Lanthanide Tag in Search For Paramagnetically Induced Residual Dipolar Couplings in Small Molecules

The structure elucidation of molecules and determination of their characteristic interactions and thermodynamic processes have become routine measurements while using Nuclear Magnetic Resonance (NMR) spectroscopy as an indispensable technique. The theoretical description of NMR spectroscopy and treatment of the dynamics of nuclear spin systems is highly dependent on quantum mechanics. More precisely, Residual Dipolar Coupling (RDC) provides global orientation information of magnetic dipole-dipole interaction in a reference frame and distance-independent angular insights to local relaxation. RDC measurements necessitates the use of an anisotropic orientation medium for the partial alignment of the target molecule with respect to the magnetic field. Such media include liquid crystals or paramagnetic centers with a lanthanide ion. Anisotropic paramagnetic tags have been successful in biomolecular NMR applications of large proteins but their use in small organic molecules remains imperfect due to challenges in designing functional lanthanide-complexes with varying degrees of nondirectional bonding in the Ln(III) inner coordination sphere. In this study, we propose a strategy for the synthesis of a lanthanide tag and the measurement of RDCs in a target organic molecule using several paramagnetic lanthanide complexes.