Search results for "Periodic table"
showing 10 items of 262 documents
Self-Organization of 2-Acylaminopyridines in the Solid State and in Solution
2010
Aggregation of 2-acylaminopyridines and their 6-methyl derivatives in chloroform solution was studied by (1)H, (13)C, and (15)N NMR spectroscopies. The results were compared with (13)C and (15)N CPMAS NMR and IR spectral as well as with X-ray structural data. Intermolecular interactions in solution and in solid state were found to have a similar nature. Relatively strong N(amide)-H···N(pyridine) intermolecular hydrogen bonds enable dimerization to take place. Steric interactions in N-pivaloyl- and N-1-adamantylcarbonyl as well as that caused by the 6-methyl group hinder formation of the dimeric aggregates stabilized by the N(amide)-H···N(pyridine) intermolecular hydrogen bonds. In general, …
Fracture Resistance of New Metal-Free Materials Used for CAD-CAM Fabrication of Partial Posterior Restorations
2020
Background and Objectives: To evaluate in vitro the fracture resistance and fracture type of computer-aided design and computer-aided manufacturing (CAD-CAM) materials. Materials and Methods: Discs were fabricated (10 ×
Evaluation of the enamel etching pattern of self-etching adhesives
2010
Objectives: To evaluate the capacity of seven self-etching adhesives (SEAs) to demineralize ground enamel in comparison with traditional phosphoric acid etchant (PAE) using SEM and statistical analysis. Materials and methods: 80 caries-free extracted human third molars were divided into 8 groups ( n = 10). Enamel bur-cut surfaces were prepared and, strictly following the manufacturers’ instructions, treated with three priming agents of two-step self-etching adhesives: Aqua Resulcin Prime (Group 1); Peak™ (Group 2); Clearfil Protect Bond (Group 3); four one-step self-etch (all-in-one) adhesives, G-Bond (Group 4); Artegral One (Group 5); Clearfil S3 Bond (Group 6); Adper Easy Bond (Group 7); …
Chemical investigation of hassium (element 108).
2002
The periodic table provides a classification of the chemical properties of the elements. But for the heaviest elements, the transactinides, this role of the periodic table reaches its limits because increasingly strong relativistic effects on the valence electron shells can induce deviations from known trends in chemical properties. In the case of the first two transactinides, elements 104 and 105, relativistic effects do indeed influence their chemical properties, whereas elements 106 and 107 both behave as expected from their position within the periodic table. Here we report the chemical separation and characterization of only seven detected atoms of element 108 (hassium, Hs), which were…
Molecular Camouflage: Making Use of Protecting Groups To Control the Self-Assembly of Inorganic Janus Particles onto Metal-Chalcogenide Nanotubes by …
2011
Hard and soft: Binding of inorganic Pt@Fe3O4 Janus particles to WS2 nanotubes through their Pt or Fe3O4 domains is governed by the difference in Pearson hardness: the soft Pt block has a higher sulfur affinity than the harder magnetite face; thus the binding proceeds preferentially through the Pt face. This binding preference can be reversed by masking the Pt face with an organic protecting group.
Effect of atomic vibrations in XANES: polarization-dependent damping of the fine structure at the Cu K-edge of (creat)2CuCl4
2016
Polarization-dependent damping of the fine structure in the CuK-edge spectrum of creatinium tetrachlorocuprate [(creat)2CuCl4] in the X-ray absorption near-edge structure (XANES) region is shown to be due to atomic vibrations. These vibrations can be separated into two groups, depending on whether the respective atoms belong to the same molecular block; individual molecular blocks can be treated as semi-rigid entities while the mutual positions of these blocks are subject to large mean relative displacements. The effect of vibrations can be efficiently included in XANES calculations by using the same formula as for static systems but with a modified free-electron propagator which accounts f…
Superheavy-element research
1979
The existence of an island of relatively stable elements beyond the present Periodic Table has been predicted by theoretical extrapolations of nuclear properties. During the past 12 years vigorous efforts have been made to discover these superheavy elements in nature and to produce them by nuclear reactions.
The impact of the properties of the heaviest elements on the chemical and physical sciences
2012
Abstract The unique role of the heaviest elements in chemical and physical sciences is discussed. With the actinide series (Z = 90-103) and the superactinide series (Z = 122-155), the heaviest elements have significantly shaped the architecture of the Periodic Table of the elements. Relativistic effects in the electron shells of the heaviest elements change the chemical properties in a given group in a non-linear fashion. Relativistically stabilized sub-shell closures give rise to a new category of elements in the Periodic Table: volatile metals. The prototype for this property is element 114 which, due to the relativistic stabilization of its 7s2 7p2 1/2 electron configuration, is volatile…
Vanadium catalysts for ethylene-norbornene copolymerization
2020
Cyclic olefin copolymers (COCs) are a promising group of materials with specific, projectable properties. In this group, copolymers of ethylene and norbornene are of particular interest. A variety of transition metal complexes are used for their synthesis, mostly elements from group 4. This review presents the application of vanadium catalysts with various types of ligands in the synthesis of ethylene-norbornene copolymers. The influence of ligands and reaction conditions on the activity of catalyst and selected properties of copolymers are described in this paper.
The crystal and molecular structure of the epoxybromo derivative of atractyligenin.
1970
Abstract The complete configuration of atractyligenin has been obtained by a three-dimensional single-crystal X-ray difiraction study. Previous structural work has been confirmed, in particular the configuration of the epoxy group. The space group is C2, with four molecules in the cell, a = 19·005, b = 7·165, c = 14·450 A, β = 108° 31′, and the final R is 0·125 for 1320 observed reflections. The stress in the molecule (as indicated by the torsional angles) and the molecular packing are discussed.