Human serum albumin (HSA), the most prominent protein in plasma, binds different classes of ligands at multiple sites. HSA provides a depot for many compounds, affects pharmacokinetics of many drugs, holds some ligands in a strained orientation providing their metabolic modification, renders potential toxins harmless transporting them to disposal sites, accounts for most of the antioxidant capacity of human serum, and acts as a NO‐carrier. The globular domain structural organization of monomeric HSA is at the root of its allosteric properties which are reminiscent of those of multimeric proteins. Here, structural, functional, biotechnological, and biomedical aspects of ligand binding to HSA are summarized.

The peculiar magnetic properties of lanthanide(III) ions may be exploited for the development of powerful NMR probes for biomedical applications. Gd^III chelates are in current clinical use as contrast agents for magnetic resonance imaging. Other paramagnetic lanthanide(III) complexes endowed with shift reagent capabilities are used for the separation of NMR resonances of species present in the inner and outer cellular compartments and for the measurement of pH and temperature.

The recently introduced new class of contrast agents (CAs) based on chemical exchange saturation transfer (CEST) may have a huge potential for the development of novel applications in the field of MRI. In this work we explored the CEST properties of a series of Lanthanide(III) complexes (Ln = Eu, Dy, Ho, Er, Tm, Yb) with the macrocyclic DOTAM‐Gly ligand, which is the tetraglycineamide derivative of DOTA (1,4,7,10‐tetraazacyclododecane‐1,4,7,10‐tetraacetic acid). These complexes possess two pools of exchangeable protons represented by the coordinated water and the amide protons. Yb‐DOTAM‐Gly displays the most interesting CEST properties when its amide N‐H resonance (16 ppm upfield H₂O signal) is irradiated. Up to 70% suppression of the water signal is obtained at pH 8. As the exchange rate of amide protons is base‐catalyzed, Yb‐DOTAM‐Gly results to be an efficient pH‐responsive probe in the 5.5–8.1 pH range. Moreover, a ratiometric method has been set up in order to remove the dependence of the observed pH responsiveness from the absolute concentration of the paramagnetic agent. In fact, the use of a mixture of Eu‐DOTAM‐Gly and Yb‐DOTAM‐Gly, whose exchangeable proton pools are represented by the coordinated water (ca. 40 ppm downfield H₂O signal at 312K) and amide protons, respectively, produces a pH‐dependent CEST effect which is the function of the concentration ratio of the two complexes. Magn Reson Med 47:639–648, 2002.