Extended Hückel MO calculations of the conformation of several amino acids

The conformation of the amino acid residues, glycine, alanine, proline, and phenylalanine have been predicted from molecular orbital calculations of appropriate model compounds. Using the current main chain rotation convention (, ) the principle conformations were found to be glycine (0, 0), alanine (240, 240), proline (120, 330) and phenylalanine (30, 330). Several secondary conformations were also found for glycine. A comparison of the predicted conformations is in good agreement with experimental data on comparable residues or model compounds.Supported by National Institutes of Health Grants No. FR 5409-07 and GM 16312-01.Recipient of a Public Health Service Research Career Development Award AM 1159-01.     

Thermal behaviour of chemically deintercalated Li1−1Ni1+xO2

The thermal behaviour of chemically deintercalated samples obtained by HCl treatment of non-stoichiometric Li/Ni mixed oxides is studied. A multi-step reduction of Ni with O₂ evolution is observed between room temperature and 800C. Two cation redistribution processes are shown by the exothermal occurrence of a spinel phase at 300C and the endothermal reduction to a rock-salt phase with random distribution of Li and Ni cations in octahedral sites at 800C.The authors wish to express their acknowledgement to CICYT and PFPI for financial support.     

Isokinetic relationships (IKRs) in organometallic and coordination chemistry: Reactions of Ru5C(CO)14{P(OPh)3} and other complexes

The linear compensation plot of H versus S for associative substitution reactions of Ru5C(CO)14 {P(OPh3)} with seven P-donor nucleophiles suggests that an isokinetic temperature, Tiso, of 253±10K exists. A detailed statistical analysis by the Linert-Exner method shows that the data are consistent with there being a genuine isokinetic temperature at 245K at which reactions with six out of the seven nucleophiles proceed at the same rate. This can be shown more easily, graphically more vividly, and with quantitatively the same or better results, by a simplified version of an earlier method due to Krug, Greiger et al. in which H values are found to depend linearly on corresponding values of G calculated at a suitably chosen temperature. This isokinetic behaviour is closely related to that shown by the linear free energy analysis of the rates in terms of the electronic and steric properties of the nucleophiles. The temperature dependence of the sensitivity of the rates to these electronic and steric properties suggests that the major factors involved are entropic rather than enthalpic, reactions with larger nucleophiles actually being favoured by enthalpic factors. Steric profiles obtained at different temperatures all pass through a common point with an isokinetic cone angle of 153°. A few examples of other reactions of organometallic or coordination compounds that show linear compensation plots of H versus S are also analysed by the Linert- Exner and Krug-Greiger methods. Some do show unambiguous isokinetic behaviour but others do not, even though the compensation plots appear to be linear.     

Molecular structure of aniline in the gaseous phase: A concerted study by electron diffraction and ab initio molecular orbital calculations

The molecular structure of free aniline has been investigated by gas-phase electron diffraction and ab initio MO calculations at the HF and MP2 levels of theory, using the 6-31G^*(6D) basis set. Least-squares refinement of a model withC _s symmetry, with constraints from MP2 calculations, has led to an accurate determination of the C-C-C angle at theipso position of the benzene ring, =119.0±0.2 (where the uncertainty represents total error). This parameter provides information on the extent of the interaction between the nitrogen lone pair and the system of the benzene ring, and could not be determined accurately by microwave spectroscopy. The angles at theortho, meta, andpara positions of the ring are 120.3±0.1, 120.7±0.1, and 119.0±0.3, respectively. Important bond distances are r _g(C-C)=1.398±0.003 å andr _g(C-N) =1.407±0.003 å. The effective dihedral angle between the H-N-H plane and the ring plane, averaged over the large-amplitude inversion motion of the amino group, is ¦¦=44±4. The equilibrium dihedral angle is calculated to be 41.8 at the HF level and 43.6 at the MP2 level, in agreement with far-infrared spectroscopic information. The MO calculations predict that the differencer(C_ortho-C_meta) -r(C_ipso-C_ortho) is 0.008–0.009 å. They also indicate that the nitrogen atom is displaced from the ring plane, on the side opposite to the amino hydrogens. The displacement is 0.049 å at the HF level and 0.072 å at the MP2 level. The two calculations, however, yield very different patterns for the minute deviations from planarity of the ring carbons.     

Thermal decomposition of calcium sulphate in carbon monoxide

Simultaneous TG and DTA studies were performed on analytical grade calcium sulfate and on samples of natural gypsum and phosphogypsum in carbon monoxide atmosphere. The decomposition temperatures and mechanism are influenced by the mineral impurities of the sample and the heating rate as well as the CO content of the gas atmosphere.

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Zusammenfassung Simultane TG- und DTA-Untersuchungen von analytisch reinem Calciumsulfat und Proben von natürlichem Gips und Phosphogips wurden in Kohlenmonoxidatmosphäre ausgeführt. Temperatur und Mechanismus der Zersetzung werden durch mineralische Verunreinigungen der Probe, durch die Aufheizgeschwindigkeit und durch den CO-Gehalt der Gasatmosphäre beeinflußt.

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. - , , .

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The authors are indebted to Professor M. Veiderma for fruitful discussions and continuous support. The scholarship from Finnish Government to one of us (R. K.) is gratefully acknowledged.     

Thermal properties of thiocyanatocopperc(II) complexes with picolines and lutidines

The thermal properties of coordination compounds of the composition Cu(NCS)₂L₂ (whereL=pyridine, 2-, 3- and 4-picoline, and 2,3-, 2,4-, 2,5-, 2,6-, 3,4- and 3,5-lutidine) are dealt with. The thermal decomposition of these compounds begins with the release of the ligandL. The compounds with pyridine derivatives containing a methyl substituent at position 2 show a markedly decreased initial decomposition temperature. It was found that X-ray irradiation caused a reduction of the central atom Cu(II) in the coordination compounds under investigation. X-ray electron spectra data showed the stability of the compounds Cu(NCS)₂L₂ withL=picoline or lutidine having a methyl substituent at position 2 to be distinctly lower in the surface layers. From the given series, the compounds Cu(NCS)₂(pyridine)₂ and Cu(NCS)₂(3,5-lutidine)₂ exhibit an analogous course of thermal decomposition in nitrogen atmosphere up to 600°. The stoichiometries of thermal decomposition are discussed.

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Zusammenfassung Der Artikel befaßt sich mit den thermischen Eigenschaften von Koordi-nationsverbindungen der Zusammensetzung Cu(NCS)₂ L ₂ (L= Pyridin, 2-, 3-, 4-Pikolin, 2,3-, 2.4-, 2,5-, 2,6-, 3,4- und 3,5-Lutidin). Die thermische Zersetzung dieser Verbindungen beginnt mit der Abspaltung des LigandenL. Die Verbindungen mit Pyridinderivaten, welche einen Methylsubstituenten in Position 2 im Pyridinring enthalten, zeigen eine deutlich herabgesetzte anfängliche Zersetzungstemperatur. Es wurde gefunden, daß die Röntgenbestrahlung eine Reduktion des zentralen Cu(II)-Atoms bei den untersuchten Koordinationsverbindungen herbeiführte. Die Daten der Röntgen-Elektronenspektren zeigten, daß die Stabilität der Verbindungen Cu(NCS)₂L₂ mitL=Pikolin oder Lutidin, welche einen Methylsubstituenten in Position 2 enthalten, in den Oberflächenschichten wesentlich geringer ist. Von der gegebenen Reihe der Verbindungen zeigen Cu(NCS)₂(Pyridin)₂ und Cu(NCS)₂(3,5-Lutidin)₂ in Stickstoff-Atmosphäre bis zu 600° einen ähnlichen Verlauf der thermischen Zersetzung. Die Stöchiometrie ihrer thermischen Zersetzung wird beschrieben.

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Résumé L'article a trait aux propriétés thermiques des composés de coordination de composition Cu(SCN)₂L₂ (L=pyridine, 2-, 3-, 4-picoline, 2,3-, 2,4-, 2,5-, 2,6-, 3,4-, 3,5-lutidine). La décomposition thermique de ces composés commence avec la libération du ligandL. Les composés avec des dérivés de la pyridine contenant un substituant méthyle en position 2 sur le cycle de la pyridine présentent une température initiale de décomposition qui se trouve abaissée de manière appréciable. On observe que le traitement aux rayons X provoque une réduction de l'atome central Cu(II) dans les composés de coordination étudiés. Les données fournies par les spectres électroniques des rayons X ont montré que la stabilité des composés Cu(SCN)₂L₂ avecL= picoline ou lutidine, ayant un substituant méthyle en position 2, est nettement plus faible dans les couches superficielles. Dans cette série de composés, Cu(SCN)₂ (pyridine)₂ et Cu(SCN)₂(3,5-lutidine)₂ montrent, en atmosphère d'azote, jusqu'à 600°, un processus analogue de décomposition thermique. La stoechiométrie de leur réaction de décomposition thermique est examinée.

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Cu(NCS)₂L₂ L=, 2-, 3-, 4- , 2,3-, 2,4-, 2,5-, 2,6-, 3,4-, 3,5-. L. 2- . , , Cu(II). , Cu(NCS)₂L₂ c L= , 2, . Cu(NCS)₂ ( )₂ Cu(NCS)₂ (3,5-)₂ 600°. .

     

Analytische Dichtegradienten-Zentrifugation bei Temperaturen zwischen +4?C und +40?C

Zusammenfassung Es wird gezeigt, da\ die bei der analytischen Dichtegradienten-Zentrifugation benötigten Parameter, die von Hearst u. Mitarb. tabelliert wurden, auch für andere Temperaturen als 25C gültig sind. Das ist von gro\er Wichtigkeit, da hochempfindliche Enzyme nur bei Temperaturen um + 4C lÄnger als 24 h nativ bleiben. Man ist deshalb auf eine Zentrifugation bei dieser Temperatur angewiesen. Weil man oft nur sehr wenig Substanz isolieren kann, bleibt nur die Dichtegradienten-Zentrifugation als Methode der Wahl. Ein Vergleich der gemessenen Molekulargewichte bei 6C und 25C zeigt keine Abweichungen, die über die Me\genauigkeit hinausgehen.

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Analytical density gradient centrifugation at temperatures between +4C and +40 C

It is shown that all the parameters needed for analytical density gradient centrifugation tabulated by Hearst et al. for 25C are valid for other temperatures, too. This will be important in the investigation of highly sensitive enzymes which are only stable at temperatures near +4C over a period of 24 h. Comparison of molecular weights determined at 6C und 25C shows no difference greater than 2%, which will be within the experimental error.

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Das Bundesministerium für Bildung und Wissenschaft hat diese Arbeiten gro\zügig unterstützt.     

Oxidation of [Co(en)2(SOCH2CO2)]+ by S2O82− and by IO4− in binary aqueous solvent mixtures at pressures up to 1.25 kbar

Second order rate constants and activation parameters H, S, and V have been measured for the oxidation of [Co(en)2(SOCH2CO2)]+ by S2O82– and by IO4– in highly aqueous H2O – t-BuOH mixtures. The changes in solvation on going from the initial to the transition state are discussed on the basis of the transfer functions Gto, Hto and Sto. Whereas Gt changes smoothly as the proportion of t-BuOH increases, the plots of Ht and TSt exhibit mirror behaviour and pass through extrema located around x2(t- BuOH)=0.038. Information on the role of solvation is complemented by the determination of activation volumes. These are discussed in terms of intrinsic and solvational contributions. It is proposed that changes in hydrophobic hydration are of principal importance in determining the response of H, S, and V to changes in solvent composition in H2O – t-BuOH mixtures.     

DTA identification of polycaprolactone

Polycaprolactone (PCL) is a new material used in orthopedics. It is characterized by an endothermic melting peak at about 61C, an endothermic decomposition peak at about 380C and an exothermic peak at about 453C. These three observed phenomena and the corresponding thermodynamic data made it easily possible to identify PCL among the other polymers previously examined with Differential Thermal Analysis (DTA).

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Zusammenfassung Polycaprolacton ist ein neuartiger Kunststoff, der in der OrthopÄdie als Knochenersatz Verwendung findet. Die Charakterisierung und Identifizierung kann durch thermoanalytische Messungen (DTA) auf Grund von endothermen VorgÄngen bei 61 und 380C und eines exothermen Vorgangs bei 453C erfolgen.

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The authors thank A. Crestin for technical contribution.     

Surface tension as a function of temperature for some molten metals

Results are given for Sn, In, and Ge from the melting points up to 1700 C, for Pb up to 1400 C, for Tl up to 1100 C, for Bi up to 1300 C, and for Cd up to 600 C. In every case the surface tension is a linear function of temperature. Estimates are made of the critical temperatures of Cd and Ge. It is shown that deductions on the structure of the melts can be drawn from surface-tension data.     

XPS study of the in-depth profile of TiO2?Al2O3 catalysts prepared by different methods

An XPS study of in-depth profiles of Ti/Al ratio in TiO₂–Al₂O₃ catalysts in conjunction with sputter-etching by Ar⁺ has revealed that the sample prepared with ammonia as precipitation reagent has constant Ti/Al ratio from surface layer to bulk, while the smaple prepared with urea has much Al in the surface layer.

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Ti/Al TiO₂–Al₂O₃ Ar⁺ , , , Ti/Al , , , .

     

Determination of hydroxyl groups and/or water on the surface of oxide catalysts by a pulse chromatographic method

A pulse chromatographic method based on the reaction of gaseous dimethylzinc tetrahydrofura nate was developed for the determination of surface hydroxyl groups and/or adsorbed water in solid porous materials. The procedure is rapid and gives results comparable to other methods. Some heterogeneous catalysts and supports have been analyzed.

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Untersuchung von durch anodische Oxydation erzeugten Aluminiumoxidschichten

Zusammenfassung An Hand von derivatographischen und röntgenographischen Untersuchungen konnte nachgewiesen werden, da\ die Lösungsgeschwindigkeit von Aluminiumoxidschichten sich wÄhrend der chromsaurenphosphorsauren Extraktion Ändert und sogar die früher für unlöslich gehaltene-Al₂O₃ Phase aufgelöst werden kann. Weiterhin konnte die bei der derivatographischen Untersuchung der anodischen Oxidschichten zwischen 350 und 450 C auftretende anomale thermische Oxydation mit der PorositÄt in Zusammenhang gebracht werden.

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Investigation of aluminium oxide layers formed by anodic oxidation diffractometric

Derivatographic and X-ray spectrographic investigations have shown that the rate of dissolution of aluminium oxide layers varies during the extraction with chromic/phosphoric acid mixture and that even the-Al₂O₃ phase can be dissolved which hitherto was regarded as insoluble. Furthermore, the derivatographic examination of the anodic oxide layers revealed a relation between the anomalous thermal oxidation occurring between 350 and 450 C and the porosity.

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Teil I: diese Z.200, 218 (1964).     

Effect of the roughness factor on the surface oxidation of ruthenium catalysts

The surface oxidation of ruthenium catalysts with different roughness factor values has been analyzed. It is shown that electro formation of oxidized species on the exposed surface of ruthenium is strongly affected by the rougher characteristics of the surface. This effect has been explained through the addition and removal of protons to and from the oxidized species.

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Relaxation of the rate of o-xylene oxidation to phthalic anhydride on vanadium catalysts

Based on numerical analysis of experimental data, the main ideas of the reaction mechanism have been confirmed and kinetic principles of the non-steady=state reaction have been determined.

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, .

     

Measurement of specific heat and energetic characterization of materials up to high temperatures

A new DSC system has been developed which not only allows quantitative results in the temperature of –160C to 700C, but also allows the quantitative determination of a variety of material properties up to 1500C. For example, the specific heat of materials can be measured to at least 1400C, while enthalpies, etc. can be measured to 1500C.

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Zusammenfassung Ein neuartiges DSC Messystem (Netzsch DSC 404) wurde entwickelt, das sich durch hohe Reproduzierbarkeit der Basislinie, grosse Empfindlichkeit und breiten Temperaturanwendungsbereich (–160C bis 700C resp. bis 1500C) auszeichnet. Die Messanordnung ermöglicht die Verwendung von unterschiedlichen GasatmosphÄren als auch Messungen im Vakuum. Es werden Beispiele der Bestimmung von SchmelzvorgÄngen, der Glasumwandlungstemperatur, der KristallinitÄt und der spezifischen WÄrme, sowohl für Polymere als auch für anorganische Materialien dargestellt und diskutiert.

     

Growth transition and morphology change in polypropylene

The growth rate of isotactic polypropylene is deduced from microscopic observations during isothermal crystallizations. A change in the growth regime is observed at 138 C and interpreted as a Regime III Regime II transition, according to Hoffman's kinetic theory of polymer crystallization. A Regime II Regime I transition is also theoretically predicted at 155 C, i. e. at a temperature outside the investigated temperature range. The Regime III Regime II transition is related to the positive to negative change in the spherulite birefringence, which is generally attributed to a change in the organization of crystalline lamellae: quadritic arrays of intercrossing lamellae atT _c < 138 C (Regime III) and preferentially radiating lamellae atT _c > 138 C (Regime II). It is suggested that such a morphological change could be interpreted using the concept of non-adjacent re-entry introduced in Hoffman's kinetic theory. This interpretation could also explain the interspherulitic ruptures observed in negative spherulites.     

Molecular orbital calculations of rotational strengths: A study of skewed diketones

A skewed glyoxal molecule is considered as a model for the study of the optical activity of -diketones. The rotational strengths are calculated for various angles of twist, between trans (=0) and cis ( = 180). The wavefunctions are computed both by the extended Hückel method and by the SCF-CNDO method, considering all 22 valence electrons. The effect of configuration interaction is studied. All two-center terms are included in the calculation of the electric and magnetic transition moments. The results predict the rotational strength of the lowest transition to be negative for 0 < < 90 when the molecule is twisted in a right-handed way and to be positive for 90 < < 180. In general, the lowest transition is followed by a transition with opposite rotational strength, in analogy to the predictions of a simple exciton model.

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Zusammenfassung Ein aus der ebenen Lage gedrehtes Glyoxalmolekül wird als Modell zum Studium der optischen AktivitÄt von -Diketonen betrachtet. Die RotationsstÄrken werden für verschiedene Drehwinkel ermittelt, zwischen trans ( = 0) und cis ( =180). Die Berechnung der Wellenfunktionen erfolgt sowohl nach der erweiterten Hückelmethode als auch nach dem SCF-CNDO-Verfahren, unter Berücksichtigung aller 22 Valenzelektronen. Der Einflu\ der Konfigurationswechselwirkung wird studiert. Die Berechnung der elektrischen und magnetischen übergangsmomente schlie\t alle Zweizentren-BeitrÄge ein. Die Resultate zeigen, da\ die RotationsstÄrke des langwelligsten übergangs im Falle eines rechtsgedrehten Moleküls negativ ist für 0 < < 90 und positiv für 90 < < 180. Im allgemeinen wird der langwelligste übergang von einem übergang mit entgegengesetzter RotationsstÄrke gefolgt, in Analogie zu den Voraussagen eines einfachen Exziton-Modells.

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Résumé Une molécule de glyoxale non-plane est considérée comme modèle pour l'étude de l'activité optique de -dicétones. Les forces rotatoires sont calculées pour différents angles de torsion, entre la position trans (=0) et cis (=180). Les fonctions d'onde sont calculées par les méthodes extended Hückel, ainsi que SCF-CNDO, en considérant les 22 electrons de valence. L'effet de l'interaction de configurations est étudié. Tous les termes bicentriques sont inclus dans le calcul des moments de transition électriques et magnétiques. Les résultats montrent que la force rotatoire de la transition de plus basse fréquence est négative pour 0 < < 90 dans une molécule tournée en sens droit et positive pour 90 < < 180. En général, la transition de plus basse fréquence est suivie d'une transition dont la force rotatoire est opposée, en analogie aux prédictions d'un simple modèle exciton.

     

Nitric oxide disproportionation on chabazite tuff

The catalytic activity of a chabazite tuff in the reaction 4NON₂O+N₂O₃ was investigated in flow conditions at temperatures between –78 °C and +85 °C. The Ca or Na enriched samples are much more active than the natural tuff; the steady state NO conversion increases with decreasing temperature.

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4NON₂O+N₂O₃ –78°C +85°C. , Ca Na , ; NO .

     

Selective hydrogenation of fatty oils on alloyed Ni?Al catalyst. I. Kinetic model

On the basis of literature data concerning the reaction mechanism, a kinetic model for the selective hydrogenation of cotton-seed oil on the S-3 commercial alloyed Ni–Al catalyst is suggested. Its parameters have been identified according to the experimental data obtained in an agitated slurry reactor at T=140–200°C and P=0.2–0.8 MPa.

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, C-3. , , t=140–120°C, P=0.2–0.8 .