H-bonding networks

The identification of hydrogen bridges are very valuable for the structure determination of flexible bioorganic complexes. Up to now their direct detection by NMR spectroscopy, via scalar couplings through hydrogen bridges, was only possible in biomacromolecules or at very low temperatures in deuterated gases. Using a arginine bisphosphonate complex and developing a relaxation optimised NMR pulse sequence we were able to detect for the first time also ^hJ-couplings in a mixture of typical organic solvents. The experimentally determined hydrogen bridges in the bioorganic model complex showed a structure deviating from the arginine fork, where the geometry and function of the model complex was adapted from. This discrepancy was explained by quantum chemical calculations and entropic effects.