Metal cation recognition

A complication in the analysis of structural data is the growing recognition that the involvement of metal cations with a ligand s 7t-electrons (often in aromatic rings) can give rise to various structural distortions. Such cation-7t... 

J.-J. Xu, H.-Q. Fang, and H.-Y. Chen, The electrochemical characteristics of an inorganic monolayer film modified gold electrode and its molecular recognition of alkali metal cation. J. Electroanal. Chem. 426,139-143 (1997). 

Most of the work on chiral recognition in the ground state deals with salts having chiral, primary alkylammonium cations. Another approach is the chiral discrimination between two enantiomeric anions present as counterions in metal-cation complexes (Lehn et al., 1978). Discrimination between enantiomeric transition states will be dealt with in the next section together with non-chiral mimicry of enzymic catalysis. 

A different concept of chiral recognition was used by Lehn et al. (1978) for the differentiation between pairs of enantiomeric anions. Following the terminology used for metallo-enzymes, the chiral crown ether [309] acts as an apo-receptor, complexing a metal cation and thus becoming a chiral metal receptor that may discriminate between enantiomeric anions (cascade-type complexation). Extraction experiments with racemic mandelic acid dissolved in... 

Chiral recognition of racemic mandelic acid in the presence of alkali metal cations by [309] ... 

The electrochemical properties of ferrocene have been utilized by many workers in the field of electrochemical molecular recognition. Saji (1986) showed that the previously synthesized (Biernat and Wilczewski, 1980) ferrocene crown ether molecule (Fig. 3 [1]), whose binding properties had previously been studied only by nmr and UV/Vis techniques (Akabori et al., 1983), could be used as an electrochemical sensor for alkali metal cations involving a combination of through-space and through-bond interactions. 

Ion recognition is a subject of considerable interest because of its implications in many fields chemistry, biology, medicine (clinical biochemistry), environment, etc. In particular, selective detection of metal cations involved in biological processes (e.g., sodium, potassium, calcium, magnesium), in clinical diagnosis (e.g., lithium, potassium, aluminum) or in pollution (e.g., lead, mercury, cadmium) has received much attention. Among the various methods available for detection of ions, and more... 

The main feature for cation recognition by tetra-bridged phosphorylated cavitands arises from the cooperative effect of the four phosphorus groups and the aromatic molecular cavity. In the phosphorus(IV) cavitands guest binding will be achieved through O (P=0) or S (P=S) coordination with different affinity for hard or soft metal ions. On the other hand, transition metal rim complexes described above can act as host for metal cation. 

The stability of the polypyridyl rhenium(I) compounds mentioned above stimulated applications of this coordination chemistry. Thus, new heterotopic bis(calix[4]arene)rhenium(I) bipyridyl receptor molecules have been prepared and shown to bind a variety of anions at the upper rim and alkali metal cations at the lower rim. A cyclodextrin dimer, which was obtained by connecting two permethylated /3-cyclodextrins with a bipy ligand, was used for the preparation of a luminescent rhenium(I) complex. The system is discussed as a model conipound to study the energy transfer between active metal centers and a bound ditopic substrate. The fluorescence behavior of rhenium(I) complexes containing functionalized bipy ligands has been applied for the recognition of glucose. ... 

The study of the interactions between organic compounds and aUtali-metal cations, in the gas phase, is related to many topics such as ion solvation, catalysis and molecular recognition. Furthermore, mass spectrometry has been used for the analyses of organolithium compounds and supramolecular assemblies that contain lithium cations. Alkali cationization is an important ionization technique, implemented for the analyses of a wide range of organic compounds. Finally, gas-phase studies are also useful for the quantitative determination of lithium cation affinity. The interaction between lithium cation and organic substances is thus related to different aspects of gas-phase chemistry and mass spectrometry. 

SCHEME 3. Isomerization of spirobenzopyran 10 to colored merocyanine 10 M is induced by recognition of alkali metal cations as well as by UV irradiation ... 

As concerns the spatial fit of host and guest, 44 forms the most stable complex with K+ (Figure 3.1) [10], since its radius of ca. 138 pm is approximately equal to the ionic radius of the guest. The dependence of stability constants of the complexes of 47, 48 and 44 with alkali metal cations on the ion diameters is shown in Figure 3.2. The complicated character of the depicted relations indicates that more factors (e.g., solvent effect) are at play in the ions recognition. 

Interestingly, a family of 1,2,3-triazole-linked dendrimers containing from 9 (compound 4, Fig. 6.4a) up to 243 peripheral ferrocene units give strong recognition of both oxoanions and metal cations with positive dendritic effect.30... 

The simplest recognition process is that of spherical substrates these are either positively charged metal cations (alkali, alkaline-earth and lanthanide cations) or the negative halide anions (see Chapt. 3). 

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