Activation of Metal Complexes

We have seen that there are examples of metal complexes in all widely accepted mechanisms of radiation modification, and metal complexes in general must be considered as excellent potential for further in vitro and in vivo studies. A review paralleling this chapter has appeared [103]. Many of the effects of ionizing radiation on DNA with respect to modification have also been reviewed in a comprehensive volume [104]. Systematic in vitro studies to correlate activity with chemical parameters e.g. reaction with the hydrated electron, hydroxyl radical etc. are clearly required. The fact that some metal complexes show a fine line between sensitization and protection is indicative of competing processes. In this respect, the point has been made that these processes are the two sides of a coin . The basic mechanism for both reactions is closely related and we can consider protection as a reductive process or repair and implying donation to a particular molecule, while sensitization can be thought of as abstracting electrons, an oxidative process [105]. 

The rationale of radiation sensitization by electron-affinic compounds involves the chemical interaction with. An alternative statement is that sequestering of e can increase concentrations of the damaging OH [106]. Suffice it to say that the reactions of metal cations with the hydrated electron are well characterized and, indeed, cover a wide range of rate constants depending on the electronic structure of the complex [107]. 

Similarly, reactions with superoxide and peroxide are well categorized. The protection by copper salts has, as we have seen, been discussed in 

Radioprotection has also been observed for metal chelates, particularly those of copper. 

Case Progress in Radiation Therapy (Ed. F. Buschke) pp. 1—18. Grune and Stratton, New York (1958). 

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More recent approaches to the effects of the ligands on the redox activity of metal complexes are based upon the assumption that the electrode potential of a redox change involving a metal complex is determined by the additivity of the electronic contribution of all the ligands linked to the metal centre, or to the overall balance between the c-donor and the 7r-acceptor capability of each ligand.3 In particular two ligand electrochemical parameters have gained popularity ... 

Influence of Solubility and Structure on the Activity of Metal Complex Oxidation Catalysts... 

The bridging coordination of M-X and M-L fragments by ambiphilic ligands, as described in this section, open interesting perspectives in catalysis. Complex 94 nicely illustrates the possibility to cooperatively activate functionalized 7i-systems by concomitant coordination to a metal center and a Lewis acid. In addition, and in line with what is typically encountered upon activation of metal complexes with Lewis... 

The Mechanism of the Reduction of (ImH)[trans-RuCl4(dmso)(Im)i by Ascorbic Acid Antitumor activity of metal complexes is not restricted to those of Pt (II) cited earlier. Some recent reports of possible candidates for the purpose of functioning as substitutes for the Pt(II) range of complexes have included Pd(II)... 

In some cases (e.g., gasoline), autoxidation of hydrocarbons is undesirable, and trace amounts of metal catalysts may often be deactivated by the addition of suitable chelating agents. The latter affect the catalytic activity of metal complexes by hindering or preventing the formation of catalyst-hydroperoxide or catalyst-substrate complexes by blocking sites of attack or by altering the redox potential of the metal ion. 

Examples of reactions of coordinated imidazoles are discussed later (see Section 3.02.5.3.5), but some conception of the effects of such coordination can be obtained by observation of the H NMR spectra where complex formation usually causes deshielding <89BSF472>. The biological activity of metal complexes of imidazoles and benzimidazoles has been reviewed <85RCR676>. 

As discussed in Section IV.A.4, hydrolysis of peptide bonds of oligopeptides or proteins by various soluble metal complexes untethered to the substrate is usually very slow under physiological conditions (pH 7.5 and 37°C). In some cases, fairly fast peptide hydrolysis was achieved, but the product was not released from the metal complex, preventing catalytic turnover. To design an effective synthetic metalloproteases manifesting high activity and catalytic turnover at near physiological pH values, it is necessary to raise the activity of metal complexes substantially and to facilitate release of hydrolysis products from the metal complexes. 

There was an attempt to raise the proteolytic activity of metal complexes either by immobilizing the catalytic center on hydrophobic resins or by raising the effective molarity of the catalytic center. We tried to achieve catalytic... 

Chemical and Biological Activity of Metal Complexes Containing Dimethyl Sulfoxide... 

In a parallel study, we have investigated the activity of metal complexes in parasitic diseases and, especially, trypanosomiasis, responsible for sleeping sickness in man. Of the parasitic diseases, this does not now present a major problem, compared to malaria, filariasis and schistosomiasis, but the prevalence of the disease has increased in latter years due to dramatic changes in the political and economic climate in the tropical areas (48). A number of platinum derivatives has been found to be active vitro and vivo against rhodesiense and the platinum complexes, as a family, may be considered active trypanocides... 

Metallodendrimers are an interesting class of molecules in the area of dendrimer chemistry. They combine dendritic structures with the specific activity of metal complex centers. Metal coordination has facilitated the synthesis of a number of dendritic, supramolecular structures. Metals have been incorporated in all of the topologically different parts of dendrimers in the repeat or branching unit, in the molecular core and in the peripheral units. Because this field of metallodendrimers has been reviewed recently [195-197], only a few examples are given below. Other supramolecular organizations such as catenanes and rotaxanes have been mentioned previously in this chapter. 

Tertiary phosphines are valuable substrates for testing catalytic activity of metal complexes toward oxygenations. 

Kumar, A., and D. Kumar. 2007. Synthesis and antimicrobial activity of metal complexes from 2-(172 -hydroxynaphthyl)benzoxazoles. Arkivoc 14 117-125. 

N. Farrell Chemical and Biological Activity of Metal Complexes Containing Dimethyl Sulfoxide (Platinum, Gold and Other Metal Chemotherapeutic Agents, ACS Symposium Series v. 209, Ed. S. J. Lippard) p. 279. ACS, Washington (1983). 

Anacona J, Toledo C (2002) Synthesis and antibacterial activity of metal complexes of dpro-floxacin. Trans Met Chem 26 228-236... 

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