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121.
Ping Yin Xian‐Yang Chen Chong‐De Li Xin‐Quan Xin 《International journal of quantum chemistry》2001,82(6):293-298
Ab initio calculations have been carried out to study the structures and relative stabilities of the planar eight‐membered ring B4N4H4 and its isoelectronic species C8H4 at the HF/6‐31G*, MP2/6‐31G*, MP2/6‐311G**, and MP4SDQ/6‐31G* levels. The analyses of Milliken population, vibration frequencies, π‐molecular orbital components, and orbital energy levels were used to evaluate the relative stabilities of these two similar systems. The homodesmotic reactions were also taken to be a useful index of relative stability for X4Y4H4 (XY=CC, BN) and gave the resonance energies with MP4SDQ/6‐31G* of C8H4 (?37.2 kcal/mol) < B4N4H4 (?29.2 kcal/mol). Furthermore, we calculated the thermodynamic functions of these reactions to discuss the influence of temperature. It is concluded that B4N4H4 may exist in theory and could be a little more stable than C8H4. © 2001 John Wiley & Sons, Inc. Int J Quant Chem 82: 293–298, 2001 相似文献
122.
We have explored the photodissociation dynamics of the reaction H(2)CO+hnu-->H+HCO in the range of 810-2600 cm(-1) above the reaction threshold. Supersonically cooled formaldehyde was excited into selected J(Ka,Kc) rotational states of six vibrational levels (1(1)4(1), 5(1), 2(2)6(1), 2(2)4(3), 2(3)4(1), and 2(4)4(1)) in the A((1)A2) state. The laser induced fluorescence spectra of the nascent HCO fragment provided detailed product state distributions. When formaldehyde was excited into the low-lying levels 1(1)4(1), 5(1), and 2(2)6(1), at E(avail)<1120 cm(-1), the product state distribution can be modeled qualitatively by phase space theory. These dynamics are interpreted as arising from a reaction path on the barrierless S0 surface. When the initial states 2(2)4(3) and 2(3)4(1) were excited (E(avail)=1120-1500 cm(-1)), a second type of product state distribution appeared. This second distribution peaked sharply at low N, Ka and was severely truncated in comparison with those obtained from the lower lying states. At the even higher energy of 2(4)4(1) (E(avail) approximately 2600 cm(-1)) the sharply peaked distribution appears to be dominant. We attribute this change in dynamics to the opening up of the triplet channel to produce HCO. The theoretical height of the barrier on the T1 surface lies between 1700 and 2100 cm(-1) and so we consider the triplet reaction to proceed via tunneling at the intermediate energies and proceed over the barrier at the higher energies. Considerable population was observed in the excited (0,0,1) state for all initial H(2)CO states that lie above the appearance energy. Rotational populations in the (0,0,1) state dropped more rapidly with (N,Ka) than did the equivalent populations in (0,0,0). This indicates that, although individual rotational states are highly populated in (0,0,1), the total v3=1 population might not be so large. Specific population was also measured in the almost isoenergetic Kc and J states. No consistent population preference was found for either asymmetry or spin-rotation component. 相似文献
123.
Yin P Wang J Xiao Z Wu P Wei Y Liu T 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(30):9174-9178
So emulsional: Two hexavanadate-organic hybrids were synthesized and their amphiphilic properties were confirmed by forming emulsions in mixtures of water and nonpolar organic solvents, and were utilized as "emulsion catalysts" in deep desulfurization reactions (see figure). Their catalytic activities show a pH-dependent behavior, which can be explained by the size-change of emulsions and the appearance of reverse emulsions. 相似文献
124.
TpMo(CO)2(5-alkenyl-eta-2,3,4-pyranyl) diene complexes function as excellent chiral scaffolds for the efficient regio- and enantiocontrolled synthesis of highly functionalized 1-oxadecaline derivatives through a novel transition metal-mediated Diels-Alder reaction. Very good to excellent yields and excellent levels of endo selectivity are obtained, and the reaction gives products with complete retention of enantiomeric purity when carried out with chiral, nonracemic scaffolds. A subtle structural modification on the diene (replacement of an H by a trans-CH3 group) leads to a complete change of regiochemistry, which is discussed from a mechanistic point of view. The role of the eta3-coordinated TpMo(CO)2 moiety is also critical to the further functionalization of the [4 + 2] cycloadducts, as illustrated by the preparation of 20 variously functionalized 1-oxadecaline derivatives (>98% ee when carried out with high enantiopurity scaffolds). 相似文献
125.
Ma KR Ma F Zhu YL Yu LJ Zhao XM Yang Y Duan WH 《Dalton transactions (Cambridge, England : 2003)》2011,40(38):9774-9781
By introducing the second organic N-heterocyclic ligands 4'-(4-pyridyl)-4,2':6',4'-terpyridine (pyterpy) and 4,4'-bipyridyl (4,4'-bipy), two examples of Cu(II)-diphosphonates, [Cu(3)(HL)(2)(Hpyterpy)(2)]·2H(2)O 1 and [Cu(4)(HL)(2)(4,4'-bipy)(H(2)O)(5)] 2 based on 1-hydroxyethylidenediphosphonic acid (H(5)L = CH(3)C(OH)(PO(3)H(2))(2)), have been hydrothermally obtained and characterized by powder X-ray diffraction, elemental analysis, IR, TG-DSC. The single-crystal X-ray diffractions reveal that compound 1 has a one-dimensional fishbone-like chain constructed by anions [Cu(3)(HL)(2)(2-)](n) while simultaneously organic cations [Hpyterpy(+)](n) suspending both sides, and compound 2 exhibits two-dimensional inorganic-organic alternate arrangement layer built from 1-D ladder-like inorganic chain with tetranuclear cluster [Cu(4)O(10)] via 4,4'-bipy linkage. The results of electrochemical measurements indicate half-wave potential of 1 (E(1/2)(1) = 1.01 V) is less than that of 2 (E(1/2)(2) = 1.20 V), indicating a good D-A system in ICT for 1. Moreover fluorescent measurements reveal that emission intensity of 1 centered at 422 nm is larger than that of 2 emitted at 420 nm, caused by intraligand π*-π emission state of organic N-heterocyclic amine (λ(ex) = 233 nm). Magnetism data indicate that compound 1 exhibits ferrimagnetic interactions between metal centers, while compound 2 has antiferromagnetic property. 相似文献
126.
Yang Xu Ming Wu Yang Liu Prof. Dr. Xi‐Zeng Feng Prof. Dr. Xue‐Bo Yin Prof. Xi‐Wen He Prof. Yu‐Kui Zhang 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(7):2276-2283
Carbon dots (Cdots) are an important probe for imaging and sensing applications because of their fluorescence property, good biocompatibility, and low toxicity. However, complex procedures and strong acid treatment are often required and Cdots suffer from low photoluminescence (PL) emission. Herein, a facile and general strategy using carbonization of precursors and then extraction with solvents is proposed for the preparation of nitrogen‐doped Cdots (N‐Cdots) with 3‐(3,4‐dihydroxyphenyl)‐L ‐alanine (L ‐DOPA), L ‐histidine, and L ‐arginine as precursor models. After they are heated, the precursors become carbonized. Nitrogen‐doped Cdots are subsequently extracted into N,N′‐dimethylformamide (DMF) from the carbogenic solid. A core–shell structure of Cdots with a carbon core and the oxygen‐containing shell was observed. Nitrogen has different forms in N‐Cdots and oxidized N‐Cdots. The doped nitrogen and low oxidation level in N‐Cdots improve their emission significantly. The N‐Cdots show an emission with a nitrogen‐content‐dependent intensity and Cdot‐size‐dependent emission‐peak wavelength. Imaging of HeLa cells, a human cervical cancer cell line, and HepG2 cells, a human hepatocellular liver carcinoma line, was observed with high resolution using N‐Cdots as a probe and validates their use in imaging applications and their multicolor property in the living cell system. 相似文献
127.
High-level expression of soluble human β-defensin-2 fused with green fluorescent protein in Escherichia coli cell-free system 总被引:2,自引:0,他引:2
Human β-defensin-2 (hBD2), a small cationic peptide, exhibits a broad range of antimicrobial activity and does not acquire
any microbial resistance. To produce this uneasily detectable, degradable, and toxic polypeptide efficiently, an alternative
approach based on the Escherichia coli cell-free biosynthesis system was proposed. The approach implies that a polypeptide of interest is synthesized as a fusion
protein linked to a green fluorescent protein (GFP) through a cleavable spacer. With batch-mode operation, a significant amount
of hBD2 fused with GFP (0.25 mg/mL) can be expressed in this cell-free system. The productivity of the fusion protein can
be improved up to 1.2 mg/mL by employing a continuous-exchange cell-free system. Furthermore, the GFP moiety provides directly
visible and quantitative monitoring of the polypeptide synthesis, and the product is soluble and stable. This work will be
helpful in allowing the rapid and visible expression of other similar defensins using an in vitro cell-free system. 相似文献
128.
Dunhua Hong Taisong Pan Dayu Feng Zhenlong Huang Feiyi Liao XiaoMei Li Yin Zhang Min Gao 《Journal of Sol-Gel Science and Technology》2014,71(3):464-469
(LaBa)Co2O5+δ (LBCO) thin films were successfully fabricated on Si (001) substrates by polymer-assisted deposition method. Microstructures were examined by X-ray diffraction technique, which confirmed the films were a single phase, pseudo cubic structure. The electrical transport properties of the films were investigated by the temperature dependence of films resistance, which suggested that LBCO films have typical semiconductor properties. After circle tests, the oxygen–hydrogen response rate did not show obvious variation in the specific temperature environment of 580 °C. This demonstrates that the LBCO thin films have a superior stability in both oxygen and hydrogen (6 % H2, 94 % N2) environment. Simultaneously, the drastic changes of films resistance (from ~106 to ~102 Ω) with the switch of redox (O2–H2) environment within such a short time (~2.2 s) indicated that LBCO films have an excellent oxygen sensitive property and extraordinary fast surface exchange rate. 相似文献
129.
Geng Tianfeng Du Chunyu Cheng Xinqun Xu Xing Jian Jiyuan He Xiaoshu Zuo Pengjian Yin Geping 《Journal of Solid State Electrochemistry》2019,23(1):101-108
Journal of Solid State Electrochemistry - Li-rich layered oxide (LrLO) cathode has attracted much attention for Li-ion batteries in recent years due to its superior capacity of exceeding... 相似文献
130.