共查询到20条相似文献,搜索用时 15 毫秒
1.
The Successive Self-nucleation and Annealing (SSA) thermal fractionation technique is briefly reviewed to highlight recent advances such as the use of high speed DSC concepts to perform faster fractionation. Additionally, recent applications of SSA to characterize confined semi-crystalline model polyethylenes in block copolymer nanophases and in situ prepared nanocomposites with carbon nanotubes are also reviewed. A novel result presented here deals with the use of a macromolecular plasticizer to improve the quality of SSA thermal fractionation. 相似文献
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CM Davis S Xiao DP Raleigh RB Dyer 《Journal of the American Chemical Society》2012,134(35):14476-14482
Understanding the folding of the β-hairpin is a crucial step in studying how β-rich proteins fold. We have studied CLN025, an optimized ten residue synthetic peptide, which adopts a compact, well-structured β-hairpin conformation. Formation of the component β-sheet and β-turn structures of CLN025 was probed independently using a combination of equilibrium Fourier transform infrared spectroscopy and laser-induced temperature jump coupled with time-resolved infrared and fluorescence spectroscopies. We find that CLN025 is an ultrafast folder due to its small free energy barrier to folding and that it exceeds the predicted speed limit for β-hairpin formation by an order of magnitude. We also find that the folding mechanism cannot be described by a simple two-state model, but rather is a heterogeneous process involving two independent parallel processes. Formation of stabilizing cross-strand hydrophobic interactions and turn alignment occur competitively, with relaxation lifetimes of 82 ± 10 and 124 ± 10 ns, respectively, at the highest probed temperature. The ultrafast and heterogeneous folding kinetics observed for CLN025 provide evidence for folding on a nearly barrierless free energy landscape, and recalibrate the speed limit for the formation of a β-hairpin. 相似文献
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Gagandeep Kaur WenHai Zhan Chao Wang Hannah Barnhill He Tian Qian Wang 《中国科学:化学(英文版)》2010,53(6):1287-1293
Cu (I) catalyzed alkyne-azide cycloaddition (CuAAC) reaction, a typical “click“ reaction, is one of the modular synthetic approaches which has been broadly used in various organic syntheses, medicinal chemistry, materials development and bioconjugation applications. We have for the first time synthesized two dialkyne derivatized fluorescent crosslinkers which could be applied to crosslink two biomolecules using CuAAC reaction. Turnip yellow mosaic virus, a plant virus with unique structural and chemical properties, was used as a prototypical scaffold to form a 2D single layer at the interface of two immiscible liquids and crosslinked with these two linkers by the CuAAC reaction. Upon crosslinking, the fluorescence of both linkers diminished, likely due to the distortion of the polymethylene backbone, which therefore could be used to indicate the completion of the reaction. 相似文献
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Due to new emerging fast separation technology and the great demand of high sample throughput in discovery, large number of samples now needed to be analyzed by mass spectrometer with high conformation accuracy. 相似文献
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Herein we combined the use of self-assembled monolayer (SAM) modified electrodes and gold coated magnetic nanoparticles (Au@MNPs) to modulate faradaic electrochemistry when nanoparticles are absorbed on and removed from, a passivated electrode using an external magnetic field. Substantial faradaic electrochemistry of potassium ferricyanide in solution is first prevented by modifying gold electrodes with 11-mercaptoundecanoic acid to form a passivating SAM. Restoration of the faradaic electrochemistry is then achieved by introducing Au@MNPs which are brought to the surface using an external magnetic field. The faradaic electrochemistry can again be suppressed by removing Au@MNPs from the SAM using another external magnetic field. 相似文献
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Cubic boron nitride (cBN) and orthorhombic boron nitride (oBN) crystals have been prepared in hydrothermal solutions by reacting H3BO3 NaN3 P and H3BO3 NaN3 N2H4 respectively. The experimental results indicated that, if the temperature was increased rapidly, both the yield and perfectness of BN crystals became poor. On the contrast, the yield and perfectness of BN crystals can be improved very much by slowly increasing the temperature of the reaction mixture. The results of X-ray powder diffraction (XRD), Fourier transform infrared spectrum (FTIR) and high resolution transmission electron microscopy (HRTEM) proved that the samples were composed of oBN and cBN. 相似文献
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Possibility was examined of using the simplest catalytic system (palladium salt and NaOH) in ethanol or in a mixture of ethanol
and water as a catalyst precursor in order to obtain high product yields in the Suzuki reaction with nonactivated aryl bromides
at room temperature without an inert atmosphere or ligand additives. 相似文献
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A. P. Novikov St. N. Kalmykov E. V. Kuzovkina B. F. Myasoedov K. Fujiwara A. Fujiwara 《Journal of Radioanalytical and Nuclear Chemistry》2009,280(3):629-634
Evolution of actinide partitioning to colloids upon subsurface migration in the vicinity of Karachay Lake (PA “Mayak”, Russia)
was studied by micro- and ultrafiltration and sequential extraction. Colloidal matter was characterized by SEM-EDX, TEM and
photon-correlation spectroscopy. Samples were collected from wells with different redox conditions i.e. from higly oxic to
rather reducing. Under oxidizing conditions uranium and neptunium is readily washed out from colloids. Plutonium and americium
are present in colloidal matter mainly as hard-soluble species. Under oxidizing conditions plutonium and americium are predominantly
bound to organic/mineral fractions (carbonates, oxides and organically bound). Under reducing conditions plutonium and americium
are present in immobile refractory fraction. It was also established that uranium and neptunium under reducing conditions
behave similarly to plutonium. This phenomenon may be explained by the fact that under reducing conditions and at considerable
concentrations of uranium and nitrite-ions these elements form low-soluble An(IV) forms. 相似文献
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Rajashri B. Sawant 《Journal of solution chemistry》2018,47(4):787-795
Volumetric, viscometric and speed of sound studies of binary mixtures of tert-butyl acetate with fluorobenzene, chlorobenzene and bromobenzene have been made over the entire range of composition, at (298.15 and 308.15) K and at atmospheric pressure (p?=?0.089 MPa). From the experimental values of density, viscosity, and speed of sound, the excess molar volumes VE, deviations in viscosity ?η and deviation in isentropic compressibility ΔK S have been calculated. The VE and ΔK S values are negative while the ?η the values are positive over the entire composition range for the binary mixtures. The derived parameters have been fitted with the Redlich–Kister polynomial equation. The interaction parameters of McAllister model are used to correlate the experimental values of density, viscosity and speed of sound. 相似文献
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The densities (ρ), viscosities (η), refractive indices (nD), and speeds of sound (u), of binary mixtures of pyridine with 1-hexanol, 1-heptanol, 1-octanol and 1-decanol, including those of pure liquids, were measured over the entire composition range at 303.15 K and atmospheric pressure. From these experimental data, the values of excess molar volumes (VE), deviations in isentropic compressibilities (Δks), viscosities (Δh), molar refractions (ΔRm), apparent and partial molar volumes (Vf,2 and ), apparent and partial molar compressibilities (Kf,2 and ), of alkanols in pyridine and their corresponding deviations (ΔV and ΔK) were calculated. The variations of these parameters with composition of the mixtures suggest that the strength of interactions in these mixtures follow the order: 1-hexanol>1-heptanol>1-octanol>1-decanol. All the excess and deviation functions were fitted to Redlich-Kister polynomial equation to determine the fitting coefficients and the standard deviations. 相似文献
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《Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy》1991,47(11):1583-1593
The 3JCH couplings at bridgehead carbons in naphthalene and quinoline derivatives have been classified as “through” ring and “cross” ring interactions. Further divisions of the couplings have been introduced in an attempt to rationalize the interactions such that they may be used for structural assignments. The influence of central π-bond order and of the heterocyclic nitrogen atom on the couplings has been discussed. From a study of the 3J couplings at C-9 and C-10 in 45 quinoline derivatives the coupling constant ranges observed were “through” ring (via 9,10-bond): J94 4.9–6.1 Hz, J95 5.5–7.3 Hz, J10.8 4.1–5.3 Hz; “cross” ring: J92 11.0–13.5 Hz, J97 6.7–9.8 Hz, J10.3 4.4–7.3 Hz, J10.6 5.2–9.1 Hz. 相似文献
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V. V. Klyubin K. A. Klyubina K. N. Makovetskaya 《Russian Journal of Physical Chemistry A, Focus on Chemistry》2018,92(2):295-299
The kinetics of crystalline iodine dissolution in ethanol at room temperature and 60°C is studied using the electronic absorption spectra of iodine solutions. Dissolution is shown to proceed for more than three months. It is found that the process begins with the formation of hydroiodic acid HI and is complete with the formation of I 3 ? anions. 相似文献
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《Arabian Journal of Chemistry》2023,16(3):104537
Previously, we have shown that water adjacent to many hydrophilic substances excludes colloidal and molecular solutes. It was labelled “exclusion zone” (EZ) or “fourth phase” water. A salient feature is its characteristic light absorbance at or near 270 nm. In this study, EZ water formed against three chemically distinct surfaces, Nafion, ghee, and Whatman-5 filter paper was extracted, characterized by UV–Visible absorbance spectroscopy, and solidified either by lyophilizing or evaporation in an oven. The resulting highly stable solid was dissolved in water and confirmed as EZ water by its characteristic absorbance at 270–280 nm. We used mass spectroscopy to verify the absence of ionizable contaminants that could reproduce the characteristic “signature EZ” spectra in the three liquid preparations, or in the solids formed from desiccated EZ water that had been reconstituted in deionized water. Hence, a solid form of EZ water may, indeed, exist at room temperature. 相似文献
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Withthedevelopmentofthecomputertechniques,abinitiocalculationbecomesthestrongimplementforstudyingthechemicalreactionsystemandamendssomemechanismsproposedbyexperiment.Forexample,inthephotodissociationofthegloxalat454.5nm,Parmenteretal.measuredamixtureofpro… 相似文献
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Ryan Fitzgerald 《Journal of Radioanalytical and Nuclear Chemistry》2010,284(1):173-174
In a recent paper, Mathew et al. detailed, for a specific titration-based assay of uranium, a “step-by-step approach to calculate
the GUM uncertainty of the measurand”, in which their uncertainty assessment was based solely on prior knowledge, ignoring
the manifest variability in their replication data. A simple analysis of the variance from their data reveals that the uncertainty
in the average of the replicated quantity (TEF) was at least 3.5 times their estimate. Since the observables that contribute
most to the final uncertainty in their method were not replicated, it is unknown whether the estimates for the uncertainties
of those quantities, and thus of the output quantity, were also underestimated. This comment demonstrates how a better uncertainty
evaluation is possible by extracting as much knowledge as possible from the extant data. 相似文献
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Drug discovery is a complicated process that involves multiple synthetic chemistry tasks. Among them, lead generation and optimization is the core business in the discovery research. During the stage of lead generation, a large library of many thousands individual compounds will be screened against a biological target to identify a set of hits that showed desirable activity. Once a hit has been identified, analog synthesis and development of SAR around this hit and establishment of relationsh… 相似文献