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61.
The bonding properties of 1-phenyl-1-propyne (PP, C6H5CCCH3) on Cu(111) at 100 K have been studied using temperature-programmed desorption (TPD), and X-ray, ultraviolet, and two-photon photoemission spectroscopies (XPS, UPS, and 2PPE). In TPD, there is no evidence for dissociation. Multilayer desorption occurs at 187 K, and monolayer desorption occurs at 320 (83.5 kJ/mol) and 390 K (102.4 kJ/mol), with the latter dominating. Based on the calibrated C(1s) XPS, the saturation monolayer coverage is one PP per four surface Cu atoms. The broad and asymmetric C(1s) intensity profile of the monolayer can be resolved into three symmetric components, with peaks at 283.6, 284.5, and 285.2 eV and intensities of 2:6:1, respectively. These are attributed, respectively, to acetylenic carbons bound to Cu, phenyl, and methyl carbons. The monolayer valence band ultraviolet photoemission spectrum profile contains four resonances attributable to PP perturbed by interactions with the Cu(111) substrate. With the exception of the highest occupied molecular orbital (HOMO) that is shifted by 0.4 eV, these are uniformly shifted by 1 eV further from the Fermi level for the multilayer. Calculated electron density plots of the occupied orbitals coupled with UPS profiles suggest a spectator role for the phenyl group and bonding to Cu via the acetylenic carbons. The adsorption of 1.0 monolayer (ML) of PP on Cu(111) lowers the work function by 0.85 eV. Using 2PPE, two unoccupied orbitals were identified at 1.0 (U1*-LUMO) and 0.6 eV (U2*-image state) below the vacuum level. A chemisorption model consistent with these spectroscopic results and the major chemisorption peak in TPD involve di-sigma-bonding of the acetylenic carbons to a pair of second-nearest neighbor surface Cu atoms (cross-bridge). 相似文献
62.
Pu Zhang Amit Fischer Yu Ouyang Jianbang Wang Yang Sung Sohn Rachel Nechushtai Eli Pikarsky Chunhai Fan Itamar Willner 《Chemical science》2021,12(43):14473
UiO-66 metal–organic framework nanoparticles (NMOFs) gated by aptamer-functionalized DNA tetrahedra provide superior biomarker-responsive hybrid nano-carriers for biomedical applications. Hybrid nano-carriers consisting of ATP-aptamer or VEGF-aptamer functionalized tetrahedra-gated NMOFs are loaded with the chemotherapeutic drug, doxorubicin (DOX). In the presence of ATP or VEGF, both abundant in cancer cells, the tetrahedra-gated NMOFs are unlocked to release the drug. Enhanced and selective permeation of the DOX-loaded ATP/VEGF-responsive tetrahedra-gated NMOFs into MDA-MB-231 breast cancer cells as compared to the reference ATP/VEGF-responsive duplex-gated NMOFs or non-malignant MCF-10A epithelial breast cells is observed. This results in enhanced and selective cytotoxicity of the tetrahedra-gated DOX-loaded NMOFs toward the malignant cells. Additional nano-carriers, consisting of photosensitizer Zn(ii) protoporphyrin IX (Zn(ii)-PPIX)-loaded VEGF-responsive tetrahedra-gated NMOFs, are introduced. The VEGF-triggered unlocking of the NMOFs yields separated G-quadruplex-VEGF aptamer complexes conjugated to the tetrahedra, resulting in the release of loaded Zn(ii)-PPIX. Association of the released Zn(ii)-PPIX to the G-quadruplex structures generates highly fluorescent supramolecular Zn(ii)-PPIX/G-quadruplex VEGF aptamer-tetrahedra structures. The efficient and selective generation of the highly fluorescent Zn(ii)-PPIX/G-quadruplex VEGF aptamer-tetrahedra nanostructures in malignant cells allows the light-induced photosensitized generation of reactive oxygen species (ROS), leading to high-efficacy PDT treatment of the malignant cells.UiO-66 metal–organic framework nanoparticles (NMOFs) gated by aptamer-functionalized DNA tetrahedra provide superior biomarker-responsive hybrid nano-carriers for biomedical applications. 相似文献
63.
64.
A simple and efficient aerobic oxidative dehydrogenation reaction method for the conversion of 2-(alkylthio)-1,4-dihydropyrimidines to 2-(alkylthio)pyrimidines using copper catalyst with no additives, such as an oxidant, acid, or base, has been developed. The reaction was successful with a wide range of 2-(alkylthio)-1,4-dihydropyrimidine substrates. 相似文献
65.
66.
J.H. Yi K.T. Kim B.-H. Jun J.M. Sohn B.G. Kim J. Joo C.-J. Kim 《Physica C: Superconductivity and its Applications》2009,469(15-20):1192-1195
MgB2 bulks were prepared by an in situ process which utilizes the reaction between boron and magnesium powder. The reaction time was fixed at 0.5 h and the temperature was changed from 600 °C to 1000 °C. The density decrease due to pore formation and mass (mainly magnesium) loss during the formation reaction of MgB2 was observed in all samples. In addition to the pore formation, a pellet expansion which can be explained by the outgrowth of MgB2 grains was also observed. Two different mechanisms were adopted to explain the pore formation; Kirkendall pores formed at a temperature below the melting point (m.p.) of magnesium by a difference in the diffusivity between magnesium and boron, and the pores formed at a temperature above the m.p. by melting of magnesium and a capillary movement. The density, Tc and Jc results suggest that the current carrying capacity can be improved by a careful control of the process parameters regarding a pore evolution. 相似文献
67.
68.
Anti-biofouling properties of comblike block copolymers with amphiphilic side chains 总被引:1,自引:0,他引:1
Krishnan S Ayothi R Hexemer A Finlay JA Sohn KE Perry R Ober CK Kramer EJ Callow ME Callow JA Fischer DA 《Langmuir : the ACS journal of surfaces and colloids》2006,22(11):5075-5086
Surfaces of novel block copolymers with amphiphilic side chains were studied for their ability to influence the adhesion of marine organisms. The surface-active polymer, obtained by grafting fluorinated molecules with hydrophobic and hydrophilic blocks to a block copolymer precursor, showed interesting bioadhesion properties. Two different algal species, one of which adhered strongly to hydrophobic surfaces, and the other, to hydrophilic surfaces, showed notably weak adhesion to the amphiphilic surfaces. Both organisms are known to secrete adhesive macromolecules, with apparently different wetting characteristics, to attach to underwater surfaces. The ability of the amphiphilic surface to undergo an environment-dependent transformation in surface chemistry when in contact with the extracellular polymeric substances is a possible reason for its antifouling nature. Near-edge X-ray absorption fine structure spectroscopy (NEXAFS) was used, in a new approach based on angle-resolved X-ray photoelectron spectroscopy (XPS), to determine the variation in chemical composition within the top few nanometers of the surface and also to study the surface segregation of the amphiphilic block. A mathematical model to extract depth-profile information from the normalized NEXAFS partial electron yield is developed. 相似文献
69.
Xue-gang Chen Shinya Fujita Michitaka Furuya Moo Young Sohn 《Discrete Applied Mathematics》2012,160(4-5):488-493
A graph is said to be bicritical if the removal of any pair of vertices decreases the domination number of . For a bicritical graph with the domination number , we say that is -bicritical. Let denote the edge-connectivity of . In [2], Brigham et al. (2005) posed the following question: If is a connected bicritical graph, is it true that In this paper, we give a negative answer toward this question; namely, we give a construction of infinitely many connected -bicritical graphs with edge-connectivity for every integer . Furthermore, we give some sufficient conditions for a connected -bicritical graph to have . 相似文献
70.
Myong Hwan Sohn 《Experiments in fluids》2010,48(4):565-575
The vortex flow characteristics of a sharp-edged delta wing with an apex strake was investigated through the visualization
and particle image velocimetry (PIV) measurement of the wing-leeward flow region, and the wing-surface pressure measurement.
The wing model was a flat-plate, and 65°-sweep cropped-delta wing with sharp leading edges. The apex strake was also a flat-plate
wing with a cropped-delta shape of 65°/90° sweep, and it can change its incidence angle. The flow Reynolds number was 2.2 × 105 for the flow visualization and 8.2 × 105 for the PIV and wing-surface pressure measurements. The physics of the vortex flow in the wing-leeward flow region and the
suction-pressure distribution on the wing upper-surface were interrelated and analyzed. The effect of a positive (negative)
strake incidence-angle was the upward movement of the strake and wing vortices away from (downward movement of the strake
and wing vortices toward) the wing-upper surface and the delayed (enhanced) coiling interaction between them. This change
of vortex flow characteristics projected directly on the suction pressure distribution on the wing upper-surface. 相似文献