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11.
We describe a density functional theory approach to solvation in molecular solvents. The solvation free energy of a complex solute can be obtained by direct minimization of a density functional, instead of the thermodynamic integration scheme necessary when using atomistic simulations. In the homogeneous reference fluid approximation, the expression of the free-energy functional relies on the knowledge of the direct correlation function of the pure solvent. After discussing general molecular solvents, we present a generic density functional describing a dipolar solvent and we show how it can be reduced to the conventional implicit solvent models when the solvent microscopic structure is neglected. With respect to those models, the functional includes additional effects such as the microscopic structure of the solvent, the dipolar saturation effect, and the nonlocal character of the dielectric constant. We also show how this functional can be minimized numerically on a three-dimensional grid around a solute of complex shape to provide, in a single shot, both the average solvent structure and the absolute solvation free energy. 相似文献
12.
Virgil Percec Anatoliy V. Popov Ernesto Ramirez‐Castillo 《Journal of polymer science. Part A, Polymer chemistry》2005,43(2):287-295
The single‐electron‐transfer/degenerative‐chain‐transfer mediated living radical polymerization (SET–DTLRP) of vinyl chloride (VC) in H2O/tetrahydrofuran at 25 °C catalyzed by thiourea dioxide [(NH2)2C?SO2] is reported. This polymerization occurs only in the presence of a basic sodium bicarbonate (NaHCO3) buffer and the electron‐transfer cocatalyst octyl viologen. The resulting poly(vinyl chloride) (PVC) has a number‐average molecular weight of 1500–7000 and a weight‐average molecular weight/number‐average molecular weight ratio of 1.5. This PVC does not contain detectable amounts of structural defects and has both active chloroiodomethyl and inactive chloromethyl chain ends. Because of possible side reactions caused by the primary sulfoxylate anion (SO), the catalytic activity of (NH2)2C?SO2 in the SET–DTLRP of VC is lower than that of the single‐electron‐transfer agent sodium dithionite. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 287–295, 2005 相似文献
13.
Summary Complexes of formula [MCl3(glyH)3] (M=Ti, V and Fe) [CrCl3(glyH)2H2O], [MCl2(glyH)2(H2O)2] (M=Co and Cu) and [NiCl2(glyH)3H2O] have been prepared and characterized by potentiometric curves, chemical analysis, magnetic properties, i.r. and electronic spectral data. 相似文献
14.
15.
Ulmer TS Ramirez BE Delaglio F Bax A 《Journal of the American Chemical Society》2003,125(30):9179-9191
NMR measurements of a large set of protein backbone one-bond dipolar couplings have been carried out to refine the structure of the third IgG-binding domain of Protein G (GB3), previously solved by X-ray crystallography at a resolution of 1.1 A. Besides the commonly used bicelle, poly(ethylene glycol), and filamentous phage liquid crystalline media, dipolar couplings were also measured when the protein was aligned inside either positively or negatively charged stretched acrylamide gels. Refinement of the GB3 crystal structure against the (13)C(alpha)-(13)C' and (13)C'-(15)N dipolar couplings improves the agreement between experimental and predicted (15)N-(1)H(N) as well as (13)C(alpha)-(1)H(alpha) dipolar couplings. Evaluation of the peptide bond N-H orientations shows a weak anticorrelation between the deviation of the peptide bond torsion angle omega from 180 degrees and the angle between the N-H vector and the C'-N-C(alpha) plane. The slope of this correlation is -1, indicating that, on average, pyramidalization of the peptide N contributes to small deviations from peptide bond planarity ( = 179.3 +/- 3.1 degrees ) to the same degree as true twisting around the C'-N bond. Although hydrogens are commonly built onto crystal structures assuming the N-H vector orientation falls on the line bisecting the C'-N-C(alpha) angle, a better approximation adjusts the C(alpha)-C'-N-H torsion angle to -2 degrees. The (15)N-(1)H(N) dipolar data do not contradict the commonly accepted motional model where angular fluctuations of the N-H bond orthogonal to the peptide plane are larger than in-plane motions, but the amplitude of angular fluctuations orthogonal the C(alpha)(i-1)-N(i)-C(alpha)(i) plane exceeds that of in-plane motions by at most 10-15 degrees. Dipolar coupling analysis indicates that for most of the GB3 backbone, the amide order parameters, S, are highly homogeneous and vary by less than +/-7%. Evaluation of the H(alpha) proton positions indicates that the average C(alpha)-H(alpha) vector orientation deviates by less than 1 degrees from the direction that makes ideal tetrahedral angles with the C(alpha)-C(beta) and C(alpha)-N vectors. 相似文献
16.
Laloup M Ramirez Fernandez Mdel M Wood M De Boeck G Henquet C Maes V Samyn N 《Journal of chromatography. A》2005,1082(1):15-24
A rapid and sensitive method for the analysis of delta9-tetrahydrocannabinol (THC) in preserved oral fluid was developed and fully validated. Oral fluid was collected with the Intercept, a Food and Drug Administration (FDA) approved sampling device that is used on a large scale in the U.S. for workplace drug testing. The method comprised a simple liquid-liquid extraction with hexane, followed by liquid chromatography-tandem mass spectrometry (LC-MS-MS) analysis. Chromatographic separation was achieved using a XTerra MS C18 column, eluted isocratically with 1 mM ammonium formate-methanol (10:90, v/v). Selectivity of the method was achieved by a combination of retention time, and two precursor-product ion transitions. The use of the liquid-liquid extraction was demonstrated to be highly effective and led to significant decreases in the interferences present in the matrix. Validation of the method was performed using both 100 and 500 MicroL of oral fluid. The method was linear over the range investigated (0.5-100 ng/mL and 0. 1-10 ng/mL when 100 and 500 microL, respectively, of oral fluid were used) with an excellent intra-assay and inter-assay precision (relative standard deviations, RSD <6%) for quality control samples spiked at a concentration of 2.5 and 25 ng/mL and 0.5 and 2.5 ng/mL, respectively. Limits of quantification were 0.5 and 0.1 ng/mL when using 100 and 500 microL, respectively. In contrast to existing GC-MS methods, no extensive sample clean-up and time-consuming derivatisation steps were needed. The method was subsequently applied to Intercept samples collected at the roadside and collected during a controlled study with cannabis. 相似文献
17.
Esther Ramirez Karine Philippot Anna M. Masdeu-Bultó 《Journal of organometallic chemistry》2004,689(24):4601-4610
The synthesis of palladium nanoparticles is performed by hydrogenation of a precursor, Pd2(dba)3 (1) or [Pd(C3H5)Cl]2 (2) in the presence of either a weakly coordinating ligand (hexadecylamine, HDA) or good ligands (polyphosphines). It is shown in the case of 1 that good ligands lead to stable spherical nanoparticles of small size (near 2 nm) whereas the protective effect of HDA depends on the amount of ligand added as a result of equilibria present at the surface of the particles as monitored by solution NMR spectroscopy. The decomposition of 2 being very fast, the particle growth cannot be controlled except in the case of the use of a large excess of HDA which leads to spongelike particles resulting from the agglomeration of initially obtained nanocrystallites. 相似文献
18.
Rolando Ramirez Carlos Eduardo Schnorr Jordana Georgin Matias Schadeck Netto Dison S. P. Franco Elvis Carissimi Delmira Wolff Luis F. O. Silva Guilherme Luiz Dotto 《Molecules (Basel, Switzerland)》2022,27(22)
Brazil’s production and consumption of açai pulp (Euterpe oleracea) occur on a large scale. Most of the fruit is formed by the pit, which generates countless tons of residual biomass. A new purpose for this biomass, making its consumption highly sustainable, was presented in this study, where activated carbon (AC) was produced with zinc chloride for later use as an adsorbent. AC carbon formed by carbon and with a yield of 28 % was satisfactorily used as an adsorbent in removing the herbicide 2,4-dichlorophenoxyacetic acid (2,4-D). Removal efficiency was due to the highly porous surface (Vp = 0.467 cm3 g−1; Dp = 1.126 nm) and good surface área (SBET = 920.56 m2 g−1). The equilibrium data fit the Sips heterogeneous and homogeneous surface model better. It was observed that the increase in temperature favored adsorption, reaching a maximum experimental capacity of 218 mg g−1 at 328 K. The thermodynamic behavior indicated a spontaneous, favorable, and endothermic behavior. The magnitude of the enthalpy of adsorption was in agreement with the physical adsorption. Regardless of the herbicide concentration, the adsorbent displayed fast kinetics, reaching equilibrium within 120 min. The linear driving force (LDF) model provided a strong statistical match to the kinetic curves. AC with zinc chloride (ZnCl2), created from leftover açai biomass, is a potential alternative as an adsorbent for treating effluents containing 2,4-D. 相似文献
19.
20.
Andrew J. Guenthner Vandana Vij Timothy S. Haddad Josiah T. Reams Kevin R. Lamison Christopher M. Sahagun Sean M. Ramirez Gregory R. Yandek Suresh C. Suri Joseph M. Mabry 《Journal of polymer science. Part A, Polymer chemistry》2014,52(6):767-779
The synthesis and physical properties of new silicon‐containing polyfunctional cyanate ester monomers methyl[tris(4‐cyanatophenyl)]silane and tetrakis(4‐cyanatophenyl)silane, as well as polycyanurate networks formed from these monomers are reported. The higher crosslinking functionality compared to di(cyanate ester) monomers enables much higher ultimate glass transition temperatures to be obtained as a result of thermal cyclotrimerization. The ability to reach complete conversion is greatly enhanced by cocure of the new monomers with di(cyanate ester) monomers such as 1,1‐bis(4‐cyanatophenyl)ethane. The presence of silicon in these polycyanurate networks imparts improved resistance to rapid oxidation at elevated temperatures, resulting in char yields as high as 70% under nitrogen and 56% in air in the best‐performing networks. The water uptake in the silicon‐containing networks examined is 4–6 wt % after 96 h of immersion at 85 °C, considerably higher than both carbon‐containing and/or di(cyanate ester) analogs. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 767–779 相似文献