Catchment region partitioning of energy hypersurfaces,I

The space of internal coordinates of a molecular system is partitioned into catchment regions of various critical points of the energy hypersurface. The partitioning is based on an ordering of steepest descent paths into equivalence classes. The properties of these catchment regions and their boundaries are analyzed and the concepts of chemical structure, reaction path and reaction mechanism are discussed within the framework of the Born-Oppenheimer and energy hypersurface approximations. Relations between catchment regions and the chemically important reactive domains of energy hypersurfaces, as well as models for branching of reaction mechanisms, caused by instability domainsD , 1, are investigated.     

Über spasmolytisch wirksame 1-Phenyl-isochinoline und Bis-(phenyläthyl)-amine mit Guajacyl-gruppierung

Zusammenfassung Die Synthese des 1-Phenyl-6-methoxy-7-oxy-isochinolins, des1-(3-Methoxy-4-oxy-phenyl)-6-methoxy-7-oxy-isochinolins sowie des1-(3,5-Dimethoxy-4-oxy-phenyl)-6-methoxy-7-oxy-isochinolins wird beschrieben. Als weitere Spasmolytika wurden das Bis-(3-methoxy-4-benzyloxy--phenyläthyl)-amin, dessen N-Methylderivat und das Bis-(3-Methoxy-4-oxy--phenyläthyl)-amin dargestellt. Vereinfachte Synthesen der Ausgangsprodukte, Benzylsyringasäure, Syringaaldehyd und Benzylsyringaaldehyd, wurden ausgearbeitet. K. Kratzl undG. Billek, Mh. Chem.83, 1409 (1952).     

Computational study on the working mechanism of a stilbene light-driven molecular rotary motor: sloped minimal energy path and unidirectional nonadiabatic photoisomerization

The working mechanism of a geometrically overcrowded, chiral stilbene light-driven molecular rotary motor [(2R,2R)-2,2',7,7'-tetramethyl-1,1'-bis(indanylidene), 3] has been investigated by a potential energy surface (PES) study. The reaction paths of the two photoinitiated cis-trans (or E/Z) isomerization processes, namely, (P,P)-stable-cis→(M,M)-unstable-trans-3 and (P,P)-stable-trans→(M,M)-unstable-cis-3, have been explored at the CASPT2//CASSCF level of theory. The minimal energy reaction paths (MEPs) of these two processes are nearly parallel on the PESs, separated by a ridge of high inversion barrier. The MEPs have a remarkably steep slope, which drives C═C bond rotation unidirectionally. The asymmetric bias on the excited-state MEPs is caused by the substituents on the "fjord" region as well as by the phenyl moieties. The overall photoisomerization reaction can be described as a three-state (1B→2A→1A) multimode mechanism: The molecule excited to the 1B state first crosses one of the sloped 1B/2A seams, and then follows two cooperative torsional reaction modes to cross preferentially one of the two 2A/1A conical intersections to reach the isomerized ground-state product.     

Kinetics of oxidative regeneration of zeolites

The analysis of the kinetic data on the oxidation of nondesorbed macromolecules in NaX zeolites confirms a hypothesis concerning two mechanisms of deactivation of microporous adsorbents in multicycle processes. An equation to describe the kinetics of two-stepoxidation of nondesorbed substances is suggested.

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NaX. . , .

     

Flow injection chemiluminescence determination of l-cysteine in amino acid mixture and human urine with the BrO3 −–quinine system

In this paper, a novel flow injection chemiluminescence (CL) determination of l-cysteine is proposed. The method is based on the CL reaction of l-cysteine and KBrO₃ in acidic medium. The CL intensity was greatly enhanced in the presence of quinine. The CL intensity was linear with l-cysteine concentration in the range of 0.2–80 g L^–1, and the detection limit was 0.1 g L^–1 (3). A complete analysis, including sampling and injecting, could be performed in 1 min, giving a throughput of about 60 h^–1. The relative standard deviation was 1.6% for 0.8 g L^–1 l-cysteine (n=11). The proposed method was satisfactorily applied to the determination of cysteine in an amino acid mixture and human urine. The mechanism of the CL reaction is also discussed.     

A mathematical model of the logical structure of chemistry. A bridge between theoretical and experimental chemistry and a general tool for computer-assisted molecular design

Summary A mathematical model of the logical structure of chemistry is suggested. The model is based on the phenomenon of convertibility between chemical species which is expressed by the so-called convertibility function . In the center of the model there is the potential energy (hyper)surface, PES. A heuristic modification of the general convertibility function is presented. Several algorithms have been developed for an analysis of PES which is described by paths, and for heuristic obtaining of PES paths. The notion ofK-barrier of conformational PES is introduced as well as an algorithm for its computation.     

Phase transformation of ammonium nitrate by thermal factors and inoculation

The reason for the special thermal behaviour of ammonium nitrate (AN) has been examined. Under certain experimental conditions more transition temperatures were obtained than hitherto found (37–42°, 50° and 86°). With Du Pont DSC curves several exothermic peaks or exothermic oscillations were shown after the endothermic peak at 51°, indicating that phase IV had been transformed to metastable phase III, as a consequence of which the IIIII transformation at 86° also became possible. On repeated cycling the exothermic peak decreased or disappeared if the IIIII transformation had developed to a greater extent. A successful IVIII transformation was induced by inoculation of AN with phase III, an unusual procedure in investigating the phase transformation of AN. The use of the method is obvious with regard to the fact that all transformations are controlled by the rate of nucleation.

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Zusammenfassung Die Ursachen des besonderen thermischen Verhaltens von Ammoniumnitrat (AN) wurden untersucht. Unter gewissen Versuchsbedingungen wurden mehrere Übergangstemperaturen erhalten als bisher gefunden wurden (37°–42°, 51° und 86 °C). An Du Pont DSC Thermogrammen wurden mehrere exotherme Peaks oder exotherme Oszillationen nach dem endothermen Peak bei 51 °C nachgewiesen, welche zeigen, daß die Phase IV in die metastabile Phase III umgewandelt wurde. Infolgedessen wurde die Umwandlung IIIII bei 86 °C ebenfalls möglich. Bei wiederholtem Meßzyklus nahm der exotherme Peak ab oder verschwand, wenn die Umwandlung IIIII sich in größerem Maße entwickelte. Eine erfolgreiche IV III Umwandlung wurde durch Inokulierung mit der Phase III von AN induziert, was ein ungewöhnliches Verfahren bei der Untersuchung der Phasenumwandlung von AN ist. Die Vorteile dieser Methode sind offensichtlich, da sämtliche Umwandlungen durch die Geschwindigkeit der Nuklierung geregelt werden.

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Résumé On a étudié les causes du comportement thermique spécial du nitrate d'ammonium. Dans certaines conditions d'expériences, on a obtenu des températures de transition en plus grand nombre qu'il n'avait été trouvé auparavant (37–42 °C, 51 °C et 86 °C). On a mis en évidence sur des enregistrements obtenus à l'aide d'un appareil d'analyse calorimétrique différentielle DSC Dupont, plusieurs pics exothermiques ou oscillations exothermiques après le pic endothermique à 51°C, ce qui indique que la phase IV a été transformée en phase métastable III. Par conséquent, la transformation IIIII à 86 °C devient également possible. Lors du cyclage répété, le pic exothermique diminue ou disparaît si la transformation IIIII s'est développée dans une plus grande mesure. On induit avec certitude une transformation IVIII en inoculant le nitrate d'ammonium avec la phase III, procédure insolite dans l'étude des transformations de phases du nitrate d'ammonium. L'avantage de la méthode est évident, puisque toutes les transformations sont contrôlées par la vitesse de nucléation.

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. , (37–42°, 51° 86 °C). , , 51°C, , IV - III, 86 ° IIIII. , IIIII . IVIII , III, . , .

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The author is grateful to Prof. Z. G. Szabó for helpful criticism and for valuable discussions.     

Abhängigkeit der freien Enthalpie-Änderung von der Netzebenenzahl bei Bildung von Mikroparakristallen

Zusammenfassung Das anhand vieler sorgfältiger Reflexprofilanalysen abgeleitete ^*-Gesetz läßt sich auch thermodynamisch verstehen, wenn man die Fragilität der Valenzwinkel durch ein entsprechendes MuldenpotentialU einführt. Dies liefert in dem Ausdruck für die ÄnderungG der freien Enthalpie bei Teilchenbildung neben den bekannten, von der Teilchengröße unabhängigen zwei Termen für freie Oberflächenenergie und freie VolümenthalpieG _v einen dritten, mit der ZahlN der Netzebenen wachsenden Summanden. Diese sog. Volum-StörenthalpieA ₀g² N ist also auch abhängig von der relativen statistischen Varianzg der Abständed von Gitterbausteinen benachbarter Netzebenen. Durch Einführung des ^*-Gesetzes ergibt sich die Beziehung ¦G_v¦ /A ₀ K()=0.06 mitK()=356 g² /¯ d¦G_v¦=1–1–. Im Grenzfall=1 ist die kritische Keimgröße gleich der mittleren statistischen Größe der Mikroparakristalle. Dieser Fall wird für Metallschmelzen diskutiert.=0 stellt den anderen Grenzfall der Kristallbildung dar.Herrn Prof. Dr. K. Kobayashi zum 70. Geburtstag zugedacht.     

Platinum traces in airborne particulate matter. Determination of whole content, particle size distribution and soluble platinum

Summary During a period of almost one year airborne dust was collected at the area of ISAS, Dortmund. The total platinum content varied from 0.6 to 130 µg/kg, respectively from 0.02 to 5.1 pg/m³. The impactor measurements resulted in an equal distribution of platinum in combination with particle sizes ranging between 0.5 and 8 µm. The lowest concentrations were observed for the larger particles (>8m). The soluble platinum in airborne dust was determined to be 30 to 43% of the total amount of platinum and 2.5 to 6.9% in tunnel dust.Dedicated to Professor Dr. Wilhelm Fresenius on the occasion of his 80th birthday     

Gas-phase electronic absorption spectroscopy of substituted bis(η<Superscript>6</Superscript>-benzene)chromium derivatives: Rydberg transitions in bis(η<Superscript>6</Superscript>-anisole)chromium and bis(η<Superscript>6</Superscript>-2,6-dimethylpyridine)chromium

Gas-phase electronic absorption spectra of chromium bisarene complexes with oxygen- and nitrogen-containing ligands, (⁶-PhOMe)₂Cr (1) and (⁶-2,6-Me₂C₅H₃N)₂Cr (2), were first measured. Rydberg bands disappearing on going to the condensed-phase spectra were revealed. The first ionization potentials of complexes 1 and 2 (5.30 and 5.40 eV, respectively) were determined from the Rydberg frequencies. The Rydberg transitions were assigned and the corresponding Rydberg term values and quantum defects were determined. The effect of heteroatoms on the Rydberg structure parameters was revealed by comparing the spectra of complexes 1 and 2 with those of unsubstituted analogs. The appearance, in the ligand side chain, of an oxygen atom capable of being involved in conjugation with the -electron system of the aromatic ring results in substantial broadening of the observed Rydberg bands. This can be associated with an increased ligand contribution to the HOMO of the sandwich compound. The influence of the oxygen atom on the ionization energy of the molecule is insignificant. In contrast to this, introduction of a nitrogen atom into the carbocycle leads to a noticeable increase in the ionization potential of the molecule, while the ligand contribution to the HOMO of the complex remains practically unchanged.Based on materials of a lecture presented at the International Conference Modern Trends in Organoelement and Polymer Chemistry dedicated to the 50th anniversary of the A. N. Nesmeyanov Institute of Organoelement Compounds of the Russian Academy of Sciences (Moscow, May 30–June 4, 2004).Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1854–1859, September, 2004.     

Direction of nucleophilic substitution in α, β-unsaturated imino compounds with a donor substituent in the beta position

A mechanism of conversion of -aminovinyl ketones into -aminovinylimines is disclosed. It has been found that in this and a series of other reactions (various conversions of -aminovinyl ketones, -aminovinylimines, and -alkoxyvinylimino salts and their vinyl analogs, cyano compounds, etc.), the intermediate determining the course of the reaction is an ,-unsaturated imino cation. The result of the reaction depends on the site and efficiency of the nucleophilic attack by tautomeric imino salt compounds possessing an unshared electron pair distributed over the various electrophilic sites of the molecule.     

Solid-Phase Extraction with Slurry Injection of the Resin Into ETAAS for Trace Determination of Thallium in Natural Water

Thallium in natural water samples was determined by electrothermal atomic absorption spectrometry after 1000-fold enrichment by mini solid-phase extraction from a 100-mL sample solution. A Tl-pyrrolidine-1-carbodithioate complex formed in a sample solution of pH 1.6 was extracted on fine particles of a cellulose nitrate resin dispersed in the sample solution. The cellulose nitrate resin was then collected on a membrane filter (25mm^ø) by filtration under suction using a glass funnel with an effective filtration area of 0.64cm². As a result, a circular thin layer of the resin phase with a diameter of 9mm was obtained. Then the resin phase was carved out by an acrylate resin puncher with a 10-mm^ø hole to put it into a sample cup containing 100µL of 10mM HNO₃ containing 0.5mM NaCl. The resin phase was suspended in the solution by ultrasonication. 1000-fold enrichment was thus attained within 15min, and the suspension was delivered to electrothermal atomic absorption spectrometry. The linear calibration graph was obtained in the range of 0–4ng of Tl in 100mL of a sample solution. The detection limit obtained by 3 method was 0.19ng. The proposed method was applied to the determination of Tl in natural water samples. The results showed the concentration of Tl in seawater was 12.1±1.8pgmL^–1 for the calibration graph method and 12.6±1.4pgmL^–1 for the standard addition method. A snowmelt sample contained 20.7±1.0pgmL^–1 of Tl.     

Formation mechanism of anomalous “golf ball-like” composite polymer particles by seeded emulsion polymerization

Recently, the authors found that anomalous polystyrene/polybutyl acrylate composite particles, whose surfaces had many dents, were produced by emulsifier-free seeded emulsion polymerization of butyl acrylate with polystyrene seed particles. Such a particle was named a golf ball-like particle. In this article, the morphology and the formation mechanism of the golf ball-like composite polymer particles were studied.Part CLV of the series Studies on Suspension and Emulsion     

A new computational microscope for molecules: High resolution MEDLA images of taxol and HIV-1 protease,using additive electron density fragmentation principles and fuzzy set methods

Based on the molecular electron density lego assembler (MEDLA) method, a computational microscope was developed that generates accurate images of bodies of large molecules at a resolution far exceeding current experimental techniques. The MEDLA microscope can be tuned to display the high electron density regions of formal chemical bonds; or to show the low density regions of hydrogen bonds and secondary interactions, or to display local shape requirements important in molecular recognition. The power of the method is illustrated by examples of detailed images of taxol, an important anti-cancer agent, and HIV-1 protease, a protein of 1564 atoms. A mathematical framework of the approach, based on fuzzy sets, and the fundamentals of several additional applications of the additive, fuzzy fragmentation principle are presented.     

Negative temperature coefficient phenomenon in exchange reactions between alkene oxides and alkyl-β-hydroxyalkyl sulfides

Conclusions The temperature dependence of the initial rate of the exchange reaction in the propylene oxide-octyl--hydroxyethyl sulfide system shows a maximum and a minimum between 60 and 110C, the maximum at 90C. This behavior may be explained by the participation in the reaction of an associate that is formed from a molecule of propylene oxide and two molecules of hydroxyethyl sulfide. Computer calculations have been made for this scheme of the reaction over a wide temperature range.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 1, pp. 51–57, January, 1985.     

Trimeric Mechanism of Proton Transfer in Imidazole

The energy, electronic, and structural characteristics of the tautomeric transformation of imidazole were calculated by the quantum-chemical semiempirical AM1 method. It was concluded on the basis of the calculated data that proton transfer in the tautomeric transformation 1H-imidazole3H-imidazole can take place by a trimeric mechanism.     

Some transformations of α,ω-bis(1,3-thiazan-2-thion-4-on-3-yl)alkanes

The reaction of ,-bis(1,3-thiazan-2-thion-4-on-3-yl)alkanes with hydrazine gives the corresponding ,-di(4-thiosemicarbazido)alkanes, which are readily acylated. Subsequent dehydration of the acylation products gives the corresponding 5,5-dialkyl-,-bis(2,3-dihydro-1,2,4-triazole-3-thion-4-yl)alkanes, which are converted to 5,5-dialkyl- , -bis (1,2,4-triazol4-yl)alkanes by known methods. The UV and ER spectral data are presented.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 8, pp. 1060–1062, August, 1977.     

Order and structure of the outer valence MO'S of some derivatives of pentafluorobenzene

Conclusions According to the data from the photoelectron spectra and the MNDO calculations, the orbitals of the functional group and the upper -orbitals of the ring in the compounds C₆F₅X with X=NCO and N₃ interact; however, their interaction is less effective than the interaction in the molecules of the hydrocarbon analogs; when X=NO₂, NO, CHO, COCH₃, COCF₃, and CF₃, the orbitals of the substituent and the upper orbitals of the ring do not interact.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 4, pp. 861–865, April, 1989.We thank A. A. Bliznyuk and A. A. Voityuk, for supplying the MNDO-86 program.     

Use of a stopped-flow technique for investigation and determination of thiourea and its <Emphasis Type="Italic">N</Emphasis>-methyl derivatives as inducers of the iodine–azide reaction

A stopped-flow technique has been used to investigate the behaviour of 2-thiourea, 1-methyl-2-thiourea, 1,3-dimethyl-2-thiourea, and 1,1,3,3-tetramethyl-2-thiourea in the induced iodine–azide reaction. This technique enables the progress of the reaction to be followed by monitoring the decrease in the absorbance of the iodine–starch complex at 595 nm. The effect of the concentration of the reagents on the rate of the reaction was investigated and a kinetic method for determination of the compounds is proposed. 2-Thiourea, 1-methyl-2-thiourea, and 1,3-dimethyl-2-thiourea can be determined in the range 3–75 mol L^–1 and 1,1,3,3-tetramethyl-2-thiourea in the range 2–200 mol L^–1.     

Effect of molecular size on the threshold energy producing a51Cr hot atom

The lowest retention values of⁵¹Cr hot atom in various forms of the -diketonetype complexes, Cr(bzac)₃, Cr(dpm)₃ and Cr(dbm)₃, as well as Cr(acac)₃ as a reference, were obtained in the experimental condition in which they are regarded as the primary retentions. From these retention values, the threshold energies for producing a hot atom, the appearance energies, were estimated using the calculated relationship between the primary retention and appearance energy, which was obtained by the recoil energy spectra computed by the method recently developed by us. The appearance energy increased steeply with increasing molecular weight of the complex. A theoretical interpretation for this result was attempted by setting a model in which a hot atom is produced in the center of the complex and receives the stopping action by the surrounding ligand molecule. The agreement between the observed and calculated values was good.