Chromophoric macrocycles from the oxidation of bis(aminofurazanylic) ethers of 1,2-diols

A series of chromophoric azofurazan-containing macrocycles 6a–c and 7a–d were synthesized from bis(aminofurazanylic) ethers of 1,2-diols 4a–d by dibromoisocyanurate oxidation. The macrocycle closure is a result of NN bond formation. An ion-binding ability of these compounds was tested. The macrocycles were characterized by NMR, MS, IR, and UV spectroscopy. The X-ray crystal structures of the macrocycles 6a, 7c , and linear counterpart 12 are reported. © 2004 Wiley Periodicals, Inc. Heteroatom Chem 15:131–145, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/hc.10226     

CVD-diamond 13C: A new SRS-active crystal

Stimulated Raman scattering has been discovered in a monoisotopic ¹³C diamond single crystal grown by chemical vapor deposition. The first results of the experimental study of impulsive χ⁽³⁾-nonlinear lasing under femtosecond IR pumping are presented.     

Straightforward one-pot synthesis of benzofuroxans from o-halonitrobenzenes in ionic liquids

Treatment of o-halonitrobenzenes with sodium azide in a [empyrr][BF4]/Bu4NBr/H2O system gives benzofuroxans in high yields, with the recovery and reuse of the ionic liquid for at least ten times.     

Predicting the DNA sequence dependence of nanopore ion current using atomic-resolution Brownian dynamics

It has become possible to distinguish DNA molecules of different nucleotide sequences by measuring ion current passing through a narrow pore containing DNA. To assist experimentalists in interpreting the results of such measurements and to improve the DNA sequence detection method, we have developed a computational approach that has both the atomic-scale accuracy and the computational efficiency required to predict DNA sequence-specific differences in the nanopore ion current. In our Brownian dynamics method, the interaction between the ions and DNA is described by three-dimensional potential of mean force maps determined to a 0.03 nm resolution from all-atom molecular dynamics simulations. While this atomic-resolution Brownian dynamics method produces results with orders of magnitude less computational effort than all-atom molecular dynamics requires, we show here that the ion distributions and ion currents predicted by the two methods agree. Finally, using our Brownian dynamics method, we find that a small change in the sequence of DNA within a pore can cause a large change in the ion current, and validate this result with all-atom molecular dynamics.     

Phase diagram and high-pressure boundary of hydrate formation in the ethane-water system

Dissociation temperatures of gas hydrate formed in the ethane-water system were studied at pressures up to 1500 MPa. In situ neutron diffraction analysis and X-ray diffraction analysis in a diamond anvil cell showed that the gas hydrate formed in the ethane-water system at 340, 700, and 1840 MPa and room temperature belongs to the cubic structure I (CS-I). Raman spectra of C-C vibrations of ethane molecules in the hydrate phase, as well as the spectra of solid and liquid ethane under high-pressure conditions were studied at pressures up to 6900 MPa. Within 170-3600 MPa Raman shift of the C-C vibration mode of ethane in the hydrate phase did not show any discontinuities, which could be evidence of possible phase transformations. The upper pressure boundary of high-pressure hydrate existence was discovered at the pressure of 3600 MPa. This boundary corresponds to decomposition of the hydrate to solid ethane and ice VII. The type of phase diagram of ethane-water system was proposed in the pressure range of hydrate formation (0-3600 MPa).     

Digital Colorimetry of Indicator Test-Systems Using a Smartphone and Chemometric Analysis in Determination of Quinolones in Pharmaceuticals

Journal of Applied Spectroscopy - A combined approach was developed for the identification and determination of quinolone antibiotics in pharmaceuticals using solid-state fluorescence digital...     

X-ray diffraction characterization of epitaxial CVD diamond films with natural and isotopically modified compositions

Comparative investigations of homoepitaxial diamond films with natural and modified isotopic compositions, grown by chemical vapor deposition (CVD) on type-Ib diamond substrates, are carried out using double-crystal X-ray diffractometry and topography. The lattice mismatch between the substrate and film is precisely measured. A decrease in the lattice constant on the order of (Δa/a)_relax ～ (1.1–1.2) × 10^–4 is recorded in isotopically modified ¹³С (99.96%) films. The critical thicknesses of pseudomorphic diamond films is calculated. A significant increase in the dislocation density due to the elastic stress relaxation is revealed by X-ray topography.     

A multigroup diffusion solver using pseudo transient continuation for a radiation-hydrodynamic code with patch-based AMR

We present a scheme to solve the nonlinear multigroup radiation diffusion (MGD) equations. The method is incorporated into a massively parallel, multidimensional, Eulerian radiation-hydrodynamic code with Adaptive Mesh Refinement (AMR). The patch-based AMR algorithm refines in both space and time creating a hierarchy of levels, coarsest to finest. The physics modules are time-advanced using operator splitting. On each level, separate “level-solve” packages advance the modules. Our multigroup level-solve adapts an implicit procedure which leads to a two-step iterative scheme that alternates between elliptic solves for each group with intra-cell group coupling. For robustness, we introduce pseudo transient continuation (Ψtc). We analyze the magnitude of the Ψtc parameter to ensure positivity of the resulting linear system, diagonal dominance and convergence of the two-step scheme. For AMR, a level defines a subdomain for refinement. For diffusive processes such as MGD, the refined level uses Dirichlet boundary data at the coarse–fine interface and the data is derived from the coarse level solution. After advancing on the fine level, an additional procedure, the sync-solve (SS), is required in order to enforce conservation. The MGD SS reduces to an elliptic solve on a combined grid for a system of G equations, where G is the number of groups. We adapt the “partial temperature” scheme for the SS; hence, we reuse the infrastructure developed for scalar equations. Results are presented. We consider a multigroup test problem with a known analytic solution. We demonstrate utility of Ψtc by running with increasingly larger timesteps. Lastly, we simulate the sudden release of energy Y inside an Al sphere (r = 15 cm) suspended in air at STP. For Y = 11 kT, we find that gray radiation diffusion and MGD produce similar results. However, if Y = 1 MT, the two packages yield different results. Our large Y simulation contradicts a long-standing theory and demonstrates the inadequacy of gray diffusion.