Thermally stimulated depolarization current spectra of cross-linked polyethylene and the influence of cross-linking byproducts

Cross-linked polyethylene (XLPE) is notable for its use as power cable insulation. Its longevity is limited by space charge buildup linked to impurities such as the byproducts left behind by the cross-linking agent dicumyl peroxide (DCP). The goal of this work is to determine the impacts of these byproducts on charge trapping and detrapping in XLPE using the thermally stimulated depolarization current technique. XLPE with byproducts has one source of trapped charge, which originates from the byproducts. XLPE that was thermally treated via degassing exhibits two other sources of trapped charge, which are charge injection and dipolar relaxations. Oxidation from degassing was shown to control the trapping from these sources, which is useful knowledge for processing this material prior to its use. Reintroducing acetophenone, one of the major byproducts of DCP, suppresses those two peaks once more, showing that it controls the overall space charge buildup characteristics in XLPE.     

A reversible safety-catch method for the hydrogenolysis of N-benzyl moieties

The benzyl groups of β-hydroxy-N-benzyl sulfonamides are labile toward hydrogenolysis-unlike N-benzyl sulfonamides lacking the β-hydroxy moiety. We find that N-acyl-N-benzyl sulfonamides undergo hydrogenolysis under very mild conditions. Based upon these observations, we developed a reversible safety-catch method using tert-butoxycarbonyl moieties to activate N-benzyl sulfonamides toward hydrogenolysis. We also explored the utility of the safety-catch activation method for other nitrogen-based functionality such as N-benzyl carboxamides, imides, and related functionality.     

Molecular orbital description of the polythiazyl polymer Part 1. MNDO calculations of models of (SN)x

Semiempirical MNDO calculations are performed on various models for the polythiazyl polymer with increasing chain sizes. Population analysis, geometry optimization and the evolution of the frontier orbital energies are discussed. A low-lying broken symmetry structure with (SN)₂ repeating units is detected.     

The Compressibilities of Liquid Phase Host-Guest Systems

The compressibilities of seven liquidphase, macrocyclic host-guest systems were determinedat approximately 25 °C and 3.4 × 10⁷ Pa.Each two-component system consisted of a cyclodextrin,a calixarene, or a crown ether as host and anappropriate solvent as guest. In each case studied,the host-guest system was found to be lesscompressible than the pure solvent, with thedifferences ranging from 2 to 18% of the magnitudesof the pure solvent compressibilities. These findingshave enabled us to better understand how strong,ambient pressure, intermolecular host–guestinteractions influence the compressibility ofsolutions. Both inclusion and solvationcontribute.     

Absorption in the ν3 Band of UF6 Dissolved in Solid Xenon

The ν₃ band of UF₆ isolated in solid xenon is shown to consist of a single sharp spectral feature.     

Novel one pot synthesis of polysubstituted pyrazolo[1,5-a]- and imidazo[1,2-a]pyrimidines

We have described a convenient regioselective one-pot approach to pyrazolo[1,5-a]- and imidazo[1,2-a]pyrimidine derivatives from α,β-unsaturated imines generated in situ and amino heterocycles. Reaction is general with respect to all three components, namely (i) nitrile, (ii) aldehyde, and (iii) amino heterocycle reagents. Good yields (52-77%), convenient isolation of the targeted molecules are the distinct characteristics of the developed protocol.     

液相色谱-电喷雾离子阱质谱法测定贝类中软骨藻酸

记忆缺失性贝类毒素(amnesicshellfishtoxin,简称.ASP)主要成分软骨藻酸(domoicacid,简称DA)是一种氨基酸类的生理活性物质(图1),因最早从红藻属的树枝软骨藻(chondriaarmata)分离出来而被命名为软骨藻酸。自1987年加拿大首次发生集体贝类食品中毒事件后,人们从赤潮藻类中的硅藻属(diatom)的多列尖刺菱形藻(nitzschpungensf.multiseries)中检测到了DA,随后,美国、加拿大、北欧一些国家,澳大利亚、日本等国先后从紫贻贝(myltilusedulis)、扇贝(pectenmaximus)、文蛤(callistachione)等贝类体内以及鲭鱼和石蟹的内脏中检测到了DA。鱼、贝通过滤食毒藻,将DA富积在体内,人类因食用被DA污染的鱼、贝而中毒,中毒症状包括恶心、呕吐、腹痛、腹泻等,同时有晕眩、     

Ruthenium‐Grafted Vinylhelicenes: Chiroptical Properties and Redox Switching

The properties of mono‐ and bis‐Ru–vinyl[6]helicene complexes ( 2 a and 2 b , respectively), recently synthesized by using molecular engineering of helicenes based on the grafting of lateral organometallic substituents on the π‐helical backbone through a vinyl bridge, are presented. These helicene derivatives are thoroughly characterized, with special attention given to their chiroptical properties and redox switching activity. The UV/Vis and electronic circular dichroism (ECD) spectra of P and M enantiopure species, both in the neutral and oxidized states ([ 2 a ] ^{. +}, [ 2 b ] ^{. +}, and [ 2 b ]²⁺), are analyzed with the aid of quantum‐chemical calculations. The extended π‐conjugation facilitated by the vinyl moiety, clearly visible in the electronic structures of 2 a , b , introduces new active bands in the ECD spectra that consequently lead to a significant increase in optical rotation of Ru–vinylhelicenes compared with the organic precursors. The vibrational circular dichroism (VCD) spectra were measured and calculated for both the organic and organometallic species and constitute the first examples of VCD for metal‐based helicene derivatives. Finally, the redox‐triggered chiroptical switching activity of 2 a , b is examined in detail by using ECD spectroscopy. The modifications of the ECD spectra in the UV/Vis and NIR region are well reproduced and rationalized by calculations.     

Mechanistic Study of the Titanocene(III)‐Catalyzed Radical Arylation of Epoxides

An atom‐economical and catalytic arylation of epoxide‐derived radicals is described. The key step of the catalytic system is a sequential electron and proton transfer for the rearomatization of the radical σ‐complex and catalyst regeneration. Kinetic, computational, spectroscopic, and cyclovoltammetric investigations highlight the key issues of the reaction mechanism and catalyst stabilization by collidine hydrochloride. Studies employing radicophiles rule out the participation of cations as reactive intermediates.