Neutral diterpenoids of oleoresins of five species of conifers of Transcarpathia

The compositions of the neutral diterpenoids of the oleoresins of five species of conifers growing in the Transcarpathia have been studied. It has been found that the oleoresins ofAbies alba M.,Larix decidua M., andPicea excelsa L. contain more than 50% of neutral diterpenoids. The group and qualitative compositions of the oxygen-containing diterpenoids have been determined. In the oleoresins ofAbies alba,Picea excelsa, andPicea abies tertiary alcohols — cis-abienol and isocembrol — predominate, while inLarix decidua the main component is the hydroxy ester larixyl acetate. Primary alcohols related to the resin acids have been found in all the oleoresins investigated. Features of the distribution of diterpenoids according to the species of conifers have been revealed. The results obtained are necessary for the chemotaxonomy of conifers of the family Pinceae.Novosibirsk Institute of Organic Chemistry, Siberian Branch, Academy of Sciences of the USSR. Translated from Khimiya Prirodynkh Soedinenii, No. 6, pp. 812–816, November–December, 1988.     

Study of kinetics of glass transition of metallic glasses

In this study, the kinetics of glass transitions of Ti₅₀Cu₂₀Ni₃₀ and Fe₆₇Co₁₈B₁₄Si₁ metallic glasses are studied using thermal analysis technique, i.e., differential scanning calorimetry, by means of continuous heating of the sample at various heating rates. In the present study, based on the heating rate dependence of glass transition temperature (T _g), the activation energy (E) of the glass transition region is determined by two most frequently used approaches, i.e., Moynihan's method and Kissinger's equation. The fragility index, m, is also calculated using T _g, which is a measure of glass-forming ability of the given system. The result shows that the fragility index, m, of the given systems is <16. This indicates that the given systems are strong liquids with excellent glass-forming ability.     

Influence of the Degree of Dehydroxylation of Kaolinite on the Properties of Aluminosilicate Glasses

The degree of dehydroxylation of kaolinite, D_TG and D_IR, respectively, is characterized by thermogravimetric analysis (TG) and Fourier transform infrared spectroscopy (FTIR). The relation between DTG and DIR based on the infrared absorptions at 3600–3700, 915, 810, and 540 cm⁻¹ is established. Three regions can clearly be distinguished: the dehydroxylation region (D_TG<0.9), the metakaolinite region (0.9<D_TG<1) and the ‘spinel’ region(D_TG=1). The effect of the degree of dehydroxylation of kaolinite on the amount of reactive material is measured by the reaction enthalpy, ΔH, of the low-temperature reaction of the dehydroxylated kaolinite with a potassium silicate solution using differential scanning calorimetry (DSC). |ΔH| increases almost linearly with DTG in the dehydroxylation region. In the metakaolinite region, ΔH and thus the amount of reactive material, becomes constant. |ΔH| is sharply decreasing when metakaolinite transforms into other phases in the ‘spinel’ region. No significant differences in the reactivity of the dehydroxylates is detected with DSC. According to FTIR, the use of partially dehydroxylated kaolinite is not influencing the molecular structure of the low-temperature synthesized aluminosilicates, but residual kaolinite is retrieved as an additive. This revised version was published online in August 2006 with corrections to the Cover Date.     

Hydrogenation of complexes of diastereotopicN-benzoyldehydrodipeptides

The replacement of theN-acetyl group by anN-benzoyl group inN-acyldehydrodipeptides results, first, in an increase in the asymmetric induction in their hydrogenation in the case ofN-Bz-Phe-(S)-Glu.N-Bz-(S)-Phe-(S)-Glu is obtained with a diastereomeric excess (de) of 52 %. Second, no poisoning of the Pd-catalyst by sulfur inN-Bz-Phe-(S)-Met occurs, andN-Bz-(R)-Phe(S)-Met is obtained with ade of 26 %. The formation of complexes ofN-Bz-Phe-AA with Ca²⁺ and Mg²⁺ ions does not, as a rule, affect the diastereoselectivity of the hydrogenation. The structure of the dehydrodipeptides has been determined on the basis of¹H NMR spectra, potentiometric titration, and molecular mechanics calculations.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 884–887, May, 1994.This work was carried out with the financial support of the Russian Foundation for Basic Research (Project 93-03-4646).     

The construction of graph models for calculations of the properties of substitution isomers of basis structures on the basis of additivity of energy contributions

A method for the construction of additive models for calculations of the properties of substitution isomers of basis structures is described for the example of a series of X-substituted methylsilanes CH_{3 − k} X _k -SiH_{3 − l} X _l (where X = CH₃, F, Cl, …, k, l = 0, 1, 2, 3). The method is based on similarity of subgraphs in graphs of several molecules and the arrangement of polygonal numbers (triangular, tetrahedral) of the Pascal triangle. Parameters taking into account multiple nonvalence interactions (-C-Si<, >C-Si<, …) through two atoms along the molecular chain of an X-substituted methylsilane (X = CH₃) were for the first time explicitly included in the calculation scheme. Taking these interactions into account allows us to completely differentiate all the structural isomers of certain molecules and obtain numerical parameter values for predicting properties P under consideration in various approximations. Numerical calculations of Δ_f H _{g,298 K}^o were performed for 16 alkylsilanes (as X-substituted methylsilanes), including 7 compounds not studied experimentally.     

Influence of polarity of medium on fluorescence characteristics of alkylaminobenzophenones

A study has been made of the instantaneous fluorescence spectra of 4,4′-bis-dimethylaminobenzophenone (Michler’s ketone, MK), 4,4′-bis-diethylaminobenzophenone (DEAB), and 4-dimethylaminobenzophenone (DMAB) in various solvents, at room temperature. It has been shown that an increase of the solvent polarity leads to an increase of fluorescence intensity and a shift of the fluorescence band maximum toward longer wavelengths. The presence of traces of water in the solutions increases the fluorescence intensity and gives a red shift of the maximum. From the relationships found between the position of the fluorescence maximum and the polarity of the solvent, estimates have been made of the dipole moment of the luminescent state, which is 1.6·10⁻²⁷ C·m for the MK, 2.1·10⁻²⁷ C·m for the DEAB, and 0.8·10⁻²⁷ C·m for the DMAB. L. V. Pisarzhevskii Institute of Physical Chemistry, National Academy of Sciences of the Ukraine, 31 Nauka Prospect, 252039 Kiev, Ukraine. Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 33, No. 1, pp. 36–40, January–February, 1997.     

Relative stability of isomers of polynuclear complexes of molybdenum oxides

Molybdenum(VI) oxide MoO₃ has been studied and the composition of polynuclear molybdenum oxides in the gas phase Mo _x O_{3x ? y} (x = 1–6, y = 0–2) has been determined by laser desorption/ionization time-of-flight mass spectrometry. Quantum-chemical calculations of bond energies, interatomic distances, charge distributions, and molybdenum-molybdenum bond orders for the isomers of neutral polynuclear molecular compounds Mo _x O3 _{x ? y} have been performed with the use of the PBE functional with a relativistically corrected potential implemented as the PRIRODA program package. On the basis of the bond energies, the relative stability of the isomers has been estimated. For the Mo _x O _y isomers (x ≥ 3), cyclic structures have been predicted to be more favorable. For the predicted most stable isomers of each Mo _x O _y composition, the bond energies of their positive and negative ions have been calculated. The positive ionization of Mo _x O _y leads to a considerable decrease in the bond energy of the isomer and the negative ionization, to its increase by about 0.1 au.     

Kinetic Analysis of the Decomposition of Chelates of Di-alkyldithiocarbamate of Cd(II)

The thermal decomposition kinetics of the solid complexes Cd(S₂ CNR₂ )₂ , where R =C₂ H₅ , n -C₃ H₇ , n -C₄ H₉ or iso -C₄ H₉ , was studied by using isothermal and non-isothermal thermogravimetry. The superimposed TG/DTG/DSC curves revealed that thermal decomposition reactions occur in the liquid phase. The kinetic model that best fitted the experimental isothermal TG data was the one-dimensional phase-boundary reaction-controlled process R₁ . The thermal analysis data suggested the thermal stability sequence Cd(S₂ CNBuⁿ ₂ )₂ >Cd(S₂ CNPrⁿ ₂ )₂ >Cd(S₂ CNBuⁱ ₂ )₂ >Cd(S₂ CNEt₂ )₂ , which accords with the sequence of stability of the apparent activation energies. This revised version was published online in July 2006 with corrections to the Cover Date.     

Heat of formation of lanthanum-lead alloys

In the La? Pb system the heats of formation were measured, using a differential direct isoperibol calorimeter, and checking composition and state of the samples by chemical, metallographic and X-ray analyses. For the various compounds the _H (for the reaction among solid phases at 300 K) correspond to the following values (Kcal/g · at.): La₅Pb₃ = ?17.2₅ ± 0.5, La₄Pb₃ = ?16.7 ± 0.5, La₅Pb₄ = ?16.5 ± 0.5, La₃Pb₄ = ?15.3 ± 0.5, LaPb₂ = ?14.4 ± 0.5, LaPb₃ = ?13.7 ± 0.5. The results obtained are briefly discussed and compared with those calculated using the method suggested by MIEDEMA .     

Types of rotary crystal state of solid solutions of paraffins

Thermal deformations and polymorphous transformations of solid solutions of paraffins in C₁₇–C₁₉, C₁₉–C₂₁, C₂₁–C₂₃, C₂₂–C₂₄, and C₂₃–C₂₄ systems are investigated by thermal X-ray diffractometry using a temperature step of several tenths of a degree. It is examined how the length of a molecular chain of a homolog (n) and the difference in length (Δn) between the chains as well as the molecular composition of a solid solution affect these transitions, and the data are compared with those for the individual homologs of paraffins. St. Petersburg University. Translated fromZhurnal Struktumoi Khimii, Vol. 39, No. 3, pp. 380–394, May–June, 1998. This work was supported by RFFR grant No. 97-05-65534 and ISSEP grants No. 156p and a97-2633.     

Kinetics of the Formation of Goethite in the Presence of Sulfates and Chlorides of Monovalent Cations

The synthesis of goethite by oxidation of Fe²⁺in presence of metallic iron was undertaken in an aqueous medium containing indifferent salts such as Na₂SO₄, (NH₄)₂SO₄, NaCl, and NH₄Cl. Temperature and bubbling air rate were maintained, respectively, at 70°C and 1 L/min. The influence of anions and cations on the kinetics of each step of the process has been followed distinctly, the iron dissolution rate has been determined by the variation of the medium acidity, and the precipitation of goethite has been determined by gravimetric measurements. With respect to Cl⁻, the SO₄²⁻anion decreases the rate of the two reactions. NH₄⁺acts as an inhibitor when it is present at low concentrations and as an accelerator for higher concentrations; the limit corresponding to the change of NH₄⁺behavior depends on the nature of the counter ion. The reaction product is composed of pure goethite in the presence of sulfate salts, whereas a mixture of goethite and lepidocrocite, respectively, 60–70 and 40–30%, was observed in the presence of chloride salts.     

Heats of formation of multi-substituted positive ions of organic species

The difference (ΔΔ_fH°) between heats of formation of many multi-substituted odd- and even-electron positive ions can be described by a linear equation: ΔΔ_fH° = A + Bm, where m is the number of substituents or ligands, relative to the unsubstituted reference ion, and m = 1, 2 or 3; A and B are the intercept and slope, respectively. The correlation quality for 59 types of odd- and 26 types of even-electron ions, which involve C, Si, Sn, H, F, Cl, Br, I, O, S, N and P atoms, was analyzed. Unknown heats of formation of related ions and the proton affinities of some organic molecules were predicted using the linear equation.     

DTA study of the hydration of systems of interest in the field of building materials manufacture

The hydration processes of mixtures containing calcined gypsum, blastfurnace slag or fly ash, portland cement and/or hydrated lime, able to generate calcium trisulphoaluminate and silicate hydrates, have been studied by means of differential thermal analysis. Samples were aged at 55°,70° and 85°C for 16, 24 and 48 hours, followed by a further curing at room temperature and humidity up to 28 days.In the case of the systems containing slag, the optimum pre-curing temperature is 55°C and increasing the pre-curing time from 16 to 48 hours leaves the hydration degree almost unchanged.In the case of the systems containing fly ash the optimum pre-curing temperature is 85°C. Increasing the pre-curing time from 16 to 24 hours enhances the hydration degree. The further increase to 48 hours reduces the selectivity towards calcium trisulphoaluminate hydrate.In all the systems investigated the post-curing at room temperature and humidity has no significant effect on the hydration degree.Finally, the influence of the nature of raw materials depends not only on the characteristics of each component, but also on those of the others.

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Zusammenfassung Mittels DTA wurden die Hydratationsprozesse von Gemischen aus Gips, Hochofenschlacke oder Flugasche, Portlandzement und/oder Löschkalk untersucht, die zur Bildung von Calciumtrisulfoaluminat und Silikathydraten fähig sind. Die Proben wurden bei 55°, 70° und 85°C für 16, 24 und 48 Stunden lang, im Anschluß daran durch Aushärten bei Raumtemperatur und normaler Luftfeuchte 28 Tage lang gealtert.Bei der Verwendung von Schlacke beträgt die optimale Vorhärtungstemperatur 55°C und die Erhöhung der Vorhärtungsperiode von 16 auf 48 Stunden ließ den Hydratationsgrad unverändert.Bei der Verwendung von Flugasche beträgt die optimale Vorhärtungstemperatur 85°C. Die Erhöhung der Vorhärtungsperiode von 16 auf 14 Stunden steigert auch den Hydratationsgrad. Eine weitere Steigerung auf 48 Stunden setzt die Selektivität gegenüber Calciumtrisulfoaluminat-Hydrat herab.In keinem der untersuchten Systeme hatte das Nachhärten bei Raumtemperatur und normaler Luftfeuchte einen signifikanten Einfluß auf den Hydratationsgrad.Letztendlich hängt der Einfluß der Ausgangsmaterialien nicht nur von den Eigenschaften jeder einzelnen Komponente, sondern auch von denen der anderen Komponenten ab.

     

Graphical representation of the state of orientation of polymer systems

The orientation distribution function for noncrystalline structural units in polymer systems cannot be determined completely from any experimental source; only the second and/or fourth moments of the distribution function, i.e., the second and/or fourth orders of the generalized orientation factors F_lm^j, can be evaluated. It is there-fore necessary to estimate the distribution function from F_2m^j and F_4m^j. In this paper, a graphical representation of the state of orientation is first discussed in terms of plots of F₄₀^j against F₂₀^j for several types of distribution functions for uniaxial orientation. These are three types of extreme concentration of the distribution at particular polar angles θ₀ given by θ₀ = 0, 0<θ₀<π/2, and θ₀ = π/2; five types of rather realistic distributions having single maxima at θ_j = 0, θ₀, π/2 and double maxima at θ_j = 0, π/2, and a single minimum at θ_j = θ₀; and four types of more realistic distributions including Kratky's floating rod model in an affine matrix. Second, estimation of the distribution function for uniaxial orientation from F₄₀^j and F₂₀^j is discussed quantitatively in terms of the mean-square error by three approximation methods: (a) expansion of the distribution function in finite series of spherical harmonics through the fourth order, (b) approximation of the distribution function as a composite of two components, random orientation and a particular orientation distribution given by N_a (cos²θ_j)^a, N_a being a constant, and (c) approximation of the distribution function by N_a (cos²θ_j)^a alone. It is concluded that when the orientation distribution is sharp, estimation by the second method of approximation gives a smaller error than the first.     

Application of the theory of design of experiments in examination and elimination of the matrix effect

Summary A method of experimental optimization of an analytical procedure aimed at elimination of the matrix effect is proposed which is based on the theory of design of experiments. The criterion functions Q are formulated, which are expressed by regression coefficients in the empirical mathematical model approximating the relationship between a quantity R and the concentrations of sample components. R denotes, for example, the measured signal (e.g. absorbance, emission intensity), the concentration of a component being determined read from the calibration graph, or the error of determination. The quantities Q depend, in general, on the conditions of analysis which can be expressed by the factors z ₁..., z _M (e.g., in AAS — observation height, gas flux, concentrations of the auxiliary substances in a sample, etc.). It is assumed that the extreme of a function Q corresponds to the optimum conditions of analysis. In this paper the relationship between a quantity Q and the factors z is approximated by the polynomial model. The regression coefficients in this model are estimated on the basis of the results of an experiment carried out according to the composite rotatable design. The extreme of the model is found mathematically. Various criterion functions Q are discussed. An example concerning determination of Mg and Ca in AlCl₃ reagent by AAS is presented.

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Anwendung der Theorie der Versuchsplanung zur Untersuchung und Eliminierung des MatrixeffektsBestimmung von Mg and Ca in AlCl₃ mit Hilfe der AAS

Zusammenfassung Ein auf der Theorie der Versuchsplanung beruhendes Verfahren zur experimentellen Optimierung einer analytischen Methode mit dem Ziel der Eliminierung des Matrixeffekts wird beschrieben. Die Kriteriumfunktionen Q werden formuliert, die durch Regressionskoeffizienten in einem mathematischen Modell ausgedrückt werden, das der Beziehung zwischen einem Wert R und den Konzentrationen der Bestandteile angenähert ist. Hierbei bedeutet R z. B. das gemessene Signal (Extinktion, Emissionsintensität), den von der Eichkurve abgelesenen Konzentrationswert oder den Fehler der Bestimmung. Der Wert Q hängt im allgemeinen von den Analysenbedingungen ab, die durch die Faktoren z ₁... z _M (bei der AAS zum Beispiel die Beobachtungshöhe, der Gasstrom, die Konzentration von Hilfssubstanzen usw.) ausgedrückt werden können. Es wird angenommen, daß der Extremwert einer Funktion Q den optimalen Analysenbedingungen entspricht. Die Beziehung zwischen Q und den Faktoren z wird durch ein Polynommodell angenähert. Die Regressionskoeffizienten in diesem Modell werden aufgrund von Versuchsergebnissen bestimmt. Der Extremwert des Modells wird mathematisch berechnet. Verschiedene Kriteriumfunktionen Q werden diskutiert. Als Beispiel wird die Bestimmung von Mg und Ca in AlCl₃ mit Hilfe der AAS beschrieben.

     

Structure of the blue forms of bisphthalocyanines of rare-earth elements

Using electron spectroscopy, X-ray photoelectron spectroscopy, and ESR spectroscopy, the blue forms of bisphthalocyanines of rare-earth elements were found to have structures of sandwich-type complexes with isoelectronic phthalocyanine ligands linked with tetravalent metal ions, [Pc^2–Ln⁴⁺Pc^2–]⁰. A comparative spectral and electrochemical study of the blue and green forms oftert-butyl-substituted bisphthalocyanines was carried out for almost the whole series of rare-earth metals. Lutetium octa(perfluoro-tert-butyl)- and perchlorobisphthalocyanines were synthesized for the first time.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 425–430, March, 1995.This study was financially supported by the Russian Foundation for Basic Research (grant No. 94-03-08903).     

Determination of the Quantum Yield of Intersystem Crossing of Rose Bengal

The quantum yield of intersystem crossing (Φ_isc) of a sensitizer is related to the quantum yield of singlet-oxygen production (Φ(¹O₂)) by the efficiency of the energy transfer (φ_et) and is an important parameter in the evaluation of potential applications of sensitized photo-oxidations. Using two different laser photolysis techniques, the energy-transfer method and the partial saturation method, Φ_isc of rose bengal has been determined in MeOH and in aqueous solutions. The results confirm that with Φ_isc(H₂O) = 1.05(± 0.06) and Φ_isc(MeOH)=0.90(±0.08), the generally assumed relation Φ_isc · φ_et = Φ(¹O₂), with φ_et = 1, cannot be maintained any longer (Φ(¹O₂, H₂O) = 0.75 and Φ(¹O₂, MeOH) = 0.76). During these experiments, a second intermediate has been observed which is produced from the triplet state of rose bengal and, stabilized in a anionic micellar solution, has been shown to be the radical cation of the sensitizer. The efficiency of the electron transfer has been evaluated from transient absorption and bleaching recordings, and it seems conclusive to attribute the results to the difference between Φ_isc and Φ(¹O₂).     

Synthesis of CeO2 by thermal decomposition of oxalate and kinetics of thermal decomposition of precursor

CeO₂ was synthesized by calcining Ce₂(C₂O₄)₃·8H₂O above 673 K in air. The precursor and its calcined products were characterized using thermogravimetry and differential scanning calorimetry, Fourier transform infrared spectra, X-ray powder diffraction, scanning electron microscopy, and UV–Vis absorption spectroscopy. The result showed that cubic CeO₂ was obtained when the precursor was calcined above 673 K in air for 2 h. The UV–Vis absorption spectroscopy studies showed that superfine CeO₂ behaved as an excellent UV-shielding material. The thermal decomposition of the precursor in air experienced two steps, which are: first, the dehydration of eight crystal water molecules, then the decomposition of Ce₂(C₂O₄)₃ into cubic CeO₂. The values of the activation energies associated with the thermal decomposition of Ce₂(C₂O₄)₃·8H₂O were determined based on the Starink equation.