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Atomic clusters

Wan-Ting Chang, Po-Yi Lee, Jian-Hong Liao, Samia Kahlal, Jean-Yves Saillard, Chen-Wei Liu
The first atomically and structurally precise silver-nanoclusters stabilized by Se-donor ligands, [Ag20{Se2P(OiPr)2}12] (3) and [Ag21{Se2P(OEt)2}12]+(4), have been isolated by ligand replacement reaction of [Ag20{S2P(OiPr)2}12] (1) and [Ag21{S2P(OiPr)2}12]+ (2), respectively. Further, doping reactions of 4 with Au(PPh3)Cl resulted in the formation of [AuAg20{Se2P(OEt)2}12]+, (5). Structures of 3, 4 and 5 were determined by single crystal X-ray diffraction. The anatomy of cluster 3 with an Ag20 core having C3 symmetry is very similar to that of its dithiophosphate analogue 1...
May 22, 2017: Angewandte Chemie
Hiraku Ohno, Kazuki Takeda, Satomi Niwa, Tomotaka Tsujinaka, Yuya Hanazono, Yu Hirano, Kunio Miki
High-potential iron-sulfur protein (HiPIP) is a soluble electron carrier protein of photosynthetic bacteria with an Fe4S4 cluster. Although structural changes accompanying the electron transfer are important for understanding of the functional mechanism, the changes have not been clarified in sufficient detail. We previously reported the high-resolution crystal structures of HiPIP from a thermophilic purple bacterium Thermochromatium tepidum in the reduced state. In order to perform a detailed comparison between the structures in different redox states, the oxidized structure should also be revealed at high resolution...
2017: PloS One
Sergey M Novikov, Vladimir N Popok, Andrey B Evlyukhin, Muhammad Hanif, Per Morgen, Jacek Fiutowski, Jonas Beermann, Horst-Guenter Rubahn, Sergey I Bozhevolnyi
: Plasmonics sensor configurations utilizing localized plasmon resonances in silver nanostructures typically suffer from rapid degradation of silver in ambient atmospheric conditions. In this work, we report on the fabrication and detailed characterization of ensembles of monocrystalline silver nanoparticles (NPs), which exhibit a long-term stability of optical properties under ambient conditions without any protective treatments. Ensembles with different densities (surface coverages) of size-selected NPs (diameters from 12...
May 25, 2017: Langmuir: the ACS Journal of Surfaces and Colloids
Yang Wang, Xiaoting Liu, Wei Xu, Ying Yue, Bao Li, Lixin Wu
Various covalent decorations and structural transformations of a series of R-C(CH2OH)3 triol ligands on Co(II)/Co(III)-centered Anderson-Evans polyoxomolybdates were studied in aqueous and/or organic solution. Single-crystal X-ray structural analysis demonstrated that four manners, including (1) double-sided χ/χ-isomer and (2) double-sided δ/χ-isomer with Co(II) central heteroatom, and (3) single-sided δ-isomer and (4) double-sided δ/δ-isomer with Co(III) central heteroatom, appeared on the decoration of the mother polyanion [Co(II/III)(OH)6Mo6O18](4-/3-)...
May 25, 2017: Inorganic Chemistry
Po-Wei Hsu, Zhen-He Liao, Ting-Chieh Hung, Hsuan Lee, Yu-Cheng Wu, Yu-Ling Lai, Yao-Jane Hsu, Yuwei Lin, Jeng-Han Wang, Meng-Fan Luo
Self-organized alloying of Au with Rh in nanoclusters on an ordered thin film of Al2O3/NiAl(100) was investigated via various surface probe techniques under ultrahigh-vacuum conditions and calculations based on density-functional theory. The bimetallic clusters were formed on the sequential deposition of vapors of Au and Rh onto Al2O3/NiAl(100) at 300 K. The formation was more effective on the oxide seeded with Rh, since all post-deposited Au joined the pregrown Rh clusters; for metal deposition in the reverse order, some separate Rh clusters were formed...
May 24, 2017: Physical Chemistry Chemical Physics: PCCP
M Alcolea Palafox, V K Rastogi, S P Singh
The effect of the sulphur atom on 2-thiouracil (2TU) and 2-thiouridine molecules, as compared with uracil and uridine molecules, respectively, was carried out in several environments. The predicted IR spectrum of 2TU in the isolated state was compared with that obtained for uracil molecule and with those reported experimentally in matrix isolation. Its crystal unit cell in the solid state was simulated through a tetramer form using DFT methods for the first time. The calculated Raman spectrum was compared to the experimental ones in the solid state...
May 24, 2017: Journal of Biomolecular Structure & Dynamics
Qingying Jia, Shraboni Ghoshal, Jingkun Li, Wentao Liang, Guangnan Meng, Haiying Che, Shiming Zhang, Zi-Feng Ma, Sanjeev Mukerjee
Many industrial catalysts are composed of metal particles supported on metal oxides (MMO). It is known that the catalytic activity of MMO materials is governed by metal and metal oxide interactions (MMOI), but how to optimize MMO systems via manipulation of MMOI remains unclear, due primarily to the ambiguous nature of MMOI. Herein, we develop a Pt/NbOx/C system with tunable structural and electronic properties via a modified arc plasma deposition method. We unravel the nature of MMOI by characterizing this system under reactive conditions utilizing combined electrochemical, microscopy, and in situ spectroscopy...
May 23, 2017: Journal of the American Chemical Society
Hongjun Zheng, Marcus A Tofanelli, Christopher J Ackerson, Kenneth L Knappenberger
We examined the electronic relaxation dynamics for mono and bimetallic Au144-xAgx(SC8H9)60 monolayer-protected clusters (MPCs) using femtosecond time-resolved transient extinction spectroscopy. MPCs provide compositionally well-defined model systems for structure-specific determination of nanoscale electronic properties. Based on pulse-energy-dependent transient extinction data, we quantified electron-phonon coupling constants for three distinct Au144-xAgx(SC8H9)60 MPC samples, where x = 0, 0 < x < 30, and x ∼ 30, as Gx=0 = (1...
May 23, 2017: Physical Chemistry Chemical Physics: PCCP
Rania Kazan, Bei Zhang, Thomas Bürgi
A CuAu38 bimetallic nanocluster was synthesized by adding a single copper atom to the Au38(2-PET)24 nanocluster. The absence of CuxAu38-x(2-PET)24 doped species was demonstrated by MALDI-TOF mass spectrometry. A separation of bimetallic clusters was attained for the first time where isomers of the E2 enantiomer of the Au38Cu1(2-PET)24 adduct were successfully isolated from their parent cluster using chiral HPLC. The CD of the isolated isomers revealed a change in their electronic structure upon copper addition...
May 23, 2017: Dalton Transactions: An International Journal of Inorganic Chemistry
Chuantao Zhu, Alexander Soldatov, Aji P Mathew
TEMPO (2,2,6,6-tetramethylpiperidine-1-oxylradical)-mediated oxidation nanofibers (TOCNF), as a biocompatible and bioactive material, have opened up a new application of nanocellulose for the removal of water contaminants. This development demands extremely sensitive and accurate methods to understand the surface interactions between water pollutants and TOCNF. In this report, we investigated the adsorption of metal ions on TOCNF surfaces using experimental techniques atthe nano and molecular scales with Cu(ii) as the target pollutant in both aqueous and dry forms...
May 22, 2017: Nanoscale
Dávid Mester, Péter R Nagy, Mihály Kállay
A reduced-cost density fitting (DF) linear-response second-order coupled-cluster (CC2) method has been developed for the evaluation of excitation energies. The method is based on the simultaneous truncation of the molecular orbital (MO) basis and the auxiliary basis set used for the DF approximation. For the reduction of the size of the MO basis, state-specific natural orbitals (NOs) are constructed for each excited state using the average of the second-order Møller-Plesset (MP2) and the corresponding configuration interaction singles with perturbative doubles [CIS(D)] density matrices...
May 21, 2017: Journal of Chemical Physics
R O Jones, O Ahlstedt, J Akola, M Ropo
Density functional/molecular dynamics simulations have been performed on liquid antimony (588 atoms and six temperatures between 600 K and 1300 K) and on neutral Sb clusters with up to 14 atoms. We study structural patterns (coordination numbers, bond angles, and ring patterns, structure factors, pair distribution functions) and dynamical properties (vibration frequencies, diffusion constants, power spectra, dynamical structure factors, viscosity) and compare with available experimental results and with the results of our previous simulations on Bi...
May 21, 2017: Journal of Chemical Physics
Qi Wei, Jia-Jia Wang, Jie Zhang, Guo-Yu Yang
Two three-dimensional (3D) zeolitic open-framework aluminoborates (ABOs) [Zn(ma)(en)2][AlB5O10] (1) and [Zn(ma)(en)2][AlB6O11(OH)] (2) (ma = methylamine, en = ethylenediamine) were successfully made under solvothermal conditions, which represent the first examples using similar metal complex (MC) with mixed amines as the structure-directing agents in ABOs. Notice that the central atom in the MC is coordinated by mixed amines is uncommon. However, they exhibit distinctly different structures: 1 crystallizes in a centrosymmetric [Al(B5O10)]n(2n-) zeolitic framework built by pentaborate (B5O10) clusters and AlO4 tetrahedra, exhibiting a 4-connected cag topology, while 2 contains hexaborate (B6O11(OH)) clusters and AlO4 groups, further alternately joined to form a noncentrosymmetric [AlB6O11(OH)]n(2n-) zeolitic framework with 7-/9-, 8-/10-ring helical channels and large 13-ring channels, showing a dia topology...
May 19, 2017: Inorganic Chemistry
Jörg Grunenberg
The first quantum-mechanical calculations of all relevant potential constants in both the iron-molybdenum cofactor and the iron-vanadium cofactor of nitrogenase suggest that the carbide is bound to the center of the enzyme much more strongly than hitherto assumed. Previous studies seemed to indicate a dummy function of the interstitial carbon, with a weak force constant (ca. 0.32 N cm(-1) ). Our new investigations confirm a different picture: the central carbon atom binds the iron-sulfur cluster through six covalent C-Fe bonds...
May 19, 2017: Angewandte Chemie
Cristina Femoni, Guido Bussoli, Iacopo Ciabatti, Marco Ermini, Mohammad Hayatifar, Maria C Iapalucci, Silvia Ruggieri, Stefano Zacchini
The reaction of [Rh7(CO)16](3-) with BiCl3 under N2 and at room temperature results in the formation of the new heterometallic [Bi@Rh12(CO)27](3-) cluster in high yields. Further controlled addition of BiCl3 leads first to the formation of the dimeric [(Bi@Rh12(CO)26)2Bi](5-) and the closo-[Bi@Rh14(CO)27Bi2](3-) species in low yields, and finally, to the [Bi@Rh17(CO)33Bi2](4-) cluster. All clusters were spectroscopically characterized by IR and electrospray ionization mass spectrometry, and their molecular structures were fully determined by X-ray diffraction studies...
May 18, 2017: Inorganic Chemistry
Yahui Zhang, Dawei Yang, Ying Li, Baomin Wang, Xiangyu Zhao, Jingping Qu
The thioether-dithiolate-bridged heterotrinuclear complexes [Cp*Fe(μ-1k(3)SSS':2k(2)SS-tpdt)M(μ-2k(2)SS:3k(3)SSS'-tpdt)FeCp*][PF6]2 (Cp* = η(5)-C5Me5; tpdt = S(CH2CH2S)2; 2, M = Co; 3, M = Ni; 4, M = Pd) have been prepared by a reaction of [Cp*Fe(η(3)-tpdt)] (1) with complexes CoCl2, NiCl2(PPh3)2, and PdCl2(PPh3)2, respectively. Similarly, treatment of complex 1 with CuCl(PPh3) or AgPF6 afforded two heterotrinuclear complexes, [Cp*Fe(μ-1k(3)SSS':2k(2)SS-tpdt)M(μ-2k(2)SS:3k(3)SSS'-tpdt)FeCp*][PF6] (5, M = Cu; 6, M = Ag), while reaction of 1 with the complex AuCl(PPh3) gave a heterobinuclear complex, [Cp*Fe(μ-1k(3)SSS':2k(1)S-tpdt)Au(PPh3)][PF6] (7)...
May 18, 2017: Dalton Transactions: An International Journal of Inorganic Chemistry
Eugene Paulechka, Andrei Kazakov
An accurate and cost-efficient methodology for the estimation of the enthalpies of formation for closed-shell compounds composed of C, H, O, and N atoms is presented and validated against critically-evaluated experimental data. The computational efficiency is achieved through the use of the Resolution-of-Identity (RI) and Domain-Based Local Pair-Natural Orbital Coupled Cluster (DLPNO-CCSD(T)) approximations, which results in drastic reduction in both the computational cost and the number of necessary steps for a composite quantum chemical method...
May 17, 2017: Journal of Physical Chemistry. A
K R Krishnadas, Ananya Baksi, Atanu Ghosh, Ganapati Natarajan, Thalappil Pradeep
Monolayer protected clusters exhibit rich diversity in geometric and electronic structures. However, structure-reactivity relationships in these clusters are rarely explored. In this context, [Ag44(SR)30](4-), where -SR is an alkyl/aryl thiolate, is an interesting system due to its geometrically and electronically closed-shell structures and distinct charge states. We demonstrate that these structural features of [Ag44(SR)30](4-) are distinctly manifested in its solution-state reaction with another cluster, [Au25(SR)18](-)...
May 22, 2017: ACS Nano
Hsin-Yi Tiffany Chen, Jyh-Pin Chou, Cheng-Yang Lin, Chih-Wei Hu, Ya-Tang Yang, Tsan-Yao Chen
A ternary metallic CuPdPt nanocatalyst (NC) is synthesized using a wet chemical reduction method, which is sequentially designed, in the presence of acid treated carbon nanotubes. This NC is a nanocrystal with a configuration of a Cu@Pd core and atomic Pt clusters (∼9 wt%) on the top (Cu@Pd/Pt). A residual current of 92.6%, 5.2 times higher than that of commercial Pt catalysts (at 0.85 V vs. RHE), is retained after 40 000 cycles of an accelerated degradation test (ADT). Atomic and electronic structure analyses show that such exclusive stability mainly results from electron localization at Pt clusters in heterogeneous interfaces of the Cu-Pd core...
May 17, 2017: Nanoscale
Mingyang Chen, David A Dixon
The structures of TiO2 ultra-small nanoparticles (USNPs) at the atomistic level have been predicted because of their potential importance in catalytic, environmental, biological and energy applications. Low energy (TiO2)n clusters and USNPs (n up to 80 at the B3LYP/DZVP2 level, and up to 384 at the PM6 level) were found using a novel bottom-up global optimization approach that is based on all-atom real-space calculations. These structures include USNPs that belong to 1-D, 2-D and 3-D USNP series where all the members share the same fragment types and local translational symmetries...
May 17, 2017: Nanoscale
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