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Dipolar field

Alexander I Greenwood, Mary C Clay, Chad M Rienstra
Typically, the process of NMR-based structure determination relies on accurately measuring a large number of internuclear distances to serve as restraints for simulated annealing calculations. In solids, the rotational-echo double-resonance (REDOR) experiment is a widely used approach to determine heteronuclear dipolar couplings corresponding to distances usually in the range of 1.5-8Å. A challenge in the interpretation of REDOR data is the degeneracy of symmetric subunits in an oligomer or equivalent molecules in a crystal lattice, which produce REDOR trajectories that depend explicitly on two or more distances instead of one...
February 28, 2017: Journal of Magnetic Resonance
Monu Kaushik, Mian Qi, Adelheid Godt, Björn Corzilius
High-spin complexes act as polarizing agents (PAs) for dynamic nuclear polarization (DNP) in solid-state NMR spectroscopy and feature promising aspects towards biomolecular DNP. We present a study on bis(Gd-chelate)s which enable cross effect (CE) DNP owing to spatial confinement of two dipolar-coupled electron spins. Their well-defined Gd⋅⋅⋅Gd distances in the range of 1.2-3.4 nm allowed us to elucidate the Gd⋅⋅⋅Gd distance dependence of the DNP mechanism and NMR signal enhancement. We found that Gd⋅⋅⋅Gd distances above 2...
March 20, 2017: Angewandte Chemie
Yue Pan, Qiangling Zhang, Wenzhao Zhou, Xue Zou, Hongmei Wang, Chaoqun Huang, Chengyin Shen, Yannan Chu
Proton transfer reaction mass spectrometry (PTR-MS) has played an important role in the field of real-time monitoring of trace volatile organic compounds (VOCs) due to its advantages such as low limit of detection (LOD) and fast time response. Recently, a new technology of proton extraction reaction mass spectrometry (PER-MS) with negative ions OH(-) as the reagent ions has also been presented, which can be applied to the detection of VOCs and even inorganic compounds. In this work, we combined the functions of PTR-MS and PER-MS in one instrument, thereby developing a novel technology called dipolar proton transfer reaction mass spectrometry (DP-PTR-MS)...
March 17, 2017: Journal of the American Society for Mass Spectrometry
Chen Yan, Xiaolong Wang, T V Raziman, Olivier J F Martin
Plasmonic antennas and planar structures have been undergoing intensive developments in order to control the scattering and absorption of light. One specific class, extrinsic chiral surfaces, that does not possess twofold rotational symmetry exhibits strong asymmetric transmission for different circular polarizations under obliquely incident illumination. In this work, we show that the design of those surfaces can be optimized with complex multipolar resonances in order to twist the fluorescence emission from nearby molecules...
March 17, 2017: Nano Letters
Lijun Liu, Issei Nakamura
We illustrate the effects of chain connectivity on the solvation energy of ions immersed in polymer liquids by developing a new coarse-grained molecular dynamics simulation. Our theory accounts for the dielectric response of the polymers through the connection of dipolar, monomeric units with nonlinear springs. In stark contrast to the standard Born solvation energy of ions, our results depend substantially on the chain length of the polymers. We also demonstrate the marked difference in the solvation energies of the ions immersed in non-polymeric particle mixtures, single-component polymers, polymer blends, and block copolymers...
March 17, 2017: Journal of Physical Chemistry. B
Carles Navau, Rosa Mach-Batlle, Albert Parra, Jordi Prat-Camps, Sergi Laut, Nuria Del-Valle, Alvaro Sanchez
Magnetic sensors are key elements in our interconnected smart society. Their sensitivity becomes essential for many applications in fields such as biomedicine, computer memories, geophysics, or space exploration. Here we present a universal way of increasing the sensitivity of magnetic sensors by surrounding them with a spherical metamaterial shell with specially designed anisotropic magnetic properties. We analytically demonstrate that the magnetic field in the sensing area is enhanced by our metamaterial shell by a known factor that depends on the shell radii ratio...
March 17, 2017: Scientific Reports
Sungsool Wi, Robert Schurko, Lucio Frydman
Cross-polarization (CP) experiments employing frequency-swept radiofrequency (rf) pulses have been successfully used in static spin systems for obtaining broadband signal enhancements. These experiments have been recently extended to heteronuclear I, S = spin-1/2 nuclides under magic-angle spinning (MAS), by applying adiabatic inversion pulses along the S (low-γ) channel while simultaneously applying a conventional spin-locking pulse on the I-channel ((1)H). This study explores an extension of this adiabatic frequency sweep concept to quadrupolar nuclei, focusing on CP from (1)H (I = 1/2) to (2)H spins (S = 1) undergoing fast MAS (νr = 60 kHz)...
March 14, 2017: Journal of Chemical Physics
F Donado, J M Sausedo-Solorio, R E Moctezuma
We study a two-dimensional nonvibrating granular system as a model of a magnetorheological fluid. The system is composed of magnetic steel particles on a horizontal plane under a vertical sinusoidal magnetic field and a horizontal static magnetic field. When the amplitude of the horizontal field is zero, we find that the motion of the particles has characteristics similar to those of Brownian particles. A slowing down of the dynamics is observed as the particle concentration increases or the magnitude of the vertical magnetic field decreases...
February 2017: Physical Review. E
Valentin Flauraud, Gabriel D Bernasconi, Jérémy Butet, Duncan T L Alexander, Olivier J F Martin, Juergen Brugger
While plasmonic antennas composed of building blocks made of the same material have been thoroughly studied, recent investigations have highlighted the unique opportunities enabled by making compositionally asymmetric plasmonic systems. So far, mainly heterostructures composed of nanospheres and nanodiscs have been investigated, revealing opportunities for the design of Fano resonant nanostructures, directional scattering, sensing and catalytic applications. In this article, an improved fabrication method is reported that enables precise tuning of the heterodimer geometry, with interparticle distances made down to a few nanometers between Au-Ag and Au-Al nanoparticles...
March 14, 2017: ACS Nano
Andre G Campos, Denys I Bondar, Renan Cabrera, Herschel A Rabitz
We show that a laser pulse can always be found that induces a desired optical response from an arbitrary dynamical system. As illustrations, driving fields are computed to induce the same optical response from a variety of distinct systems (open and closed, quantum and classical). As a result, the observed induced dipolar spectra without detailed information on the driving field are not sufficient to characterize atomic and molecular systems. The formulation may also be applied to design materials with specified optical characteristics...
February 24, 2017: Physical Review Letters
M Virumbrales-Del Olmo, A Delgado-Cabello, A Andrada-Chacón, J Sánchez-Benítez, E Urones-Garrote, V Blanco-Gutiérrez, M J Torralvo, R Sáez-Puche
Single domain superparamagnetic ferrite nanoparticles with the composition MFe2O4 (M = Fe, Co, Zn) have been prepared by thermal decomposition of metal acetylacetonates in diphenyl ether or dibenzyl ether, using oleic acid in the presence of oleylamine as a stabilizing agent. The Fe, Co and Zn ferrite nanoparticles are monodisperse with diameters of 4.9, 4.4 and 4.7 nm, respectively. The TG and IR results indicate that four or six carboxylate groups per nm(2) are bonded at the surface of the particles acting as chelating and/or bridging bidentate ligands depending on the composition...
March 10, 2017: Physical Chemistry Chemical Physics: PCCP
Mohammed Salah, Najia Komiha, Oum Keltoum Kabbaj, Rachida Ghailane, Khadija Marakchi
The 1,3-dipolar cycloaddition of methyl 2-trifluorobutynoate with various azides has been studied in terms of several theoretical approaches at DFT/B3LYP/6-311++G(d,p) level of theory. The mechanism of regioselectivity of these reactions was investigated through the evaluation of the potential energy surface of the cycloaddition process calculations and density DFT-based reactivity indices. These approaches were successfully applied to prediction of preferable regio-isomers for various reactions of 1,3-dipolar cycloadditions...
March 1, 2017: Journal of Molecular Graphics & Modelling
Joshua K Hamilton, Peter G Petrov, C Peter Winlove, Andrew D Gilbert, Matthew T Bryan, Feodor Y Ogrin
Microscopic swimming devices hold promise for radically new applications in lab-on-a-chip and microfluidic technology, diagnostics and drug delivery etc. In this paper, we demonstrate the experimental verification of a new class of autonomous ferromagnetic swimming devices, actuated and controlled solely by an oscillating magnetic field. These devices are based on a pair of interacting ferromagnetic particles of different size and different anisotropic properties joined by an elastic link and actuated by an external time-dependent magnetic field...
March 9, 2017: Scientific Reports
Taeyoung Choi, William Paul, Steffen Rolf-Pissarczyk, Andrew J Macdonald, Fabian D Natterer, Kai Yang, Philip Willke, Christopher P Lutz, Andreas J Heinrich
Spin resonance provides the high-energy resolution needed to determine biological and material structures by sensing weak magnetic interactions. In recent years, there have been notable achievements in detecting and coherently controlling individual atomic-scale spin centres for sensitive local magnetometry. However, positioning the spin sensor and characterizing spin-spin interactions with sub-nanometre precision have remained outstanding challenges. Here, we use individual Fe atoms as an electron spin resonance (ESR) sensor in a scanning tunnelling microscope to measure the magnetic field emanating from nearby spins with atomic-scale precision...
March 6, 2017: Nature Nanotechnology
Jonathan F Stebbins, Ryan J McCarty, Aaron C Palke
Most applications of high-resolution NMR to questions of short-range order/disorder in inorganic materials have been made in systems where ions with unpaired electron spins are of negligible concentration, with structural information extracted primarily from chemical shifts, quadrupolar coupling parameters, and nuclear dipolar couplings. In some cases, however, the often-large additional resonance shifts caused by interactions between unpaired electron and nuclear spins can provide unique new structural information in materials with contents of paramagnetic cations ranging from hundreds of ppm to several per cent and even higher...
March 1, 2017: Acta Crystallographica. Section C, Structural Chemistry
Asif Equbal, P K Madhu, Beat H Meier, Niels Chr Nielsen, Matthias Ernst, Vipin Agarwal
Major advances have recently been made in the field of heteronuclear dipolar decoupling in solid-state nuclear magnetic resonance (NMR). These developments have improved the resolution and sensitivity of the NMR spectrum of spins coupled to protons. One such new scheme, denoted as rCW(ApA), has proven to be robust with practically no need for parameter optimization [A. Equbal et al. Chem. Phys. Lett., 635, 339 (2015)]. Most of the experiments with rCW(ApA) have been carried out in the regimes of slow to moderate magic-angle spinning while simultaneously applying high decoupling radio-frequency amplitudes...
February 28, 2017: Journal of Chemical Physics
Angela C Stelson, Sonny J Penterman, Chekesha M Liddell Watson
Hierarchical C60 colloidal films are assembled from nanoscale to macroscale. Fullerene molecular crystals are grown via seeded cosolvent precipitation with mixed solvent [tetrahydronaphthalene (THN)/trimethylpyridine (TMP)] and antisolvent 2-propanol. The fullerene solutions are aged under illumination, which due to the presence of TMP reduces the free monomer concentration through fullerene aggregation into nanoparticles. The nanoparticles seed the growth of monodisperse fullerene colloids on injection into the antisolvent...
March 1, 2017: Small
Lukas N Wirz, Jane R Allison
Residual dipolar couplings (RDCs), unlike most other types of NMR observables, provide orientational information, reporting on the alignment of inter-spin vectors (ISVs) relative to the magnetic field. A great challenge in using experimental RDCs to restrain molecular dynamics (MD) simulations is how to represent this alignment. An alignment tensor is often used to parameterise the contribution of molecular alignment to the angular dependence of RDCs. All ISVs that share the same tensor have fixed relative alignment, i...
February 20, 2017: Progress in Biophysics and Molecular Biology
M Decker, T Pertsch, I Staude
We study resonant photonic-plasmonic coupling between a gold dipole nanoantenna and a silicon nanodisc supporting electric and magnetic dipolar Mie-type resonances. Specifically, we consider two different cases for the mode structure of the silicon nanodisc, namely spectrally separate and spectrally matching electric and magnetic dipolar Mie-type resonances. In the latter case, the dielectric nanoparticle scatters the far fields of a unidirectional Huygens' source. Our results reveal an anticrossing of the plasmonic dipole resonance and the magnetic Mie-type dipole resonance of the silicon nanodisc, accompanied by a clear signature of photonic-plasmonic mode hybridization in the corresponding mode profiles...
March 28, 2017: Philosophical Transactions. Series A, Mathematical, Physical, and Engineering Sciences
Elizaveta V Melik-Gaykazyan, Maxim R Shcherbakov, Alexander S Shorokhov, Isabelle Staude, Igal Brener, Dragomir N Neshev, Yuri S Kivshar, Andrey A Fedyanin
Subwavelength silicon nanoparticles are known to support strongly localized Mie-type modes, including those with resonant electric and magnetic dipolar polarizabilities. Here we compare experimentally the efficiency of the third-harmonic generation from isolated silicon nanodiscs for resonant excitation at the two types of dipolar resonances. Using nonlinear spectroscopy, we observe that the magnetic dipolar mode yields more efficient third-harmonic radiation in contrast to the electric dipolar (ED) mode. This is further supported by full-wave numerical simulations, where the volume-integrated local fields and the directly simulated nonlinear response are shown to be negligible at the ED resonance compared with the magnetic one...
March 28, 2017: Philosophical Transactions. Series A, Mathematical, Physical, and Engineering Sciences
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