On theA 0-acceptability of rational approximations to the exponential function with only real poles

We consider rational approximations to the exponential function with real poles, ₁ ^–1 ,..., _m ^–1 , that correspond to implicit Runge-Kutta collocation methods. We show that if _i 1/2,i=1,...,m, the rational approximation isA ₀-acceptable.     

Abiotic Sequence‐Coded Oligomers as Efficient In Vivo Taggants for the Identification of Implanted Materials

Sequence‐defined oligourethanes were tested as in vivo taggants for implant identification. The oligomers were prepared in an orthogonal solid‐phase iterative approach and thus contained a coded monomer sequence that can be unequivocally identified by tandem mass spectrometry (MS/MS). The oligomers were then included in small amounts (1 wt %) in square‐centimeter‐sized crosslinked poly(vinyl alcohol) (PVA) model films, which were intramuscularly and subcutaneously implanted in the abdomen of rats. After one week, one month, or three months of implantation, the PVA films were explanted. The rat tissues exposed to the implants did not exhibit any adverse reactions, which suggested that the taggants are not harmful and probably not leaching out from the films. Furthermore, the explanted films were immersed in methanol, as a solvent for oligourethanes, and the liquid extract was analyzed by mass spectrometry. In all cases, the oligourethane taggant was detected, and its sequence was identified by MS/MS.     

A new 2-alkylhydroquinone glucoside from Phagnalon saxatile (L.) Cass

A new 2-alkylhydroquinone glucoside, 1-O-β-d-glucopyranosyl-1,4-dihydroxy-2-((E) 2-oxo-3-butenyl)benzene (1), in addition to nine known compounds were isolated from the aerial parts of Phagnalon saxatile (L.) Cass. (Asteraceae). Their structures were identified based on spectroscopic methods including 1D and 2D NMR, mass spectrometry (HR-ESI-MS), UV spectral analyses and by comparison with literature data. The cytotoxic activity of three isolated compounds (1–3) was evaluated against fibrosarcoma (HT1080), human lung cancer (A549) and breast cancer (MCF7) cell lines.     

Catalytic Dinitrogen Reduction to Ammonia at a Triamidoamine–Titanium Complex

Catalytic reduction of N₂ to NH₃ by a Ti complex has been achieved, thus now adding an early d‐block metal to the small group of mid‐ and late‐d‐block metals (Mo, Fe, Ru, Os, Co) that catalytically produce NH₃ by N₂ reduction and protonolysis under homogeneous, abiological conditions. Reduction of [Ti^IV(Tren^TMS)X] (X=Cl, 1A ; I, 1B ; Tren^TMS=N(CH₂CH₂NSiMe₃)₃) with KC₈ affords [Ti^III(Tren^TMS)] ( 2 ). Addition of N₂ affords [{(Tren^TMS)Ti^III}₂(μ‐η¹:η¹‐N₂)] ( 3 ); further reduction with KC₈ gives [{(Tren^TMS)Ti^IV}₂(μ‐η¹:η¹:η²:η²‐N₂K₂)] ( 4 ). Addition of benzo‐15‐crown‐5 ether (B15C5) to 4 affords [{(Tren^TMS)Ti^IV}₂(μ‐η¹:η¹‐N₂)][K(B15C5)₂]₂ ( 5 ). Complexes 3 – 5 treated under N₂ with KC₈ and [R₃PH][I], (the weakest H⁺ source yet used in N₂ reduction) produce up to 18 equiv of NH₃ with only trace N₂H₄. When only acid is present, N₂H₄ is the dominant product, suggesting successive protonation produces [{(Tren^TMS)Ti^IV}₂(μ‐η¹:η¹‐N₂H₄)][I]₂, and that extruded N₂H₄ reacts further with [R₃PH][I]/KC₈ to form NH₃.     

Cleavable Binary Dyads: Simplifying Data Extraction and Increasing Storage Density in Digital Polymers

Digital polymers are uniform macromolecules that store monomer‐based binary sequences. Molecularly stored information is usually extracted from the polymer by a tandem mass spectrometry (MS/MS) measurement, in which the coded chains are fragmented to reveal each bit (i.e. basic coded monomer unit) of the sequence. Here, we show that data‐extraction can be greatly simplified by favoring the formation of MS/MS fragments containing two bits instead of one. In order to do so, digital poly(alkoxyamine phosphodiester)s, containing binary dyads in each repeat unit, were prepared by an orthogonal solid‐phase approach involving successive phosphoramidite and radical‐radical coupling steps. Three different sets of monomers were considered to build these polymers. In all cases, four coded building blocks—two hydroxy‐nitroxides and two phosphoramidite monomers—were required to build the dyads. Among the three studied monomer sets, one combination allowed synthesis of uniform sequence‐coded polymers. The resulting polymers led to clear dyad‐containing fragments in MS/MS and could therefore be efficiently decoded. Additionally, an algorithm was created to detect specific dyad fragments, thus enabling automated sequencing.     

Application of capillary electrophoresis in migration studies of food contact materials – part 1: Substituted phenolic additives

A method has been developed to determine 11 phenolic antioxidants in the food simulants distilled water, 3% acetie acid, and 15% ethanol, using; micellar capillary electrophoresis (MCE). All the phenols could he analyzed within 35 min. The analytical recovery from spiked simulants was 80 to 119% except for 2,6-di-tert-butyl-4hydroxytoluenc (BHT) and octyl gallate, which could not be recovered from 3% acetic acid simulant. Calibration graph correlation coefficients for the 11 phenols were 0.982 to 0.999. Limits of detection (LoDs) were from 2.8 to 8.6 mg/L. These LoDs are well below European Union migration limits for these substances. It is concluded therefore that MCE offers a rapid and reliable analysis for the control of migration from plastics intended for food contact which employ these phenols as antioxidants.     

Sheath liquid interface for the coupling of normal-phase liquid chromatography with electrospray mass spectrometry and its application to the analysis of neoflavonoids

A novel interface that allows normal-phase liquid chromatography to be coupled with electrospray ionization (ESI) is reported. A make-up solution of 60 mM ammonium acetate in methanol, infused at a 5 microl min(-1) flow-rate at the tip of the electrospray probe, provides a sheath liquid which is poorly miscible with the chromatographic effluent, but promotes efficient ionization of the targeted analytes. Protonated molecules generated in the ESI source were subjected to tandem mass spectrometric experiments in a triple-quadrupole mass spectrometer. The main fragmentation reactions were characterized for each analyte and specific mass spectral transitions were used to acquire chromatographic data in the multiple reaction monitoring detection mode. Results obtained during optimization of the sheath liquid composition and flow-rate suggest that the electrospray process was mainly under the control of the make-up solution, and that it forms an external charged layer around a neutral chromatographic mobile phase core. This sheath liquid interface was implemented for the analysis of some neoflavonoid compounds and its performance was evaluated. Limits of detection were established for calophillolide, inophyllum B, inophyllum P and inophyllum C at 100, 25, 15 and 100 ng ml(-1), respectively.     

Preparation of cruciferous phytoalexin related metabolites, (−)-dioxibrassinin and (−)-3-cyanomethyl-3-hydroxyoxindole, and determination of their absolute configurations by vibrational circular dichroism (VCD)

Cruciferous phytoalexin related metabolites, (−)-dioxibrassinin (1) and (−)-3-cyanomethyl-3-hydroxyoxindole (2) were prepared from isatin as racemates and were resolved by chiral HPLC. Their absolute configurations were determined by the new chiroptical technique, vibrational circular dichroism (VCD), as well as by the conventional electronic circular dichroism (ECD). It is concluded that the absolute configurations of the naturally occurring (−)-1 and (−)-2 are both S.     

Synthesis amd characterization of [Et4,N]2[Mo(CO)4(SR)2] (R = Ph,Bz): New,potentially chelating bis-thiolate species

The new complexes [Et₄N]₂ [Mo(CO)₄(SR)₂] (R = Ph, Bz) have been prepared by reaction of [Et₄N] [SR] with (norbornadiene)Mo(CO)₄ at low temperature. The IR spectra and electrochemical behavior of these two species are different, perhaps implicating different conformational isomers with respect to the thiolate ligands. These complexes may prove to be valuable reagents for the synthesis of new heterometallic compounds, by virtue of their cis-monodentate thiolate ligands.     

The high pressure mediated intramolecular Diels-Alder reaction of furan dienes: a synthetic approach towards daphnanes.

Furan $\text{2}$ undergoes intramolecular Diels-Alder reaction when subjected to high (14kbar) pressures to give a mixture of $\text{endo}$ and $\text{exo}$ adducts in which the $\text{exo}$ adduct is formed as the kinetic product, at variance with the expected course of events.