8-Hydroxyquinolines (8HQs) are a family of lipophilic metal ion chelators that have been used in a range of analytical and pharmaceutical applications over the last 100 years. More recently, CQ (clioquinol; 5-chloro-7-iodo-8-hydroxyquinoline) and PBT2 (5,7-dichloro-2-[(dimethylamino)methyl]-8-hydroxyquinoline) have undergone clinical trials for the treatment of Alzheimer’s disease and Huntington’s disease. Because CQ and PBT2 appear to redistribute metals into cells, these compounds have been redefined as copper and zinc ionophores. Despite the attention surrounding the clinical trials and the clear link between 8HQs and metals, the fundamental solution chemistry of how these compounds bind divalent metals such as copper and zinc, as well as their mechanism(s) of action in mammalian systems, remains poorly understood. Here, we used a combination of X-ray absorption spectroscopy (XAS), high-energy resolution fluorescence detected (HERFD) XAS, electron paramagnetic resonance (EPR), and UV–visible absorption spectroscopies to investigate the aqueous solution chemistry of a range of 8HQ derivatives. To circumvent the known solubility issues with 8HQ compounds and their complexes with Cu(II), and to avoid the use of abiological organic solvents, we have devised a surfactant buffer system to investigate these Cu(II) complexes in aqueous solution. Our study comprises the first comprehensive investigation of the Cu(II) complexes formed with many 8HQs of interest in aqueous solution, and it provides the first structural information on some of these complexes. We find that halogen substitutions in 8HQ derivatives appear to have little effect on the Cu(II) coordination environment; 5,7-dihalogenated 8HQ conformers all have a pseudo square planar Cu(II) bound by two quinolin-8-olate anions, in agreement with previous studies. Conversely, substituents in the 2-position of the 8HQ moiety appear to cause significant distortions from the typical square-planar-like coordination of most Cu(II)-bis-8HQ complexes, such that the 8HQ moieties in the Cu(II)-bis-8HQ complex are rotated approximately 30–40° apart in a “propeller-like” arrangement.
Summers, Kelly L., Pushie, M. Jake, Sopasis, George J., James, Ashley K., Dolgova, Natalia V., Sokaras, Dimosthenis, Kroll, Thomas, Harris, Hugh H., Pickering, Ingrid J., & George, Graham N. (2020). Solution Chemistry of Copper(II) Binding to Substituted 8-Hydroxyquinolines. Inorganic Chemistry, 59(19). https://doi.org/10.1021/acs.inorgchem.0c01356
Summers, Kelly L., Pushie, M. Jake, Sopasis, George J., et al., "Solution Chemistry of Copper(II) Binding to Substituted 8-Hydroxyquinolines," Inorganic Chemistry 59, no. 19 (2020), https://doi.org/10.1021/acs.inorgchem.0c01356
@article{osti_1769889,
author = {Summers, Kelly L. and Pushie, M. Jake and Sopasis, George J. and James, Ashley K. and Dolgova, Natalia V. and Sokaras, Dimosthenis and Kroll, Thomas and Harris, Hugh H. and Pickering, Ingrid J. and George, Graham N.},
title = {Solution Chemistry of Copper(II) Binding to Substituted 8-Hydroxyquinolines},
annote = {8-Hydroxyquinolines (8HQs) are a family of lipophilic metal ion chelators that have been used in a range of analytical and pharmaceutical applications over the last 100 years. More recently, CQ (clioquinol; 5-chloro-7-iodo-8-hydroxyquinoline) and PBT2 (5,7-dichloro-2-[(dimethylamino)methyl]-8-hydroxyquinoline) have undergone clinical trials for the treatment of Alzheimer’s disease and Huntington’s disease. Because CQ and PBT2 appear to redistribute metals into cells, these compounds have been redefined as copper and zinc ionophores. Despite the attention surrounding the clinical trials and the clear link between 8HQs and metals, the fundamental solution chemistry of how these compounds bind divalent metals such as copper and zinc, as well as their mechanism(s) of action in mammalian systems, remains poorly understood. Here, we used a combination of X-ray absorption spectroscopy (XAS), high-energy resolution fluorescence detected (HERFD) XAS, electron paramagnetic resonance (EPR), and UV–visible absorption spectroscopies to investigate the aqueous solution chemistry of a range of 8HQ derivatives. To circumvent the known solubility issues with 8HQ compounds and their complexes with Cu(II), and to avoid the use of abiological organic solvents, we have devised a surfactant buffer system to investigate these Cu(II) complexes in aqueous solution. Our study comprises the first comprehensive investigation of the Cu(II) complexes formed with many 8HQs of interest in aqueous solution, and it provides the first structural information on some of these complexes. We find that halogen substitutions in 8HQ derivatives appear to have little effect on the Cu(II) coordination environment; 5,7-dihalogenated 8HQ conformers all have a pseudo square planar Cu(II) bound by two quinolin-8-olate anions, in agreement with previous studies. Conversely, substituents in the 2-position of the 8HQ moiety appear to cause significant distortions from the typical square-planar-like coordination of most Cu(II)-bis-8HQ complexes, such that the 8HQ moieties in the Cu(II)-bis-8HQ complex are rotated approximately 30–40° apart in a “propeller-like” arrangement.},
doi = {10.1021/acs.inorgchem.0c01356},
url = {https://www.osti.gov/biblio/1769889},
journal = {Inorganic Chemistry},
issn = {ISSN 0020-1669},
number = {19},
volume = {59},
place = {United States},
publisher = {American Chemical Society (ACS)},
year = {2020},
month = {09}}
SLAC National Accelerator Laboratory, Menlo Park, CA (United States). Stanford Synchrotron Radiation Lightsource (SSRL)
Sponsoring Organization:
Australian Research Council (ARC); Canadian Institutes of Health Research (CIHR); National Institutes of Health (NIH); Natural Sciences and Engineering Research Council of Canada (NSERC); USDOE Office of Science (SC), Basic Energy Sciences (BES); USDOE Office of Science (SC), Biological and Environmental Research (BER)
Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, Vol. 266, Issue 1-3https://doi.org/10.1016/0168-9002(88)90449-4
Abragam, Anatole; Horowitz, J.; Pryce, Maurice Henry Lecorney
Proceedings of the Royal Society of London. Series A. Mathematical and Physical Sciences, Vol. 230, Issue 1181, p. 169-187https://doi.org/10.1098/rspa.1955.0120