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31.
Ortho-para hydrogen conversion kinetics has been measured in the stoichiometric Ar(H 2 ) 2 compound, at pressures from 3 to 35 GPa, from the intensity of the rotational Raman transitions. The conversion rate increases with pressure by almost a factor 50 in the investigated pressure range. A comparison is made with pure hydrogen, where a similar increase is also observed. For long times and low ortho concentration, the conversion kinetic deviates from the law derived for uniform distribution of the ortho-hydrogen molecules in the crystal. The magnitude of this effect, due to the limited diffusion rate of the hydrogen molecules in the crystal, allows the measurement of the diffusion coefficient. 相似文献
32.
An RP-HPLC method for the determination of four phenolic compounds: gallic acid (GA), pyrogallol (PY), resorcinol (RE) and ellagic acid (EA), derived from hydrolysable tannins is reported. Separation was achieved on a SunFire C18 (250 x 4.6 mm id, 5 microm) column at 40 degrees C with gradient elution. UV detection at 280 nm was applied. The developed method was validated in terms of linearity, accuracy and precision. Satisfactory repeatability and between day precision were noticed with RSD values lower than 3%. Recoveries from different biological samples ranged from 91.50 to 105.25%. The LODs were estimated as 1.70 mg/L for PY, 1.68 mg/L for GA, 1.52 mg/L for RE and 0.98 mg/L for EA with a 20 microL injection volume. The method was applied for the determination of these compounds in oak leaves and in ruminal fluid and urine samples taken from beef cattle fed with oak leaves. The proposed method could be used in ruminant nutrition studies to verify the effect that a diet rich in tannins have on ruminal fermentation and to determine the toxicity of these compounds. 相似文献
33.
Antônio Gomes dos Santos Neto Franciele de Matos Morawski Ana Caroline Ferreira Santos Cláudia Quintino da Rocha Roberto Batista de Lima Marília Oliveira Fonseca Goulart Clenilton Costa dos Santos Flávio Colmati Antônio Euzébio Goulart Santana Marco Aurélio Suller Garcia Auro Atsushi Tanaka 《Electroanalysis》2023,35(5):e202200390
Here, we report multiwalled carbon nanotubes (MWCNTs) functionalized with γ-cyclodextrins (γCD) as a novel electrochemical strategy for Rutin determination, showing superior performance than β-cyclodextrins (βCD) modified MWCNTs, suggesting an adequate environment for host-guest interactions. Under optimized conditions, the sensor showed a linear range of 39–975 nmol L−1 and a limit of detection of 7 nmol L−1. When tested with quercetin, catechin, and caffeine, the platform presented high selectivity with an interference response <10 %. The method was employed to quantify Rutin in spiked pharmaceutical and herbal extracts, providing recovery of 93–98.4 %. Also, HPLC-PDA confirmed the method‘s accuracy. 相似文献
34.
Dr. Andreas Eitzinger Justus Reitz Patrick W. Antoni Prof. Dr. Herbert Mayr Dr. Armin R. Ofial Jun.-Prof. Max M. Hansmann 《Angewandte Chemie (International ed. in English)》2023,62(40):e202309790
A series of mesoionic, 1,2,3-triazole-derived N-heterocyclic olefins (mNHOs), which have an extraordinarily electron-rich exocyclic CC-double bond, was synthesized and spectroscopically characterized, in selected cases by X-ray crystallography. The kinetics of their reactions with arylidene malonates, ArCH=C(CO2Et)2, which gave zwitterionic adducts, were investigated photometrically in THF at 20 °C. The resulting second-order rate constants k2(20 °C) correlate linearly with the reported electrophilicity parameters E of the arylidene malonates (reference electrophiles), thus providing the nucleophile-specific N and sN parameters of the mNHOs according to the correlation lg k2(20 °C)=sN(N+E). With 21<N<32, the mNHOs are much stronger nucleophiles than conventional NHOs. Some mNHOs even excel the reactivity of mono- and diacceptor-substituted carbanions. It is exemplarily shown that the reactivity parameters thus obtained allow to calculate the rate constants for mNHO reactions with further Michael acceptors and predict the scope of reactions with other electrophilic reaction partners including carbon dioxide, which gives zwitterionic mNHO-carboxylates. The nucleophilicity parameters N correlate linearly with a linear combination of the quantum-chemically calculated methyl cation affinities and buried volumes of mNHOs, which offers a valuable tool to tailor the reactivities of strong carbon nucleophiles. 相似文献
35.
Bastiaan Kooij Paul Varava Farzaneh Fadaei-Tirani Rosario Scopelliti Dimitrios A. Pantazis Gerard P. Van Trieste III David C. Powers Kay Severin 《Angewandte Chemie (International ed. in English)》2023,62(4):e202214899
Homometallic copper complexes with alkenylidene ligands are discussed as intermediates in catalysis but the isolation of such complexes has remained elusive. Herein, we report the structural characterization of copper complexes with bridging and terminal alkenylidene ligands. The compounds were obtained by irradiation of CuI complexes with N-heterocyclic diazoolefin ligands. The complex with a terminal alkenylidene ligand required isolation in a crystalline matrix, and its structural characterization was enabled by in crystallo photolysis at low temperature. 相似文献
36.
Roman Bashkurov Dr. Alexander Kaushansky Dr. Boris Tumanskii Dr. Natalia Fridman Dr. Dmitry Bravo-Zhivotovskii Prof. Dr. Yitzhak Apeloig 《Angewandte Chemie (International ed. in English)》2023,62(18):e202300847
Thermolysis of a 1 : 1 mixture of tris(di-tert-butylmethylsilyl)germane 9 and bis(di-tert-butylmethylsilyl)germane 17 at 100 °C produces unexpectedly octagermacubane 18 , having two 3-coordinate Ge0 atoms (40 % yield). 18 was characterized by X-ray crystallography and it is a singlet biradical (according to DFT quantum mechanical calculations and the absence of an EPR signal). Reactions of 18 with CH2Cl2 and H2O yield the novel dichloro-octagermacubane 24 and hydroxy-octagermacubane 25 , respectively. Reduction of 18 with tBuMe2SiNa in THF produces an isolable octagermacubane radical anion 26-Na . Based on X-ray crystallography, EPR spectroscopy and DFT quantum mechanical calculations, 26-Na is classified as a Ge-centered radical anion. 相似文献
37.
Hongyuan Zhao Qiujie Wang Ziying Wen Haibo Sun Sujun Ji Xuan Meng Ruiling Zhang Junke Jiang Zhe Tang Feng Liu 《Angewandte Chemie (International ed. in English)》2023,62(52):e202316336
The achievement of significant photoluminescence (PL) in lanthanide ions (Ln3+) has primarily relied on host sensitization, where energy is transferred from the excited host material to the Ln3+ ions. However, this luminous mechanism involves only one optical antenna, namely the host material, which limits the accessibility of excitation wavelength-dependent (Ex-De) PL. Consequently, the wider application of Ln3+ ions in light-emitting devices is hindered. In this study, we present an organic–inorganic compound, (DMA)4LnCl7 (DMA+=[CH3NH2CH3]+, Ln3+=Ce3+, Tb3+), which serves as an independent host lattice material for efficient Ex-De emission by doping it with trivalent antimony (Sb3+). The pristine (DMA)4LnCl7 compounds exhibit high luminescence, maintaining the characteristic sharp emission bands of Ln3+ and demonstrating a high PL quantum yield of 90–100 %. Upon Sb3+ doping, the compound exhibits noticeable Ex-De emission with switchable colors. Through a detailed spectral study, we observe that the prominent energy transfer process observed in traditional host-sensitized systems is absent in these materials. Instead, they exhibit two independent emission centers from Ln3+ and Sb3+, each displaying distinct features in luminous color and radiative lifetime. These findings open up new possibilities for designing Ex-De emitters based on Ln3+ ions. 相似文献
38.
采用共沉淀法合成了掺杂 L a、 Gd、 Y的 Tb-邻氨基苯甲酸配合物 ,研究其荧光性能 ,结果显示 ,掺杂L a、Gd、Y后 ,对 Tb配合物的发光有增敏作用 ,讨论了不同的掺杂离子 (L a、Gd、Y)及掺杂量对其荧光性能的影响。发现 ,当掺杂离子取代大部分 Tb3+时 ,其发光增强仍十分显著。 相似文献
39.
Synthesis and Crystal Structures of the Zinc Amido Complexes [Zn(NPh2)2]2 and [Zn(NPh2)2(THF)2] Zinc diphenylamide is prepared from Zn[N(SiMe3)2]2 and diphenylamine by transamination reaction. The compound is characterized by a crystal structure analysis. According to it [Zn(NPh2)2]2 forms centrosymmetric dimeric molecules with Zn–N distances of 185.9 pm for the terminally bonded NPh2– ligand and Zn–N distances of 204.0 and 202.6 pm in the four-membered ring. From tetrahydrofuran solutions [Zn(NPh2)2(THF)2] crystallizes as monomeric molecular complex with Zn–N bond lengths of 192.2 pm in average. 相似文献
40.
The Reaction of Dialkylaluminium Chlorides with Bis(trimethylsilyl)hydrazine: Formation of the Adducts R2AlCl · NH2NHSiMe3 Containing the Unstable Monotrimethylsilylhydrazine Bis(trimethylsilyl)hydrazine did not react with dialkylaluminium chlorides R2AlCl [R = CH2CMe3, CMe3 and CH(SiMe3)2] by the formation of trimethylchlorosilane, but by dismutation to yield tris(trimethylsilyl)hydrazine and trimethylsilylhydrazine. The unstable, sterically less shielded NH2NHSiMe3 was stabilized by the coordination to the coordinatively unsaturated aluminium compounds. The adducts R2AlCl · NH2NHSiMe3 were formed, which were characterized by crystal structure determinations with R = CMe3 and CH(SiMe3)2. In all cases, the hydrazine derivative binds to the aluminium atoms via the more basic NH2 nitrogen atom. The adduct Me3CAlCl2 · NH2N(SiMe3)2 containing intact 1,1‐bis(trimethylsilyl)hydrazine as a ligand was isolated in a trace amount and also characterized by a crystal structure determination. 相似文献