Profiting from Complexation

Ruthenium complexes used to lead research in photochemistry of metal compounds, but rhodium complexes have recently overtaken them as the key target compounds due to their applications in OLEDs. This is a lively and ever-changing field for example, over 90% of luminescent iridum(III) complexes have been reported only in the six years to the beginning of 2009. With their luminescence tuneable through ligand choice, iridium complexes are firm candidates for optical display applications. 

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The use of samarium(II) iodide in synthesis permits the assembly of complex molecules as already shown in many examples. They profit from the electron-transfer ability of samarium(II) iodide thus, if ketones are employed as substrates the furnished ketyl-radical can react in a multitude of different ways. 

The caterpillars enhanced survival implies that their imitation signals and reward secretions are worth the energy expended on their synthesis and dissemination. On the other hand, it is questionable whether ants really profit from their deal with the caterpillars. Had they eaten the caterpillar forthwith on their first encounter, the ants would have gained about the same number of calories as from milking it over its lifetime. However, the situation is complex, and only more information can settle some issues here. One possibility is that the nectar affords compounds the ants must have in their diet but would not obtain by consuming the caterpillars them-... 

While there have been a considerable number of structural models for these multinuclear zinc enzymes (49), there have only been a few functional models until now. Czamik et al. have reported phosphate hydrolysis with bis(Coni-cyclen) complexes 39 (50) and 40 (51). The flexible binuclear cobalt(III) complex 39 (1 mM) hydrolyzed bis(4-nitro-phenyl)phosphate (BNP-) (0.05 mM) at pH 7 and 25°C with a rate 3.2 times faster than the parent Coni-cyclen (2 mM). The more rigid complex 40 was designed to accommodate inorganic phosphate in the in-temuclear pocket and to prevent formation of an intramolecular ju.-oxo dinuclear complex. The dinuclear cobalt(III) complex 40 (1 mM) indeed hydrolyzed 4-nitrophenyl phosphate (NP2-) (0.025 mM) 10 times faster than Coni-cyclen (2 mM) at pH 7 and 25°C (see Scheme 10). The final product was postulated to be 41 on the basis of 31P NMR analysis. In 40, one cobalt(III) ion probably provides a nucleophilic water molecule, while the second cobalt(III) binds the phosphoryl group in the form of a four-membered ring (see 42). The reaction of the phosphomonoester NP2- can therefore profit from the special placement of the two metal ions. As expected from the weaker interaction of BNP- with cobalt(in), 40 did not show enhanced reactivity toward BNP-. However, in the absence of more quantitative data, a detailed reaction mechanism cannot be drawn. 

In order to further profit from the dual complexing ability of CDs, we have studied Fenton-type processes in the presence of CDs. Several classes of compounds showed enhanced degradation rates in the presence of CDs in aqueous solution PCBs, PAHs, TNT, and chlorinated phenoxyacetic acids [38,102]. Dissolved natural organic matter typically inhibits Fenton degradation by sequestering the iron away from the pollutant [31,32]. However, addition of cyclodextrins overcame the inhibitory effect of the NOM and resulted in enhanced degradation rates [38]. 

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