Reactions in the presence of organic phosphites,I: High temperature amidation in the absence of solvents

When reacted for periods of 5–10 min at temperatures of about 280–300°C in the presence of certain organic phosphites polymers that contain available carboxy and aliphatic amine groups undergo amidation. This reaction can increase the molecular weight of many aliphatic polyamides by their self-reaction in an extruder. Block or graft copolymers can be formed by reacting polymers that contain aliphatic amines with others that contain carboxyl. Studies of model compounds in the companion article (II) indicate that polymerization proceeds through an diaryloxy or dialkoxy amino phosphine intermediate to produce amide bonds and disubstituted phosphite reaction by-products. In the absence of primary amines in the reaction mixture an ester is slowly formed from the carboxyl end group of the polymer and the oxysubstituent of the phosphite. In no case was a phosphorus-containing mixed anhydride detected. The mechanistic identity of the low temperature reactions in article II and the high temperature reactions in this article has not been proved conclusively, however.     

Syntheses of Retinol Glycosides Using β-glucosidase in SCCO<Subscript>2</Subscript> Media

β-Glucosidase isolated from sweet almond catalyzed syntheses of water soluble retinol glycosides were carried out in SCCO₂ media with carbohydrates—D-glucose 2, D-galactose 3, D-mannose 4, D-fructose 5, and D-sorbitol 6. Retinol glycosides yields were in the 9–34% range. Reaction with D-fructose 5 gave a highest yield of 34%. Excellent regioselectivity was observed with D-mannose 4 and D-sorbitol 6 which gave exclusively C1β-mannoside and C1-D-sorbitolide.     

Direct observation of the flux-line vortex glass phase in a type II superconductor

The order of the vortex state in La1.9Sr0.1CuO4 is probed using muon-spin rotation and small-angle neutron scattering. A transition from a Bragg glass to a vortex glass is observed, where the latter is composed of disordered vortex lines. In the vicinity of the transition the microscopic behavior reflects a delicate interplay of thermally induced and pinning-induced disorder.     

Global errors of numerical ODE solvers and Lyapunov's theory of stability

The error made by a numerical method in approximating the solutionof the initial value problem (t) = f (t,x), x (0) = x₀, t 0, x (t) R^d varies with the time of integration.The increase of the global error ||(t; h)– x (t)||, where (t, h) is an approximationderived by a numerical method with time step h, with time tdetermines the feasibility of approximating the solution accuratelyfor increasing t. However, the best available theoretical boundsinvolve the Lipshitz constant and are exponential in t for someproblems where the actual increase of global error is only linearin time. Using techniques from Lyapunov's theory of stability, we provethat the increase of global errors is linear in time for trajectoriesof dynamical systems which fall into a hyperbolic and attractingcycle or into a hyperbolic and attracting torus, with the flowon the torus being quasi-periodic. The increase is linear fornon-linear problems when certain stability properties of thesolution can be verified. The error analysis uses a conditioningfunction E(t) associated with the exact solution, which capturesthe propagation and accumulation of global errors. Received 4 January 1999. Accepted 15 December 1999.     

Microstructural study of thin films of 5 mol% gadolinia doped ceria prepared by pulsed laser ablation

Microstructural characterization of thin films of 5 mol% gadolinia doped ceria films deposited by pulsed laser ablation in the energy range 100–600 mJ/pulse has been investigated, as deposited films were found to be nanocrystalline with preferred orientation. X-ray diffraction analysis revealed that the size of the nanocrystals of doped ceria does not vary significantly with increasing laser energy, whereas transmission electron microscopy study showed a uniform distribution of nanocrystal of 8–10 nm for energies ≤200 mJ/pulse and nanocrystals embedded in a large crystalline matrix of doped ceria for energies in the range 400–600 mJ/pulse. Although the laser-ablated films were totally free from secondary phases, lattice imaging of the large grained doped ceria showed growth-induced defects, such as dislocations and ledges.     

Applications of Raman spectroscopy in dentistry part II: Soft tissue analysis

Raman spectroscopy is rapidly moving from an experimental technique for the analysis of biological molecules to a tool for the real-time clinical diagnosis and in situ evaluation of the oral tissue in medical and dental research. The purpose of this study is to identify various applications of Raman spectroscopy, to evaluate the contemporary status, and to explore future directions in the field of dentistry. Several in-depth applications are presented to illustrate Raman spectroscopy in early diagnosis of soft tissue abnormalities. Raman spectroscopy allows researchers to analyze histological and biochemical composition of biological tissues. The technique not only demonstrates its role in the disclosure of dysplasia and malignancy, but also in performing guided biopsies, diagnosing sialoliths, and assessment of surgical margins. Raman spectroscopy is used to identify the molecular structures and their components to give substantial information about the chemical structure properties of these molecules. In this article, we acquaint the utilization of Raman spectroscopy in analyzing the soft tissues in relation to dentistry.     

Synthesis of novel Ru(2)C under high pressure-high temperature conditions

We report here, for the first time, synthesis of the Fe(2)N type hexagonal phase of ruthenium carbide by a high pressure-high temperature technique using a laser heated diamond anvil cell (LHDAC). The synthesis is carried out by laser heating a mixture of pure elements, Ru and C, at very low 'pressure' of 5?GPa and T?～?2000?K. The structure of the temperature quenched high pressure phase is characterized by in situ high pressure x-ray diffraction (HPXRD) and is corroborated by ex situ TEM imaging and diffraction, carried out for the first time on the retrieved sample synthesized by LHDAC. The lattice parameters of Ru(2)C at ambient pressure are found to be a?=?2.534???and c?=?4.147??. In situ HPXRD studies up to 14.2?GPa yield a bulk modulus of 178(4)?GPa. Electronic structure calculations reveal the system to be metallic in nature with a degree of covalence along the Ru-C bond. As ruthenium is isoelectronic to osmium, this result for Ru(2)C has significant implications in the synthesis and study of osmium carbides.     

Metabolomic Profiling,Antioxidant and Enzyme Inhibition Properties and Molecular Docking Analysis of Antarctic Lichens

The lichen species Lecania brialmontii, Pseudephebe pubescens, and Sphaerophorus globosus are part of the prominent lichenoflora of the Antarctic territory. In this work, we report the metabolomic identification of ethanolic extracts of these species, their antioxidant and cholinesterase enzyme inhibitory activity, and conduct a molecular docking analysis with typical compounds. Eighteen compounds were identified by UHPLC-ESI-QTOF-MS in L. brialmontii, 18 compounds in P. pubescens, and 14 compounds in S. globosus. The content of phenolic compounds was variable among the species, ranging from 0.279 to 2.821 mg AG/g, and all three species showed high inhibition potential on the cholinesterase enzymes. Molecular docking showed important interactions between AChE and BChE with the selected compounds. This study evidences the chemical fingerprint of three species of the order Lecanorales that support the continuation of the study of other biological activities and their potential for medical research.     

Solvent-Free Depolymerization of Plastic Waste Enabled by Plastic-Catalyst Interfacial Engineering

Depolymerization of condensation polymers by chemolysis often suffers from the large usage of solvents and homogeneous catalysts such as acids, bases, and metal salts. The catalytic efficiency of heterogeneous catalysts is largely constrained by the poor interfacial contact between solid catalysts and solid plastics below melting points. We report here our discovery of autogenous heterogeneous catalyst layer on polyethylene terephthalate surfaces during the generally believed homogeneous catalytic depolymerization process. Inspired by the “contact mass” concept in industrial chlorosilane production, we further demonstrate that the construction of plastic-catalyst solid-solid interfaces enables solvent-free depolymerization of polyethylene terephthalate by vapor phase methanolysis at relatively low temperatures. Trace amounts of earth-abundant element (zinc) introduced by electrostatic adsorption is sufficient for catalyzing the depolymerization. The concept of plastic-catalyst contact mass interfacial catalysis might inspire new pathways for tackling plastic waste problems.