Ligand concentration, selectivity control

Several spectroscopic techniques, namely, Ultraviolet-Visible Spectroscopy (UV-Vis), Infrared (IR), Nuclear Magnetic Resonance (NMR), etc., have been used for understanding the mechanism of solvent-extraction processes and identification of extracted species. Berthon et al. reviewed the use of NMR techniques in solvent-extraction studies for monoamides, malonamides, picolinamides, and TBP (116, 117). NMR spectroscopy was used as a tool to identify the structural parameters that control selectivity and efficiency of extraction of metal ions. 13C NMR relaxation-time data were used to determine the distances between the carbon atoms of the monoamide ligands and the actinides centers. The II, 2H, and 13C NMR spectra analysis of the solvent organic phases indicated malonamide dimer formation at low concentrations. However, at higher ligand concentrations, micelle formation was observed. NMR studies were also used to understand nitric acid extraction mechanisms. Before obtaining conformational information from 13C relaxation times, the stoichiometries of the... 

Multidomain proteins of the above quoted families and profilin participate not only in lamellipodial protmsion during locomotion but also in cell adhesion VASP and profilin are both regular components of nascent adhesion complexes in spreading tissue culture cells (Hiittelmaier et al. 1998 and unpublished observations). In summary, the numerous profilin ligands and their different local concentrations may control actin polymerization, in conjunction with profilin-actin complexes, in a time- and space-controlled manner. Figure 3 presents a hypothetical model with selected examples of such processes at the cell membrane. 

Rhodium-catalysed addition of sulfonic acids to terminal alkynes, affording vinyl sulfonates, has been developed. Its selectivity is controlled by ligand concentration. ... 

The control of enzyme activity by the environment of a polyatomic framework is a vast topic, which I shall not attempt to cover fully in this report. Instead I will concentrate on some selected interactions between and within polypeptide chains that influence enzymatic activity. First, elementary steps involved in ligand-protein, intraprotein, and interprotein interactions are considered. Then enzymes consisting of a single polypeptide chain are discussed, followed by enzymes consisting of multiple polypeptide chains. The concluding sections are concerned with multienzyme complexes and enzymes associated with membranes. 

Selectivity of Mg2+ against Ca2+ is achieved by using RO ligands such as phenoles, enolates, or hydroxide, and using nitrogen donors (e.g., 8-hydroxy-quinolinate or diazo-phenol dyes). In biology this may not be necessary as biology can control Ca2+ concentration very well. 

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