Porous Coordination Polymer Based on Bipyridinium Carboxylate Linkers with High and Reversible Ammonia Uptake.

The zwitterionic bipyridinium carboxylate ligand 1,1'-bis(4-carboxyphenyl)-4,4'-bipyridinium (pc1) in the presence of cadmium chloride affords novel porous coordination polymers (PCPs): [Cd4(pc1)3Cl6]·CdCl4·guest (1) crystallizing in the P3̅1c space group. In the structure, [Cd4Cl6(CO2)6] building units are linked together by six pc1 ligands, leading to a 3D high-symmetrical network exhibiting hexagonal channels along the c axis. The walls of this PCP consist of cationic electron-acceptor bipyridinium units. The PCP 1 reversibly adsorbs H2O and CH3OH up to about 0.1 g/g at saturation showing the adsorption isotherms characteristic of a moderately hydrophilic sorbent. Adsorption of ammonia (NH3) follows a different pattern, reaching an exceptional uptake of 0.39 g/g (22.3 mmol/g) after the first adsorption cycle. Although the crystalline structure of 1 collapses after the first adsorption, the solid can be regenerated and maintains the capacity of 0.29 g/g (17 mmol/g) in the following cycles. We found that the high NH3 uptake is due to a combination of pore filling taking place below 150 h·Pa and chemisorption occurring at higher pressures. The latter process was shown to involve two phenomena: (i) coordination of NH3 molecules to Cd(2+) cations as follows from (113)Cd NMR and (ii) strong donor-acceptor interactions between NH3 molecules and pc1 ligands.

ZrO2/ZnO/TiO2 Nanocomposite Coatings on Stainless Steel for Improved Corrosion Resistance, Biocompatibility, and Antimicrobial Activity.

The ultrathin nanocomposite coatings made of zirconium oxide (ZrO2), zinc oxide (ZnO), and titanium oxide (TiO2) on stainless steel (SS) were prepared by the radio frequency sputtering method, and the effects of the nanocomposite coating on corrosion protection and antibacterial activities of nanocomposite coated SS were investigated. Scanning electron microscopy was conducted to observe surface morphology of nanocomposite coatings with distinct distribution of grains with the formation on SS substrate. From the electrochemical impedance spectroscopy results, ZrO2/ZnO/TiO2 nanocomposite coating showed excellent corrosion protection performance at 37 °C during immersion in simulated body fluid and saliva solution for 12 and 4 weeks, respectively. The impedance of ZrO2/ZnO/TiO2 (40/10/50) nanocomposite coated SS exhibited values about 5 orders of magnitude higher than that of uncoated SS with polarization at the low-frequency region. Cell viability of ZrO2/ZnO/TiO2 nanocomposite coated SS was examined under mouse fibroblasts culture (L929), and it was observed that the nanocomposite coating improves proliferation through effective cellular attachment compared to uncoated SS. From the antimicrobial activity results, ZrO2/ZnO/TiO2 nanocomposite-coated SS showed killing efficiency of 81.2% and 72.4% against Gram-negative Escherichia coli and Gram-positive Staphylococcus aureus, respectively.

Unprecedented stacking of MV2+ dications and MV˙+ radical cations in the mixed-valence viologen salt (MV)2(BF4)3 (MV = methylviologen).

Using a slow liquid-gas diffusion method, the mixed-valence viologen salt (MV)2(BF4)3 (1) and the radical cation salt (MV)(BF4) (2) are crystallized. Both structures contain regular stacks of MV˙(+) radical cations (2) or alternating MV˙(+) and MV(2+) entities (1). A short intrastack intermolecular separation (3.23 Å) unprecedently reveals strong interactions between MV(2+) and MV˙(+) in 1.