Electrostatic potentials of molecules and prediction of the lewis acid-base properties of solvents,part II. Application of electrostatic parameters

Summary Electrostatic parameters,UN andUP, introduced previously, have been applied to predict solvent acid and base properties. TheUN parameter correlates well with the electrostatic component of solvent basicity. This parameter also significantly improves correlations between Koppel-Paju, Kamlet-Taft and Gutmann basicity scales. TheUP parameter combined with Mullikan charges at hydrogen atoms of the solvent molecules allows an estimation of solvent acidity parameters in the frame of the two-parameter similarity model. The results show that parameters computed with the MNDO method for isolated molecules are suitable for molecules of nonaqueous solvents in liquid state.

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Elektrostatische Potentiale von Molekülen und Voraussage von Lewis-Säure-Base-Eigenschaften von Lösungsmitteln, 2. Mitt.: Anwendung elektrostatischer Parameter

Zusammenfassung Die in der vorhergehenden Arbeit eingeführten elektrostatischen ParameterUN undUP wurden zu Vorhersagen von Säure- und Base-Eigenschaften von Lösungsmitteln angewandt. DerUN-Parameter korreliert gut mit der elektrostatischen Komponente der Lösungsmittelbasizität und verbessert auch signifikant Korrelationen zwischen der Koppel-Paju, Kamelt-Taft und Gutmann'schen Basizitätsskala. DerUP-Parameter, in Kombination mit Mullikan-Ladungen an den Wasserstoffatomen der Lösungsmittelmoleküle, erlaubt die Abschätzung von Solvens-Aciditäts-Parametern im Rahmen eines Zweiparameter-Vergleichsmodells. Die Ergebnisse zeigen, daß die über die MNDO-Methode für isolierte Moleküle berechneten Parameter zur Beschreibung von nichtwäßrigen Lösungsmitteln geeignet sind.

     

Isomerization and Decomposition of a Criegee Intermediate in the Ozonolysis of Alkenes: Dynamics Using a Multireference Potential

The isomerization and decomposition dynamics of the simplest Criegee intermediate CH₂OO have been studied by classical trajectory simulations using the multireference ab initio MR‐PT2 potential on the fly. A new, accelerated algorithm for dynamics with MR‐PT2 was used. For an initial temperature of 300 K, starting from the transition state from CH₂OO→CH₂O₂ , the system reaches the dioxirane structure in around 50 fs, then isomerizes to formic acid (in ca. 2800 fs), and decomposes into CO+H₂O at around 2900 fs. The contributions of different configurations to the multiconfigurational total electronic wave function vary dramatically along the trajectory, with diradical contributions being important for transition states corresponding to H‐atom transfers, while being only moderately significant for CH₂OO. The implications for reactions of Criegee intermediates are discussed.     

The sporothriolides. A new biosynthetic family of fungal secondary metabolites

The biosynthetic gene cluster of the antifungal metabolite sporothriolide 1 was identified from three producing ascomycetes: Hypomontagnella monticulosa MUCL 54604, H. spongiphila CLL 205 and H. submonticulosa DAOMC 242471. A transformation protocol was established, and genes encoding a fatty acid synthase subunit and a citrate synthase were simultaneously knocked out which led to loss of sporothriolide and sporochartine production. In vitro reactions showed that the sporochartines are derived from non-enzymatic Diels–Alder cycloaddition of 1 and trienylfuranol A 7 during the fermentation and extraction process. Heterologous expression of the spo genes in Aspergillus oryzae then led to the production of intermediates and shunts and delineation of a new fungal biosynthetic pathway originating in fatty acid biosynthesis. Finally, a hydrolase was revealed by in vitro studies likely contributing towards self-resistance of the producer organism.

A new family of fungal biosynthetic pathways is elucidated based on the use of fatty acid and citrate-like intermediates.

Gamma-lactone and alkyl citrate compounds derived from oxaloacetate are widespread natural products in fungi and often possess potent biological activities. Examples include sporothriolide 1,^1,2 piliformic acid 2,³ tyromycin 3⁴ and the cyclic maleidrides including byssochlamic acid 4^5,6 among others (Fig. 1). In some cases, for example those of 4 and squalestatin S1 5,⁷ detailed molecular studies have revealed that a dedicated polyketide synthase (PKS) produces a carbon skeleton that is then condensed with oxaloacetate by a citrate synthase (CS) to give an early alkyl citrate intermediate that is further oxidatively processed. In other cases, such as 1 and the sporochartines 6, the biosynthetic pathways are not yet clear.Open in a separate windowFig. 1Structures of γ-lactone and alkyl citrate metabolites from fungi. Bold bonds show oxaloacetate-derived carbons where known.Sporochartines 6a–6d^8,9 from the fungus Hypoxylon monticulosum CLL 205 (now referred to as Hypomontagnella spongiphila)¹⁰ possesses potent cytotoxicity (IC₅₀: 7.2 to 21.5 μM) vs. human cancer cell lines and are proposed to be Diels Alder (DA) adducts of the furofurandione sporothriolide 1, itself a potent antifungal agent (EC₅₀: 11.6 ± 0.8 μM),¹¹ and trienylfuranol A 7,¹² originally obtained from an endophytic fungus Hypoxylon submonticulosum DAOMC 242471 (now referred to as Hypomontagnella submonticulosa).¹³ Since the biosynthesis of sporothriolide 1 and related compounds is unknown, and biological DA reactions in fungi are currently of high interest,¹⁴ we decided to examine the biosynthesis of the sporochartines 6 in the Hypomontagnella spp. strains MUCL 54604 and CLL 205 (ref. 10 and 13) in detail.     

Spectrophotometric studies on the solvatochromism of the Fe(CN)2(phen)2 complex

Summary The solvatochromic behaviour ofbis-(cyano)-bis-(9,10-phenanthroline)-iron(II) has been reexamined spectrophotometrically in a series of 19 solvents including water, alcohols and dipolar. aprotic media. Satisfactory correlations between the wave numbers of the long-wavelength band and solvent acceptor numbers are obtained in all media; only values, for carboxylic acids deviate from the regression line.

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Spektrophotometrische Untersuchungen über die Solvatochromie der Komplexverbindung Fe(CN)₂(phen)₂

Zusammenfassung Das solvatochrome Verhalten vonbis-(Cyano)-bis-(9,10-phenanthrolin)-eisen(II) wurde in 19 Lösungsmitteln, darunter Wasser, Alkohole und dipolare aprotische Medien, spektrophotometrisch überprüft. In allen Medien wurden zufriedenstellende Korrelationen zwischen den Wellenzahlen der langwelligen Bande und den Akzeptorzahlen der Lösungsmittel erhalten; lediglich die Werte für Carbonsäuren weichen von der Ausgleichgeraden ab.

     

Minimum Number of Palettes in Edge Colorings

A proper edge-coloring of a graph defines at each vertex the set of colors of its incident edges. This set is called the palette of the vertex. In this paper we are interested in the minimum number of palettes taken over all possible proper colorings of a graph.     

Development of an LC–MS/MS method for analysis of interconvertible Z/E isomers of the novel anticancer agent, Bp4eT

This study was focused on a liquid chromatography/tandem mass spectrometry (LC/MS/MS) method development for quantification of a novel potential anticancer agent, 2-benzoylpyridine 4-ethyl-3-thiosemicarbazone (Bp4eT), in aqueous media. Solid Bp4eT was found to consist predominantly of the Z isomer, while in aqueous media, both isomers coexist. Sufficient separation of both isomers was achieved on a Synergi 4u Polar RP column with a mobile phase composed of 2 mM ammonium formate, acetonitrile, and methanol (30:63:7; v/v/v). The photo diode array analysis of both isomers demonstrated different absorption spectra which hindered UV-based quantification. However, an equal and reproducible response was found for both isomers using an MS detector, which enables the determination of the total content of Bp4eT (i.e., both E− and Z− isomeric forms) by summation of the peak areas of both isomers. 2-Hydroxy-1-naphthylaldehyde 4-methyl-3-thiosemicarbazone (N4mT) was selected as the internal standard. Quantification was performed in selective reaction monitoring using the main fragments of [M+H]⁺ (240 m/z for Bp4eT and 229 m/z for N4mT). The method was validated over 20–600 ng/ml. This procedure was applied to a preformulation study to determine the proper vehicle for parenteral administration. It was found that Bp4eT was poorly soluble in aqueous media. However, the solubility can be effectively improved using pharmaceutical cosolvents. In fact, a 1:1 mixture of PEG 300/0.14 M saline markedly increased solubility and may be a useful drug formulation for intravenous administration. This investigation further accelerates development of novel anticancer thiosemicarbazones. The described methods will be useful for analogs currently under development and suffering the same analytical issue.     

Thermal characteristics analysis of an IGBT using a fiber Bragg grating

This paper proposes a new method to develop a thermal model of an insulated gate bipolar transistor (IGBT) employing an optical fiber sensor mounted on the chip structure. Some features of the sensor such as electromagnetic immunity, small size and fast response time, allow the identification of temperature changes generated by the energy loss during device operation through direct measurement. In fact, this measurement method is considered impossible with conventional sensors. The online monitoring of the junction temperature enables identify the thermal characteristics of the IGBT. The results are used to develop an accurate model to simulate the heat generated during the device conduction and switching processes. The model showed a difference of only 0.3% between the measured and simulated results, besides allowing evaluate separately the heat generated by each turn-ON/OFF process.     

Kaluza,Klein, confinement,and nuclear forces

The nonsymmetric Kaluza-Klein and Jordan-Thiry theories are reviewed as interesting propositions of physics in higher dimensions. It is shown how a dielectric model of confinement can be derived from interference effects in these theories. It is postulated that the old puzzle of nuclear physics,-particles, can be connected to the skewon fieldg _[v] and the scalar field in the nonsymmetric Jordan-Thiry theory. Similarities are pointed out between the nonsymmetric Jordan-Thiry Lagrangian in the flat space limit and the soliton bag model Lagrangian. Finally the nonsymmetric Jordan-Thiry Lagrangian is proposed as the bosonic part of the strong interaction Lagrangian.On leave of absence from the Institute of Philosophy and Sociology of the Polish Academy of Science, 00-330 Warsaw, Poland.     

Type-I Intermittency and Crisis-Induced Intermittency in a Semiconductor Laser under Injection Current Modulation

The dynamics of a negative gain suppression factor laser diode subjectedto injection current modulation is similar to that of a damped nonlinearoscillator under periodic forcing. Quasi-periodicity, frequency lockingand chaos may be present, depending on the values of the forcingparameters. We have found, for some parameter values, type-Iintermittent behavior and crisis-induced intermittency. Scaling lawswere obtained for the duration of the laminar phase and the chaos-chaosswitchings, respectively. The scale exponents are very close to thoseexpected for one-dimensional unimodal maps.