Copper proteins synthetic models

Although complete strucmral details are rare, considerable progress has been made in understanding the mode of action of copper proteins, synthetic modelling being a major factor in this. " Biologically active copper centres can be divided into three main types ... 

Tolman W.B. (1995) Synthetic Modeling of the Interactions of Nitrogen Oxides with Copper Proteins Copper Nitrosyl Complexes Relevant to Putative Denitrification Intermediates, Adv. Chem. Ser., 246, 195. 

The interest in catechol oxidase, as well as in other copper proteins with the type 3 active site, is to a large extent due to their ability to process dioxygen from air at ambient conditions. While hemocyanin is an oxygen carrier in the hemolymph of some arthropods and mollusks, catechol oxidase and tyrosinase utilize it to perform the selective oxidation of organic substrates, for example, phenols and catechols. Therefore, establishment of structure-activity relationships for these enzymes and a complete elucidation of the mechanisms of enzymatic conversions through the development of synthetic models are expected to contribute greatly to the design of oxidation catalysts for potential industrial applications. 

The structures of type II copper sites have not as yet generated as much interest, but the hetero-dinuclear structures of type IIC copper sites and the unusual protein donor ligands found in type IIB copper sites are noteworthy. The synthetic model approach to gain insight into the structures and functions of these types of copper sites will be also described. The diverse functions of a variety of proteins containing type IIA copper sites inspired many chemists to mimic the functions with synthetic copper complexes, even though the spectroscopic properties of the complexes are not unusual. Results of these studies will be reviewed and different aspects of the reactions relating to enzymatic catalysis will be discussed. 

A considerable number of crystal structures of type I copper sites in proteins are now available, so there may be no particular advantage in the synthetic model approach to prove the coordination structure of type I. Yet, inorganic chemists still have an opportunity to utilize the spectroscopic and structural bases established by model studies to understand the precise electronic structure of type I copper. One should keep in mind that the generally accepted interpretation derived from spectroscopic and theoretical studies on the proteins (47-49) has not been definitely proved experimentally. A systematic comparison of a series of copper(II) thiolate complexes having an unusual distorted coordination structure is required for a conclusive description of the electronic structure of the type I copper. The synthetic approach is ultimately the most adequate way to clarify how the ligand donors and geometry affect the electronic property and function of type I copper as an electron transfer center. 

Synthetic Modeling of the Interactions of Nitrogen Oxides with Copper Proteins... 

Since the choice is difficult due to the huge amount of examples, the selection is based either on aesthetic criteria (77) and (78), or on important applications. In a review, Synthetic Models for Binuclear Copper Proteins, Sorrell reports his previous results with pyrazole ligands which mimics histidyl-imidazole <89T3>. 

ELECTRCX HEMICAL STUDIES OF SYNTHETIC MODELS OF COPPER PROTEINS... 

ABSTRACT. After a brief survey of the different types of natural copper proteins, and their metal-centred main functions, the characteristics of "good" synthetic models are outlined. Electrochemical studies, by cyclic voltammetry and/or differential pulse polarography, of some representative models are overviewed. Recent, unpublished, results on several copper complexes intended to mimick the Type I copper sites are described and briefly discussed. 

Natural copper proteins are very complex molecules, the greatest contribution to the molecular weight coming from their proteic parts. In order to avoid this complexity and focus the attention on their copper active centres, a vast amount of synthetic models of these centres have been prepared and characterized. Nevertheless, it is not to be expected that such low-molecular weight compounds would reproduce the properties of the natural proteins because they lack the protein backbone [13]. 

What then would be hypothetical, ideal, synthetic models Possibly copper complexes obeying the following criteria the structural features of the model complex must be very similar to those of the natural copper protein the ligand system must be such that only very small structural changes would result from redox processes cycles of oxidation-reduction processes must not be strongly reflected on the life-time of the complex the associated redox potentials of the model copper complex, as well as its spectral and magnetic properties, must be very close to those of the copper protein to be mimicked. 

One of the characteristic properties of the Type I copper active sites is the relatively high potential for their Cu(II)/Cu(I) processes, in comparison with that of the Cu2+(aq.)/Cu+(aq.) couple. Consequently a reasonable synthetic model will necessarily have a high potential, within the range found for natural proteins (see Table 1). 

Most of the synthetic models we found in our literature survey are concerned with hemocyanine, the oxygen transport protein in arthropods and molluscs, and tyrosinase, which catalyzes the two-electron oxidation of phenolic compounds. Both proteins contain a coupled binuclear copper active site, a Type III copper centre,"which reversibly binds dioxygen as peroxide bridging between the two copper ions" [153]. The Cu-Cu distance is of the order of 300-400 pm, and a tetragonal coordination is achieved with donor nitrogen atoms of imidazole ligands from histidine [142]. 

This limited survey of the literature, and arbitrary choice of topics, on copper proteins and some synthetic models of their active metal centres can hopefully be considered a representative sample of the enormously vast amount of work that has been published on the subject. 

Electrochemical Studies of Synthetic Models of Copper Proteins J.O. Cabral... 

Moreover, within the recent developments in Bioelectrochemistry, relevant attention has been devoted to the electrochemistry of redox proteins and redox enzymes (H.A.O. Hill), as welt as of synthetic models of copper proteins (J.O. Cabral). 

A spinning molecule on a copper surface and a soccer-ball molecule tethered to a protein may seem no more useful than a spinning ice-skater or a tetherball. Nonetheless, advocates of nanotechnology cite a wealth of potential applications for this new field, including tailored synthetic membranes that can collect specific toxins from industrial waste and computers that process data much faster than today s best models. The list of possible benefits from nanotechnology is limited only by our imaginations. 

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