Syntheses and structures of magnesium pyridine thiolates--model compounds for magnesium binding in photosystem I

Novel magnesium pyridine-2-thiolates were prepared by using alkane elimination chemistry. The resulting complexes display a metal coordination environment composed of sulfur/nitrogen bonding from the intramolecularly stabilized mercaptopyridine ligand, in addition to coordination by the oxygen centers from two THF donors. The compounds are well-suited model compounds for the magnesium centers in Photosystem I, in which magnesium, situated in the central chlorophyll ligand, is bound to sulfur from a nearby methionine residue. All compounds were characterized by (1)H, (13)C NMR, and IR spectroscopy, in addition to Xray crystallography.     

Glycosylidene Carbenes. Part 6. Synthesis of alkyl and fluoroalkyl glycosides

The syntheses of glycosides from the diazirine 1 and a range of alcohols under thermal and/or photolytic conditions are described. Yields and diastereoselectivities depend upon the pK_HA values of the alcohols, the solvent, and the reaction temperature. The glycosidation of weakly acidic alcohols (MeOH, EtOH, i-PrOH, and t-BuOH, 1 equiv. each) in CH₂Cl₂ at room temperature leads to the glycosides 2–5 in yields between 60 and 34% (Scheme 1 and Table 1). At ?70 to ?60°, yields are markedly higher. In CH₂Cl₂, diastereoselectivities are very low. In THF, at ?70 to ?60°, however, glycosidation of i-PrOH leads to α-D -/β-D - 4 in a ratio of 8:92. More strongly acidic alcohols, such as CF₃CH₂OH, (CF₃)₂ CHOH, and (CF₃)₂C(Me)OH, and the highly fluorinated long-chain alcohols CF₃(CF₂)₅(CH₂)₂OH ( 11 ) and CHF₂(CF₂)₉CH₂OH ( 13 ) react (CH₂Cl₂, r.t.) in yields between 73 and 85% and lead mainly to the β-D -glucosides β-D - 6 to β-D - 8 , β-D - 12 , and β-D - 14 (d.e. 14–68%). Yields and diastereoselectivities are markedly improved, when toluene, dioxane, 1,2-dimetoxyethane, or THF are used, as examined for the glycosidation of (CF₃)₂C(Me)OH, yielding (1,2-dimethoxyethane, 25°) 80% of α-D -/ β-D - 8 in a ratio of 2:98 (d.e. 96%; Table 4). In EtCN, (CF₃)₂C(Me)OH yields up to 55% of the imidate 10 . Glycosidation of di-O-isopropylideneglucose 15 leads to 16 (CH₂Cl₂, r.t.; 65%, α-D / β-D = 33:67). That glycosidation occurs by initial protonation of the intermediate glycosylidene carbene is evidenced, for strongly acidic alcohols, by the formation of 10 , derived from the attack of (CF₃)₂MeCO^? on an intermediate nitrilium ion (Scheme 4), and for weakly acidic alcohols, by the formation of α-D - 9 and β-D - 9 , derived by attack of i-PrO^? on intermediate tetrahydrofuranylium ions. A working hypothesis is presented (Scheme 3). The diastereoselectivities are rationalized on the basis of a protonation in the σ plane of the intermediate carbene, the stabilization of the thereby generated ion pair by interaction with the BnO? C(2) group, with the solvent, and/or with the alcohol, and the final nucleophilic attack by RO^? in the π plane of the (solvated) oxonium ion.     

Highly Reproducible Flexible Ion-selective Electrodes for the Detection of Sodium and Potassium in Artificial Sweat

It is well known that potentiometric sensors provide a versatile, cost-effective, and efficient platform for wearable applications. Unfortunately, mass production and commercialization of such devices is often constrained by the requirement of a calibration step, which is due to the poor sensor-to-sensor reproducibility and the need of conditioning the electrodes in the analyte before use. Herein, we fabricated calibration-free flexible sensors including ion-selective electrode and reference electrode by integrating single-walled carbon nanotubes (SWCNTs) with poly(3-octylthiophene) (POT) and applying on polyethylene terephthalate (PET) substrate. The developed sodium and potassium ion-selective electrodes (ISEs) display excellent repeatability, selectivity, stability as well as high sensor-to-sensor reproducibility, with a standard deviation of as low as 1.0 mV in artificial sweat microliter samples volume.     

Probe electrode study of cathodically polarized PtIr-YSZ interfaces

Journal of Solid State Electrochemistry - Local cathodic polarizations of yttria-stabilized zirconia were carried out with a PtIr probe as the working electrode in a controlled atmosphere high...     

Bonding Properties of a Novel Inorganometallic Complex, Ru(SnPh(3))(2)(CO)(2)(iPr-DAB) (iPr-DAB = N,N'-Diisopropyl-1,4-diaza-1,3-butadiene), and its Stable Radical-Anion, Studied by UV-Vis, IR, and EPR Spectroscopy, (Spectro-) Electrochemistry, and Density Functional Calculations

Ru(SnPh(3))(2)(CO)(2)(iPr-DAB) was synthesized and characterized by UV-vis, IR, (1)H NMR, (13)C NMR, (119)Sn NMR, and mass (FAB(+)) spectroscopies and by single-crystal X-ray diffraction, which proved the presence of a nearly linear Sn-Ru-Sn unit. Crystals of Ru(SnPh(3))(2)(CO)(2)(iPr-DAB).3.5C(6)H(6) form in the triclinic space group P&onemacr; in a unit cell of dimensions a = 11.662(6) ?, b = 13.902(3) ?, c = 19.643(2) ?, alpha = 71.24(2) degrees, beta = 86.91(4) degrees, gamma = 77.89(3) degrees, and V = 2946(3) ?(3). One-electron reduction of Ru(SnPh(3))(2)(CO)(2)(iPr-DAB) produces the stable radical-anion [Ru(SnPh(3))(2)(CO)(2)(iPr-DAB)](*-) that was characterized by IR, and UV-vis spectroelectrochemistry. Its EPR spectrum shows a signal at g = 1.9960 with well resolved Sn, Ru, and iPr-DAB (H, N) hyperfine couplings. DFT-MO calculations on the model compound Ru(SnH(3))(2)(CO)(2)(H-DAB) reveal that the HOMO is mainly of sigma(Sn-Ru-Sn) character mixed strongly with the lowest pi orbital of the H-DAB ligand. The LUMO (SOMO in the reduced complex) should be viewed as predominantly pi(H-DAB) with an admixture of the sigma(Sn-Ru-Sn) orbital. Accordingly, the lowest-energy absorption band of the neutral species will mainly belong to the sigma(Sn-Ru-Sn)-->pi(iPr-DAB) charge transfer transition. The intrinsic strength of the Ru-Sn bond and the delocalized character of the three-center four-electron Sn-Ru-Sn sigma-bond account for the inherent stability of the radical anion.     

Calcium,Strontium, and Barium Acetylides—New Evidence for Bending in the Structures of Heavy Alkaline Earth Metal Derivatives

An unprecedented ligand bending mode is displayed by the acetylide ligands in the first structurally characterized σ‐bound organometallic strontium and barium complexes [M([18]crown‐6)(CCSiPh₃)₂] (M=Sr, Ba). Furthermore, the observed decrease of the angle at the sp‐hybridized C atom on descending Group 2 (see structures depicted) affords new information that will lead to a better understanding of the bonding in alkaline earth metal compounds.     

Removal of Water-Soluble Extractives Improves the Enzymatic Digestibility of Steam-Pretreated Softwood Barks

Softwood bark contains a large amounts of extractives—i.e., soluble lipophilic (such as resin acids) and hydrophilic components (phenolic compounds, stilbenes). The effects of the partial removal of water-soluble extractives before acid-catalyzed steam pretreatment on enzymatic digestibility were assessed for two softwood barks—Norway spruce and Scots pine. A simple hot water extraction step removed more than half of the water-soluble extractives from the barks, which improved the enzymatic digestibility of both steam-pretreated materials. This effect was more pronounced for the spruce than the pine bark, as evidenced by the 30 and 11% glucose yield improvement, respectively, in the enzymatic digestibility. Furthermore, analysis of the chemical composition showed that the acid-insoluble lignin content of the pretreated materials decreased when water-soluble extractives were removed prior to steam pretreatment. This can be explained by a decreased formation of water-insoluble “pseudo-lignin” from water-soluble bark phenolics during the acid-catalyzed pretreatment, which otherwise results in distorted lignin analysis and may also contribute to the impaired enzymatic digestibility of the barks. Thus, this study advocates the removal of extractives as the first step in the processing of bark or bark-rich materials in a sugar platform biorefinery.     

Synthesis of (±)-Desmarestene and (±)-Viridiene,the Two Sperm Releasing and Attracting Pheromones from the Brown Algae Desmarestia aculeata and Desmarestia viridis

Desmarestene 1 6-(1Z,3-butadienyl)-1,4-cycloheptadiene and viridiene 3 cis-3-(1Z, 3-butadienyl)-4-vinylcyclopentene are chemical messengers for male gametes of the brown algae Desmarestia aculeate and Desmarestia viridis. Total syntheses of 1 , 3 and their stereoisomers 1a , 3a - c are reported. Gas-chromatographic comparison of synthetic 1 and 3 with the corresponding natural products has established their structural identity.