A theoretical investigation of alpha-carbon kinetic isotope effects and their relationship to the transition-state structure of S(N)2 reactions

[reaction: see text] The transition structures and alpha-carbon 12C/13C kinetic isotope effects for 22 S(N)2 reactions between methyl chloride and a wide variety of nucleophiles have been calculated using the B1LYP/aug-cc-pVDZ level of theory. Anionic, neutral, and radical anion nucleophiles were used to give a wide range of S(N)2 transition states so the relationship between the magnitude of the alpha-carbon kinetic isotope effect and transition-state structure could be determined. The results suggest that the alpha-carbon 12C/13C kinetic isotope effects for S(N)2 reactions will be large (near the experimental maximum) and that the curve relating the magnitude of the KIE to the percent transfer of the alpha-carbon from the nucleophile to the leaving group in the transition state has a broad maximum. This means very similar KIEs will be found for early, symmetric, and late transition states and that one cannot use the magnitude of these KIEs to estimate transition-state structure.     

Polarography of disodium pentacyanonitrosylferrate(II): Part 2. Determination at Therapeutic Levels in Serum,Plasma, and Whole Blood

Disodium pentacyanonitrosylferrat(II) (sodium nitroprusside) is determined at therapeutic (ng ml^?1) levels in plasma, serum and blood with conventional and high-performance differential pulse polarography (d.p.p. and h.p.d.p.p.) at a dropping mercury electrode or a static mercury drop electrode. Serum or plasma (3 ml) is treated with perchloric acid containing 1 mg ml^?1 potassium hexacyanoferrate(II), centrifuged for 10 min and subjected to polarography. For spiked serum, calibration graphs are linear over the range 30–1000 ng ml^?1 sodium nitroprusside, regardless of the polarographic technique; the estimated detection limit is 15 ng ml^?1 (5 × 10^?8 M). Calculated therapeutic levels range from 100 to 1000 ng ml^?1. Similar results were obtained for spiked plasma. A similar procedure is suitable for whole blood and was used to study the in-vitro degradation of sodium nitroprusside (200 ng ml^?1) on incubation at 37°C. The in-vitro loss is rapid (t_{$\text{1}\text{2}$} ≈ 6 min) but meaningful in-vivo levels can be obtained when the blood is collected in a 0.9% sodium chloride solution at 0°C. Thiocyanate, the main metabolite of nitroprusside, and thiosulphate, which is a potential antidote for cyanide, do not interfere.     

Haloacrylic acids XI. Photochemical reactions of aliphatic aldehydes with methyl trifluoroacrylate

Photochemically initiated reactions of aliphatic aldehydes, namely acetaldehyde, propionaldehyde and butyraldehyde, with methyl trifluoroacrylate afforded γ-ketoesters of the type R-CO-CF₂CHF-COOCH₃ in the liquid phase. In the gas phase reaction further products were formed by addition of the aldehyde fragments to the olefinic bond of the methyl trifluoroacrylate.     

Glycosides of marine invertebrates. XXVI. Holothurin A from the Pacific Ocean holothurianHolothvria squamifera. Isolation of the native aglycone

The known triterpene tetraoside holothurin A has been isolated from the Pacific Ocean holothurianHolothuria squamifera. By using two independent methods — enzymatic cleavage and two-stage Smith degradation — 22,25-epoxyholost-9(11)-ene-3,12,17-triol, C₃₀H₄₆O₆, which is the native aglycone of holothurin A, was obtained. The structure of the native aglycone has been established on the basis of the results of IR, mass, and PMR spectroscopy.Pacific Ocean Institute of Bioorganic Chemistry, Far Eastern Scientific Center, Academy of Sciences of the USSR, Vladivostok. Translated from Khimiya Prirodnykh Soedinenii, No. 4, pp. 448–451, July–August, 1984.     

Gas-Chromatographic Determination of Alkyl Acetates in Aqueous Solutions with Chromatomembrane Gas Extraction

Methods were developed for the gas-chromatographic determination of alkyl acetates in aqueous solutions in the concentration range of 0.01–100 mg/L with the chromatomembrane gas extraction of analytes from a flow of the test liquid. The analytical potentialities of the direct-flow and counterflow techniques of chromatomembrane gas extraction were compared. It was demonstrated that the interfering effect of petroleum products on the results of analysis can be eliminated by using an additional chromatomembrane cell.     

Low temperature specific heats of very dilute alloys of Ce in Al

Measurements of the specific heat of two alloys of Ce (0.00275 and 0.0121 at % Ce) in Al have been made in the region 0.3<T<3.8 K. Within the limits of detection (<1 ppm), the alloys contained no metallic impurities other than Ce and their homogeneity was checked by neutron activation analysis. For the alloys in their normal electronic states, the change/c was found to be 6±3 and 3.5±1.5mJ/at% K². The behavior of the alloys in their superconducting states (e.g.: the shift ofT _c with the concentration of Ce; the correlation betweenT _C/T_C0 andC/C ₀) indicates the existence of short-lived local moments associated with the Ce impurities.     

Small-angle x-ray scattering and inhomogeneities of the electron density in polycrystalline and epitaxial PbS films

The dependence of the characteristics of the macro- and microporosity on the condensation temperature has been studied for condensation temperatures from 30 to 450°C by small-angle x-ray scattering, hydrostatic weighing, and low-temperature desorption of argon in polycrystalline and single-crystal lead sulfide films with thickness 3–5 m condensed for normal incidence of the molecular beam on polycrystalline and single-crystal substrates. The porosity of the polycrystalline films is an order of magnitude greater than in the epitaxial films. In polycrystalline condensates, the pores are elongated and are oriented along the normal to the film. The pores in the epitaxial films have a platelet form with faces along the {100} planes and are parallel to the direction of growth of the condensate. At high substrate temperature (about 400°C), more nearly equiaxial pores, with additional {110} faces are formed, as a result of the plastic deformation of the condensate by thermal macrostresses.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 8, pp. 46–52, August, 1979.     

Observations on the hydrogen peroxide-iodic acid-manganese(II)-organic species oscillating system

The effect of acidity and manganese (II) concentration on the title reaction has been examined for acetone and malonic acid as the organic species. Cerium (III) has been shown to replace manganese (II) without loss of the oscillatory behavior. Some mechanistic details are given.

---

Был исследован эффект кислотности и концентрации марганца (II) в заглавной реакции на примере ацетона и малоновой кислоты, как органических компонентов. Было обнаружено, что замена марганца (II) на церий (III) не приводит к исчезновению осциллирующего поведения. Приводятся некоторые детали механистической модели.

     

Zur Bestimmung der Konzentration von Leerstellen und Versetzungen plastisch deformierter Metalle mittels Positronenannihilation

The use of positron annihilation to estimate the concentration of crystal defects is described and a model for the estimation of defect concentrations is given in case that more than one kind of defects are present. This model is based on the recovery of one kind of defects to another in steps. From angular correlation measurements of cold-worked and recovered Pd have been concluded that it is possible to distinguish between vacancies and dislocations in the experiment. Using a value of μ = 2 · 10¹⁵ s⁻¹ for the trapping rate per unit defect concentration, the data for 7.5% thickness reduction yields values in the expected order of magnitude for dislocation density and vacancy concentration. The study of the change of the angular correlation shape by plastic deformation shows that the narrowing of the angular correlation is caused by the reduction of both, indensity and width of the gaussian part which originates in annihilation with core electrons.     

Prediction and realisation of high mobility and degenerate p-type conductivity in CaCuP thin films

Phosphides are interesting candidates for hole transport materials and p-type transparent conducting applications, capable of achieving greater valence band dispersion than their oxide counterparts due to the higher lying energy and increased size of the P 3p orbital. After computational identification of the indirect-gap semiconductor CaCuP as a promising candidate, we now report reactive sputter deposition of phase-pure p-type CaCuP thin films. Their intrinsic hole concentration and hole mobility exceed 1 × 10²⁰ cm⁻³ and 35 cm² V⁻¹ s⁻¹ at room temperature, respectively. Transport calculations indicate potential for even higher mobilities. Copper vacancies are identified as the main source of conductivity, displaying markedly different behaviour compared to typical p-type transparent conductors, leading to improved electronic properties. The optical transparency of CaCuP films is lower than expected from first principles calculations of phonon-mediated indirect transitions. This discrepancy could be partly attributed to crystalline imperfections within the films, increasing the strength of indirect transitions. We determine the transparent conductor figure of merit of CaCuP films as a function of composition, revealing links between stoichiometry, crystalline quality, and opto-electronic properties. These findings provide a promising initial assessment of the viability of CaCuP as a p-type transparent contact.

We synthesize air-stable, p-type CaCuP thin films with high hole concentration and high hole mobility as potential p-type transparent conductors. We study their optoelectronic properties in detail by advanced experimental and computational methods.