Multifrequency ESR and NMR Analysis of the Metal-ATP Interaction

Multifrequency ESR analysis allows a new interpretation of the correlation times involved in nuclear relaxation. In this study the metal-ATP interaction, so important in ecosystem energy mechanisms, was interpreted in the light of new multifrequency ESR and NMR experimental data. ESR spectra of the Mn(II)-ATP complex were recorded at 2-4 GHz (S-band), 9 GHz (X-band) and 35 GHz (Q-band). A loop-gap resonator was used to enhance the etaQ0 product at low frequencies. The ESR line shapes at different temperatures and frequencies led to the interpretation of the predominant relaxation mechanism involved. The NMR relaxation rates, also recorded at different temperatures and frequencies, are discussed in terms of a motional model taking into account a distribution of correlation times. Structural and dynamic features were analysed in order to determine the effective correlation time contributing to nuclear paramagnetic relaxation. A comprehensive analysis of the multifrequency ESR spectra is crucial for the correct interpretation of the NMR spectra and of the metal-ATP interaction.