Surfactant–Thermal Method to Synthesize a Novel Two‐Dimensional Oxochalcogenide

A new two‐dimensional (2D) oxosulfide, (N₂H₄)₂Mn₃Sb₄S₈(μ₃‐OH)₂ ( 1 ), has been successfully synthesized under surfactant–thermal conditions with hexadecyltributylphosphonium bromide as the surfactant. Compound 1 has a layered structure and contains a novel [Mn₃(μ₃‐OH)₂]_n chain along the b‐axis. The photocatalytic activity for compound 1 has been demonstrated under visible‐light irradiation and continuous H₂ evolution was observed. Our results indicate that surfactant–thermal synthesis could be a promising method for growing novel crystalline oxochalcogenides with interesting structures and properties.     

Linking (n − 2)-dimensional panels inn-space II: (n − 2, 2)-frameworks and body and hinge structures

An (n – 1, 2)-framework inn-space is a structure consisting of a finite set of (n – 2)-dimensional panels and a set of rigid bars each joining a pair of panels using ball joints. A body and hinge (or (n + 1,n – 1)-) framework inn-space consists of a finite set ofn-dimensional bodies articulated by a set of (n – 2)-dimensional hinges, i.e., joints in 2-space, line hinges in 3-space, plane-hinges in 4-space, etc. In this paper we characterize the graphs of all rigid (n – 1, 2)- and (n + 1,n – 1)-frameworks inn-space. Rigidity here is statical rigidity or equivalently infinitesimal rigidity.     

Almost Minimum Diameter Orientations of Semicomplete Multipartite and Extended Digraphs

 An orientation of a digraph D is a spanning subdigraph of D obtained from D by deleting exactly one arc between x and y for every pair x≠y of vertices such that both x y and y x are in D. Almost minimum diameter orientations of certain semicomplete multipartite and extended digraphs are considered, several generalizations of results on orientations of undirected graphs are obtained, some conjectures are posed. Received: August 31, 2000 Final version received: October 30, 2001 Acknowledgments. Part of this work was done when the first author was visiting the Department of Mathematics, National University of Singapore. The departmental hospitality and financial support are very much appreciated.     

On the Cayley factorization of calotte conditions

The calotte condition is the projective condition that a cycle of lines radiating from the vertices of a planen-gon be the correct projection of a ring of faces surrounding ann-gonal piece of plane in space, the spatial figure being not entirely coplanar. This condition can be expressed as a homogeneous bracket polynomial. In general, this polynomial is not Cayley factorable. Henry Crapo conjectured that it becomes so when multiplied by a product ofn−4 brackets. It is the purpose of this article to prove this conjecture.     

A Useful Method for Oxidative Deoximation with Photooxygenation

Photooxygenatlon of oximc derivatives in methanolic sodium hydroxide solution at ice temperature enabled the recovery of the parent ketones in high yield. This method is useful to deprotect a ketoxime.     

Structure and properties of zirconium oxide thin films prepared by filtered cathodic vacuum arc

Zirconium oxide (ZrO₂) thin films deposited at room temperature by the filtered cathodic vacuum arc (FCVA) technique are detailed in terms of the film structure, composition, morphology, and optical and mechanical properties, which are tailored by the oxygen (O₂) flow rate during deposition. The relationships between the film structure, composition, morphology, and properties are emphasized. With an increasing O₂ flow rate, the film evolves in structure from amorphous, through a pure monoclinic phase with varying preferential orientation, to amorphous again, accompanied by an increase in the O/Zr atomic ratio and a conversion of Zr ions from low oxidation states into Zr⁴⁺. Such a structural trend arises from the change in composition, and influences the film morphology and mechanical properties so that the amorphous films exhibit small clusters on the surface and smoother morphology as well as lower hardness compared with the polycrystalline films. The film composition rather than the density dominates the optical properties, where the transmittance and the optical band gap increase with increasing O/Zr values, while the refractive index and extinction coefficients behave conversely with the lowest refractive index (2.16 at 550 nm) approaching the bulk value (2.2) . PACS  68.55.Jk; 78.66.Nk; 68.37.Ps     

Micromechanical properties of carbon nitride films deposited by radio-frequency-assisted filtered cathodic vacuum arc

Super-hard and elastic carbon nitride films have been synthesized by using an off-plane double-bend filtered cathodic vacuum arc combined with a radio-frequency nitrogen-ion beam source. A nanoindenter was used to determine the micromechanical properties of the deposited films. X-ray photoelectron spectroscopy was used to study the composition and bonding structure of the deposited films. The influence of nitrogen ion energy on the structure and micromechanical properties of the deposited films was systematically studied. As the nitrogen ion energy is increased, the microhardness, Young’s modulus and elastic recovery also increase, reaching a maximum of 47 GPa, 400 GPa, and 87.5%, respectively, at a nitrogen ion energy of 100 eV. Further increase in nitrogen ion energy results in a decrease in microhardness, Young’s modulus and elastic recovery of the deposited films. The formation of five-membered rings, as indicated by XPS, which causes bending of the basal planes and forms a three-dimensional rigid covalent bond network, contributes to the super-hardness, Young’ s modulus and high elastic recovery of the films deposited at a nitrogen ion energy of 100 eV. Revised version: 29 October 2001 / Accepted: 7 November 2001 / Published online: 2 May 2002     

Synthetic Modulation of an Unstable Dehydrosecodine-type Intermediate and Its Encapsulation into a Confined Cavity Enable Its X-ray Crystallographic Observation

Numerous indole alkaloids such as the iboga- and aspidosperma-type are believed to be biosynthesized via a common hypothetical intermediate, dehydrosecodine. The highly reactive nature of dehydrosecodine-type compounds has hampered their isolation and structural elucidation. In this study, we achieved the first X-ray structural determination of a dehydrosecodine-type compound by integrating synthetic optimization of the reactivity and stabilizing the fragile molecule by encapsulation into a supramolecular host. Formation of a 1 : 1 complex of the dehydrosecodine-type labile guest bearing both vinyl indole and dihydropyridine units with the host was observed. This integrated approach not only provides insights into the biosynthetic conversions but also allows stabilization and storage of the reactive and otherwise short-lived intermediate within the confined hydrophobic cavity.     

Temporal phase retrieval from a complex field in digital holographic interferometry

We describe a novel method of processing complex phasors in digital holographic interferometry (DHI). Unlike the commonly used digital phase subtraction method that operates on the phase itself, the proposed method operates on the complex phasor instead. Two temporal phase retrieval algorithms are developed in which the complex phasor of each pixel is measured and analyzed as a function of time. The developed algorithms are demonstrated in profile measurement of step heights. Experimental results show that the proposed phase retrieval algorithms for DHI perform well compared with conventional methods.     

Evaluation of chemical labeling strategies for monitoring HCV RNA using vibrational microscopy

Raman and coherent anti-Stokes Raman scattering (CARS) microscopies have the potential to aid in detailed longitudinal studies of RNA localization. Here, we evaluate the use of carbon-deuterium and benzonitrile functional group labels as contrast agents for vibrational imaging of hepatitis C virus (HCV) replicon RNA. Dynamic light scattering and atomic force microscopy were used to evaluate the structural consequences of altering HCV subgenomic replicon RNA. Modification with benzonitrile labels caused the replicon RNA tertiary structure to partially unfold. Conversely, deuterium-modified replicon RNA was structurally similar to unmodified replicon RNA. Furthermore, the deuterated replicon RNA provided promising vibrational contrast in Raman imaging experiments. The functional effect of modifying subgenomic HCV replicon RNA was evaluated using the luciferase gene as a genetic reporter of translation. Benzonitrile labeling of the replicon RNA prevented translation in cell-based luciferase assays, while the deuterated replicon RNA retained both translation and replication competency. Thus, while the scattering cross-section for benzonitrile labels was higher, only carbon-deuterium labels proved to be non-perturbative to the function of HCV replicon RNA.