Solvent-induced shift of the lowest singlet π → π* charge-transfer excited state of p-nitroaniline in water: an application of the TDDFT/EFP1 method

The combined time-dependent density functional theory effective fragment potential method (TDDFT/EFP1) is applied to a study of the solvent-induced shift of the lowest singlet π → π* charge-transfer excited state of p-nitroaniline (pNA) from the gas to the condensed phase in water. Molecular dynamics simulations of pNA with 150 EFP1 water molecules are used to model the condensed-phase and generate a simulated spectrum of the lowest singlet charge-transfer excitation. The TDDFT/EFP1 method successfully reproduces the experimental condensed-phase π → π* vertical excitation energy and solvent-induced red shift of pNA in water. The largest contribution to the red shift comes from Coulomb interactions, between pNA and water, and solute relaxation. The solvent shift contributions reflect the increase in zwitterionic character of pNA upon solvation.     

Rigid Plastic Plates under a Concentrated Moving Load∗

A rigid-plastic rectangular plate subjected to a moving transverse load is analyzed. The load is too large for the plate to be supported under static conditions. The present study indicates that there is a critical value for the moving load, above which the crossing cannot be made, irrespective of its speed. The relation between the moving load and its speed is given for values less than ciritical, as well as the distribution of displacement for a simply supported rectangular plate.     

Biegung metallischer Kreisplatten mit elastischer Unterlage

Übersicht Vorgestellt wird die Analyse rotationssymmetrischer Platten, welche auf einer elastischen Bettung ruhen. Die Platten bestehen aus elastisch/perfekt-plastischem Werkstoff, für den Tresca's Fließ bedingung und die assoziierte Fließregel gelten. Vorgeschlagen wird eine Methode zur analytischen Beschreibung des Verformungsvorgangs unter einer statischen Last, die monoton anwächst. Lösungsbeispiele werden angegeben.

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Bending of metallic circular plates resting on an elastic subgrade

Summary Rotationally symmetric plates resting on an elastic (Winkler) subgrade are studied. They are made of an elastic, perfectly plastic material obeying Tresca's yield condition and associated flow rule. The proposed method gives closed form solutions for monotonically loaded sandwich type plate. Examples for clamped and free edge plates are given.

     

Spectroscopic characterization of a Tm3+:SrGdGa3O7 crystal

3 O₇ crystal have been recorded at room temperature and at approximately 8 K. Room-temperature luminescence lifetimes of ¹D₂, ¹G₄, ³H₄, and ³F₄ states have been measured for Tm concentration ranging from [%at.]0.5 to [%at.]9. Based upon these data the crystal field splitting of luminescent states has been derived and radiative transitions rates have been evaluated. Strong self-quenching of luminescence originating in the ¹G₄ and ³H₄ states has been found in this activator–host combination. Peak emission cross section of the potential laser transition at 1800 nm was determined to be 3.9×10^-21 cm² and the gain coefficient versus wavelength was estimated and discussed. Received: 14 April 1998/Revised version: 10 August 1998     

Impact of AlN-aperture on optical and electrical properties of nitride VCSEL

This paper reports a numerical analysis of nitride VCSELs with indium-tin-oxide current spreading layers and AlN apertures. The results show that the thickness, location and diameter of the AlN aperture significantly influence the optical and electrical properties of the VCSEL.     

Radiationless deactivation of hybridization-sensitive DNA probe

In this study we attempt to determine the deactivation mechanism of a hybridization-sensitive DNA probe by using steady state absorption and fluorescence spectroscopy. Thiazole orange or 2,2′-Methylenebis(N-alkylbenzothiazole) is covalently linked to a single nucleotide in the DNA probe. Radiationless deactivation of the fluorophores is mainly determined by photo-induced isomerization of the methine bridge. Experiments done using solutes of differing molecular weight (sucrose, glucose and glycerin) to provide solutions of similar viscosity reveals the importance of solution viscosity and fluorophore conformation on radiationless deactivation. The quantum yield of the fluorophore in high viscous solutions can be explained by a simple diffusion model. This linear relationship is broken when a dimer conformation of the fluorophore starts to form, which in turn influences the emission intensity of the fluorophore.     

Unexpected Behavior of the Heaviest Halogen Astatine in the Nucleophilic Substitution of Aryliodonium Salts

Aryliodonium salts have become precursors of choice for the synthesis of ¹⁸F‐labeled tracers for nuclear imaging. However, little is known on the reactivity of these compounds with heavy halides, that is, radioiodide and astatide, at the radiotracer scale. In the first comparative study of radiohalogenation of aryliodonium salts with ¹²⁵I^? and ²¹¹At^?, initial experiments on a model compound highlight the higher reactivity of astatide compared to iodide, which could not be anticipated from the trends previously observed within the halogen series. Kinetic studies indicate a significant difference in activation energy (E_a=23.5 and 17.1 kcal mol^?1 with ¹²⁵I^? and ²¹¹At^?, respectively). Quantum chemical calculations suggest that astatination occurs via the monomeric form of an iodonium complex whereas iodination occurs via a heterodimeric iodonium intermediate. The good to excellent regioselectivity of halogenation and high yields achieved with diversely substituted aryliodonium salts indicate that this class of compounds is a promising alternative to the stannane chemistry currently used for heavy radiohalogen labeling of tracers in nuclear medicine.     

Chromatographic Determination of Total Cholesterol in Human Lung Healthy and Cancer Tissues of the Same Patient

JPC – Journal of Planar Chromatography – Modern TLC - Cholesterol is an essential component of mammalian cells, but its role in cancer is unclear. We have determined the total...