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排序方式: 共有285条查询结果,搜索用时 15 毫秒
1.
Shoaib Ahmad 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2002,18(3):309-318
The mechanisms and processes of the formation of the regenerative soot in a graphite hollow cathode discharge that produces
and emits carbon clusters are presented. Mass spectrometry with a specially designed E×B velocity filter analyzes the entire range of the charged clusters from C
1 to ∼C
4300. The state of the carbon vapour within the source is evaluated by using the characteristic line emissions from the carbonaceous
discharge whose formative mechanisms depend upon the kinetic and potential sputtering of the sooted cathode. The carbonaceous
discharge generates atomic and ionic C and its clusters C
m (m≥ 2), noble gas metastable atoms and ions, energetic electrons and photons in the cavity of the graphite hollow cathode. The
parameters of soot formation and its recycling depend critically on the discharge parameters, the geometry of the hollow cathode
and 3D profile of the cusp magnetic field contours.
Received 2nd July 2001 and Received in final form 10 September 2001 相似文献
2.
Martin L. Bennink Dessy N. Nikova Kees O. van der Werf Jan Greve 《Analytica chimica acta》2003,479(1):3-15
Atomic force microscopy (AFM) imaging of static DNA-protein complexes, in air and in liquid, can be used to directly obtain quantitative and qualitative information on the structure of different complexes. For example, DNA length, the location of preferential binding sites for proteins and bending of DNA as a result of the complexation can all be measured. Recording consecutive AFM images of DNA and protein molecules under conditions that they are still able to move and interact, or dynamic AFM imaging, however, can reveal information on the dynamic aspects of the interactions between these molecules. Here, an overview is given of the technical challenges that need to be considered for successful dynamic AFM imaging studies of individual DNA-protein interactions. Necessary technical improvements to the AFM set-up and the development of new sample preparation methods are described in this paper. 相似文献
3.
An additive procedure (SIBFA) is developed for the rapid computation of conformational energy variations in very large molecules. The macromolecule is built out of constitutive molecular fragments and the intramolecular energy is computed as a sum of interaction energies between the fragments. The electrostatic and the polarization components are calculated using multicenter multipole expansions of theab initio SCF electron density of the fragments. The repulsion component is obtained as a sum of bond and lone pair interactions.Tests of the procedure on a series of model compounds containing ether oxygens and pyridine-like nitrogens are reported and compared with the results of correspondingab initio SCF calculations. The resulting methodology is compatible with the simultaneous computation of intermolecular interactions. 相似文献
4.
Luca Bernazzani Maria Rita Carosi Celia Duce Paolo Gianni Vincenzo Mollica 《Journal of solution chemistry》2006,35(11):1567-1585
Excess molar volumes, V
m
E, over the whole composition range for binary mixtures of 1-butanol, 2-butanol, and 2-methyl-2-propanol + 1-octanol, or 2-octanol, or di-n-butyl ether, or n-hexylacetate were determined at 298.15 K from density measurements carried out with a vibrating-tube densimeter. Small V
m
E values, both positive and negative, are displayed by mixtures containing 1- or 2-octanol, whereas positive and larger values are always found for mixtures containing dibutyl ether and hexylacetate. These results can be justified in terms of H-bonding interactions and/or steric hindrance due to the branched alkyl chains. Partial molar volumes at infinite dilution of the isomeric butanols in the C8 compounds were also calculated from the apparent molar volumes in dilute solution. The solute-solvent interactions and the effects of the local organisation of the solvent around the butanol molecules were discussed using the void and cavity volumes as different estimates of the intrinsic volume of the molecules. The volumetric behavior of butanols seems to be determined by the solute-solvent interactions rather than packaging effects. 相似文献
5.
D. Mihrin Dr. P. W. Jakobsen A. Voute Dr. L. Manceron Prof. R. Wugt Larsen 《Chemphyschem》2019,20(23):3238-3244
The high-resolution infrared absorption spectrum of the donor bending fundamental band ν of the homodimer (HCN)2 has been collected by long-path static gas-phase Fourier transform spectroscopy at 207 K employing the highly brilliant 2.75 GeV electron storage ring source at Synchrotron SOLEIL. The rovibrational structure of the ν transition has the typical appearance of a perpendicular type band associated with a Σ–Π transition for a linear polyatomic molecule. The total number of 100 assigned transitions are fitted employing a standard semi-rigid linear molecule Hamiltonian, providing the band origin ν0 of 779.05182(50) cm−1 together with spectroscopic parameters for the degenerate excited state. This band origin, blue-shifted by 67.15 cm−1 relative to the HCN monomer, provides the final significant contribution to the change of intra-molecular vibrational zero-point energy upon HCN dimerization. The combination with the vibrational zero-point energy contribution determined recently for the class of large-amplitude inter-molecular fundamental transitions then enables a complete determination of the total change of vibrational zero-point energy of 3.35±0.30 kJ mol−1. The new spectroscopic findings together with previously reported benchmark CCSDT(Q)/CBS electronic energies [Hoobler et al. ChemPhysChem. 19 , 3257–3265 (2018)] provide the best semi-experimental estimate of 16.48±0.30 kJ mol−1 for the dissociation energy D0 of this prototypical homodimer. 相似文献
6.
Jian Zhang Zhao‐Ji Li Yi‐Hang Wen Yao Kang Jian‐Kai Cheng Yuan‐Gen Yao 《无机化学与普通化学杂志》2004,630(15):2731-2735
Two new metal succinates modified by rigid bipyridines, Cd(4, 4′‐bpy)(C4H4O4)·1/4H2O ( 1 ) and Cu(2, 2′‐bpy)(C4H4O4)0.5(NO3)(H2O) ( 2 ) (bpy = bipyridine), have been synthesized by hydrothermal reactions and structurally determined. Complex 1 crystallizes in the orthorhombic space group Cmca with the cell parameters a = 11.696(2), b = 15.554(2), c = 15.874(3) Å, α = β = γ = 90.00°, V = 2888(3) Å3, Z = 8. Complex 2 crystallizes in the triclinic space group with a = 7.077(1), b = 9.838(2), c = 10.461(2) Å, α = 71.941(3)°, β = 73.078(3)°, γ = 74.502(3)°, V = 649.8(2) Å3, Z = 2. In complex 1 , a 2‐D network was formed by Cd‐succinato bonding. The 2‐D networks are pillared by 4, 4′‐bpy ligands, forming a 3‐D grid framework. The 2‐fold interpenetration of the resulting 3‐D frameworks completes the molecular structure. In complex 2 , the CuII atom adopts a distorted octahedral in which the CuII atoms are bridged by two H2O molecules into an infinite zigzag chain, [Cu2(H2O)2(C4H4O4)]n. The neighboring chains are further linked by π‐π stacking interactions into a 2‐D network, and the interlayer hydrogen bonds lead to the final 3‐D crystal structure. 相似文献
7.
A new ion-pair complex,[BzMeQl]2[Ni(mnt)2] 1 ([BzMeQl]+=1-benzyl-4-methylquino-linium,mnt2-= maleonitriledithiolate) has been synthesized and structurally characterized by IR,ESI-MS and X-ray diffraction methods. Complex 1 is of triclinic,space group P1,with a=9.079(2),b=10.154(2),c=11.243(2),α=81.58(1),β=69.63(1),γ=68.02(1)°,V=940.1(3)3,Dc=1.427 g/cm3,Z=1,F(000)=418 and R=0.0442. A 2D layer structure is formed via the cation-cation π…π and C–H…π interactions observed in the solid state of the complex. 相似文献
8.
Nowicka AM Zabost E Donten M Mazerska Z Stojek Z 《Analytical and bioanalytical chemistry》2007,389(6):1931-1940
A method is presented for the electroanalytical characterization of interactions of dsDNA with a drug, under conditions that
both agents are dissolved in the phosphate buffer solution and both are electroactive. Normal pulse, square wave, differential
pulse, and cyclic voltammetries were employed in the measurements of the drug and dsDNA oxidation signals at carbon electrodes.
UV–Vis spectroscopy was used as a non-electrochemical method to support the electroanalytical data. An anticancer drug, C-1311
(5-diethylaminoethyl-amino-8-hydroxyimidazoacridinone), has been selected for the examination. Normal pulse voltammetry was
particularly useful in showing that under the conditions employed neither dsDNA nor the drug were adsorbed at the electrode
surface. Necessary conditions for the appearance of the well-defined dsDNA voltammetric signal (guanine peak) are: rigorous
chemical and biological purity in the cell and appropriate purity of DNA. An analysis of the obtained results confirmed that
there were two modes of interaction between C-1311 and dsDNA: by intercalation and electrostatically. In the presence of excess
NaCl the electrostatic interactions deteriorate. The binding constants (K
1 and K
2, respectively) and the number (n) of nucleic base pairs (bp) and the number (m) of phosphate groups (pg) interacting with one molecule of drug have been determined. For strong interactions (intercalation)
the values of the binding constant, K
1, and the binding-site size, n, equal 3.7 × 104 M−1 and 2.1, respectively. For the weak electrostatic interactions the K
2 and m parameters equal 0.28 × 104 M−1 and 4.7. The intercalation process is rather slow and its rate (the conditions of pseudo-first-order reaction) was estimated
to equal 7 × 10−4 s−1. The possibility of independent determination of both interacting agents was very useful in the study.
Figure Intercalation of C-1311 into a dsDNA fragment 相似文献
9.
Hao Chen Yishuo Sun Meihui Liu Fuyou Li Qian Peng Hui Huang 《Angewandte Chemie (International ed. in English)》2023,62(20):e202302629
The dual-ratiometric thermometry is one of highly accurate methods for microscopic thermal measurement in biological systems. Herein, a series of chromone derivatives with noncovalently intramolecular interactions (NIIs) were designed and synthesized for ratiometric thermometers. The triplet states of these organic compounds were systematically tuned upon regulating the conformation with NIIs to yield efficient room temperature phosphorescence and large wavelength difference between fluorescence and phosphorescence simultaneously. As a result, an unprecedent organic 3D dual-ratiometric thermometer was established based on the intensity ratio and lifetime ratio of fluorescence/phosphorescence vs temperature, which was used for in vitro and in vivo bio-thermometry with high accuracy. This work provides a novel method to achieve organic dual ratiometric thermometers via tuning the triplet excited states. 相似文献
10.
Dr. Qingpei Liu Dan Zhang Shuaibiao Gao Xianhua Cai Dr. Ming Yao Yao Xu Yifu Gong Ke Zheng Yigui Mao Liyan Yang Dr. Dengfeng Yang Dr. István Molnár Dr. Xiaolong Yang 《Angewandte Chemie (International ed. in English)》2023,62(6):e202214379
Orsellinic acid (OA) derivatives are produced by filamentous fungi using nonreducing polyketide synthases (nrPKSs). The chain-releasing thioesterase (TE) domains of such nrPKSs were proposed to also catalyze dimerization to yield didepsides, such as lecanoric acid. Here, we use combinatorial domain exchanges, domain dissections and reconstitutions to reveal that the TE domain of the lecanoric acid synthase Preu6 of Preussia isomera must collaborate with the starter acyl transferase (SAT) domain from the same nrPKS. We show that artificial SAT-TE fusion proteins are highly effective catalysts and reprogram the ketide homologation chassis to form didepsides. We also demonstrate that dissected SAT and TE domains of Preu6 physically interact, and SAT and TE domains of OA-synthesizing nrPKSs may co-evolve. Our work highlights an unexpected domain–domain interaction in nrPKSs that must be considered for the combinatorial biosynthesis of unnatural didepsides, depsidones, and diphenyl ethers. 相似文献