Human serum albumin (HSA) is a monomeric, globular, multi-carrier and the most abundant protein in the blood. HSA displays multiple ligand binding sites with extraordinary binding capacity for a wide range of ions and molecules. For decades, HSA's ability to bind to various ligands has led many scientists to study its physiological properties and protein structure; indeed, a better understanding of HSA-ligand interactions in human blood, at the atomic level, will likely foster the development of more potent, and overall more performant, diagnostic and therapeutic tools against serious human disorders such as diabetes, cardiovascular disorders, and cancer. Here, we present a concise overview of the current knowledge of HSA's structural characteristics, and its coordination chemistry with transition metal ions, within the scope and limitations of current techniques and biophysical methods to reach atomic resolution in solution and in blood serum. We also highlight the overwhelming need of a detailed atomistic understanding of HSA dynamic structures and interactions that are transient, weak, multi-site and multi-step, and allosterically affected by each other. Considering the fact that HSA is a current clinical tool for drug delivery systems and a potential contender as molecular cargo and nano-vehicle used in biophysical, clinical and industrial fields, we underline the emerging need for novel approaches to target the dynamic functional coordination chemistry of the human blood serum albumin in solution, at the atomic level.

Complex formation between quinine and natural cyclodextrins (CD) was studied using NMR spectroscopy. The strongest association was observed for complexes of neutral quinine molecule with βCD. Association constants for monokationic quinine were one order of magnitude smaller, while dikationic quinine did not bind to CDs. Distribution of complexation-induced shifts and ROESY spectra revealed bimodal quinine binding in complexes built up by βCD and γCD. Complex formation resulted in decrease of vicinal coupling constant between H2 and H9 protons owing to the rotation about C2–C9 bond and in consequence in mutual reorientation of two main constituents of quinine: quinoline and quinuclidine. DFT calculations allowed to establish that H2 and H9 protons are antiperiplanar in the prevailing quinine conformer(s) in aqueous solution. Conformers with synclinal H2, H9 protons become to participate in quinine complexed with CDs.

A new ¹⁹F NMR method is presented which can be used to detect weak protein binding of small molecules with up to mM affinity. The method capitalizes on the synthetic availability of unique SF5 containing compounds and the generation of five-quantum coherences (5QC). Given the high sensitivity of 5QC relaxation to exchange events (i.e. reversible protein binding) fragments which bind to the target with weak affinity can be identified. The utility of the method in early stage drug discovery programs is demonstrated with applications to two model proteins, the neurotoxic NGAL and the prominent tumor target β-catenin.