Solvent-dependent release of bromine from bromoquercetins

Quercetin, 6-bromoquercetin (3), and 8-bromoquercetin (4) undergo H/D exchange at 6- and 8-positions, in acetone-d₆ and methanol-d₄, catalyzed by acids and bases. The base-catalyzed process is faster, and in acetone-d₆ the half-lives of H-8 and H-6 are 56.5 and 48.6 h, respectively. A high regioselectivity at the position 8 of quercetin is observed under acid-catalysis in both solvents but in methanol-d₄ regioselectivity is retained even under base-catalysis. On the other hand, 6,8-dibromoquercetin (2), 4 and 6,8-dibromo-2′-hydroxyquercetin (5) manifest the ability of exchanging bromine with hydrogen (or deuterium) under acid-catalysis in acetone and other enolizable ketones (e.g., methyl ethyl ketone, acetylacetone, and isophorone). These bromophenols release bromine from their 8-position only, in a slow bromination process that likely involves their protonated form (arenium ion I) as brominating agent and the enol of the above ketones as Br-acceptor. The arenium ion I of these bromophenols is expected to be a powerful electrophile and its formation is most likely to be rate-determining.     

Ion track effect on point defect production in SiC

Low-temperature (40 K) photoluminescence (PL) measurements were used to follow the defect formation induced in the 4H-SiC epitaxial layer by irradiation with 200 keV H⁺ and 800 keV C⁺ in the fluence range of 5×10⁹–3.5×10¹² ions/cm². After irradiation, the PL spectra show the formation of some sharp lines, called “alphabet lines”, located in the wavelength range of 425–443 nm, due to the recombination of excitons at structural defects induced by ion beams. The analysis of luminescence line intensity versus ion fluence allows us to mark two different groups of peaks, namely the P1 group (e, f and g lines) and the P2 group (a, b, c and d lines). The normalised yield of P1 group lines increases with ion fluence and reaches a maximum value, while the normalised yield of P2 group lines exhibits a threshold fluence and then increases until a saturation value is reached. These different trends indicate that, while the P1 group lines are related to the primary defects created by ion beams (interstitial defects, vacancies), the P2 group lines can be associated with some complex defects (divacancy, antisites). The trends are similar for irradiation with H⁺ and C⁺ ions; however, the defect formation occurs in the fluence range of 5×10⁹–10¹¹ ions/cm² for C⁺ irradiation and 10¹¹–4×10¹² ions/cm² for H⁺ irradiation. Taking into account the different values of energy deposited in elastic collision, a dependence on the ion type was found: the C⁺ ion results in being less effective in defect production as a higher defect recombination occurs inside its dense cascade.     

Lattice location of light implanted ions in Si and Ge after laser annealing

Abstract

Radiation damage produced by short ranged (ranges 20–30 μm) charged particles (alpha particles and fission fragments) in thick plastic track detectors (thickness ≈ 150 μm) has been enlarged to produce “through” holes by using a combination of electrochemical and chemical etching processes. A series of experiments were conducted with a view to optimize the operating conditions required to produce through holes with most suitable profiles for a particular application at hand. This novel technique has been employed in producing thick nuclear track filters using fission fragments from U-235 fission and alpha particles from radon and its daughters.     

Laser pulse annealing in semiconductors

Mechanisms of the defect creation in alkali halides induced by electronic excitation, suggested within these three decades, are surveyed, emphasizing how they are related to the overall yield of defect creation in solids. The experimental and theoretical studies which are critical check points for proposed mechanisms are discussed in detail. It is pointed out that the processes of localization of the wave functions of the electrons and holes and the conversion of localized electronic energy to the motion of the lattice atoms should be understood. The mechanisms of the dynamic motion of atoms to which the electronic energy is imparted and of the stabilization of the primary products, the neutral interstitials and vacancies in the halogen sublattice, are also discussed.     

Impurity redistribution during laser irradiation in ion implanted silicon

(100) Silicon wafers implanted with 2 × 10^{15 31}P+/cm² at 100 keV have been annealed using a scanning beam of incoherent light. The main results obtained after annealing are: (a) the carrier concentration profile shows a complete dopant activation without diffusion of the implanted ions; (b) the values of carrier mobility are similar to those obtained by furnace annealing; (c) an improvement of minority carrier diffusion length is often observed; (d) a very good damage recovery is obtained. Transmission Electron Microscopy observations show that the residual damage is confined within a region at 0.2 μm depth and consists of dislocation loops of about 50 Å diameter. It is concluded that this technique can be used to obtain very good annealing of implanted layers.     

Thermodynamic Protonation Parameters of some Sulfur-Containing Anions in NaCl<Subscript>aq</Subscript> and (CH<Subscript>3</Subscript>)<Subscript>4</Subscript>NCl<Subscript>aq</Subscript> at <Emphasis Type="Italic">t</Emphasis>=25 °C

Protonation constants of one thiocarboxylate (thioacetate) and four sulfur-containing carboxylates (2-methylthioacetate, thiolactate, thiomalate, 3-mercaptopropionate) were determined by potentiometric measurements in a wide ionic strength range [0≤I≤5 mol⋅L⁻¹ in NaCl and 0 ≤I≤3 mol⋅L⁻¹ in (CH₃)₄NCl] at t=25 °C. For two of these ligands (2-methylthioacetate and thiolactate), the protonation enthalpies were also determined by calorimetric measurements in NaCl ionic medium [0 ≤I≤5 mol⋅L⁻¹] at t=25 °C. Individual UV spectra of the protonated and unprotonated 3-mercaptopropionate species, together with values of the protonation constants, were obtained by spectrophotometric titrations. Results were analyzed in terms of their dependence on the ionic medium by using different thermodynamic models [Debye-Hückel type, SIT (Specific ion Interaction Theory) and Pitzer’s equations]. Differences among protonation constants obtained in different media were also interpreted in terms of weak complex formation.     

Single and double pH-driven Cu2+ translocation with molecular rearrangement in alkyne-functionalized polyamino polyamido ligands

A new series of ligands, containing one (L1H(2)-L4H(2)) or two (L5H(4)-L6H(4)) 1,4,8,11-tetraaza-5,7-dione units and functionalized with a propargyl group on the C atom between the C=O moieties, has been synthesized. Protonation constants for the ligands and formation constants of their Cu(2+) complexes have been determined in water, and the coordination geometry of the complexes existing at various pH values has been investigated by coupled pH-metric and spectrophotometric titrations. Ligands capable of simple uptake of Cu(2+) with the formation of neutral, square-planar complexes containing the -2-charged diamino-diimido donor sets and ligands containing further coordinating groups (quinoline or pyridine) capable of single and double cation translocation have been investigated. The role of the substituents on the amino groups and the structural role played by the propargyl group have been examined as regards Cu(2+) complexation and translocation. In the double-translocating ligand L6H(4), when the two Cu(2+) ions move inside the diamino-diamido donor set, the slim propargyl group allows an unprecedented folding of the whole ligand with apical coordination of one pyridine to form a five-coordinate, square-pyramidal Cu(2+) ion. The crystal and molecular structures of this unusual [L6Cu(2)] complex have been determined by X-ray diffraction. Finally, oxidation of Cu(2+) to Cu(3+) has been studied by cyclic voltammetry in water, which revealed that the redox reaction occurs only when the copper cation is within the diamino-diimido compartment. Moreover, both functionalization of the primary amines with bulky substituents and apical coordination of Cu(2+) make access to the 3+ oxidation state more difficult and disrupt the reversibility of the electrochemical process.     

Shear driven planar Couette and Taylor-like instabilities for a class of compressible isotropic elastic solids

We study the possibility for an isotropic elastic body to support forms of instability induced by shear stress states which are reminiscent of the planar Couette and the Taylor–Couette patterns observed in the flow of viscous fluids. Here, we investigate the emergence of bifurcating periodic deformations for an infinitely long compressible elastic block confined between and attached to parallel plates which are subject to a relative shear displacement. We specialize our analysis by considering a generalized form of the Blatz–Ko strain energy function and show through numerical representative examples that planar Couette modes are always preferred with respect to the twisting Taylor–Couette modes. Finally, we introduce a suitably restricted form of the strong ellipticity condition for the incremental elasticity tensor and discuss its significance in this bifurcation problem.     

Heavy fragments emission in the 84Kr on 12C reaction at 35 MeV/nucleon

Heavy residues of collisions of ⁸⁴Kr + ¹²C at 35 MeV/amu were measured using time of flight ΔE?E telescopes. An important part of the total cross section leads to events that have all the characteristics of an equilibrated composite system decaying by heavy fragment emission. The experimental yields are well reproduced using a statistical model.