Effect of impurities on laser-induced air breakdown at 1.06 μ

Experiments have been performed to determine the reduction of the laser-induced breakdown threshold of 1 atmosphere air due to the presence of particulate matter. SiO₂ and carbon fibers with diameters ranging from 6.6 μ to 68 μ were placed in the focal volume and irradiated by 30 nsec, 1.06 μ laser pulses. The reduction in breakdown threshold is found to be comparable to that previously reported for 10.6 μ radiation. Within the experimental accuracy, the breakdown threshold scales as λ^-2.     

Determination of amphetamine-type stimulants in oral fluid by solid-phase microextraction and gas chromatography-mass spectrometry

A method for the simultaneous identification and quantification of amphetamine (AMP), methamphetamine (MET), fenproporex (FEN), diethylpropion (DIE) and methylphenidate (MPH) in oral fluid collected with Quantisal? device has been developed and validated. Thereunto, in-matrix propylchloroformate derivatization followed by direct immersion solid-phase microextraction and gas chromatography-mass spectrometry were employed. Deuterium labeled AMP was used as internal standard for all the stimulants and analysis was performed using the selected ion monitoring mode. The detector response was linear for the studied drugs in the concentration range of 2-256 ng mL(-1) (neat oral fluid), except for FEN, whereas the linear range was 4-256 ng mL(-1). The detection limits were 0.5 ng mL(-1) (MET), 1 ng mL(-1) (MPH) and 2 ng mL(-1) (DIE, AMP, FEN), respectively. Accuracy of quality control samples remained within 98.2-111.9% of the target concentrations, while precision has not exceeded 15% of the relative standard deviation. Recoveries with Quantisal? device ranged from 77.2% to 112.1%. Also, the goodness-of-fit concerning the ordinary least squares model in the statistical inference of data has been tested through residual plotting and ANOVA. The validated method can be easily automated and then used for screening and confirmation of amphetamine-type stimulants in drivers' oral fluid.     

An adaptive scheme to treat the phenomenon of quenching for a heat equation with nonlinear boundary conditions

The paper treats of the numerical approximation for the following boundary value problem: $$ \left\{ \begin{gathered} u_t (x,t) - u_{xx} (x,t) = 0, 0 < x < 1, t \in (0,T), \hfill \\ u(0,t) = 1, u_x (1,t) = - u^{ - p} (1,t), t \in (0,T), \hfill \\ u(x,0) = u_0 (x) > 0, 0 \leqslant x \leqslant 1, \hfill \\ \end{gathered} \right. $$ where p > 0, u ₀ ∈ C ²([0, 1]), u ₀(0) = 1, and u′ ₀(1) = ?u ₀ ^?p (1). Conditions are specified under which the solution of a discrete form of the above problem quenches in a finite time, and we estimate its numerical quenching time. It is also proved that the numerical quenching time converges to real time as the mesh size goes to zero. Finally, numerical experiments are presented which illustrate our analysis.     

Enhancement of F-centre colouration during plastic deformation of alkali halides

Stimulated growth of F-centres was observed by irradiating alkali-halide single crystals during uniaxial deformation at controlled rates. Quantitative monitoring of the phenomena was performed for pure KCl at L.N.T. as well as in the range from R.T. to 106°C. Distinct forms for the kinetics of growth were obtained in the two regions. A correlation was also established between the growth of excess colouration and the evolution of stress, in the higher temperature range. The data on the kinetics, stress dependence and temperature dependence suggest that the production of excess F-centres arises from the radiolysis of vacancy-producing debris (possibly, dislocation dipoles) that are also effective agents of hardening. The process is limited by thermally activated annealing, with an activation energy appropriate for free-vacancy migrations. It is suggested that the limiting reaction is a recombination of the excess negative-ion vacancies with an antimorph defect, contained in a complementary type of dislocation debris.     

Excited-state absorption in oxidized cytochrome c solution

Nonlinear absorption dynamics of oxidized cytochrome c in water solution was investigated at 532 nm with Z-scan and pump–probe techniques. The optical characterization of this compound is very important owing to its similarity with hematoporphyrin-based drugs commonly used in photodynamic therapy for cancer treatment. We observed a saturable absorption process related to the excited singlet population, followed by a fast decay to the ground state. The optical excitation and subsequent relaxation were interpreted with a three-energy-level diagram, allowing the first singlet excited-state absorption cross section and lifetime determination. PACS 42.65.Sf; 78.66.Qn; 42.62.Be     

Degenerate two-photon absorption spectra in azoaromatic compounds.

A systematic study of the degenerate two-photon absorption (2PA) spectra of seven azoaromatic compounds in dimethyl sulfoxide solution is reported, which employed the Z-scan technique with femtosecond laser pulses from the bottom of the azo compound absorption bands up to 1100 nm. The 2PA peaks for pseudostilbene-type azo compounds (Disperse Orange (DO) 3, Disperse Red (DR) 13, DR1, DR19, and DR19-Cl) were observed at twice the peak wavelength of the linear absorption. However, such peaks were not observed for other azo compounds (PAMINO and DIAMINO) because of the symmetry of these molecules. A resonance enhancement of the 2PA cross-section was observed for all compounds. The 2PA peak and the nonlinear resonance enhancement behavior could be adjusted with a model based on perturbation theory. Such knowledge can be a guideline to the understanding of the 2PA process in azoaromatic compounds.     

Synthesis,spectroscopic/electrochemical characterization and DNA interaction study of novel ferrocenyl‐substituted porphyrins

We report the synthesis and characterization of two new meso‐ferrocenylporphyrins, with the ferrocenyl unit attached at the para position of a C₆F₄ group by a C? N bond with ? NH(CH₂)₂NH? ( 2a ) and ? NH(CH₂)₄NH? ( 2b ) spacers. Compounds 2a and 2b were characterized through elemental analyses, electrospray ionization high‐resolution mass spectrometry, ¹H NMR, UV–visible and fluorescence spectroscopies, electrochemistry and spectroelectrochemistry. The free base porphyrin 2 was included for comparison purposes. The binding ability of 2 and the porphyrin derivatives 2a and 2b with calf thymus DNA was determined using UV–visible and fluorescence spectroscopies. The results suggest that the interaction of these systems most probably occurs through π‐stacking by non‐classical modes involving the partial insertion of the C₆F₅ ring between adjacent base pairs on DNA and possible hydrogen interaction with the aliphatic ? NH(CH₂)_nNH? (n = 2 or 4) groups with calf thymus DNA. Moreover, we also demonstrate that porphyrins generate singlet oxygen species and show good photostability after irradiation.     

Cationic diiron and diruthenium μ-allenyl complexes: synthesis, X-ray structures and cyclization reactions with ethyldiazoacetate/amine affording unprecedented butenolide- and furaniminium-substituted bridging carbene ligands

The novel cationic diiron μ-allenyl complexes [Fe(2)Cp(2)(CO)(2)(μ-CO){μ-η(1):η(2)(α,β)-C(α)(H)=C(β)=C(γ)(R)(2)}](+) (R = Me, 4a; R = Ph, 4b) have been obtained in good yields by a two-step reaction starting from [Fe(2)Cp(2)(CO)(4)]. The solid state structures of [4a][CF(3)SO(3)] and of the diruthenium analogues [Ru(2)Cp(2)(CO)(2)(μ-CO){μ-η(1):η(2)(α,β)-C(α)(H)=C(β)=C(γ)(R)(2)}][BPh(4)] (R = Me, [2a][BPh(4)]; R = Ph, [2c][BPh(4)]) have been ascertained by X-ray diffraction studies. The reactions of 2c and 4a with Br?nsted bases result in formation of the μ-allenylidene compound [Ru(2)Cp(2)(CO)(2)(μ-CO){μ-η(1):η(1)-C(α)=C(β)=C(γ)(Ph)(2)}] (5) and of the dimetallacyclopentenone [Fe(2)Cp(2)(CO)(μ-CO){μ-η(1):η(3)-C(α)(H)=C(β)(C(γ)(Me)CH(2))C(=O)}] (6), respectively. The nitrile adducts [Ru(2)Cp(2)(CO)(NCMe)(μ-CO){μ-η(1):η(2)-C(α)(H)=C(β)=C(γ)(R)(2)}](+) (R = Me, 7a; R = Ph, 7b), prepared by treatment of 2a,c with MeCN/Me(3)NO, react with N(2)CHCO(2)Et/NEt(3) at room temperature, affording the butenolide-substituted carbene complexes [Ru(2)Cp(2)(CO)(μ-CO){μ-η(1):η(3)-C(α)(H)[upper bond 1 start]C(β)C(γ)(R)(2)OC(=O)C[upper bond 1 end](H)] (R = Me, 10a; R = Ph, 10b). The intermediate cationic compound [Ru(2)Cp(2)(CO)(μ-CO){μ-η(1):η(3)-C(α)(H)[upper bond 1 start]C(β)C(γ)(Me)(2)OC(OEt)C[upper bond 1 end](H)](+) (9) has been detected in the course of the reaction leading to 10a. The addition of N(2)CHCO(2)Et/NHEt(2) to 7a gives the 2-furaniminium-carbene [Ru(2)Cp(2)(CO)(μ-CO){μ-η(1):η(3)-C(α)(H)[upper bond 1 start]C(β)C(γ)(Me)(2)OC(OEt)C[upper bond 1 end](H)](+) (11). The X-ray structures of 10a, 10b and [11][BF(4)] have been determined. The reactions of 4a,b with MeCN/Me(3)NO result in prevalent decomposition to mononuclear iron species.     

New Oleanane-type glycosides and secoiridoid glucoside from Aptandra zenkeri

Abstract

Four new saponins, camelliagenin A and B derivatives, and one new secoiridoid glucoside were isolated from the stem bark of Aptandra zenkeri Engl. (Aptandraceae) together with two known secoiridoid glucosides. Their structures were determined based on a combination of 1D- and 2D-NMR experiments techniques and HR-ESI-MS analysis. This is the first report on saponins in genus Aptandra.