Transition metal ions specific element

Lantern structure, in bridging triazenide transition metal complexes, 30 10, 32 Lantern-type complexes, see Dinuclear complexes, quadruply bridged Lanthanides, see also Metals, ions specific elements... 

Electron-transfer (ET) reactions play a central role in all biological systems ranging from energy conversion processes (e.g., photosynthesis and respiration) to the wide diversity of chemical transformations catalyzed by different enzymes (1). In the former, cascades of electron transport take place in the cells where multicentered macromolecules are found, often residing in membranes. The active centers of these proteins often contain transition metal ions [e.g., iron, molybdenum, manganese, and copper ions] or cofactors as nicotinamide adenine dinucleotide (NAD) and flavins. The question of evolutionary selection of specific structural elements in proteins performing ET processes is still a topic of considerable interest and discussion. Moreover, one key question is whether such stmctural elements are simply of physical nature (e.g., separation distance between redox partners) or of chemical nature (i.e., providing ET pathways that may enhance or reduce reaction rates). 

In order to carry out most biochemical reactions, metalloenzymes generally utilize the rarer transition metal ions. Elements such as zinc, copper, iron, nickel, and cobalt are found in low concentrations in plasma and seawater and yet the enzyme has to select the appropriate metal ion from them. There is evidence for the existence of proteins that can chaperone specific metal ions to their appropriate sites in apoenzymes, protecting the metal ions from adverse reactions as they are guided to their required location [5]. How does the enzyme attempt to select out the one metal ion it requires The answer is that the chemistry of the metal ion is used as a basis for selection. Each metal ion has some property that is different from that of most others, but, in fact, there is often considerable overlap in these properties so that a given enzyme may bind one of several different cations in one specific site. Some relevant data are provided in Tables 1 and 2. The metalloenzyme contains within its overall design an arrangement of preferred side-chain functional groups with the correct size hole to bind the required metal ions in an appropriate hydrophobic or hydrophilic environment. Thus the metalloenzyme binds metal ions... 

This description of the main group ions of the first three columns of the periodic table shows that with the exception of alkali metal ions all these ions are adsorbed specifically the same is true of other ions, especially the heavy metal ions, which generally are of greatest practical interest. The other main group elements form anions or oxoanions directly. In the case of equal valence, the transition metal ions resemble each other more than the main group elements do, so more generalization should be possible. 

With the addition of each new shell to the atomic core, or with the partial filling of a new valence shell, there are characteristic periodic effects, many of which are already evident in molecular structure (e.g., transition metals and transition metal ion complexes). Shell effects which are specific to solids are discussed here with respect to the cohesive energies of the elements. 

Unreducible ions of the transition metal component of supported catalysts, which survive a severe reduction, are clear evidence of a strong interaction between the support and the metallic element. Currently there is a discussion in the literature on this subject, specifically 1) Do some Pt-ions survive a severe reduction 2) Are they accessible 3) Do they play a role in the metal-support interaction and reactions of hydrocarbons ... 

The ion exchange resin selected for this study was a copolymer of styrene with divinylben ne with a weakly basic iminodiacetic function group. The reason for this choice is that it has been studied in the extraction of transition metal and other ions (8-10), is commercially available, and is being used in industrial applications. At first it would appear that the prevalent complexation of iminodiacetic acid with most metallic elements would preclude the type of selectivity sought for the Sc extraction. But such separations are possible by the exploitation of specific chemical behavior and complexation characteristics. 

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