Comparison of reversed-phase liquid chromatography-mass spectrometry with electrospray and atmospheric pressure chemical ionization for analysis of dietary tocopherols

ESI and APCI ionization techniques in both negative and positive ion modes were evaluated for simultaneous LC-MS analysis of the four tocopherol homologues (alpha, beta, gamma and delta). The ESI and APCI ionization of tocopherols in positive ion mode was not efficient and proceeded via two competitive mechanisms, with the formation of protonated pseudo-molecular ions and molecular ions, which adversely influenced the repeatability of MS signal. Ionization in negative ion mode in both ESI and APCI was more efficient as it only produced target deprotonated pseudo-molecular ions. The APCI in negative ion mode showed larger linearity range, lower detection limits and was less sensitive to the differences in chemical structure of analytes and nature of applied solvents than negative ion ESI. Negative ion APCI was, therefore, chosen for the development of LC-MS method for simultaneous determination of the four tocopherols in foods. A baseline separation of the tocopherols was achieved on novel pentafluorophenyl silica-based column Fluophase PFP. The use of methanol-water (95:5, v/v) as a mobile phase was preferable to the use of acetonitrile-water due to considerable gain in MS signal. The limits of quantifications were 9 ng/mL for alpha-tocopherol, 8 ng/mL for beta- and gamma- and 7.5 ng/mL for delta-tocopherol when 2 microL was injected. This method was successfully applied to determination of tocopherols in sunflower oil and milk.     

Chiral, bridged bis(imidazolin-2-ylidene) complexes of palladium

Varieties of chiral, bridged bisimidazolium salts as well as the synthesis of palladium complexes of general formula with the corresponding chelating N-heterocyclic carbene ligands is reported. This is the first systematic study of chiral bis(imidazolin-2-ylidene)palladium(II) complexes bearing chiral groups on the endocyclic nitrogens. Structural proof of such a chiral palladium(II) complex is presented by way of an X-ray diffraction study of complex 3a.     

Conversion of Ni(II)-allylporphyrins to alpha,beta-unsaturated formylporphyrins via a nickel-promoted reaction

A new route to alpha,beta-unsaturated formylporphyrins begins with the synthesis of allyl-substituted porphyrins via the Suzuki cross-coupling reaction of bromoporphyrins and allylboronic acid pinacol ester in 50-95% yield. Treatment of allyl-substituted porphyrins with nickel acetate in N,N-dimethylformamide (DMF) then affords mono- and diacroleinylporphyrins in up to 70% yield.     

Behavior of Highly Diluted Electrolytes in Strong Electric Fields—Prevention of Alumina Deposition on Grading Electrodes in HVDC Transmission Modules by CO2‐induced pH‐Control

Alumina deposition on platinum grading electrodes in high voltage direct current (HVDC) transmission modules is an unsolved problem that has been around for more than three decades. This is due to the unavoidable corrosion of aluminum heat sinks that causes severe damage to electrical power plants and losses in the range of a million Euro range per day in power outage. Simple experiments in a representative HV test setup showed that aluminates at concentrations even below 10^?8 mol L^?1 can deposit on anodes through neutralization by protons produced in de‐ionized water (κ≤0.15 μS cm^?1) at 20–35 kV (8 mA) per electrode. In this otherwise electrolyte‐poor aqueous environment, the depositions are formed three orders of magnitude below the critical precipitation concentration at pH 7! In the presence of an inert electrolyte such as TMAT (tetramethylammonium‐p‐toluenesulfonate), at a concentration level just above that of the total dissolved aluminum, no deposition was observed. Deposition can be also prevented by doping with CO₂ gas at a concentration level that is magnitudes lower than that of the dissolved aluminum. From an overview of aqueous aluminum chemistry, the mystery of the alumina deposition process and its inhibition by CO₂ is experimentally resolved and fully explained by field accumulation and repulsion models in synergism with acid–base equilibria. The extraordinary size of the alumina depositions is accounted for in terms of proton tunneling through “hydrated” alumina, which is supported by quantum chemical calculations. As a consequence, pulse‐purging with pure CO₂ gas is presented as a technical solution to prevent the deposition of alumina.     

On-site detection of Phytophthora spp.—single-stranded target DNA as the limiting factor to improve on-chip hybridization

We report on a lab-on-a-chip approach for on-site detection of Phytophthora species that allows visual signal readout. The results demonstrate the significance of single-stranded DNA (ssDNA) generation in terms of improving the intensity of the hybridization signal and to improve the reliability of the method. Conventional PCR with subsequent heat denaturation, sodium hydroxide-based denaturation, lambda exonuclease digestion and two asymmetric PCR methods were investigated for the species P. fragariae, P. kernoviae, and P. ramorum. The positioning of the capture probe within the amplified yeast GTP-binding protein (YPT1) target DNA was also of interest because it significantly influences the intensity of the signal. Statistical tests were used to validate the impact of the ssDNA generation methods and the capture-target probe position. The single-stranded target DNA generated by Linear-After-The-Exponential PCR (LATE-PCR) was found to produce signal intensities comparable to post-PCR exonuclease treatment. The LATE-PCR is the best method for the on-site detection of Phytophthora because the enzymatic digestion after PCR is more laborious and time-consuming. Figure

?     

Polymer Cages as Universal Tools for the Precise Bottom‐Up Synthesis of Metal Nanoparticles

A template synthesis allows the preparation of monodisperse nanoparticles with high reproducibility and independent from self‐assembly requirements. Tailor‐made polymer cages were used for the preparation of nanoparticles, which were made of cross‐linked macromolecules with pendant thiol groups. Gold nanoparticles (AuNPs) were prepared in the polymer cages in situ, by using different amounts of cages versus gold. The polymer cages exhibited a certain capacity, below which the AuNPs could be grown with excellent control over the size and shape. Control experiments with a linear diblock copolymer showed a continuous increase in the AuNP size as the gold feed increased. This completely different behavior regarding the AuNP size evolution was attributed to the flexibility of the polymer chain depending on cross‐linking. Moreover, the polymer cages were suitable for the encapsulation of AgNPs, PdNPs, and PtNPs by the in situ method.     

Total Syntheses of Linear Polythiazole/Oxazole Plantazolicin A and Its Biosynthetic Precursor Plantazolicin B

Plantazolicin A, a linear decacyclic natural product, exhibits desirable selective activity against the causative agent of anthrax toxicity. The total synthesis of plantazolicin A and its biosynthetic precursor plantazolicin B was successfully achieved by an efficient, unified, and highly convergent route featuring dicyclizations to form 2,4‐concatenated oxazoles and the mild synthesis of thiazoles from natural amino acids. This report represents the first synthesis of plantazolicin B and includes the first complete characterization data for both natural products.     

Structural,Biochemical, and Computational Studies Reveal the Mechanism of Selective Aldehyde Dehydrogenase 1A1 Inhibition by Cytotoxic Duocarmycin Analogues

Analogues of the natural product duocarmycin bearing an indole moiety were shown to bind aldehyde dehydrogenase 1A1 (ALDH1A1) in addition to DNA, while derivatives without the indole solely addressed the ALDH1A1 protein. The molecular mechanism of selective ALDH1A1 inhibition by duocarmycin analogues was unraveled through cocrystallization, mutational studies, and molecular dynamics simulations. The structure of the complex shows the compound embedded in a hydrophobic pocket, where it is stabilized by several crucial π‐stacking and van der Waals interactions. This binding mode positions the cyclopropyl electrophile for nucleophilic attack by the noncatalytic residue Cys302, thereby resulting in covalent attachment, steric occlusion of the active site, and inhibition of catalysis. The selectivity of duocarmycin analogues for ALDH1A1 is unique, since only minor alterations in the sequence of closely related protein isoforms restrict compound accessibility.