Ligand complexation shifts

The shift in the voltammogram for a metal ion in the presence of a ligand may be used to determine both the metal-ligand complex s stoichiometry and its formation constant. To derive a relationship between the relevant variables we begin with two equations the Nernst equation for the reduction of O... 

Dysfunction of the GABAa receptor complex such that the effects of all benzodiazepine receptor ligands are shifted in the direction of inverse agonism. In this case, fiumazenil (which normally has zero efficacy) should induce anxiety in anxious patients but have no effects in healthy subjects because they have normal receptors. 

Even the allyl anion can be seen as an example of resonance-enhanced coordination. As shown in Section 4.9.2, r -CsHs- complexation is accompanied by a shift toward the localized H2C —CH=CH2 resonance structure that places maximum anionic character at the metal-coordinated carbon atom. In effect, the carbanionic lone pair nc is shared between intramolecular nc 7icc (allylic resonance) and intermolecular nc—>-n M (metal coordination) delocalizations, and the former can be diminished to promote the latter, if greater overall stabilization of the metal-ligand complex is achieved thereby. 

Comparison with axial ligand complexes formed by Ni porphyrins in coordinating solvents (e. g. pyrrolidine, piperidine, and pyridine), however, shows a clear distinction between the frequencies of the "form 5" marker lines of the reconstituted proteins and those of the 6-coordinate models (9). The shifts of the 6-coordinate species relative to the 4-coordinate species are larger than for the form labeled 5 (Figure 1) of the proteins. The shifts for the 6-coordjnate models are about -41 cm ( iq)> i cm (i/g), and -41 cm (i/ ) for the core-size markers ana -12 cm... 

For the monocyclic complexes 1-7, oxidation to Ni(III) occurs at +0.90-+0.93 V and reduction to Ni(I) at -1.46--1.55 V vs SCE. However, in the macropolycyclic ligand complexes 9-14, oxidation and reduction occur at + 1.25-+1.60 V and at -0.94-—1.40 V vs SCE, respectively. That is, electrochemical oxidation of Ni(II) complex to Ni(III) species is easier for the monocyclic complexes, whereas electrochemical reduction to Ni(I) is easier for the macropolycyclic complexes. The anodic shifts in both oxidation and reduction potentials for Ni(II) macropolycyclic complexes in part may be attributed to the tertiary nitrogen donors of the ligands. 

---