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21.
E.W. Knapp 《Journal of computational chemistry》1992,13(7):793-798
Simulation data from an off-lattice polymer model are compared with data from the Rouse model. The polymer model is built of sequentially connected rigid monomer units that represent the amide planes of a protein backbone. The time propagation of the dynamics of the polymer model is performed by a Monte Carlo method. The elementary Monte Carlo steps correspond to local confomational changes in a window of three consecutive monomer units. The time autocorrelation functions of end-to-end distances from segments within the linear chain molecule are considered in detail. Both models exhibit a stretched exponential decay pattern. A comparison of the data from the Rouse model and the computer simulation provide an estimate of the time unit of 15 ps for a full scan of the algorithm for local conformational changes along the chain. With a conservative estimate of the parameters governing the Rouse model this time unit is four orders of magnitude longer than the elementary time step of a conventional computer simulation of polymer dynamics based upon the classical equations of motion for all atoms. © 1992 by John Wiley & Sons, Inc. 相似文献
22.
Furn F. Knapp 《Journal of mass spectrometry : JMS》1979,14(6):341-344
The 70 eV mass spectrum of phenyl ω-dimethoxyethyl telluride [C6H5? Te? CH2CH(OR)2, R?CH3]contains an intense peak at m/z 238 which corresponds to a rearrangement ion [C6H5? Te? OR]+. The formation of this species is further illustrated by the presence of a peak at m/z 241 in the spectrum of the hexadeuterated analog (R?CD3) and a peak at m/z 252 in the spectrum of the ethyl analog (R?CH2CH3). These combined results illustrate the presence of only one of the alkoxyl groups in the rearrangement ion. Several other abundant ions that contain oxygen but not tellurium are present in the spectra of these compounds. High resolution analyses have aided in the determination of the origin and composition of several of the characteristic ions formed upon electron impact fragmentation of phenyl ω-dimethoxyethyl telluride. 相似文献
23.
24.
KANG Yong-Feng LIU Lei YAN Wen-Jin XU Zhao-Qing ZHOU Yi-Feng HAN Zhi-Jian NI Ming DA Chao-Shan WANG Rui 《有机化学》2004,24(Z1):163
Development of new or improved methods for the asymmetric preparation of chiral propargylic alcohols has gained considerable significance during the past years because they are useful building blocks for the synthesis of many biologically active compounds and natural products.[1] A series of chiral tridentate ligands were conveniently synthesized from amino acids with good yields (Scheme 1).[2] A preliminary study of the enantioselective alkynylation of benzaldehyde catalyzed by this chiral tridentate ligand was carried out and up to 83% ee of chiral propargyl alcohols was obtained (Table 1 ). A further investigation of the tridentate ligand is currently underway. 相似文献
25.
Comparison of microwave-assisted acid leaching techniques for the determination of heavy metals in sediments, soils, and sludges 总被引:2,自引:0,他引:2
Microwave-assisted EPA method 3051 for nitric acid leaching of environmentally key elements from sediments, soils, and sludges
was tested, and the influence of leaching temperature and time on element recovery for an estuarine sediment (CRM 277) was
investigated. The extraction efficiencies for four certified reference materials applying EPA method 3051, an optimized nitric
acid procedure, and an aqua regia (HCl/HNO3 3:1) procedure were compared. Digestions were carried out in a high-pressure microwave system offering simultaneous temperature
and pressure control for all digestion vessels employed. Eight elements (Cd, Co, Cr, Cu, Hg, Ni, Pb, and Zn) were determined
by ICP-AES and ICP-MS. Extraction efficiency strongly depended on the applied leaching parameters and varied for certain elements
among different materials when a nitric acid procedure was applied. In general, element recoveries obtained from the aqua regia procedure were superior to those obtained from nitric acid procedures and showed good agreement with the 95% confidence interval
of the certified value for most of the elements investigated.
Received: 27 March 1998 / Revised: 29 June 1998 / Accepted: 3 July 1998 相似文献
26.
Vapor-liquid equilibria have been investigated experimentally for the nitrogen-isobutane system at temperatures from 120 K
to 220 K and at pressures up to 150 bar. Below 126.5 K, two liquid phases were observed as pressure was increased to near
the vapor pressure of pure nitrogen. The equilibrium ratio of nitrogen in the binary system and the Henry’s law constants
for nitrogen in isobutane were determined from experimental data. The experimental phase equilibrium data were correlated
by means of the Peng-Robinson equation of state. 相似文献
27.
Electron transfer (ET) processes in reaction centers (RC) of photosystem II (PSII) are prerequisites of oxygen generation. They are promoted by energy transfer from antenna to RC. Here, we calculated the redox potentials of chlorophylla/beta-carotene (Chla/Car) in PSII CP43/CP47 antenna complexes, solving the linearized Poisson-Boltzmann (LPB) equation based on the PSII crystal structure. The majority of antenna Chla redox potentials for reduction/oxidation were lower than those of RC Chla. Hence, ET events with excess electrons remain localized in the RC. Simultaneously antenna Chla can serve as an efficient cation sink to rereduce RC Chla if normal PSII function is inhibited. Especially three antenna Chla (Chl-47, Chl-18, and Chl-12) and two Car bridging the space between Chl(Z(D1)) and cytochrome (cyt) b559 have the same level of oxidation redox potential. Together with Chl(Z(D2)) they form an electron hole transfer pathway and temporary storage device guiding from the oxidized P680(+.) Chla to the cyt b559. This path may play a photoprotective role as efficient electron hole quencher. 相似文献
28.
Summary Interferences in the flameless determination of cadmium using the HGA 72 were studied for HCl, HNO3, H2SO4, HClO4 and HF and found to be depending on different thermal pretreatment. The interferences of cations were much smaller than for anions. The results are discussed with respect to thermal stability as well as atomization rate of the compositions under investigation. Special emphasis is put upon the presence of interactions between interferents, which in some cases can be used to eliminate interferences.
Statistische Untersuchungen über Störungen bei der flammenlosen AtomabsorptionsspektralphotometrieII. Cadmium
Zusammenfassung Interferenzen, die bei der flammenlosen Bestimmung von Cadmium in der HGA 72 auftreten, wurden bei HCl, HNO3, H2SO4, H3PO4, HClO4 und HF studiert; die AbhÄngigkeit ihres Auftretens von der thermischen Vorbehandlung wird gezeigt. Interferenzen von Kationen sind kleiner. Die Ergebnisse werden im Hinblick auf die thermische StabilitÄt und die Atomisierungsgeschwindigkeit der Proben diskutiert. Besonders betont wird die Gegenwart von Wechselwirkungen zwischen Störungen, die manchmal auch benützt werden können, um Interferenzen auszuschalten.
Part I: Z. Anal. Chem. [10] 相似文献
29.
Angle-resolved photoemission measurements for GaAs(110) have been extended to hv= 100 eV. These results show that dominant emission peaks are due to direct transitions. Weaker one-dimensional density of states features sometimes observed are due to surface umklapp/secondary cone and lifetime effects. Accurate band dispersions for all four valence bands GaAs along the [110] direction are given using simple normal emission and off-normal emission methods. Electron and hole lifetimes are directly determined. 相似文献
30.
Samuel P. Douglas Shreya Mrig Dr. Caroline E. Knapp 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(31):8062-8081
This Minireview compares two distinct ink types, namely metal-organic decomposition (MOD) and nanoparticle (NP) formulations, for use in the printing of some of the most conductive elements: silver, copper and aluminium. Printing of highly conductive features has found purpose across a broad array of electronics and as processing times and temperatures reduce, the avenues of application expand to low-cost flexible substrates, materials for wearable devices and beyond. Printing techniques such as screen, aerosol jet and inkjet printing are scalable, solution-based processes that historically have employed NP formulations to achieve low resistivity coatings printed at high resolution. Since the turn of the century, the rise in MOD inks has vastly extended the range of potentially applicable compounds that can be printed, whilst simultaneously addressing shelf life and sintering issues. A brief introduction to the field and requirements of an ink will be presented followed by a detailed discussion of a wide array of synthetic routes to both MOD and NP inks. Unindustrialized materials will be discussed, with the challenges and outlook considered for the market leaders: silver and copper, in comparison with the emerging field of aluminium inks. 相似文献