Effect of intercalating agents on structure and properties of dimer acid‐based polyamide modified by in situ doping of Na‐montmorillonite

Under the condition of 0.4% (mass), the effects of intercalating agents on conglomeration structure and thermal and mechanical properties of dimer acid‐based polyamide (DAPA) were investigated. The results show that layer‐stripped Na‐montmorillonite (MMT) with octadecyl trimethyl ammonium chloride caused a sharp decrease of content of the γ crystal phase in DAPA, thus bringing out decrease in mechanical properties and increase in IZOD notched impact strength while a sharp increase of content with the γ crystal phase in DAPA modified by Na‐MMT with dioctadecyl dimethyl ammonium chloride. Thus, it brought out a large increase in mechanical properties and a limited increase in IZOD notched impact strength. The decomposition reaction processes of DAPA modified by Na‐MMT and Na‐MMT with octadecyl trimethyl ammonium chloride were one step ranging from 410 to 500°C, respectively. The thermal decomposition reaction processes of DAPA modified by Na‐MMT with dioctadecyl dimethyl ammonium chloride were two steps. Copyright © 2016 John Wiley & Sons, Ltd.     

A halide‐free pyridinium‐substituted η3‐cycloheptatrienide–Pd complex

We report the synthesis and characterization of a novel 4‐(dimethylamino)pyridinium‐substituted η³‐cycloheptatrienide–Pd complex which is free of halide ligands. Diacetonitrile{η³‐[4‐(dimethylamino)pyridinium‐1‐yl]cycloheptatrienido}palladium(II) bis(tetrafluoroborate), [Pd(C₂H₃N)₂(C₁₄H₁₆N₂)](BF₄)₂, was prepared by the exchange of two bromide ligands for noncoordinating anions, which results in the empty coordination sites being occupied by acetonitrile ligands. As described previously, exchange of only one bromide leads to a dimeric complex, di‐μ‐bromido‐bis({η³‐[4‐(dimethylamino)pyridinium‐1‐yl]cycloheptatrienido}palladium(II)) bis(tetrafluoroborate) acetonitrile disolvate, [Pd₂Br₂(C₁₄H₁₆N₂)₂](BF₄)₂·2CH₃CN, with bridging bromide ligands, and the crystal structure of this compound is also reported here. The structures of the cycloheptatrienide ligands of both complexes are analogous to the dibromide derivative, showing the allyl bond in the β‐position with respect to the pyridinium substituent. This indicates that, unlike a previous interpretation, the main reason for the formation of the β‐isomer cannot be internal hydrogen bonding between the cationic substituents and bromide ligands.     

Computational, 1H NMR,and X‐ray structural studies on 1‐arylurazole tetrazane dimers

Nitrogen‐centered urazole radicals exist in equilibrium with tetrazane dimers in solution. The equilibrium established typically favors the free‐radical form. However, 1‐arylurazole radicals bearing substituents at the ortho position favor the dimeric form. We were able to determine the structure of one of the dimers (substituted at both ortho positions with methyl groups), namely 1,2‐(2,4‐dimethylphenyl)‐2‐[2‐(2,4‐dimethylphenyl)‐4‐methyl‐3,5‐dioxo‐1,2,4‐triazolidin‐1‐yl]‐4‐methyl‐1,2,4‐triazolidine‐3,5‐dione, C₂₄H₂₈N₆O₄, via X‐ray crystallography. The experimentally determined structure agreed well with the computationally obtained geometry at the B3LYP/6‐311G(d,p) level of theory. The preferred syn conformation of these 1‐arylurazole dimers results in the two aromatic rings being proximate and nearly parallel, which leads to some interesting shielding effects of certain signals in the ¹H NMR spectrum. Armed with this information, we were able to decipher the more complicated ¹H NMR spectrum obtained from a dimer that was monosubstituted at the ortho position with a methyl group.     

Dimerization of a mixed‐carbene PdII dibromide complex by elemental iodine

A monomeric Pd^II complex bearing a mixed carbocyclic/N‐heterocyclic carbene ligand and two bromides was reacted with an excess of elemental iodine, which resulted in the surprising removal of one bromide ligand and dimerization of the mixed‐carbene complex to form di‐μ‐bromido‐bis{[1‐(cyclohepta‐2,4,6‐trien‐2‐yl‐1‐ylidene‐κC ¹)‐3‐(2,6‐diisopropylphenyl)imidazol‐2‐ylidene]palladium(II)} bis(pentaiodide) dichloromethane monosolvate, [Pd₂Br₂(C₂₂H₂₄N₂)₂](I₅)₂·CH₂Cl₂. The dimeric complex features a slightly distorted square‐planar core of two Pd^II centres bridged by two bromide ligands, which lie in the same plane as the seven‐ and five‐membered rings of the bidentate carbene ligand. The counter‐ions in the single crystal were found to be pentaiodide monoanions featuring their typical V‐shape, whereas for the bulk material, a mixture of Br/I interhalides is proposed.     

The effect of the iterative triple and quadruple cluster amplitudes on the adiabatic potential curve in the coupled cluster calculations of the ground electronic state of the Yb dimer

The dissociation energy, equilibrium internuclear distance, and spectroscopic constants for the ¹Σ ground state of the Yb₂ molecule are calculated. The relativistic effects are introduced through generalized relativistic effective core potentials with very high precision. The scalar relativistic coupled cluster method particularly well suited for closed‐shell van der Waals systems is used for the correlation treatment. Extensive generalized correlation basis sets were constructed and used. The relatively small corrections for high‐order cluster amplitudes and spin—orbit interactions are taken into account using smaller basis sets and the spin—orbit density functional theory. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2011     

Thermal degradation behavior of polyamides having 2- and 4-hydroxycinnamic acid dimer components

Two new types of polyamides having anti head-to-tail hydroxycinnamic acid dimer component in the main chain were synthesized. Their thermal degradation behavior was investigated by TG-DSC analysis in comparison with those of their model compounds and the polyamides derived from anti head-to-head coumarin dimer. The key reactions in the thermal degradation were clarified to be lactonization and cyclic imide formation. The polyamide, derived from 4-hydroxycinnamic acid dimer and hexamethylenediamine, showed good heat stability. © 1993 John Wiley & Sons, Inc.     

钾分子中里德堡态的紫外辐射研究

本文报道了在K-K₂系统中,利用双光子共振激发钾原子8s、6d态,观察到了K₂在(310～365nm)里德堡态的紫外辐射.钾分子里德堡态的布居,受到了多种激发过程影响.文中对其发射和激发过程进行了详细讨论.     

1，3-二甲基尿嘧啶二聚体的飞行时间质谱裂解规律研究

采用不同进样方式、不同电子轰击能量和不同反应气压力测定了1,3 二甲基尿嘧啶二聚体(DMUD) 的4个立体异构体A、B、C、D的化学电离(CI)和电子轰击电离(EI)飞行时间质谱.不同方式所测得的CI谱结 果一致,4个异构体出现了强度不同的准分子离子峰(m/z=281),由此推断它们结构之间的相对稳定性次序为: B(trans syn)>D(cis syn)>A(trans anti)>C(cis anti).这一结论被低能量(25eV)电子轰击的EI谱所证实, 并且与合成产物的比例相吻合.EI谱用任何方式测谱均不出现分子离子峰(m/z=280),而出现其单体离子(m/z =140)且为基峰。给出了DMUD的飞行时间质谱裂解途径,同时对CI谱的裂解碎片进行了细致的讨论.     

Facile synthesis of a cis-syn thymine dimer building block and its incorporation into oligodeoxynucleotides

The synthesis of a building block containing the photobiologically relevant cis-syn thymine cyclobutane photoproduct and its incorporation into oligonucleotides by the phosphoramidite-based solid-phase synthesis is reported. Compared to previous syntheses, this route is extremely short and allows such modified oligonucleotides to be easily available for biological studies.