1H NMRD PROFILES OF PARAMAGNETIC COMPLEXES AND METALLOPROTEINS

In the last ten years several novel theories for the analysis of 1H NMRD profiles have been proposed for different paramagnetic systems. These resulted in novel equations and computer programs for numerical calculations. In this review we tried to summarize the classical theory as well as some recent theoretical treatments, and to show their applicability to the different metal ion systems by selecting some experimental profiles which exhibit the most characteristic features. In the last few years dedicated instruments, called field-cycling relaxometers, have appeared on the market. These instruments now allow to measure nuclear relaxation rates on strong NMR signals over fields that can range smoothly between a few kHz up to about 50 MHz. On the other hand the availability of spectrometers working at very high magnetic fields (up to 900 MHz) allows researchers to obtain relaxation profiles covering 5 orders of magnitude in proton Larmor frequency, thus allowing a more informative analysis of the data, and a better understanding of high field effects. The NMRD technique is thus a precious tool to obtain information on, for instance, water-metal ion ligands and on the electron relaxation time of the paramagnetic species. Understanding electron relaxation is important to be able to predict the NMR behavior of paramagnetic compounds at high field and to master high resolution NMR experiments on paramagnetic systems. Further perspectives are represented by applications of relaxometry for in vitro and in vivo measurements, in order to efficiently monitor the relaxing properties of the compounds in their “working” environment, the most relevant field being that of the characterization of novel and specialized contrast agents for MRI