Stability constants dipeptide complexes

NMR signals of the amino acid ligand that are induced by the ring current of the diamine ligand" ". From the temperature dependence of the stability constants of a number of ternary palladium complexes involving dipeptides and aromatic amines, the arene - arene interaction enthalpies and entropies have been determined" ". It turned out that the interaction is generally enthalpy-driven and counteracted by entropy. Yamauchi et al. hold a charge transfer interaction responsible for this effect. 

Stability constants for Cu11 complexation of Gly—X and X—Gly dipeptides show that even relatively small alkyl side chains can influence coordination. 3 At low pH, for example, the bidentate chelates N(amino),0(peptide) of L-Leu-Gly and L-Ile-Gly are the thermodynamically less stable, presumably due to steric hindrance from the branched side chains. Similar coordination by Gly—X is virtually independent of the nature of X. This latter result is not unexpected since only the Gly moiety is coordinating. However, on raising the solution pH (> 4) the peptide deprotonation that occurs to give tridentate N(amino),N(peptide),0(carboxyl) chelation is slightly inhibited by the Leu and lie residues (by 0.7-0.8 log units). 

Table 3. Stability constants of metal-complexes with some diastereoisomeric dipeptides...

Earlier studies established that imidazole coordination as part of a chelate structure requires the His residue to be near the amino end. This important positional feature of His is also apparent in the dipeptides Gly-His and His-Gly. As can be seen from Table 8 the His-Gly stability constants are invariably larger and the range of complexes formed also differs. Sundberg and Martin have reviewed the solution and solid state properties of His-containing peptides. More recently Gergely and his group have reexamined the coordinating properties of Gly-L-His, L-His-Gly and... 

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