Models of Metal Binding

Leenheer, J. A., Brown, G. K., MacCarthy, P. and Cabaniss, S. E. (1998). Models of metal binding structures in fulvic acid from the Suwannee River, Georgia, Environ. Sci. Technol., 32, 2410-2416. 

Khai, N. M., I. Obom, S. Hillier, and J. P. Gustafsson. 2008. Modeling of metal binding in tropical Fluvisols and Acrisols treated with biosoUds and wastewater. Chemosphere 70, no. 8 1338-1346. 

C. C. Tang, D. Davalian, P. Huand, and R. Breslow (1978), Models of metal binding sites in zinc enzymes. Synthesis of tris [4(5)-imidazolyl] carbinol (4-TIC), tris (2-imidazolyl)-carbinol(2-TIC), and related ligands and studies on metal complex binding constants and spectra. J. Amer. Chem. Soc. 100, 3918-3922. 

Spin-pairing model of dioxygen binding and its application to various transition metal systems as well as hemoglobin cooperativity. R. S. Drago and B. B. Corden, Acc. Chem. Res., 1980, 13, 353-360 (39). 

The detection of metal-binding proteins, especially of Cd- and Hg-binding metallothioneins or of the merR protein, induced numerous studies of model compounds of Cd and Hg with more or less simple sulfur- and selenium-containing ligands. 

Chan, J. Huang, Z. Merrifield, M. E. Salgado, M. T. Stillman, M. J. Studies of metal binding reactions in metallothioneins by spectroscopic, molecular biology, and molecular modeling techniques. Coord. Chem. Rev. 2002,... 

Playle, R.C., D.G. Dixon, and K. Bumison. 1993b. Copper and cadmium binding to fish gills estimates of metal-gill stability constants and modelling of metal accumulation. Canad. Jour. Fish Aquat. Sci. 50 2678-2687. 

The emphasis in the following sections will be on exploratory model reactions carried out with phosphazene cyclic trimers or tetramers, although the analogous macromolecules systems have also been studied in several cases. First, I will summarize the various types of metal binding sites that are accessible at the present time. Synthetic procedures leading to the incorporation of several of these sites and their role in metal binding will then be discussed. 

Horton et al. analyzed the Mn -binding properties of hammerhead ribozyme-substrate complexes by EPR [81]. The results are consistent with the two-phase folding model. They found two classes of metal-binding sites with higher affinity and lower affinity, by monitoring the number of bound Mn + ions per hammerhead ribozyme-substrate complex at various concentrations of NaCl. They observed, in the presence of a constant concentration of Mn + ions, a sudden decrease in the number of bound low-affinity Mn ions at a lower concentration of NaCl, followed by a slow decrease or a plateau value of the number of bound high-affinity Mn ions at a higher concentration of NaCl. For example, in the absence of NaCl and in the presence of either 0.3 mmol/1 or 1 mmol/1 Mn + ions, the number of bound Mn ions per hammerhead ribozyme-substrate complex was approximately 14. Addition... 

The Dewar-Chatt-Duncanson model of the binding of an olefin in a transition metal complex involves two types of interactions. Transfer of electron density from the relatively high-lying olefinic ic-orbital to the metal (cf. 20) represents a Lewis acid Lewis base interaction (a-bonding). A metal-olefin jr-bond due to interaction... 

A great deal of work has been done on complexes of y-carboxyglutamate, and of small peptides containing single and di-y-carboxyglutamate residues as models for the interaction of Ca2+ with gla proteins. It appears that these are not useful predictors of metal-binding behaviour.264 266... 

Vanadyl salen is readily converted at 100°C with H2S in the absence of a catalyst to a vanadium sulfide and a free organic ligand (or decomposition products). Vanadyl phthalocyanine is more stable with respect to ring attack and demetallation. Rates relative to catalytic reactions have not been measured. If VO-salen is an appropriate model of vanadium binding in asphaltenes, asphaltenic metals are more readily converted to sulfides under hydrotreating conditions than the porphyrinic metals. This suggests... 

Hiemstra, T. and van Riemsdijk, W.H. (1999) Surface structural ion adsorption modeling of competitive binding of oxyanions by metal (hydr)oxides. Journal of Colloid and Interface Science, 210(1), 182-93. 

Let us now put the above principles into practice by considering the assembly of multiple-helical compounds. A simple chemical model for the formation of helicates involves the twisting of molecular threads , as shown in Figure 7-27. The incorporation of metal-binding domains into these threads allows the use of metal ions to control the twisting. 

Turner, D.R., Varney, M.S., Whitfield, M., Mantoura, R.F.C. and Riley, J.P. (1986) Electrochemical studies of copper and lead complexation by fulvic acid. I. Potentiometric measurements and a critical comparison of metal binding models. Geochim. Cosmochim. Acta, 50, 289-297. 

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