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|Title:||Structure-Activity relationship and Molecular Bonding Parameters from room-temperature multifrequency ESR spectra of antitumor copper(II) complexes||Authors:||Basosi, Riccardo||Issue Date:||1988||Project:||None||Journal:||THE JOURNAL OF PHYSICAL CHEMISTRY||Abstract:||
A rigorous unambiguous way to extract all the necessary magnetic parameters for copper complexes in the fluid phase, bya combination of multifrequency ESR spectroscopy and computer simulation, is presented. By this method, which has theobvious advantage of not changing the physical state of the system, homologue copper complexes with very different cytotoxicand pharmacological activities (CuKTS and CuKTSMJ were examined. Having extracted the spin Hamiltonian parametersand the rotational correlation time from the room-temperature ESR spectra of the two complexes at multiple frequencies,small differences were found in the isotropic nitrogen coupling constants. This was never appreciated before because of theaggregation occurring in the samples at low temperature. This difference was precisely determined through an accuratecomputer simulation and sensitivity analysis procedure, and discussed in terms of a difference in molecular bonding parametersbetween CuKTS and CuKTSM2, using a simple LCAO molecular orbital scheme. The planar geometry previously proposedby Campbell et al. on the basis of frozen solution ESR data was eventually confirmed for CuKTS with the predicted sp2hybridization for the nitrogen atoms coordinating the copper ion. In the case of CuKTSMz the hybridization coefficientn and the mixing coefficient aN have higher values consistent with an sp3 hybridization and an "out of planarity" of the chelatingring around the metal ion. A speculation on the possible correlation between the difference in the chemical arrangementand the well-known difference in the pharmacological behavior is proposed in the framework of the structurefunction relationship
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