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61.
Seong-Wook Kim Hyeonjung Jung Dr. Mahmut Sait Okyay Dr. Hyuk-Jun Noh Sein Chung Young Hyun Kim Jong-Pil Jeon Prof. Dr. Bryan M. Wong Prof. Dr. Kilwon Cho Dr. Jeong-Min Seo Prof. Dr. Jung-Woo Yoo Prof. Dr. Jong-Beom Baek 《Angewandte Chemie (International ed. in English)》2023,62(42):e202310560
The development of covalent organic frameworks (COFs) with efficient charge transport is of immense interest for applications in optoelectronic devices. To enhance COF charge transport properties, electroactive building blocks and dopants can be used to induce extended conduction channels. However, understanding their intricate interplay remains challenging. We designed and synthesized a tailor-made COF structure with electroactive hexaazatriphenylene (HAT) core units and planar dioxin (D) linkages, denoted as HD-COF. With the support of theoretical calculations, we found that the HAT units in the HD-COF induce strong, eclipsed π–π stacking. The unique stacking of HAT units and the weak in-plane conjugation of dioxin linkages leads to efficient anisotropic charge transport. We fabricated HD-COF films to minimize the grain boundary effect of bulk COFs, which resulted in enhanced conductivity. As a result, the HD-COF films showed an electrical conductivity as high as 1.25 S cm−1 after doping with tris(4-bromophenyl)ammoniumyl hexachloroantimonate. 相似文献
62.
Sara M. Rodriguez Ysidro N. Motta Michael R. Hill Laura M. Oelke Carly C. Carter Thomas R. Cundari Muhammed Yousufuddin 《Acta Crystallographica. Section C, Structural Chemistry》2023,79(4):158-163
An asymmetric bis(silyl) niobocene hydride complex, namely, bis(η5-cyclopentadienyl)(fluorodimethylsilyl)hydrido(iododimethylsilyl)niobium, [Nb(C5H5)2(C2H6FSi)(C2H6ISi)H] or Cp2NbH(SiIMe2)(SiFMe2), has been studied to determine the effect of the silyl ligand on the position of the hydride attached to the Nb atom. It has been shown that when a Group 17 atom is substituted onto one of the silyl ligands, there is a greater interaction between the hydride and this ligand, as demonstrated by a shorter Si…H distance. In the present work, we have investigated the effect when the silyl ligands are substituted by different Group 17 atoms. We present here the structure and DFT calculations of Cp2NbH(SiIMe2)(SiFMe2), showing that the position of the hydride is located between the two silyl ligands. The results from our investigation show that the hydride is closer to the silyl ligand that is substituted by fluorine. 相似文献
63.
64.
Chelation of vanadium(V) by difluoromethylene bisphosphonate, a structural analogue of pyrophosphate
Crans DC Holder AA Saha TK Prakash GK Yousufuddin M Kultyshev R Ismail R Goodman MF Borden J Florian J 《Inorganic chemistry》2007,46(16):6723-6732
The structural and functional analogy between difluoromethylene bisphosphonate (CF2PP) and pyrophosphate (PPi) is investigated in a reaction with V(V) in the form of vanadate. The reaction of CF2PP with vanadate was investigated using 1.00 M KCl as supporting electrolyte over the ranges 3 < or = [CF2PP] < or = 60 mM and 2.06 < or = pH < or = 11.80. 51V, 19F, and 31P NMR spectroscopic studies showed that a 1:1 species was formed with an H+-dependent formation constant of 110 M-1 at pH 7.22. Results of solution experiments and ab initio calculations are consistent with CF2PP coordinating V(V) in a bidentate manner, as previously reported for PPi. Below pH 4, a minor complex forms, which is consistent with a 1:2 stoichiometry. This complex was also observed with pyrophosphate. The X-ray crystal structure of the monoprotonated difluoromethylene bisphosphonate anion (H[CF2PP]3-)-toludine complex is presented. The H[CF2PP]3- anion crystallized in the triclinic space group P with a = 12.7629(7) A, b = 13.3992(7) A, c = 17.1002(9) A, and V = 2584.4(2) A3, and Z = 2. Sheets of the layers of anions are connected through a network of H-bonds and separated by a layer of toludine cations. The structural features are investigated, and the CF2PP anion was found to be longer and wider than the corresponding PPi. Given the larger size of this anion compared to PPi, the chelation affinity upon CF2 substitution was found to be 4-5-fold reduced at neutral pH. 相似文献
65.
Saitô H Kawase Y Kira A Yamamoto K Tanio M Yamaguchi S Tuzi S Naito A 《Photochemistry and photobiology》2007,83(2):253-262
The 3D structure of bacteriorhodopsin (bR) obtained by X-ray diffraction or cryo-electron microscope studies is not always sufficient for a picture at ambient temperature where dynamic behavior is exhibited. For this reason, a site-directed solid-state 13C NMR study of fully hydrated bR from purple membrane (PM), or a distorted or disrupted lattice, is very valuable in order to gain insight into the dynamic picture. This includes the surface structure, at the physiologically important ambient temperature. Almost all of the 13C NMR signals are available from [3-13C]Ala or [1-13C]Val-labeled bR from PM, although the 13C NMR signals from the surface areas, including loops and transmembrane alpha-helices near the surface (8.7 angstroms depth), are suppressed for preparations labeled with [1-13C]Gly, Ala, Leu, Phe, Tyr, etc. due to a failure of the attempted peak-narrowing by making use of the interfered frequency of the frequency of fluctuation motions with the frequency of magic angle spinning. In particular, the C-terminal residues, 226-235, are present as the C-terminal alpha-helix which is held together with the nearby loops to form a surface complex, although the remaining C-terminal residues undergo isotropic motion even in a 2D crystalline lattice (PM) under physiological conditions. Surprisingly, the 13C NMR signals could be further suppressed even from [3-13C]Ala- or [1-13C]Val-bR, due to the acquired fluctuation motions with correlation times in the order of 10(-4) to 10(-5) s, when the 2D lattice structure is instantaneously distorted or completely disrupted, either in photo-intermediate, removed retinal or when embedded in the lipid bilayers. 相似文献
66.
Suzuki Y Okonogi M Yamauchi K Kurosu H Tansho M Shimizu T Saitô H Asakura T 《The journal of physical chemistry. B》2007,111(30):9172-9178
beta-Strand peptides are known to assemble into either antiparallel (AP) or parallel (P) beta-sheet forms which are very important motifs for protein folding and fibril formations occurring in silk fibroin or amyloid proteins. Well-resolved 1H NMR signals including NH protons were observed for alanine tripeptides (Ala)3 with the AP and P structures as well as (Ala)n (n = 4-6) by high-field/fast magic-angle spinning NMR. Amide NH and amino NH3+ 1H signals of (Ala)3 with the P structure were well resonated at 7.5 and 8.9 ppm, respectively, whereas they were not resolved for the AP structure. Notably, NH 1H signals of (Ala)3 and (Ala)4 taking the P structure are resonated at higher field than those of the AP structure by 1.0 and 1.1 ppm, respectively. Further, NH 15N signals of (Ala)3 with the AP structure were resonated at lower field by 2 to 5 ppm than those of (Ala)3 with the P structure. These relative 1H and 15N hydrogen bond shifts of the P structure with respect to those of the AP structure are consistent with the relative hydrogen bond lengths of the interstrand N-H...O=C bonds. Distinction between the two crystallographically independent chains present in the AP and P structures was feasible by 15N chemical shifts but not by 1H chemical shifts because of insufficient spectral resolution in the latter. Calculated 1H and 15N shielding constants by density functional theory are generally consistent with the experimental data, although some discrepancies remain depending upon the models used. 相似文献
67.
提出了一种求解二维线性边值问题的新的τ_方法·对该问题进行了理论分析和数值求解·结果表明了本文方法的优点和有效性 相似文献
68.
Madathumpady Abubaker Habeeb Muhammed Pramod Kumar Verma Samir Kumar Pal Dr. R. C. Arun Kumar Soumya Paul Ramakrishnapillai Vyomakesannair Omkumar Dr. Thalappil Pradeep Prof. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2009,15(39):10110-10120
A novel interfacial route has been developed for the synthesis of a bright‐red‐emitting new subnanocluster, Au23, by the core etching of a widely explored and more stable cluster, Au25SG18 (in which SG is glutathione thiolate). A slight modification of this procedure results in the formation of two other known subnanoclusters, Au22 and Au33. Whereas Au22 and Au23 are water soluble and brightly fluorescent with quantum yields of 2.5 and 1.3 %, respectively, Au33 is organic soluble and less fluorescent, with a quantum yield of 0.1 %. Au23 exhibits quenching of fluorescence selectively in the presence of Cu2+ ions and it can therefore be used as a metal‐ion sensor. Aqueous‐ to organic‐phase transfer of Au23 has been carried out with fluorescence enhancement. Solvent dependency on the fluorescence of Au23 before and after phase transfer has been studied extensively and the quantum yield of the cluster varies with the solvent used. The temperature response of Au23 emission has been demonstrated. The inherent fluorescence of Au23 was used for imaging human hepatoma cells by employing the avidin–biotin interaction. 相似文献
69.
Aqueous to organic phase transfer of water soluble sub-nanocluster, Au25SG18 (-SG, glutathione thiolate) is demonstrated using the phase transfer reagent, tetraoctylammonium bromide. The phase transfer
occurred by the electrostatic attraction between the hydrophilic carboxylate anion of the glutathione ligand on the cluster
surface in the aqueous phase and the hydrophobic tetraoctylammonium cation in the toluene phase. Detailed spectroscopic characterization
of the phase transferred cluster using optical absorption, photoluminescence and X-ray photoelectron spectroscopy showed that
the cluster retains its integrity during the phase transfer. The interaction of the cluster with the phase transfer reagent
can be studied with infrared spectroscopy. The phase transferred cluster can be dried and redissolved in an organic medium,
just as the original cluster. This is the first report of the phase transfer of a sub-nanocluster, keeping the cluster core
intact. The effect of dilution and pH on phase transfer of this cluster is studied in detail. This method promises several
possibilities to explore the properties, reactivity and applications of sub-nanoclusters both in the aqueous and organic phases.
Dedicated to Prof. C.N.R. Rao on his 75th birthday, whose work on phase transfer of nanoparticles has inspired this work. 相似文献
70.
Electrical and dielectric properties of Al/p-Si and Al/perylene/p-Si type diodes in a wide frequency range 下载免费PDF全文
The perylene(C20H12) layer effect on the electrical and dielectric properties of Al/p-Si(MS) and Al/perylene/p-Si(MPS) diodes have been investigated and compared in the frequency range of 0.7 kHz–2 MHz. Experimental results show that C–V characteristics give an anomalous peak for two structures at low frequencies due to interface states(Nss) and series resistance(Rs). The increases in C and G/ω at low frequencies confirm that the charges at interface can easily follow an ac signal and yield excess capacitance and conductance. The frequency-dependent dielectric constant(ε) and dielectric loss(ε) are subtracted using C and G/ω data at 1.5 V. The ε and ε values are found to be strongly dependent on frequency and voltage, and their large values at low frequencies can be attributed to the excess polarization coming from charges at traps. Plots of ln(σac)–ln(ω) for two structures have two linear regions, with slopes of 0.369 and 1.166 for MS, and of 0.077 and 1.061 for MPS, respectively. From the C 2–V characteristics, the doping acceptor atom concentration(NA) and barrier height(ΦB) for Schottky barrier diodes(SBDs) of MS and MPS types are also obtained to be 1.484 × 1015 and 1.303 × 1015cm 3, and 1.10 and 1.13 eV, respectively. 相似文献