Robust topological edge states from one-dimensional diatomic chain photonic crystals

The Su–Schrieffer–Heeger (SSH) model can occur in a one-dimensional (1D) diatomic chain photonic crystal (PC) in which a unit cell includes two same slabs (atoms). With different intervals of the two slabs, the two combined 1D PCs can support topological edge states in all photonic boundary bandgaps. These topological edge states come from the inversion of topological phase of the bands through the band folding effect. When the sum of the two atom intervals in the two different 1D PCs equals to the unit cell length, these edge state frequencies keep invariant.

Powder X-ray diffraction of trimethoprim Form I, C14H18N4O3

Trimethoprim crystallizes in the triclinic space group P-1 (#2) with a = 10.5085(3), b = 10.5417(2), c = 8.05869(13) Å, α = 101.23371(21), β = 112.1787(3), γ = 112.6321(4)°, V = 743.729 Å3, and Z = 2. A reduced cell search in the Cambridge Structural Database yielded three previous structure determinations, using data collected at 100 K, 173 K, and room temperature. In this work, the sample was ordered from the United States Pharmacopeial Convention (USP) and analyzed as-received. The room temperature (295 K) crystal structure was refined using synchrotron (λ = 0.412826 Å) powder diffraction data and optimized using density functional theory techniques. We found similar hydrogen bonding patterns with the previous determinations. In addition, we identified two C–H⋯O hydrogen bonds, which also contribute to the crystal energy. When comparing the previously reported trimethoprim structure determinations, the unit cell length lattice parameters were found to contract at lower temperatures, particularly 100 K. All structures show reasonable agreement, with unit cell length differences ranging between 0.05 and 0.15 Å. The diffraction data for this study were collected on beamline 11-BM at the Advanced Photon Source, and the powder X-ray diffraction pattern of the compound has been submitted to ICDD® for inclusion in the Powder Diffraction File™ (PDF®).

Tunable plasmons in regular planar arrays of graphene nanoribbons with armchair and zigzag-shaped edges

Recent experimental evidence for and the theoretical confirmation of tunable edge plasmons and surface plasmons in graphene nanoribbons have opened up new opportunities to scrutinize the main geometric and conformation factors, which can be used to modulate these collective modes in the infrared-to-terahertz frequency band. Here, we show how the extrinsic plasmon structure of regular planar arrays of graphene nanoribbons, with perfectly symmetric edges, is influenced by the width, chirality and unit-cell length of each ribbon, as well as the in-plane vacuum distance between two contiguous ribbons. Our predictions, based on time-dependent density functional theory, in the random phase approximation, are expected to be of immediate help for measurements of plasmonic features in nanoscale architectures of nanoribbon devices.

The double-stranded ladder-like structure of poly[[bis(μ2-acetato-κ2O:O′)bis(acetato-κO)bis(μ-4,4′-bipyridine-κ2N:N′)dicopper(II)] 4-nitrophenol disolvate tetrahydrate]

The reaction of 4,4′-bipyridine with copper acetate in the presence of 4-nitrophenol led to the formation of the title compound, {[Cu(CH3COO)2(C10H8N2)]·C6H5NO3·2H2O}n. The complex forms a double-stranded ladder-like coordination polymer extending along thebaxis. The double-stranded polymers are separated by 4-nitrophenol and water solvent molecules. The two CuIIcentres of the centrosymmetric Cu2O2ladder rungs have square-pyramidal coordination environments, which are formed by two acetate O atoms and two 4,4′-bipyridine N atoms in the basal plane and another acetate O atom at the apex. The ladder-like double strands are separated from each other by one unit-cell length along thecaxis, and are connected by the water and 4-nitrophenol molecules through a series of O—H...O and C—H...O hydrogen-bonding interactions and two unique intermolecular π–π interactions.

Analysis of cryo-electron micrographs of HbS fibers

We are studying the structure of deoxy-sickle hemoglobin (HbS) fibers by cryo-electron microscopy (cryo-EM). Cryo-EM affords potentially higher resolution than negative staining in part because the electron scattering by unstained protein includes internal structure which may be poorly depicted by an envelope of negative stain. This advantage, however, is partially compromised by a low signal to noise ratio (snr) and low image contrast. Our cryo-EM images were recorded with specimen doses of 7 e-/Å2 at 100 keV, ca. 100 nm defocus, and 39,000 magnification on Kodak SO-163 film.Helical particles usually have a constant pitch. Thus the rotation about the axis is coupled to translation along the length of the particle. HbS fibers, however, have a variable pitch which ranges from 6° to 12° rotation per unit cell length (63 Å). Consequently, the rotation of HbS fibers is partially decoupled from translation and the twist of each unit cell and its relative angular rotation about fiber the axis cannot be determined by particle symmetry.

The influence of π-bonding and steric factors on helahalogeno-metallates

A comparison of the asymmetric stretching frequency v3 and unit cell length a0 for a series of hexahalogeno-metallates A2MX6 [A = K+, Rb+, Cs+ and NH4+, M = Ru, Os, Sn and Te and X = Cl,Br] has been made. Trends observed for the tellurium and tin compounds may be related to stericfactors whereas possible M → X dπ-pπ bonding may explain the opposite trend found for ruthenium and osmium compounds.