CIAT with simultaneous epimerization at two stereocenters. Synthesis of substituted beta-methyl-alpha-homophenylalanines

Diastereoselective aza-Michael additions of phenylethylamine to 3-aroylbutenoic acids are reported. During these processes, efficient control over two new stereogenic centers on the Michael acceptor has been possible via crystallization-induced asymmetric transformation (CIAT). As an application, a convenient two-step synthesis of anti-beta-methylhomophenylalanines is also described.     

Autocorrelation infrared analysis of mineralogical samples: the influence of user controllable experimental parameters

Autocorrelation infrared (ACIR) analysis is based upon the application of the autocorrelation function corr(alpha,omega') = integral(-infinity)(infinity) alpha(omega + omega') alpha(omega) d omega to standard Fourier transform infrared (FTIR) transmission spectra. We present a rigorous examination of the effect of experimental parameters such as dilution ratio, spectral resolution, grinding time and pressing conditions upon the ACIR analysis of haematite. Results were found to vary by less than 4.5% irrespective of sample preparation, instrumental and data collection parameters. For a series of perovskite samples, the relationship between the measured effective linewidth and material composition appears to be reproducible, even though the absolute magnitudes of delta corr values do not. Our results further indicate that the ACIR technique is indeed valid for comparative analysis of synthetic sample sequences that vary slightly in composition or structural state, provided that primary spectra are all recorded by the same instrument.     

Investigation,by single photon ionisation (SPI)–time-of-flight mass spectrometry (TOFMS), of the effect of different cigarette-lighting devices on the chemical composition of the first cigarette puff

Soft single-photon ionisation (SPI)–time-of-flight mass spectrometry (TOFMS) has been used to investigate the effect of different cigarette-lighting devices on the chemical composition of the mainstream smoke from the first cigarette puff. Lighting devices examined were a Borgwaldt electric lighter, a propane/butane gas lighter, a match, a candle, and the burning zone of another cigarette. To eliminate the effects of the different masses of tobacco burnt by use of the different lighting methods a normalisation procedure was performed which enabled investigation of changes in the chemical patterns of the resulting smoke. When another cigarette was used as the lighting device, elevated levels of ammonia and other nitrogen-containing substances were observed. These are high in the sidestream smoke of the cigarette used for lighting and would be drawn into the mainstream smoke of the cigarette being lit. In contrast, smoke from the cigarette lit by the electric lighter contained slightly higher normalised amounts of isoprene. Lighting the cigarette by use of a candle resulted in larger amounts of substances, e.g. benzene, which most probably originated from thermal decomposition of wax. The composition of the first puff of smoke obtained by use of the three lighting methods with open flames (gas lighter, match, and candle) was usually similar whereas the composition of the smoke produced by use of the electric lighter and the cigarette as the lighter were more unique. The chemical patterns generated by the different lighting devices could, however, be separated by principal-component analyses. Two additional test series were also studied. In the first the cigarette was lit with an electric lighter, then extinguished, the ash was cut off, and the cigarette was re-lit. In the second the cigarette was heated in an oven to 80 °C for 5 min before being lit. These treatments did not result in changes in the chemical composition compared with cigarettes lit in the ordinary way. Figure Time-of-flight mass spectrometry (TOFMS) has been used to investigate the effect of different cigarette-lighting devices on the chemical composition of the mainstream smoke from the first cigarette puff     

Oxidative Reactions of the MoIV Dialkyl Complex [{(3‐CF3C6H4NCH2CH2)2NMe}Mo(CH2SiMe3)2]

The structure of [(CF₃N₂NMe)Mo(CH₂SiMe₃)₂] (in which (CF₃N₂NMe)^2? is [(3‐CF₃C₆H₄NCH₂CH₂)₂NMe]^2?) is approximately trigonal bipyramidal with one axial and one equatorial alkyl ligand. Heating of solutions of [(CF₃N₂NMe)Mo(CH₂SiMe₃)₂] in [D₆]benzene in the presence of five equivalents of 2‐butyne led to diamagnetic [(CF₃N₂NMe)Mo(CHSiMe₃)(η²‐MeC?CMe)], whose structure is approximately square pyramidal with the alkyne occupying the axial site. Addition of one equivalent of cyclohexene sulfide to [(CF₃N₂NMe)Mo(CH₂SiMe₃)₂] at room temperature produced the diamagnetic, dimeric molybdenum(IV) sulfido complex, [{(CF₃N₂NMe)MoS}₂]. This complex is composed of two approximately trigonal bipyramidal centers, each containing one axial and one equatorial sulfur atom. Oxidation of [(CF₃N₂NMe)Mo(CH₂SiMe₃)₂] with hexachloroethane resulted in formation of tetramethylsilane, HCl, and the sparingly soluble, red alkylidyne complex, [{(CF₃N₂NMe)Mo(CSiMe₃)Cl}₂]. This complex forms a dimer through bridging chlorides. The oxidation reactions of [(CF₃N₂NMe)Mo(CH₂SiMe₃)₂] with 2‐butyne, cyclohexene sulfide, or C₂Cl₆ are all proposed to proceed by α‐hydrogen abstraction in the Mo^VI species to yield (initially) the Mo?CHSiMe₃ species and tetramethylsilane.     

Irreversible and Reversible Deactivation of Bilirubin Oxidase by Urate

Oxygen is electroreduced to water on a carbon cathode coated with wired bilirubin oxidase in a pH 7.4 0.15 M NaCl phosphate buffer solution at 37 °C at much lesser polarization than it is on a pure platinum cathode in 0.5 M H₂SO₄. While the wired bilirubin oxidase cathode operates for over a week in the aerated or oxygenated buffer solution, it is degraded rapidly when in serum. We reported earlier that in the presence of O₂ an intermediate product of the electrooxidation of urate, which is a normal serum component, irreversibly damages the wired bilirubin oxidase and also reported that the electrocatalyst is irreversibly damaged, in the absence of urate, when it is brought, by disconnecting the electrode, to the O₂/H₂O half cell potential at pH 7.4. Here we report that a) dissolved bilirubin oxidase is irreversibly and rapidly damaged by urate in the presence of O₂; and b) that the immobilized wired bilirubin oxidase electrocatalyst is not only irreversibly deactivated by urate in the presence of O₂ in a few hours, but is initially reversibly deactivated, in 1 min or less, by the urate in the presence of O₂.     

Electrochemical Detection of MS2 Phage Using a Bead‐based Immunoassay and a NanoIDA

A microbead based sandwich immunoassay for MS2 bacteriophage was developed using an interdigitated array (IDA) electrode with nanoscale dimensions (220 nm electrode width, 620 nm gap). The IDA was fabricated using an electron beam lithographic lift‐off technique. After an antibody‐assisted capture of MS2 using paramagnetic microbeads, a β‐galactosidase labeled secondary antibody was used to convert p‐aminophenyl‐β‐D ‐galactopyranoside (PAPG) into the redox active p‐aminophenol (PAP). Amperometric detection of PAP with IDA electrodes at +300 and ?200 mV vs. a Ag/AgCl reference electrode was used to measure the result, detecting MS2 concentrations as low as 10 ng/mL.     

Electrochemical gating of single osmium molecules tethered to Au surfaces

The electrochemical study of electron transport between Au electrodes and the redox molecule Os[(bpy)₂(PyCH₂ NH₂CO-]ClO₄ tethered to molecular linkers of different length (1.3 to 2.9 nm) to Au surfaces has shown an exponential decay of the rate constant k _ET ⁰ with a slope β = 0.53 consistent with through bond tunneling to the redox center. Electrochemical gating of single osmium molecules in an asymmetric tunneling nano-gap between a Au(111) substrate electrode modified with the redox molecules and a Pt-Ir tip of a scanning tunneling microscope was achieved by independent control of the reference electrode potential in the electrolyte, E _ref ? E _s, and the tip-substrate bias potential, E _bias. Enhanced tunneling current at the osmium complex redox potential was observed as compared to the off resonance set point tunneling current with a linear dependence of the overpotential at maximum current vs. the E _bias. This corresponds to a sequential two-step electron transfer with partial vibration relaxation from the substrate Au(111) to the redox molecule in the nano-gap and from this redox state to the Pt-Ir tip according to the model of Kuznetsov and Ulstrup (J Phys Chem A 104: 11531, 2000). Comparison of short and long linkers of the osmium complex has shown the same two-step ET (electron transfer) behavior due to the long time scale in the complete reduction-oxidation cycle in the electrochemical tunneling spectroscopy (EC-STS) experiment as compared to the time constants for electron transfer for all linker distances, k _ET ⁰.     

Continuum states from time-dependent density functional theory

Linear response time-dependent density functional theory is used to study low-lying electronic continuum states of targets that can bind an extra electron. Exact formulas to extract scattering amplitudes from the susceptibility are derived in one dimension. A single-pole approximation for scattering phase shifts in three dimensions is shown to be more accurate than static exchange for singlet electron-He(+) scattering.