Layer-by-layer deposition of open-pore mesoporous TiO<Subscript>2</Subscript>-Nafion® film electrodes

The formation of variable thickness TiO₂ nanoparticle-Nafion® composite films with open pores is demonstrated via a layer-by-layer deposition process. Films of about 6 nm diameter TiO₂ nanoparticles grow in the presence of Nafion® by “clustering” of nanoparticles into bigger aggregates, and the resulting hierarchical structure thickens with about 25 nm per deposition cycle. Film growth is characterized by electron microscopy, atomic force microscopy, and quartz crystal microbalance techniques. Simultaneous small-angle X-ray scattering and wide-angle X-ray scattering measurements for films before and after calcination demonstrate the effect of Nafion® binder causing aggregation. Electrochemical methods are employed to characterize the electrical conductivity and diffusivity of charge through the TiO₂-Nafion® composite films. Characteristic electrochemical responses are observed for cationic redox systems (diheptylviologen^2+/+, \({\text{Ru}}{\left( {{\text{NH}}_{3} } \right)}^{{3 + /2 + }}_{6} \), and ferrocenylmethyl-trimethylammonium^2+/+) immobilized into the TiO₂-Nafion® nanocomposite material. Charge conduction is dependent on the type of redox system and is proposed to occur either via direct conduction through the TiO₂ backbone (at sufficiently negative potentials) or via redox-center-based diffusion/electron hopping (at more positive potentials).     

Sparsely substituted chlorins as core constructs in chlorophyll analogue chemistry. I. Synthesis

Five routes to stable chlorins bearing 0 or 1 meso substituents have been investigated, among which reaction of a 9-bromo-1-formyldipyrromethane and 2,3,4,5-tetrahydro-1,3,3-trimethyldipyrrin proved most effective. Application of this route afforded metallochlorins [Cu(II), Zn(II), and Pd(II)] including the chlorin lacking any β-pyrrole and meso substituents.     

Sparsely substituted chlorins as core constructs in chlorophyll analogue chemistry. II. Derivatization

Stable chlorins bearing few or no substituents have been subjected to a variety of reactions including demetalation, magnesium insertion, oxochlorin formation, and bromination followed by Suzuki coupling. The kinetics of deuteration also have been determined for two oxochlorins and a series of chlorins bearing 0, 1, 2, or 3 meso-aryl substituents.     

Investigation of pyrrolizidine alkaloids and their N-oxides in commercial comfrey-containing products and botanical materials by liquid chromatography electrospray ionization mass spectrometry

Pyrrolizidine alkaloids (PAs) and their N-oxides are found in several plant families throughout the world. PAs are potentially toxic to the liver and/or lungs in humans and may cause acute liver failure, cirrhosis, pneumonitis, or pulmonary hypertension. PAs are also carcinogenic to animals, and they have been linked to the development of hepatocellular and skin squamous cell carcinomas as well as liver angiosarcomas. According to experimental studies, the quantity of PAs in some herbal teas and dietary supplements is sufficient to be carcinogenic in exposed individuals. A method for the extraction and identification of PAs and their N-oxides in botanical materials and commercial comfrey-containing products has been developed using liquid chromatography electrospray ionization mass spectrometry. Following optimization of the extraction procedure and the chromatographic conditions, the method was applied to the analysis of 10 herbal remedies. All of the products that were labeled to contain comfrey were found to contain measurable quantities of PAs.     

Identification of marker proteins for Bacillus anthracis using MALDI-TOF MS and ion trap MS/MS after direct extraction or electrophoretic separation

Direct extraction of bacterial vegetative cells or spores followed by matrix-assisted laser desorption ionization/time of flight mass spectrometry (MALDI TOF MS) has become popular for bacterial identification, since it is simple to perform and mass spectra are readily interpreted. However, only high-abundance proteins that are of low mass and ionize readily are observed. In the case of B. anthracis spores, small acid-soluble spore proteins (SASPs) have been the most widely studied. Additional information can be obtained using tandem mass spectrometry (MS-MS) to confirm the identity of proteins by sequencing. This is most readily accomplished using ion trap (IT) MS-MS. However, enzymatic digestion of these proteins is needed to generate peptides that are within the mass range of the ion trap. The use of sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE), or other forms of electrophoresis, allows one to focus on specific proteins of interest (e.g. the high mass exosporium glycoproteins BcIA and BcIB) that provide additional species- and strain-specific discrimination.     

Ionic Liquid Ordering at an Oxide Surface

The interaction of the ionic liquid [C₄C₁Im][BF₄] with anatase TiO₂, a model photoanode material, has been studied using a combination of synchrotron radiation photoelectron spectroscopy and near‐edge X‐ray absorption fine structure spectroscopy. The system is of interest as a model for fundamental electrolyte–electrode and dye‐sensitized solar cells. The initial interaction involves degradation of the [BF₄]^? anion, resulting in incorporation of F into O vacancies in the anatase surface. At low coverages, [C₄C₁Im][BF₄] is found to order at the anatase(101) surface via electrostatic attraction, with the imidazolium ring oriented 32±4° from the anatase TiO₂ surface. As the coverage of ionic liquid increases, the influence of the oxide surface on the topmost layers is reduced and the ordering is lost.     

Density functional analysis of group 10 organometallic diphosphinito complexes for catalytic formation of C‐P bonds

New group 10 metalloorganic complexes are proposed as the basis of new catalysts for the formation of carbon‐phosphorous bonds. Density functional theory (DFT) is applied, using multiple DFT functionals, to model molecular geometry as well as electron density distribution in the highest occupied molecular orbitals (HOMOs) expected to carry out a reductive catalytic cycle. DFT/M06 analysis predicts a robust planar geometry, regardless of alteration of major components. Precursors for rapid catalyst generation should begin with an electron‐withdrawing monodentate ligand. Palladium and platinum catalysts have lower chemical hardness, but the electron distribution in the HOMO of the nickel‐based catalyst is preferred for reductive catalytic mechanisms. Both electron density and chemical hardness, however, are affected by the choice of metal ion and the composition of the monodentate ligand bound to it. Group 10 metalloorganic complexes are modeled as precursors for generating new catalysts for a minimally wasteful method of forming bonds commonly found in biochemically active compounds. Suitable precursors have an accessible metal center, as well as significant the HOMO/LUMO involvement at the metal center. All complexes studied offer similar geometries, but precursor transformation into catalyst depends on the electron‐withdrawing ligand being exchanged. Catalyst turn over number is predicted to depend primarily on the central metal. © 2016 Wiley Periodicals, Inc.     

Triazole–containing zinc(II)dipicolylamine-functionalised peptides as highly selective pyrophosphate sensors in physiological media

A small family of linear bis[zinc(II)dipicolylamine] (bis[Zn(II)-DPA])-functionalised peptidic anion receptors has been prepared where the Zn(II)-DPA binding sites have been installed via either a reductive amination reaction or a copper(I)-catalysed azide-alkyne cycloaddition reaction. The latter reaction connects the Zn(II)-DPA binding site and the peptide backbone through a 1,2,3-triazole linkage. Subsequent anion binding studies using indicator displacement assays were conducted to elucidate the effect of the triazole linker on the anion-binding properties of these novel receptors and it was found that the triazole-containing receptors exhibited stronger affinity and slightly improved selectivity for pyrophosphate over adenosine triphosphate and adenosine diphosphate compared to the analogous receptors which did not bear the triazole linker.     

A Bioinspired Synthesis of (±)‐Rubrobramide, (±)‐Flavipucine,and (±)‐Isoflavipucine

A biomimetic synthesis of naturally occurring lactams rubrobramide, flavipucine, and isoflavipucine is described. The key step is a regioselective Darzens reaction between isobutyl glyoxal and an α‐bromo‐β‐ketoamide. The construction of the core tricyclic ring system of rubrobramide was achieved by a cascade reaction in a single step from an α,β‐epoxy‐γ‐lactam. Furthermore, the absolute configuration of naturally occurring (+)‐rubrobramide was determined by vibrational circular dichroism. (±)‐Flavipucine and (±)‐isoflavipucine were synthesized from an epoxyimide, which was prepared by reaction of isobutyl glyoxal with a protected α‐bromo‐β‐ketoamide. Deprotection of the epoxyimide and formation of the pyridone ring gave (±)‐flavipucine, which was converted into (±)‐isoflavipucine by thermal isomerization.