Flexible ligands adaptation

In addition, to facihtate the adaptation of the hgand to the RNA binding site, the ligand flexibility might have an additional effect on the recognition... 

We have shown that the conformational behavior of natural aminoglycosides is characterized by a remarkable flexibility, with different conformations, even non-exo-anomeric ones, in fast exchange. This feature allows the adaptation of these ligands to the spatial and electronic requirements of the different receptors. The large diversity of structures adopted by aminoglycosides in the binding pocket of the different RNA receptors and the enzymes involved in bacterial resistance is consistent with this view. 

Furthermore, isomerization of the heptadentate XXXI, coordinated to Ni(II) via transmetallation (91), occurs again aimed at its adaptation to a octahedral coordination sphere around ions with d8 configuration. In the case of the more flexible pentadentate ligands, XXXII and its analogue with three methylene groups (L2) (92), formation of monomeric (with XXXII) and dimeric (with L2), but also of polymeric (with L2) Ni(II) complexes with an octahedral environment around the metal is possible (94). 

---