Pattern recognition of the multiplet structure of NMR spectra

A new method of analysis of high-resolution NMR spectra was suggested, and an algorithm and the PAREMUS program package for assignment of patterns of the spectral components based on pattern recognition theory were developed. High effectiveness of the method has been exemplified by determination of the values and relative signs of the interring¹H−¹H and¹³C−¹H spin-spin coupling constants in 1,2,3-trichloronaphthalene. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya. No. 3, pp. 444–451, March, 1997.     

Low-molecular-mass metabolites of fungi. III. Stachybotrolide fromStachybotrys alternans

The new nitrogen-free compound stachybotrolide has been detected among the products of the vital activity ofStachybotrys alternans. The structure of stachybotrolide has been determined on the basis of IR, mass, and¹H and¹³C NMR spectra. To interpret the latter we have made use of DEPT, 2M NMR¹H−¹H chemical shift correlation (¹H−¹H COSY or HMQC) and 2M NMR correlations of¹H−¹³C long-range interactions (HMBC). Institute of the Chemistry of Plant Substances, Academy of Sciences of the Republic of Uzbekistan, Tashkent, fax (371) 120 64 75. Translated from Khimiya Prirodnykh Soedinenii, No. 5, pp. 679–683, September–October, 1998.     

Triterpene glycosides ofAstragalus and their genins LVII. The structure of cyclopycnanthogenin

A new cycloartane methysteroid cyclopycnanthogenin, has been found in stems of the plantAstragalus pycnanthus Boriss. (Leguminosae). Its structure has been determined on the basis of IR, mass, and¹H and¹³C NMR spectra with the involvement of DEPT experiments and 2M¹H−¹H and¹H−¹³C chemical shift correlations [¹H−¹H COSY and¹H−¹³C (HMQC)] and also 2M NMR correlations of long-range¹H−¹³C interactions (HMBC). Cyclopycnanthogenin is 6α, 16β, 25-trihydroxy-20R, 24S-epoxycycloartane-3-one. Institute of the Chemistry of Plant Substances, Academy of Sciences of the Republic of Uzbekistan, Tashkent, fax (3712) 40 64 75. Translated from Khimiya Prirodnykh Soedinenii, No. 4, pp. 515–518, July–August, 1998.     

Rhaposerine and rhaserolide, new sesquiterpene lactones fromRhaponticum serratuloides

Two new crystalline guaianolides,viz., rhaposerine and rhaserolide, were isolated from an ethanolic extract of the above-ground part of the plantRhaponticum serratuloides by column chromatography along with sesquiterpene lactones,viz., centaurepensin and acroptilin, which have been found in other plants. The chemical structures of the title lactones were established by¹H and¹³C NMR spectroscopy and 2D¹H−¹H (COSY) and¹³C−¹H (COSY and COLOC) NMR spectroscopy. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 2010–2014, October, 1999.     

Dependence of geminal1H−1H and31P−1H spin-spin coupling constants on the specific intramolecular C−H...X interaction

Participation of the proton in a specific intramolecular C−H...X (X=N, 0) interaction leads to an increase in its geminal¹H−¹H and¹H−³¹P spin-spin coupling constants (SSCC). According toab initio calculations carried out in the 6–31G^** basis set, the observed effect is mainly due to the change in the diamagnetic spin-orbital contribution to SSCC. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 306–309, February, 1997.     

Ajanolide A, a new germacranolide fromAjania fruticulosa

A new germacranolide, ajanolide A, was isolated from aerial parts ofAjania fruticulosa by means of extraction with CHCl₃ and adsorption chromatography. This compound was identified as (1(10)E,3S,4Z,6R,7S,11R)-3-acetoxygermacra-1(10),4-dien-12,6-olide ((1S,7S,10R,13R)-7-acetoxy-4,8,13-trimethyl-11-oxabicyclo[8.3.0]trideca-4(E),8(Z)-dien-12-one) by X-ray diffraction analysis. 2D¹H−¹H (COSY) and¹³C−¹H (COSY) NMR spectroscopy was used for assigning the¹H and¹³C NMR signals in the spectra of ajanolide A. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 167–170, January, 1998.     

Theoretical study on the complexation of bambus[6]uril with the chloride, bromide, and iodide anions

Abstract  

By using quantum mechanical DFT calculations, the most probable structures of the bambus[6]uril·Cl⁻, bambus[6]uril·Br⁻, and bambus[6]uril·I⁻ anionic complex species were derived. In these three complexes, each of the considered univalent halide anions, included in the center of the macrocyclic cavity, is bound by 12 weak C–H⋯X⁻ (X⁻ = Cl⁻, Br⁻, I⁻) hydrogen bonds between methine hydrogen atoms on the convex face of the glycoluril units and the respective anion. The lengths of the C–H⋯X⁻ hydrogen bonds increase in the order Cl⁻ < Br⁻ < I⁻.     

Simultaneous determination of60Co,131I and137Cs in model radioactive waste water by reverse radiometric flow injection analysis with the aid of a multichannel analyzer

Reverse radiometric flow injection analysis was used for the simultaneous determination of⁶⁰Co,¹³¹I and¹³⁷Cs in model radioactive waste water. A NaI (Tl) scintillation detector coupled to a Canberra MCA was used for measuring the activity of¹³⁷Cs at 662 keV,⁶⁰Co at 1173 keV and 1332 keV, and¹³¹I at 364 keV.     

Temperature dependence of pulse-height distribution in liquid scintillator

The differential pulse-height distributions for²⁴¹Am,^131mXe,¹⁴C and³H are investigated as a function of temperature. The spectra are shifted toward higher pulseheights with decreasing temperature. During the measurement, the temperature of photomultipliers of liquid scintillation system are kept at 8.8 °C. The counting efficiency of¹⁴C and³H increases with decreasing temperature. The mechanism involved in this effect is discussed.     

Liquid scintillation radioassay for multiple radionuclide mixtures by the most probable value theory

Multiple radionuclide mixtures which have similar scintillation pulse height distributions can be accurately radioassayed by the most probable value theory. This liquid scintillation technique is based on the construction of more observation equations than the number of nuclides to be analyzed. The technique has been applied to³H–¹⁴C–¹²⁵I and³H–¹⁴C–⁵¹Cr mixture samples, and found to be very practicable with the aid of computerized data processing for mixture samples having a wide range (ca. 10 times) of activity ratios.     

13C and19F NMR study of α,β-difluorostyryl derivatives of transition metal carbonylates. A method of signal assignment based on the carbon—fluorine spin-spin coupling constants

The¹³C and¹⁹F NMR spectra ofZ- andE-isomers of β-X-substituted α,β-difluorostyrenes (X=F, Cl, CpFe(CO)₂, Re(CO)₅, Re₂(CO)₉Na) were studied. Direct and long-range (across 1–5 bonds) spin-spin coupling constants and the (¹³C−¹²C) isotope shifts in the¹⁹F NMR spectra were determined. The study of the¹³C satellites in the¹⁹F NMR spectra of substituted difluorostyrenes permitted assignment of the¹³C NMR signals of the vinylic carbon atoms. Similarly, the signals in¹⁹F NMR spectra were assigned based on coupling constants of fluorine withipso-carbon. These assignments were found to be in good agreement with the data available from the literature (X=F, Cl). The developed approach was applied to the elucidation of the structure ofZ−PhCF=CClFe(CO)₂Cp. Translated fromIzvestiya Akademii Nauk, Seriya Khimicheskaya. No. 8, pp. 1575–1579, August, 1998.     

Application of bremsstrahlung activation analysis for the determination of carbon and nitrogen in sodium

Carbon and nitrogen are determined by means of the photonuclear reactions:¹²C(γ n)¹¹C and¹⁴N(γ, n)¹³N. This article presents a simultaneous chemical separation method for the isolation of¹¹C and¹³N. It is based mainly on combustion of the sample, after irradiation and etching, in a mixture of oxidising acid fused salts (B₂O₃ and Pb₃ O₄) containing a dispersing agent (NaCl and KCl) and the respective carriers. Each analysis takes about 40 min altogether. Minimum carbon and nitrogen contents of a few 10⁻² μg·g⁻¹ can be measured. The influence of the main competitive nuclear reactions on neighbouring elements, including the sodium itself, is examined.     

Intermolecular interactions in 2,4-dinitrophenylhydrazine hydrochloride hydrate: X-ray structural and quantum mechanical study

2,4-dinitrophenylhydrazine hydrochloride hydrate (I) was determined by X-ray crystallography, and the intermolecular interaction energies were calculated in terms of Natural Bond Orbital analysis. The asymmetric unit of (I) consists of a dinitrophenylhydrazinium cation, a chloride anion and a water molecule. The interatomic distances and angles in (I) show no unusual values. In the structure there are intermolecular N—H⊎⊎⊎O, N—H⊎⊎⊎Cl, O—H⊎⊎⊎Cl, C—H⊎⊎⊎O hydrogen bonds with bonding energy ranging form 16.03 to 0.76 kcal mol⁻¹. These hydrogen bonds create the following N1 motifs: 6D, S(5), S(6), C(6), C(9). N₁D motifs become infinite at the third level and are 2C₃²(6), C₃²(7).      

Qualitative and quantitative measurements of radioiodines

Some methods for measurements of radioiodines are discussed. Three isotopes of iodine are presented in detail;¹²⁵I,¹²⁹I and¹³¹I. Limited discussions of¹²³I and¹²⁶I are also given. Measurements of these isotopes are examined for both the NaI(TI) and liquid scintillation systems. The properties of the decay schemes are utilized to explain the mode of measurements of the isotopes in these two types of detectors. Methods of standardization of the radioiodines are discussed. Special emphasis is given to the direct standardization of¹²⁵I as compared to so called “Mock¹²⁵I” standards.     

Activation of CH4 and H2 molecules by cationic zirconium(IV) complexes: a DFT study

Reactions of methane and hydrogen molecules with [(η⁵-C₅H₅)₂ZrCH₃]⁺ and (η⁵-C₅H₅)₂ZrH₃]⁺ cations were studied using nonempirical density functional theory (DFT). In all cases, the reactions begin with the formation of agostic complexes between the substrate molecules and1 or2. Transformation of these intermediates into transition states when moving along the reaction coordinate requires only slight changes in the geometry. The dihydrogen molecule reacts with1 exothermically (−8.8 kcal mol⁻¹) and barrierlessly to form2 and CH₄. Exchange of σ-bonded ligands in the1−CH₄ system proceeds through a symmetric transition state with an activation energy of 15.0 kcal mol⁻¹. According to calculations, organometallic Zr^IV complexes are promising for activation of C−H and H−H bonds under mild conditions. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2248–2254, December, 1999.     

2-Phenyl-1-boraadamantane complexes. Synthesis and intramolecular dynamics

The reaction of triallylborane with 3-phenylprop-1-yne at 135–140 °C followed by treatment of the reaction mixture with MeOH afforded 7-benzyl-3-methoxy-3-borabicyclo[3.3.1]non-6-ene (1) in 81% yield. Hydroboration of compound1 with a solution of BH₃ in THF yielded the tetrahydrofuran complex of 2-phenyl-1-boraadamantane (2). The reactions of trimethylamine or pyridine with compound2 afforded the trimethylamine (3) or pyridine (4) complexes of 2-phenyl-1-boraadamantane. respectively. Hindered rotation about the C(2)−Ph bond in adduct3 was observed by¹H and¹³C NMR spectroscopy. The activation energy of this process is 58.6 kJ mol⁻¹ (determined by 2D¹H−¹H EXSY spectroscopy).     

Simultaneous determination method of radon-222 and radon-220 by a toluene extraction-liquid scintillation counter

A new determination method for²²²Rn and²²⁰Rn in water sample was developed by extracting radon with toluene and applying the integral counting method with a liquid scintillation counter. The essential characteristics of the methods are, (1) extraction of radon with toluene from water, (2) finding absolute counts and making corrections for the quenching effect by the adoption of the integral counting method, (3) the determination of²²²Rn and²²⁰Rn was performed by counting the activity of²²⁰Rn with its descendants and of ThB (²¹²Pb) with its descendants in a radioactive equilibrium, respectively, (4) realizing high sensitivity by simultaneous counting of α, β⁻ particles emitted from the decay products formed in toluene. The lowest detection limit obtained by the present method was 5.0·10⁻¹³ Ci/l for²²²Rn and 6.8·10⁻⁸ Ci/l for²²⁰Rn in water.     

Molecular architecture and conformation of macromolecules of novel polysilanes

Molecular-weight parameters of new silane homo- and copolymers were analyzed. For all polymers, theM _w values are close ((6.0–8.6)·10⁴), the curves of molecular weight distribution are unimodal, andM _w/M _n=2−2.5. Cyclic fragments or those containing the −C=C− groups make the major contribution to the polysilane chain rigidity. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2430–2433, December, 1998.     

Low-molecular-weight metabolites of fungi. II. Refinement of the structure of stachybotrin

The structure of stachybotrin has been reconsidered in the light of¹H,¹³C,¹H−¹H COSY, HMQC, and HMBC NMR spectra, and the revised structure has been confirmed by x-ray structural analysis. Institute of the Chemistry of Plant Substances, Academy of Sciences of the Republic of Uzbekistan, Tashkent, fax (371) 120 64 75. Translated from Khimiya Prirodnykh Soedinenii, No. 5, pp. 666–669, September–October, 1998.     

Calibration of alkyl-substituted fluorocyclopropanes on gas chromatographic columns by radioactive tracer techniques

A new method utilizing a radio-gas chromatographic system, for the calibration of various gas chromatographic columns with less than 10⁻¹²M of tritium-labelled samples is described. The minimum detectable level of³H,³⁸Cl,¹⁸F,^80mBr,⁸²Br,³⁵S and¹⁴C labelled compounds employed for column calibration is discussed. In addition, the relative retention times of nine previously unpublished alkyl-substituted fluorocyclopropanes on five gas chromatographic columns are given.