Acids, carboxylic chelated

Matrix metalloproteinases (MMPs) are a class of zinc- and calcium-dependent enzymes that are responsible for the metabolism of extracellular matrix proteins [27]. Increased activity of MMPs has been associated with pathological diseases such as arthritis, cancer, multiple sclerosis and Alzheimer s disease [28-31]. Therefore, they constitute an important group of drug targets. Their inhibition is accomplished by blocking the active site of the catalytic domain with ligands that contain hydroxamic or carboxylic acids to chelate the Zn metal. The identification of low molecular weight compounds that contain different scaffolds may lead to the development of a new class of specific inhibitors. 

In addition to phosphate and halide anion binding, carboxylate chelation by sapphyrin macrocycles has been the subject of recent investigation. To date, two crystal structures have been solved. A 2 1 complex formed between diprotonated sapphyrin 3 and trifluoroacetic acid shows that the oxyanions are chelated above and below the sapphyrin plane (Figure 10). ° Greater complexity of organi-... 

In the amino acids, the chelated three-center bonds have the - NH3 group as donor, and they are almost invariably unsymmetrical. The primary and strong interaction is to one of the carboxylate (or sulfate) oxygen atoms, the secondary (and weaker) interaction to the other oxygen atom resulting from stereochemical constraints imposed by packing of the molecules in the crystal lattice. 

The use of bipy or terp as the auxiliary ligand can also lead to the formation of the monomeric or dimeric structures. In [PrL3(bipy)2] (HE = trichloroacetic acid) [42], the three carboxylates chelate (ti ) to Pr(III), whereas the two bipy coordinate to the metal center with their two nitrogen atoms. [TbE3(terp)(H20)]2 (E = 4-aminobenzonic acid) is a dimer, where the... 

Under natural conditions, Wright and Schnitzer (1963) consider that fulvic acid is the chief ligand bringing about the movement of iron and aluminum in podzol development. Their studies indicate that fulvic acid consists of an aromatic nucleus to which carboxyls, hydroxyls and carbonyls are attached as functional groups. The fulvic acid probably chelates with iron and aluminum, etc., as it moves downward, and at lower levels precipitation occurs. This ability of fractions of soil organic matter to make iron mobile probably accounts for the fact that plants can obtain their required amounts even though the soil iron is present only in very insoluble forms. 

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