Chromatographic determination of D-amino acids as native constituents of vegetables and fruits

Summary Free D-amino acids (D-AA) were detected as native constituents in juices of vegetables (cultivars of cabbage, tomato, carrot, garlic) and fruits (organes, clementine, grapefruit, lemon, apples, pear, grapes) using gas chromatography (GC) or high-performance liquid chromatography (LC). For investigation by GC, AA enantiomers were converted into theirN(O)-pentafluoropropionyl 2-propyl esters and resolved on a Chirasil-L-Val capillary column. For determination by LC, precolumn derivatization of AA enantiomers usingo-phthaldialdehyde together with the chiral thiolsN-isobutyryl-L-cysteine orN-isobutyryl-D-cysteine and fluorescence detection of the diastereomeric isoindole derivatives, resolvable on an octadecylsilyl stationary phase, were used. D-Ala (0.6–3.8%) was detected in all freshly pressed plant juices usually in the highest relative amounts. Other D-AA detected were D-Asx (0.1–1.9%), D-Glx (0–1.3%), D-Ser (0–1.7%), D-Arg (0.4–1.2%, in grapes, orange, grapefruit, and clementine) and D-Leu and D-Val (1% in cabbage). Absolute amounts of native D-AA were totally 28–57 mol L^–1 in fruit juices, 14.5 mol L^–1 in a tomato juice and 8.5 mol L^–1 in a carrot juice.Presented in part as lecture at 3rd International Congress on Amino Acids, Peptides and Analogues, August 23–27, 1993, Vienna; and as posters at 31st Scientific Meeting of German Society of Nutrition, Giessen, March 17th and 18th, 1994 [19]; and at Analytica Conference, April 19–22, 1994, Munich [20].     

Crystal Structure Study of the Metastable β-modification of Glycine and its Transformation into the α-modification

Crystal structure refinement was performed of the metastable modification of glycine (space gr. P2₁, a = 5.092(2) , b = 6.273(3) , c = 5.384(3), = 113.17(4)°, Z = 2, R = 0.0274). The crystals were obtained by a new method (not described in the literature): they were precipitated from a water solution with the addition of glacial acetic acid. The crystal structure of the glycine modification [space gr. P2₁/n, a =5.106(1) , b = 11.979(5) , c = 5.463(2) , = 111.75(2)°:, Z =4] was refined for comparison. Transition from the to the modification in a damp atmosphere was revealed, resulting in the formation of a strongly strained crystal of a mosaic structure. The orientation of the crystallographic axes in the newly formed crystal of the modification relative to the axes in the initial crystal of the modification was determined. It is shown that as in glycine, the lengths of the intramolecular C—O bonds in the modification are fairly similar [1.248(2) and 1.253(2) ] and the previously found significant difference between them is most likely due to the errors of the photomethod. A comparative analysis of the crystal structures of the and glycine modifications (glycine zwitterion packings and structure of intermolecular hydrogen bond networks) was performed. Data of the analysis are used to discuss the properties of the glycine modifications, the possible reasons for the stability of the modification in dry air, the difficulties of crystal growth from solutions, and the ease of crystallization of the modification under various conditions.     

Chemical algebra. II: Discriminating pairing products

The algebra of stereogenic pairing equlibria is presented in a very general context. Starting from the notions of fuzzy subgroup and conjugacy link, chemical pairing constants between molecular speciesu andv having a skeletal symmetry groupG are formulated as pairing products on aG-Hilbert space. Discriminating pairing productsK are defined by the conditions: K 1 and K = 1 the representative vectors of the paired species areG-equivalent. WhenG has only two elements, the pairing product is always discriminating. For several skeletal symmetries, if the vectors are enantiomorphic (v = u, ² =e, G), thenK is greater than 1 and reaches 1 only ifu is achiral: chirality indexes and general permutational indexes are then defined fromK(u u). The general model is illustrated by some examples.     

Average electron momenta in many-electron atoms

In many-electron atoms, the average electron momentum p represents the mean momentum of a single electron when all the electron motions are averaged. If any two electrons are considered simultaneously, however, the average momentum p splits into two different momenta, low momentum p_< and high momentum p_>. For the 102 atoms He through Lr in their ground states, the momenta p_< and p_> are systematically examined at the Hartree–Fock limit level. It is also shown that the sum p_>+p_< and the difference p_>–p_< of the two momenta constitute upper and lower bounds to the electron-pair relative momentum p₁₂=|p₁–p₂| and to the electron-pair center-of-mass momentum P=|p₁+p₂|/2. The tightness of the bounds is discussed for the 102 atoms.     

The composition of volatile and particulate hydrocarbons in urban air

Summary The hydrocarbon composition of the particle and gas phases in the urban atmosphere has been studied by filtration and parallel adsorption on active charcoal and polyurethane foam (PUF). Gas chromatography (GC) and GC coupled to mass spectrometry (GC-MS) have been used for the analysis of the organic matter extracts obtained with each system. In the case of the particle and PUF samples these extracts were fractionated into aliphatic and aromatic compounds. This approach has allowed to identify up to 247 hydrocarbon molecules showing that C0–C5 alkylbenzenes are the major compounds in the charcoal extracts whereas C14–C23 n-alkanes, C0–C4 alkylnaphthalenes, C0–C4 alkylbiphenyls and C3–C5 alkylbenzenes are those predominantly found in the PUF materials. The particles essentially contain C17–C38 n-alkanes and parent polycyclic aromatic hydrocarbons (PAH). These qualitative differences are paralleled by a progressive concentration decrease from the more to the less volatile hydrocarbons. Thus, the total charcoal extracts average 80 g/m³, the PUF compounds represent 4 /m³ and the particle hydrocarbons 0.7 g/m³. These latter airborne materials are essentially composed of petrogenic residues 0.6 g/m³ (aliphatic fraction) whereas the pyrolytic PAH only involve 0.08 g/m³.     

Zeolite content determination in kaolinic clays via thermal effects

For application in catalysis and adsorption processes, zeolites are synthesized on the surface of spray-dried kaolin microspheres. Various thermal effects are used for the rapid characterization of the zeolite type and content. From DTA measurements, the exothermic lattice break-down peak gives information on the zeolite type and the thermal stability of the sample. Measurements of the heats of immersion by a very simple and quick method allow conclusions about the type and the sorption properties of the zeolite part of the clay. The most precise method to estimate the zeolite content was a standardized technique of desorption and readsorption of water or organic compounds by means of a thermobalance.

---

Zusammenfassung Zur Anwendung in der Katalyse und bei Adsorptinsprozessen werden Zeolithe auf der Oberfläche sprüh-getrockneter Kaolin-Mikrokugeln eingesetzt. Verschiedene thermische Effekte werden zur schnellen Charakterisierung des Zeolith-Typs und -Gehalts genutzt. Der exotherme DTA-peak beim Gitterzusammenbruch liefert Informationen über Zeolith-Typ und thermische Stabilität der Probe. Eine sehr einfache Schnellmethode zur Messung der Immersionswärmen erlaubt Schlussfolgerungen über Typ und Sorptionseigenschaften des zeolithischen Anteils des Tons. Die genaueste Methode zur Bewertung des Zeolithgehalts war eine standardisierte thermogravimetrische Desorptions- und Readsorptions-Methode mit Wasser oder organiscen Verbindungen.

---

, , , . . , . , , . , .

     

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.     

Kinetics and mechanism of elimination of methoxyphenethyl chlorides in the gas phase

The kinetics for the gas phase elimination of o-and m-methoxy-2-phenylethyl chlorides have been investigated over the temperature range of 390-464°C and pressure range of 38–119 Torr. The reactions in seasoned vessels and in the presence of the free radical inhibitor propene, are homogeneous and unimolecular and follow a first-order rate law. The o-anisyl and p-anisyl substituents at the -position of ethyl chloride assist anchimerically the elimination processes. The formation of a cyclic product, benzodihydrofuran, from o-methoxy-2-phenylethyl chloride suggests an intimate ion pair mechanism operating in this reaction.

---

- --2- 390–464°C 38–119 . - , , , . - - - . , , --2- , .

     

Mechanism of the liquid-phase oxidation of diethyl sulfide catalyzed by heteropoly acids

It has been established that in the oxidation of diethyl sulfide by¹⁸O₂ in CH₃C¹⁶O₂H–H₂ ¹⁶O solution at 369 K catalyzed by heteropoly acids, sulfoxide and sulfone with 44–54%¹⁸O enrichment are formed. The process is accompanied by isotope exchange of molecular oxygen.

---

, ¹⁸O₂ CH₃C¹⁶O₂H–H₂ ¹⁶O 369 ¹⁸O 44–54%, .

     

Modification of catalytic properties of silica-supported rhodium

A sharp change in the catalytic properties of rhodium in benzene hydrogenation, propane hydrogenolysis and n-hexane conversion has been found for catalysts prepared via interaction between Rh(CO)₂Cl₂ and silica modified by Sn, Pb, Mo and W ions.

---

, Rh(CO)₂Cl₂ , Sn, Pb, Mo W, , , -.

     

Electronic spectrum and thermal decomposition of nickel(II) complex with bis(N-γ-pyridyl-4-phenylbenzamide-hydrazone)

The unit cell parameters and the space group of the investigated compound were determined by means of X-ray diffraction.Analysis of the diffusion-reflection spectra of the crystalline powder and the absorption spectra of its alcoholic solutions permitted identification and quantitative characterization of the absorption bands of the crystalline complex of NiL₂(ClO₄)₂·3H₂O.Application of differential-thermal analysis allowed determination of the mechanism of thermal decomposition of the compound. From these measurements, the expected configuration of the basic molecule was verified, involving determination of the number of non-coordinated water molecules.

---

Zusammenfassung Mittels Röntgendiffraktionsmethoden wurden Gitterzellenkonstanten sowie die Raumgruppe der untersuchten Verbindung bestimmt. Durch Analyse der erhaltenen Diffusions-Reflexionsspektren von kristallinem Pulver und des Absorptionsspektrums einer alkoholischen Lösung der Verbindung war es möglich, die Absorptionsbanden des Kristallkomplexes NiL₂(ClO₄)₂·3H₂O zu identifizieren und quantitativ zu charakterisieren. Anwendung von Differentialthermoanalyse ermöglicht die Bestimmung des Mechanismus der Zersetzungsreaktion der Verbindung. Durch diese Messungen, einschliesslich der Bestimmung der Anzahl nichtkoordinierter Wassermoleküle, wurde die erwartete Konfiguration des Grundmoleküles überprüft.

---

NiL₂(ClO₄)₂·₂, L-N-- -4- . L-N---4- . , , . . , .

     

Testing the photocatalytic activity of cyanogen-and thiocyanogen-based inorganic polymers

The photocatalytic properties of some cyanogen-and thiocyanogen-based inorganic polymers, such as paracyanogens containing different metals (Hg, Ag, Cu), polythiocyanogens of different iodine contents, polycyanogen and poly (cyanogenthiocyanate), have been tested in two systems. Cu-containing paracyanogen and the iodine-poor polythiocyanogens catalyze the photoreduction of methylviologen under visible light, furthermore the Cu-containing paracyanogen catalyzes the photoreduction of water to hydrogen under UV irradiation.

---

, , , , (Hg, Ag, Cu), , (), . , , , , , , -.

     

Characterization of the redox-reactivity of transition metal oxides by temperature-programmed limited thermal decomposition (TPLTD)

The concept of labile lattice oxygen (LLO) as a consequence of the Mars-Van Krevellen model was reminded, and contrasted with the surface oxygen species. Methods of characterizing of the Me-O bond strength were reviewed emphasizing the temperature-programmed limited thermal decomposition (TPLTD). A series of Ag_xV₂Mo_yO_z was characterized by TPLTD. Two forms of LLO were distinguished. The weaker form is independent on Ag-doping, in contrast to the stronger one. Activation energy of TPLTD of the stronger bound LLO was a linear function of the anion vacancy concentration.

---

Zusammenfassung Aus dem Konzept des labilen Gittersauerstoffs (LLO) als Konsequenz des Mars-Van Krevellen-Modells wird die Rolle der Oberflächen-Sauerstoff-Spezies hervorgehoben. Ein Überblick über die Methoden zur Charakterisierung der Me-O-Bindung wird unter besonderer Betonung der temperaturprogrammierten begrenzten thermischen Zersetzung (TPLTD) gegeben.Eine Reihe Ag _x V₂Mo _y O₂ wurde mittels TPLTD charakterisiert, dabei konnten zwei Arten von LLO unterschieden werden. Die schwächere Form ist im Gegensatz zu der stärkeren unabhängig vom Silbergehalt. Die Aktivierungsenergie der TPLTD der stärker gebundenen LLO hängt linear von der Konzentration der Anionenfehlstellen ab.

---

, - , . Me- . Ag_xV₂Mo_yO_z, . , , . n.

     

Influence of composition and of activation temperature upon the adsorption and thermodesorption of ammonia on aluminium oxide-silica gels

Aluminium oxide gel and aluminium oxide-silica gels of different compositions were prepared and activated at different temperatures. The adsorption of NH₃ was studied in a McBain type balance at 20 torr and 5×10^–3 torr at 25°. The thermodesorption of NH₃ was studied at 5×10^–3 torr between 25 and 550° at a constant heating rate of 4°/min. The desorption was followed by recording the thermogravimetric curve and the pressure oscillations in the system (p — T curve). The influence of composition and activation temperature is discussed. Chemisorption of a monomolecular layer is assumed in three main types of pores, together with the formation of a second monomolecular layer held by hydrogen bonds.

---

Zusammenfassung Aluminiumoxyd und Aluminiumoxyd-Kieselsäure Gele von verschiedener Zusammensetzung wurden erzeugt und bei unterschiedlichen Temperaturen aktiviert. Die Adsorption von NH₃ wurde mit Hilfe einer McBain Waage unter 20 und 5 · 10^–3 Torr Druck bei 25°, weiterhin die Thermodesorption von NH₃ unter 5 · 10^–3 Torr Druck zwischen 25 und 550° mit 4°/Min. Aufheizungsgeschwindigkeit untersucht. Die Desorption wurde durch die thermogravimetrische Kurve und durch Registrieren der Druckschwankungen in dem System (p — T Kurve) verfolgt. Man diskutiert den Einfluß von Zusammensetzung und Aktivierungstemperatur. Man nimmt eine Chemisorption einer monomolekularen Schicht in drei Porenhaupttypen gemeinsam mit der Ausbildung einer zweiten durch Wasserstoffbindungen gebundenen monomolekularen Schicht an.

---

Résumé On a préparé des gels d'oxyde d'aluminium et des gels de silice et d'oxyde d'aluminium de diverses compositions; les préparations ont ensuite été activées à différentes températures. On a étudié l'adsorption de NH₃ à l'aide d'une balance de type McBain à 25° sous des pressions de 20 et de 5.10³torr ainsi que la désorption thermique sous 5.10^–3 torr entre 25 et 550° avec une vitesse de chauffage de 4°/mn. On a suivi la désorption en enregistrant les courbes thermogravimétriques et les oscillations de pression dans le système (courbesp — T). On a discuté l'influence de la composition et de la température d'activation. On suppose une chemisorption d'une couche monomoléculaire dans trois types principaux de pores ainsi que d'une seconde couche monomoléculaire maintenue par ponts d'hydrogène.

---

- . (NH₃) 20 . . 5 · 10^–3 . . 25°. 5 · 10^–3 . . 25° – 550° 4°/ . (p—T ). . , , .

     

Analytical investigation of a four-variable model of the BZ reaction

It is proved analytically that the four-variable model reported in the preceding paper [1] has a unique stationary solution for each set of rate constants. An upper and a lower boundary for the stationary concentrations are established.

---

, , , . .

     

Phase diagrams of MgF2-(Y,Ln)F3 systems

By means of thermal and X-ray analyses with oxygen control, 14 phase diagrams of the systems MgF₂-(Y, Ln)F₃ have been obtained, where Ln are all lanthanides except Pm and Eu. All the systems are eutectic. Solid solutions up to 12 mole% MgF₂, which decompose by the eutectoid scheme, were detected based on high-temperature modifications of trifluorides of Y, Er, Tm, Yb and Lu, with a structure of the-YF₃ type.

---

Zusammenfassung Durch Einsatz der Thermo- und Röntgenanalyse mit Sauerstoffkontrolle wurden 14 Phasendiagramme der Systeme MgF₂-(Y, Ln)F₃ erhalten, wobei Ln sämtliche Lanthanoide mit Ausnahme von Pm und Eu sind. Alle Systeme zeigten sich eutektisch. Feste, sich nach dem eutektoiden Schema zersetzende Lösungen bis zu 12 Mol% MgF₂ wurden an Hand der Hochtemperatur-Änderungen der Trifluoride von Y, Er, Tm, Yb, Lu mit-YF₃-Struktur nachgewiesen.

---

Résumé 14 diagrammes de phases des systèmes MgF₂ — (Y, Ln) F₃, où Ln représente tous les lanthanoïdes à l'exception de Pm et Eu ont été établis par études aux rayons X et analyse thermique, avec contrôle de l'oxygène. Tous ces systèmes présentent un eutectique. Des solutions solides jusqu'à 12 moles % de MgF₂ à décomposition eutectoïde ont été décelées à l'aide des transitions à haute température des trifluorures d'Y, Er, Tm, Yb et Lu du type-YF₃.

---

- , 14 MgF₂ — (Y, Ln)F₃, Ln- , u. -. 12 .% MgF₂, , Y, r, Tm, Yb, Lu, -YF₃.

     

Kinetics of dehydration and thermal decomposition of Sr(NO3)2.4H2O and its deuterated analogue with a view to obtaining SrO

The kinetics and mechanism of thermal dehydration of Sr(NO₃)₂.4H₂O and its deuterated analogue were studied by means of DTA, TG and DSC. The temperatures, enthalpies and weight losses of phase transitions were measured. The dehydration occurs in a stepwise manner, and the composition of the intermediate depends on the rate of thermal decomposition. The kinetic parameters (E ^* andZ) for the two steps of dehydration at a heating rate of 5 deg min^–1 were calculated. A correlation was found between the dispersity of the end-product of the thermal decomposition (SrO) and the conditions of its preparation.

---

Zusammenfassung Kinetik und Mechanismus der thermischen Entwässerung von Sr(NO₃)₂.4H₂O und der deuterierten Verbindung Sr(NO₃)₂.4D₂O wurden mittels TG-DTA und DSC untersucht. Temperaturen, Enthalpien und Gewichtsverluste der Phasenumwandlungen wurden gemessen. Der Prozess verläuft stufenweise, die Zusammensetzung des Zwischenprodukts hängt von der Zersetzungsgeschwindigkeit ab. Die kinetischen ParameterE ^* undZ der beiden Entwässerungsstufen bei einer Aufheizgeschwindigkeit von 5 Grad min^–1 wurden berechnet. Zwischen der Dispersität des Endproduktes SrO und seinen Bildungsbedingungen wurde eine Korrelation gefunden.

---

, . . , . , 5 /, E Z. .

     

Die analytische Charakteristik des k?uflichen und des gereinigten Schwefels

Ohne ZusammenfassungVortrag, gehalten auf der Tagung der Gesellschaft Deutscher Chemiker — Fachgruppe Analytische Chemie — am 25. Oktober 1958 in Marburg/Lahn.Dissertation, Chemisches Institut der Universität Köln.     

A new concept explaining catalytic synergy between two solid phases

We propose a new mechanism for explaining the synergy between MoS₂ and Co₉S₈ in hydrodesulfurization. We suppose that spill-over hydrogen produced by Co₉S₈ exerts an effect ofremote control on the active center of MoS₂, a slight reduction leading to hydrogenation centers and stronger reduction to hydrodesulfurization centers.

---

MoS₂ CoS₈ . , , CO₉S₈, MoS₂, , , , .