Chelate binding

Figure 20.15 An affinity chromatography support containing iminodiacetic acid groups chelated with nickel may be used to remove excess enzyme after reactions to produce antibody-enzyme conjugates. The nickel chelate binds to the antibody in the Fc region, retaining the conjugate while allowing free enzyme to pass through the gel unretarded.

Chelators bind metals so that they are more readily excreted in the urine. In the past, chelators were routinely prescribed to people with elevated blood lead levels in an effort to accelerate the excretion of lead in the urine. Unless the blood levels are excessively elevated the current treatment is to determine the source of the lead exposure and take remedial action. The problem with chelators is that they are non-specific and bind useful agents such as calcium. 

A very interesting aspect of platinum-DNA interactions concerns the nature of the resulting adducts and their relative quantities. Due to the bifunctional nature of cis-Pt, several types of adducts in the DNA can be expected to be formed, to be distinguished in (1) interstrand chelates (binding of two nucleobases that are each positioned in one of the complementary DNA strands), (2) intrastrand chelates (binding of two nucleobases within the same DNA strands), (3) intrabase chelates (binding to two different atoms in one base), and (4) DNA-protein cross-links. 

Low Molecular Weight Gd3+Chelates Binding to Serum Proteins. . 212... 

The second approach involves the addition of a chelated form of the transition metal, for example, Ci2-dien plus zinc(II) (where Ci2-dien is 4-dodecyldiethylenediamine), into the mobile phase (Fig. 2.7). In this example, the triamine chelate binds strongly to the metal ion, forming a complex cationic counterion. The metal chelate represents a conformationally semirigid structure with a local polarized charge center. As such, not only is there the typical electrostatic attraction of anions for the positively charged... 

Chelation Binding of an inorganic ion (e.g., heavy metal) by an organic molecule. 

We also investigated chelate binding by dimers of a synthetic hydrophobic macrocycle, in place ofthecyclodextrins [187]. In the systems examined the chelate effect was weaker than that seen with the cyclodextrin dimers. We also studied the strong binding of cholesterol by some cyclodextrin dimers and a cyclodextrin polymer, and saw that the large sterol could occupy parts of two binding cavities [188]. 

Changes in electron spin relaxation can affect relaxivities when chelates bind to proteins and rotational rates become slowed. For the Gd(BOM)3DTPA system, Aime found that went from 15.3 ns to 57.9 ns when the complex bound to HSA, while for MS-325 went from 2.1 ns to 2.5 ns [52]. Both of these relaxation changes were calculated for a magnetic field value of 0.47 T from data obtained by NMR at 25 °C. The authors advise caution in making use of data... 

Complete removal of zinc and thus inactivation of the enzyme can be accomplished in these systems at low D-PEN concentrations if a secondary scavenger chelator is added to the system. Such chelators bind metal that has been released from the enzyme but do not participate in the release.In the case of carboxypeptidase A, aM thionein (apo-metallothionen see Metallothioneins) inhibits catalysis by only about 10% over a 15-min period consistent with its action as a secondary chelator. However, in the presence of 250 aM D-PEN and aM thionein total inhibition is achieved in less than 15 min. D-PEN accelerates zinc equilibration between carboxypeptidase A and thionein (Scheme 1). This is accomplished by D-PEN catalyzing the release of Zn from the enzyme. Since D-PEN is in vast excess over both the enzyme and thionein, the enzyme-released zinc would be expected to bind to D-PEN first. However, since thionein binds zinc more tightly than D-penicillamine and can accept 7 moles of zinc per mole of thionein, it should be the ultimate acceptor of the released zinc. 

Some TCA masks have been presented as chelated TCA. Chelation is a medical therapy that aims to detoxify the body of harmful minerals and metals. Chemically, chelation is the process by which an organic substance (the chelator) binds metal ions (iron, copper, lead, calcium, etc.) into inactive, non-toxic and water-soluble complexes that are easily eliminated in the urine. Intravenous chelation therapy (e.g. with ethylenediamine tetra acetic acid, EDTA) is often used to treat poisoning with heavy metals, including lead. The use of the term chelation therefore seems inappropriate as far as TCA is concerned, and has no chemical basis since TCA is not a metal. The little information available states that chelation reduces the speed of penetration of TCA and therefore its depth of action. Might what we call chelation be partial inactivation of the TCA The directions of use for Accu Peel state that a process called chelation allows the TCA to reach an even depth at the same time as using lower concentrations of TCA . Might chelation, on the contrary, be a process that activates the TCA But how can TCA be activated ... 

Intercalation between complementary intrastrand nucleobases (type III) shows an intrahelical disposition of (i) in the case of A-T chelation, bindings appear at Ni adenine and N3 thymine (ii) in the case of the G-C chelation, the bindings appear at Ni guanine and N3 cytosine (Figure 7.6). The first approach is characteristic for Hg ", and the second for Cu " and Cd ". The binding is also possible to N7 guanine, N3 cytosine and to O from Cg, respectively C2. 

Fig. 7.6 Internal chelatization binding of to adjacent nucleobase pairs of DNA strands (a)...

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