Correlations hydrogen complex stability

Toropov AA, Toropova AP (2002) QSPR modeling of complex stability by optimization of correlation weights of the hydrogen bond index and the local graph invariants. Russ. J. Coord. Chem. 28 877-880. 

About 60 structural analogs of enniatin have been synthesized. A detailed discussion of their properties is given in Ref.217 Compared to the valinomycin analogs, the various enniatins exhibit only weak correlation between their individual de-psipeptide structure and complex stability/ion selectivity. The flexibility of the enniatin compounds and their inability to form intramolecular hydrogen bonds are believed to account for these characteristics. 

Correlation between hydrogen-bond stability and J-coupling through a hydrogen bond has been studied theoretically by Kawahara et The relationship has been found to be dependent on the type of the nucleus forming the H-bond the linear correlation has been observed in N-H O/N type or 0-H "N type H-bonded complexes, but not in 0 H"0 type H-bonded complexes. 

Rossotti et al [Fa 70] found that the ratio of stability constants obtained by equilibrium measurements in solvent mixtures similar to the above was independent of the composition of the solvent. McBryde et al showed that in most of the systems they examined, the ratio of the first two stepwise complex stability constants did not depend on the solvent. In the case of the stepwise acid dissociation constants this correlation was approximately true only for ethylenediamine for glycine the ratio of the protonation constants increase with increase in the concentration of the organic component. However, if the formation of the glycine complexes is defined as a reaction between the protonated ligand and the metal ion, accompanied by the liberation of a hydrogen ion, the ratio of the equilibrium constants is approximately independent of the composition of the solvent mixture. 

It has been suggested that in the crown-ether complexes, crystal stability is correlated with an increase in the X—H acidity of the guest9). Bifurcated hydrogen bonds are also common in these host/guest complexes, and their occurrence has been correlated with an increase in the acidity of the X—H groups10>. 

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