Tuning of the ionization potential of paddlewheel diruthenium(II, II) complexes with fluorine atoms on the benzoate ligands

A series of paddlewheel diruthenium(ii, ii) complexes with various fluorine-substituted benzoate ligands were isolated as THF adducts and structurally characterized: [Ru(2)(F(x)PhCO(2))(4)(THF)(2)] (F(x)PhCO(2)(-) = o-fluorobenzoate, o-F; m-fluorobenzoate, m-F; p-fluorobenzoate, p-F; 2,6-difluorobenzoate, 2,6-F(2); 3,4-difluorobenzoate, 3,4-F(2); 3,5-difluorobenzoate, 3,5-F(2); 2,3,4-trifluorobenzoate, 2,3,4-F(3); 2,3,6-trifluorobenzoate, 2,3,6-F(3); 2,4,5-trifluorobenzoate, 2,4,5-F(3); 2,4,6-trifluorobenzoate, 2,4,6-F(3); 3,4,5-trifluorobenzoate, 3,4,5-F(3); 2,3,4,5-tetrafluorobenzoate, 2,3,4,5-F(4); 2,3,5,6-tetrafluorobenzoate, 2,3,5,6-F(4); pentafluorobenzoate, F(5)). By adding fluorine atoms on the benzoate ligands, it was possible to tune the redox potential (E(1/2)) for [Ru(2)(II,II)]/[Ru(2)(II,III)](+) over a wide range of potentials from -40 mV to 350 mV (vs. Ag/Ag(+) in THF). 2,3,6-F(3), 2,3,4,5-F(4), 2,3,5,6-F(4) and F(5) were relatively air-stable compounds even though they are [Ru(2)(II,II)] species. The redox potential in THF was dependent on an electronic effect rather than on a structural (steric) effect of the o-F atoms, although more than one substituent in the m- and p-positions shifted E(1/2) to higher potentials in relation to the general Hammett equation. A quasi-Hammett parameter for an o-F atom (σ(o)) was estimated to be ～0.2, and a plot of E(1/2)vs. a sum of Hammett parameters including σ(o) was linear. In addition, the HOMO energy levels, which was calculated based on atomic coordinates of solid-state structures, as well as the redox potential were affected by adding F atoms. Nevertheless, a steric contribution stabilizing their static structures in the solid state was present in addition to the electronic effect. On the basis of the electronic effect, the redox potential of these complexes is correlated to the HOMO energy level, and the electronic effect of F atoms is the main factor controlling the ionization potential of the complexes with ligands free from the rotational constraint, i.e. complexes in solution.     

Chemical synthesis of Helicobacter pylori lipopolysaccharide partial structures and their selective proinflammatory responses

Helicobacter pylori is a common cause of gastroduodenal inflammatory diseases such as chronic gastritis and peptic ulcers and also an important factor in gastric carcinogenesis. Recent reports have demonstrated that bacterial inflammatory processes, such as stimulation with H. pylori lipopolysaccharide (LPS), initiate atherosclerosis. To establish the structures responsible for the inflammatory response of H. pylori LPS, we synthesized various kinds of lipid A structures (i.e., triacylated lipid A and Kdo‐lipid A compounds), with or without the ethanolamine group at the 1‐phosphate moiety, by a new divergent synthetic route. Stereoselective α‐glycosylation of Kdo N‐phenyltrifluoroacetimidate was achieved by use of microfluidic methods. None of the lipid A and Kdo‐lipid A compounds were a strong inducer of IL‐1β, IL‐6, or IL‐8, suggesting that H. pylori LPS is unable to induce acute inflammation. In fact, the lipid A and Kdo‐lipid A compounds showed antagonistic activity against cytokine induction by E. coli LPS, except for the lipid A compound with the ethanolamine group, which showed very weak agonistic activity. On the other hand, these H. pylori LPS partial structures showed potent IL‐18‐ and IL‐12‐inducing activities. IL‐18 has been shown to correlate with chronic inflammation, so H. pylori LPS might be implicated in the chronic inflammatory responses induced by H. pylori. These results also indicated that H. pylori LPS can modulate the immune response: NF‐κB activation through hTLR4/MD‐2 was suppressed, whereas production of IL‐18 and IL‐12 was promoted.     

Psb30 is a photosystem II reaction center subunit and is required for optimal growth in high light in Chlamydomonas reinhardtii

The psb30 (ycf12) gene is conserved in a wide variety of oxygenic-photosynthetic organisms except angiosperms and some marine cyanobacteria. Psb30 protein is found in cyanobacterial photosystem II (PSII) core complexes and is dispensable for PSII structure and function. The most recent three-dimensional structure of cyanobacterial PSII core complex has revealed that Psb30 is located in proximity of PsbJ, PsbK, and PsbZ. However Psb30 has not yet been detected in PSII complexes from eukaryotic photosynthetic organisms. Here we found the expression of the chloroplast psb30 gene in the green alga Chlamydomonas reinhardtii by immunoblotting and Psb30 is exclusively co-purifies with PSII core complex and is significantly reduced in PSII-deficient mutants. Partial disintegration of PSII core complex and subsequent fractionation of the resulting subcomplexes revealed that Psb30 is exclusively associated with PSII reaction center. We have generated chloroplast transformants in which the psb30 gene is disrupted and the resulting ΔPsb30 cells showed decreased oxygen evolution activity by 15%, grew photosynthetically under moderate light, and displayed increased sensitivity to high light relative to wild type. We conclude that Psb30 is a PSII reaction center subunit and is required for optimal PSII function under high light environments.     

Cyclizations producing hydrindanones with two methyl groups at the juncture positions mediated by samarium diiodide and electrolysis

One-electron reductive intramolecular cyclization of enones with ketones or aldehydes mediated by samarium diiodide and electrolysis to afford cis-trimethyl- hydrindanolones. The reactions gave selectivities ranging from 1:1 to 100:0 depending on the conditions.