A novel synthesis route for brookite rich titanium dioxide photocatalyst involving organic intermediate

Journal of Sol-Gel Science and Technology - High temperature stable brookite rich titanium dioxide of average crystallite size 20&;nbsp;nm has been prepared by a novel aqueous sol–gel...     

Unified approach to photo-and electro-production of mesons with arbitrary spins

A new approach to identify the independent amplitudes along with their partial wave multipole expansions, for photo-and electro-production is suggested, which is generally applicable to mesons with arbitrary spin-parity. These amplitudes facilitate direct identification of different resonance contributions.      

1/f Noise in dye-sensitized solar cells and NIR photon detectors

All electronic devices are plagued with 1/f noise originating from many causes. The most important factors contributing to 1/f noise in a semiconductor is believed to be recombination of carriers and their trapping at defects and impurity sites. Adsorption of moisture and electron acceptor molecules enhances the intensity of 1/f noise. Amazingly, some molecular species that strongly chelate to the semiconductor surface, suppress 1/f noise owing to passivation of the recombination sites. Thus in addition to sensitization, the dye adsorbed on the nanocrystallites plays a key role in mitigation of recombinations. For this reason dye-sensitized heterojunctions could also find application as low noise NIR photon detectors. Experiments conducted with oxide semiconductors (TiO₂, ZnO, SnO₂) indicate that the mode of binding of dyes at specific sites determines the extent to which the recombination and 1/f noise are suppressed. The transport of electrons in a nanocrystalline matrix is diffusive with a diffusion coefficient D depending on the trapping and detrapping processes. Thus passivation of trapping sites by the adsorbed dye is expected to increase the response time which can be expressed as τ  L²/D, where L = thickness of the nanocrystalline film. Measurement techniques and construction of a dye-sensitized NIR photon detector will be discussed.     

Magnetic properties of Ca-doped SrRuO3 from full-potential calculations

We have carried out accurate generalized-gradient-corrected fully-relativistic full-potential calculations for Sr_1−xCa_xRuO₃ (x=0, 0.25, 0.5, 0.75, and 1) in para-, ferro-, and A-, C-, and G-type antiferromagnetic configurations. We have performed electronic structure calculations for the experimentally observed orthorhombic structure as well as the hypothetical cubic structure. Our results are analyzed with the help of total, site-, spin-, and orbital-projected density of states. The total-energy studies show that CaRuO₃ stabilizes in the G-type antiferromagnetic state. The octahedral tilting owing to the relatively small radius of Ca²⁺ leads to weak hybridization between Ru 4d and O 2p. This weak hybridization along with exchange splitting causes a pseudogap-like feature close to the Fermi level, which should stabilize G-type antiferromagnetic ordering in CaRuO₃. However, powder neutron diffraction data on CaRuO₃ taken at 8 and do not show any magnetic peaks, implying that CaRuO₃ exhibits a spin-glass-like state with dominant short-range antiferromagnetic interaction. The calculated magnetic ground state of Sr_1−xCa_xRuO₃ is found to be consistent with the experimental findings. We have also calculated optical spectra as well as X-ray and ultra-violet photoemission spectra and Ru and O K-edge X-ray absorption spectra for G-type CaRuO₃ and found good agreement with available experimental spectra.     

Synthesis of cryptophycins via an N-acyl-beta-lactam macrolactonization

An efficient and concise approach to the synthesis of the macrolide core of the cryptophycins has been developed. A novel macrolactonization utilizing a reactive acyl-beta-lactam intermediate incorporates the beta-amino acid moiety within the 16-membered macrolide core. This modular approach, involving a cyanide-initiated acyl-beta-lactam ring opening followed by cyclization, was successfully applied to the total synthesis of cryptophycin-24. The strategy was also used in an efficient synthesis of the 6,6-dimethyl-substituted dechlorocryptophycin-52. In this case, the cyanide-initiated ring opening of the bis-substituted 2-azetidinone followed by macrolactonization was achieved through a catalytic process.     

Ion solvation in water clusters

We describe here molecular dynamics computer simulations performed to study the solvation of ions (Cl^? and Na⁺) in water clusters. Our simulations show that the calculated structure and dynamics of the clusters is very sensitive to the potential model which is used to describe the interactions. From the comparison with thermodynamic data and data from the photoelectron spectra we conclude that in Cl^?(H₂O)_n (n≤20) clusters the ion is located on the surface of the cluster.