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Dipolar field

Maciej Ptak, Mirosław Mączka, Anna Gągor, Adam Sieradzki, Bartosz Bondzior, Przemysław Dereń, S Pawlus
We report the synthesis, crystal structure, dielectric, vibrational and emission spectra of heterometallic MOFs, [C2H5NH3][Na0.5Cr0.5(HCOO)3] (EtANaCr), [C2H5NH3][Na0.5Al0.5(HCOO)3] (EtANaAl) and [C2H5NH3][Na0.5Al0.475Cr0.025(HCOO)3] (EtANaAlCr). These compounds crystallize in non-centrosymmetric monoclinic polar structures (space group Pn) and undergo order-disorder phase transitions upon heating to the monoclinic centrosymmetric structure (space group P21/n) at 369 (EtANaAl) and 373 K (EtANaCr). In principle, they are ferroelectric below these temperatures...
October 18, 2016: Physical Chemistry Chemical Physics: PCCP
Jonas Bugase, Johannes Berner, Thomas M Fischer
A mixture of an ester based ferrofluid with silicone oil and 2,6-lutidine is exposed to an external magnetic field. We find a region of composition of the ternary mixture, where weak magnetic fields of the order of a few kA m(-1) induce a modulated phase with a pattern characterized by equilibrium size droplets of the minority phase immersed into the extended majority phase. While the pattern resembles in many ways the pattern of immiscible magnetic fluids, the dependence of the characteristic parameters of the pattern on the magnetic field are completely different than in immiscible fluids...
September 23, 2016: Soft Matter
Takahiro Shimada, Le Van Lich, Koyo Nagano, Jian-Shan Wang, Jie Wang, Takayuki Kitamura
Topological objects of nontrivial spin or dipolar field textures, such as skyrmions, merons, and vortices, interacting with applied external fields in ferroic materials are of great scientific interest as an intriguing playground of unique physical phenomena and novel technological paradigms. The quest for new topological configurations of such swirling field textures has primarily been done for magnets with Dzyaloshinskii-Moriya interactions, while the absence of such intrinsic chiral interactions among electric dipoles left ferroelectrics aside in this quest...
October 7, 2016: Scientific Reports
Katharina Keller, Michal Zalibera, Mian Qi, Vanessa Koch, Julia Wegner, Henrik Hintz, Adelheid Godt, Gunnar Jeschke, Anton Savitsky, Maxim Yulikov
The four Mn(ii) complexes Mn-DOTA, Mn-TAHA, Mn-PyMTA, and Mn-NO3Py were characterized by electron paramagnetic resonance (EPR), electron-nuclear double resonance (ENDOR), and relaxation measurements, to predict their relative performance in the EPR pulse dipolar spectroscopy (PDS) experiments. High spin density localization on the metal ions was proven by ENDOR on (1)H, D, (14)N, and (55)Mn nuclei. The transverse relaxation of the Mn(ii) complexes appears to be slow enough for PDS-based spin-spin distance determination...
September 14, 2016: Physical Chemistry Chemical Physics: PCCP
Alysha Dicke, Tata Gopinath, Yingjie Wang, Gianluigi Veglia
Water plays a central role in membrane protein folding and function. It not only catalyzes lipid membrane self-assembly, but it is also affects the structural integrity and conformational dynamics of membrane proteins. Magic angle spinning (MAS) solid-state NMR is the technique of choice for measuring water accessibility of membrane proteins in a site-specific manner, providing a ruler for membrane protein topology and insertion within lipid bilayers. However, sensitivity and resolution of membrane protein samples for MAS experiments is often dictated by hydration levels, which affect membrane proteins structural dynamics...
October 5, 2016: Journal of Physical Chemistry. B
Dmitry Sivun, Cynthia Vidal, Battulga Munkhbat, Nikita Arnold, Thomas A Klar, Calin Hrelescu
Bulk gold shows photoluminescence (PL) with a negligible quantum yield of ~10(-10), which can, however, be increased by orders of magnitude in case of gold nanoparticles. This bears huge potential to use noble metal nanoparticles as fluorescent and unbleachable stains in bio-imaging or for optical data storage. Commonly, the enhancement of PL yield is attributed to nanoparticle plasmons, specifically to the enhancements of scattering or absorption cross sections. Tuning the shape or geometry of gold nanostructures (e...
October 4, 2016: Nano Letters
Gabi Steinbach, Sibylle Gemming, Artur Erbe
Despite its prominent role in the dynamics of soft materials, rotational friction remains a quantity that is difficult to determine for many micron-sized objects. Here, we demonstrate how the Stokes coefficient of rotational friction can be obtained from the driven torsional oscillations of single particles in a highly viscous environment. The idea is that the oscillation amplitude of a dipolar particle under combined static and oscillating fields provides a measure for the Stokes friction. From numerical studies we derive a semi-empirical analytic expression for the amplitude of the oscillation, which cannot be calculated analytically from the equation of motion...
September 29, 2016: Scientific Reports
Alessandro Veltri, Arkadi Chipouline, Ashod Aradian
The plasmonic response of a metal nanoparticle in the presence of surrounding gain elements is studied, using a space and time-dependent model, which integrates a quantum formalism to describe the gain and a classical treatment for the metal. Our model fully takes into account the influence of the system geometry (nanosphere) and offers for the first time, the possibility to describe the temporal evolution of the fields and the coupling among the multipolar modes of the particle. We calculate the lasing threshold value for all multipoles of the spaser, and demonstrate that the dipolar one is lowest...
2016: Scientific Reports
Kristoffer Basse, Ravi Shankar, Morten Bjerring, Thomas Vosegaard, Niels Chr Nielsen, Anders B Nielsen
We present a theoretical analysis of the influence of chemical shifts on amplitude-modulated heteronuclear dipolar recoupling experiments in solid-state NMR spectroscopy. The method is demonstrated using the Rotor Echo Short Pulse IRrAdiaTION mediated Cross-Polarization ((RESPIRATION)CP) experiment as an example. By going into the pulse sequence rf interaction frame and employing a quintuple-mode operator-based Floquet approach, we describe how chemical shift offset and anisotropic chemical shift affect the efficiency of heteronuclear polarization transfer...
September 7, 2016: Journal of Chemical Physics
Taerin Chung, Tugba Koker, Fabien Pinaud
The assembly of plasmonic metal nanoparticles into hot spot surface-enhanced Raman scattering (SERS) nanocluster probes is a powerful, yet challenging approach for ultrasensitive biosensing. Scaffolding strategies based on self-complementary peptides and proteins are of increasing interest for these assemblies, but the electronic and the photonic properties of such hybrid nanoclusters remain difficult to predict and optimize. Here, split-green fluorescence protein (sGFP) fragments are used as molecular glue and the GFP chromophore is used as a Raman reporter to assemble a variety of gold nanoparticle (AuNP) clusters and explore their plasmonic properties by numerical modeling...
September 8, 2016: Small
Alessandro Mandoli
The explosively-growing applications of the Cu-catalyzed Huisgen 1,3-dipolar cycloaddition reaction between organic azides and alkynes (CuAAC) have stimulated an impressive number of reports, in the last years, focusing on recoverable variants of the homogeneous or quasi-homogeneous catalysts. Recent advances in the field are reviewed, with particular emphasis on systems immobilized onto polymeric organic or inorganic supports.
2016: Molecules: a Journal of Synthetic Chemistry and Natural Product Chemistry
Dustin A Gilbert, Jung-Wei Liao, Brian J Kirby, Michael Winklhofer, Chih-Huang Lai, Kai Liu
Magnetic interactions in magnetic nanostructures are critical to nanomagnetic and spintronic explorations. Here we demonstrate an extremely sensitive magnetic yoking effect and tunable interactions in FePt based hard/soft bilayers mediated by the soft layer. Below the exchange length, a thin soft layer strongly exchange couples to the perpendicular moments of the hard layer; above the exchange length, just a few nanometers thicker, the soft layer moments turn in-plane and act to yoke the dipolar fields from the adjacent hard layer perpendicular domains...
2016: Scientific Reports
Serguei Tchoumakov, Marcello Civelli, Mark O Goerbig
We investigate Weyl semimetals with tilted conical bands in a magnetic field. Even when the cones are overtilted (type-II Weyl semimetal), Landau-level quantization can be possible as long as the magnetic field is oriented close to the tilt direction. Most saliently, the tilt can be described within the relativistic framework of Lorentz transformations that give rise to a rich spectrum, displaying new transitions beyond the usual dipolar ones in the optical conductivity. We identify particular features in the latter that allow one to distinguish between semimetals of different types...
August 19, 2016: Physical Review Letters
Niall J English, José-A Garate
An extensive suite of non-equilibrium molecular-dynamics simulation has been performed for ∼0.85-0.9 μs of human aquaporin 4 in the absence and presence of externally applied static and alternating electric fields applied along the channels (in both axial directions in the static case, taken as the laboratory z-axis). These external fields were of 0.0065 V/Å (r.m.s.) intensity (of the same order as physiological electrical potentials); alternating fields ranged in frequency from 2.45 to 500 GHz. In-pore gating dynamics was studied, particularly of the relative propensities for "open" and "closed" states of the conserved arginines in the arginine/aromatic area (itself governed in no small part by external-field response of the dipolar alignment of the histidine-201 residue in the selectivity filter)...
August 28, 2016: Journal of Chemical Physics
Vegard Flovik, Ferran Macià, Erik Wahlström
The collective dynamics in populations of magnetic spin torque oscillators (STO) is an intensely studied topic in modern magnetism. Here, we show that arrays of STO coupled via dipolar fields can be modeled using a variant of the Kuramoto model, a well-known mathematical model in non-linear dynamics. By investigating the collective dynamics in arrays of STO we find that the synchronization in such systems is a finite size effect and show that the critical coupling-for a complete synchronized state-scales with the number of oscillators...
2016: Scientific Reports
Saïd Bakhti, Alexandre V Tishchenko, Xavier Zambrana-Puyalto, Nicolas Bonod, Scott D Dhuey, P James Schuck, Stefano Cabrini, Selim Alayoglu, Nathalie Destouches
In this work we theoretically and experimentally analyze the resonant behavior of individual 3 × 3 gold particle oligomers illuminated under normal and oblique incidence. While this structure hosts both dipolar and quadrupolar electric and magnetic delocalized modes, only dipolar electric and quadrupolar magnetic modes remain at normal incidence. These modes couple into a strongly asymmetric spectral response typical of a Fano-like resonance. In the basis of the coupled mode theory, an analytical representation of the optical extinction in terms of singular functions is used to identify the hybrid modes emerging from the electric and magnetic mode coupling and to interpret the asymmetric line profiles...
2016: Scientific Reports
Wai-Yip Lo, Na Zhang, Zhengxu Cai, Lianwei Li, Luping Yu
As the semiconductor companies officially abandoned the pursuit of Moore's law, the limitation of silicone-based semiconductor electronic devices is approaching. Single molecular devices are considered as a potential solution to overcome the physical barriers caused by quantum interferences because the intermolecular interactions are mainly through weak van der Waals force between molecular building blocks. In this bottom-up approach, components are built from atoms up, allowing great control over the molecular properties...
September 20, 2016: Accounts of Chemical Research
V I Yukalov
Statistical systems composed of atoms interacting with each other trough nonintegrable interaction potentials are considered. Examples of these potentials are hard-core potentials and long-range potentials, for instance, the Lennard-Jones and dipolar potentials. The treatment of such potentials is known to confront several problems, e.g., the impossibility of using the standard mean-field approximations, such as Hartree and Hartree-Fock approximations, the impossibility of directly introducing coherent states, the difficulty in breaking the global gauge symmetry, which is required for describing Bose-Einstein condensed and superfluid systems, the absence of a correctly defined Fourier transform, which hampers the description of uniform matter as well as the use of local-density approximation for nonuniform systems...
July 2016: Physical Review. E
Jan Dommerholt, Floris P J T Rutjes, Floris L van Delft
A nearly forgotten reaction discovered more than 60 years ago-the cycloaddition of a cyclic alkyne and an organic azide, leading to an aromatic triazole-enjoys a remarkable popularity. Originally discovered out of pure chemical curiosity, and dusted off early this century as an efficient and clean bioconjugation tool, the usefulness of cyclooctyne-azide cycloaddition is now adopted in a wide range of fields of chemical science and beyond. Its ease of operation, broad solvent compatibility, 100 % atom efficiency, and the high stability of the resulting triazole product, just to name a few aspects, have catapulted this so-called strain-promoted azide-alkyne cycloaddition (SPAAC) right into the top-shelf of the toolbox of chemical biologists, material scientists, biotechnologists, medicinal chemists, and more...
April 2016: Top Curr Chem (J)
Thomas Carell, Milan Vrabel
Bioorthogonal chemistry has emerged as a new powerful tool that facilitates the study of structure and function of biomolecules in their native environment. A wide variety of bioorthogonal reactions that can proceed selectively and efficiently under physiologically relevant conditions are now available. The common features of these chemical reactions include: fast kinetics, tolerance to aqueous environment, high selectivity and compatibility with naturally occurring functional groups. The design and development of new chemical transformations in this direction is an important step to meet the growing demands of chemical biology...
February 2016: Top Curr Chem (J)
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