Quantum chemical studies on the tautomerism of some potentially tautomeric aminoindazole derivatives

The aqueous phase AM1, PM3, and PM5 calculation data had indicated that when a potentially tautomeric amino group is placed at 3C position of the indazole ring the ring-chain tautomerism becomes feasible. However, when the amino group is placed at 4–7C of the indazole ring only the annular tautomerism was found to be feasible and no effect of amino group to provoke a ring chain tautomerism was observed. On the other hand amino form of 3 amino substituted indazole was found to be predominant over imino forms whereas for the 4–7 amino substituted indazoles imino forms were found to be predominant over amino forms. The attempt to apply soft–hard base and soft nucleophile–electrophile criteria to protonation and tautomerism phenomena was successful.     

Halogen-Bonding Heteroditopic [2]Catenanes for Recognition of Alkali Metal/Halide Ion Pairs

The first examples of halogen bonding (XB) heteroditopic homo[2]catenanes were prepared by discrete Na⁺ template-directed assembly of oligo(ethylene glycol) units derived from XB donor-containing macrocycles and acyclic bis-azide precursors, followed by a Cu^I-mediated azide-alkyne cycloaddition macrocyclisation reaction. Extensive ¹H NMR spectroscopic studies show the [2]catenane hosts exhibit positive cooperative ion-pair recognition behaviour, wherein XB-mediated halide recognition is enhanced by alkali metal cation pre-complexation. Notably, subtle changes in the catenanes’ oligo(ethylene glycol) chain length dramatically alters their ion-binding affinity, stoichiometry, complexation mode, and conformational dynamics. Solution-phase and single-crystal X-ray diffraction studies provide evidence for competing host-separated and direct-contact ion-pair binding modes. We further demonstrate the [2]catenanes are capable of extracting solid alkali-metal halide salts into organic media.     

Exploiting the Catenane Mechanical Bond Effect for Selective Halide Anion Transmembrane Transport

The first examples of [2]catenanes capable of selective anion transport across a lipid bilayer are reported. The neutral halogen bonding (XB) [2]catenanes were prepared via a chloride template-directed strategy in an unprecedented demonstration of using XB⋅⋅⋅anion interactions to direct catenane assembly from all-neutral components. Anion binding experiments in aqueous-organic solvent media revealed strong halide over oxoanion selectivity, and a marked enhancement in the chloride and bromide affinities of the catenanes relative to their constituent macrocycles. The catenanes additionally displayed an anti-Hofmeister binding preference for bromide over the larger iodide anion, illustrating the efficacy of employing sigma-hole interactions in conjunction with the mechanical bond effect to tune receptor selectivity. Transmembrane anion transport studies conducted in POPC LUVs revealed that the catenanes were more effective anion transporters than the constituent macrocycles, with high chloride over hydroxide selectivity, which is critical to potential therapeutic applications of anionophores. Remarkably these outperform existing acyclic halogen bonding anionophores with regards to this selectivity. Record chloride over nitrate anion transport selectivity was also observed. This represents a rare example of the direct translation of intrinsic anion binding affinities to anion transport behaviour, and demonstrates the key role of the catenane mechanical bond effect for enhanced anion transport selectivity.     

In situ implantation of PolyPOSS blocks in Nafion matrix to promote its performance in direct methanol fuel cell

Fabrication of recast Nafion^®-117 membrane using the dipolar aprotonic solvent will normally lead to a random matrix. On the contrary, when a designed amount of vinyl-pendant octasiloxane (Q₈M₈^V) cubic molecules was included into the Nafion^® matrix during the recasting process and then subjected to polymerization, a nonrandom matrix was obtained. This paper provides an insight into the matrix-formatting role of rigid poly(Q₈M₈^V) blocks, generated in situ in Nafion^® matrix, according to thermal analyses (thermogravimetric analysis (TGA), dynamic mechanical analysis (DMA) and Differential Scanning Calorimetry (DSC)) and electron microscopic images of the resulting composite matrix. The P(Q₈M₈^V) played a role in restricting random extensions of proton-conducting channels (PCCs) and promoted ordered assembling of Nafion^® molecules. As a result, compared with the recast pristine Nafion^® membrane, the composite membranes containing P(Q₈M₈^V) of 5–15 wt.% manifested obvious improvement on both repression of methanol permeability and promotion of power density output of the single direct methanol fuel cell (DMFC).     

Raman spectroscopy of carbon nitride films deposited using the filtered cathodic vacuum-arc technique combined with a radio-frequency nitrogen-ion beam

TiO₂–Fe₂O₃ semiconducting films were prepared by the resistive evaporation method on a glass substrate. Impedance and optical absorption measurements were made on these samples. From the impedance analysis (assuming an equivalent RC circuit), it was observed that the admittance and impedance functions are frequency dependent. From the optical absorption spectrum, the energy band-gap value was found to be 1.15 eV. The charge-carrier concentration (N) is calculated by using Mott–Schottky relations. I-V measurements were also made on these samples. Received: 2 November 1999 / Accepted: 24 August 2000 / Published online: 9 November 2000     

α-Iithioalkylphosphonates as Functional Group Carriers. an in Situ Acrylic Ester Synthesis

Condensation of α -lithioalkylphosphonates with diethylcarbonate in the presence of LDA generates carbetoxy-alkylphoshonate anions which upon treatment at room temperature with aldehydes constitutes an in situ acrylic ester synthesis.     

Optimization of arches using genetic algorithm

An optimization procedure is presented for the minimum weight and strain energy optimization for arch structures subjected to constraints on stress, displacement and weight responses. Both thickness and shape variables defining the natural line of the arch are considered. The computer program which is developed in this study can be used to optimize thick, thin and variable thickness curved beams/arches. An automated optimization procedure is adopted which integrates finite element analysis, parametric cubic spline geometry definition, automatic mesh generation and genetic algorithm methods. Several examples are presented to illustrate optimal arch structures with smooth shapes and thickness variations. The changes in the relative contributions of the bending, membrane and shear strain energies are monitored during the whole process of optimization.     

Shape measurement by multi-illumination method in digital holographic interferometry

In this paper, temporal phase unwrapping and short time Fourier transform (STFT) are proposed for shape measurement of an object with height steps by digital holographic interferometry (DHI). A series of digital holograms is recorded with a high-speed CCD camera using a multi-illumination method. Each pixel is processed along the time axis independently of other pixels. Two novel methods are proposed to process the wrapped phase maps: the first method is based on complex phasor (CP) and temporal phase unwrapping, and the second method is based on CP and STFT. In the STFT method, continuous phase maps are obtained by integration of the exacted instantaneous frequency. The continuous phase map can characterize the profile of the object with height steps. An experiment is conducted to verify the validity of the proposed methods.