ABSTRACT
The complex [Ru(bpy)2(ttma)](+) (bpy = 2,2'-bipyridine; ttma = 3-hydroxy-2-methyl-thiopyran-4-thionate, 1, has previously been shown to undergo an unusual C-H activation of the dithiomaltolato ligand upon outer-sphere oxidation. The reaction generated alcohol and aldehyde products 2 and 3 from C-H oxidation of the pendant methyl group. In this report, we demonstrate that the same products are formed upon photolysis of 1 in presence of mild oxidants such as methyl viologen, [Ru(NH3)6](3+) and [Co(NH3)5Cl](2+), which do not oxidize 1 in the dark. This reactivity is engendered only upon excitation into an absorption band attributed to the ttma ligand. Analogous experiments with the homoleptic Zn(ttma)2, 4, also result in reduction of electron acceptors upon excitation of the ttma absorption band. Complexes 1 and 4 exhibit short-lived visible fluorescence and long-lived near-infrared phosphorescence bands. Singlet oxygen is both generated and quenched during aerobic excitation of 1 or 4, but is not involved in the C-H activation process.
Subject(s)
Photolysis , Ruthenium Compounds/chemistry , Singlet Oxygen/chemistry , Zinc Compounds/chemistry , Crystallization , Electrochemistry , Ligands , Models, Molecular , Molecular Structure , Oxidation-Reduction , Photochemical ProcessesABSTRACT
The increasing prevalence of drug resistant bacteria is a pandemic problem. Metallo-ß-lactamases (MBLs) are one of the main causes of drug resistance due to hydrolysis of ß-lactam antibiotics. Thus, the development of effective inhibitors of MBLs remains urgent. The compound thiomaltol was used as a lead compound to investigate its ability to inhibit metallo-ß-lactamase from Bacillus anthracis (Bla2), which causes anthrax. Kinetic evaluation with nitrocefin as a substrate indicates that thiomaltol inhibits Bla2 in a time-dependent manner with an IC(50) value of 290 µM after 20 min preincubation. Progress curve analysis and reversibility tests suggest that thiomaltol is a reversible, slow-binding inhibitor with a K(i) of 85 ± 30 µM. Furthermore, studies on the modality of inhibition and in silico analysis indicate thiomaltol to be a competitive inhibitor. The results demonstrate that thiomaltol is a promising lead compound for slow binding inhibitor design of Bla2.
Subject(s)
Bacillus anthracis/enzymology , Enzyme Inhibitors/pharmacology , Pyrans/pharmacology , Thiones/pharmacology , beta-Lactamase Inhibitors , Anti-Bacterial Agents/chemistry , Anti-Bacterial Agents/pharmacology , Cephalosporins/metabolism , Computer Simulation , Inhibitory Concentration 50 , Kinetics , Molecular Docking Simulation , Molecular Structure , Pyrans/chemistry , Thiones/chemistry , beta-Lactamases/metabolismABSTRACT
Recently, rutile nanotwins were synthesized using high temperature organic solvent methods, yielding two kinds of common high-quality rutile twinned nanocrystals, (101) and (301) twins, accompanied by minor rutile nanorods (Lu et al 2012 CrystEngComm 14 3120-4). In this report, the atomic structures of the rutile and anatase nanocrystals are directly resolved with no need for calculation or image simulation using atomic resolution STEM techniques. The locations of the oxygen rows in the rutile twins' boundaries are directly determined from both HAADF images and ABF images. To the best of our knowledge, this is the first time oxygen columns have been distinguished in rutile twin boundaries using HAADF and BF imaging.
