Noncovalent interactions and paramagnetic relaxation probes. Investigation of the correlation times

An EPR and NMR combined analysis has been carried out in the study of noncovalent interactions involving metal ions. Manganous ion was chosen as the paramagnetic relaxation probe. The 5’-ATP-Mn(II)-(apo-BCA) and the 5’-ATP-Mn(II)-Trp ternary systems have been investigated under different experimental conditions. The EPR line shape was analyzed in terms of a relaxation model based on a distribution of ZFS sites. Typical inverted spectra have been found whenever stacking interaction occurred. Paramagnetic contributions of Tt;l and T2;’ to 13C and IH relaxation rates were investigated by taking into account a distribution of correlation times and the competition between T, and 7, connected with the formation of ternary species.