Spin-orbit ab initio study of alkyl halide dissociation via electronic curve crossing

An ab initio study of the role of electronic curve crossing in the photodissociation dynamics of the alkyl halides is presented. Recent experimental studies show that curve crossing plays a deterministic role in deciding the channel of dissociation. Coupled repulsive potential energy curves of the low-lying n-sigma(*) states are studied including spin-orbit and relativistic effects. Basis set including effect of core correlation is used. Ab initio vertical excitation spectra of CH(3)I and CF(3)I are in agreement with the experimental observation. The curve crossing region is around 2.371 A for CH(3)I and CF(3)I. The potential curves of the repulsive excited states have larger slope for CF(3)I, suggesting a higher velocity and decreased intersystem crossing probability on fluorination. We also report the potential curves and the region of curve crossing for CH(3)Br and CH(3)Cl.     

Thermal and Temporal Aging of Silica Gels in Monomer Solutions

In previous work we have introduced the idea of preparing ambient pressure dried silica aerogels by increasing the wet gels' stiffness by aging in a TEOS solution until shrinkage during drying is almost eliminated. The present work elucidates the possibilities for obtaining ambient pressure dried aerogels employing this idea, however, cheap water soluble sodium silicate (water glass) precursors have been used to increase the economic feasibility of the process.We have shown how the G modulus of water glass based gels can be increased by aging in TEOS solution and gels with a density down to 0.2 g/cm3 can be obtained. These wet gels show a higher reactivity towards TEOS compared to TEOS based gels. We have also introduced the idea of aging wet gels in a solution where the monomers are provided from water glass instead of TEOS and some initial results on G modulus and density are included.     

Inclusion of dynamic σ-π polarization in π-electronab initio calculations

Summary A method is presented, whereby dynamic - polarization, i.e. the correlation effect expressed by simultaneous (-*, -*) excitations, can be approximately included in a multi-reference configuration interaction (MRCI) or multi-configurational self-consistent field (MC-SCF) calculation, without need to explicitly correlate the sigma orbitals. The method, which we call the capacitance matrix method, is based on the use of conventional one-electron integrals, from which a polarization potential (SPP) contribution is computed and added to the one- and two-electron Hamiltonian. In the present form, the method requires one parameter for each type of atom, and one for each type of bond. These parameters were adjusted to reproduce the dynamic - polarization energy, computed by restricted multi-reference CI calculations, of a number of states of different hydrocarbons, and the agreement was within a few percent. Using the same parameters in CAS (Complete Active Space) SCF calculations of various states of benzene gives excitation energies, when SPP is included, which is comparable to those obtained by much more elaborate MRCI calculations.     

Acremolin,a new 1H-azirine metabolite from the marine-derived fungus Acremonium strictum

Acremolin (1), a novel modified base, was isolated from the culture broth of the marine fungus Acremonium strictum. Based on combined spectroscopic analyses, the structure of this compound was that of a methyl guanine base containing an isoprene unit. In addition, the presence of a 1H-azirine moiety is unprecedented among natural products. This compound exhibited weak cytotoxicity against an A549 cell line.     

X-ray fluorescent spectroscopy study of the charge state of heteroatoms in organic compounds of third row elements. 7. Thiocyanates and isothiocyanates

We propose an x-ray spectral criterion as a characteristic of organic and inorganic thiocyanates and isothiocyanates. We establish the lack of interaction between the level of the unshared electron pair of sulfur and the _cC-orbitals in thiocyanates.Translated from Izvestiya Akademii Nauk SSSR, Seriya, Khimicheskaya, No. 11, pp. 2519–2521, November, 1989.     

Changes in intratumor heterogeneity in blood perfusion in intradermal human melanoma xenografts during tumor growth assessed by DCE-MRI

The purpose of this study was to use dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) to search for systematic intratumor heterogeneity in blood perfusion in human melanoma xenografts growing intradermally in BALB/c-nu/nu mice. Six xenografted tumors of an amelanotic human melanoma line (A-07) were included in the study. DCE-MRI was performed daily for 5 days by using spoiled-gradient recalled sequences. Tumor images of E.F (E is initial extraction fraction and F is perfusion) were produced by subjecting DCE-MRI data to Kety analysis. E.F was used as a measure of tumor blood perfusion, since comparative studies have shown that E.F is closely related to blood perfusion in A-07 tumors. The E.F images indicated that the intratumor heterogeneity in blood perfusion was similar in all investigated tumors. The blood perfusion was low in the center of the tumors and increased toward the tumor periphery in the dorsal and ventral direction by a factor of 3-4, but not in the lateral and medial direction. The magnitude of the heterogeneity increased by a factor of approximately 2 during tumor growth. In conclusion, intradermal human melanoma xenografts show significant systematic intratumor heterogeneity in blood perfusion.     

Nitrogen isotope analysis of ammonium in aqueous solutions using a perfluorosulfonated ionomer membrane for solid-phase microextraction

The use of custom-made solid-phase microextraction (SPME) fibers coated with a perfluorosulfonated ionomer, Nafion, was investigated for nitrogen isotopic analysis of ammonium in aqueous solutions. Aqueous ammonium was converted to ammonia by addition of a base, followed by absorption from the headspace, desorption in the injection port of a gas chromatograph, and analysis by gas chromatography/combustion/isotope ratio mass spectrometry (GC/C/IRMS). Fibers coated with a Nafion tubing were chosen due to a higher fiber-gas distribution constant and a higher Nafion thickness than fibers coated with Nafion solution, both leading to a higher amount of ammonia absorbed at equilibrium. The Nafion membrane-coated fiber absorbed approximately 20 times more than a commercial polydimethylsiloxane (PDMS) fiber. The isotopic fractionation between fiber and gas was 1.0117 +/- 0.0009 (standard deviation, SD, of all measurements) at an initial ammonia gas concentration of 21-210 microM. At 390 microM initial gas concentration it was slightly lower. When sampling from liquid samples, an ammonium concentration of 10 mM was needed to obtain a sufficient amount of ammonia absorbed. Modeling of the absorption at different temperatures showed that the absorption was approximately constant in the temperature range suitable for SPME experiments. Absorption at room temperature was therefore used for simplicity. A pilot study was conducted in which absorption was achieved from a single 9 microL droplet of sample. The preliminary results showed that delta(15)N analysis was possible for only 0.4-0.5 micromol of ammonium with a SD of 0.8 per thousand (n = 5).     

Asymptotic Behavior of One-Parameter Semigroups and Rigidity of Holomorphic Generators

We study the asymptotic behavior of one-parameter continuous semigroups of holomorphic mappings. We present angular characteristics of their trajectories at their Denjoy–Wolff points, as well as at their regular repelling points (whenever they exist). This enables us to establish new rigidity properties of holomorphic generators via the asymptotic behavior of the semigroups they generate. Received: May 11, 2007. Accepted: July 22, 2007.     

High efficiency white luminescence of alumina doped ZnO

The application of alumina-doped ZnO (AZO) films as luminescent material for large area lighting sources has been evaluated. Thin films were grown on quartz using magnetron sputtering and subsequently annealed under argon atmosphere in a rapid thermal annealing experiment. Below 550 °C, red-shift of the optical band gap and increase of the visible emission are observed in agreement with Al diffusion and formation of interstitial oxygen atoms. At temperatures higher than 800 °C, diffusion is activated and Ostwald ripening leads to the formation of larger grains and an increase of the crystalline phase. The photoluminescence (PL) intensity is enhanced, specifically in the UV range. As a result the emission spectrum of AZO thin films can be adjusted by the annealing conditions, with equal contributions from the UV and orange parts of the PL spectrum resulting in an efficient white emission as quantified using the color space map of the Commission Internationale de l'Éclairage.     

High‐performance liquid chromatography/mass spectrometric and proton nuclear magnetic resonance spectroscopic studies of the transacylation and hydrolysis of the acyl glucuronides of a series of phenylacetic acids in buffer and human plasma

The use of high‐performance liquid chromatography/mass spectrometry (HPLC/MS) and proton nuclear magnetic resonance (¹H NMR) spectroscopy for the kinetic analysis of acyl glucuronide (AG) isomerisation and hydrolysis of the 1‐β‐O‐acyl glucuronides (1‐β‐O‐AG) of phenylacetic acid, (R)‐ and (S)‐α‐methylphenylacetic acid and α,α‐dimethylphenylacetic acid is described and compared. Each AG was incubated in both aqueous buffer, at pH 7.4, and control human plasma at 37°C. Aliquots of these incubations, taken throughout the reaction time‐course, were analysed by HPLC/MS and ¹H NMR spectroscopy. In buffer, transacylation reactions predominated, with relatively little hydrolysis to the free aglycone observed. In human plasma incubations the calculated rates of reaction were much faster than for buffer and, in contrast to the observations in buffer, hydrolysis to the free aglycone was a significant contributor to the overall reaction. A diagnostic analytical methodology based on differential mass spectrometric fragmentation of 1‐β‐O‐AGs compared to the 2‐, 3‐ and 4‐positional isomers, which enables selective determination of the former, was confirmed and applied. These findings show that HPLC/MS offers a viable alternative to the more commonly used NMR spectroscopic approach for the determination of the transacylation and hydrolysis reactions of these AGs, with the major advantage of having the capability to do so in a complex biological matrix such as plasma. Copyright © 2010 John Wiley & Sons, Ltd.