Wide ligand profiling

Modem cross coupling chemistry is heavily dominated by the use of palladium and nickel complexes as the catalysts, which show an impressively wide scope and an excellent compatibility with many functional groups.2 This favorable application profile usually overcompensates the disadvantages resulting from the high price of the palladium precursors, the concerns about the toxicity of nickel salts, the need for ancillary ligands to render the complexes sufficiently active and stable, and the extended reaction times that are necessary in certain cases. 

In the ion-association extraction systems, hydrophobic and interfacially adsorbable ions are encountered very often. Complexes of Fe(II), Cu(II), and Zn(II) with 1,10-phenanthro-line (phen) and its hydrophobic derivatives exhibited remarkable interfacial adsorptivity, although the ligands themselves can hardly adsorb at the interface, except for protonated species [19-21]. Solvent extraction photometry of Fe(II) with phen is widely used for the determination of trace amounts of Fe(II). The extraction rate profiles of Fe(II) with phen and its dimethyl (DMP) and diphenyl (DPP) derivatives into chloroform are shown in Fig.9. In the presence of 0.1 M NaC104, the interfacial adsorption of phen complex is most remarkable. The adsorption of the extractable complex must be considered in the analysis of the extraction kinetic mechanism of these systems. The observed initial rate r° shows the relation... 

These data form part of an increasing body of evidence that demonstrates the significant conformational flexibility of the porphyrin skeleton in the solid and in solution. Since a wide spectrum of photosynthetic and enzymatic reactions proceed via tt radicals of porphyrin derivatives, the consequences of the macrocyles flexibility are considered for distances and orientations between donors and acceptors, interactions with ligands, nearby charges or polar groups, electronic profiles and the gaps between the aj and a u highest occupied orbitals. 

Until about 1980, it was widely accepted that the benzodiazepine structure was a prerequisite for the anxiolytic profile and for the recognition of and binding to the benzodiazepine receptor. More recently, however, a chemically unrelated drug, the cyclopyrrolone zopiclone, has been shown to be a useful sedative hypnotic with a benzodiazepine-like profile. Other chemical classes of drugs that are also structurally dissimilar to the benzodiazepines (e.g. triazolopyridazines) have also been developed and shown to have anxiolytic activity in man these non-benzodiazepines also act via the benzodiazepine receptor. Thus the term "benzodiazepine receptor ligand" has been introduced to describe all drugs, irrespective of their chemical structure, that act on benzodiazepine receptors and thereby modulate inhibitory transmission in the brain. 

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