Ligands, metal binding

Fig. 5. Structure-based alignment of the sequences of the water-soluble Rieske fragment from bovine heart bci complex (ISF), the water-soluble Rieske fragment from spinach b f complex (RFS), and of the Rieske domain of naphthalene dioxygenase (NDO) and of the metal binding loops of rubredoxin (RXN) and transcriptional factor TFIIS (TFI). The numbering of the j3 strands is the same for the ISF and RFS. The metal binding ligands are highlighted the asterisks indicate those residues that are fully conserved between the three Rieske proteins.

Direct Photolysis of Surface-Located Inner Coordination Sphere Complexes. In the presence of a strong metal binding ligand, the underlying central metal ion in the surface layer of a metal oxide can exchange its structural OH" ions for the ligand. Thus, the association of citrate with an iron oxyhydroxide surface may be represented ... 

Another possible strategy towards colloids stabilized by micellar systems is the use of nonamphiphibc block copolymers containing metal binding ligands in only one of the blocks. For example, a poly(styrene)-fc ock-poly(m-vinyltriphenylphosphine) (PS-b-PPH) was examined with respect to its colloid formation properties (Fig. 6.5) [46]. 

Incorporation of Metal-Binding Ligands in a Peptide Chain... 

The preparation of new chelating agents containing vicinal thiols, such as the EDTA-bis-(0-2,3-dimercaptopropyl)ester (43), could lead to new metal-binding ligands which... 

The nitrone of piperidine reacts with phenyl vinyl ether to yield a 1,3-dipolar cycloaddition product. Benzylation led to a ring-opened product which was converted to a hydroxamic acid. This is desired functionality in medicinal chemistry because it is a metal-binding ligand <03S1221>. 

Peptides and proteins could be efficient metal binding ligands, because they have the functional groups for metal binding in their amino acid residues, and they can be produced at low cost by recombinant technologies. While many peptides and proteins are known to work as metal transport proteins in biological systems, metallothioneins (cysteine rich proteins with molecular weight of ca. 7 kDa) have attracted researchers attention for decades because they bind heavy metals in vivo [2]. The metallothioneins are considered to be involved in detoxication and metabolism of heavy metals. 

In this work, a fusion protein has been engineered from maltose binding protein (pmal) and human metallothionein (MT). The fusion protein (pmal-MT) has been expressed in E. coli, and purified with an amylose column. The purified fusion protein was immobilized on a solid matrix, and its characteristics as metal binding ligand have been studied. We have found that the pmal-MT ligand efficiently binds gallium ion, one of the valuable rare metals desired to be recovered from aqueous solution [3]. Different binding mechanisms for two metal ions have been elucidated based on HSAB (hard and soft acids and bases) theory [4]. 

In related work, Dong and Martin developed an assay that detects the catalytic activity of the enzymes pig liver esterase and porcine kidney leucine aminopeptidase by using substrates which have been labeled with metal-binding ligands [57], The enzymes catalyze changes in the substrates that affect their ability to bind to non-luminescent Ru complexes to form mixed-ligand complexes capable of ECL. 

Both plants and yeast are known to produce phytochelatins (PC ), peptide metal-binding ligands, in response to heavy metal (especially Cd2+) toxicity heavy metal ions activate the enzyme, PC synthase (PCS), which produces PC s from glutathione (GSH) see equation (7.1). 

Marshall, G.R., Amruta Reddy, P., Schall, O.F., Naik, A., Beusen, D.D., Ye, Y., Slomczynska, U. Combinatorial chemistry of metal-binding ligands. Chapter 5 in Advances in Supramolecular Chemistry Vol.8, pp. 174-243, 2002, Cerberus Press, FL... 

In a related strategy, Lehn and coworkers have prepared more rigid two-metal-binding and three-metal-binding ligands based on fused terpyridine derivatives, and have shown that these organize two or three terpyridine metal complexes in a rack-type arrangement, as in (40). The structures were supported by and C NMR spectroscopy, and a crystal structure for the diruthenium system was obtained [48]. 

To explore whether incorporation of native DNA structural elements such as the sugar-phosphate backbone into synthetic binders could be employed to dictate the formation of defined complexes such as helicates, the dinucleoside mimic (81) has been synthesised. In (81), the nucleic base has been replaced by the metal-binding ligand 2,2 -bipyridine, linked to the sugar by a methylene bridge... 

Enterobactin is a cyclic triester of 2,3-dihydroxy-N-benzoyl-L-serine (Fig. 6). It is accumulated by E. coli and other bacteria when grown under low iron conditions and mediates the anabolic utilization of iron by these microbes, as do the hydroxamate siderochromes mentioned above (13, 21). In enterobactin, however, the metal-binding ligands are provided by catechol groups and the sustaining backbone is held together by ester, rather than by amide, bonds. 

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