Affinity order

By comparing the level of the binding isotherms (figure 3) for both metals and pectins, it became possible to set up an affinity order of pectins, whatever their origin, for the five metal ions Cu2+ Pb + Zn2+ Ni2+ > Ca2+. This scale, already found by pH-measurements, confirmed that Cu2+ and Pb2+ were more strongly bound than the other thi cations with no difference between pectins. 

Note that the excess of metal elements made the whole including the surface in a somewhat reduced state except for carbon as CO and C02. So far the process described is one of slow change as the temperature decreased, with reactions closely following affinities of the elements for one another. However, relative affinities change with temperature decrease and as temperature decreased further, the possibility of reactions to restore equilibrium appropriate to all relevant affinity orders was prevented by barriers to reactions, both physical and chemical at the lower temperatures. Thus, Earth developed a huge energy store beneath the cool surface and this is an important part of its later ecosystem. 

A tetraamidinium functionalized, bowl-type cavitand (receptor 8) was developed by Diederich and Sebo [47]. This receptor was found to complex 1,3-dicarboxylate anions with good selectivity and a 1 2 binding stoichiometry both in CD3OD and D20, as revealed by standard Job plot analysis. In contrast, various nucleotide phosphates were found to be bound with a 1 1 stoichiometry in D20. In the case of the adenosine phosphates, the association constants increased as a function of nucleotide charge [i.e., the affinity order (K., M-1) was cAMP (1400) < AMP (10000)charged receptor (8) also showed moderate selectivity towards AMP (Ka = 10 000 M-1) over other nucleotide monophosphate anions, such as GMP (FCa = 5200 M-1), CMP (fCa = 3500 M-1), TMP (K l — 5900 M ), and UMP (Ka-3800M ) in D20 containing TRIS buffer (2.5 mM, pH 8.3). 

An order statistics approach could also be used to choose a library size. Given an affinity distribution p(Ka) and a minimum desired affinity, order statistics calculations can yield the number of ligands needed to include at least a specified number of ligands with this affinity or greater with a specified probability (Fig, 11). 

In the literature, the affinity order of smectites is usually given for alkali and alkali earth cations, in that order, as follows (Laudelout et al. 1968 Sawhney 1972 Maes and Cremers 1977 Bergaya et al. 2008) ... 

The two affinity orders are in good agreement. The affinity order of cations is in agreement with the aforementioned charge/size ratio. The following discrepancies are seen in the preceding affinity order ... 

As mentioned in Chapter 1, Section 1.3.3.2, potassium and lithium ions can fit into the cavities of the silicate crystal lattice and decrease the layer charge. It is also the case for montmorillonite (Gast 1972 Maes and Cremers 1977 Eberl 1980 Goulding and Talibudeen 1980 Bouabid et al. 1991 Komadel et al. 2003), so the affinity order is modified. 

As indicated in Table 5.3d, significant negative enthalpies and entropies of exchange for the exchange of halide ions on quaternary ammonium resins could be interpreted in terms of pure electrostatic interactions. However such a coulombic model invoking solvated ion size or distance of closest approach fails to conform to the observed affinity order I > Br > CI > F . If one includes a larger polyatomic anion such as perchlorate, Cl 04 the experimental sequence is Cl 04 > I > Br"> Cr > F" which clearly contradicts any simple coulombic attraction theory. 

The affinity order is reflected also in the maximum limits to exchange, which are collected in Figures 2 and 3 for all the ions, including propyl,... 

Early work on the exchange properties of amorphous zirconium phosphate has been summarized by Amphlett (29). In addition, Ahrland et al. (13,15) have studied the exchange behavior of representative fission product ions, for which they found an affinity order of UO, Ce, Y " ", Sr +, Cs+, Rb+, Na+, when amorphous gels of high P04/Zr ratios were used. The separation of certain transplutonium ions (250) on amorphous... 

Amine Proton Affinity (Order) BF3 (Order) A/-/° for amine—BMe adduct formation (kJ/mol) BMej (Order) B(f-Bu)3 (Order)... 

In order to study the interaction between 10 and the imide ftinctionality of nucleobases in aqueous solution, potentiometric pH titrations of 10 were conducted in the presence of an equimolar amount of dT and its homologues. In fact, the complexation constants with 10 were all found to be greater than with 8 and so this supports our prediction of an additional binding force from a stacking interaction. Among the imide -containing bases, the affinity order dT (log K = 7.2), AZT (7.2) > BU (7.0) > U (6.9) > Ff (6.6) > AU (6.3) is consistent with the order of the basicities of the conjugate base N(3) (Fig. 5a). Moreover, a linear relationship... 

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