Abstract
Although copper based complexes have been widely used in homogeneous catalysis, more recently they are attracting considerable attention as pharmaceutical therapeutic agents. Of paramount importance in their efficacy of use is their structure and electronic properties, which can be thoroughly probed using advanced EPR techniques. In this study, a series of [Cu(acac)(N-N)]+ Casiopeina type complexes were investigated, bearing a series of diimine N-N ligands (including bipy, phen, Py-bipy and dppz). All complexes displayed rhombic g and CuA tensors, although the extent of rhombicity was dependent on the N-N ligand. Greater Cu(II)-N2 in-plane distortion, away from the square planar arrangement, was detected by CW W-band EPR for the smaller bipy and phen ligands compared to the larger Py-bipy and dppz ligands. Changes in ligand spin density distributions (over the 1H and 14N nuclei) were revealed by CW Q-band ENDOR. The largest components of the 1H imine and 14N hyperfine coupling decreased as the ligand size increased, following the trend bipy > phen > Py-bipy > dppz. These results indicate how even small structural and electronic (spin density) perturbations within the Casiopeina family of Cu(II) complexes can be probed by advanced EPR methods.
Highlights
The Casiopeinas are a class of mixed chelate, cationic copper complexes which have well known antineoplastic properties
The continuous wave (CW) Q-band (35 GHz) Electron Paramagnetic Resonance (EPR) and Electron Nuclear Double Resonance (ENDOR) measurements were recorded on a Bruker Elexsys E500 spectrometer using a Bruker ER5106 QT-E Q-band resonator operating at 10 kHz field modulation and 10 K for ENDOR
Casiopeina type copper complexes have been studied for many years, as they show promising potential as therapeutic agents
Summary
The Casiopeinas are a class of mixed chelate, cationic copper complexes which have well known antineoplastic properties. They have the general formula [Cu(O-O)(N-O)]+ or [Cu(O-O)(N-N)]+, where O-O typically represents an acetylacetonate (abbreviated to acac) or salicylaldehydate (sal) chelate ligand, N-O denotes an aminoacidate or peptide, and N-N generally indicates an aromatic diimine such as 1,10-phenanthroline (phen) or 2,20-bipyridine (bipy) [1]. Whilst some Casiopeinas have been found to be active on cisplatin-resistant cell lines [4,15], a considerable amount of work is still required before they can be used in a clinical setting [16]. Adduct formation between the copper complex and the DNA may induce conformational change within a strand of DNA and cause denaturation This could contribute to the therapeutic mechanism of Casiopeinas.
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Published Version
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