Tryptophan-copper complex

Crystal stmctures of complexes of copper(II) with aromatic amine ligands and -amino acids " " and dipeptides" have been published. The stmctures of mixed ligand-copper complexes of L-tryptophan in combination with 1,10-phenanthroline and 2,2 -bipyridine and L-tyrosine in combination with 2,2 -bipyridine are shown in Figure 3.2. Note the subtle difference between the orientation of the indole ring in the two 1,10-phenanthroline complexes. The distance between the two... 

The positive CD Cotton effect at 260 nm and the negative Cotton effect at 274 nm may be at least partly attributed to amino-acid residues. The side-chain residues of L-cystine, L-phenylalanine. L-tyrosine or L-tryptophan cause Cotton effects at 250—310 nm (101). However, copper complexes of simple amino acids show CD extremes at 245— 290 nm. Therefore, some contribution to the 260 nm band of erythro-... 

A number of new copper complexes have also been found to have antiinflammatory activity. Copper(II)(j8-oxo-2-thiophenepropionitrile) is effective in treating rat polyarthritis [175]. The copper complex of glycyl-L-histidyl-L-lysine, Cu(II)(GHL), is claimed to have anti-inflammatory activity and increase the rate of wound healing [176, 177] consistent with earlier reports of increased gastric wound healing rates associated with Cu(II)(aspirinate)4 and Cu(II)(tryptophanate)2 treatment [178]. Copper(II)(L-histidinate)2, Cu(II)-... 

The above method, contrary to the methods of estimation of amino acids based on copper complexes, is selective. A threefold excess of several common amino acids (including histamine) does not interfere. The method thus enables free histidine to be determined in protein hydrolysates, provided that the histidine concentration is sufficiently high. Tryptophane deforms the polaro-graphic waves when present in an amount corresponding to half that of histidine (above 1 mg/10 ml.). Mercaptoamino acids also interfere, but most of the types of compounds are destroyed during the protein acidic hydrolysis. Glycine affects the end-point if present in amounts larger than 10 mg/10 ml. of the sample. 

First, the pH-dependence of the enantioselectivity of the reaction between 3.8c and 3.9 catalysed by the copper(L-tryptophan) complex has been studied. Above pH 5 the enantioselectivity reaches a plateau value (Figure 3.3). The diminished enantioselectivities observed at lower pH most likely... 

Figure 3.5. Gibbs energies of complexation of 3.8a-g to the copper(II)(Lr tryptophan) complex versus those for complexation to copper aquo ion.

Copper(II) complexes of amino acids have been explored as chiral Lewis acid catalysts in the Diels-Alder reaction of 3-phenyl-l-(2-pyridyl)-2-propen-l-one with cyclopentadiene. The best results were obtained using /V-methyl-/.-tryptophan, but more interestingly, the highest ee values for the major endo adduct were achieved in aqueous solution273. 

Among protein aromatic groups, histidyl residues are the most metal reactive, followed by tryptophan, tyrosine, and phenylalanine.1 Copper is the most reactive metal, followed in order by nickel, cobalt, and zinc. These interactions are typically strongest in the pH range of 7.5 to 8.5, coincident with the titration of histidine. Because histidine is essentially uncharged at alkaline pH, complex-ation makes affected proteins more electropositive. Because of the alkaline optima for these interactions, their effects are most often observed on anion exchangers, where complexed forms tend to be retained more weakly than native protein. The effect may be substantial or it may be small, but even small differences may erode resolution enough to limit the usefulness of an assay. 

Accordingly, Hammett constants or combinations of the argnments a and b can be used to estimate both complex stabilities of substituted aromatics with donor site atoms other than C in biology/biochemistry. Therefore the connection between the rest of the protein and tyrosine phenolate, tryptophan indole or histidine imidazole moieties is taken to be one huge substituent (e.g. in the frequent cases where three histidine residues coordinate to one copper or zinc ion or with tyrosine residues in water photooxidation), possibly introducing charge effects by pH, phosphorylation ( P switch ) or by complexation of other metals like Ca on the outer periphery of the molecule. 

A calibration curve obtained with standard protein solutions [e.g., bovine serum albumin (BSA)] is used to obtain total protein in the unknown. Under optimum conditions, and in the absence of reactive side chains, it has been shown that two electrons are transferred per tetrapeptide unit however, proteins, with significant proline or hydroxyproline content, or with side chains that can complex copper (such as glutamate) yield less color. The side chains of cysteine, tyrosine and tryptophan contribute one, four and four electrons, respectively.3 Note that different proteins will produce different color intensities, primarily as a result of different tyrosine and tryptophan contents. 

Stability constants of mixed ligand complexes containing ATP, tryptophan (Trp) and copper(ii) have been obtained. The reaction of amines with [Cu(Bz-AlaO)2],-H2O (Bz-AlaO = A -benzoyl-DL-alaninato) gives adducts [Cu(Bz-AlaO)2],B (n = 1, B = piperazine, 3-Me-py, 4-Me-py, 2,2 -bipy, 4,4 -bipy, or phen n = 2, B = piperidine or morpholine). The crystal structure of aqua(glycyl)-L-tryptophanatocopper... 

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