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# Van der waal

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#1
P Chanphai, H A Tajmir-Riahi
The conjugation of tRNA with folic acid-chitosan conjugates was studied, using multiple spectroscopic methods and transmission electron microscopy (TEM). Thermodynamic analysis ΔH -14 to -10 (KJ. Mol(-1)) and ΔS 14 to -1 (J. Mol(-1), K(-1)) showed tRNA-folic acid-chitosan bindings occur via H-bonding, hydrophobic and van der Waals contacts. The loading efficacy and the stability of tRNA conjugates were enhanced as folic acid-chitosan size increased. TEM analysis showed major tRNA morphological changes, upon folic acid-chitosan conjugation...
July 19, 2017: International Journal of Biological Macromolecules
#2
Andrew J Archer, Blesson Chacko, Robert Evans
In classical density functional theory (DFT), the part of the Helmholtz free energy functional arising from attractive inter-particle interactions is often treated in a mean-field or van der Waals approximation. On the face of it, this is a somewhat crude treatment as the resulting functional generates the simple random phase approximation (RPA) for the bulk fluid pair direct correlation function. We explain why using standard mean-field DFT to describe inhomogeneous fluid structure and thermodynamics is more accurate than one might expect based on this observation...
July 21, 2017: Journal of Chemical Physics
#3
Alexander A Govyadinov, Andrea Konečná, Andrey Chuvilin, Saül Vélez, Irene Dolado, Alexey Y Nikitin, Sergei Lopatin, Fèlix Casanova, Luis E Hueso, Javier Aizpurua, Rainer Hillenbrand
Van der Waals materials exhibit intriguing structural, electronic, and photonic properties. Electron energy loss spectroscopy within scanning transmission electron microscopy allows for nanoscale mapping of such properties. However, its detection is typically limited to energy losses in the eV range-too large for probing low-energy excitations such as phonons or mid-infrared plasmons. Here, we adapt a conventional instrument to probe energy loss down to 100 meV, and map phononic states in hexagonal boron nitride, a representative van der Waals material...
July 21, 2017: Nature Communications
#4
Naoko Sato, Yurina Aoyama, Junpei Yamanaka, Akiko Toyotama, Tohru Okuzono
Particle adhesion onto hydrogels has recently attracted considerable attention because of the potential biomedical applications of the resultant materials. A variety of interactions have been taken advantage of for adsorption, including electrostatic forces, hydrophobic interactions and hydrogen bonding. In this study, we report significant adsorption of submicron-sized silica particles onto hydrogel surfaces in water, purely by van der Waals (vdW) attraction. The vdW forces enabled strong adhesions between dielectric materials in air...
July 21, 2017: Scientific Reports
#5
Bingjie Liu, Youming Zou, Shiming Zhou, Lei Zhang, Zhe Wang, Hexuan Li, Zhe Qu, Yuheng Zhang
Fe3GeTe2 is a promising candidate for van der Waals bonded ferromagnet because of its high Curie temperature and the prediction that its ferromagnetism can maintain upon exfoliating down to single layer. Here, we have reported the critical behavior to understand its ferromagnetic exchange. Based on various techniques including modified Arrott plot, Kouvel-Fisher plot, and critical isotherm analysis, a set of reliable critical exponents (β = 0.327 ± 0.003, γ = 1.079 ± 0.005, and δ = 4...
July 21, 2017: Scientific Reports
#6
Igor S Nefedov, J Miguel Rubi
We predict the existence of lateral drag forces near the flat surface of an absorbing slab made of an anisotropic material. The forces originate from the fluctuations of the electromagnetic field, when the anisotropy axis of the material forms a certain angle with the surface. In this situation, the spatial spectra of the fluctuating electromagnetic fields becomes asymmetric, different for positive and negative transverse wave vectors components. Differently from the case of van der Waals interactions in which the forward-backward symmetry is broken due to the particle movement, in our case the lateral motion results merely from the anisotropy of the slab...
July 21, 2017: Scientific Reports
#7
Natalia Bedoya Martínez, Benedikt Schrode, Andrew O F Jones, Tommaso Salzillo, Christian Ruzié, Nicola Demitri, Yves Henri Geerts, Elisabetta Venuti, Raffaele Guido Della Valle, Egbert Zojer, Roland Resel
A combined experimental and theoretical approach, consisting of lattice phonon Raman spectroscopy and density functional theory (DFT) calculations, is proposed as a tool for lattice dynamics characterization and polymorph phase identification. To illustrate the reliability of the method, the lattice phonon Raman spectra of two polymorphs of the molecule 2,7-dioctyloxy[1]benzothieno[3,2-{\it b}]benzothiophene are investigated. We show that DFT calculations of the lattice vibrations based on the known crystal structures, including many body dispersion van der Waals (MBD-vdW) corrections, predict experimental data within an accuracy of $\ll$ 5 \ru{} ($\ll$ 0...
July 21, 2017: Journal of Physical Chemistry Letters
#8
Jane S Murray, Giuseppe Resnati, Peter Politzer
Close contacts, defined as interatomic separations less than the sum of the respective van der Waals radii, are commonly invoked to identify attractive nonbonded interactions in crystal lattices. While this is often effective, it can also be misleading because (a) there are significant uncertainties associated with van der Waals radii, and (b) it may not be valid to attribute the interactions solely to specific pairs of atoms. The interactions within crystal lattices are Coulombic, and the strongest positive and/or negative regions do not always correspond to the positions of atoms; they are sometimes located between atoms...
#9
Shunfeng Wang, Junyong Wang, Weijie Zhao, Francesco Giustiniano, Leiqiang Chu, Ivan Verzhbitskiy, Justin Zhou Yong, Goki Eda
We report on efficient carrier-to-exciton conversion and planer electroluminescence from tunnel diodes based on a metal-insulator-semiconductor van der Waals heterostack consisting of few-layer graphene (FLG), hexagonal boron nitride (hBN), and monolayer tungsten disulfide (WS2). These devices exhibit excitonic electroluminescence with extremely low threshold current density of a few pA∙μm-2, which is several orders of magnitude lower compared to the previously reported values for the best planar EL devices...
July 21, 2017: Nano Letters
#10
Christina Nilofer, Anshul Sukhwal, Arumugam Mohanapriya, Pandjassarame Kangueane
Several catalysis, cellular regulation, immune function, cell wall assembly, transport, signaling and inhibition occur through Protein- Protein Interactions (PPI). This is possible with the formation of specific yet stable protein-protein interfaces. Therefore, it is of interest to understand its molecular principles using structural data in relation to known function. Several interface features have been documented using known X-ray structures of protein complexes since 1975. This has improved our understanding of the interface using structural features such as interface area, binding energy, hydrophobicity, relative hydrophobicity, salt bridges and hydrogen bonds...
2017: Bioinformation
#11
Xiaoyong Pan, Weizhi Wang, Lin Ke, Nan Zhang
In this report, we showed the existence of RET induced intermolecular pairing force by comparing their fluorescence behaviors under room illumination vs standing in dark area for either PFluAnt solution or PFluAnt&PFOBT mixture. Their prominent emission attenuation under room illumination brought out the critical role of photo, i.e. RET induced intermolecular pairing force in induction of polymer aggregation. Constant UV-Vis absorption and fluorescence spectra in terms of both peak shapes and maximum wavelengths implied no chemical decomposition was involved...
July 20, 2017: Scientific Reports
#12
Sara Azimi, Afsaneh Zonouzi, Omidreza Firuzi, Aida Iraji, Mina Saeedi, Mohammad Mahdavi, Najmeh Edraki
Alzheimer's disease is characterized by chronic neurodegeneration leading to dementia. The main cause of neurodegeneration is considered to be the accumulation of amyloid-β. Inhibiting BACE1 is a well-studied approach to lower the burden of amyloid-β aggregates. We designed a series of imidazopyridines-based compounds bearing phthalimide moieties as inhibitors of BACE1. The compounds 8a-o were synthesized by the Groebke-Blackburn-Bienaymé three-component reaction of heteroaromatic amidines, aldehydes and isocyanides...
June 24, 2017: European Journal of Medicinal Chemistry
#13
Aaron W Chen, Alejandro L Briseno, Maria M Santore
With increased interest in graphene-based sensors for biomolecules and other targets, we investigated the impact of ionic strength on the steady-state emissions from fluorescein labels on proteins adsorbing on pristine CVD (chemical vapor deposited)-graphene on a silica support. Using the model system of fluorescein-tagged fibrinogen we demonstrated that, for fluorescein tags on adsorbed fibrinogen, emission intensity was very sensitive to the salt concentration. This behavior was not seen for fluorescein-tagged fibrinogen in solution...
July 6, 2017: Journal of Colloid and Interface Science
#14
Shasha Song, Yang Liu, Aixin Song, Zengdian Zhao, Hongsheng Lu, Jingcheng Hao
Stimuli-response magnetic hydrogels were prepared in the mixtures of magnetic surfactants, (CnTAFB(C), n=12, 14, 16), and chiral amphiphiles, sodium cholate (SC). The gelation behavior of CnTAFB(C)/SC were studied in detail. The results proved that the hydrophobicity of surfactants and the hydration radius (Rh) of anions played a vital role in the gelation process. The microstructure of the hydrogels were determined to be three-dimensional network of fibrous aggregates. The formation of the hydrogel fibrils was considered to be mainly driven by a delicate balance of multiple non-covalent interactions including hydrophobic interaction, electrostatic interaction, hydrogen bonding, van der Waals force, and the steric effect of SC molecule...
July 10, 2017: Journal of Colloid and Interface Science
#15
Linfeng Wang, Xiang Zhou, Tianbao Ma, Dameng Liu, Lei Gao, Xin Li, Jun Zhang, Yuanzhong Hu, Hui Wang, Yadong Dai, Jianbin Luo
Graphene and other two-dimensional materials have been proved to be able to offer low friction. Here we assembled van der Waals heterostructures with graphene and molybdenum disulphide monolayers. The Raman spectrum together with a modified linear chain model indicate a two-orders-of-magnitude decrease in the interlayer lateral force constant, as compared with their homogeneous bilayers, indicating a possible routine to achieve superlubricity. The decrease in the interlayer lateral force constant is consistent with the ultrasmall potential energy corrugation during sliding, which is derived from density functional theory calculations...
July 20, 2017: Nanoscale
#16
Chao Li, Xiao Yan, Xiongfei Song, Wen-Zhong Bao, Shi-Jin Ding, David Wei Zhang, Peng Zhou
Heterostructure field effect transistors (hetero-FETs) are experimentally demonstrated,consisting of van der Waals heterostructure channels based on two-dimensionalsemiconductor. By optimally selecting the band alignment of heterostructure channels,different output characteristics of the hetero-FETs were achieved. In atomically thinWSe2/MoS2 hetero-FET with staggered energy band, the oscillating transfer characteristic and negative transconductance were realized. With near broken-gap alignment in MoTe2/SnSe2 heterostructure channel, a superior reverse biased current was obtained in the hetero-FETs, which can be analyzed as typical tunnelling current...
July 20, 2017: Nanotechnology
#17
Shen-Shu Sung
Recent site-resolved hydrogen exchange measurements have uncovered significant discrepancies between simulations and experimental data during protein folding, including the excessive intramolecular hydrogen bonds in simulations. This finding indicates a possibility that intramolecular charge-charge interactions have not included sufficient dielectric screening effect of the electronic polarization. Scaling down peptide atomic charges according to the optical dielectric constant is tested in this study. As a result, the number of intramolecular hydrogen bonds is lower than using unscaled atomic charges while reaching the same levels of helical contents or β-hairpin backbone hydrogen bonds, because van der Waals interactions contribute substantially to peptide folding in water...
July 20, 2017: Protein Science: a Publication of the Protein Society
#18
Timo Leskinen, Joanna Witos, Juan José Valle Delgado, Kalle Sakari Lintinen, Mauri A Kostiainen, Susanne Kristina Wiedmer, Monika Österberg, Maija-Liisa Mattinen
Coating of colloidal lignin particles (CLPs), or lignin nanoparticles (LNPs), with proteins was evaluated in order to establish a safe, self-assembly-mediated modification technique to tune their surface chemistry. Gelatin and poly- L-lysine formed the most pronounced protein corona on the CLP surface, as determined by dynamic light scattering (DLS) and zeta potential measurements. Spherical morphology of individual protein coated CLPs was confirmed by transmission electron (TEM) and atomic force (AFM) microscopy...
July 19, 2017: Biomacromolecules
#19
Hang Xiao, Xiaoyang Shi, Feng Hao, Xiangbiao Liao, Yayun Zhang, Xi Chen
We developed ReaxFF parameters for phosphorus and hydrogen to give a good description of the chemical and mechanical properties of pristine and defected black phosphorene. ReaxFF for P/H is transferable to a wide range of phosphorus and hydrogen containing systems including bulk black phosphorus, blue phosphorene, edge-hydrogenated phosphorene, phosphorus clusters and phosphorus hydride molecules. The potential parameters were obtained by conducting global optimization with respect to a set of reference data generated by extensive ab initio calculations...
July 19, 2017: Journal of Physical Chemistry. A
#20
Yun-Fei Xu, Wei Chen, Efthimios Kaxiras, Cynthia M Friend, Robert J Madix
The critical role of non-covalent van der Waals (vdW) interactions in determining the relative stability of alkoxy intermediates has been demonstrated for the Cu(110) surface using a combination of experiment and theory. The results may be significant for the selectivity control of copper-based reactions of alcohols. Previous examination of this effect on Au(110) was also extended to include higher molecular weight alcohols; on Cu(110) and Au(110) the hierarchy for the strength of binding of the alkoxys was found to be the same within experimental accuracy, with alkoxy species of greater chain length being more stable...
July 19, 2017: Journal of Physical Chemistry. B
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