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1.
Polar oxide substrates for graphene growth: A first-principles investigation of graphene on MgO(111)
Kyung-Ah Min Jinwoo Park Junga Ryou Suklyun Hong Aloysius Soon 《Current Applied Physics》2013,13(5):803-807
Given the recent excitement over the truly two-dimensional carbon “super” material – graphene, there is now much effort and focus on the various possibilities of engineering the band gap of graphene for its device applications. One possible and promising route will be to grow graphene directly on some non-metallic substrates. In this paper, we address the atomic and electronic structure of various graphene structures on the polar MgO(111) using first-principles density-functional theory (DFT) calculations. We find that graphene generally interacts strongly with the O-terminated polar oxide surface, forming strong chemical bonds, inferred from both energetics and detailed density-of-states analysis. We compare our theoretical findings with available experimental results, offering a possible direction for future band gap engineering of graphene on such oxide substrates. 相似文献
2.
The rate of enzymatic degradation of surface‐modified microbial polyesters, poly[(R)‐3‐hydroxybutyrate] and poly[(R)‐3‐hydroxybutyrate‐co‐3‐hydroxyvalerate], was studied. The plasma treatments were carried out in a CF3H or O2 environment. It was found that the CF3H plasma‐treated polyesters exhibited significant retardation of enzymatic erosion because of the surface fluorocarbon groups induced by CF3H plasma. These surface fluorocarbon groups act as retardants on enzymatic degradation due to increased hydrophobicity and of the inactivity of enzymes. However, the increased surface hydrophilicity of polyesters induced by O2 plasma results in no significant acceleration of the enzymatic erosion, which may be due to the thin modified layer.
3.
The stereoselective isomerization of unsymmetrical diallyl ethers to allyl (E)-vinyl ethers was carried out in the presence of a cationic iridium(I) catalyst. The catalyst prepared in situ by treating [Ir(cod)(PPh2Me)2]PF6 with hydrogen was found to be an excellent catalyst to selectively isomerize the less substituted allyl group to an (E)-vinyl ether. 相似文献
4.
Simultaneous Arrangement of up to Three Different Molecules on the Pore Surface of a Metal–Macrocycle Framework: Cooperation and Competition 下载免费PDF全文
Dr. Shohei Tashiro Tsutomu Umeki Dr. Ryou Kubota Prof. Dr. Mitsuhiko Shionoya 《Angewandte Chemie (International ed. in English)》2014,53(32):8310-8315
Porous crystals are excellent materials with potential spatial functions through molecular encapsulation within the pores. Co‐encapsulation of multiple different molecules further expands their usability and designability. Herein we report the simultaneous arrangement of up to three different guest molecules, TTF (tetrathiafulvalene), ferrocene, and fluorene, on the pore surfaces of a porous crystalline metal–macrocycle framework (MMF). The position and orientation of adsorbed molecules arranged in the pore were determined by single‐crystal X‐ray diffraction analysis. The anchoring effect of hydrogen bonds between the hydroxy groups of the guest molecules and inter‐guest cooperation and competition are significant factors in the adsorption behaviors of the guest molecules. This finding would serve as a design basis of multicomponent functionalized nanospaces for elaborate reactions that are realized in enzymes. 相似文献
5.
The modification of the InAs quantum dots (QDs) by the GaAs capping growth was studied by using cross-sectional STEM and atomic force microscopy. In case of the GaAs capping growth at 450 °C, it was found that the lateral size of the InAs QDs significantly decreases rather than the height and that this size-shrinkage effect is enhanced for the large QDs. The shrinkage behavior is mainly attributed to the indium surface segregation, strongly depending on the surface strain of the QDs. The growth process of the GaAs capping layer plays an important role for achieving the size ordering of the embedded QDs. 相似文献
6.
Using density functional theory calculations, we have investigated the interactions between hydrogen molecules and metalloporphyrins. A metal atom, such as Ca or Ti, is introduced for incorporation in the central N(4) cavity. Within local density approximation (generalized gradient approximation), we find that the average binding energy of H(2) to the Ca atom is about 0.25 (0.1) eV/H(2) up to four H(2) molecules, whereas that to the Ti atom is about 0.6 (0.3) eV per H(2) up to two H(2) molecules. Our analysis of orbital hybridization between the inserted metal atom and molecular hydrogen shows that H(2) binds weakly to Ca-porphyrin through a weak electric polarization in dihydrogen, but is strongly hybridized with Ti-porphyrin through the Kubas interaction. The presence of d orbitals in Ti may explain the difference in the interaction types. 相似文献
7.
Metal-macrocycle framework (MMF): supramolecular nano-channel surfaces with shape sorting capability
Hollow nanostructures for the functional assembly of chemical groups with inner surface geometry and regulable stoichiometry enable steric design of interior reaction centers. Herein we report a metal-macrocycle framework (MMF) that forms single-crystalline nanochannels with five distinct enantiomeric pairs of guest binding pockets. During crystal-soaking experiments, the MMF crystals can encapsulate aromatic molecules with high site selectivity. First, constitutional isomers of dibromobenzene are captured and sorted into different binding pockets. Second, each of the optical isomers of (1R/1S)-1-(3-chlorophenyl)ethanol is included diastereoselectively into one of an enantiomeric pair of binding pockets. An advantage of this strategy is that the interior walls can be "repainted" via replacement of the trapped molecules with alternatives. Such guest uptake behaviors would allow highly regioselective or stereoselective reactions within the nanochannel. 相似文献
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9.
Min Jueng Kang Chaeyoung Kim Hyobin Jeong Byoung-Kyu Cho Ae Lan Ryou Daehee Hwang Inhee Mook-Jung Eugene C Yi 《Experimental & molecular medicine》2013,45(6):e29
O-linked N-acetylglucosamine (O-GlcNAc) represents a key regulatory post-translational modification (PTM) that is reversible and often reciprocal with phosphorylation of serine and threonine at the same or nearby residues. Although recent technical advances in O-GlcNAc site-mapping methods combined with mass spectrometry (MS) techniques have facilitated study of the fundamental roles of O-GlcNAcylation in cellular processes, an efficient technique for examining the dynamic, reciprocal relationships between O-GlcNAcylation and phosphorylation is needed to provide greater insights into the regulatory functions of O-GlcNAcylation. Here, we describe a strategy for selectively identifying both O-GlcNAc- and phospho-modified sites. This strategy involves metal affinity separation of O-GlcNAcylated and phosphorylated peptides, β-elimination of O-GlcNAcyl or phosphoryl functional groups from the separated peptides followed by dithiothreitol (DTT) conjugation (BEMAD), affinity purification of DTT-conjugated peptides using thiol affinity chromatography, and identification of formerly O-GlcNAcylated or phosphorylated peptides by MS. The combined metal affinity separation and BEMAD approach allows selective enrichment of O-GlcNAcylated peptides over phosphorylated counterparts. Using this approach with mouse brain synaptosomes, we identified the serine residue at 605 of the synapsin-1 peptide, 603QASQAGPGPR612, and the serine residue at 692 of the tau peptide, 688SPVVSGDTSPR698, which were found to be potential reciprocal O-GlcNAcylation and phosphorylation sites. These results demonstrate that our strategy enables mapping of the reciprocal site occupancy of O-GlcNAcylation and phosphorylation of proteins, which permits the assessment of cross-talk between these two PTMs and their regulatory roles. 相似文献
10.
Recently, we have reported a metal-macrocycle framework (MMF) with five enantiomerically paired molecular binding pockets that exhibit site-selective guest arrangement on the nano-channel surface in soaking experiments using a variety of guest molecules. The guest inclusion is based largely on molecular exchange between solvent molecules such as CH3CN and guest molecules on the surface. Herein, we report that the molecular arrangement on the nano-channel surface varies with size, shape and/or chemical properties of functional groups of guests, mono-substituted benzene derivatives, such as benzonitrile, acetophenone and nitrobenzene. In their inclusion complexes, polar nitrile, acetyl and nitro groups serve as molecular anchors to a macrocyclic cavity through hydrogen bonding. Notably, benzonitrile and benzenesulphonic acid bind only to one pair of enantiomeric binding pockets. Such a highly site-selective binding would enable further multi-component surface modifications in the MMF. 相似文献