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991.
Thilini D. Kondasinghe Hasina Y. Saraha Shane T. Jackowski Jennifer L. Stockdill 《Tetrahedron letters》2019,60(1):23-28
α4/7-Conotoxin LvIA is an isoform-selective inhibitor of the α3β2 nicotinic acetylcholine receptor. An efficient strategy for the synthesis of this toxin is critical to advancing its utility as a probe for receptor function and as a potential pharmaceutical lead target. On-resin methods for peptide synthesis offer potential synthetic advantages; however, strategies for on-resin formation of multiple disulfides have historically been low-yielding. Here, we harness the reactivity of the Allocam protecting group and employ a 3-amino acid spacer strategy to synthesize α4/7-conotoxin LvIA via three different on-resin strategies, each of which results in an isolated yield higher than previous fully on-resin approaches. 相似文献
992.
Twenty‐eight novel ferrocenyl ionic compounds, composed of mononuclear 1‐ferrocenylmethylalkyldimethylammoniums, 1‐ferrocenylmethyl‐3‐alkylimidazoliums, or their dinuclear analogs and [Fe(CN)6]3– anion, were designed and synthesized to tackle significant volatility and migration tendency of ferrocene‐based burning rate catalysts (BRCs) used currently in the composite solid propellants. The new compounds were characterized by UV/Vis, FT‐IR, and elementary analysis. The crystal structures of compounds 2· 5H2O and 3· CH2Cl2 · 4H2O verified the successful preparation of the desired ionic compounds. The TG tests at 70 °C for 24 h revealed that the new compounds exhibit lower volatility than catocene. The cyclic‐voltammetry results suggested that new compounds are quasi‐reversible or irreversible redox systems. TheTG/DSC analyses exhibited that the compounds are of highly thermal stability. Their catalytic effects on the thermal degradation of ammonium perchlorate (AP), 1,3,5‐trinitro‐1,3,5‐triazacyclohexane (RDX), and 1,3,5,7‐tetranitro‐1,3,5,7‐tetrazacyclooctane (HMX) were investigated. The results showed that most of the compounds exert great effects on the thermal degradation of AP and RDX during combustion. 11 and 2 are comparable to catocene in the thermal decomposition of AP and RDX, respectively, and can therefore be used as alternatives of catocene in a composite solid propellant. Some new compounds are unexpectedly active in promoting the thermal disintegration of HMX. 相似文献
993.
Direct thermally induced reactions between rare earth metals (Ln = Y,Ce, Dy, Ho, and Er) activated by Hg metal and 3,5‐diphenylpyrazole (Ph2pzH) or 3,5‐di‐tert‐butylpyrazole (tBu2pzH) yielded either homoleptic complexes [Lnn(R2pz)3n] or a heteroleptic complex [Ln(Ph2pz)3(Ph2pzH)2] From Ph2pzH, [Ce3(Ph2pz)9], [Dy2(Ph2pz)6], [Ho2(Ph2pz)6], and [Y(Ph2pz)3(Ph2pzH)2] were isolated. The first has a bowed trinuclear Ce3 backbone with two η2 pyrazolate ligands on the terminal metal atoms and one on the middle, and bridging by both μ‐η2:η2 and μ‐η2:η5 ligands between the terminal and the central Ce atoms. Although both the Dy and Ho complexes are dinuclear, the former has the rare μ‐η2:η1 bridging whilst the latter has μ‐η2:η2 bridging. Thus the dysprosium complex is seven‐coordinate and the holmium is eight‐coordinate, in contrast to any correlation with Ln3+ ionic radii, and the series has a remarkable structural discontinuity. The heteroleptic Y complex is eight coordinate with three chelating Ph2pz and two transoid unidentate Ph2pzH ligands. From tBu2pzH, dimeric [Ln2(tBu2pz)4] (Ln = Ce, Er) were isolated and are isomorphous with eight coordinate Ln atoms ligated by two chelating terminal tBu2pz and two μ‐η2:η2 tBu2pz donor groups. They are also isomorphous with previously reported La, Nd, Yb, and Lu complexes. 相似文献
994.
Artem L. Gushchin Bee‐Lean Ooi Pernille Harris Pavel A. Abramov Maxim N. Sokolov 《无机化学与普通化学杂志》2019,645(4):398-401
The aqueous solution chemistry of niobium is underexplored, and well characterized aqua complexes are scarce. In this contribution, a new niobium aqua complex was obtained by treatment of Zn‐reduced ethanolic solution of NbCl5 with HCl in the presence of a selenide source (ZnSe). This is the first example of selenium containing aqua complex of niobium. The yellow‐green aqua complex was isolated by cation‐exchange chromatography and transformed into corresponding isothiocyanate complex by ligand exchange, which was crystallized as (PyH)4.5[H1.5Nb4SeO5(NCS)10] · 0.5H2O. X‐ray structural analysis revealed a metal‐metal bonded tetranuclear {Nb4(μ4‐Se)(μ2‐O)5}4+ core with a capping μ4‐Se ligand. 相似文献
995.
依托人教版《化学反应原理(选修4)》教材,利用数字化实验测定无限稀释冰醋酸过程中的电导率和pH的变化,通过宏观现象观察和图像辨识,从微观上深入解析弱电解质的电离特征,突破越稀越电离的认识边界。在激发学生学习兴趣和学习动力的同时,从“宏观辨识与微观探析”维度帮助学生形成整合的弱电解质结构性知识,探索化学平衡的思维规律。 相似文献
996.
A new aromatic diamine, 4-(4-trifluoromethyl)phenyl-2,6-bis[4-(4-amino-2-trifluoromethylphenoxy)phenyl]pyridine, was synthesized by a modified Chichibabin reaction of 4-(4-nitro-2-trifluoromethylphenoxy)acetophenone with 4-triflouromethylbenzaldehyde, followed by catalytic reduction. A series of fluorinated pyridine-containing aromatic poly(ether imide)s (PEIs) were prepared from the diamine monomer with various aromatic dianhydrides via conventional two-step thermal imidization method. The resulting PEIs had inherent viscosities values of 0.68–0.90 dL/g, and could be cast and thermally converted into transparent, flexible, and tough polymer films. These PEIs were predominantly amorphous, had good solubility in common solvents such as NMP, DMAc and m-cresol at room temperature, and displayed excellent thermal stability with the glass transition temperatures of 258–315?°C, the temperatures at 5% weight loss of 550–585?°C, and the residue of higher than 55% at 750?°C in nitrogen. Moreover, the PEIs films showed outstanding mechanical properties with tensile strengths of 74.8–103.5?MPa, tensile moduli of 1.08–1.45?GPa, and elongations at break of 10.6–24.4%. These PEIs also exhibited low dielectric constants of 2.81–2.98 (1?MHz) and water uptake 0.39–0.68%, as well as high optical transparency with the UV cutoff wavelength in the 350–378?nm range and the wavelength of 80% transparency in the range of 412–510?nm. 相似文献
997.
The high resolution infrared spectra of monoisotopic F35Cl18O3 and F37Cl18O3 have been studied in the region of the ν4 fundamentals, centered at 1278.3 and 1263.3 cm−1, respectively. Large perturbations are observed in both bands due to a Fermi type anharmonic resonance with the ν2 + ν5 combination bands, centered at 1270.7 cm−1 in F35Cl18O3 and 1257.3 cm−1 in F37Cl18O3. In particular, they affect the kl > 0 levels of the v4 = 1 and v2 = v5 = 1 states which cross at kl ? 18 in F35Cl18O3 and kl ? 3 in F37Cl18O3, due to the opposite values of and . The Δl = Δk = ±2 and Δl = 0, Δk = ±3 essential resonances are also effective in the excited states of the dyad in F35Cl18O3, while in F37Cl18O3 only the Δl = Δk = ±2 one is active. In the spectrum of F35Cl18O3 3423 transitions have been assigned, 10% of them belonging to ν2 + ν5. The rovibrational parameters and the interaction constants between the v4 = 1 and v2 = v5 = 1 levels have been obtained. The depertubed band origins of ν4 and ν2 + ν5 are 1277.310567(165) and 1271.753733(195) cm−1, respectively, and the anharmonic resonance constant is 2.804416(153) cm−1. For F37Cl18O3, 3022 transitions have been assigned, 38% belonging to the ν2 + ν5 combination band. The depertubed band origins are 1260.856338(123) and 1259.872338(134) cm−1, for ν4and ν2 + ν5 and the constant is 2.9350669(405) cm−1. The equilibrium geometry of perchloryl fluoride, re (ClO) = 139.7(3) pm, re (ClF) = 161.0(5) pm, and αe (OClO) = 115.7(4) degree, has been determined using the Ae and Be equilibrium constants of the four symmetric isotopologues of perchloryl fluoride, F35/37Cl16O3 and F35/37Cl18O3. 相似文献
998.
Ling-Ling Xing 《Journal of Physics and Chemistry of Solids》2008,69(9):2341-2343
Using the assumption δT=δT0(V/V0)k and the Grüneisen parameter γ macroscopic definition expression, we obtained a relationship for the volume dependence of the Grüneisen parameter γ. We have calculated the Grüneisen parameter γ with this relationship for NaCl and ε-Fe at high pressure under study. The calculated values of γ are found to show fairly in good agreement with available experimental data. 相似文献
999.
Resul Aksoy 《Journal of Physics and Chemistry of Solids》2008,69(9):2138-2140
In situ high-pressure angle dispersive synchrotron X-ray diffraction studies of molybdenum diselenide (MoSe2) were carried out in a diamond-anvil cell to 35.9 GPa. No evidence of a phase transformation was observed in the pressure range. By fitting the pressure-volume data to the third-order Birch-Murnaghan equation of state, the bulk modulus, K0T, was determined to be 45.7±0.3 GPa with its pressure derivative, K′0T, being 11.6±0.1. It was found that the c-axis decreased linearly with pressure at a slope of −0.1593 when pressures were lower than 10 GPa. It showed different linear decrease with the slope of a −0.0236 at pressures higher than 10 GPa. 相似文献
1000.
Recent reports of the melting curve of sodium at high pressure have shown that it has a very steep descent after a maximum of around 1000 K at 31 GPa. This maximum does not occur due to a solid-solid phase transition. According to the Lindemann criterion, this behaviour should be apparent in the evolution of the Debye temperature with pressure. In this work, we have performed an “ab initio” analysis of the behaviour of both the Debye temperature and the elastic constants up to 102 GPa, and find a clear trend at high pressure that should cause a noticeable effect on the melting curve. 相似文献