Total synthesis of (+)-ent-cyclizidine: absolute configurational confirmation of antibiotic M146791

The first total synthesis of the enantiomer of the indolizidine alkaloid, cyclizidine, was accomplished from readily available d-serine as the starting chiron. The relevant key reactions involve the stereocontrolled construction of the indolizidine ring system with the required functionality and further elaboration to install the cyclopropyl dienyl side chain. With this total synthesis, the absolute configuration of the natural product based on a redetermination of its X-ray structure has been confirmed.     

Electron spin resonance in the photo-excited triplet state of free base porphin in a single crystal of n-octane

E.S.R. experiments have been performed on the lowest triplet state of free base porphin (H₂P) in a n-octane single crystal at 1·3 K. The results demonstrate that the large majority of guest molecules occur in two orientations. While the molecules in these two orientations are coplanar, they have their N-H H-N axes at right angles. The fine structure results show that the two molecular orientations have zero-field splittings that differ by a few per cent in magnitude. Further, the 65 cm^-1 doublet separation which appears in the fluorescence spectrum of H₂P is related to the occurrence of these two orientations.

Resolved hyperfine structure is obtained for the two in-plane canonical orientations of the magnetic field and also when the field bisects the angle between these two directions. From an analysis of the fine structure and hyperfine structure results it is established that the zero-field splitting pattern is described by the parameters (average over the two orientations) the x axis is taken along the N-H H-N direction and z is the out-of-plane axis. From a computer simulation of the hyperfine structure it further follows that this structure is dominated by a high spin density at the methine carbons; with the coupling constants of the C-H fragment proposed by Hirota et al. the methine density is found to be ρ_m = 0·163.

In order to interpret the experimental results the zero-field splitting parameters and spin density distribution have been calculated for the lower triplet states of H₂P on the basis of a set of PPP-SCF-MO-CI calculations. From these calculations it follows that the lowest triplet state must correspond to the excitation e_g ←a _2u in Gouterman's four-orbital model. In terms of the D _2h symmetry of the H₂P molecule the assignment is ³ B _2u (b _3g ←b _1u ). For this assignment the calculations yield .     

Quantitative analysis of triphenylboron in environmental water samples by liquid chromatography/mass spectrometry.

Liquid chromatography/mass spectrometry (LC/MS) has been applied to the analysis of triphenylboron, which has been produced as a substitute for organotin compounds, in water. Although commercial triphenylboron compounds are produced as pyridinyl complexes, the chemical form in water is supposed to be mainly triphenylboron after liberating pyridine. The triphenylborons were extracted from water with an Empore C18 extraction disk under acidic condition, and the extracts were introduced directly into a liquid chromatograph-mass spectrometer equipped with a negative ion electrospray ionization interface. Identification of the compounds was performed with specific ions produced from the triphenylboron, and a quantitative analysis was carried out using the peak areas. The average recoveries from distilled water, seawater and river water at 0.30 ng/ml were 92.3, 100 and 85.3%, respectively. A detection limit of 0.023 ng/ml for triphenylboron was achieved.     

Isotopically selective CVD of silicon by IRMPD of Si2F6

The IRMPD of Si₂F₆ by a CO₂ TEA laser was applied to isotopically selective CVD of silicon. A white film, probably consisting of polymers of SiF₂, was deposited on a metal foil during the irradiation of natural Si₂F₆ with the laser radiation at 951.19 cm^–1 and about 1.5 J cm^–2. Upon heating, the film became dark brown, evolving SiF₄. The³⁰Si content was found to be as high as about 20%.     

Kinetic studies on the formation of ternary complexes in the reaction of diaquonitrilotriacetatonickelate(II) with amino acids in aqueous solution

Summary Kinetics of formation of ternary complexes in the reaction of Ni(NTA)(H₂O) ₂ ^– with several amino acids, LH^± (glycine, -alanine, -alanine, L-valine and L-phenylalanine) have been studied by a pH indicator method using stopped-flow spectrophotometry. The results conform to 1/k_obs = 1/k + [H⁺]/ kKT_L where K is the equilibrium constant for formation of Ni(NTA)(–L)(H₂O)^2–, and k is the specific rate constant for the subsequent rate-determining ring-closure step leading to Ni(NTA)(=L)^2–. For the different amino acids studied, the k values decrease in the sequence: glycine > -alanine > L-phenylalanine > L-valine > -alanine. These k values areca. 1000 times lower than the values for complexation of Ni(NTA)(H₂O) ₂ ^– with NH₃ and imidazole and the spread in k values is much less than the pK_a values of the amino acids. The relative rates are enthalpy controlled and the S values are highly negative in conformity with ring closure as the rate determining step.     

Ascent of open-circuit voltage on diamond-like carbon photovoltaic cell by infrared heating-assisted pulsed-laser deposition

Phosphorus-doped diamond-like carbon (DLC) films were deposited on quartz and p-type silicon (p-Si) substrates by pulsed-laser deposition. Open-circuit voltage (V _oc) and short-circuit density (I _sc/cm²) from a heating process converted from one type of electrode to another and the two types of electrode pattern are shown by the V–I characteristics. The first heating process was by a ceramic heater, and the other was by an infrared heater. We adopted two electrode patterns, from a bipectinate electrode and a plot pattern electrode, to measure electric photovoltaic characteristics. We were able to upgrade V _oc and I _sc/cm² to 35∼45 mV, and 0.24 μA/cm², respectively, under infrared heating. V _oc by the plot pattern electrode was over 2 V under infrared heating and ceramic heating did not match this on deposition by the PLD method.