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991.
Peterka DS Kim JH Wang CC Poisson L Neumark DM 《The journal of physical chemistry. A》2007,111(31):7449-7459
The photoionization and photoelectron spectroscopy of pure He droplets were investigated at photon energies between 24.6 eV (the ionization energy of He) and 28.0 eV. Time-of-flight mass spectra and photoelectron images were obtained at a series of molecular beam source temperatures and pressures to assess the effect of droplet size on the photoionization dynamics. At source temperatures below 16 K, where there is significant production of clusters with more than 10(4) atoms, the photoelectron images are dominated by fast electrons produced via direct ionization, with a small contribution from very slow electrons with kinetic energies below 1 meV arising from an indirect mechanism. The fast photoelectrons from the droplets have as much as 0.5 eV more kinetic energy than those from atomic He at the same photon energy. This result is interpreted and simulated within the context of a "dimer model", in which one assumes vertical ionization from two nearest-neighbor He atoms to the attractive region of the He2+ potential energy curve. Possible mechanisms for the slow electrons, which were also seen at energies below IE(He), are discussed, including vibrational autoionizaton of Rydberg states comprising an electron weakly bound to the surface of a large HeN+ core. 相似文献
992.
Park HY Jeon YK Shin HJ Kim IJ Kang HC Jeong SJ Chung DH Lee CW 《Experimental & molecular medicine》2007,39(2):195-204
The BubR1 mitotic-checkpoint protein monitors proper attachment of microtubules to kinetochores, and links regulation of chromosome-spindle attachment to mitotic-checkpoint signaling. Thus, disruption of BubR1 activity results in a loss of checkpoint control, chromosomal instability caused by a premature anaphase, and/or the early onset of tumorigenesis. The mechanisms by which deregulation and/or abnormalities of BubR1 expression operate, however, remain to be elucidated. In this study, we demonstrate that levels of BubR1 expression are significantly increased by demethylation. Bisulfite sequencing analysis revealed that the methylation status of two CpG sites in the essential BubR1 promoter appear to be associated with BubR1 expression levels. Associations of MBD2 and HDAC1 with the BubR1 promoter were significantly relieved by addition of 5-aza-2'-deoxycytidine, an irreversible DNA methyltransferase inhibitor. However, genomic DNA isolated from 31 patients with colorectal carcinomas exhibited a +84A/G polymorphic change in approximately 60% of patients, but this polymorphism had no effect on promoter activity. Our findings indicate that differential regulation of BubR1 expression is associated with changes in BubR1 promoter hypermethylation patterns, but not with promoter polymorphisms, thus providing a novel insight into the molecular regulation of BubR1 expression in human cancer cells. 相似文献
993.
Kim EK Kwon KB Han MJ Song MY Lee JH Lv N Ka SO Yeom SR Kwon YD Ryu DG Kim KS Park JW Park R Park BH 《Experimental & molecular medicine》2007,39(2):149-159
We demonstrated previously that Coptidis rhizoma extract (CRE) prevented S-nitroso-N-acetylpenicillamine-induced apoptotic cell death via the inhibition of mitochondrial membrane potential disruption and cytochrome c release in RINm5F (RIN) rat insulinoma cells. In this study, the preventive effects of CRE against cytokine-induced beta-cell death was assessed. Cytokines generated by immune cells infiltrating pancreatic islets are crucial mediators of beta-cell destruction in insulin-dependent diabetes mellitus. The treatment of RIN cells with IL-1beta and IFN-gamma resulted in a reduction of cell viability. CRE completely protected IL-1beta and IFN-gamma-mediated cell death in a concentration-dependent manner. Incubation with CRE induced a significant suppression of IL-1beta and IFN-gamma-induced nitric oxide (NO) production, a finding which correlated well with reduced levels of the iNOS mRNA and protein. The molecular mechanism by which CRE inhibited iNOS gene expression appeared to involve the inhibition of NF-kappaB activation. The IL-1beta and IFN-gamma-stimulated RIN cells showed increases in NF-kappaB binding activity and p65 subunit levels in nucleus, and IkappaB alpha degradation in cytosol compared to unstimulated cells. Furthermore, the protective effects of CRE were verified via the observation of reduced NO generation and iNOS expression, and normal insulin-secretion responses to glucose in IL-1beta and IFN-gamma-treated islets. 相似文献
994.
Shin Y Yoon SH Choe EY Cho SH Woo CH Rho JY Kim JH 《Experimental & molecular medicine》2007,39(1):97-105
Expression of matrix metalloproteinase-9 (MMP-9) is associated with airway remodeling and tissue injury in asthma. However, little is known about how MMP-9 is up-regulated in airway epithelial cells. In this study, we show that phorbol myristate acetate (PMA) induces MMP-9 expression via a protein kinase Calpha (PKCalpha)-dependent signaling cascade in BEAS-2B human lung epithelial cells. Pretreatment with either GF109203X, a general PKC inhibitor, or Go6976, a PKCalpha/beta isozyme inhibitor, inhibited PMA-induced activation of the MMP-9 promoter, as did transient transfection with PKCalpha antisense oligonuclotides. PMA activated NF-kappaB by phosphorylating IkappaB in these cells and this was also inhibited by GF109203X and Go6976, suggesting that PKCa acts as an upstream regulator of NF-kappaB in PMA-induced MMP-9 induction. Our results indicate that a "PKCalpha-NF- kappaB"-dependent cascade is involved in the signaling leading to PMA-induced MMP-9 expression in the lung epithelium. 相似文献
995.
Giseop Kwak Hong‐Qing Wang Kyu‐Han Choi Kyu‐Ho Song Soon‐Hak Kim Hyeok‐Soo Kim Sam‐Jong Lee Ho‐Young Cho Eon‐Ju Yu Hyo‐Jeong Lee Eun‐Jung Park Lee‐Soon Park 《Macromolecular rapid communications》2007,28(12):1317-1324
New poly(diphenylacetylene)s with alkoxy and fluoroalkyl groups as electron‐donating and electron‐withdrawing groups, respectively, were synthesized by using a WCl6‐n‐Ph4Sn catalyst. The polymer solutions emitted strong, bluish‐green lights when photo‐excited. The polymers that contained the electron‐donating alkoxy groups showed longer fluorescence‐maximum peaks when compared to the polymers that contained the electron‐withdrawing fluoroalkyl groups. However, such an effect of the substituent on the absorption property was not clearly seen. The emission bands of the solid films did not show any significant red shift, relative to that of the dilute solution.
996.
The new [Li(DME)3+] salt of the previously-known tetra(tert-butyl)erbate(III) anion [Er(t-Bu)4−] has been prepared and structurally characterized. The erbium(III) center is ligated by four tert-butyl groups in an approximately tetrahedral arrangement. The C–Er–C angles between the tert-butyl groups range from 108.8(3)° to 111.2(3)° and the Er–C distances range from 2.352(6) to 2.395(6) Å. The lithium cation is surrounded by three DME molecules, which form a distorted octahedral coordination sphere. Attempts to oxidize the analogous terbate complex [Li(DME)3][Tb(t-Bu)4] and its cerium analog to electrically neutral tetra(alkyl)lanthanide(IV) compounds are described. 相似文献
997.
A new pentacoordinated ferrous compound [TPAFeCl]+ (TPA = tris(2-pyridylmethyl)amine) was synthesized from the reaction between H3TPA(ClO4)3 and Fe(PnPr3)2Cl2 in MeCN. The unique trigonal bipyramidal [TPAFeCl]+ complex was characterized as a S = 2 high spin complex based on the crystallographic structure, magnetic susceptibility, 1H NMR spectrum and semi-empirical ZINDO/S calculations. Crystal of [TPAFeCl]2(FeCl4)(MeCN)2 was monoclinic with a = 12.019(2) Å, b = 27.550(5) Å, c = 14.138(2) Å, β = 94.168(3)°, V = 4668.9(13) Å3, space group C/c, and the unit cell contained a racemic mixture of Δ and Λ isomers with ferrous tetrachloride anion. 相似文献
998.
Ji-Ye Lee Young Ah Kim Mi Yeon Kim Yong Tae Lee Bruce D. Hammock Hye-Sung Lee 《Analytica chimica acta》2012
This study was performed to demonstrate the importance of selecting an appropriate membrane when developing immunochromatographic assays (ICAs) for the sensitive detection of low-molecular weight compounds. Based on our findings, we propose a theoretical basis for selecting such a membrane. When eluting the sample solution for the competitive ICA using colloidal gold label for low-molecular analytes, the degree of binding inhibition is proportional to the collision frequency between the antibody-colloidal gold (Ab–CG) and analyte before Ab–CG binding to the capture antigen and a higher concentration of pesticides around the Ab–CG leads to a greater degree of inhibition. Therefore, we propose that the relative migration speed of the analyte and Ab–CG on the test strip is critically important for selecting a membrane in the development of sensitive competitive ICAs. We developed a novel method to estimate such a relative migration speed. We demonstrated the applicability of this proposal by using it to select an appropriate membrane for the development of an ICA of the pesticide diazinon. 相似文献
999.
Kim Kyoung Heon Tucker Melvin P. Keller Fred A. Aden Andy Nguyen Quang A. 《Applied biochemistry and biotechnology》2001,91(1-9):253-267
Two-stage dilute acid pretreatment followed by enzymatic cellulose hydrolysisis an effectivemethod for obtaining high sugar
yields from wood residuessuchassoftwood forest thinnings. In the first-stage hydrolysis step, most of the hemicellulose is
solubilized using relatively mild conditions. The soluble hemicellu losic sugars are recovered from the hydrolysateslurry
by washing with water. The washed solids are then subjected tomoresevere hydrolysis conditions to hydrolyze approx 50% of
the cellulose to glucose. The remaining cellulose can further be hydrolyzed with cellulase enzyme. Our process simulation
indicates that the amount of water used in the hemicellulose recovery step has a significan tim pact on the cost of ethanol
production. It is important to keep water usage as low as possible while mainta ining relatively high recovery of solublesugars.
To achieve this objective, a prototype pilot-scale continuous countercurrent screw extractor was evaluated for the recovery
of hemicellulose from pretreated forest thinnings. Using the 274-cm (9-ft) long extractor, solubles recoveries of 98, 91,
and 77% were obtained with liquid-to-insoluble solids (L/1S) ratios of 5.6, 3.4, and 2.1, respectively. An empirical equation
was developed to predict the performance of the screwextractor. This equation predicts that soluble sugar recovery above 95%
can be obtained with an L/IS ratio as low as 3.0. 相似文献
1000.
Sun-Jae Kim E.G. Lee S.D. Park C.J. Jeon Y.H. Cho C.K. Rhee W.W. Kim 《Journal of Sol-Gel Science and Technology》2001,22(1-2):63-74
The photocatalytic characteristics of nanostructured TiO2 ultrafine powder with rutile phase produced using the homogeneous precipitation process at low temperatures (HPPLT) were compared with those of commercial P-25 TiO2 powder by flame hydrolysis. The TiO2 powder by the HPPLT showed much higher photoactivity in the removal rate, showing lower pH values in the solution than the P-25 powder when eliminating metal ions such as Pb and Cu from the aqueous metal-EDTA solutions. This can be inferred as the more rapid photo-oxidation or -reduction of metal ions from the aqueous solution, together with relatively higher efficiencies in the use of an electron-hole pair formed on the surface of the TiO2 particles under UV light irradiation. Also, in the view of the TiO2 particle morphology, compared to the well-dispersed spherical P-25 particles, the agglomerated TiO2 secondary particles by the HPPLT consist of acicular typed primary particles with a thickness in the range of 3–7 nm and the primary particles radialize in all directions, which would be more effective to photocatalytic reactions without the large electron-hole recombination on the surface of the TiO2 particle under UV light irradiation. It can be, therefore, thought that the higher photoactivity of the rutile TiO2 powder by the HPPLT in the aqueous solutions results mainly from having a larger surface area by the acicular shaped primary particles with very thin thickness and radialization in all directions. 相似文献