Effect Of R3 Research Articles

An efficient approach to angular tricyclic molecular architecture via Nazarov-like cyclization and double ring-expansion cascade

A modular and efficient method for constructing angular tri-carbocyclic architectures containing quaternary carbon center(s) from 1,3-dicycloalkylidenyl ketones is established, which involves an unconventional synergistic cascade of a Nazarov cyclization and two ring expansions. It features high selectivity, mild conditions and convenient operation, wide scope and easy availability of substrate. Substitution with R1 and R2 at the 4πe-system with electron-donating group favors this reaction, while that with electron-withdrawing group or proton disfavors. The electron-donating group as R1 directs the initial ring expansion at its own site, while the p-π- or n-π- associated substituent as R2 favors selectively the later ring expansion near its location because of the beneficial maintenance of an original conjugated system. The stereoselectivity has proved to be governed by either the steric effect of R3 and R4 at the expanded rings, or the migration ability of the migrating atom. Density Functional Theory calculation suggests the initial Nazarov cyclization would be the rate-determining step. A racemic total synthesis of the natural (±)-waihoensene is realized in 18 steps by use of this methodology.

The anti-inflammatory effect of R3 in atherosclerosis is associated with inhibition of NLRP3 inflammasome

The anti-inflammatory effect of R3 in atherosclerosis is associated with inhibition of NLRP3 inflammasome

Effect of R3+ (R = Pr, Nd, Eu and Gd) substitution on the structural, electrical, magnetic and optical properties of Mn-ferrite nanoparticles

Undoped and rare earth substituted manganese ferrite (MF) nanoparticles, Mn0.9R0.1Fe2O4 (where R = Nd, Pr, Eu and Gd) were synthesized by sol–gel technique. The structural, morphological and magnetic properties of the as-synthesized samples were determined and characterized by X-ray diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR), Transmission Electron Microscopy (TEM) and Vibrating Sample Magnetometer (VSM). The XRD spectra reveal the formation of the single-phase cubic spinel structure. The average crystallite size evaluated from XRD data was found to be in the range of 8.19–21.4 nm and is consistent with the results of TEM. In addition, lattice parameter is found to increase with the rare earth (Pr, Nd, Eu, and Gd) substitution. DC electrical resistivity as a function of temperature was studied by using two-probe technique and found to decrease with increase in temperature which reveals the semiconducting nature of the samples. Simultaneously, the optical analysis shows significant decreases in band gap energy with rare earth content and ranging from 2.03 to 1.73 eV. It is also seen that rare earth substituted manganese ferrites show soft ferrimagnetic behavior and saturation magnetization decreases with the substitution of rare earths. Because of the soft ferrimagnetic behavior, samples have expected application in magnetic hyperthermia for cancer therapy and various other applications.

Co-Dopant Influence on the Persistent Luminescence of BaAl2O4:Eu2+,R3+

The R3+ (rare earth) co-dopants may have a surprisingly important role in persistent luminescence – enhancement of up to 1–3 orders of magnitude may be obtained in the performance of these phosphor materials – depending strongly on the R3+ ion, of course. In this work, the effects of the R3+ co-dopants in the BaAl2O4:Eu2+,R3+ materials were studied using mainly thermoluminescence (TL) and synchrotron radiation XANES methods. In BaAl2O4, the conventional and persistent luminescence both arise from the 4f7→4f65d1 transition of Eu2+, yielding blue–green emission color. The former, in the presence of humidity, turns to more bluish because of creation of an additional Eu2+ luminescence centre which is not, however, visible in persistent luminescence. The trap structure in the non-co-doped BaAl2O4:Eu2+ is rather complex with 4–5 TL bands above room temperature. With R3+ co-doping, this basic structure is modified though no drastic change can be observed. This underlines the fact that even very small changes in the trap depths can produce significant modifications in the persistent luminescence efficiency. It should be remembered that basically the persistent luminescence performance is controlled by the Boltzmann population law depending exponentially on both the temperature and trap depth.Some mechanisms for persistent luminescence have suggested the presence of either divalent R2+ or tetravalent RIV during the charging of the Eu2+ doped materials. The present XANES measurements on BaAl2O4:Eu2+,R3+ confirmed the presence of only the trivalent form of the R3+ co-dopants excluding both of these pathways. It must thus be concluded, that the energy is stored in intrinsic and extrinsic defects created by the synthesis conditions and charge compensation due to R3+ co-doping. Even though the effect of the R3+ co-dopants was carefully exploited and characterized, the differences in the effect of different R3+ ions with very similar chemical and spectroscopic properties could not be explained in a satisfactory manner. More work is – and perhaps a completely new approach may be – needed.

Synchrotron Radiation Study of the M2MgSi2O7:Eu2+ Persistent Luminescence Materials

The synchrotron radiation luminescence and excitation spectra of the Eu2+ doped M2MgSi2O7 (M = Ca, Sr, Ba) materials were investigated at the SUPERLUMI station of HASYLAB at DESY, Germany. The measurement of the band gap (Eg) energy of all three host lattices using the excitation spectra of Eu2+ gave values around 7 eV. The measured band gap energies were very similar but slightly higher than those calculated with the DFT-methods. The effect of R3+ co-doping was studied at different temperatures between 10 K and room temperature. A significant increase in the band gap energy was observed with decreasing temperature. In contrast, no noteworthy change in this value was observed as a function of the R3+ co-doping ion.

Effects of R3 and R□ R terms on R2 inflation

To study the generality of inflation from lagrangians containing higher orders of curvature, we consider the effects of R 3 and R□ R terms on the R 2 inflationary scenario. Both direct analysis and conformal techniques are used. We find that both terms restrict the initial conditions which will lead to a satisfactory inflationary cosmology.

Effect of R3+ Ions on the Structure and Properties of Lanthanum Borate Glasses

Glass formation in the systems (mole percent) 25La2O3· xR2O3· (75 ‐ X)B2O3 (R = Al, Ga) and (25 ‐ x)La2O3· xLn2O3· 75B2O3 (Ln = Gd, Er, Y) was investigated. Up to 25 mol% Al2O3 or Ga2O3 can be substituted for B2O3, but more than ∼ 5 mol% Ln2O3 substituted for La2O3 caused macro phase separation. X‐ray diffraction and infrared analysis of these glasses and their devitrified products indicate that the basic structural units are similar to (B3O6)∞ chains found in binary 25La2O3* 75B2O3 glass. However, the BO4 units in the (B3O6)∞ chains are replaced by AlO4 or GaO4, units when Al2O3 or GaZO3 is substituted for B2O3. In these systems, Al2O3, Ga2O3, and B2O3 act as glass formers, whereas Ln2O3 and La2O3 act as network modifiers. The substitution of either R2O3 or Ln2O3 in the lanthanum borate system changes the separation distance between adjacent (B3O6)∞ chains. The effect of this structural change on the molar volume, transformation temperature, thermal expansion coefficient, and transformation‐range viscosity is discussed.