Complexes of ions

The opportunity of use of a ternary complex of ions Eu(III) with oxatetracycline (OxTC) and citrat-ions (Cit) for luminescent detection of OxTC in milk after chromatographic isolation is shown. 

The way in which oui pjesenl undeislanding of the stereochemical intricacies of Ni has evolved illustrates rather well the inteiplay of theory and cxpcruiicnt. On the basis of valence-bond theory, three types of complex of ions were anticipated. These were ... 

With respect to the carrier mechanism, the phenomenology of the carrier transport of ions is discussed in terms of the criteria and kinetic scheme for the carrier mechanism the molecular structure of the Valinomycin-potassium ion complex is considered in terms of the polar core wherein the ion resides and comparison is made to the Enniatin B complexation of ions it is seen again that anion vs cation selectivity is the result of chemical structure and conformation lipid proximity and polar component of the polar core are discussed relative to monovalent vs multivalent cation selectivity and the dramatic monovalent cation selectivity of Valinomycin is demonstrated to be the result of the conformational energetics of forming polar cores of sizes suitable for different sized monovalent cations. 

Since hydrofluoride synthesis is based on thermal treatment at relatively high temperatures, the possibility of obtaining certain fluorotantalates can be predicted according to thermal stability of the compounds. In the case of compounds whose crystal structure is made up of an octahedral complex of ions, the most important parameter is the anion-cation ratio. Therefore, it is very important to take in to account the ionic radius of the second cation in relation to the ionic radius of tantalum. Large cations, are not included in the... 

Where solvent exchange controls the formation kinetics, substitution of a ligand for a solvent molecule in a solvated metal ion has commonly been considered to reflect the two-step process illustrated by [7.1]. A mechanism of this type has been termed a dissociative interchange or 7d process. Initially, complexation involves rapid formation of an outer-sphere complex (of ion-ion or ion-dipole nature) which is characterized by the equilibrium constant Kos. In some cases, the value of Kos may be determined experimentally alternatively, it may be estimated from first principles (Margerum, Cayley, Weatherburn Pagenkopf, 1978). The second step is then the conversion of the outer-sphere complex to an inner-sphere one, the formation of which is controlled by the natural rate of solvent exchange on the metal. Solvent exchange may be defined in terms of its characteristic first-order rate constant, kex, whose value varies widely from one metal to the next. 

J. P. Hunt and H. L. Friedman, Prog. Inorg. Chem. 30, 359 (1983). This review is concerned with the structure of hydration complexes of ions and includes a discussion of the x-ray or neutron diffraction method for determining structure of ions in solution. 

A benzo[18]crown-6 adduct (72) of Cgg (not shown) has been synthesized by the addition of the corresponding o-quinodimethane 71 in toluene [58]. The solubility of 72 in pro tic solvents such as MeOH strongly increases after the complexation of ions, as shown by extraction experiments. The combination of the crown ether and the fullerene moiety in 72 provides a highly amphiphilic character. This behavior allowed the preparation of Langmuir-Blodgett films of monolayers on mica of 72 and its complex. 

Describe one or more metabolic functions of ions or chelate complexes of ions derived from each of the following metallic elements Ca, Mg, Fe, Cu,... 

Statistical theories treat the decomposition of the reaction complex of ion-molecule interactions in an analogous manner to that employed for unimolecular decomposition reactions.466 One approach is that taken by the quasiequilibrium theory (QET).467 Its basic assumptions are (1) the rate of dissociation of the ion is slow relative to the rate of redistribution of energy among the internal degrees of freedom, both electronic and vibrational, of the ion and (2) each dissociation process may be described as a motion along a reaction coordinate separable from all other internal... 

Rhenium complexes 22a,b were designed as ditopic receptors for the cooperative complexation of ion pairs [21]. As proved by H NMR titration experiments in CD3CN,the receptors form complexes of 2 1 stoichiometry with alkali metal cations (interaction with both ethyl acetate cavities on the lower rim) and exhibit [16] a positive allosteric effect for iodide complexation compare... 

Two chiral [2.2.1]cryptands, one incorporating the methyl 4,6-O-benzylidene-a-D-mannopyranoside unit (70), the other the methyl 4,6-0-[(S)-phenylethylidene]-a-D-mannopyranoside unit (77), may exhibit the same two different modes of complexa-tion as before binding of primary alkylammonium cations via hydrogen bonds between the NH-f group and the heteroatoms of the ligand or cascade complexation of ion pairs. Chart 2 shows the constitutions of the two cryptands 70 and 77 and is also indicative that the approach of guest molecules may occur from the more sterically hindered side. 

It can be seen that the added complexity of ion association is likely to make any simple model of ion-ion interactions very difficult to apply without a number of ad hoc assumptions concerning ionic radii. This is particularly true for ionic strengths in excess of 0.01 M or for low-dielectric-constant media. However, a further difficulty is raised by the problem of the nature of an ion pair. If we consider the simple case of univalent ions A+ B forming an ion pair, it is possible to picture the pair as varying in character from one in which the charges remain separated by the sum of the ionic radii of A+ + B to a molecule in which A and B form a covalent bond, not necessarily even polar in character. Nor is it necessarily true that a given species will behave the same in different solvents. If there is a tendency to covalent bond formation, then it is quite possible that the polarity of the A—B bond will depend on the dielectric constant of the solvent. Covalently bound molecules which ionize are considered as weak electrolytes, and they are not treated by the methods of Bjerrum, which are meant for strong electrolytes. The differences may not always be clear, but the important interactions for the weak electrolyte are with the solvent, and these we shall consider next. 

To illustrate the complexities of ion channels, there is recent evidence that the bacterial CIC channel is actually an H+/C1 transporter (Accardi and Miller, 2004). The bacterial and eukaryotic structures do possess strong similarity, however, and the eukaryotic case ClC-0 is indeed a true channel (Chen and Chen, 2001). 

Such features make SIMS a powerful technique for surface analysis. However, SIMS as a surface analysis technique has not yet reached a mature stage because it is still under development in both theoretical and experimental aspects. This lack of maturity is attributed to the complicated nature of secondary ion yield from a solid surface. Complexity of ion yield means that SIMS is less likely to be used for quantitative analysis because the intensity of secondary ions is not a simple function of chemical concentrations at the solid surface. SIMS can be either destructive or non-destructive to the surface being analyzed. The destructive type is called dynamic SIMS it is particularly useful for depth profiling of chemistry. The nondestructive type is called static SIMS. Both types of SIMS instruments are widely used for surface chemical examination. 

The photophysics of the thiacarbocyanines (9) have been assessed. Particular attention was paid to dimerisation and other studies with related compounds have examined the complexation of ions with tram and cis-isomers of (10). These crown ethers showed high selectivities for heavy ions such as Ag" and Hg ". Another report has described the influence of ethene bond isomerism on the ability of the crown ethers (11) to complex These... 

FIGURE 2.3 (A) ESI-FTICR mass spectrum of a mixture of carbonic anhydrase II (CAII) and combinatorial library (289 components, 1). (B) MS-MS spectrum of the isolated complex of ions [CAII + Zn + 1] ". The expanded view shows the region of the singly charged inhibitors l , and the doubly expanded region shows the high resolution achieved in the experiment and the amino acid residue composition of the inhibitor ions. (Reprinted from Gao et al. [18], used with permission. Copyright 1996 by the American Chemical Society.)... 

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