Understanding the Chloride Affinity of Barbiturates for Anion Receptor Design.

Due to their potential binding sites, barbituric acid (BA) and its derivatives have been used in metal coordination chemistry. Yet their abilities to recognize anions remain unexplored. In this work, we were able to identify four structural features of barbiturates that are responsible for a certain anion affinity. The set of coordination interactions can be finely tuned with covalent decorations at the methylene group. DFT-D computations at the BLYP-D3(BJ)/aug-cc-pVDZ level of theory show that the C-H bond is as effective as the N-H bond to coordinate chloride. An analysis of the electron charge density at the C-H⋅⋅⋅Cl- and N-H⋅⋅⋅Cl- bond critical points elucidates their similarities in covalent character. Our results reveal that the special acidity of the C-H bond shows up when the methylene group moves out of the ring plane and it is mainly governed by the orbital interaction energy. The amide and carboxyl groups are the best choices to coordinate the ion when they act together with the C-H bond. We finally show how can we use this information to rationally improve the recognition capability of a small cage-like complex that is able to coordinate NaCl.

Hydroxyl Radical Generation and DNA Nuclease Activity: A Mechanistic Study Based on a Surface-Immobilized Copper Thioether Clip-Phen Derivative.

Coordination compounds of copper have been invoked as major actors in processes involving the reduction of molecular oxygen, mostly with the generation of radical species the assignment for which has, so far, not been fully addressed. In the present work, we have carried out studies in solution and on surfaces to gain insights into the nature of the radical oxygen species (ROS) generated by a copper(II) coordination compound containing a thioether clip-phen derivative, 1,3-bis(1,10-phenanthrolin-2-yloxy)-N-(4-(methylthio)benzylidene)propan-2-amine (2CP-Bz-SMe), enabling its adsorption/immobilization to gold surfaces. Whereas surface plasmon resonance (SPR) and electrochemistry of the adsorbed complex indicated the formation of a dimeric Cu(I) intermediate containing molecular oxygen as a bridging ligand, scanning electrochemical microscopy (SECM) and nuclease assays pointed to the generation of a ROS species. Electron paramagnetic resonance (EPR) data reinforced such conclusions, indicating that radical production was dependent on the amount of oxygen and H2 O2 , thus pointing to a mechanism involving a Fenton-like reaction that results in the production of OH(.) .