ABSTRACT
NMR spectroscopy offers the possibility of studying the conformational behavior of (bio)molecules in solution and eventually the dynamic aspects related to it. In general, the architecture of biomolecules in the solid state does not differ greatly from that observed in solution, even for structures less conformationally defined than the pseudo-cyclic ionophores, despite the plethora of reasons one could advance against that idea. Additionally, pulse NMR is particularly suited to measure dynamic effects as, e.g., relaxation times. For most purposes, however, and certainly from determinations obtained in solution, the uncertainties are a more or less realistic reflexion of the proposed values for these solution conformations obtained by NMR spectroscopy. The recognition of homogeneous zones of increased or decreased lipophilicity with attendant ASIS effects allows one to assign a posteriori some signals in the NMR spectrum, once the conformation of the ionophore has been revealed. This is also the only way to assign by lH NMR, e.g., methoxy protons and methyl groups.
