Integration of impurities with large-angle grain boundaries in d-transition metals

The approximation of the liquid model of grain boundaries is used to calculate the bonding energy F of carbon and oxygen interstitial impurities with largeangle grain boundaries in d-transition metals and impurities of d-transition metals in group VIA elements: chromium, molybdenum, and tungsten. It is shown that in the case of interstitial impurities as well as substitutional impurities in d-transition metals the bonding energy is determined by the characteristics of the d-band occupation.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 4, pp. 70–75, April, 1979.     

BF3-catalyzed addition of thiols to (+)-camphene

BF₃-catalyzed addition of some thiols to (+)-camphene was examined. Reactions with aromatic thiols and hetaryl thiols result in terpene sulfides of camphene or bornane structure in accordance with the Markovnikov’s rule, whereas with remain thiols the reaction proceeds against the Markovnikov’s rules preserving the original structure of the molecule.     

Concurrent combined verification: reducing false positives in automated NMR structure verification through the evaluation of multiple challenge control structures

Automated structure verification using ¹H NMR data or a combination of ¹H and heteronuclear single‐quantum correlation (HSQC) data is gaining more interest as a routine application for qualitative evaluation of large compound libraries produced by synthetic chemistry. The goal of this automated software method is to identify a manageable subset of compounds and data that require human review. In practice, the automated method will flag structure and data combinations that exhibit some inconsistency (i.e. strange chemical shifts, conflicts in multiplicity, or overestimated and underestimated integration values) and validate those that appear consistent. One drawback of this approach is that no automated system can guarantee that all passing structures are indeed correct structures. The major reason for this is that approaches using only ¹H or even ¹H and HSQC spectra often do not provide sufficient information to properly distinguish between similar structures. Therefore, current implementations of automated structure verification systems allow, in principle, false positive results. Presented in this work is a method that greatly reduces the probability of an automated validation system passing incorrect structures (i.e. false positives). This novel method was applied to automatically validate 127 non‐proprietary compounds from several commercial sources. Presented also is the impact of this approach on false positive and false negative results. Copyright © 2012 John Wiley & Sons, Ltd.     

Growth and optical properties of filamentary GaN nanocrystals grown on a hybrid SiC/Si(111) substrate by molecular beam epitaxy

The potential to grow filamentary GaN nanocrystals by molecular beam epitaxy on a silicon substrate with a nanosized buffer layer of silicon carbide has been demonstrated. Morphological and optical properties of the obtained system have been studied. It has been shown that the intensity of the photoluminescence spectrum peak of such structures is higher than that of the best filamentary GaN nanocrystals without the buffer silicon carbide layer by a factor of more than two.     

Translational diffusion coefficient of a nitroxide radical in an ionic liquid, as determined via EPR spectroscopy, cyclic voltammetry, and chronoammetry

Values of the translational diffusion coefficient of a spin probe (2,2,6,6-tetramethyl-4-oxypiperidine-1-oxyl) are determined via cyclic voltammetry, chronoammetry, and EPR in ionic liquid (1-butyl-3methylimidazolium tetrafluoroborate) at 295 K. They are found to be (8 ± 3) × 10^?12, (9 ± 3) × 10^?12, and (11 ± 4) × 10^?12 m²/s, respectively.     

Synthesis and some properties of anionic chloranilate complexes of iron(iii). Crystal and molecular structure of rubidium and cesium chloranilatoferrates

New anionic chloranilate complexes of iron(iii) Cs[Fe(C₆O₄Cl₂)₂(H₂O)₂]·4H₂O (1), Rb[Fe(C₆O₄Cl₂)₂(H₂O)₂]·4H₂O (2), Rb₂[Fe(C₆O₄Cl₂)₂(H₂O)₂]₂·5H₂O (3), Cs₃Fe(C₆O₄Cl₂)₃ (4), (Bu₄N)Fe(C₆O₄Cl₂)₂ (5), (Bu₄N)₄Fe₂(C₆O₄Cl₂)₅ (6), and (R₄N)₃Fe(C₆O₄Cl₂)₃ (R = Pr (7), Bu (8), C₅H₁₁ (9)) were synthesized in an aqueous medium. The Mössbauer spectra of the synthesized chloranilatoferrates are characteristic of the high-spin state of Fe^III in an octahedral oxygen coordination. The crystal and molecular structures of compounds 1–3 were determined by X-ray diffraction. The complex anions [Fe(C₆O₄Cl₂)₂(H₂O)₂]^2? involved in these compounds are composed of two chelate chloranilate ions and two water molecules trans-(1,2) or cis-coordinated (3) to the iron atom. Since tetraalkylammonium tris(chloranilato)ferrates 7–9 and binuclear complex 6 are soluble in many organic solvents, they are promising precursors for the synthesis of metal-organic coordination polymers. Tetrabutylammonium bis(chloranilato)ferrate (Bu₄N)Fe(C₆O₄Cl₂)₂ (5) is the first example of the preparation of an anionic chloranilate complex of iron(iii) with a plausible chain structure in an aqueous medium.     

Investigations and Modeling of the Effect of Magnetic Nanoparticles on MR Image Contrast

The investigations of nuclear magnetic resonance (NMR) relaxation of protons in aqueous solution and 2% agar–agar gel in the presence of magnetic nanoparticles were performed. To identify the effect of magnetic nanoparticles on the contrast of magnetic resonance images, the dependences of the MR signal intensity on the parameters of the two pulse radio-frequency (RF) sequences (spin-echo, gradient-echo) most commonly used in MRI for different values of the magnetic nanoparticle (MNP) concentration were simulated and analyzed. Recommendations for choosing the optimal values of pulse RF sequence parameters for MR imaging (MRI) in the presence of MNPs are formulated. MRI studies of phantom samples with 2% agar–agar gel containing MNPs have been performed for choosing the fast pulse RF sequence which shows the greatest contrast effect on MR images. A program for modeling magnetic resonance tomograms and determination of optimal values of pulse RF sequence parameters to achieve the best contrast of magnetic resonance images is developed. This program allows to reduce the time of MRI studies, to assess the possibility of using MNPs for contrast of MR images and to simulate the MR image in the presence of magnetic nanoparticles at the planning stage of procedures in MR-guided theranostics.