Metal chelates, reviews

In the rhizosphere, microorganisms utilize either organic acids or phytosiderophores to transport iron or produce their own low-molecular-weight metal chelators, called siderophores. There are a wide variety of siderophores in nature and some of them have now been identified and chemically purified (54). Pre.sently, three general mechanisms are recognized for utilization of these compounds by microorganisms. These include a shuttle mechanism in which chelators deliver iron to a reductase on the cell surface, direct uptake of metallated siderophores with destructive hydrolysis of the chelator inside the cell, and direct uptake followed by reductive removal of iron and resecretion of the chelator (for reviews, see Refs. 29 and 54). 

In this review, well-defined metal-containing PAEs are described whose primary structure is represented by one of the schematic drawings A-C and E shown in Fig. 2. In contrast to the structures shown in the A-C systems, E has a conjugated phenyleneethynylene with metal chelates as end groups. PAEs containing metal complex as side groups (D) have, up to now, not been described in the literature. The classes of compounds such as metal-bridged alkynes, the poly(metallayne)s, and polymer carbyne complexes (structures G and H) do not in fact represent PAEs. 

Perhaps the most significant benzopyridine fungicides are the normal metal chelate compounds derived from 8-hydroxyquinoline (33), itself manufactured from quinoline by sulfonation/caustic fusion. Applications of (33) have been reviewed (56CRV217). Related compounds include quinacetol sulfate (34) (B-77MI20901) and halacrinate (35) (B-77MI20901). 

Vanadyl compounds hydrolyze much more easily than any other metal chelates of the first transition series, and in some conditions the vanadyl 1 1 chelates prefer combination with hydroxyl to a second ligand molecule.385 Unless otherwise stated formation constants fixyz presented in this review correspond to the reaction shown in equation (15). 

The sulfide group forms a large number of complexes where it is in chelation with a different heteroatom. Among the common heteroatoms are N, P and As. These complexes are too numerous to list here, but individual complexes can be found from Table 9 or from refs. 1224 and 1667. It is also possible to synthesize compounds which will form bi-, tri- and tetra-dentate complexes to platinum(II), where sulfur, selenium and tellurium.are the only atoms which coordinate to the metal. A review of complexes formed from ligands of the type RS(CH2) SR has been recently published.1734 This article outlines the synthesis, reactions and spectroscopy of these complexes, and allows the complexes of platinum to be placed in context with those of other transition metals. 

In view of the presence of active functional groups at suitable sites in the above ligands and their substituted derivatives, these tend to form coordination compounds/chelates with a large number of metals. Excellent reviews have been published on the complex compounds of biguanides151152 and guanylureas, 51 and biuret.153,154... 

Chemical structures of several chelators. Ferroxamine (ferrioxamine) without the chelated iron is deferoxamine. It is represented here to show the functional groups the iron is actually held in a caged system. The structures of the in vivo metal-chelator complexes for dimercaprol, succimer, penicillamine, and unithiol (not shown), are not known and may involve the formation of mixed disulfides with amino acids. (Modified and reproduced, with permission, from Meyers FH, Jawetz E, Goldfien A Review of Medical Pharmacology, 7th ed. McGraw-Hill, 1980.)... 

The data found in a number of monographs [127-129] and reviews [86,ISO-135] allows the creation, for some classes of coordination, of a concrete ligand environment and facilitates the selection of metal contributing to the controlled formation of definite polyhedrons. This situation is present especially in a series of metal chelates with the most widely used coordination numbers of the central atom, i.e., 4, 5, and 6. 

Due to the success of m-platin in anticancer therapy, medicinal chemists have rapidly begun to evaluate the utility of metal complexes as antimalarials [91-94], We will not report all of the bioinorganic compounds that have been synthesized and tested. In the following, we will just focus on the most representative agents. For example, we will not review the metal chelators. 

Many synthetic dyes such as porphyrins, acridine, thlonlne and flavin dyes have been used in photosensltlzatlon of electron transfer reactions. In the past few years several promising organometalllc compounds have been prepared as substitutes for the natural labile chlorophyll. These organometalllcs Include a variety of metals, chelated to bipyridine or porphyrin ligands ( ). The photophysical properties of these sensitizers and their potential use in artificial photosynthetic devices have been extensively reviewed ( 7, ). In particular, sensitizers such as... 

Chen, C.H. and Shi, J. (1998) Metal chelates as emitting materials for organic electroluminescence. Coordination Chemistry Reviews, 171, 161-174. 

The present section and Section IV.A.4 complement each other. The GC of metal chelates derived from monothio-/3-diketones, /3-diketones, -dithioketones and /3-keto-enamines was reviewed. The discussion includes column phenomena, analytical improvements and limitations and various applications . A study of the GC behavior of Group 13 /9-diketonates 37 shows that when the chelate contains a Mef group its volatility is enhanced, while a Ph group tends to decrease it. When R and R are alkyl groups the retention time of the chelates increases with the molecular weight, but it does not depend on the volatility however, the retention time of the chelates containing a Mef group is almost inversely correlated with the volatility . ... 

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