Do the interstellar molecules CCCO and CCCS rearrange when energised?

Neutrals CCCO, CC(13)CO, CCCS and CC(13)CS have been prepared by one-electron vertical (Franck-Condon) oxidation of the precursor anion radicals (CCCO)(-*), (CC(13)CO)(-*), (CCCS)(-*) and (CC(13)CS)(-*)respectively in collision cells of a reverse sector mass spectrometer. Ionisation of the neutrals to decomposing cations shows the neutrals to be stable for the microsecond duration of the neutralisation-ionisation ((-)NR(+)) experiment. No rearrangement of the label in energised CC(13)CO or CC(13)CS occurs during these experiments. In contrast, minor rearrangement of (CC(13)CO)(+*) is observed [(CC(13)CO)(+*)-->(OCC(13)C)(+*), while significant rearrangement occurs for (CC(13)CS)(+*) [(CC(13)CS)(+*)-->(SCC(13)C)(+*)]. Theoretical calculations at the CCSD(T)/aug-cc-pVDZ//B3LYP/6-31G(d) level of theory show that the cationic rearrangements occur by stepwise processes via key rhombic structures. Overall, the degenerate processes result in O and S migration from C-3 to C-1. The cations (CCCO)(+*) and (CCCS)(+*) require excess energies of > or = 516 and > or = 226 kJ mol(-1) respectively to effect rearrangement.     

In situ conformational analysis of fibrinogen adsorbed on Si surfaces

Fibrinogen is a major plasma protein. Previous investigations of structural changes of fibrinogen due to adsorption are mostly based on indirect evidence after its desorption, whereas our measurements were performed on fibrinogen in its adsorbed state. Specific enzyme-linked immunosorption experiments showed that the amount of adsorbed fibrinogen increased as the surface became more hydrophobic. Atomic force microscopy (AFM) investigations revealed the trinodular shape of fibrinogen molecules adsorbed on hydrophilic surfaces, whereas all of the molecules appeared globular on hydrophobic surfaces. The distribution of secondary structures in adsorbed fibrinogen was quantified by in situ Fourier-transform infrared (FTIR) analysis. Substrates of identical chemical bulk composition but different surface hydrophobicity permit direct comparison among them. Adsorption properties of fibrinogen are different for each degree of hydrophobicity. Although there is some increase of turn structure and decrease of β-sheet structure, the secondary structure of adsorbed fibrinogen on hydrophilic surface turned out to be rather similar to that of the protein in solution phase with a major -helix content. Hydrophilic surfaces exhibit superior blood compatibility as required for medical applications.     

Synthese von Metallkomplexen des Tetra-(2,3-anthra)-tetraazaporphins und Vergleich ihrer Elektronenabsorptionsspektren mit denen anderer anellierter Tetraazaporphinsysteme

Copper, nickel and aluminium derivatives of tetra-2,3-anthratetraazaporphin bearing different substituents in the anthracen part have been prepared. The absorption spectra of these substances in different solvents are given and compared with metal complexes of other linearly annellated tetraazaporphins. In the series of vanadyl complexes of tetraazaporphin (_max 597 nm), tetra-[1,2-(4-tert-butyl)-benzo]-tetraazaporphin (_max 698 nm), tetra-[2,3-(6-tert-butyl)-naphtho]-tetraazaporphin (_max 807 nm), tetra-2,3-(anthra)-tetraazaporphin (_max 932 nm), tetra-2,3-(tetraceno)-tetraazaporphin (_max 1055 nm), the absorption maxima of the Q-band are shifted per annellated benzene ring about 100 nm to longer wave lengths.

     

SANS study of the interactions among DNA, a cationic surfactant, and polystyrene latex particles

The compaction of DNA by a cationic surfactant both in the bulk and adsorbed on the surface of latex particles was followed for the first time by SANS. In the bulk, a decrease in the overall size of the DNA coil in the presence of the cationic surfactant was observed at a negative-to-positive charge ratio far below the phase separation region, at a negative-to-positive charge ratio of 18. Additionally, large surfactant aggregates seem to form within the DNA-surfactant complex. On the other hand, DNA adsorbs onto the surface of latex particles, forming a thick layer, as evidenced by the fitting of the SANS data to a core-shell form factor. Addition of a cationic surfactant to the DNA-coated latex particles at a negative-to-positive charge ratio of 38 induces a slight decrease in the size of the particle layer, where the cationic surfactant is evenly distributed within the adsorbed layer. A further decrease of the negative-to-positive charge ratio to 18 induces a dramatic change in the SANS data that suggests significant compaction of the adsorbed layer and the formation of large surfactant aggregates, similar to those detected in the bulk.     

Determination of mercury and arsenic in fresh water by neutron activation analysis

Neutron activation analysis has been applied for the determination of Hg and As in freshwater samples. Preconcentration of Hg and As from the samples before irradiation by using active carbon for scavenging the chelate complex of Hg with dithizone at pH 1 and Fe(OH)₃ for co-precipitating arsenic was used. After irridiation, mercury was determined by direct counting of the irradiated active carbon. Arsenic was separated from Fe(OH)₃ by precipitating arsenic in the metal form after removing¹²²Sb by extraction in 2N HCl with Ni-diethyldithiophosphoric acid in carbon tetrachloride. The method is simple and reliable.     

Chemical composition of the resin essential oil of Canarium album from Vietnam

The composition of the essential oil obtained from the resin of Canarium album (Lour.) Raeusch, Burseraceae, growing in Vietnam, was studied by GC and GC/MS. Twenty-nine compounds representing 95.2% of the oil were identified. Monoterpenoids made up 93.2% of the oil, with β-pinene (33.3%), α-terpinene (19.4%), γ-terpinene (14.1%), and terpinen-4-ol (11.9%) as the main components. Sesquiterpenoids made up 2.0% of the oil, and the content of each individual was below 0.5% of the oil. Published in Khimiya Prirodnykh Soedinenii, No. 5, pp. 421–422, September–October, 2006.     

Contribution à la phytochimie du genre Gentiana XXI; Les cinnamoyl-C-glucosylflavones et leurs O-glucosides dans Gentiana punctataL.

Phytochemistry of genus Gentiana XXI: The cinnamoyl-C-glucosylflavones and their O-glucosides in Gentiana punctata L . Three new ( 1 – 3 ) and three previously identified ( 4 – 6 ) cinnamoyl-C-glucosyl-flavones have been isolated from the leaves of Gentiana punctata L . The structures of the new compounds were established as: trans-cafeoyl-2″-iso-orientin-4′-O-β-D -glucoside ( 1 ), trans-feruloyl-2″-isovitexin-4′-O-β-D -glucoside ( 2 ) and trans-feruloyl-2″-isovitexin ( 3 ). Isoscoparine ( 8 ) and O-β-D -glucosyl-2″-iso-orientin ( 7 ) were also isolated and identified.     

Copolymerisation radicalaire du méthacrylate de méthyle et du chlorure de vinylidène avec ou sans dérive de composition

Two sets of methylmethacrylate-vinylidene chloride copolymers were prepared via radical copolymerization in dimethylformamide. The first set is carried out in batches. Gas-chromatographic analysis of samples allows a kinetic study from which the reactivity ratios r_M - 2.73 and r_C - 0.24 are derived. For the second set a new apparatus, briefly described, has been used. It permits to keep constant the composition of the monomer mixture, through addition of methyl methacrylate, monitored by a chromatographic analysis. The two sets of copolymers are analyzed using nuclear magnetic resonance (60 MHz) leading to the triad distribution, from which the reactivity ratios are derived. Owing to the composition drift, the method cannot be applied to the first set of copolymers; but in that case, it is possible to calculate the triad distribution, the knowledge of the reactivity ratios, and the calculation fits quite well the experimental results.     

The C-H and alpha(C-X) bond dissociation enthalpies of toluene, C6H5-CH2X (X = F, Cl), and their substituted derivatives: a DFT study

The homolytic C-H bond dissociation enthalpies (BDEs) of toluene and its para- and meta-substituted derivatives have been estimated by using the (RO)B3LYP/6-311++G(2df,2p)//(U)B3LYP/6-311G(d,p) procedure. The performance of two other hybrid functionals of DFT, namely, B3PWP91 and O3LYP, has also been evaluated using the same basis sets and molecules. Our computed results are compared with the available experimental values and are found to be in good agreement. The (RO)B3LYP and (RO)O3LYP procedures are found to produce reliable BDEs for the C-H bonds in toluene and the C-X (X = F, Cl) bond in alpha-substituted toluene (C6H5-CH2X) and their substituted derivatives. The substituent effect on the BDE values has been analyzed in terms of the ground-state effect and the radical effect. The effect of polarization of the C-H bond on the substituent effect is also analyzed. The BDE(C-H) and BDE(C-X) values for alpha-substituted (X = F and Cl) toluenes with a set of para substituents are presented for the first time.     

Synthese „anorganischer”︁ Tintenfisch-Moleküle. II

Synthesis of “Inorganic” Pode-type Molecules. II The reaction of the amino compounds Me_yB? NMe₂ (B ? As, y ? 2; B ? Si, y ? 3) with 1, n-dioles results in the formation of the compounds HO(CH₂)_nOBMe_y. These compounds can be used as the arms of pode-type molecules Me_xA[? O(CH₂)_nOBMe_y]_z with A ? Si, As. The influence of A, B, n, and z in the rearrangement of these molecules is examined. A second type of pode molecules can be prepared by the reaction of Me₂As? R? OH (R ? CH₂CH₂, CH₂CH₂(OCH₂CH₂)₂) with the amino compounds Me_x(NMe₂)_z (A ? As, Si). These reactions result in the formation of molecules as Me_xA(ORAsMe₂)_z.