Ions, specifically bound

In the treatment of poisoning by lead or other metal ions, higher concentrations of chelant can be safely obtained in humans by administering Na2CaEDTA rather than Na EDTA. The metal ion is bound by displacing small amounts of Ca " that the body can tolerate. Use of Na EDTA would result in calcium chelation and thus serious depletion of calcium in the body fluids (44). Removal of iron in Cooley s anemia is accompHshed by using chelants that are relatively specific for iron (45). 

Such a result may be put in parallel with the determination of the bound cations obtained by ion-specific electrode or dual-wavelength spectrophotometric method, and analysed in terms of cooperativity [7,29,31]. 

The determination of the structure of the iron transporter, ferric-binding, protein (hFBP)t from Haemophilus influenzae (Bruns et ah, 1997) at 0.16 nm resolution shows that it is a member of the transferrin superfamily, which includes both the transferrins and a number of periplasmic binding proteins (PBP). The PBPs transport a wide variety of nutrients, including sugars, amino acids and ions, across the periplasm from the outer to the inner (plasma) membrane in bacteria (see Chapter 3). Iron binding by transferrins (see below) requires concomitant binding of a carbonate anion, which is located at the N-terminus of a helix. This corresponds to the site at which the anions are specifically bound in the bacterial periplasmic sulfate- and... 

The net charge at the hydrous oxide surface is established by the proton balance (adsorption of H or OH" and their complexes at the interface and specifically bound cations or anions. This charge can be determined from an alkalimetric-acidimetric titration curve and from a measurement of the extent of adsorption of specifically adsorbed ions. Specifically adsorbed cations (anions) increase (decrease) the pH of the point of zero charge (pzc) or the isoelectric point but lower (raise) the pH of the zero net proton condition (pznpc). 

Some colloid chemists often place these specifically bound cations and anions in the Stern layer (see Chapter 3.2). From a coordination chemistry point of view it does not appear very meaningful to assign a surface-coordinating ion to a layer different than H or OH in a =MeOH group. 

Heterogeneous nucleation of CaF2 on Ce02. It occurs only in pH range where Ca2+ and F are specifically bound to the CeOz surface. This surface coordination, accompanied by partial dehydration of the ions, appears to be a prerequisite for the nucleation. IP = Ion Product. (Data H. Hohl)... 

Table I lists isomorphous replacements for various metalloproteins. Consider zinc enzymes, most of which contain the metal ion firmly bound. The diamagnetic, colorless zinc atom contributes very little to those physical properties that can be used to study the enzymes. Thus it has become conventional to replace this metal by a different metal that has the required physical properties (see below) and as far as is possible maintains the same activity. Although this aim may be achieved to a high degree of approximation [e.g., replacement of zinc by cobalt(II)], no such replacement is ever exact. This stresses the extreme degree of biological specificity. The action of an enzyme depends precisely on the exact metal it uses, stressing again the peculiarity of biological action associated with the idiosyncratic nature of active sites. (The entatic state of the metal ion is an essential part of this peculiarity.) Despite this specificity, the replacement method has provided a wealth of information about proteins that could not have been obtained by other methods. Clearly, there will often be a compromise in the choice of replacement. Even isomorphous replacement that should retain structure will not necessarily retain activity at all. However, it has become clear that substitutions can be made for structural studies where the substituted protein is inactive (e.g., in the copper proteins and the iron-sulfur proteins). It is also possible to substitute into metal coenzymes. Many studies have been reported of the...

RNA folding and catalysis requires nonspecifically associated cations and often specifically bound ions for function. Specificity and affinity of DNA-binding proteins has been shown to be affected by ions in solution. 

The presence of chemical guest species in the water pool of soft-core RMs can modify the organization of the micellar components. The chemical guest species may compete with the surfactant for water molecules to build its own hydration shell. Ions may be specifically bound to the charged groups of the micellar wall resulting in dramatically changed properties of micelles. 

In Fig. 4.8 the effect of the initial-state wave functions is explored, for the case where the crucial electron-electron interaction is the two-body Coulomb interaction (4.14a) and for the case where this interaction is the two-body contact interaction (4.14d), which is not restricted to the position of the ion. In both cases, the form factor includes the function (4.23), which favors momenta such that pi + p2 is large. This is clearly visible for the contact interaction (4.14d) and less so for the Coulomb interaction (4.14a) whose form factor also includes the factor (4.19), which favors pi = 0 (or p2 = 0)- We conclude that (i) the effect of the specific bound state of the second electron is marginal and (ii) that a pure two-body interaction, be it of Coulomb type as in (4.14a) or contact type as in (4.14d), yields a rather poor description of the data. A three-body effective interaction, which only acts if the second electron is positioned at the ion, provides superior results, notably the three-body contact interaction (4.14b), cf. the left-hand panel (d). This points to the significance of the interaction of the electrons with the ion, which so far has not been incorporated into the S-matrix theory beyond the very approximate description via effective three-body interactions such as (4.14b) or (4.14c). 

The iron-ovotransferrin spectrum of Aasa et al. (7) consisted of a 3-component part around g = 4.1 and a low field part around g = 8.8 (Fig. 11). Some samples showed weak lines on the wings of the main line and these were thought to be due to non-specifically bound metal ions. No other lines were found. Windle et al. 137) independently found an asymmetric 3-component spectrum centered at g = 4.27 and attributed to Fe3+. 

This result is interesting but perhaps not very satisfying, since it puts an upper limit on the metal-anion distance without unequivocally revealing whether the anion is directly coordinated to the metal ion. To get at this question, we attached a nitroxyl spin-labeled anion to transferrin to determine whether its electron paramagnetic resonance signal was broadened by interaction with specifically bound Fe(III) (49). The mechanism of such broadening would be similar to that in the NMR experiments, but now there is an electron-electron interaction rather than an electron-nuclear interaction as before. 

The chemistry of the group 13 metals makes binding studies difficult, as careful control of pH and bicarbonate concentration is necessary to prevent formation of species such as Al(OH)4 and Ga(OH)4". Nevertheless, UV difference spectra have shown that Al3+, Ga3 +, In3+, and Tl3 all form transferrin complexes with two metal ions per molecule (126, 144-146). Ae values imply the ionization of two tyrosines per bound metal ion, as for other specifically bound metals. NMR studies using 13C-enriched bicarbonate show virtually identical spectra for Al3+ and Ga3+, implying equivalent metal-anion environments (99). 

Soil chemistry and structure determine the amount and availability of minerals and water to organisms. For instance, soil pH determines whether Ca2+, PO43-, and other essential ions are bound tightly to its particles or are free to be absorbed by organisms, or else leached away in water runoff. Likewise, plants tend to adapt to a specific soil pH. Soil is a restrictive environment for most animals, because relatively little food and oxygen are available, and movement through densely packed dirt, rocks, sand, and organic debris is difficult. On the... 

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