Bis-Catecholamide-Based Materials for Uranium Extraction.

Invited for this month's cover is the collaborating group of Dr Guilhem Arrachart and Dr Stéphane Pellet-Rostaing at Institut de Chimie Séparative de Marcoule (ICSM). The cover picture shows a person going uranium fishing thanks to the use of bis-catecholamide materials. These materials have shown interesting performance for the recovery of uranium in saline environments such as seawater. More information can be found in the Research Article by G. Arrachart, S. Pellet-Rostaing, and co-workers.

Bis-Catecholamide-Based Materials for Uranium Extraction.

This work reports the synthesis of formo-phenolic resins containing four catecholamide (CAM) moieties with admixture of phenol, catechol or resorcinol. These chelating resins have been developed to selectively extract U(VI) from seawater. This media is a challenging environment due to a pH around 8.2 and a large excess of alkaline and earth-alkaline cations. From the various sorption experiments investigated, the results indicate that the synthesized material exhibit good sorbent properties for U(VI) with uptake capacity about 50 mg/g for the more promising resins with a pronounced selectivity for uranium even under saline conditions. Thermodynamic and kinetic adsorption data were determined for the best resin (Langmuir adsorption model and pseudo-second order model).

Electrocatalytic reduction of CO2 in water by a C-functionalized Ni-cyclam complex grafted onto carbon.

We present here a novel strategy based on the covalent grafting of a C-functionalized Ni-cyclam complex onto glassy carbon to achieve heterogeneous electrocatalytic CO2 reduction in neutral water at low overpotential (-500 mV vs. NHE), with moderate turnover number (TON = 454), high selectivity (85% CO produced) and good faradaic efficiency (56% CO). Direct comparison with the N-functionalized Ni-cyclam analogue highlights the benefits of this approach in terms of CO2 electroreduction.

Copper(II) and zinc(II) complexation with N-ethylene hydroxycyclams and consequences on the macrocyclic backbone configuration.

We report a series of four cyclams and cross-bridged cyclams, N-functionalized by one hydroxyethyl arm, which may incorporate additional methyl(s) group(s). The Cu(II) and Zn(II) complexes of these ligands were synthesized and fully characterized. The investigation of the metal complexes in solid-state and in solution was carried via X-ray diffraction, NMR, EPR, absorption spectroscopy and DFT calculations. The influence of N-functionalization on their structural/stereochemical properties, electrochemical behavior and kinetic inertness was carefully studied and identified. N-Functionalization by a hydroxyethyl group did not influence importantly the stereochemical properties of the complexes. However, it stabilized the complexes kinetically and electrochemically. As for N-methylation, it induces significant distortion of the coordination geometry, decreasing the kinetic inertness of the complexes and stabilizing Cu+. Overall, this work expanded the family of cyclam and cross-bridged cyclam metal complexes and provides a detailed analysis of their structural features. The rather large body of data accumulated for this family of complexes provides opportunities to design systems with pre-determined properties for specific applications.

Complexation of C-Functionalized Cyclams with Copper(II) and Zinc(II): Similarities and Changes When Compared to Parent Cyclam Analogues.

Herein, we report a comprehensive coordination study of the previously reported ligands cyclam, CB-cyclam, TMC, DMC, and CB-DMC and of their C-functional analogues, cyclam-E, CB-cyclam-E, TMC-E, DMC-E, and CB-DMC-E. This group of ligands includes cyclam, cross-bridged cyclams, their di- or tetramethylated derivatives, and the analogues bearing an additional hydroxyethyl group on one ß-N position of the ring. The Cu(II) and Zn(II) complexes of these macrocycles have been highlighted previously for the biological interest, but the details of their structures in the solid state and in solution remained largely unexplored. In particular, we analyzed the impact that adding noncoordinating N-methyl and C-hydroxyethyl functionalities has in the structures of the complexes. All the Cu(II) and Zn(II) complexes were synthesized and investigated using single crystal X-ray diffraction and NMR, electronic absorption, and EPR spectroscopies, along with DFT studies. Dissociation kinetics experiments in acidic conditions and electrochemical studies were also performed. Special attention was paid to analyze the different configurations present in solution and in the solid state, as well as the impact of the C-appended hydroxyethyl group on the coordination behavior. Various ratios of the trans-I, trans-III, and cis-V configurations have been observed depending on the degree of N-methylation and the presence of the ethylene cross-bridge.