Ligand binding metal ions

Effective metal ion adsorbent has been prepai ed by the immobilization of propylthioethyleamine ligand onto the surface of silica gel (SN-SiO,).The effectiveness of this material to bind metal ions has been attributed to the complexation chemistry between the ligand and the metal. We are investigating properties of propylthioethyleamine grafted on the surface of silica and possibility of application of the obtained surface for preconcentration of heavy metals such as zinc, lead, cadmium, copper, etc. from water solutions. 

Several model systems related to metalloenzymes such as carboxypeptidase and carbonic anhydrase have been reviewed. Breslow contributed a great deal to this field. He showed how to design precise geometries of bis- or trisimidazole derivatives as in natural enzymes. He was able to synthesize a modified cyclodextrin having both a catalytic metal ion moiety and a substrate binding cavity (26). Murakami prepared a novel macrocyclic bisimidazole compound which has also a substrate binding cavity and imidazole ligands for metal ion complexation. Yet the catalytic activities of these model systems are by no means enzymic. 

Cysteine can bind to either one or two metal ions, and is frequently found as a ligand to iron (in Fe-S clusters—see later) and to Cu+ (for example in the copper chaperones, which transfer copper to specific copper-binding proteins). Histidine can bind metal ions in two... 

Importantly, unmodified PAMAM and PPI dendrimers have functional groups within their interior as well as on their exterior. Specifically, PAMAM dendrimer interiors contain both tertiary and secondary (amide) amines, and both of these are ligands for many metals [19,82,83,87,89]. For example, Turro et al. [87, 89] investigated the binding of Cu + ions to integer and half-integer PAMAM dendrimers. Their EPR results indicated that Cu + can bind to both exterior acid and amine groups, as well as to interior tertiary amines and amides. Similarly, PPI dendrimers have interior tertiary amines and are also able to bind metal ions, such as Cu +, Zn +, and Ni + within their interior [90,100]. 

Polycondensates. Miscellaneous copolycondensates with ligands as comonomers bind metal ions to produce conducting materials. Table 3 collects a few available data on such systems. 

Cascade-type binding [3.24] of anionic species occurs when a ligand first binds metal ions, which then serve as interaction sites for an anion. Such processes occur for instance in lipophilic cation-anion pairs [1.31] and with Cu(ll) complexes of bis-tren 33, of macrocyclic polyamines [3.25, 3.26] and of calixarenes [3.27]. 

In the crown ethers (18) the interactions between the ligand and metal ion are considered to be more electrostatic in nature, rather than the covalent binding observed for the transition metal complexes of the aza, thia, and phospha macrocycles. The thermodynamic properties of these macrocycles have been extensively studied, with numerous reviews covering complexation, selectivity, and structural aspects, some with extensive tables of thermodynamic data. Considerable efforts have been made to correlate the interrelationship between cavity size of the macrocycles and stability of alkali and alkaline earth metal complexes. From X-ray and CPK models, cavity radii are determined as 0.86-0.92A for 15-crown-5 (64), 1.34-1.43 A for 18-crown-6 (65), and about 1.7 A for 21-crown-7 (66). For complex formation between the alkali metal ions and 18-crown-6, the maximum stability... 

Outer-sphere complexes at the nucleoside and nucleotide are more favorable than intermolecular chelating because the indirect binding ligands to metal ion provide fewer geometrical and steric constraints for a larger number of ligands. 

Ligands assigned by Pearson as hard appear in normal type, borderline in bold, and soft in italics. For Pearson, aliphatic amines are hard and aromatic amines borderline. Since imidazole binds metal ions through a borderline pyridine-type nitrogen, imidazole is also classed as borderline in the hgand scale. Use of CH3Hg+ in place of Hg + yields a virtually identical ordering with a lesser span of 13 log units. 

Roots (or mycelia) tend to deliver ligands themselves to the soil which bind metal ions from soil solntion... 

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