Compression of silver in a diamond anvil cell: Pressure dependences of strength and grain size from X-ray diffraction data

Two silver samples, coarse grained (c-Ag, grain size 300±30 nm) and nanocrystalline (n-Ag, grain size 55±6 nm), are compressed in a diamond anvil cell in separate experiments. The pressure is increased in steps of ∼3 GPa and the diffraction pattern recorded at each pressure. The grain size and compressive strength are determined from the analysis of the diffraction line-widths. The grain size of c-Ag decreases rapidly from 300±30 nm at ambient pressure to 40±8 nm at 15 GPa, and then gradually to 20±3 nm at 40 GPa. After pressure release to ambient condition, the grain size is 25±4 nm. The strength at ambient pressure is 0.18±0.05 GPa and increases to 1.0±0.3 GPa at 40 GPa. The grain size of n-Ag decreases from 55±6 nm at ambient pressure to 17±4 nm at 15 GPa and to 14±3 nm at 55 GPa. After release of pressure to ambient condition, the grain size is 50±7 nm. The strength increases from 0.51±0.07 GPa at ambient pressure to 3.5±0.4 GPa at 55 GPa. The strength is found to vary as the inverse of the square-root of the grain size. The results of the present measurements agree well with the grain-size dependence of strength derived from the hardness versus grain size data at ambient pressure available in the literature.     

Nanostructured CuO/SrTiO3 bilayered thin films for photoelectrochemical water splitting

Bilayered thin films of CuO/SrTiO₃ with varying thickness of CuO were deposited by sol–gel spin-coating technique on indium tin oxide substrate and used as photoelectrode in the photoelectrochemical cell for water splitting reaction. Maximum photocurrent density of 1.85 mA/cm² at ?0.9 V/saturated calomel electrode was exhibited by 590-nm-thick CuO/SrTiO₃ bilayered photoelectrode, which is approximately eight times higher than that for CuO and 30 times higher than that for SrTiO₃. The bilayered system offered increased photocurrent density and enhanced photoconversion efficiency, attributed to improved conductivity, which ameliorate separation of the photo-generated carriers at the CuO/SrTiO₃ interface and higher value of flatband potential. Details about synthesis and various characterisations involving X-ray diffraction and scanning electron microscopy have been discussed. An energy band diagram has been proposed to dwell upon the mechanism of charge carrier transfer across the interface.     

An atomic scale mechanism for the antimalarial action of chloroquine from density functional theory calculations

The X-ray crystal structures of complexes between the antimalarial drugs quinine, quinidine and halofantrine and their biological target, iron(III) ferriprotoporphyrin IX (FePPIX), have been reported in the literature (de Villiers et al. in ACS Chem Biol 7:666, 2012; J Inorg Biochem 102:1660, 2008) and show that all three drugs utilize their zwitterionic alkoxide forms to coordinate to the iron atom via Fe–O bonds. In this work, density functional theory calculations with implicit solvent corrections have been used to model the energetics of formation of these complexes. It is found that the cost of formation of the active zwitterionic form of each drug is more than offset by the energy of its binding to FePPIX, such that the overall energies for complexation of all three drugs with FePPIX are moderately favourable in water, and rather more favourable in n-octanol as solvent. The calculations have been extended to develop an analogous model for the complex between FePPIX and chloroquine, whose structure is not presently known from experiment.     

Oxygen‐Initiated Stereoselective Thermal Isomerisation of a Cyclobutane Derivative in the Solid State

Solid‐state [2+2] photochemical cycloaddition reactions have been extensively studied after the classical work of Schmidt in the 1960s. Of these, trans‐1,2‐bis(4′‐pyridyl)ethylene (bpe) is one of the well‐studied alkenes to synthesize tetrakis(4‐pyridyl)cyclobutane (tpcb). However, almost all the solid‐state [2+2] cycloaddition reactions of bpe yielded, almost exclusively, one of the four possible isomers, namely, the rctt‐tpcb (r=regio c=cis and t=trans). Here we describe a stereoselective synthesis of the tetrahedrally disposed rtct‐tpcb by the solid‐state thermal isomerization of the rctt‐isomer in atmospheric air. We propose that this isomerization occurs through a topochemical unimolecular mechanism by a radical chain pathway, initiated by molecular oxygen. This is supported by the nature of products formed in air and nitrogen, detection of a radical in ESR spectral studies, ESI‐MS crossover experiments, VT PXRD studies along with QM, MD and docking calculations. The formation of a unique isomer by thermal isomerization may be a general phenomenon to quantitatively synthesize other useful stereoisomers from the existing isomers of cyclobutane derivatives.     

F-Doped Co3O4 photocatalysts for sustainable H2 generation from water/ethanol

p-Type Co(3)O(4) nanostructured films are synthesized by a plasma-assisted process and tested in the photocatalytic production of H(2) from water/ethanol solutions under both near-UV and solar irradiation. It is demonstrated that the introduction of fluorine into p-type Co(3)O(4) results in a remarkable performance improvement with respect to the corresponding undoped oxide, highlighting F-doped Co(3)O(4) films as highly promising systems for hydrogen generation. Notably, the obtained yields were among the best ever reported for similar semiconductor-based photocatalytic processes.     

Investigation of the influence of incomplete fusion on complete fusion of <Superscript>12</Superscript>C-induced reactions at ≈ 4–7.2 MeV/nucleon

In this paper, we present the results of our investigation of reaction dynamics leading to incomplete fusion of heavy ions at moderate excitation energies, especially the influence of incomplete fusion on complete fusion of ¹²C -induced reactions at specific energies ≈ 4–7.2M eV/nucleon. Excitation functions of various reaction products populated via complete and/or incomplete fusions of a ¹²C projectile with ⁹³Nb, ⁵⁹Co and ⁵²Cr targets were measured at several specific energies ≈ 4–7.2 MeV/nucleon, using a recoil catcher technique, followed by off-line γ-ray spectrometry. The measured excitation functions were compared with theoretical values obtained using the PACE4 statistical model code. For representative non-α-emitting channels in the ¹²C + ⁹³Nb system, the experimentally measured excitation functions were, in general, found to be in good agreement with the theoretical predictions. However, for α-emitting channels in the ¹²C + ⁹³Nb, ¹²C + ⁵⁹Co, and ¹²C + ⁵²Cr systems, the measured excitation functions were higher than the predictions of the theoretical model code, which may be credited to incomplete fusion reactions at these energies. An attempt was made to estimate the incomplete fusion fraction for the present systems, which revealed that the fraction was sensitive to the projectile energy and mass asymmetry of the entrance channel.     

Three new dicyclic solutions of (21, 42, 20, 10, 9)-designs

We give three dicyclic solutions of a (21, 42, 20, 10, 9)-design which are new. Though the parameters of this design belong to the series (4t + 1, 8t + 2, 4t, 2t, 2t − 1), 4t + 1 = 21 is not a prime power.     

SWKB formalism for confined quantum systems

A formalism is developed to study spatially confined one‐dimensional quantum mechanical systems in the framework of the supersymmetric Wentzel–Kramers–Brillouin (SWKB) method. The approximation technique is applied to estimate the energy eigenvalues of two confined potentials—the harmonic oscillator V(x)=x² and the screened Coulomb potential V(x)=−V₀sech²x. The results thus obtained are found to be in better agreement with the exact numerical values than are those from the ordinary WKB approach. © 2000 John Wiley & Sons, Inc. Int J Quant Chem 79: 267–273, 2000     

Thermal Cleavage of Cyclobutane Rings in Photodimerized Coordination‐Polymeric Sheets

Three coordination polymers, [Cd₂(pvba)₂(tbdc)(dmf)₂] ( 1 ), [Co₂(pvba)₂(tbdc)(dmf)₂(H₂O)₂] ( 2 ), and [Ni₂(pvba)₂(tbdc)(dmf)₂(H₂O)₂] ( 3 ) (H₂tbdc=2,3,5,6‐tetrabromobenzenedicarboxylic acid, Hpvba=trans‐2‐(4′‐pyridyl)vinylbenzoic acid), were synthesized by solvothermal methods. The solid‐state structures of compounds 1 and 2 were determined by X‐ray crystallography. In compounds 1 and 2 , the bimetallic cores acted as secondary building units that connected the tbdc ligands in one direction and a pair of pvba ligands, which were aligned in a head‐to‐tail parallel manner, in the orthogonal direction to form sheet structures. The C?C bonds in these pvba ligand pairs in all three compounds were well‐aligned to undergo quantitative [2+2] cycloaddition reactions in the solid state under UV irradiation, thereby yielding their cyclobutane derivatives. This photochemical reaction appeared to facilitate structural transformations from one 2D structure into another in the solid state. The photoreactive Co^II‐ and Ni^II coordination polymers exhibited a reversible dehydration–rehydration reaction that was accompanied by color changes from pink to purple and green to yellow, respectively, owing to a change in coordination number from six to five. Magnetic studies showed that compound 2 was an antiferromagnet, which displayed a field‐dependent transition with a critical field (H_c) of 40 kOe at 2 K; the antiferromagnetic interaction between the Co₂ units was strengthened and weakened by dehydration and UV irradiation, respectively. The cyclobutane ligand in the photodimerized products was cleaved on heating to yield a mixture of trans‐ and cis‐isomers of pvba, as monitored by ¹H NMR spectroscopy. The Cd^II coordination polymer underwent quantitative cleavage of the cyclobutane ring whilst the other two underwent partial cleavage.