Natural metal complexes

Based on the models of natural metal complexes synthetic metal complexes have been developed for different purposes. They consist of a synthetic polymer, which is the replacement of the biopolymer protein in the natural metal complexes, and a specific synthetic ligand that is able to bind the metal ions. The basic model of synthetic metal complexes is shown in Figure 7. 

The field of application of this method is quite large, especially at the level of all classes of biological macromolecules, e.g., polysaccharides, antibiotics, natural metal complexes, etc. This is shown by the observation of ions with masses of 4000 units produced by peptides composed of 29 amino acid residues [84]. The method seems to be sensitive in the ng and pg range of sample detection. 

Oligomers of Non-natural Metal Complex Amino Acids... 

Fig. 3.33 (a) Schematic drawing of natural (left) and non-natural metal complex amino acid (right). 

Magnetic circular dicliroism (MCD) is independent of, and thus complementary to, the natural CD associated with chirality of nuclear stmcture or solvation. Closely related to the Zeeman effect, MCD is most often associated with orbital and spin degeneracies in cliromophores. Chemical applications are thus typically found in systems where a chromophore of high symmetry is present metal complexes, poriihyrins and other aromatics, and haem proteins are... 

In mordant dyes, phenols, naphthols, and enolizable carbonyl compounds, such as pyrazolones, are generally the couplers. As a rule, 2 1 metal complexes are formed ia the afterchroming process. A typical example of a mordant dye is Eriochrome Black T (18b) which is made from the important dyestuff iatermediate nitro-l,2,4-acid, 4-amiQO-3-hydroxy-7-nitro-l-naphthalenesulfonic acid [6259-63-8]. Eriochrome Red B [3618-63-1] (49) (Cl Mordant Red 7 Cl 18760) (1, 2,4-acid — l-phenyl-3-methyl-5-pyrazolone) is another example. The equiUbrium of the two tautomeric forms depends on the nature of the solvent. 

In this case the efficiency of metal complex modifiers is controlled not only by their thermal stability, the nature of the metal and the ligand used, but depends considerably on the reactions in the solution, mainly on exchange reaction like Me,L -i- Me = MeU + Me L, which variously affect the... 

As one would expect, in those cases in which the ionic liquid acts as a co-catalyst, the nature of the ionic liquid becomes very important for the reactivity of the transition metal complex. The opportunity to optimize the ionic medium used, by variation of the halide salt, the Lewis acid, and the ratio of the two components forming the ionic liquid, opens up enormous potential for optimization. However, the choice of these parameters may be restricted by some possible incompatibilities with the feedstock used. Undesired side reactions caused by the Lewis acidity of the ionic liquid or by strong interaction between the Lewis acidic ionic liquid and, for example, some oxygen functionalities in the substrate have to be considered. 

Many transition metal-catalyzed reactions have already been studied in ionic liquids. In several cases, significant differences in activity and selectivity from their counterparts in conventional organic media have been observed (see Section 5.2.4). However, almost all attempts so far to explain the special reactivity of catalysts in ionic liquids have been based on product analysis. Even if it is correct to argue that a catalyst is more active because it produces more product, this is not the type of explanation that can help in the development of a more general understanding of what happens to a transition metal complex under catalytic conditions in a certain ionic liquid. Clearly, much more spectroscopic and analytical work is needed to provide better understanding of the nature of an active catalytic species in ionic liquids and to explain some of the observed ionic liquid effects on a rational, molecular level. 

Vibrational spectra of transition metal complexes and the nature of the metal-ligand bond. D. W. James and M. J. Nolan, Prog. Inorg. Chem., 1968,9,195-275 (198). 

Kinetic studies of colloidal metal complex species relevant to natural waters. C. H. Langford and M. K, S. Mak, Comments Inorg. Chem., 1983, 2, 127-143 (21). 

---