Diastereoselective ortho-lithiation of [5]ferrocenophanes

Planarly chiral ferrocene derivatives with bridged cyclopentadienyl rings are interesting ligands in asymmetric catalysis. A planar stereogenic unit is conveniently introduced by diastereoselective ortho-lithiation. The directed lithiation of several [5]ferrocenophane derivatives followed by quenching with chlorodiphenylphosphane led to planarly chiral ligands. The sense of diastereoselection was studied by computational methods. Absolute configuration of methoxy phosphane was determined by single crystal X-ray diffraction study.     

Solution of porous medium type systems by linear approximation schemes

Summary The convergence of semi-discrete and discrete linear approximation schemes is analysed for nonlinear degenerate parabolic systems of porous medium type. The enthalpy formulation and variational technique are used. The semi-discretization used reduces the original parabolic P.D.E. to linear elliptic P.D.E. The algebraic correction arising from nonlinearities is treated by Newton-like iterations in finite steps. Some numerical experiments are discussed and compared with the analytical solutions.Supported by the Alexander von Humboldt-Foundation in 1989, and by SFB 123, University Heidelberg     

Bipartite labelings of trees and the gracesize

Let T = (V, E) be a tree whose vertices are properly 2-colored. A bipartite labeling of T is a bijection f: V ← {0, 1, ?, | E |} for which there is a k such that whenever f(u) ≤ k < f(v), then u and v have different colors. The α-size of the tree T is the maximum number of distinct values of the induced edge labels |f(u) - f(v)|, uv ? E, taken over all bipartite labelings f of T. We investigate the asymptotic behavior of the α-size of trees. Let α(n) be the smallest α-size among all the trees with n edges. As our main result we prove that 5(n + 1)/7 ≤ α(n) ≤ (5n + 9)/6. A connection with the graceful tree conjecture is established, in that every tree with n edges is shown to have “gracesize” at least 5n/7. © 1995 John Wiley & Sons, Inc.     

Remarks on my paper: packing of incongruent circles on the sphere

The paper [3] contains an upper bound to the weighted density of a packing of circles on the unit sphere with radii from a given finite set. This bound is attained by many packings and has applications to problems of solidity. In the present note it is shown that a certain condition imposed on the set of admissible radii can be removed by modifying the original proof of the theorem.     

Fibrillar Networks of Glycyrrhizic Acid for Hybrid Nanomaterials with Catalytic Features

Self‐assembly of the naturally occurring sweetening agent, glycyrrhizic acid (GA) in water is studied by small‐angle X‐ray scattering and microscopic techniques. Statistical analysis on atomic force microscopy images reveals the formation of ultralong GA fibrils with uniform thickness of 2.5 nm and right‐handed twist with a pitch of 9 nm, independently of GA concentration. Transparent nematic GA hydrogels are exploited to create functional hybrid materials. Two‐fold and three‐fold hybrids are developed by introducing graphene oxide (GO) and in situ‐synthesized gold nanoparticles (Au NPs) in the hydrogel matrix for catalysis applications. In the presence of GO, the catalytic efficiency of Au NPs in the reduction of p‐nitrophenol to p‐aminophenol is enhanced by 2.5 times. Gold microplate single crystals are further synthesized in the GA hydrogel, expanding the scope of these hybrids and demonstrating their versatility in materials design.     

New isostructural transition metal complexes with a non‐innocent dithiolate ligand

Three new complexes with 3,6‐dichlorobenzene‐1,2‐dithiol (bdtCl₂), namely methyltriphenylphosphonium bis(3,6‐dichlorobenzene‐1,2‐dithiolato‐κ²S,S′)cobaltate(1−), (C₁₉H₁₈P)[Co(C₆H₂Cl₂S₂)₂], (I), bis(methyltriphenylphosphonium) bis(3,6‐dichlorobenzene‐1,2‐dithiolato‐κ²S,S′)cuprate(2−) dimethyl sulfoxide disolvate, (C₁₉H₁₈P)₂[Cu(C₆H₂Cl₂S₂)₂]·2C₂H₆OS, (II), and methyltriphenylphosphonium bis(3,6‐dichlorobenzene‐1,2‐dithiolato‐κ²S,S′)cuprate(1−), (C₁₉H₁₈P)[Cu(C₆H₂Cl₂S₂)₂], (III), have been synthesized and characterized by single‐crystal X‐ray diffraction. The X‐ray structure analyses of all three complexes confirm that the four donor S atoms form a slightly distorted square‐planar coordination arrangement around the central metal atom. An interesting finding for both the Cu^II and Cu^III complexes, i.e. (II) and (III), respectively, is that the coordination polyhedra are principally the same and differ only slightly with respect to the interatomic distances.     

Fire hazard and heat of combustion of sunflower seed hull pellets

This study is concerned with the investigation of the impact of heat flux on the fire hazard and the effective heat of combustion of sunflower seed hull pellets. Pellets produced by pressing common sunflower seed hulls (Helianthus annuus L.) were investigated. The samples were dried on water content of 0 mass% at a temperature of 103 ± 2 °C. The fire hazard and the heat of combustion have been determined via the cone calorimeter and by the testing procedure per ISO 5660-1:2015 at three heat fluxes (25, 35 and 50 kW m⁻²). The peak heat release rate increases with the increasing of the heat flux from 446 (at a heat flux of 25 kW m⁻²) to 601 kW m⁻² (at a heat flux of 50 kW m⁻²). The carbon monoxide yield lies in the interval from 82.50 (at a heat flux of 25 kW m⁻²) to 154.15 g kg⁻¹ (at a heat flux of 50 kW m⁻²). The effective heat of combustion decreases with the increasing of the heat flux from 15.84 (at a heat flux of 25 kW m⁻²) to 14.58 MJ kg⁻¹ (at a heat flux of 50 kW m⁻²).

     

Stress characterization of elastodynamics with continuously distributed defects

A pure stress formulation of linear nonhomogeneous anisotropic elastodynamics with continuously distributed defects (EcDD) is proposed, and well known solutions of ECDD corresponding to stationary and moving concentrated plastic fields in an infinite body are recovered by direct integration of the stress field equation. A new interpretation of the solutions is given.     

Sorption of cesium from water solutions on potassium nickel hexacyanoferrate-modified <Emphasis Type="Italic">Agaricus bisporus</Emphasis> mushroom biomass

In order to gain biosorbent that would have the ability to bind cesium ions from water solution effectively, potassium nickel hexacyanoferrate(II) (KNiFC) was incorporated into the mushroom biomass of Agaricus bisporus. Cesium sorption by KNIFC-modified A. bisporus biosorbent was observed in batch system, using radiotracer technique using ¹³⁷Cs radioisotope. Kinetic study showed that the cesium sorption was quite rapid and sorption equilibrium was attained within 1 h. Sorption kinetics of cesium was well described by pseudo-second order kinetics. Sorption equilibrium was the best described by Freundlich isotherm and the distribution coefficient was at interval 7,662–159 cm³ g⁻¹. Cesium sorption depended on initial pH of solution. Cesium sorption was very low at pH₀ 1.0–3.0. At initial pH 11.0, maximum sorption of cesium was found. Negative effect of monovalent (K⁺, Na⁺, NH₄ ⁺) and divalent (Ca²⁺, Mg²⁺) cations on cesium sorption was observed. Desorption experiments showed that 0.1 M potassium chloride is the most suitable desorption agent but the complete desorption of cesium ions from KNiFC-modifed biosorbent was not achieved.