Photochemical catalytic CO2 reduction to formate and methanol has been demonstrated in an aqueous homogeneous system at pH 5.0 comprising ruthenium(II) trisphenanthroline as the chromophore, pyridine as the CO2 reduction catalyst, KCl, and ascorbic acid as a sacrificial reductant, using visible light irradiation at 470 ± 20 nm. Isotopic labeling with (13)CO2 yields the six-electron-reduced product (13)CH3OH. After 1 h photolysis, the two-electron-reduced product formate and the six-electron-reduced product methanol are produced with quantum yields of 0.025 and 1.1 × 10(–4), respectively. This represents 76 and 0.15 turnovers per Ru for formate and methanol, respectively, and 152 and 0.9 turnovers per Ru on an electron basis for formate and methanol, respectively. The system is inactive after 6 h irradiation, which appears largely to be due to chromophore degradation. A partial optimization of the methanol yield showed that high pyridine to Ru ratios are needed (100:1) and that the optimum pH is near 5.0. The presence of potassium salts enhances the yield in formate and methanol by 8- and 2-fold, respectively, compared to electrolyte-free solutions; however, other alkali and alkali earth cations have little effect. The addition of small amounts of solid metal catalysts immobilized on carbon had either no effect (M = Pt or Pd) or deleterious effects (M = Ni or Au) on methanol production. Addition of colloidal Pt resulted in no methanol production at all. This is in notable contrast with the pyridine-based electrocatalysis of CO2 to methanol in which metallic or conductive surfaces such as Pt, Pd, or p-type GaP are necessary for methanol formation.
Only a small fraction of vitamin B 12 -requiring organisms are able to synthesize B 12 de novo, making it a common commodity in microbial communities. Initially recognized as an enzyme cofactor of a few enzymes, recent studies have revealed additional B 12 -binding enzymes and regulatory roles for B 12 . Here we report the development and use of a B 12 -based chemical probe to identify B 12 -binding proteins in a nonphototrophic B 12 -producing bacterium. Two unexpected discoveries resulted from this study. First, we identified a light-sensing B 12 -binding transcriptional regulator and demonstrated that it controls folate and ubiquinone biosynthesis. Second, our probe captured proteins involved in folate, methionine, and ubiquinone metabolism, suggesting that it may play a role as an allosteric effector of these processes. These metabolic processes produce precursors for synthesis of DNA, RNA, and protein. Thereby, B 12 likely modulates growth, and by limiting its availability to auxotrophs, B 12 -producing organisms may facilitate coordination of community metabolism.
Geminal dicationic ionic liquids
(ILs) often display higher thermal
stabilities, viscosities, and densities compared to traditional monocationic
ILs. Also, dicationic ILs have advantages in terms of tuning of their
physicochemical properties by different structural modifications.
They can be considered as a combination of three structural moieties:
(1) cationic head groups, (2) an alkane linker chain, and (3) the
associated anions. Two types of each imidazolium, pyrrolidinium, and
phosphonium cations were joined by different alkane linkages (C6, C9, and C12) to develop 18 different
dications. These dications were paired with two different anions (NTf2
– and PFOS–) to synthesize
36 different dicationic ILs. The effect of variations in the structural
moieties of these related ILs on their physicochemical properties,
including melting points, densities, viscosities, solubilities, and
thermal stabilities, were evaluated. ILs synthesized in this study
displayed TGA thermal stabilities in the range 330–467 °C.
Also, nine ILs with high TGA stability and low melting points were
tested with inverse gas chromatography, and some of them displayed
stabilities up to 400 °C.
Phospholipids make up one of the more important classes of biological molecules. Because of their amphipathic nature and their charge state (e.g., negatively charged or zwitterionic) detection of trace levels of these compounds can be problematic. Electrospray ionization mass spectrometry (ESI-MS) is used in this study to detect very small amounts of these analytes by using the positive ion mode and pairing them with fifteen different cationic ion pairing reagents. The phospholipids used in this analysis were phosphatidylethanolamine (PE), phosphatidylcholine (PC), phosphatidylglycerol (PG), phosphatidylserine (PS), phosphatidylinositol (PI), phosphatidic acid (PA), 1,2-diheptanoyl-sn-glycero-3-phosphocholine (DHPC), cardiolipin (CA) and sphingosyl phosphoethanolamine (SPE). The analysis of these molecules was carried out in the single ion monitoring (SIM) positive mode. In addition to their detection, a high performance liquid chromatography and mass spectrometry (HPLC-MS) method was developed in which the phospholipids were separated and detected simultaneously within a very short period of time. Separation of phospholipids was developed in the reverse phase mode and in the hydrophilic interaction liquid chromatography (HILIC) mode HPLC. Their differences and impact on the sensitivity of the analytes are compared and discussed further in the paper. With this technique, limits of detection (LODs) were very easily recorded at low ppt (ng L(-1)) levels with many of the cationic ion pairing reagents used in this study.
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