Generation of high-energy broadband femtosecond deep-ultraviolet pulses by highly nondegenerate noncollinear four-wave mixing in a thin transparent solid

We present a simple and efficient technique for the generation of ultrashort deep-ultraviolet pulses based on four-wave mixing of noncollinear laser pulses in a thin solid. Sub-30-fs pulses (Fourier-limit of 13 fs) centered at 270 nm, with energies up to 6 μJ, were obtained by mixing the fundamental and the second harmonic of a Ti:sapphire amplifier in fused silica. Temporal characterization was performed with a dispersionless self-diffraction FROG setup. Spectra as broad as 20 nm were also obtained that can in principle support sub-4-fs deep-ultraviolet pulses.The results are well described by two-dimensional numerical simulations.     

N,N′‐Bis(2‐hydroxycyclohexyl)‐N,N′‐bis(2‐hydroxyethyl)ethane‐1,2‐diaminium dichloride

The achiral meso form of the title compound, C₁₈H₃₈N₂O₄²⁺·2Cl⁻, crystallizes to form undulating layers consisting of chains linked via weak hydroxyalkyl C—H...Cl contacts. The chains are characterized by centrosymmetric hydrogen‐bonded dimers generated via N—H...Cl and hydroxycycloalkyl O—H...Cl interactions. trans‐N‐Alkyl bridges subdivide the chains into hydrophilic segments flanked by hydrophobic cycloalkyl stacks along [001].     

Nanoporous piezo- and ferroelectric thin films

Nanoporous barium titanate and lead titanate thin films (～100 nm calculated from ellipsometric data) are prepared starting from sol-gel solutions modified with a commercially available block-copolymer and evaporation-induced self-assembly methodology. The tuning of the thermal treatment followed by in situ ellipsometry allows the decomposition of the organic components and of the structuring agent leading to the formation of porous tetragonal crystalline perovskite structures as observed by XRD, HRTEM, SEM, and ellipsoporosimetry. Both nanoporous barium titanate and lead titanate thin films present local piezoelectric and ferroelectric behavior measured by piezoresponse force microscopy (PFM), being promising platforms for the preparation of the generation of new multifunctional systems.     

A novel methodology for evaluation of formation constants of complexes: example of lanthanide-Arsenazo III complexes

A novel method is proposed for the computation of formation constants of complexes. It makes use essentially of the data from the first stages of the titration and is based on the Taylor expansion of the concentration of the ligand as a function of the titrant concentration. The applicability of the methodology is examplified by the computation of the complexation constants of lanthanides (Ln) by 3,6-bis[(2-arsonophenyl)azo]-4,5-dihydroxy-2,7-naphtalenedisulphonic acid disodium salt (Arsenazo III). Arsenazo III is known to form stable complexes with a large variety of ions. The spectrophotometric study of these complexes in the visible domain is facilitated by the presence of chromophore groups in the ligand. In the present work, spectral deconvolution was used to improve the accuracy in the determination of formation constants of complexes between Arsenazo III and lanthanides. It turns out that all the 11 lanthanides studied here form the same type of complexes with this ligand. For each of them, the three formation constants correspond, respectively, to Ln to Ar ratios 1:1, 1:2 and 2:2. Their approximate values are in the ranges: K₁₁=10⁵; K₁₂=10¹⁰; K₂₂=10¹⁵. Accurate values are given in the text. The results are compared with those obtained with the classical iteration method which makes use of the whole titration curve. The two techniques give satisfactorily convergent results. The new methodology might be useful in the treatment of the competition of two ligands for the complexation of the same lanthanide, where the first stages of the titration of only one of the complexants is experimentally available.     

Diiso­propyl­phosphitocobalamin–acetone–water (1/3.48/7.56)

The di­iso­propyl­phosphite ligand in the title diiso­propyl­phosphitocobalamin compound, [Co(C₆₈H₁₀₂N₁₃O₁₇P₂)]·3.48C₃H₆O·7.56H₂O, coordinates to the Co^III atom via its P atom. The crystal structure is isomorphous with that of other cobalamins that adopt packing type II [Gruber, Jogl, Klintschar & Kratky (1998). Vitamin B₁₂ and B₁₂ Proteins, edited by Kräutler, Arigoni & Golding, pp. 335–347. New York: Wiley–VCH], with a Co—P bond length [2.227 (1) Å] similar to that found in other phosphitocobalamins. The structural trans influence in cobalamins is discussed.     

Validated HPLC method for the standardization of Phyllanthus niruri (herb and commercial extracts) using corilagin as a phytochemical marker

Phyllanthus niruri L., commonly known in Brazil as ‘quebra‐pedra’, has long been used in the treatment of diverse diseases and especially urolithiasis. The therapeutic effects of P. niruri are attributed to various compounds present in the plant, including the hydrolysable tannin corilagin. In the present study, high‐performance liquid chromatography (HPLC‐/PAD) profiles of leaves and commercial extracts of P. niruri were examined and three compounds, found to be present in all of the samples studied, were isolated by open column chromatography over C₁₈ silica gel followed by preparative HPLC. These compounds were identified by nuclear magnetic resonance as corilagin, rutin and ethyl 3,4,5‐trihydroxybenzoate. Corilagin, which has been proposed as a phytochemical marker for P. niruri, was employed as an external standard in the development and validation of a rapid and efficient qualitative and quantitative HPLC assay for the analyte. The method may be applied in the standardization of herbs and phytomedicines commercialized in Brazil as quebra‐pedra. Copyright © 2009 John Wiley & Sons, Ltd.     

An interfacial complex in ZnO and its influence on charge transport

The segregation of native defects and Bi impurities to a high-angle grain boundary in ZnO is studied by first-principles calculations. It is found that the presence of Bi(Zn) increases the concentration of native defects of acceptor type in the grain boundary. This leads to the formation of a Bi(Zn)+V(Zn)+O(i) interfacial complex under O-rich conditions and exhibits a localized acceptor state. This state, which is different from that of the isolated impurity, gives the grain boundary p-type character and when embedded between n-type ZnO grains is consistent with the double Schottky barrier model for Bi-doped ZnO varistors.     

Segregation Effects at a High-Angle Twist Boundary in ZnO

Ab initio density functional plane-wave pseudopotential calculations were performed for a = 7 ( = 21.79°) [0001] twist boundary in ZnO with and without the presence of Sb impurities. The segregation energies revealed a significant driving force for segregation and it was shown that the formation of an Sb monolayer was favoured. Decreased coordination in the boundary core suggested a trend towards the formation of an intergranular phase. The impurity states caused by the monolayer were located within the band gap and higher in energy relative to the state produced by a single impurity. Charge transfer to the Sb monolayer was observed indicating a possible enhancement of the grain boundary potential barrier.     

Necrosis Depth and Photodynamic Threshold Dose with Redaporfin-PDT

Predicting the extent of necrosis in photodynamic therapy (PDT) is critical to ensure that the whole tumor is treated but vital structures, such as major blood vessels in the vicinity of the tumor, are spared. The models developed for clinical planning rely on empirical parameters that change with the nature of the photosensitizer and the target tissue. This work presents an in vivo study of the necrosis in the livers of rats due to PDT with a bacteriochlorin photosensitizer named redaporfin using both frontal illumination and interstitial illumination. Various doses of light at 750 nm were delivered 15 min postintravenous administration of redaporfin. Sharp boundaries between necrotic and healthy tissues were found. Frontal illumination allowed for the determination of the photodynamic threshold dose—1.5 × 10¹⁹ photons cm⁻³—which means that the regions of the tissues exposed to more than 11 mm of ROS evolved to necrosis. Interstitial illumination produced a necrotic radius of 0.7 cm for a light dose of 100 J cm⁻¹ and a redaporfin dose of 0.75 mg kg⁻¹. The experimental data obtained can be used to inform and improve clinical planning with frontal and interstitial illumination protocols.     

Fermionic Representation of Two-Dimensional Dimer Models

Dimer models in two dimensions give rise to well-known statistical lattice problems, which can be exactly solved by the same combinatorial techniques associated with the Ising model and which have been used to account for the phase transitions in a number of physically interesting systems. More recently, dimer models have been regarded as classical limits of the quantum ground state of some antiferromagnetic systems. We then revisit an early transfer-matrix calculation for the dimer model on the simple square lattice. We write a spin representation for the transfer matrix associated with the canonical partition function of two paradigmatic dimers models, on the 4–8 lattice, with an Ising-type transition, and on the brick lattice, with a peculiar commensurate–incommensurate transition. Using standard techniques, the problem is reduced to the calculation of the eigenvalues of a system of free fermions.