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61.
62.
Yonghwi Kim Tao Yang Gyeongwon Yun Mohammad Bagher Ghasemian Jaehyoung Koo Eunsung Lee Sung June Cho Kimoon Kim 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2015,127(45):13471-13476
A new approach to the synthesis of hierarchical micro‐ and mesoporous MOFs from microporous MOFs involves a simple hydrolytic post‐synthetic procedure. As a proof of concept, a new microporous MOF, POST‐66(Y), was synthesized and its transformation into a hierarchical micro‐ and mesoporous MOF by water treatment was studied. This method produced mesopores in the range of 3 to 20 nm in the MOF while maintaining the original microporous structure, at least in part. The degree of micro‐ and mesoporosity can be controlled by adjusting the time and temperature of hydrolysis. The resulting hierarchical porous MOF, POST‐66(Y)‐wt, can be utilized to encapsulate nanometer‐sized guests such as proteins, and the enhanced stability and recyclability of an encapsulated enzyme is demonstrated. 相似文献
63.
Nishat Arshi Junqing Lu Yun Kon Joo Jae Hong Yoon Bon Heun Koo 《Surface and interface analysis : SIA》2015,47(1):154-160
Nanocrystalline tantalum nitride (TaN) thin films have been deposited by reactive direct current magnetron sputtering technique on Si/SiO2 (100) substrate with nitrogen flow rate ranging from 0, 3, 5, 7, 9 to 11 standard cubic centimeter per minute (sccm). Structural properties, surface morphology, chemical composition and and resistivity of the TaN films were investigated by X‐ray diffraction (XRD), field emission scanning electron microscopy, X‐ray photoemission spectroscopy (XPS) and four‐point probe measurements, respectively. In the XRD spectra, a classical formation sequence of tantalum nitride phases in the order of Ta‐Ta2N‐TaN‐Ta4N5 and decreasing amount of metallic Ta were observed with increasing nitrogen flow. The electrical resistivity of the TaN film was found to increase with increasing N/Ta ratio as a result of the increased electron scattering from interstitial N atoms. In the XPS analysis, two groups of Ta4f doublets relating to different TaN phases were observed in the core level spectra of TaN films. No strong coupling was observed between the Ta4f doublets and the Ta4p and the N1s groups. The appropriate nitrogen flow was believed to be helpful in the bonding and formation of stoichiometric TaN. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
64.
Three new uni-dimensional alkali metal titanium fluoride materials, A2TiF5·nH2O (A=K, Rb, or Cs; n=0 or 1) have been synthesized by hydrothermal reactions. The structures of A2TiF5·nH2O have been determined by single-crystal X-ray diffraction. The Ti4+ cations have been reduced to Ti3+ during the synthesis reactions. All three A2TiF5·nH2O materials contain novel 1-D chain structures that are composed of the slightly distorted Ti3+F6 corner-sharing octahedra attributable to the Jahn-Teller distortion. The coordination environment of the alkali metal cations plays an important role to determine the degree of turning in the chain structures. Complete structural analyses, Infrared and UV-vis diffuse reflectance spectra, and thermal analyses are presented, as are electronic structure calculations. 相似文献
65.
This work describes a quantitative method to detect DNA damage in the presence of Pb and Cd ions using a surface modified microarray chip and a laser induced fluorescence microscopy (LIFM). The detection was carried out by the immobilization of a single-stranded DNA oligomer, tagged with a Cy5 fluorophore on a polydimethylsiloxane (PDMS) microarray chip followed by LIFM. Sulfosuccinimidyl-4-(N-maleimidomethyl) cyclohexane-1-carboxylate (Sulfo-SMCC) was attached as a cross-linker via the formation of covalent amide bonds. Then, the single-stranded DNA oligomer containing Cy5 as a fluorophore and thiol functional groups at both terminals, was bonded to the linker by reaction with sulfhydryl group. As the DNA oligomers were reacted with metal ions of Pb and Cd, the un-cleaved DNA oligomers were quantitatively identified by monitoring Cy5 fluorescence. Cadmium showed a quenching constant of 0.84 in the Stern–Volmer plot, whereas lead gave 0.22, indicating that cadmium ions suppress fluorescence more than lead ions. When optimized, fluorescence reductions of 23% (± 2.1) for Pb and 25% (± 1.4) for Cd were observed in air and decreased to almost < 5.0% in a radical scavenger of 5 mM. The cleaved DNA was also confirmed by MALDI-TOF-MS. In result, this experimental method using a microarray chip with surface modification provided quantitative determination of DNA oligomer damage with reproducible results, significantly reduced sample volumes and analysis times. 相似文献
66.
Isotope-labeled N-acetyl dipeptides (Ac-Xxx-Ala) are coupled to the primary amines of tryptic peptides and then analyzed by tandem mass spectrometry.
Amide bond cleavage between Xxx and Ala provides both low- and high-mass isotope-coded signals for quantification of peptides.
Especially, facile cleavage at the modified lysine side chain yields very strong high-mass quantitation signals in a noise-free
region. Tagging tryptic peptides with isobaric N-acetyl dipeptides is a viable strategy for accurate quantification of proteins, which can be used with most quadrupole ion
trap mass spectrometers carrying the 1/3 mass cut-off problem. 相似文献
67.
We present the development of a microfluidically cryo-cooled planar coil for magnetic resonance (MR) microscopy. Cryogenically cooling radiofrequency (RF) coils for magnetic resonance imaging (MRI) can improve the signal to noise ratio (SNR) of the experiment. Conventional cryostats typically use a vacuum gap to keep samples to be imaged, especially biological samples, at or near room temperature during cryo-cooling. This limits how close a cryo-cooled coil can be placed to the sample. At the same time, a small coil-to-sample distance significantly improves the MR imaging capability due to the limited imaging depth of planar MR microcoils. These two conflicting requirements pose challenges to the use of cryo-cooling in MR microcoils. The use of a microfluidic based cryostat for localized cryo-cooling of MR microcoils is a step towards eliminating these constraints. The system presented here consists of planar receive-only coils with integrated cryo-cooling microfluidic channels underneath, and an imaging surface on top of the planar coils separated by a thin nitrogen gas gap. Polymer microfluidic channel structures fabricated through soft lithography processes were used to flow liquid nitrogen under the coils in order to cryo-cool the planar coils to liquid nitrogen temperature (-196 °C). Two unique features of the cryo-cooling system minimize the distance between the coil and the sample: (1) the small dimension of the polymer microfluidic channel enables localized cooling of the planar coils, while minimizing thermal effects on the nearby imaging surface. (2) The imaging surface is separated from the cryo-cooled planar coil by a thin gap through which nitrogen gas flows to thermally insulate the imaging surface, keeping it above 0 °C and preventing potential damage to biological samples. The localized cooling effect was validated by simulations, bench testing, and MR imaging experiments. Using this cryo-cooled planar coil system inside a 4.7 Tesla MR system resulted in an average image SNR enhancement of 1.47 ± 0.11 times relative to similar room-temperature coils. 相似文献
68.
A general and facile synthesis of enantiopure 1-deoxyazasugars was achieved from stereoselective dihydroxylation of a common synthetic intermediate, piperidine ring fused oxazolidin-2-one, originating from a commercially available starting substrate, chiral aziridine-2-carboxylate, in high yields. 相似文献
69.
Sung Kyu Choi Namjip Koo 《Nonlinear Analysis: Theory, Methods & Applications》2011,74(17):6530-6536
In this paper we improve on the monotone property of Lemma 1.7.3 in Lakshmikantham et al. (2009) [5] for the case g(t,u)=λu with a nonnegative real number λ. We also investigate the Mittag-Leffler stability of solutions of fractional differential equations by using the fractional comparison principle. 相似文献
70.
We report on oxygen surface exchange studies in ~450-nm-thick nanocrystalline titania films with an average grain size of ~13 nm by electrical conductivity relaxation along with the conductivity measurements at varying temperatures and oxygen partial pressures (pO(2)s). By electrochemical impedance spectroscopy technique, the high temperature conductivity was measured in the pO(2) range from ~10(-16) to ~10(-6) Pa at temperatures from 973 to 1223 K and activation energy, ΔE(a), for conduction was estimated as ~3.23 eV at pO(2) ~10(-11) Pa. Under reducing atmosphere (pO(2) < 10(-6) Pa), two distinct n-type conduction regimes were observed and corresponding predominant defects are discussed while, at high pO(2) regime (pO(2) >10(-6) Pa), ionic conduction appears dominant leading to a conductivity plateau. The surface relaxation was observed to have two independent time constants likely originating from microstructural effects. The surface exchange coefficients are measured as ~10(-8)-10(-7) m∕s and ~10(-9)-10(-8) m∕s for each contribution with ΔE(a)s of 2.79 and 1.82 eV, respectively, without much pO(2) dependence across several orders of pO(2) range of ~10(-16)-10(-6) Pa in the temperature range between 973 and 1223 K. The results are of potential relevance to understanding the near-surface chemical phenomena in nanocrystalline titania which is of great interest for energy and environmental studies. 相似文献