Metal cation chelation

Roshal AD, Grigorovich AV, Doroshenko AO et al (1998) Flavonols and crown-flavonols as metal cation chelators. The different nature of Ba2+ and Mg2+ complexes. J Phys Chem A 102 5907-5914... 

Separation is based on the reversible chelate-complex formation between the chiral selector covalently bonded to the chromatographic support, and the chiral solute with transition metal cations. Chelation properties of both the chiral selector and the chiral solute are required. Compounds therefore need to have two polar functional groups in a favorable arrangement to each other, like a )3-amino acids, amino alcohols and a-hydroxy acids, which can form rings membered with central chelating metal ions, like Cu(II), Zn(II), Cyclic... 

For the determination of metal cations, chelation complexes formed with oxine (8-hydroxyquinolein), alizarine or benzoine are used. These complexes are extractable with organic solvents. 

For the determination of metal cations, chelates are created with oxine (8-hydroxyquinoline), alizarine or benzoin, then extracted by organic solvents. In biochemistry, fluorescence has numerous applications for the quantification of proteins or nucleic acids by means of reagents which can affix with specificity to these compounds. This approach, sometimes very elaborate, in association with electrophoresis constitutes a more sensitive and less restricting method than detection by radioactive substrates. 

It is apparent from the aforementioned biochemical systems that the electrochemical and electronic absorptive properties of porphyrins as well as supramolecular effects, including metal cation chelation, are essential aspects of porphyrin activity in nature, for instance, either as a component... 

Heavy metals Cation Polystyrene matrix Chelating functional groups Mineral acids... 

The formation of a single complex species rather than the stepwise production of such species will clearly simplify complexometric titrations and facilitate the detection of end points. Schwarzenbach2 realised that the acetate ion is able to form acetato complexes of low stability with nearly all polyvalent cations, and that if this property could be reinforced by the chelate effect, then much stronger complexes would be formed by most metal cations. He found that the aminopolycarboxylic acids are excellent complexing agents the most important of these is 1,2-diaminoethanetetra-aceticacid (ethylenediaminetetra-acetic acid). The formula (I) is preferred to (II), since it has been shown from measurements of the dissociation constants that two hydrogen atoms are probably held in the form of zwitterions. The values of pK are respectively pK, = 2.0, pK2 = 2.7,... 

Dagnall and West8 have described the formation and extraction of a blue ternary complex, Ag(I)-l,10-phenanthroline-bromopyrogallol red (BPR), as the basis of a highly sensitive spectrophotometric procedure for the determination of traces of silver (Section 6.16). The reaction mechanism for the formation of the blue complex in aqueous solution was investigated by photometric and potentiometric methods and these studies led to the conclusion that the complex is an ion association system, (Ag(phen)2)2BPR2, i.e. involving a cationic chelate complex of a metal ion (Ag + ) associated with an anionic counter ion derived from the dyestuff (BPR). Ternary complexes have been reviewed by Babko.9... 

Dyestuffs which form complexes with specific metal cations can serve as indicators of pM values 1 1-complexes (metal dyestuff = 1 1) are common, but l 2-complexes and 2 1-complexes also occur. The metal ion indicators, like EDTA itself, are chelating agents this implies that the dyestuff molecule possesses several ligand atoms suitably disposed for coordination with a metal atom. They can, of course, equally take up protons, which also produces a colour change metal ion indicators are therefore not only pM but also pH indicators. 

With a-alkyl-substituted chiral carbonyl compounds bearing an alkoxy group in the -position, the diastereoselectivity of nucleophilic addition reactions is influenced not only by steric factors, which can be described by the models of Cram and Felkin (see Section 1.3.1.1.), but also by a possible coordination of the nucleophile counterion with the /J-oxygen atom. Thus, coordination of the metal cation with the carbonyl oxygen and the /J-alkoxy substituent leads to a chelated transition state 1 which implies attack of the nucleophile from the least hindered side, opposite to the pseudoequatorial substituent R1. Therefore, the anb-diastereomer 2 should be formed in excess. With respect to the stereogenic center in the a-position, the predominant formation of the anft-diastereomer means that anti-Cram selectivity has occurred. 

Chelating ligands bind much more tightly to their metal cations than do ligands that possess only one donor atom. A good example is the ethylenediamine complex with. The ethylenediamine complex is much more stable than the analogous ammonia complex ... 

The metal ions are often added as salts of organic compounds, which form chelates. This causes a delayed gelation. Likewise, the components of the gelling agent are pumped down in two stages. Some metal cations cannot be used with brines. On the other hand, brines are often produced from wells, and it is desirable to find uses for them to avoid disposal processes. 

Metal cations can catalyze reactions of certain dienophiles. For example, Cu2+ strongly catalyzes addition reactions of 2-pyridyl styryl ketones, presumably through a chelate involving the carbonyl oxygen and pyridine nitrogen.31... 

In the ligand l,2-bis-(2-pyridylethynyl)benzene the pyridyl N atoms easily attain the appropriate separation for trans-chelation of metal cations. The 1 1 complex of the ligand with palladium(II) chloride has been structurally characterized.171,182... 

Complexation, or chelation, is the process by which metal ions and organic or other non-metallic molecules (called ligands) can combine to form stable metal-ligand complexes. The complex that is found will generally prevent the metal from undergoing other reactions or interactions that the free metal cation would. Complexation may be important in some situations however, the current level of understanding of the process is not very advanced, and the available information has not been shown to be particularly useful to quantitative modeling (5). 

It is for long known that all aforementioned acids form stable complex (chelate) compounds with numerous, especially transition metal cations (see, e.g., Refs. [21, 22]). This fact is pointed out in practically all papers on the subject. However, the composition of complex compounds, their stability, the type of bonding between metal cations and carboxylic anions on various stages of the synthesis, and possible role of steric factors in these phenomena are discussed in a very small number of publications. 

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. 

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