Trans or (Unusual) Cis Geometry in d(2) Octahedral Dioxo Complexes. A DFT Study

Geometry optimization of the cis and the trans isomers of several octahedral dioxo complexes of d(2) electronic configuration are performed using the gradient-corrected density functional theory (B3LYP and, for some key structures, BP86). With only monodentate sigma donor ligands (ReO(2)(NH(3))(4)(+), 7), the usual energy order is found (i.e., the trans isomer is the most stable). Complexes with a chelating bidentate ligand, OsO(2)(OCH(2)CH(2)O)(NH(3))(2) (10) and ReO(2)(HN=CHCH=NH)(NH(3))(2)(+) (11), are used as models for the experimental complexes 5 and 2 in which the arrangement of the O=M=O unit is trans and cis, respectively. Our calculations actually show an inversion of the relative energy of the two isomers in going from 10 to 11: while the trans isomer is found to be the most stable in 10, the unusual cis diamagnetic isomer is favored by about 29 kcal mol(-)(1) in 11. This result is traced to the geometric and electronic properties of the bidentate ligand, in particular an acute bite angle and good pi acceptor character. In complex 14 with a bipyridine chelating ligand (weaker pi acceptor than diaza-1,4-butadiene in 11), this energy difference is, however, reduced to 7.5 kcal mol(-)(1) (partial geometry optimization).     

Quadrupole mass spectrometric study of positive ions from RF plasmas of pure CH4, CH4/H2, and CH4/Ar systems

Quadrupole mass spectrometry has been employed to characterize the ionic species in the discharges of pure CH₄, CH₄/H₂, and CH₄/Ar systems. For pure methane, the major positive ions in the discharge at low pressure (e.g., 0.15 torr) are CH ₃ ⁺ , C₂H ₃ ⁺ , CH ₂ ⁺ , C₂H ₂ ⁺ , CH ₄ ⁺ , C₂H ₄ ⁺ , and C₂H ₅ ⁺ at high pressure (e.g., 0.5 torr) the major ions are CH ₃ ⁺ , C₂H ₃ ⁺ , C₂H ₅ ⁺ , C₃H ₃ ⁺ , C H₃H ₇ ⁺ , C₄H ₇ ⁺ , C₅H ₇ ⁺ , C₆H ₅ ⁺ , and C₇H ₇ ⁺ . The relative abundances of C₁ ions decrease with increasing pressure, whereas those of higher-order ions increase with pressure. For 5% CH₄ + 95% H₂ mixture, in addition to those sampling from the pure methane plasma at the lower pressure, H _n ⁺ ions have also been detected. For 5% CH₄ +95% Ar mixture, the principal ions are CH ₃ ⁺ , CH ₂ ⁺ , CH⁺, CH ₅ ⁺ , Ar⁺, and ArH⁺; the ions containing more than two carbon atoms are negligible. In these discharges, the CH ₃ ⁺ and C₂H ₃ ⁺ are the most important positive ions in C₁ and C₂ ions, respectively. The ions detected are believed to come from the sheath between the electrode and the luminous plasma, and have high kinetic energy. An ion-molecule reaction mechanism is proposed which can well explain the observed main features of ionic products.Died June 1, 1991.     

Structure électronique et spectres de resonance paramagnétique électronique des radicaux vinyle et cyclopropyle

Résumé Une méthode de calcul dérivant des théories de champ self-consistant est utilisé pour l'étude des radicaux vinyle et cyclopropyle. L'énergie électronique et les écarts hyperfins dûs aux hydrogènes et au ¹³C ont été évalués en fonction de la géométrie du carbone radicalaire. L'angle C=-H du radical vinyle a été trouvé de l'ordre de 150°. Il est montré que les radicaux vinyle et cyclopropyle ont une structure électronique similaire qui ne peut être totalement expliquée ni par un modèle ni par un modèle classique, chaque radical présentant à la fois les deux caractères.

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A method of calculation derived from self-consistent field theories is used for a study of vinyl and cyclopropyl radicals. Electronic energy, hydrogens and ¹³C hyperfine splittings are evaluated as a function of the carbon geometry. The C=-H bond angle is found to be about 150°. It is shown that vinyl and cyclopropyl radicals have a similar electronic structure which cannot be completely interpreted neither by a classical model nor by a one, each radical presenting both and character.

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Zusammenfassung Nach einer auf dem SCF-Verfahren basierenden Methode werden Elektronenenergie, H- und ¹³C-Hyperfeinaufspaltung in Vinyl- und Cyclopropylradikalen in Abhängigkeit vom Bindungswinkel am berechnet, der sich im ersten Fall zu 150° ergibt. Es zeigt sich, daß die Elektronenstruktur der beiden behandelten Radikale ähnlich ist und daß sie weder durch ein reines - noch ein reines -Modell zu beschreiben ist.

     

First boundary value problem in elasticity: Bounds for the displacements and Saint-Venant's principle

Summary We consider here the Dirichlet's problem for the Lamé's equations without body force in a semi-infinite cylinder (0z<) with cross-sectionS _z , the displacementsu _i vanishing on the cylindrical surface. We give in this paper an explicit decay estimate for aL ₂-norm ofu _i . The evaluation is of the type wherek ₁ andk ₂ are determined constants andI(f _i ) an integral depending only on the displacementsf _i prescribed onS ₀. Our results consequently reinforce the Saint-Venant's principle.

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Résumé On considère ici le problème de Dirichlet pour les équations de Lamé sans force volumique dans un cylindre semi-infini (0z<) de section droiteS _z , les déplacementsu _i étant nuls sur la surface cylindrique. On donne dans ce travail une estimation explicite de la décroissance pour une norme (dansL ₂) desu _i . L'évaluation est du type oùk ₁ etk ₂ sont des constantes déterminées etI(f _i ) une intégrale ne dépendant que des déplacementsf _i imposés surS ₀. Notre résultat, par conséquent, renforce le principe de Saint-Venant.

     

A Cutting Planes Algorithm for the <Emphasis Type="Italic">m</Emphasis>-Salesmen Problem

The existence of reliable and flexible FORTRAN programs for integer linear programming has recently enabled the development of very efficient algorithms for the travelling salesman problem. The main characteristic of these algorithms is the relaxation of most of the constraints of the problem during its solution. The same approach can be used for the solution of the m-salesmen problem in which m salesmen starting from the same city must visit only once n cities at minimum cost. The number of salesmen can be fixed in advance or allowed to vary, upper and lower bounds set on the number of salesmen and even fixed costs associated with the salesmen. The results obtained so far are very encouraging. Problems of up to 100 cities have been solved optimally for the m-travelling salesmen case and other more complex problems are currently under study.     

Synthesis of methylenedioxy-bearing 1-aryl-3-carboxylisoquinolines using a modified Ritter reaction procedure

This paper describes original approaches aimed at the preparation of electron-rich 1-aryl-3-carboxylisoquinolines. Our first attempt led to an efficient preparation of 1-hydroxyisoquinoline-3-carboxylic acid methyl ester starting from bromophthalide via a rearrangement of 2-acetylamino-2-(3-oxo-1,3-dihydroisobenzofuran-1-yl)-malonic acid dimethyl ester. However, as its eventual application to the synthesis of methylenedioxy-bearing substrates seemed rather long, a second approach involving an extension of the Ritter reaction to safrole was devised. We thus report that, under proper experimental settings, the use of 54% tetrafluoroboric acid in ether enables a Ritter reaction between safrole and 3,4,5-trimethoxybenzonitrile yielding 17% of 7-methyl-5-(3,4,5-trimethoxyphenyl)-7,8-dihydro-[1,3]dioxolo[4,5-g]isoquinoline. This acidic reagent avoids the extensive decomposition seen when using the classical Ritter reaction conditions (i.e.: concentrated sulfuric acid). Further chemical transformations of this methyl-bearing dihydroisoquinoline led to the methylenedioxy-bearing 1-aryl-3-carboxylisoquinoline. These derivatives are related to the peripheral benzodiazepine receptor ligand PK 11195 as well as falcipain-2 inhibitors and other potential antitumor agents.     

Human immunoglobulin adsorption investigated by means of quartz crystal microbalance dissipation, atomic force microscopy, surface acoustic wave, and surface plasmon resonance techniques

Time-resolved adsorption behavior of a human immunoglobin G (hIgG) protein on a hydrophobized gold surface is investigated using multitechniques: quartz crystal microbalance/dissipation (QCM-D) technique; combined surface plasmon resonance (SPR) and Love mode surface acoustic wave (SAW) technique; combined QCM-D and atomic force microscopy (AFM) technique. The adsorbed hIgG forms interfacial structures varying in organization from a submonolayer to a multilayer. An "end-on" IgG orientation in the monolayer film, associated with the surface coverage results, does not corroborate with the effective protein thickness determined from SPR/SAW measurements. This inconsistence is interpreted by a deformation effect induced by conformation change. This conformation change is confirmed by QCM-D measurement. Combined SPR/SAW measurements suggest that the adsorbed protein barely contains water after extended contact with the hydrophobic surface. This limited interfacial hydration also contributed to a continuous conformation change in the adsorbed protein layer. The viscoelastic variation associated with interfacial conformation changes induces about 1.5 times overestimation of the mass uptake in the QCM-D measurements. The merit of combined multitechnique measurements is demonstrated.     

Theoretical Evaluation of Steric Effects in [ReH(5)(PR(3))(2)(SiR(3))(2)] Complexes with the IMOMM Method

A theoretical study including full geometry optimizations is carried out at the IMOMM(MP2:MM3) (IMOMM = integrated molecular orbital molecular mechanics) computational level on the [ReH(5)(PPh(i)()Pr(2))(2)(SiHPh(2))(2)] and [ReH(5)(PCyp(3))(2)(SiH(2)Ph)(2)] systems, the results being compared with available experimental diffraction data, as well as with MP2 results on the model system [ReH(5)(PH(3))(2)(SiH(3))(2)]. A simple scheme for the analysis of the relative weight of different contributions to the "steric" distortion is also proposed and applied to the same [ReH(5)(PPh(i)()Pr(2))(2)(SiHPh(2))(2)] and [ReH(5)(PCyp(3))(2)(SiH(2)Ph)(2)] species.     

Detection of genetically modified corn (Bt176) in spiked cow blood samples by polymerase chain reaction and immunoassay methods

The fate of DNA and protein transgenic sequences in products derived from animals fed transgenic crops has recently raised public interest. Sensitive molecular tests targeting the Bt176 genetic construct and the transgenic Cry1Ab protein were developed to determine whether plant sequences, especially transgenic sequences, are present in animal products. A protocol for total DNA extraction and purification from cow whole blood samples was first drawn up and assessed by spiking with known amounts of DNA from Bt176 maize. The limit of detection for transgenic sequences (35S promoter and Bt176-specific junction sequence) was determined by both the polymerase chain reaction-enzyme-linked immunosorbent assay (PCR-ELISA) and the 5'-nuclease PCR assay. Four additional PCR systems were built to substantiate the results. The first detects a mono-copy maize-specific sequence (ADH promoter). Two others target multi-copy sequences from plant nucleus (26S rRNA gene) and chloroplast (psaB gene). The last one, used as a positive control, targets a mono-copy animal sequence (alpha(s1)-casein gene). Both methods detected a minimum spiking at 25 copies of Bt176 maize/mL in 10 mL whole blood samples. The sandwich ELISA kit used detected down to 1 ng transgenic Cry1Ab protein/mL spiked whole blood.     

Syntheses and structural studies on two cycloruthenapentadienyl complexes: [(CO)3RuC4(CH2OH)4]Ru(CO)3·H2O and [(CO)3RuC4(CH2CH2OH)2(C2H5)2]Ru(CO)3

Syntheses and single-crystal X-ray diffraction studies have been completed on two cycloruthenapentadienyl (CO)₆Ru₂L₂ derivatives, with L = CH₂OHC = CCH₂OH and C₂H₅C=CCH₂CH₂OH respectively. Crystal data are as follows: for [(CO)₃RuC₄(CH₂OH)₄]Ru(CO)₃·H₂O, P2₁/c, a 13.72(1), b 9.501(4), c 14.86(1) Å, β 101.10(6)°, R_w = 0.052 for 1911 reflections; for [(CO)₃RuC₄(CH₂CH₂OH)₂(C₂H₅)₂]Ru(CO)₃, P2₁/c, a 9.191(3), b 16.732(4), c 14.903(3) Å, β 113.61(4)°, R_w = 0.042 for 2865 reflections. Both compounds are built up from binuclear units, each unit being regarded as a Ru(CO)₃ fragment π-bonded to a cycloruthenapentadienyl ring. The molecular parameters are compared with those of known cyclometallapentadienyl complexes of transition metals. The presence of a semi-bridging CO group is discussed.