On the origin of optical activity in tris-diamine complexes of Co(III) and Rh(III): a simple model based on time-dependent density function theory

Time-dependent density functional theory (TD-DFT) is applied to the CD spectra of Lambda(deltadeltadelta)-(+)-[Co(S-pn)n(en)(3-n)]3+ (n = 1, 2, 3) and Lambda(deltadeltadelta)-(+)-[Co(en)3]3+ as well as the stereoisomers Delta-((delta)n(lambda)(3-n))-(-)-[Co(S-pn)n(en)(3-n)]3+ (n = 1, 2, 3) and Delta(deltadeltadelta)-(-)-[Co(en)3]3+. Theory is able to reproduce the major differences in the CD spectra of the species with a Lambda-configuration and their isomers with a Delta-configuration in both the d-d and ligand-to-metal CT region. It is further possible to rationalize the trend in terms of a larger azimuthal distortion away from the octahedral geometry in the Lambda-conformation compared to the Delta-configuration. Considerations were also given to the CD spectra of the lel3-isomer, Delta(lambdalambdalambda)-(-)-[Rh(R-pn)3]3+ and the ob-isomer, Lambda(lambdalambdalambda)-(+)-[Rh(S-pn)3]3+.     

Low-tempereture photolysis of diazoketones: the conformational isomerism of benzoylphenylmethylene and the IR spectrum of anthronylidene

Low-temperature photolysis of benzoylphenyldiazomethane, 1, and diazoanthrone, 2, in the polycrystal phase resulted in the high-intensity ESR spectra of benxoylphenymethylene 1a and anthronylidene 2a, respectively. Photolyses of argon matrix-isolated 1 and 2, coupled with IR spectroscopy, have now been carried out. Photolysis of 1 yielded the IR spectrum of diphenylketene as the only IR-observable product and indicated the presence in the matrix of the two s-E, s-Z, isomers of 1. On the other hand, photolysis of 2 yielded the IR spectrum of carbene 2a as the only observable product.     

On the empirical validity of koopmans’ theorem

The application of Koopmans' theorem is investigated within the context of the LCAO interpretation of a general SCF formalism. An empirical criterion for the validity of the assumption of identity of corresponding orbitals in the ion and parent system is discussed. Calculations on He, Li, Be and pyridine are reported.

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Zusammenfassung Die Gültigkeit von Koopmans' Theorem läßt sich mittels eines verallgemeinerten SCF-Formalismus prüfen. Ein Kriterium für das Zutreffen der Annahme, einander entsprechende Einteilchenzustände in Atom und Tochter-Ion seien identisch, wird in diesem Zusammenhang diskutiert. Die Rechnungen sind am Helium, Lithium, Beryllium und Pyridin durchgeführt worden.

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Résumé La validité du théorème de Koopmans dans un formalisme SCF général est étudiée au cadre d'une interprétation LCAO. Un critère empirique pour l'identité des orbitales de l'ion et du système père correspondant est discuté. Nous rapportons des calculs sur He, Li, Be et pyridine.

     

Secondary kinetic isotope effects: Deuterium abstraction by chlorine atoms from the CD3 group in CD3CH2Cl,CD3CHDCl,and CD3CD2Cl

The occurrence and magnitude of secondary kinetic isotope effects in the gas phase has been determined for deuterium abstraction from the CD₃ group in CD₃CH₂Cl, CD₃CHDCl, and CD₃CD₂Cl by photochemically generated ground-state chlorine atoms. Over the temperature range 10–94°C a discernible “inverse” kinetic isotope effect is observed. Both the pre-exponential factors and activation energies decrease with deuterium substitution in the vicinal chloromethyl group. The opposing trends result in a net effect close to unity.     

Comparison of the effective core potential and model potential methods in studies of electron correlation energy in molecules: Dihalides and halogen hydrides

Summary The effective core potential and model potential methods were used in post-SCF calculations on HC1, HBr, Cl₂, and Br₂ in order to gain insight into the effect of insufficient representation of inner nodes in the valence orbitals of the approximate methods. The results show that while the correlation energy may be slightly overestimated (by 1–7%), both the electric moment functions and the quantities depending on energy differences are consistently similar for the methods studied and close to the results from all-electron calculations.Dedicated to Prof. Klaus Ruedenberg     

Application of Kirkwood-Buff theory to electrolyte solutions. III. Activity coefficients of aqueous NaCl between 273.15 and 573.15 K

Using a theory recently developed for the interpretation of activity coefficients of 1:1 electrolytes up to high concentrations in aqueous solution at 25°C, we have analysed available data for aqueous sodium chloride solutions up to saturation in the temperature range 273.15–573.15 K. The approach, which is based on Kirkwood-Buff theory and uses the truncated Poisson-Boltzmann equation to obtain the required information about the various ion-ion radial distributions, is able to fit the results to high accuracy with minimum of parameters, viz, three, of which one is the distance of closest approach, the other two relate to ion-solvent interactions and/or higher order terms in the ion-ion interaction.     

A New Family of Nonstoichiometric Layered Rare-Earth Tin Antimonides, RESn(x)()Sb(2) (RE = La, Ce, Pr, Nd, Sm): Crystal Structure of LaSn(0.75)Sb(2)

A new class of nonstoichiometric layered ternary rare-earth tin antimonides, RESn(x)()Sb(2) (RE = La, Ce, Pr, Nd, Sm), has been synthesized through reaction of the elements at 950 degrees C. In the lanthanum series LaSn(x)()Sb(2), tin can be incorporated from a maximum content of x approximately 0.7 or 0.8 to as low as x approximately 0.10. The structure of lanthanum tin diantimonide with the maximum tin content, LaSn(0.75)Sb(2), has been determined by single-crystal X-ray diffraction methods. It crystallizes in the orthorhombic space group -Cmcm with a = 4.2425(5) ?, b = 23.121(2) ?, c = 4.5053(6) ?, and Z = 4. The isostructural rare-earth analogues were characterized by powder X-ray diffraction. The structure of LaSn(0.75)Sb(2) comprises layers of composition "LaSb(2)" in which La atoms are coordinated by Sb atoms in a square-antiprismatic geometry. Between these layers reside chains of Sn atoms distributed over three crystallographically independent sites, each partially occupied at about 20%. The structure of LaSn(0.75)Sb(2) can be regarded as resulting from the excision of RE-Sb and Sb-Sb bonds in the related structures of binary rare-earth diantimonides, RESb(2), and then intercalation of Sn atoms between layers.     

A study of radionuclides in vegetation on abandoned uranium tailings

A study has been carried out of the uptake of uranium and other radionuclides by plants growing on abandoned tailings from an uranium mining operation. Assay methods included instrumental neutron activation analysis, delayed neutron counting, fission track imaging, and counting of natural radioactivity. Care was taken to avoid contamination of the plant material and a number of methods are described to identify such contamination. All plants observed showed high uptake of radionuclides, compared to plants studied from naturally uraniferous and control areas. Graminoid (grass-like) plants showed significant uptake in the above-ground parts while woody plants showed exceedingly high uranium accumulation in the root portions. These results have significance in determination of the spread of radioactive material from such sites.     

Synthesis and derivatization of ethynyl alpha,alpha-dibromomethyl ketones: formation of highly functionalized vinyl triflates

[reaction: see text] We describe the synthesis of alpha,alpha-dibromomethyl ynones (8) and their subsequent derivatization to vinyl acetates (10). These vinyl acetates feature a 1,1-dibromo-olefin moiety, which is readily exploited in palladium-catalyzed Sonogashira, Stille, and Suzuki cross-coupling reactions with alkynes, stannanes, and boronic acids, respectively. A novel one-pot process then directly converts the resulting vinyl acetates 11-13 to the vinyl triflate derivatives 14a-j.     

A highly sensitive method for quantification of myosin light chain phosphorylation by capillary isoelectric focusing with laser-induced fluorescence detection

Activation of myosin II by phosphorylation of the 20 kDa regulatory light chains (LC20) has been implicated in numerous contractile and motile events, e.g., smooth muscle contraction, cytokinesis, and cell migration. The ability to analyze LC20 phosphorylation in minute samples is critical to determine the importance of LC20 phosphorylation in diverse physiological processes. We have developed a method for the separation and quantification of unphosphorylated, monophosphorylated, and diphosphorylated LC20 with a detection limit of 1 pg (50 amol). LC20 is initially isolated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and transblotted to a polyvinlyidene difluoride (PVDF) membrane. The region of the membrane containing the LC20 band (identified by electrophoresis of purified LC20 in a neighboring lane) is cut out and fluorescently labeled with Alexa Fluor 488 C5 maleimide. The labeled LC20 is eluted from the membrane with detergent and subjected to capillary isoelectric focusing (CIEF) to separate unphosphorylated, mono-, and diphosphorylated LC20, which are detected and quantified by laser-induced fluorescence (LIF). A linear relationship between log(peak area) and log(LC20 amount) is observed over the range of 50 amol-150 fmol. Quantification of LC20 phosphorylation by CIEF with LIF detection was compared with three commonly used methods with much lower levels of sensitivity: urea/glycerol-PAGE with Western blotting, phosphorylation by [gamma-32P]ATP with Cerenkov counting, and phosphorylation by [gamma-32P]ATP followed by SDS-PAGE, autoradiography, and scanning densitometry. All four methods gave very similar quantitative results, the major difference being that the new method exhibits 3000-fold enhanced sensitivity. This method is therefore applicable to quantitative analysis of phosphorylation of minute quantities of LC20.