Continuous flow membrane-less air cathode microbial fuel cell with spunbonded olefin diffusion layer

The power production performance of a membrane-less air-cathode microbial fuel cell was evaluated for 53 days. Anode and cathode electrodes and the micro-fiber cloth separator were configured by sandwiching the separator between two electrodes. In addition, the air-facing side of the cathode was covered with a spunbonded olefin sheet instead of polytetrafluoroethylene (PTFE) coating to control oxygen diffusion and water loss. The configuration resulted in a low resistance of about 4Ω and a maximum power density of 750 mW/m2. However, as a result of a gradual decrease in the cathode potential, maximum power density decreased to 280 mW/m2. The declining power output was attributed to loss of platinum catalyst (8.26%) and biomass growth (38.44%) on the cathode. Coulombic efficiencies over 55% and no water leakage showed that the spunbonded olefin sheet covering the air-facing side of the cathode can be a cost-effective alternative to PTFE coating.     

Synthesis of novel glycophanes derived from glucuronic acid by ring closing alkene and alkyne metathesis

Cyclophanes and their analogues are of interest in bioactive molecule development and in biomimetic, supramolecular and materials chemistry. Novel hybrids of sugars and cyclophanes (glycophanes) have been prepared via the coupling of alkenyl and alkynyl glucopyranosiduronic acids with phenylene-1,4-diamine and xylene-1,4-diamine and subsequent intramolecular metathesis. Structural studies showed that the geometric arrangements of the sugar groups in the macrocycles containing secondary amides differ from those in macrocycles that contain tertiary amides. This is due to the amides adopting different configurational preferences. The compounds had low solubility in water, precluding an investigation of their recognition phenomena in this medium.     

Assignment of pre-edge features in the Ru K-edge X-ray absorption spectra of organometallic ruthenium complexes

The nature of the lowest energy bound-state transition in the Ru K-edge X-ray absorption spectra for a series of Grubbs-type ruthenium complexes was investigated. The pre-edge feature was unambiguously assigned as resulting from formally electric dipole forbidden Ru 4d ← 1s transitions. The intensities of these transitions are extremely sensitive to the ligand environment and the symmetry of the metal centre. In centrosymmetric complexes the pre-edge is very weak since it is limited by the weak electric quadrupole intensity mechanism. By contrast, upon breaking centrosymmetry, Ru 5p-4d mixing allows for introduction of electric dipole allowed character resulting in a dramatic increase in the pre-edge intensity. The information content of this approach is explored as it relates to complexes of importance in olefin metathesis and its relevance as a tool for the study of reactive intermediates.     

Synthesis, solution behaviour and molecular structures of 16-electron closo-2-(Ph3P)-1-N,2-[μ-(η-CH2CH=Ch2)]-1-N-(σ-CH2CH=CH2)-2,1- RhCB10H10, the first η-olefinic monocarbon metallacarborane

The first η²-olefinic monocarbon metallacarbone closo-2-(Ph₃P)-1-N,2-[μ-(η²-CH₂CH=Ch₂)]-1-N-(σ-CH₂CH=CH₂)-2,1- RhCB₁₀H₁₀ has been prepared by the reaction of the dimeric anion {[Ph₃PRhB₁₀H₁₀CNH₂]₂-μ-H}⁻[PPN]⁺ with allyl bromide and characterized by a combination of spectroscopic methods and a single-crystal X-ray diffraction study. The variable temperature ¹H and ¹³C NMR studies revealed the fluxional behavior of the η²-olefinic complex in CD₂Cl₂ solution which is associated with the allyl side-chain exchange process.     

Purification and characterization of OleA from Xanthomonas campestris and demonstration of a non-decarboxylative Claisen condensation reaction

OleA catalyzes the condensation of fatty acyl groups in the first step of bacterial long-chain olefin biosynthesis, but the mechanism of the condensation reaction is controversial. In this study, OleA from Xanthomonas campestris was expressed in Escherichia coli and purified to homogeneity. The purified protein was shown to be active with fatty acyl-CoA substrates that ranged from C(8) to C(16) in length. With limiting myristoyl-CoA (C(14)), 1 mol of the free coenzyme A was released/mol of myristoyl-CoA consumed. Using [(14)C]myristoyl-CoA, the other products were identified as myristic acid, 2-myristoylmyristic acid, and 14-heptacosanone. 2-Myristoylmyristic acid was indicated to be the physiologically relevant product of OleA in several ways. First, 2-myristoylmyristic acid was the major condensed product in short incubations, but over time, it decreased with the concomitant increase of 14-heptacosanone. Second, synthetic 2-myristoylmyristic acid showed similar decarboxylation kinetics in the absence of OleA. Third, 2-myristoylmyristic acid was shown to be reactive with purified OleC and OleD to generate the olefin 14-heptacosene, a product seen in previous in vivo studies. The decarboxylation product, 14-heptacosanone, did not react with OleC and OleD to produce any demonstrable product. Substantial hydrolysis of fatty acyl-CoA substrates to the corresponding fatty acids was observed, but it is currently unclear if this occurs in vivo. In total, these data are consistent with OleA catalyzing a non-decarboxylative Claisen condensation reaction in the first step of the olefin biosynthetic pathway previously found to be present in at least 70 different bacterial strains.     

Expeditious synthesis of enantiopure symmetrical macroheterocycles by ring-closing metathesis of ether and tether-linked 1,2-O-isopropylidenefuranosides

Bis-olefinic symmetrical carbohydrate derivatives were prepared by joining two 1,2-O-isopropylidenefuranose units either through an ether linkage or by a tether of variable size. The ring-closing metathesis (RCM) of these substrates using Grubbs' first-generation catalyst led to the synthesis of enantiopure symmetrical macroheterocycles containing nine- to twenty-five-membered rings fused to the 1,2-O-isopropylidenefuranose ring.     

Synthesis and characterization of the inclusion compound of a ferrocenyldiimine dioxomolybdenum complex with heptakis-2,3,6-tri-O-methyl-β-cyclodextrin

A dioxomolybdenum(VI) complex bearing the diimine ligand N,N′-bis(ferrocenylmethylene)ethylenediamine (FcNN) has been prepared in good yield by the reaction of FcNN with MoO₂Cl₂(THF)₂. One isomeric form was identified by ¹H NMR (including NOE experiments), corresponding to the cis,cis geometry with respect to the CN bonds of the free ligand. The polynuclear complex was immobilized in permethylated β-cyclodextrin (TRIMEB) by addition of the guest to a solution of TRIMEB in a mixture of dichloromethane and nitromethane. Removal of the solvent led to the isolation of an inclusion compound with a 2:1 host:guest stoichiometry. For comparison, an inclusion compound containing just the ligand FcNN and TRIMEB was prepared using a similar method. The products were characterized in the solid state by powder X-ray diffraction (XRD), thermogravimetric analysis (TGA), FT-IR and ¹³C CP MAS NMR spectroscopy. UV-Vis measurements were also carried out in solution. Both the complex MoO₂Cl₂(FcNN) and its inclusion compound with TRIMEB catalyze with high selectivity the liquid phase epoxidation of cyclooctene using tert-butyl hydroperoxide (TBHP) as the oxidant. In general, the catalytic behavior of the Mo^VI complex was not markedly affected by encapsulation in TRIMEB, although observed activities were slightly lower.     

Partial synthesis of ganglioside and lysoganglioside lipoforms as internal standards for MS quantification

Within recent years, ganglioside patterns have been increasingly analyzed by MS. However, internal standards for calibration are only available for gangliosides GM1, GM2, and GM3. For this reason, we prepared homologous internal standards bearing nonnatural fatty acids of the major mammalian brain gangliosides GM1, GD1a, GD1b, GT1b, and GQ1b, and of the tumor-associated gangliosides GM2 and GD2. The fatty acid moieties were incorporated after selective chemical or enzymatic deacylation of bovine brain gangliosides. For modification of the sphingoid bases, we developed a new synthetic method based on olefin cross metathesis. This method was used for the preparation of a lyso-GM1 and a lyso-GM2 standard. The total yield of this method was 8.7% for the synthesis of d17:1-lyso-GM1 from d20:1/18:0-GM1 in four steps. The title compounds are currently used as calibration substances for MS quantification and are also suitable for functional studies.     

On the identity and reactivity patterns of the “second oxidant” of the T252A mutant of cytochrome P450cam in the oxidation of 5-methylenenylcamphor

Density functional calculations show that in the absence of Compound I, the primary oxidant species of P450, the precursor species, Compound 0 (FeOOH), can effect double bond activation of 5-methylenylcamphor (1). The mechanism is initiated by homolytic cleavage of the O–O bond and formation of an OH radical bound to the Compound II species by hydrogen bonding interactions. Subsequently, the so-formed OH radical can either activate the double bond of 1 or attack the meso position of the heme en route to heme degradation. The calculations show that double bond activation is preferred over attack on the heme. Past the double bond activation, the intermediate can either lead to epoxidation or to a glycol formation. The glycol formation is predicted to be preferred, although in the P450_cam pocket the competition may be closer. Therefore, in the absence of Compound I, Compound 0 will be capable of epoxidizing double bonds. Previous studies [E. Derat, D. Kumar, H. Hirao, S. Shaik, J. Am. Chem. Soc. 128 (2006) 473–484] showed that in the case of a substrate that can undergo only C–H activation, the bound OH prefers heme degradation over hydrogen abstraction. Since the epoxidation barrier for Compound I is much smaller than that of Compound 0 (12.8 vs. 18.9 kcal/mol), when Compound I is present in the cycle, Compound 0 will be silent. As such, our mechanism explains lucidly why T252A P450_cam can epoxidize olefins like 5-methylenylcamphor but is ineffective in camphor hydroxylation [S. Jin, T.M. Makris, T. A. Bryson, S.G. Sligar, J.H. Dawson, J. Am. Chem. Soc. 125 (2003) 3406–3407]. Our calculations show that the glycol formation is a marker reaction of Compound 0 with 5-methylenylcamphor. If this product can be found in T252A P450_cam or in similar mutants of other P450 isozymes, this will constitute a more definitive proof for the action of Cpd 0 in P450 enzymes.     

Synthesis, characterization and olefin metathesis studies of a family of ruthenium phosphonium alkylidene complexes

The synthesis of four ruthenium phosphonium alkylidene complexes [(H₂IMes)Cl₂RuCH(PCy₃)]⁺[A]⁻ (1, A = B(C₆F₅)₄; 2, A = BF₄; 3, A = OTf; 4, A = BPh₄), differing only in the anion is described. The X-ray structures of 1, 3 and 4 show them to be isostructural in the cation, with no interaction between the Ru centers and the anion. Ring closing metathesis of a substrate to a six-membered methylcyclohexene at 0 °C in CD₂Cl₂ using 1 mol% catalyst, shows that catalysts 1-4 behave very similarly, and exhibit superior activity in comparison to Grubbs second generation and fast-initiating catalysts.