RELAXOMETRY AND PARAMAGNETIC METAL-IONS IN BIOLOGICAL-SYSTEMS

This paper gives an overview of the impact of relaxometry in bioinorganic chemistry. It is taken from a lecture dedicated to Seymour It Koenig that the author presented at the 5th Chianti Workshop in Magnetic Resonance, San Miniato, Pisa, Italy, May 30-June 5, 1993. After a short introduction and the definition of relaxometry, the basic principles of field-cycling relaxometry are illustrated, with reference to the Koenig-Brown relaxometer. Through a brief survey of early relaxometric data on paramagnetic solutions dating back to the 1950s and 1960s, attention is devoted to Koenig's discovery, in the 1970s, of anomalous relaxometric profiles of metalloprotein solutions and of the theoretical problems encountered in their interpretation. Then the advances made in the 1980s in the theory of electron nucleus interactions in slowly-rotating systems are summarized. These advances were largely due to the fruitful interactions between Koenig, Bertini and his group at the University of Florence and the author, first at the University of Florence and later at the University of Bologna. After a short digression on obtaining electron relaxation rates from relaxometric measurements and on their physical meaning, recent progresses in understanding the detailed relaxometric behaviour of aqueous solutions of paramagnetic metal ions are presented. Again, Koenig's physical insight into the phenomena is highlighted. Finally, the exciting perspectives of the 1990s in the field of contrast agents, particularly in the theoretical understanding of superparamagnets, where Koenig is again at the forefront, are briefly described.