The Binding of Metal Ions

Mammalian metallothioneins typically bind seven metal ions in cluster structures, with bridging sulfur groups, as seen in the x-ray structure of the Cd5Zn2MT complex (86). It is therefore difficult to develop a simple formation-constant description for the binding of metal ions to MT (87), considering that protonation-deprotonation equilibria of the free protein itself should also be taken into account. However, the usefulness of Table VIII as a guide to the affinity of metal ions for mercapto donor ligands is seen in that the ability of metal ions to... 

Meares, C.F. (1986) Chelating agents for the binding of metal ions to antibodies. Nucl. Med. Biol. 13, 311-318. 

The most dramatic rate retardations of proton transfers have been observed when the acidic or basic site is contained within a molecular cavity. The first kinetic and equilibrium studies of the protonation of such a basic site were made with large ring bicyclic diamines [72] (Simmons and Park, 1968 Park and Simmons, 1968a). It was also observed (Park and Simmons, 1968b) that chloride ion could be trapped inside the diprotonated amines. The binding of metal ions and small molecules by macrocyclic compounds is now a well-known phenomenon (Pedersen, 1967, 1978 Lehn, 1978). In the first studies of proton encapsulation, equilibrium and kinetic measurements were made with several macrobicyclic diamines [72] using an nmr technique. 

Stability constants (ethylendiamine, glycinate, oxalate), surface complex formation constants and solubility products (sulfides) of transition ions. The surface complex formation constant is for the binding of metal ions to hydrous ferric oxide =Fe-OH + Me2+ =FeOMe++ H+ K. ... 

In a simplified form Eq. (ii) was used, decades ago, to assess metal ion adsorption to surfaces, by plotting log ([Meads] / [Me2+]) vs pH. (Kurbatov et al., 1951). The slope of this curve gives an idea on n. The model for this "Kurbatov-plot" assumes that the adsorbent =S is present in large excess and that the adsorption at constant pH is not affected by surface charge. Fig. 2.11 gives an example for the binding of metal ions to amorphous Si02. 

Discuss the binding of metal ions and of ligands in terms of the Lewis-acid-base theory. 

Metal reclamation from acid mine drainage and contaminated surface- and groundwater and wastewaters has been extensively studied. Technologies for metal removal from solution are based on the microbial—metal interactions discussed earlier the binding of metal ions to microbial cell surfaces the intracellular uptake of metals the volatilization of metals and the precipitation of metals via complexation with microbially produced ligands. 

Many important questions can be asked about the binding of metal ions within living cells. For example, What fraction of a given metal ion is free and what fraction is bound to organic molecules To what ligands is a metal bound Since many metal ions are toxic in excess, it is clear that homeostatic mechanisms must exist. How do such mechanisms sense the free metal ion activity within cells How does the body get rid of unwanted metal ions Answers to all these questions depend upon the quantitative differences in the binding of metal ions to the variety of potential binding sites found within a cell. 

Triple Helicates. The steric information contained in the oligo-bipy strands based on bipy units connected in the 6,6 positions is designed to yield double helices on complexation of metal ions undergoing tetrahedral coordination. Steric effects due to the 6,6 -disubstitution hinder the binding of metal ions of octahedral coordination geometry, which would be expected to lead to triple helical complexes. 

The binding of metal ions to peptides and proteins is a consequence of these molecules containing a great number of potential donor atoms through both the peptide backbone and amino acid side chains. The complexes formed exist in a variety of conformations that are sensitive to the pH environment of the complex [2,3]. With at least 20 amino acid combinations available, some with coordinating side chains, which can be linked in any particular order and length, the number of ligands that... 

Chemists have a variety of different interests in the transferrins. One interest concerns the chemistry of the binding of metal ions. No prosthetic or unusual chemical groupings are present in the proteins, and the binding is rather a property of the unique folding and juxtaposition of the normal chemical groupings in protein molecules (49). Another interest is in the mechanism of the release of iron by the serum transferrin to the tissues. The iron is so tightly bound that some investigators have attempted to invoke a special enzymatic mechanism for the dissociation in the tissues, but no evidence for this has been found. 

It is inferred that carboxyl ligands are important in the binding of metal ions. Thus, increasing the nmnber of such groups should increase the biomaterial-binding ability. This is achieved through succination, acetylation, and graft copolymerization of the biomaterial. 

The positive shift of red in the presence of metal ions is ascribed to the binding of metal ions (M" ) with Nlm (Eq. 3). 

When ET from an electron donor (D) to an electron acceptor (A) is coupled with the binding of metal ions (M" ) to the product radical anion (A ) (see above), the AS value becomes largely negative. This occurs due to restricted geometry in binding of metal ions in the transition state, whereas the value becomes smaller because of the metal ion binding that thermodynamically stabilizes the product radical anion. In contrast, the value ofET without binding of metal ions is normally... 

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