Metal ion chelators

As strong metal ion chelators due to their catechol structure, tea flavonoids are able to bind and thus decrease the level of free cellular ferric and ferrous ions, which are required for the generation of reactive oxygen radicals via the Fenton reaction (Yang and Wang, 1993). 

Elling, C. E., Thirstrup, K., Holst, B., and Schwartz, T. W., Conversion of agonist site to metal-ion chelator site in the beta(2)-adrenergic receptor, Proc. Natl. Acad. Sci. USA, 96(22), 12322-12327, 1999. Gether, U., Uncovering molecular mechanisms involved in activation of G-protein-coupled receptors, Endocr. 

In this laboratory, we also include the metal ion chelators EDTA (ethylene diamine tetraacetic acid binds, e.g., Mg2 1 -ions) and EGTA (ethylene glycol-bis(2-aminoethyl)-Al,iV,iV/,iV/,-tetraacetic acid binds, e.g., Ca2+-ions) in our lysis buffers. These agents help prevent phosphatase action (by the metal ion-dependent phosphatase PP2C, which is not inhibited by microcystin-LR), metal (Ca2+) dependent proteinases, and protein kinases, which require divalent cations such as Mg2 1 (and, in some cases, also Ca2+). We also use a mix of proteinase inhibitors that inhibit a broad range of proteolytic enzymes, including serine and cysteine proteinases. 

Much attention has been devoted to the examination of chiral enolate systems in which metal ion chelation may play an important role in establishing a fixed stereochemical relationship between the resident chirality and the enolate moiety. This has resulted in the conclusion that enolate geometry is critical in the definition of 7r-l acial selection. The following sections discuss this effort in several different chemical systems. 

The enolization product depends on the structure of the carbonyl substrate When //-OH is present in the carbonyl compound, (Z)-enolate is the major product due to the metal ion chelation,200 whereas (fs)-enolate is the major product in the absence of a //-OH group.22 It is worth noting that the yield is normally low for //-OH carbonyl substrates because of the tendency for //-elimination. 

Evans and Takacs23 demonstrated a diastereoselective alkylation based on metal ion chelation of a lithium enolate derived from a prolinol-type chiral auxiliary. This method can provide effective syntheses of a-substituted carbox-... 

Transition metals (iron, copper, nickel and cobalt) catalyse oxidation by shortening the induction period, and by promoting free radical formation [60]. Hong et al. [61] reported on the oxidation of a substimted a-hydroxyamine in an intravenous formulation. The kinetic investigations showed that the molecule underwent a one-electron transfer oxidative mechanism, which was catalysed by transition metals. This yielded two oxidative degradants 4-hydroxybenzalde-hyde and 4-hydroxy-4-phenylpiperidine. It has been previously shown that a-hydroxyamines are good metal ion chelators [62], and that this can induce oxidative attack on the a-hydroxy functionality. 

Any substance that stabihzes the concentration of one of its dissociated species, most commonly a proton (or more properly a hydronium ion). The free concentration of a metal ion may also be buffered by use of a metal ion-chelator complex, such as Ca EGTA or KMgEDTA. 

Selected entries from Methods in Enzymology [vol, page(s)] Buffer capacity, 63, 4 choice, 63, 19, 20, 285 metal ion chelation effects, 63, 225, 226, 287, 298, 299 dielectric constant effect on pK, 63, 226 dilution, 63, 20 equilibrium constant effects, 63, 18 heavy water, 63, 226, 227 ionic strength effects, 63, 226,... 

To this end, the authors perform a second comet assay. Only limited results, however, are shared PM2 5 from only one city (Baton Rouge) was tested using only one cell line (K562 myeloid leukemia cells), thereby following a broad-to-narrow approach. The results are presented in excerpt 4E. As shown in Eigure 3 (excerpt 4E), cells were exposed to (A) a blank extract, (B) a PM2 5 extract, (C, D, E) a PM2 5 extract mixed with one of three different free radical scavengers, (E) a positive control, and (G, El) a PM2 5 extract mixed with one of two different metal-ion chelators. The free radical scavengers remove free radicals the... 

Possible biochemical functions (Quinn et al, 1992) of camosine include control of pH, immunostimulant, wound healing agent, antioxidant, metal-ion chelator, carbonyl scavenger, and antiglycator (Table 3.3). The evidence for some of these proposals is highly varied, however. 

Laboratory research has demonstrated that the liquid corona technology can treat a variety of wastewater contaminants such as carbon tetrachloride, metal ion chelators, and industrial dyes. The technology successfully reduced initial organic contaminant concentrations (by more than 99%) for the following contaminants after exposure to corona discharge trichloroethylene (TCE), ethylene-diamine-tetraacetic acid (EDTA), and benzoic acid. Additionally, liquid corona has demonstrated removal success with carbon tetrachloride, pentachlorophenol, and perchloroethylene. 

The structural design of a fuel stabilizer molecule can enable some compounds to function in metal ion chelation. Most stabilizers have nitrogen atoms within the structure of the compound. The electron pair on nitrogen can function in metal chelation if the nitrogen atoms are oriented in the appropriate conformation. 

On the basis of this evidence it was postulated that a 1 to 1 complex is formed between the metal ion and the amino acid ester, in which the metal ion chelates with the amino group and the carbonyl oxygen of the ester, and that this chelate is attacked by hydroxide ion to give the products of reaction through the intermediate formation of a tetrahedral addition compound. 

Major applications of chitosan were previously focused on sludge dewatering, food processing, and metal ion chelation until the mid-1980s. Further, it has received considerable attention for its commercial applications in agriculture, chemistry, biomedical, food, cosmetic, and biotechnology industries (Alasalvar et ah, 2002 Knorr, 1984 Kurita,... 

Metal ion chelates of various porphyrins, differing in their substituents at positions 1-8, are intimately involved in a great number of life processes. Iron protoporphyrin (13) is the most common form and serves as the cofactor of a large number of enzymes. Usually (13) is non-covalently bound to its conjugate apoenzymes. Examples of covalently attached (13) are provided by c-type cytochromes, the attachment being between two vinyl side chains of (13) and two cysteine residues of the protein. Other biologically important derivatives of porphyrin include chlorophyll a (14), bacteriochlorophyll a and heme a (B-79MI11002). 

Polymerizable indazole derivatives have received some attention with respect to the preparation of redox polymers and metal ion chelating polymers (73MI11102). Monomers such as 3-vinyl-4,7-dihydro-1//-4,7-indazoledione (63) are readily prepared by 1,3-dipolar cycloaddition of vinyldiazomethane to 1,4-benzoquinones. Crosslinked, low swelling, recyclable redox polymers have been prepared from these monomers. 

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