Reactions of H atoms and OH radicals with ascorbic acid: A pulse radiolysis Fourier transform ESR study

Using pulse radiolysis, free radicals of ascorbic acid were generated by reactions of the primary radicals H and OH in acidic and basic aqueous solutions. The formation and the decay of several radicals of ascorbic acid were detected by time resolved Fourier transform electron spin resonance within a time interval of 100 ns to 1 ms. The rate constant of addition of H atoms to ascorbic acid (1.3·10⁸ dm³· mol⁻¹·s⁻¹) was directly determined by the change of line width of the low field line of the H atom in the presence of ascorbic acid. The addition of OH radicals to ascorbic acid results in different radical structures, detected by highly resolved Fourier transform ESR spectra.     

Stickstoffisotopenanalysen an Pyrimidinderivaten mittles Protonenresonanz

Die in hochaufgelösten Protonenresonanzspektren von ¹⁵N-markierten Pyrimidinderivaten infolge der indirekten Spin-Spin-Kopplung zwischen ¹⁵N und dem um zwei Bindungen entfernten Proton auftretenden Aufspaltungen liefern Aussagen über den Ort der Markierung im Pyrimidinring. Quantitative Angaben über die relative Häufigkeiten von ¹⁵N in diesen Positionen werden unter Verwendung der Rechentechnik erhalten. Die Ergebnisse über die relative Häufigkeiten von ¹⁵N im gesamten Molekül stimmen gut mit den massenspektrometrischen Werten überein.     

NMR Experiments on Ion Permeation in Irradiated Model Membranes

In aqueous solutions of sonicated egg-lecithin vesicles (5 weight-%) the ¹H-NMR parameters line width, area, and chemical shift of the signal of the (CH₃)₃N⁺ group were determined in dependence on the dose of gamma radiation (0 … 12 kGy). The application of curopium ions made it possible, by means of a line shape analysis, to calculate these parameters for the inside as well as for the outside lipid layer.

With increasing ⁶⁰Co-radiation dose the line widths increase linearly. The line width for the outside lipid layer increases significantly more rapidly than for the inside layer. This fact allows us to conclude that there exists a preferred radiation damage of the outside lipid layer. The asymmetry may he a consequence of an indirect radiation action mediated by the radicals of the water radiolysis.

From the temporal change of the NMR parameters information can be obtained about the radiation action on transport processes in the vesicles. Beginning at a threshold value (approx. 5 kGy) the permeation of the En^{+ ++} ions to the (CH₃)₃N⁺ head groups previously not accessible increases significantly.     

The effects of a thiol-containing quinazolinedione derivative (MECH) on the lipid oxidation in bilayer liposomes

In order to investigate the radical chemistry of 3-(2-mercaptoethyl)quinazoline-2,4(1H, 3H)-dione (MECH) in homogeneous and liposomal solutions experiments were performed with pulse radiolysis, γ radiolysis and the chemical radical intiator 2,2'-azobis(2-amidinopropane) dihydrochloride (AAPH). It is shown that the thiol group represents the most sensitive group to radical attack. The thiyl radical originating from MECH is detected indirectly by product analysis and by pulse radiolysis. The thiyl radical can abstract bisallylic hydrogens from polyunsaturated fatty acids. This is shown by pulse radiolysis in homogeneous and liposomal solutions via the formation of the pentadienyl radical which has a strong and characteristic absorption band at 280 nm.     

The ArNe-N2O van der Waals trimer: a high resolution spectroscopic study of its rotational spectrum,structure and dynamics

A new ternary van der Waals complex of the type rare gas-rare gas'-linear molecule, ArNe-N₂O, was investigated using a pulsed molecular beam cavity Fourier transform microwave spectrometer. The rotational spectra of six isotopomers of the trimer were studied in detail. These include Ar²⁰Ne-¹⁴N¹⁴NO, Ar²²Ne-¹⁴N¹⁴NO, Ar²⁰Ne-15N¹⁴NO, Ar²²Ne-¹⁵N¹⁴N0, Ar²⁰Ne-¹⁴N¹⁵NO and Ar²²Ne-¹⁴N¹⁵NO. Nuclear quadrupole hyperfine structures of the rotational transitions that are due to the one or two ¹⁴N nuclei were resolved and analysed. The resulting spectroscopic constants were used to provide structural and dynamical information about the trimer. Based on the quartic centrifugal distortion constants, a harmonic force field analysis was performed to estimate the frequencies of the van der Waals vibrational modes. A perturbation of the electronic charge distribution at the site of the central ¹⁴N nucleus of N²0 upon complex formation was detected and discussed. Differences of structural parameters of the trimer as compared to those of the respective dimer units are indicative of the presence of significant three-body non-additive contributions to the interaction energy.     

Robust chaos synchronization based on adaptive fuzzy delayed feedback ${\bf{\mathcal{H}}}_{\bf{\infty}}$ control

In this paper, we propose a new adaptive H_￥\mathcal H_\infty synchronization strategy, called an adaptive fuzzy delayed feedback H_￥\mathcal H_\infty synchronization (AFDFHS) strategy, for chaotic systems with uncertain parameters and external disturbances. Based on Lyapunov–Krasovskii theory, Takagi–Sugeno (T–S) fuzzy model and adaptive delayed feedback H_￥\mathcal H_\infty control scheme, the AFDFHS controller is presented such that the synchronization error system is asymptotically stable with a guaranteed H_￥\mathcal{H}_{\infty } performance. It is shown that the design of the AFDFHS controller with adaptive law can be achieved by solving a linear matrix inequality (LMI), which can be easily facilitated by using some standard numerical packages. An illustrative example is given to demonstrate the effectiveness of the proposed AFDFHS approach.     

Nitridokomplexe des Technetium(V)

Folgende Komplexe des funfuertigen Tichnitiums wurden dargestellt und charakterisiert T_cNCl₂[P(C₆H₅)₃]₂ (A)

T_c NCl₂ (PR₂C₆H₅)₃ [R = CH₃ (B) bzw. C₂H₅ (C)]

T_cN[(C₂H₅)₂NCS₂]₂ (D)

Die Darstellung von (A) erfolgt anlog der entsprechenden Rheniumkomplexes; (B), (C) und (D) wurden durch Reaktron von (A) mit uberschunssigem PR₂C₆H₅ bzw. Na(C₂H₅)₂NCS₂ durch Substitutionsreaktionen orhalten. Die genannten Komplexe sind bomerkenswert hydrolysebestandig. Here IR- und ¹H-NMR-Spektren warden diskutiert