Photocatalytic effects of Fe(III) compounds on the hydroxylation of benzoic acid by hydrogen peroxide initiated by UV-radiation

The addition of FeCl₃ and Na₂[Fe(CN)₅NO] increases the quantum yields of photochemical hydroxylation of benzoic acid by hydrogen peroxide. The photocatalytic effects operate especially when the radiation is absorbed by benzoic acid. When hydrogen peroxide is excited, the catalytic effects in the hydroxylation are small.

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FeCl₃ Na₂[Fe(CN)₅NO] , . , . .

     

Calibration of laser-ablation ICP-MS. Can we use synthetic standards with pneumatic nebulization?

An approach for the determination of trace element concentrations in high purity metals, using an inductively coupled plasma mass spectrometer (ICP-MS) with a laser-ablation system for direct solid sample introduction after calibration with nebulized liquid standards was made. Due to the inherent differences in the rate of sample introduction with laser-ablation and pneumatic nebulization, a matrix element must be used as an internal standard. This is problematical for elements that have no isotope with a relative abundance of less than 0.1 %, since the ion signals would be too high for direct measurement, and reduction of the ablation rate would compromise the sensitivity for trace elements. Due to the high stability of ICP-unit and mass filter of the instrument used, it was found that the tail of a mass-peak of the matrix element could be used as an internal standard. Therefore, a position at –0.5 amu from the matrix-isotope (e.g. ^62.5Cu in copper samples) was used for internal standardization. The standard deviation of this signal in a period of 2.5 h was 3.6% RSD with no notable drift when the laser ablation was used for sample introduction. The calibration of the matrix-element by nebulizing liquid standards showed that the ion signal measured on the peak-tail is directly proportional to the element concentration in the ICP. This indicates that the peak shape is not only stable, but also independent of the peak height. The advantages of this method lie in the easy preparation of calibration standards for quantitative measurements with a laser-ablation system and access to homogeneous standards for materials, that are difficult to homogenize in the solid state. The calibration of the traces is performed relatively to a fixed concentration of the matrix element. Calibrations were carried out for trace concentrations in high purity copper and good recoveries were obtained for high-purity reference standards. Received: 23 February 1998 / Revised: 20 July 1998 / Accepted: 25 July 1998     

Evidence for the Generation of Singlet Oxygen (<Superscript>1</Superscript>O<Subscript>2</Subscript>, <Superscript>1</Superscript>Δ<Subscript>g</Subscript>) from Ozone Promoted by Inorganic Salts

Summary.  Evidence for novel chemical sources of singlet oxygen based on the conversion of ozone by tin(II) in acetic acid or nitrite ions in water was found by screening a selection of inorganic salts by means of a sensitive detector for exothermic processes (SEDEX) and a N₂-cooled Ge-diode for singlet oxygen luminescence measurements. Corresponding author. E-mail: heinz.falk@jku.at Received July 18, 2002; accepted August 23, 2002     

A Study of the Influence of Hydrophobicity of Activated Carbon on the Adsorption Equilibrium of Aromatics in Non-Aqueous Media

The effect of hydrophobicity on the adsorption of aromatics on metal-free activated carbons was studied. Adsorption isotherms for phenol, aniline, benzene, and xylene were generated in cyclohexane and heptane media, using seven carbons with different surface heterogeneity. The hydrophobicity of these carbons was probed using flow microcalorimetry (FMC). Surface polarity and solvent and adsorbate hydrophobicity were found to influence the adsorption capacity. For adsorbates that do not form hydrogen bonds with oxygen on the carbon surface, higher surface acidity lowers adsorption capacity due to increased polarity. In contrast, for adsorbates that can form hydrogen bonds with surface oxygen, the capacity is enhanced at higher surface acidities. A higher solvent hydrophobicity was found to decrease capacity for all the aromatic adsorbates studied, except at high surface polarity, where the effect of the solvent was found to be minimal.     

A direct method for the alkylation of adenosine nucleosides at position 8.

Alkylation of adenosine derivatives at carbon 8 can be conveniently achieved by lithiation followed by reaction with an alkyl halide.     

Structural aspects of polyimides. I. Polymerization and degradation of endo-N-phenylnadimide and endo-N-isobutylnadimide

The isomerization, polymerization, and degradation aspects of endo-N-phenylnadimide and endo-N-isobutylnadimide (NPNI-N and NIBNI-N) were investigated using infrared analysis (IR), differential thermal analysis (DTA), gel permeation chromatography (GPC), thermogravimetric analysis (TG), and capillary gas chromatography-mass spectroscopic (GC–MS) techniques. Although the endotherm related to the retro-Diels–Alder reaction is not registered in the DTA thermographs, on-line mass spectrometric studies revealed the occurrence of this process. The formation of the Diels–Alder adduct of cyclopentadiene with N-isobutylnadimide (NIBNI) during the polymerization of NIBNI-N is proved. GPC studies on NPNI-N and NIBNI-N cured at 300°C for 3.0 h showed the average degree of polymerization to be three to four. The polymers obtained by curing NPNI-N and NIBNI-N at 300°C for 3.0 h showed 109.8 kJ/mol as the activation energy for degradation. The dynamic and isothermal pyrolysis studies clearly indicated the presence of intact norbornyl units in the polymer, and the breakage of ? CH₂? bridges in the strained norbornyl structural elements was found to be the point of aromatization during degradation.     

Infrared spectra of the ammonium ion in crystals: Part IV. Motions of the NH3D+ ion in ammonium perchlorate and in other weakly hydrogen-bonded ammonium compounds

Molecular motion of the ammonium ion has been investigated by IR spectroscopy in a series of ammonium salts which have been reported to be weakly hydrogen-bonded. Infrared spectra of the Isotopically isolated NH₃D⁺ ion in NH₄ClO₄, and NH₄BF₄ have been recorded between 295 and 22 K. Broadening of the N-D stretching bands, in each case, is attributed to short residence time and indicates rapid reorientation of the NH₃D⁺ ion. The band broadening persists down to the lowest temperature. The spectra of the NH₃D⁺ ion in NH₄BPh₄, NH₄SO₃F, NH₄SO₃Me and NH₄PF₆ have been recorded between 295 and 90 K. No significant lifetime broadening has been found in the spectra of the NH₃D⁺ ion in these salts.     

Bounds on a trauma outcome function via optimization

One measure of the effectiveness of institutional trauma and burn management based on collected patient data involves the computation of a standard normal Z statistic. A potential weakness of the measure arises from incomplete patient data. In this paper, we apply methods of fractional programming and global optimization to efficiently calculate bounds on the computed effectiveness of an institution. The measure of effectiveness (i.e., the trauma outcome function) is briefly described, the optimization problems associated with its upper and lower bounds are defined and characterized, and appropriate solution procedures are developed. We solve an example problem to illustrate the method.