Crystal Structure of 2, 8, 14, 20-<Emphasis Type="Italic">tert</Emphasis>-Butylpyrogallol[4]arene

Abstract  The aromatic derivative 2, 8, 14, 20-tert-butylpyrogallol[4]arene was synthesized by the acid catalyzed condensation of pivalaldehyde and pyrogallol in refluxing aqueous ethanol. Single crystal X-ray analysis revealed that the molecule crystallizes in the monoclinic crystal system; space group: P2₁/c. Unit cell dimensions: a = 11.1175(7) ?, α = 90°, b = 23.4525(15) ?, β = 101.6720(10)°, c = 21.9595(14) ?, γ = 90°, D_calc = 1.205 Mg/m³ g/m³ for Z = 4. In the solid state, the macrocycle is found to adopt a crown structure that is unique for the rcct conformation. Graphical abstract   Crystal Structure of 2, 8, 14, 20- tert -Butylpyrogallol[4]arene Eric E. Dueno, Allen D. Hunter, Matthias Zeller, Thomas A. Ray, Ralph N. Salvatore, Cesar H. Zambrano Acid catalyzed condensation of pyrogallol and pivalaldehyde in refluxing aqueous ethanol afforded a pyrogallol[4]arene derivative in good yield. Single crystal X-ray diffraction analysis revealed that a new calyx-like structure was formed under the reaction conditions. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.

S Q E D 4 and Q E D 4 on the Null-Plane

We study the scalar electrodynamics (S Q E D ₄) and the spinor electrodynamics (Q E D ₄) in the null-plane formalism. We follow Dirac’s technique for constrained systems to analyze the constraint structure in both theories in detail. We impose the appropriate boundary conditions on the fields to fix the hidden subset first class constraints that generate improper gauge transformations and obtain a unique inverse of the second-class constraint matrix. Finally, choosing the null-plane gauge condition, we determine the generalized Dirac brackets of the independent dynamical variables, which via the correspondence principle give the (anti)-commutators for posterior quantization.     

Improvement of mechanical and tribological properties in steel surfaces by using titanium-aluminum/titanium-aluminum nitride multilayered system

Improvement of mechanical and tribological properties on AISI D3 steel surfaces coated with [Ti-Al/Ti-Al-N]_n multilayer systems deposited in various bilayer periods (Λ) via magnetron co-sputtering pulsed d.c. method, from a metallic binary target; has been studied in this work exhaustively. The multilayer coatings were characterized in terms of structural, chemical, morphological, mechanical and tribological properties by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), scanning electron microscopy, nanoindentation, pin-on-disc and scratch tests, respectively. The failure mode mechanisms were studied by optical microscopy. Results from X-ray diffraction analysis revealed that the crystal structure of TiAl/TiAlN multilayer coatings has a tetragonal and FCC NaCl-type lattice structures for Ti-Al and Ti-Al-N, respectively, i.e., it was found to be non-isostructural multilayers. An enhancement of both hardness and elastic modulus up to 29 GPa and 260 GPa, respectively, was observed as the bilayer periods (Λ) in the coatings were decreased. The sample with a bilayer period (Λ) of 25 nm and bilayer number n = 100 showed the lowest friction coefficient (∼0.28) and the highest critical load (45 N), corresponding to 2.7 and 1.5 times better than those values for the coating deposited with n = 1, respectively. These results indicate an enhancement of mechanical, tribological and adhesion properties, comparing to the [Ti-Al/Ti-Al-N]_n multilayer systems with 1 bilayer at 26%, 63% and 33%, respectively. This enhancement in hardness and toughness for multilayer coatings could be attributed to the different mechanisms for layer formation with nanometric thickness such as the novel Ti-Al/Ti-Al-N effect and the number of interfaces that act as obstacles for the crack deflection and dissipation of crack energy.