Nucleation of the β-modification of isotactic polypropylene

The effects of the organic pigments C.I.P. RED 177 and C.I.P. Yellow 83 as nucleating agents on the crystallization of polypropylene were studied by DSC. The anthraquinone pigment exerted a significant effect, resulting in structural modifications with lower melting point, and particularly the -modification. The DSC curves exhibit four transition regions, with the following temperature intervals: I. 415–417 K, II. 423–425 K, III. 430–432 K and IV. 438–439 K. For evaluation of the -nucleation effect of pigments, the ratio (H ₁+H ₂)/(H ₃+H ₄) was suggested.     

Band structure of even and ions of odd polyenes

The analysis of experimental data for singlet transitions (E _n) of even polyenes (I), cations (II) and anions (III) of odd polyenes show that for infinite chains E (I)/E (II)=E (I)/E (III) = 2:1. It is shown that the energy gap is equal for the three systems. In cases (II) and (III) there is a level (NBMO) in the gap which is vacant in (II) and occupied in (III). That is why the first optical transition in (II) and (III) depends on the semiwidth of the gap.     

Synthesis of 2β, 3β, 14α-trihydroxy-Δ4,7-6-ketosteroids and their derivatives

A scheme using -sitosterol as an example for synthesizing 2, 3, 14-trihydroxy-^4,7-6-ketosteroids and their derivatives from 3-hydroxy-⁵-steroids was developed.Institute of Bioorganic Chemistry, National Academy of Sciences of Belarus, 220141, Belarus, Minsk, ul, akad. Kuprevicha, 5/2. Translated from Khimiya Prirodnykh Soedinenii, No. 3, pp. 244–248, May–June, 2000.     

Ring-Ring Tautomerism in the Series of Isoxazolidine and Δ2-Isoxazoline Derivatives

We have studied the reaction of 5-hydroxy-3,3,5-trimethylisoxazolidine and 5-hydroxy-3,5-dimethyl-²-isoxazoline with derivatives of thiosemicarbazide and also thiocarbonohydrazine. Both reactions serve as a method for synthesis of the previously unknown 5-thiosemicarbazido(thiocarbonohydrazino)isoxazolidines and -²-isoxazolines. ¹H and ¹³C NMR spectroscopy revealed a tendency of the indicated compounds toward ring-chain and ring-ring tautomeric conversions in solutions involving the 1,2,4-triazolidine, ²-pyrazoline, and 1,2,4,5-tetrazine rings.     

Energetics of intramolecular hydrogen bonds and conformations of ω-diphenylphosphoryl- and ω-diphenylthiophosphoryl-substituted aliphatic alcohol molecules

A series of conformationally heterogeneous and energetically multilevel -diphenylphosphoryl- and -diphenylthiophosphoryl-substituted aliphatic alcohols, whose molecules are capable of five-, six-, and seven-membered ring closure due to the OH...O=P or OH...S=P intramolecular hydrogen bond (IHB), was studied by IR spectroscopy and molecular mechanics. The data obtained confirm the previous assumption that the energy of IHB (E _IHB) differs substantially from the difference of enthalpies of conformers with and without IHB (–H ), which is experimentally determined by the temperature dependence of the intensity of IR (OH) absorption bands. The measured –H values can be positive, zero, or negative at significant IHB effects, i.e., at high (OH) and E _IHB values.     

Studies of the energy spectrum of α, ω- substituted polymethine chains. II. Polymethine chains with odd number of methine groups

The analysis of the experimental data for the energy of the longest wavelength optical transitions _n,opt of substituted polymethines X (CH)_2n+1 X shows that in the asymptotic case (n) _,opt does not tend to zero, as it follows from the empirically established correlations, but has a finite, non-zero value. It is shown that the energy gap of odd polymethines is the same as that of the even polymethines - the polyenes (E 2 eV). The substituents (X N, O, B) are responsible for the appearance of levels in the gap. These, depending on the substituent character, are vacant (X B) or occupied (X N, O). The transition from or to such a level determines the longest wavelength optical transition energy of polymethines.     

Transformed steroids

A preparative method for 9a-hydroxylation of ⁵-3-hydroxysteroids using the fungi ofCircinella sp. 10Kh-1220 not capable of modifying theA ring has been developed. It is established that the yields of the main and the side products greatly depend on the transformation conditions, mycelium age, and the structure of the steroid substrate. Under the optimal transformation conditions novel 9-hydroxysubstituted derivatives of androstenolone, pregnenolone, 16-dehydro-16,17-epoxy-, and-16-methoxypregnenolone have been obtained in 36–80 % yields.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 737–743, April, 1994.     

SCF perturbation theory for unimolecular reactions

A CNDO/2 SCF perturbation theory is presented for interpreting the form of CNDO/2 potential energy surfaces of unimolecular reactions. The analysis is performed by calculating the energy change E arising from a distortion of the molecular geometry along the reaction coordinate. E is decomposed into different perturbational contributions which are appropriate for an interpretation of the perturbation energy E. Moreover, E is resolved into energy parts arising from a single occupied orbital and contributions due to pairwise orbital interactions. In this way one evaluates numerically how the form of the occupied and unoccupied orbitals determines the magnitude of E. If the distortion occurs along a definite symmetry coordinate, group-theoretical arguments can be applied to discuss the magnitude of characteristic components of the perturbation energy. The SCF perturbation theory is used to analyze the isomerization of ethylene, cis-2-butene and cis-2-butenenitrile.This work was partially supported by Nato-Grant No. 1072     

Substituent effect and enthalpy-entropy compensation on the inclusion ofβ-cyclodextrin with 1-substituted naphthalenes

The inclusion complexation of-CD with 1-substituted naphthalenes has been investigated by fluorescence spectroscopy. It was observed that the association constants were influenced by the molar refraction (R _m), hydrophobic constant ( _x ), and Hammett constant ( _x ) of substituents in the guest compounds. The thermodynamic parameters G⁰, H ⁰, and S ⁰ determined by measuring the temperature-dependentK _a values shows that inclusion complex formation is enthalpy driven. The results are discussed in terms of enthalpy-entropy compensation.     

Determination of kinetic parameters of the FeCl3/FeCl2 systemvia a novel treatment of chronoamperometric data

Summary Computer based methods for the processing of chronoamperometric datavia convolutions are discussed. On the example of the quasi-reversible Fe³⁺/Fe²⁺ couple, their application for data acquisition and determination of the heterogeneous electrochemical parameters is demonstrated. The plot of Q/i vs. t/i is superior to that employingi/I ₁, being less sensitive to distortions by charging currents once these have died away and by the effects of damping on the initially rapidly varying currents. Cyclic voltammetry is often combined with convolution or deconvolution, and digital simulation studies are also frequently performed to confirm the results.

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Bestimmung kinetischer Parameter des Systems FeCl₃/FeCl₂ mittels einer neuen Verarbeitung chronoamperometrischer Daten

Zusammenfassung Computerunterstützte Verfahren zur Verarbeitung chronoamperometrischer Daten mittels Faltungsintegralen werden diskutiert. Am Beispiel des quasireversiblen Systems Fe³⁺/Fe²⁺ wird die Anwendung der neuen Methoden zur Datenerfassung und zur Bestimmung der heterogenen elektrochemischen Parameter gezeigt. Der Plot von Q/i gegen t/i ist dem voni/I ₁ überlegen, da er durch Ladeströme und Dämpfung der ursprünglich stark variierenden Ströme weniger stark beeinflußt wird. Cyclische Voltammetrie wird häufig im Zusammenhang mit Konvolutions- und Dekonvolutionsmethoden angewandt; digitale Simulation zur Überprüfung der Ergebnisse wird ebenfalls oft eingesetzt.

     

A thermodynamic and structural study of the interactions of pyridino- and diketopyridino-18-crown-6 ligands with some primary organic ammonium cations

Equilibrium constant (K), enthalpy change (H), and entropy change (S) values have been determined calorimetrically at 25°C in 90%MeOH 10%H₂O (v/v) for the interactions of pyridino-18-crown-6 (P18C6) and diketopyridino-18-crown-6 (K₂P18C6) with perchlorate salts of ammonium, benzylammonium,-phenylethylammonium,-phenylethylammonium, and-(1-naphthyl)ethyl-ammonium cations. The crystal structure of the complex of P18C6 with benzylammonium perchlorate was determined by X-ray crystallography. The¹H 1D and 2D NMR spectra of some of these complexes were used to elucidate their structural features in solution. The logK values for the interaction of the ammonium cations with P18C6 are larger than those with K₂P18C6, probably due to the higher degree of structural flexibility of P18C6. Ligand K₂P18C6 displays appreciable - interaction with the-(1-naphthyl)ethylammonium cation, but not with the-phenylethylammonium cation.- interaction between ligand and cationSupplementary Data relating to this article are deposited with the British Library as Supplementary Publication No SUP 00000 (22 pages)     

Kinetics of oxidation of glycine and valine by chloramine-T in hydrochloric acid medium

The kinetics of oxidation of glycine and valine by chloramine-T in hydrochloric acid medium has been studied. The rate of disappearance of chloramine-T shows a first order dependence on both chloramine-T and the amino acid, and an inverse first order with respect to [H⁺]. The solvent isotope effect was studied using heavy water. The kinetic parameters,E _a ,Arrhenius factorA, H and S and G have been calculated. A rate law in agreement with experimental results has been derived. A mechanism is proposed.

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Über die Kinetik der Oxidation von Glycin und Valin mit Chloramin-T in salzsaurem Medium

Zusammenfassung Die Kinetik der Oxidation von Glycin und Valin mit Chloramin-T in Salzsäure wurde untersucht. Die Geschwindigkeitskonstante des Wegreagierens von Chloramin-T zeigt eine Abhängigkeit erster Ordnung sowohl von Chloramin-T als auch von der Aminosäure und ist invers erster Ordnung bezüglich [H⁺]. Der Lösungsmittel-Isotopeneffekt wurde mit D₂O untersucht. Es wurden die kinetischen Parameter,E _a , derArrhenius-FaktorA, H , S und G , bestimmt. Ein Mechanismus, der in Übereinstimmung mit den experimentenllen Daten ist, wird vorgeschlagen.

     

Model calculations of changes of thermodynamic variables for the transfer of nonpolar solutes from water to water-d2

A recently introduced modified hydration shell hydrogen bond model for rationalizing the thermodynamic consequences of hydrophobic hydration is adapted for use with heavy water. The required adjustment of parameters employs the assumption that breaking hydrogen bonds in water-d₂ involves a greater enthalpy change and a larger entropy increase than bond breaking in ordinary water. It also makes some use of information derived from studies of gas solubilities in the two solvents, although a review of the data leads to serious questions about the reliability of results obtained in this way. The model permits calculations of hydrogen bonding contributions to the changes, G _t ^o , H _t ^o , S _t ^o , and C _p,t ^o , for transfer of nonpolar solutes from water to water-d₂ and implies that such data should show regular trends. Although some of the numerical results depend strongly on the values chosen for the parameters, the pattern defined by these trends is nearly independent of parameters. Predicted values of C _p,t ^o are large and positive for all nonpolar solutes, while S _t ^o is expected to be negative near 0°C, becoming progressively less negative on warming and eventually positive. Both of these quantities should be proportional to the molecular surface area of the solute. Analogous predictions regarding G _t ^o and H _t ^o can also be made, but only if it is permissible to neglect possible contributions to these quantities from van der Waals interactions.     

Application of symmetry coupling coefficients in the evaluation of the electronic spectra of d 7 ions

The optical absorption spectrum of cobalt chloride thiourea has been studied at room and liquid air temperatures. The results have been interpreted using group theoretical methods taking into account all the quartet states and several doublet states. Crystal field, electrostatic, and spin-orbit coupling interactions were included to yield the allowed transitions with the relative transition probabilities. The experimental results were interpreted for the following set of parameters: B = 750cm^–1, C = 3100cm^–1, = 7370cm^–1, = -200 cm^–1, = 500cm^–1, and = 450 cm^–1.     

Resolution of Δ2-isoxazoline-5-carboxylates by a protease fromAspergillus Oryzae providing masked synthons for enantiopure β-aminoalcohols and related structures

Summary A series of racemic ²-isoxazolinecarboxylates have been synthesized and subjected to enzymatic hydrolysis by a protease fromAspergillus oryzae in a two-phase system. Out of these compounds only isoxazoline-5-carboxylates unsubstituted at C-4 were hydrolyzed. Thus, from 3-ethoxycarbonyl-, 3-methyl-, and 3-phenyl-²-isoxazoline-5-carboxylates the corresponding (R)-configurated carboxylic acids are obtained. In contrast, an additional methyl group at C-5 changes the steric course of the hydrolysis to give predominantly the (S)-acid. The enantioselectivities obtained are in the range ofE=5–35.

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Racematspaltung von ²-Isoxazolin-5-carboxylaten mittels einer Protease vonAspergillus oryzae zur Darstellung maskierter Synthons für enantiomerenreine -Aminoalkohole und verwandte Strukturen

Zusammenfassung Zahlreiche ²-Isoxazolincarbonsäureester wurden in racemischer Form dargestellt und einer enzymatischen Hydrolyse mittels einer Protease ausAspergillus oryzae in einem Zwei-Phasen-System unterworfen. Lediglich an C-4 unsubstituierte Isoxazolin-5-carbonsäureester wurden hydrolysiert. Aus 3-Ethoxycarbonyl-, 3-Methyl- und 3-Phenyl-²-isoxazolin-5-carbonsäureestern wurden die entsprechenden (R)-konfigurierten Carbonsäuren erhalten, während eine zusätzliche Methylgruppe an C-5 eine bevorzugte Bildung der (S)-Säure bewirkte. Die erzielten Enantiomerenüberschüsse liegen im Bereich vonE=5–35.

     

Numerische Auswertung von Enzymanalysen

Zusammenfassung Für eine numerische Auswertung von Enzymanalysen erscheint es zunächst naheliegend, in die Meßpunkte eine Ausgleichsgerade einzupassen und deren Steigung als Schätzwert für die gesuchte Anfangsgeschwindigkeit E/t ₀ zu nehmen. Die Steigung der Ausgleichsgeraden liefert aber die mittlere Reaktionsgeschwindigkeit über die gesamte Meßzeit und unterschätzt E/t ₀ immer dann, wenn die Reaktion gegen Ende der Meßzeit etwas langsamer läuft. Bei automatischen Geräten muß das Auswerteverfahren auch in solchen Fällen E/t ₀ richtig schätzen. In der vorliegenden Arbeit wird eine einfache Möglichkeit, die zu diesem Ziel führt, diskutiert, nämlich die Schätzung von E/t ₀ mit einer Ausgleichsparabel, die dem Reaktionsverlauf folgen kann.

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Numerical evaluation of enzyme analyses

To calculate enzyme concentrations numerically, it seems obvious to fit a straight line into the data points and take the slope as an estimate for the starting velocity E/t ₀. This slope, however, is proportional to the average reaction rate over the total measurement interval and always underestimates E/t ₀ when the reaction is slowing down towards the end. Automatic analyzers must correctly estimate E/t ₀ even in such cases. As discussed in this article, this can be achieved by fitting a second order parabola, that can follow the reaction, into the data points.

     

Synthesis and Dehydrohalogenation of 3 β-Chloro-5 α,7 α-dibromo-6-ketosteroids of the Stigmastane and Cholestane Series

3-Chloro-5,7-dibromo-6-ketosteroids 5a and 5b are synthesized from -sitosterol (1a) and cholesterol (1b). Dehydrohalogenation of these forms 7-bromo-2,4-dien-6-ones (6a-b), 2,4-dien-6-ones (7a-b), and 14-hydroperoxy-2,4,7-trien-6-ones (8a-b). Woodward hydroxylation of dienone 6a produces 2-iodo-7-bromo-3-acetoxy-⁴-6-ketone 9 and 7-bromo-2,3-diacetoxy-⁴-6-ketone 10. 2-Iodo-3-acetoxy-^4,7,14-trien-6-one 11 is prepared analogously from trienone 8a.     

13C-NMR-Untersuchungen von Substituenteneffekten in mehrfach substituierten Benzen-und Naphthalenverbindungen: Inkrementberechnungen der13C-chemischen Verschiebungen

Summary The aryl¹³C chemical shifts of Cl-substituted 4-amino-, 4-diazonium-N,N-dimethylanilines, N,N-dimethylanilines and differently substituted naphthalenes were assigned by means of different NMR methods. The assignments were compared with chemical shifts obtained by using empirical additivity relationship for mono substituted aromatic substances. As a means of substitutent interactions, the chemical shift difference between calculated and experimental values ( _c ⁱ ) has been used. In the presence of remarkable steric and electronic substituent interactions, large deviations from additivity ( _c ⁱ values up to 15.4 ppm) were found. Which originate primarily from steric interactions between the substitutents. In order to account therefore, correction increments have been developed by employing the _c ⁱ values obtained from 1,2-disubstituted benzenes or naphthalenes. The¹³C chemical shifts of more than seventy substituted benzenes and naphthalenes have been predicted. The results corroborate that reasonable calculation of chemical shifts in sterically hindered benzenes is possible by using the extended additivity rule. The _c ⁱ values are much lower and allow reasonable structural assignments.For external users of this incremental system, a computer program for IBM compatible PC/AT was developed. By means of this program, the¹³C chemical shifts for different benzenes and naphthalenes with or without 1,2-disubstituted correction increments will be calculated and the corresponding spectrum displayed. The program can assist the successful assignment of experimental¹³C chemical shifts.

     

Dielectric properties of mixtures of acetylene tetrachloride with toluene and acetone

Relative permittivities are reported for binary liquid mixtures of acetylene tetrachloride (ATC) with toluene and acetone at 35°C. Measurements of refractive indices have also been made for the mixtures. The values of the quantity , the deviations of the relative permittivities of these mixtures from ideality, have been calculated. The negative values of obtained for ATC+ toluene mixtures may be explained as being due to a decrease in the degree of alignment of the molecular dipoles with changing composition of the mixture, whereas the positive values of obtained for ATC+acetone mixtures are attributed to the formation of molecular complex between acetone and CHCl₂CHCl₂. The values of the Kirkwood correlation parameter g for both sets of mixtures have been calculated using the relative permittivity data.     

Structural Dependence of Insecticidal Activity of 5α-Hydroxy-Δ7-6-ketosteroids

The toxicity of 5-hydroxy- ⁷ -6-ketosteroids for colorado beetleLeptinotarsa decemlineataSay. larvae was studied by topical and GI administration.