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. 

Binding of metal ions to carrier ligands occurs in competition to the ligands in the medium (Figure 9a, adapted from [192]). The metal ions react with biological carrier ligands. 

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. ... 

Example 2.3 Stoichiometry of H+ Release by Binding of Metal Ions ... 

Binding of metal ions by amorphous silica. 300 mg Si02 dm-3, [Mej = 10 5 MJ. The fraction of metal ion bound was calculated from peak currents measured with differential pulse polarography. 

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. 

A recently developed method to prepare particles of a narrow size distribution is the dendrimer-assisted method. In this method (Fig. 1.1), metal ions in a solution are complexed to a dendrimer, mostly with the amine groups in the outer shell of an OH-terminated poly(amidoamine), for example. The complexed metal ions are subsequently reduced to metal atoms which agglomerate into a metal particle. Because dendrimers can be prepared with high purity, and there is a strong binding of metal ions... 

Binding of metal ion/ complex/ chelate at a macromolecular chain, network or surface... 

Fig. 6A,B Titration with ions. The hammerhead ribozyme reaction was examined on a background of ions A data obtained by Lott et al. [54]. The proposed binding of metal ions is illustrated B data obtained by Nakamatsu et al. [87]. An unmodified ribozyme (R34 gray curve) and a modified ribozyme (7-deaza-R34 black curve) were used. The rate constants were normalized by reference to the maximum rate constant ([La ]=3 (mol/1). Reactions were performed under single-turnover conditions in the presence of 80 nmol/1 ribozyme and 40 nmol/1 substrate at 37 °C...

Fig. 18. a-Hydroxycarboxylate binding of metal ions. In this case there is a strong tendency for chelation of the metal ion, although it may lie well out of the plane of the liganding bidentate group, (a) View onto OOC-C-OH plane and (b) view along OOC-C-OH plane. 

In the previous section, we considered reporter molecules, which interact reversibly in a physical sense, for example, solvation of gas, protonation, or binding of metal ion by a ligand. Other reporter molecules reveal activity based on irreversible bond cleavage to release a distinct product. This may be more akin to the metabolism of drugs, but these reporters can be tailored to interrogate specific biological processes. 

On this occasion, we would like to emphasize that so-called cooperative phenomena or allosteric phenomena are not characteristic of biological systems alone but are often observed also in synthetic polymer systems. For example, we cite Fig. 25, which shows the adsorption of metal ions on a synthetic polymer ligand112. The adsorption of Cu ions on the polymer ligand is sigmoidal. This cooperative binding of metal ions is easily understood by following Scheme 12. 

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. 

Kinetic studies of the nucleotide analogs, y-phenylpropyl di- and triphosphate, have been undertaken to define the role of the adenosine residue in the chemical and enzymic reactions of adenosine triphosphate. A catalytic function associated with binding of metal ions at the adenine nitrogens has been ascribed to the adenosine moiety in phosphate transfer reactions in which adenosine di- or triphosphates function as the phosphate source109-"2. The pH-rate profile (Fig. 6) for the hydrolysis of -y-phenylpropyl diphosphate... 

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. 

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