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排序方式: 共有884条查询结果,搜索用时 15 毫秒
1.
Yaron Paz Ellina Kesselman Lulu Fahoum Irina Portnaya Ory Ramon 《Journal of Polymer Science.Polymer Physics》2004,42(1):33-46
The effect of two strong salting-out salts (Na2SO4 and K2SO4) on the temperature-induced phase-separation process in aqueous solutions of poly(N-isopropylacrylamide) (PNIPA) was examined by attenuated total reflectance/Fourier transform infrared spectroscopy, differential scanning calorimetry, and viscosity measurements. On the basis of these measurements, a detailed scenario of the phase-separation process was deduced. The phase-separation scenario of solutions containing PNIPA and water was altered in the presence of sulfate ions. Here, the sulfate ions induced partial intrachain collapse, manifested by a relatively compact structure well below the lower critical solution temperature. This led to a more gradual, smooth phase transition, with temperature-resolved intrachain collapse and interchain aggregation and a lesser extent of hysteresis. Although at the macrolevel one may not be able to differentiate among various scenarios altering the solvent into a poor solvent, the aforementioned microlevel measurements provided a way to expose the difference between raising the temperature and adding cosolutes. Follow-up studies on the effect of salting-in salts will be presented. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 33–46, 2004 相似文献
2.
A parametric study of sandwich-type discharge chamber nitrogen lasers has been carried out. A non-monotonic dependence of the energy emitted by the laser and the discharge chamber thickness is found. Discharge chambers with = 1 have the best electro-optical efficiency. The ratio between the electrode gap,d, and is found to be a scaling parameter. The possible influence of wall ablation in the comportment is also discussed. 相似文献
3.
Ramon Rios 《Tetrahedron letters》2006,47(48):8547-8551
A highly enantioselective catalytic asymmetric synthesis of 2H-1-benzothiopyrans is presented. The organocatalytic asymmetric domino reactions between 2-mercaptobenzaldehyde and α,β-unsaturated aldehydes proceed with excellent chemo- and enantioselectivities to give the corresponding pharmaceutically valuable benzothiopyrans in high yields with 91-98% ee. 相似文献
4.
Similarity measures between pairs of molecular wave functions are described. They are based on the geometrical structure of the LCAO–MO framework and upon multivariate analysis ideas. The theoretical framework is presented, and formulae for some integrals needed are given. Two main measures, distance and correlation coefficients, are used. Distance and correlation matrices induce relationships in the whole MO set, which can be depicted through minimal spanning tree techniques. Furthermore, principal component analysis allows a two-dimensional visualization of the Mo manifold geometrical relationships. Various examples are given in order to obtain information on how basis set, environment, excitation, bending, stretching, and electronegativity affect the induced order. For this purpose “ab initio” SCF–LCAO–MO calculations with double- and single-zeta quality basis sets have been used for various simple molecular structures: H2O, NH3, CH4, N2, O2, C2, NO, CN, and CO. The results obtained can open the way to LCAO–MO taxonomy. Using this information, other areas of interest are connected with similarity measures (SCF and CI , localization procedures, etc.), proving in this manner their potential utility. 相似文献
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6.
Dula Amarasiriwardena Steven F. Durrant Alexandra Lásztity Antoaneta Kvska Mark D. Argentine Ramon M. Barnes 《Microchemical Journal》1997,56(3):352-372
Semiquantitative analysis with accuracy of ±30 to 50% is a valuable tool for rapid screening of samples prior to quantitative determination of trace metals. In this study semiquantitative analysis software available with commercial inductively coupled plasma–mass spectrometry (ICP-MS) instrumentation is applied for rapid multielemental analysis, and the accuracy and precision of this semiquantitative analysis approach is evaluated with biological certified reference materials. Samples were prepared by high-pressure, high-temperature nitric acid vapor-phase digestion. For most elements the measured semiquantitative results are in the range of the certified values. With appropriate analyte solution dilution, the measured concentrations of the major elements (e.g., Ca) also agree with certified values. The accuracy is within ±10% for 28 element determinations that include 16 individual elements (Ag, As, Cd, Co, Cr, Cu, Fe, Mn, Mo, Ni, Pb, Rb, Sb, Sr, Tl, and Zn) and ±20% for 54 element determinations that include three more elements (Mg, V, and U) in eight certified reference materials including water. The method precision is 11 ± 11% (relative standard deviation,n= 65). 相似文献
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8.
Aviñó A Cubero E González C Eritja R Orozco M 《Journal of the American Chemical Society》2003,125(51):16127-16138
The structural, dynamical, and recognition properties of antiparallel DNA triplexes formed by the antiparallel d(G#G.C), d(A#A.T), and d(T#A.T) motifs (the pound sign and dot mean reverse-Hoogsteen and Watson-Crick hydrogen bonds, respectively) are studied by means of "state of the art" molecular dynamics simulations. Once the characteristics of the helix are defined, molecular dynamics and thermodynamic integration calculations are used to determine the expected stabilization of the antiparallel triplex caused by the introduction of 8-aminopurines. Finally, oligonucleotides containing 8-aminopurine derivatives are synthesized and tested experimentally using several approaches in a variety of systems. A very large stabilization of the triplex is found experimentally, as predicted by simulations. These results open the possibility for the use of oligonucleotides carrying 8-aminopurines to bind single-stranded nucleic acids by formation of antiparallel triplexes. 相似文献
9.
10.
The structures of the inclusion compounds formed by the host 9,9’-(ethyne-1,2-diyl)bis(fluoren-9-01) with pyridine and picolines are similar and display tubular topology. The host discriminates poorly between
these guests. The kinetics of desorption of the pyridine compound is governed by the Avrami-Erofe’ev equation A2, with an
activation energy of 111(7) kJ mol−1. 相似文献