Solution studies of systems with polynuclear complex formation. 1. The copper(II) citrate system

Interaction of the potent antitumoral compounds Casiopeinas® with blood serum and cellular bioligands

Casiopeinas® are among the few Cu^II compounds patented for their antitumor activity, but their mode of action has not been fully elucidated yet. One of them, Cas II-gly, is formed by 4,7-dimethyl-1,10-phenanthroline (Me₂phen) and glycinato (Gly). In blood and cells, Cas II-gly can keep its identity or form mixed species with serum or cytosol bioligands (bL or cL) with composition Cu^II-Me₂phen-bL/cL, Cu^II-Gly-bL/cL, or Cu^II-bL/cL. In this study, the binding of Cas II-gly with low molecular mass bioligands of blood serum (citric, L-lactic acid, and L-histidine) and cytosol (reduced glutathione (GSH), reduced nicotinamide adenine dinucleotide (NADH), adenosine triphosphate (ATP), and l-ascorbic acid) was examined through the application of instrumental (ElectroSpray Ionization-Mass Spectrometry and Electron Paramagnetic Resonance) and computational (Density Functional Theory) methods. The results indicated that mixed species Cu^II-Me₂phen-bL/cL are formed, with the bioligands replacing glycinato. The formation of these adducts may participate in the copper transport toward the target organs and facilitate the cellular uptake or, in constrast, preclude it. In the systems with GSH, NADH and L-ascorbate, a redox reaction occurs with the partial oxidation of cL to the corresponding oxidized form (GSSG, NAD⁺ and dehydroascorbate) which interact with Cu^II. Formed Cu^I ion does not give complexation reactions with reduced or oxidized form of bioligands for its 'soft' character and low affinity for oxygen and nitrogen donors compared to Cu^II. However, Cu^I could promote Fenton-like reactions with production of reactive oxygen species (ROS) related to the antitumor activity of Casiopeinas®.

A Novel "Off-On" Fluorescent Probe Based on Carbon Nitride Nanoribbons for the Detection of Citrate Anion and Live Cell Imaging

A novel fluorescent “off-on” probe based on carbon nitride (C₃N₄) nanoribbons was developed for citrate anion (C₆H₅O₇³⁻) detection. The fluorescence of C₃N₄ nanoribbons can be quenched by Cu²⁺ and then recovered by the addition of C₆H₅O₇³⁻, because the chelation between C₆H₅O₇³⁻ and Cu²⁺ blocks the electron transfer between Cu²⁺ and C₃N₄ nanoribbons. The turn-on fluorescent sensor using this fluorescent “off-on” probe can detect C₆H₅O₇³⁻ rapidly and selectively, showing a wide detection linear range (1~400 μM) and a low detection limit (0.78 μM) in aqueous solutions. Importantly, this C₃N₄ nanoribbon-based “off-on” probe exhibits good biocompatibility and can be used as fluorescent visualizer for exogenous C₆H₅O₇³⁻ in HeLa cells.

Synergistic effects of citric acid and polyethyleneimine to remove copper from aqueous solutions

Citric acid and copper are often found in the waste streams from semiconductor manufacturing. They are likely to form complexes, which modify copper speciation. This can lead to changes in sorption mechanisms and the sorption capacity. PEI-agarose adsorbents in a packed bed column are capable of removing these anionic complexes, but the competitive binding between these organic ligands and PEI for copper is not well understood and needs to be explored. The current work focuses on investigating copper sorption by PEI-agarose adsorbent in the presence of citrate ions. Copper binding capacity and copper breakthrough curves are compared and contrasted to results without additional chelator present. The presence of citric acid at the molar ratios of 0.5, 1, and 2 to copper enhances the total copper uptake in a continuous column by 175%, 100% and 75%, respectively. This is a great advantage when wastewater streams contain either low or high amounts of citric acid ligand.

A turn-on fluorescent indicator for citrate with micromolar sensitivity

A turn-on fluorescent indicator for citric acid (citrate) has been developed, displaying high emission enhancement (+1500%) and low interference by other carboxylates. The sensor is based on the non-emissive copper(II) complex of a fluorescent amino amide, which, upon addition of citrate decomplexates to yield the emissive ligand. The detection limit estimated for this new chemosensing system is about 0.5 microM. This novel approach to the analysis of citrate constitutes an alternative ca. 10(2)-10(3) times more sensitive than the standard method based on the enzyme citrate lyase.

An experiment in the electrokinetic removal of copper from soil contaminated by the brass industry

The feasibility of electrokinetic remediation of copper-contaminated soil was evaluated following eight days of electroreclamation. The results indicate that electrokinetic reclamation of Cu is totally ineffective in soil composed primarily of clay minerals and organic matter. The strong absorption of copper by this kind of soil, in our view mainly a result of retention by the clay component, makes it resistant to mobilization by the electrogenerated acidic front as well as by citrates (the competitors of natural chelating agents, i.e., humates). Such conditions, while adverse for the electroremediation process, may cause this kind of soil to act as a natural barrier to the leaching of copper ions.