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891.
892.
Getahun Z Huang CY Wang T De León B DeGrado WF Gai F 《Journal of the American Chemical Society》2003,125(2):405-411
It is well-known that the C=N stretching vibration in acetonitrile is sensitive to solvent. Therefore, we proposed in this contribution to use this vibrational mode to report local environment of a particular amino acid in proteins or local environmental changes upon binding or folding. We have studied the solvent-induced frequency shift of two nitrile-derivatized amino acids, which are, AlaCN and PheCN, in H(2)O and tetrahydrofuran (THF), respectively. Here, THF was used to approximate a protein's hydrophobic interior because of its low dielectric constant. As expected, the C=N stretching vibrations of both AlaCN and PheCN shift as much as approximately 10 cm(-1) toward higher frequency when THF was replaced with H2O, indicative of the sensitivity of this vibration to solvation. To further test the utility of nitrile-derivatized amino acids as probes of the environment within a peptide, we have studied the binding between calmodulin (CaM) and a peptide from the CaM binding domain of skeletal muscle myosin light chain kinase (MLCK(579-595)), which contains a single PheCN. MLCK(579-595) binds to CaM in a helical conformation. When the PheCN was substituted on the polar side of the helix, which was partially exposed to water, the C=N stretching vibration is similar to that of PheCN in water. In constrast, when PheCN is introduced at a site that becomes buried in the interior of the protein, the C=N stretch is similar to that of PheCN in THF. Together, these results suggest that the C=N stretching vibration of nitrile-derivatized amino acids can indeed be used as local internal environmental markers, especially for protein conformational studies. 相似文献
893.
A supercritical fluid extraction (SFE) method was developed in the present study as an effective sample pretreatment technique of petroleum distillates from fire debris. Three petroleum distillates were used as target analytes, including 95 unleaded gasoline, kerosene, and premium diesel. An orthogonal array (L16) experimental design was adopted to separately evaluate primary SFE experimental factors. The SFE efficiencies of petroleum distillates at various extraction conditions were examined and the optimized SFE conditions were identified. Experimental results demonstrated that the optimized SFE method not only provided an effective extraction method for the spiked sample, but also successfully recovered residues of petroleum distillates from fire debris. 相似文献
894.
Huang SY Anklin C Walls JD Lin YY 《Journal of the American Chemical Society》2004,126(49):15936-15937
With the growing use of high fields and ultrasensitive probes, radiation damping emerges as a significant feedback interaction in modern solution NMR. Motivated by recent observations of mysterious concentration-dependent frequency shifts, experiments carried out on a cryoprobe at 600 MHz have revealed a time-averaged frequency shift of up to +83/-81 Hz. The sizable frequency shifts arise from deviations in the phase of the radiation damping field from perfect orthogonality relative to the net transverse magnetization. The frequency shift is shown to depend on the longitudinal magnetization and probe tuning conditions through experiments and numerical simulations. Such unexpected shifts in the solvent precession frequency provide a physical explanation for the empirical practice of adjusting the irradiation frequency of the saturating B1 field in solvent presaturation to achieve optimal suppression. Additional applications of the radiation damping induced frequency shift to solvent suppression and NMR methodology are discussed. 相似文献
895.
双亲嵌段聚合物的合成与应用 总被引:8,自引:0,他引:8
本文介绍了双亲嵌段聚合物的合成方法,包括共溶剂法、聚合后功能化法、胶束聚合法、自由基界面聚合法等,以及双亲嵌段聚合物在乳液聚合、三次采油、医用高分子材料等方面的应用。 相似文献
896.
X射线辐照前后,在BaF(Cl,Br):Sm^2+中以560nm的Nd:YAG脉冲光在液氮温度下进行了双光子烧孔实验和光激励发光实验,结果表明,Sm^2+掺杂的碱土金属氟卤化物光谱烧孔过程中伴随着光激励发光过程,这一过程直接影响光谱烧孔过程的进行。 相似文献
897.
硫酸溶液中Ag+离子对Mn2+离子阳极氧化的催化作用 总被引:2,自引:0,他引:2
Anodic oxidation of Mn2+ and Ag+ ions and anodic oxidation of Mn2+ ion on platinum electrode in H2SO4 solution catalyzed by Ag+ ion are studied by using RRDE and triangle voltammetry techniques. Mn2+ ion is oxidized on the anode surface with adsorped OH group to form a certain compound containing Mn3+, which causes Mn2+difficult to be oxidized directly on anode. Near the potential of oxygen evolution from H2O decomposition, Ag+ ion is oxidized to form Ag2+ ion. This is the main reaction on anode because of its reversability. At higher potential silver oxide is formed on the anode. The oxide catalyzes the decomposition of H2O strongly. The anodic oxidation of Mn2+ion catalyzed by Ag+ takes place and Ag2+ ion and silver oxide are no longer the product of Ag+ anodic oxidation when Mn2+ exists in solution at the potential for Ag+ anodic oxidation. It is confirmed that the catalysis reaction is homogeneous and very fast. 相似文献
898.
Cheng Y Huang Q Eić M Balcom BJ 《Langmuir : the ACS journal of surfaces and colloids》2005,21(10):4376-4381
We present the first 13C magnetic resonance imaging study of CO2 transient adsorption/desorption processes in a zeolite 5A column. CO2 transient concentration profiles were measured with a centric scan spin-echo single point imaging technique. The adsorption wave profiles were determined under flow conditions, with the results analyzed by the Bohart-Adams model. The model adequately accounts for the spatial and the temporal behavior of CO2 in the column. CO2 adsorption rate constants were calculated from the fit. Desorption profiles were acquired by blowing a helium stream through a zeolite 5A column saturated with CO2. An asymmetry between the adsorption and desorption profiles is readily apparent. A linear relationship between the CO2 condensed phase concentration and square root of time was observed. 相似文献
899.
[reaction: see text] Three organoboron compounds are shown to be two-photon fluorescent sensors for fluoride anion with high sensitivity and selectivity. The recognition mechanism is attributed to the unique steric structure of the bulky dimesitylboryl group and the Lewis acid-base interaction between trivalent boron atom and fluoride anion. 相似文献
900.