Copper complexes, interactions with

The first step in this new stain protocol employs copper acetate, a metal salt that is both a good fixative ( ) and a silver stain enhancer. The mechanism of copper s stain enhancement, in this and other silver stains, may be similar to its action in the biuret reaction (15.), in which a characteristic color shift, from violet to pink, is achieved by titrating peptides in the presence of copper ions. Copper complexes formed with the N-peptide atoms of the peptide bonds are primarily responsible for this reaction. There are also some number of secondary sites which may interact with copper. Any elemental copper formed may displace positive silver ions from solution as copper has a greater tendency to donate electrons than silver, indicated by its position in the electromotive series of the elements. Following the treatment with copper acetate, the membrane is sequentially soaked in a solution containing chloride and citrate ions and then in a solution containing silver nitrate. The membrane is then irradiated with light while it is in the silver nitrate... 

Copper-thiosemicarbazide complexes interact with both the bases and the phosphate groups of native caf/thymus DNA (Pillai et al. 1977). 

Amide groups interact with copper sulphate by the complex formation mechanism as mentioned previously. 

There are three areas of activity in the field of arenediazonium salts in interaction with metals and transition elements which have some similarities to metals. First is the use of copper in the reactions of Sandmeyer (1884), Pschorr (1896), Gomberg-Bachmann (1924), and Meerwein (1939). Other transition metal catalysts (Ti and Pd) have been used for such reactions since the 1970s (see Secs. 10.8 and 10.9). Up to now only one intermediate has been directly identified, the aryldiazenido palladium complex (ArN2Pd(PPh3)3]+BF4 (Yamashita et al., 1980 see Sec. 10.9, Scheme 10-64). 

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