Spectroscopic Characterization of Cu2+ Solutions

The absorption spectra of Cu²⁺ containing solutions were recorded on a Varian Cary50 Probe spectrophotometer, in the range 350–900 nm, using a quartz cuvette with an optical path of 1 cm. To describe the species present in solution, the observed wavelength of maximum absorption at a given pH was compared with the expected λ_max value obtained from literature^{23 (link),48 (link)–50 (link)}. Circular dichroism (CD) spectra were recorded on a Jasco J-1500 spectropolarimeter in the 180–800 nm range, using a quartz cuvette with an optical path of 1 cm in the visible and near-UV range, and 0.01 cm in the 180–250 nm range. Electron paramagnetic resonance (EPR) spectra were recorded in liquid nitrogen on a Bruker ELEXSYS E500 CW-EPR spectrometer at X-band frequency (9.5 GHz) and equipped with an ER 036TM NMR teslameter and an E41 FC frequency counter. Ethylene glycol (30%) was used as a cryoprotectant. The EPR parameters were analyzed by computer simulation of the experimental spectra using WIN-EPR SIMFONIA software, version 1.2 (Bruker, Billerica, MA, USA).