Nicotinic acid ligands

FIGURE 101 Crystal structure of the cubane-like [Er4(/T3-OH)4] building blocks encapsulated by dimeric nicotinic acid ligands. The various coordination modes of the ligands are shown on the top (redrawn after Hu et al., 2007). 

TLC was combined off-line with AAS to study the stability of mixed zinc carbox-ylato complexes with two nicotinic acid ligands (Orinak et al.. 1997). The zinc content, determined in scraped fraction from silica layers, was indicative of dissociation of the complexes during TLC. TLC separation, ion-exchange cleanup, and ICP-AES were combined for determination of rare earth elements in granites and greisens (safranova et al, 1995). 

An example of the use of NMR to design inhibitors of the protein kinase p38 is shown below. The first NMR spectrum shows the resonance peaks of nicotinic acid (a) and 2-phenoxy benzoic acid (b) in the absence of a target enzyme. When a target enzyme is added, in this case the p38 MAP kinase, binding of the ligand and the enzyme causes line broadening and attenuation of the resonance peaks. This is shown by the second NMR spectrum, in which the affected peaks are those of the 2-phenoxy benzoic acid (from 7.2 ppm to 6.6 ppm), indicating the interactions between p38 MAP kinase and 2-phenoxy benzoic acid. 

Nicotinic acid is present in the more active GTF preparations isolated from yeasts. The coordination chemistry of this ligand is particularly relevant to glucose tolerance and the presence of this substance is apparently essential for the maximal activity of complexes in tests in vitro. The instability of highly purified GTF fractions has frequently been noted this may arise because the substance in vivo is stabilized by a protein. 

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