Fractal-like diffractive arrangement with multiple focal points

In this paper we introduce a diffractive structure with a geometry which contains multiple Fresnel zone plates (MFZP) disposed in an arrangement based on a fractal-like rule. The corresponding diffracted intensity in planes perpendicular to the propagation axe presents two or more focal points. Their position and magnitude depend on geometrical parameters of the MFZP and on dimensions in the fractal-like arrangement. In our simulations we also analyze the influence in diffraction pattern of different non-binary phase levels in the MFZP plane. The MFZP structures with different values of geometrical and phase parameters are addressed to an optoelectronic device liquid crystal spatial light modulator (LCSLM), the experimental and simulation results are in a good agreement. The MFZP geometry with better optical parameters in diffraction pattern is then made on glass using electron beam lithography technique.     

Single and Double Ionization of Corannulene and Coronene

Electron‐transfer processes that involve single and doubly charged cations of corannulene (C₂₀H₁₀) and coronene (C₂₄H₁₂) are examined by three different mass‐spectrometric techniques. Photoionization studies give first‐ionization energies of IE(C₂₀H₁₀)=7.83±0.02 eV and IE(C₂₄H₁₂)=7.21 ±0.02 eV. Photoionizations of the neutrals to the doubly charged cations occur at thresholds of 20.1±0.2 eV and 18.5±0.2 eV for corannulene and coronene, respectively. Energy‐resolved charge‐stripping mass spectrometry yields kinetic energy deficits of Q_min(C₂₀H=13.8±0.3 eV and Q_min(C₂₄H=12.8±0.3 eV for the transitions from the mono‐ to the corresponding dications in keV collisions. Reactivity studies of the C₂₀H and C₂₄H dications in a selected‐ion flow‐tube mass spectrometer are used to determine the onsets for the occurrence of single‐electron transfer from several neutral reagents to the dications, affording two different monocationic products. With decreasing IEs of the neutral reagents, electron transfer to doubly charged corannulene is first observed with hexafluorobenzene (IE=9.91 eV), while neutrals with lower IEs are required in the case of the coronene dication, e.g., NO₂ (IE=9.75 eV). Density‐functional theory is used to support the interpretation of the experimental data. The best estimates of the ionization energies evaluated are IE(C₂₀H₁₀)=7.83±0.02 eV and IE(C₂₄H₁₂)=7.21 ±0.02 eV for the neutral molecules, and IE(C₂₀H)=12.3±0.2 eV and IE(C₂₄H)=11.3±0.2 eV for the monocations.     

Is it biologically relevant to measure the structures of small peptides in the gas-phase?

Recent developments in sample introduction of biologically relevant molecules have heralded a new era for gas-phase methods of structural determination. One of the biggest challenges is to relate gas-phase structures, often measured in the absence of water and counter ions, with in vivo biologically active structures. An advantage of gas-phase based techniques is that a given peptide can be analysed in a variety of different forms, for example, as a function of charge state, or with additional water molecules. Molecular modelling can provide insight into experimental findings and help elucidate the differences between structural forms. Combining experiment and theory provides a thorough interrogation of candidate conformations. Here two important naturally occurring peptide systems have been examined in detail and results are assessed in terms of their biological significance.The first of these is gonadotropin-releasing hormone (GnRH), a decapeptide which is the central regulator of the reproductive system in vertebrates. We have examined several naturally occurring variants of this peptide using Ion Mobility Mass Spectrometry and Electron Capture Dissociation (ECD) in conjunction with Fourier Transform Ion Cyclotron Mass Spectrometry (FT-ICR-MS). Candidate conformations are modelled using the AMBER force field. Single amino acid changes, for example Gly6 → Ala6, or Ala6 → D-Ala6, have observable effects on the gas phase structure of GnRH. It has been shown that evolutionary primary sequence variations are key to the biological activity of GnRH, and it is thought that this is due to different binding affinities at target receptors. This work provides strong evidence that this activity is structurally based. The second system examined is the relationship between the quaternary structure and activity of two novel β-defensins. FT-ICR mass spectrometry has been employed to characterize di-sulphide bridging and dissociation based experiments utilised to investigate their structural core. Defr1, with five cysteines, exists as a covalently bound disulphide linked dimer; Defr1 Y5C with six cysteines also is observed as a dimer, but non-covalently bound, suggesting that this defensin has a tendency to aggregate. The activity of Defr1 is 10 times higher than that of Defr1 Y5C when tested against the pathogen Pseudomonas aeruginosa. The results from these studies could inform future design of novel GnRH type ligands and anti-microbial agents, and illustrate the power of gas-phase based techniques for solving peptide structures.     

Phenyl migrations in dehydroaromatic compounds. A new mechanistic link between alternant and nonalternant hydrocarbons at high temperatures

Flash vacuum pyrolysis of benzo[b]biphenylene, an alternant polycyclic aromatic hydrocarbon (PAH), gives fluoranthene, a nonalternant PAH, as the major product at 1100 degrees C in the gas phase. The most reasonable mechanism to explain this isomerization involves equilibrating diradicals of 2-phenylnaphthalene that rearrange by the net migration of a phenyl group to give equilibrating diradicals of 1-phenylnaphthalene, one isomer of which then cyclizes to fluoranthene.     

Liquid membrane-electrodes XIV

Summary FeCl ₄ ^– -selective liquid membrane-electrodes were prepared by using triphenylpyrilium, phenylbenzopyrilium and cetylpyridinium tetrachloroferrates and dichloroethane or tetrachloroethane as solvents. With regard to selectivity, sensitivity and concentration range the triphenylpyrilium electrode in dichloroethane proved to be most advantageous. Its response is practically Nernstian in the concentration range of 10^–1 to 10^–4 M FeCl ₄ ^– , ZnCl₂, CuCl₂, MnCl₂, NiCl₂, CdCl₂, AlCl₃, NO ₃ ^– and Br^– do not cause any interference.

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Flüssigmembran-Elektroden XIVUntersuchung einer Tetrachloroferrat-selektiven Flüssigmembran-Elektrode

Zusammenfassung FeCl ₄ ^– -selektive Flüssigmembran-Elektroden wurden unter Verwendung von Triphenylpyrilium-, Phenylbenzo-pyrilium- und Cetylpyridinium-tetrachloroferraten in Dichloräthan oder Tetrachloräthan als Lösungsmittel hergestellt. In bezug auf Empfindlichkeit, Selektivität und Konzentrationsbereich erwies sich die Triphenyl-pyriliumelektrode in Dichloräthan als am vorteilhaftesten. Im Bereich von 10^–1 bis 10^–4 FeCl ₄ ^– verhält sich diese Elektrode praktisch gemäß dem Nernstschen Gesetz. ZnCl₂, CuCl(in2), MnCl₂, NiCl₂, CdCl₂, AlCl₃, NO ₃ ^– und Br^– stören nicht.

Part XIII: Chem. Anal. (Warsaw) 21, 867 (1976).     

Sol-Gel Poly-Component Nano-Sized Oxide Powders

Nano-sized, amorphous and monodispersed poly-component powders in the Al₂O₃–TiO₂–MgO and Al₂O₃–TiO₂–SiO₂ systems have been obtained by the sol-gel method. These powders have been characterized by XRD, IR spectroscopy, DTA/TGA and EDAX spectrometry. This last method confirmed the composition of the ternary powders, which are formed during the gelation process.The powders were tested as precursors for obtaining advanced ceramics, as tialite, Al₂TiO₅. The samples prepared with powders obtained by sol-gel method have shown a high reactivity, and the formation of tialite was improved.