The effect of a mild base on curcumin in methanol and ethanol

Steady-state and time-resolved emission techniques were employed to study the effect of acetate, a mild base, on the luminescence of curcumin in methanol and ethanol. We found that the steady-state emission intensity as well as the average fluorescence decay time are reduced by a factor of 5 when the acetate concentration is raised to about 1.8 M. We attribute this large effect to an excited-state proton transfer (ESPT) from the acidic groups of curcumin to the acetate anion. We analyze the experimental data in terms of an ESPT reaction occurring between a photoacid and a base.     

Temperature dependence of the fluorescence properties of thioflavin-T in propanol, a glass-forming liquid

Steady-state and time-resolved emission techniques were employed to study the nonradiative process of Thioflavin-T (ThT) in 1-propanol as a function of temperature. We found that the nonradiative rate, k(nr), decreased by about 3 orders of magnitude when the temperature was lowered to 88 K. We found remarkably good correspondence between the temperature dependence of k(nr) of ThT and the dielectric relaxation times of the 1-propanol solvent.     

Predictions for the 4 GeV TJNAF inclusive electron scattering experiment and for FSI effects in EMC ratios

We express nuclear structure functions F_i^A as generalized convolutions of the structure function of a nucleon and of a nucleus, composed of point-nucleons. In computations of the latter we include final state interactions and results for F₂^A are compared with a few directly measured data on C and Fe. The above-mentioned F_i^A are primarily used for predictions of the TJNAF 89-008 inclusive scattering experiment of 4 GeV electrons on various targets. Those targets cover a broad angular, and correspondingly wide x, ² range, where the nucleon-inelastic part dominates large sections of the covered kinematics. The same model has been applied to the study of hitherto neglected final state interaction effects in the nuclear component in EMC ratios in the region 0.25 x 0.85.     

Symmetric low-frequency motion in incompressible transversely isotropic elastic plates

The problem of long-wave low-frequency extensional (symmetric) motion in a layer composed of incompressible, transversely isotropic elastic material is investigated. Motivated by appropriate approximations of the dispersion relation, a hierarchy of asymptotically approximate boundary value problems is set up and solved. A leading order system of equations is obtained for the governing extensions, together with a refined system for their second order counterparts. A one-dimensional model problem, involving impact edge loading, is set up and solved in order to illustrate the derived theory.     

Synthesis of novel [3,2-b] furan-fused pentacyclic triterpenoids via gold - Catalyzed intramolecular heterocyclization of 2-alkynyl-3-oxotriterpene acids

A direct and atom-economical synthetic route to new [3,2-b] furan-fused pentacyclic triterpenoids has been developed, using gold-catalyzed 5-exo-dig heterocyclization of accessible 2-alkynyl derivatives of betulonic, ursonic, and oleanonic acids.     

A comparative analysis of nuclear excitations by high energy electrons,protons, pions and alpha's

Cross sections for the excitation of resolved nuclear levels by electrons, protons, pions and alpha's of highest energy available are analysed. Reduced cross sections are shown to be approximately proportional to the squared form factors over a relatively wide range of squared momentum transfers t. The proportionality factors for given nucleus and projectile energy are nearly independent of t and the spin of the level, indicating the approximate validity of the DWIA. Ratios of B(El) values for the excitation of different levels in the same nucleus using various projectiles are found to agree. It further appears that the DWIA holds, though to a lesser extent, even for elastic scattering.     

The rearrangement of cyclopropylketone arylhydrazones. Synthesis of tryptamines and tetrahydropyridazines

The cyclopropyliminium rearrangement of cyclopropylketone arylhydrazones may result in two possible products. The first one forms via cyclopropane ring-opening and ring-closure to give six-membered tetrahydropyridazines. The second is formed via ring-closure resulting in a five-membered ring and subsequent Grandberg rearrangement into a tryptamine. The product ratio depends on the nature of the starting hydrazones.     

Protein conformations can be probed in top-down HDX MS experiments utilizing electron transfer dissociation of protein ions without hydrogen scrambling

Electron-transfer dissociation (ETD) is evaluated as a technique to provide local information on higher order structure and dynamics of a whole protein molecule. Isotopic labeling of highly flexible segments of a model 18 kDa protein is carried out in solution under mildly denaturing conditions by means of hydrogen/deuterium exchange (HDX), followed by transfer of intact protein ions to the gas phase by means of electrospray ionization, and mass-selection of a precursor ion for subsequent reactions with fluoranthene radical anions. The ETD process gives rise to abundant fragment ions, whose deuterium content can be measured as a function of duration of the HDX reaction in solution. No backbone protection is detected for all protein segments spanning the 25-residue long N-terminal part of the protein, which is known to lack structure in solution. At the same time, noticeable protection is evident for segments representing the structured regions of the protein. The results of this work suggest that ETD of intact protein ions is not accompanied by detectable hydrogen scrambling and can be used in tandem with HDX to probe protein conformation in solution.     

Urea nitrate, an exceptionally easy-to-make improvised explosive: studies towards trace characterization

Urea nitrate is a powerful improvised explosive, frequently used by terrorists in the Israeli arena. It was also used in the first World Trade Center bombing in New York in February 1993. It is difficult to identify urea nitrate in post-explosion debris, since only a very small fraction survives the blast. Also, in the presence of water, it readily decomposes to its original components, urea and nitric acid. It is suspected that post-blast debris of urea nitrate can be confused with ammonium nitrate, the main solid product of urea nitrate thermal decomposition. In a comprehensive study towards identification of urea nitrate in post-blast traces, a spectrophotometric technique for quantitative determination of urea nitrate was developed, and conditions were found for extraction and separation of un-exploded traces of urea nitrate with minimal decomposition. Nevertheless, out of 28 samples collected from a series of three controlled firings of urea nitrate charges, only one gave the typical adduct ion by liquid chromatography/mass spectrometry analysis. We found that urea nitrate can be extracted from solid mixtures to organic solvents by using Crown ethers as “host compounds.” The adducts thus formed are solid, crystalline compounds that can be characterized by microanalysis and spectroscopic techniques. Figure Adduct formation between urea nitrate and 18-crown-6     

Generation of magnetic field by combined action of turbulence and shear

The feasibility of a mean-field dynamo in nonhelical turbulence with a superimposed linear shear is studied numerically in elongated shearing boxes. Exponential growth of the magnetic field at scales much larger than the outer scale of the turbulence is found. The characteristic scale of the field is lB proportional S(-1/2) and the growth rate is gamma proportional S, where S is the shearing rate. This newly discovered shear dynamo effect potentially represents a very generic mechanism for generating large-scale magnetic fields in a broad class of astrophysical systems with spatially coherent mean flows.