Search results for "Phase"
showing 10 items of 6344 documents
Oxidative halogenation of substituted pyrroles with Cu(II). PartIII. Bromination and chlorination of 2-benzoylpyrrole
1992
The bromination of 2-benzoylpyrrole with copper(II) bromide in the homogeneous and the heterogeneous phase is described, giving 4- and 5-monobromo derivatives whose ratio decreases as the temperature is increased. The same reaction with copper(II) chloride in acetonitrile at 60° produces 5-chloro-2-benzoylpyrrole as the major product. 4,5-Dihalopyrroles in good yields are obtained with an excess of halogenating agent.
Sublimable Single Ion Magnets Based on Lanthanoid Quinolinate Complexes: The Role of Intermolecular Interactions on Their Thermal Stability
2018
We report the design, preparation, and characterization of two families of thermally robust coordination complexes based on lanthanoid quinolinate compounds: [Ln(5,7-Br2q)4]− and [Ln(5,7-ClIq)4]−, where q = 8-hydroquinolinate anion and Ln = DyIII, TbIII, ErIII, and HoIII. The sodium salt of [Dy(5,7-Br2q)4]− decomposes upon sublimation, whereas the sodium salt of [Dy(5,7- ClIq)4]−, which displays subtly different crystalline interactions, is sublimable under gentle conditions. The resulting film presents low roughness with high coverage, and the molecular integrity of the coordination complex is verified through AFM, MALDI-TOF, FT-IR, and microanalysis. Crucially, the single-molecule magnet …
Dragging a Polymer Chain into a Nanotube and Subsequent Release
2008
We present a scaling theory and Monte Carlo (MC) simulation results for a flexible polymer chain slowly dragged by one end into a nanotube. We also describe the situation when the completely confined chain is released and gradually leaves the tube. MC simulations were performed for a self-avoiding lattice model with a biased chain growth algorithm, the pruned-enriched Rosenbluth method. The nanotube is a long channel opened at one end and its diameter $D$ is much smaller than the size of the polymer coil in solution. We analyze the following characteristics as functions of the chain end position $x$ inside the tube: the free energy of confinement, the average end-to-end distance, the averag…
Solute retention in reversed-phase chromatography as a function of stationary phase properties: Effect of n-alkyl chain length and ligand density
1988
Two series of bonded phases were synthesized employing LiChrospher Si 100, 10 μm and n-alkyldimethylmonochlorosilanes as silanizing reagents. In series A the n-alkyl chain length, n, of the bonded phase was varied between 1 and 20 at a constant ligand density of 3.5±0.2μmol·m−2. In series B the ligand density, d, was gradually changed from 0 to 4.1μmol·m−2 on the C1, C4, C6, C8 and C18 bonded phases, respectively.
Semiconductor Nanocrystals with Multifunctional Polymer Ligands
2002
In this letter, we describe the preparation of a versatile polymer ligand, which can be attached to CdSe/ZnS semiconductor nanocrystals via a phase transfer reaction. The ligand is based on a chain of reactive esters, which can, in principle, be substituted by any compound containing amino-functionalities. The polymer/nanocrystal complexes are characterized in terms of structure and photostability.
Synthesis of glycosylated β3-homo-threonine conjugates for mucin-like glycopeptide antigen analogues
2010
Glycopeptides from the mucin family decorated with tumour-associated carbohydrate antigens (TACA) have proven to be important target structures for the development of molecularly defined anti-cancer vaccines. The strategic incorporation of β-amino acid building blocks into such mucin-type sequences offers the potential to create pseudo-glycopeptide antigens with improved bioavailability for tumour immunotherapy. Towards this end, TN and TF antigen conjugates O-glycosidically linked to Fmoc-β3-homo-threonine were prepared in good yield via Arndt–Eistert homologation of the corresponding glycosyl α-amino acid derivative. By incorporation of TN-Fmoc-β3hThr conjugate into the 20 amino acid tand…
Phase Separation and Nematic Order in Lyotropic Solutions: Two Types of Polymers with Different Stiffnesses in a Common Solvent
2021
The interplay of the isotropic-nematic transition and phase separation in lyotropic solutions of two types of semiflexible macromolecules with pronounced difference in chain stiffness is studied by Density Functional Theory and Molecular Dynamics simulations. While the width of the isotropic-nematic two-phase coexistence region is narrow for solutions with a single type of semiflexible chain, the two-phase coexistence region widens for solutions containing two types of chains with rather disparate stiffness. In the nematic phase, both types of chains contribute to the nematic order, with intermediate values of the order parameter compared to the corresponding single component solutions. As …
Photoswitchable Smectic Liquid-Crystalline Elastomers
2005
We succeeded in the synthesis of azo side chain containing polysioxanes with broad smectic C* and A phases. In these polymers the phase transition temperatures can be shifted reversibly by up to 17°C by irradiation with UV (cis) or VIS (trans) light. Thin films of these polymers in the smectie phase (both on substrates and as free-standing films) orient perfectly in a homeotropic manner. As a consequence, the aze chromophores do no longer absorb during a perpendicular illumination with light (dichroism). It is thus possible to crosslink these films photochemically to prepare photoswitchable smectic LC elastomers.
Synthesis and phase behaviour of liquid-crystalline side group polyesters
1990
Abstract Several series of liquid-crystalline side group polymers with a polyester backbone structure have been synthesized using mesogenic diethylmalonate and 1,3-propanediol derivatives. The structures of the polymer backbone and the mesogenic units have been varied systematically. As shown by differential scanning calorimetry, polarizing microscopy and X-ray diffraction, the side group polyesters exhibit nematic and/or smectic mesophases. Polyesters synthesized from mesogenic diethylmalonate derivatives can tolerate long non-mesogenic segments in the polymer main chain without losing their liquid crystal properties. X-ray studies suggest that some of the smectic polymers exhibit interdig…
Perovskite solar cells employing organic charge-transport layers
2013
Thin-film photovoltaics play an important role in the quest for clean renewable energy. Recently, methylammonium lead halide perovskites were identified as promising absorbers for solar cells(1). In the three years since, the performance of perovskite-based solar cells has improved rapidly to reach efficiencies as high as 15%(1-10). To date, all high-efficiency perovskite solar cells reported make use of a (mesoscopic) metal oxide, such as Al2O3, TiO2, or ZrO2, which requires a high-temperature sintering process. Here, we show that methylammonium lead iodide perovskite layers, when sandwiched between two thin organic charge-transporting layers, also lead to solar cells with high power-conve…