Determination of copper in medicinal plants used as dietary supplements by atomic absorption spectrometry with direct flame solid analysis

An alternative device for the direct solid analysis (DSA) for copper determination by flame atomic absorption spectrometry (FAAS) is proposed. Copper was directly determined in commercial medicinal plants used as dietary supplements. The determination of copper in solid samples by DSA–FAAS was made by using a conventional air–acetylene flame. Between 0.05 and 1.5 mg of each test, sample was weighed directly into a small polyethylene vial connected to the device used for solid introduction into the flame. Test samples were introduced into the flame as a dry aerosol using a T-quartz cell set between the burner and the optical path. The T-quartz cell has a slit in the superior part by which the solid aerosol passes to the flame. A transient signal, evaluated as integrated absorbance, is produced and it is totally integrated in 2 s. Background signals always presented absorbance values less than 0.1. It was found a characteristic mass of 0.8 ng Cu and absolute limit of detection of 1.2 ng (3 s), or 1.2 μg g⁻¹ if a sample mass of 1 mg was used. Optimized conditions for air flow rate, flame stoichiometry, and so on were established as well. No excessive grinding of the samples was needed and samples with particle of size less than 80 μm were used throughout. No statistical difference between the results from the proposed system and those obtained by sample digestion and determination by conventional FAAS was observed. With the proposed procedure, more than 50 test samples can be analyzed in 1 h and it can be easily adapted to conventional spectrometers for FAAS.     

Development of direct fluorination technology for application to materials for lithium battery

Direct fluorination of 1,3-dioxolan-2-one with elemental fluorine was successfully carried out to provide 4-fluoro-1,3-dioxolan-2-one, which was expected as an additive for lithium ion secondary battery. 4-Fluoro-1,3-dioxolan-2-one was also further fluorinated with elemental fluorine to give three isomers of difluoro derivatives by the same methodology. Another topic is the preparation of trifluoromethanesulfonyl fluoride, an intermediate of lithium battery electrolyte, by the reaction of methanesulfonyl fluoride with elemental fluorine. The use of perfluoro-2-methylpentane as a solvent gave satisfactory selectivity of trifluoromethanesulfonyl fluoride.     

Pattern of separatrices and intrinsic reaction coordinates for degenerate thermal rearrangements

A structurally stable model of the standard adiabatic gradient field of the potential energy surface for certain pericyclic reactions is derived.These reactions are not subjected to the principles of orbital isomerism or to the Woodward-Hoffmann rules.Use is made of a principle established by Ariel Fernández and Oktay Sinanolu which precludes direct meta-IRC connections between transition states.It is shown that Jahn-Teller isomers of the singlet biradicals involved in the process are not interconvertible since the biradical configuration is not a transition state but a critical point with Hessian matrix with two negative eigenvalues.The topological features of the PES obtained by combinatorial methods are in full agreement with earlier results obtained from MINDO calculations.     

Proline-catalyzed asymmetric aldol reactions of tetrahydro-4H-thiopyran-4-one with aldehydes

Proline-catalyzed enantioselective direct intermolecular aldol reactions of tetrahydro-4H-thiopyran-4-one with various aldehydes give anti adducts with high diastereo- and enantioselectivities in moderate to excellent yields. With the aromatic aldehydes best results were obtained in wet DMF whereas dry DMSO generally was superior with the aliphatic aldehydes. Desulfurization of the adducts with Raney Ni provides products equivalent to aldols from 3-pentanone with potential applications in polypropionate synthesis.     

Selective Determination of Nanogram γ-Globulin in Human Blood Serum by Resonance Light Scattering of Functionalized Nano-PbS

Functionalized nano-PbS has been prepared and characterized. The functionalized nanoparticles have good dispersibility in water. Reaction of functionalized nano-PbS with γ-globulin (γ-IgG) results an enhanced resonance light scattering (RLS) around 385nm.However, when the content of HSA is lower than 0.5μg/ml^-1 the RLS enhancement is very weak and is nonlinear to concentration of HSA. Based on these results, a new direct quantitative determination method for γ-globulin in blood serum samples without separation is established.Under optimal conditions, the enhanced RLS intensity is in proportion to the γ-IgG concentration in the range 10-500ng/mL. The limit of detection is 2.75ng/mL. This method is proved to be very sensitive, rapid, simple and selective for detection of γ-IgG in blood serum.     

Magnetic Orbitals and Mechanisms of Exchange I. Direct Exchange

Summary. The problem of direct exchange is examined in the simplest cases (formal coupling of two electrons initially isolated and hydrogen molecule). Then we consider the general case of a solid characterized by weak overlaps between the atomic orbitals of first-nearest neighbours so that the involved electrons are quasi-localized. We recall the physical origin of spin-orbit coupling. Its influence on direct exchange allows one to revisit Hunds rules and to express phenomenological Hamiltonians describing anisotropic couplings as well as the antisymmetrical Dzialoshinski-Moriya coupling.     

Application of the semilocalized approach to chemical reactivity of butadiene

The semilocalized approach to chemical reactivity (J. Mol. Struct. (Theochem) 588 (2002) 99; Int. J. Quant. Chem. 94 (2003) 302) is applied to study the addition reaction of an electrophile or nucleophile to the butadiene molecule. In accordance with the classical concept of the reaction center and its neighborhood (substituent), only one of the two H₂C=CH-fragments of butadiene is supposed to be under a direct attack of the reagent, whereas the remaining H₂C=CH-group is assumed to play the role of the substituent and thereby to participate in the process indirectly by exerting certain electron-donating or accepting effect upon the former group and/or the reagent. The main aim of the study consists in revealing the role of the H₂C=CH-substituent in the formation of the known higher reactivity of the terminal carbon atom of the attacked C=C-bond (as compared to the internal atom) irrespective of the nature of the reagent. To this end, we seek to obtain an explicit algebraic representation of the interdependence between the direction and the extent of the total influence of the H₂C=CH-substituent, on the one hand, and the nature of the reagent, on the other hand. The expressions for electron density and bond order redistributions among separate fragments of contacting molecules derived previously in the form of power series are shown to yield the above-anticipated representation. On this basis, it is demonstrated that the electron-donating effect of the initially occupied (bonding) orbital of the substituent and the electron-accepting effect of its initially vacant (antibonding) orbital upon the remaining fragments of the whole reacting system may be considered independently whatever the nature of the reagent. However, a strong interdependence is established between the actual relative extents of these two components of the total effect of the H₂C=CH-group and the electron-donating (accepting) properties of the reagent. Moreover, this group of atoms is shown to manifest itself as an electron-donating (accepting) substituent under influence of an electrophilic (nucleophilic) attack. Using this principal result of the paper, the actual reactivity of butadiene with respect to electrophile (nucleophile) is interpreted by invoking a model system of a substituted ethene containing a simple (one-orbital) electron-donating (accepting) substituent, and a terminal addition easily follows for both types of the reagent.     

Direct targeting of human plasma for matrix-assisted laser desorption/ionization and analysis of plasma proteins by time of flight-mass spectrometry

A method to analyze human plasma proteins without fractionation, directly applying a plasma-matrix mixture on the target plate of a matrix-assisted laser desorption/ionization-time of flight-mass spectrometer (MALDI-TOF-MS), has been described. Peaks of ionized plasma proteins could not be detected applying a mixture of an undiluted plasma sample and a matrix solution, but they appeared when the plasma was diluted before mixing with the matrix. Tenfold diluted plasma provided well-resolved protein peaks in the m/z range from 4000 to 30,000. The addition of a simple post-crystallization washing procedure performed on the target plate further improved the quality of mass spectra. We numbered 58 peaks in the range of 4-160 kDa and 32 out of which were assigned to the plasma protein species which have been reported. Especially high sensitivity and resolution were obtained in the region < 30 kDa, where multiple isoforms of apolipoprotein A-I, apolipoprotein A-II, apolipoprotein C-I, apolipoprotein C-II, apolipoprotein C-III, and transthyretin could be assigned. Various post-translational modifications are involved in the isoforms, e.g., proteolytic cleavage, glycosylation and chemical modifications. This method will become complementary with the present electrophoretic techniques, especially for the analysis of low-molecular-mass proteins.     

Exploiting non-abelian point group symmetry in direct two-electron integral transformations

Summary A simple and general scheme to exploit any discrete point group symmetry in two-electron integral transformations is introduced. It has been implemented together with integral pre-screening techniques in direct two-electron integral transformations. Its application has also been extended to subsequent MO integral processing steps like MP2 or solution of the coupled-perturbed Hartree-Fock equations (CPHF). Timings for representative applications are presented.