Zinc ion, chelation

Camosine s copper and zinc ion-chelating activity may also contribute to suppression of neurodegenerative conditions (Hipkiss, 2005). Zinc has been reported to be associated with the amyloid which accumulates in AD brain (Bush and Tanzi, 2002 Danscher et al, 1997 Religa et al, 2006), while copper ion-mediated oxidation of neuronal proteins may accompany both AD and PD (Smith et al., 2006). Carnosine has been found to protect cultured neurons against zinc-induced death (Kawahara et al,... 

Enantiomerically pure /J-keto sulfoxides are prepared easily via condensation of a-lithiosulfinyl carbanions with esters. Reduction of the carbonyl group in such /J-keto sulfoxides leads to diastereomeric /J-hydroxysulfoxides. The major recent advance in this area has been the discovery that non-chelating hydride donors (e.g., diisobutylaluminium hydride, DIBAL) tend to form one /J-hydroxysulfoxide while chelating hydride donors [e.g., lithium aluminium hydride (LAH), or DIBAL in the presence of divalent zinc ions] tend to produce the diastereomeric /J-hydroxysulfoxide. The level of diastereoselectivity is often very high. For example, enantiomerically pure /J-ketosulfoxide 32 is reduced by LAH in diethyl ether to give mainly the (RR)-diastereomer whereas DIBAL produces exclusively the (.S R)-diastereomer (equation 30)53-69. A second example is shown in... 

Ligands with more than one coordination site have been synthesized. A superstructured porphyrin ligand with an additional binding site for a second zinc ion was synthesized. The X-ray structure shows a bridging acetate ligand between the porphyrin cavity-bound zinc and the zinc bound to the appended tripodal chelator.778... 

Chelating aldehydes such as 2-pyridine carbaldehyde and 2-dimethylamino benzaldehyde improve the stability of the aldehyde complexes via N,0 chelation. NMR studies show that the complexes are present in solution without an excess of aldehyde and can be formed in the presence of donor ligands. The X-ray structures showed longer and weaker Zn—O bonds when more than one chelating ligand was present. IR demonstrates the variation in C=0 bond strengths and how the environment of the zinc ion will influence potential catalytic activity via reaction rates or pathways. Tetrahedral chelate complexes, and octahedral bis- and tris-chelate complexes, were isolated.843... 

The use of plants for medicinal purposes is an ancient practice. Nature, with its wealth of traditional knowledge has been the source of inspiration for numerous drugs currently used for the improvement of life as well as treatment for a cure. Considering the beneficial role of many plants and fruits, they were included in the human diets. In many instances, the knowledge of the underlying mechanism of action of a particular natural product is incomplete. Continuous investigation can lead to new mechanisms and new structures, which may open up entirely new windows and perspectives. For instance, before the discovery of apicidin and bispyri-dinium diene, it was believed that unless there is a classical chelator for zinc ion, it cannot be a HDAC inhibitor. SAHA has been approved by FDA, which is inspired from the natural product trichostatin. The natural product, romidepsin has also been approved by FDA and many are on clinical trials. Currently, isozyme-selective inhibition for HDAC is at its nascent stage. The invention of some novel molecules or invention of some novel natural product structures with synthetic modifications will solve the problem. 

Carnosine is an avid chelator of metal ions (Baran, 2000). Complexes with calcium, copper, and zinc ions have been described (Trombley et ah, 2000). It is possible, therefore, that carnosine could exert some sort of control of calcium metabolism in muscle tissue (heart or skeletal). It is also likely that the dipeptide controls the availability of zinc ions in neuronal tissue, especially the olfactory lobe where both carnosine and zinc are enriched (Bakardjiev, 1997 Bonfanti et ah, 1999 Sassoe-Pognetto et ah, 1993). Zinc-camosine complexes, called polaprezinc, are also effective in the repair of ulcers and other lesions in the alimentary tract (Matsukura and Tanaka, 2000). 

In conclusion, ID coordination polymer [Zn(tmbdc)(dmso)2]-2(DMSO) 2 has been synthesized with 2,3,5,6-tetramethyl-l,4-benzenedicarboxylic acid in DMSO. The structure contains ID chains formed by octahedraly coordinated Zn ions chelated by the carboxyl groups of tmbdc, rather than the 2D (4,4) nets constructed from paddle-wheel SBU of pairs Zn ions as found in [Zn2(bdc)2(dmso)2]-5DMSO 1. Analysis of the structure reveals that the steric hindrance of die four methyl groups of tmbdc determines the coordination environments of the zinc ions and the coordination modes of the carboxyls, and thus the final structures of the coordination polymers. The result also shows that DMSO is a stronger ancillary ligand and is also easier to be included in the structures of coordination polymers, compared to DMF. DMSO can be a better solvent for the syntheses of porous coordination polymers. 

Elimination of metal ions is a second major function of supported chelators. And a variety of conditions may be envisioned. Electroplating firms can be faced with the need to remove metal ions from solutions as part of an EPA-approved disposal protocol. A radiator shop may be faced with a need to remove waste zinc ion before allowing water to go into a sewer, in an effort to minimize the danger of killing bacteria used in sewage treatment procedures. The Berkeley Pit (vide infra) represents an outstanding example of the need to remove waste copper. 

In the binuclear complex, [(bpy)2(0H2)Zn(p2-C03)Zn(bpy)2] (N03)2-7H20 (F), the two N4-bound Znx and Zn2 ions are bridged by carbonate in monodentate and bidentate modes, the Znx being coordinated to one H20. Both the zinc ions are octahedrally coordinated with a relatively greater degree of distortion at Zn2 due to the chelating mode of the carbonate bridge. In these binuclear carbonate complexes of Zn(II) and Cu(II) an unexpected behavior, viz. Zn-0 distances < distances for carbonate coordination, was reported (341). 

Alkaline phosphatase can be reversibly denatured by thiol reduction in the presence of urea (88), a treatment which dissociates the dimer. Proteins purified from alkaline phosphatase-negative mutants that are antigenically related to alkaline phosphatase are readily and reversibly dissociated by acid (65). Normal alkaline phosphatase is more stable but at a lower pH, less than 3.0, it too forms monomers with release of zinc ions. However, chelating agents that remove zinc do not cause... 

Some of the disagreement in the metal binding work may arise from uncertainties as to whether binding was controlled by kinetics or thermodynamics. To illustrate what is meant, consider the addition of one zinc ion to apoenzyme. Is the site where this zinc ion is bound the most stable site or the one most accessible Evidently this might depend upon the time, and whether or not the concentration of zinc is controlled by a chelating agent. 

Fig. 15. Coordination sphere of the zinc ion in the FucA crystal structure liganded by the chelating inhibitor phosphoglycolohydroxamate, which is a transition state analog for activated DHAP...

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