amino-l,2-6is(2-buto Q -5-fe/t-bu(yl-phenyl)-3-phenyl-l-propanol was coated on an octadecyl-bonded silica gel column and copper sulfate solution was used as the eluent. The structure was constructed using the Molecular Editor program and optimized by MM2 calculations. The optimization was performed as the energy change was less than 10 kcal mol. The molecular weight of the chiral phase was 1449, and the final and van der Waals energies were 77.04 and —8.77 kcal mol, respectively. 

In aU the above cases, diastereomeric complexes are formed between the sample molecules and the asymmetric species in the chromatographic system and these will migrate with different velocities through the column. As an example, amino acid-copper compounds give diastereomeric complexes of well-known structures— two copper bonding sites may be occupied by the sample molecules (Fig. 21.1). Amino acid-copper compounds may be bonded to silica, as shown in Fig. 21.1, or they may be added to the mobile phase. 

The advantages are similar to those of the indirect method the additive can be chosen from a wide range and in some cases its chirality can be adapted to the separation problem the stationary phase is cheap. In fact, the reagent does not necessarily need to be optically pure (although it should not be a racemate), but decreasing enantiomeric purity reduces the separation factor. The price of the reagent can be high. The interaction between the chiral selector and the sample can be based on inclusion (e.g., with cyclodextrins), on complexation (e.g., with amino acid-copper additives), on ion pair formation (e.g.,... 

An unusual EC reaction applicable to the detection of most amino acids involves complexation with copper ions in solution. It was later shown that this also occurs at copper electrodes. Although sensitivity limits of 0.5 to 18 ng injected depending on the amino acid have been reported for this system, it is not widely used, probably because the difficulties of resolving 20-I-amino acids on reversed-phase columns. Most workers therefore use derivatisation of the amino acids prior to chromatography for their analysis. Even though many such derivatives, e.g. phenylisothiocyanate (PITC), are electroactive, most analysts favour fluorescence detection since it is more compatible with the necessary solvent gradients as well as being more selective. 

Aqueous solutions of copper(n) salts give a green to blue colour or precipitate in the presence of water-soluble amines . In organic solvents, and preferably in the absence of water, aliphatic amines form a complex with excess of copper(ii) chloride. Although the structure of this complex is unknown, it has composition 2CuCl2. amine, becoming therefore useful for quantitative analysis Amino acids yield complexes with the same salts, which are stabilised by a chelate structure 19. After isolation of the complex, it can be analysed for its copper content gravimetrically or colourimetrically " . 

---