9 results on '"Sokolov, Alexei P."'
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2. Experimental Techniques for Studies of Dynamics in Soft Materials
- Author
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Sokolov, Alexei P., Sakai, Victoria García, García Sakai, Victoria, editor, Alba-Simionesco, Christiane, editor, and Chen, Sow-Hsin, editor
- Published
- 2012
- Full Text
- View/download PDF
3. Search for a Grotthuss mechanism through the observation of proton transfer.
- Author
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Popov, Ivan, Zhu, Zhenghao, Young-Gonzales, Amanda R., Sacci, Robert L., Mamontov, Eugene, Gainaru, Catalin, Paddison, Stephen J., and Sokolov, Alexei P.
- Subjects
PROTONS ,MOLECULAR dynamics ,LIGHT scattering ,NEUTRON scattering ,BROADBAND dielectric spectroscopy ,INTRAMOLECULAR proton transfer reactions ,PROTON transfer reactions ,HYDROGEN bonding ,PHOSPHORIC acid - Abstract
The transport of protons is critical in a variety of bio- and electro-chemical processes and technologies. The Grotthuss mechanism is considered to be the most efficient proton transport mechanism, generally implying a transfer of protons between 'chains' of host molecules via elementary reactions within the hydrogen bonds. Although Grotthuss proposed this concept more than 200 years ago, only indirect experimental evidence of the mechanism has been observed. Here we report the first experimental observation of proton transfer between the molecules in pure and 85% aqueous phosphoric acid. Employing dielectric spectroscopy, quasielastic neutron, and light scattering, and ab initio molecular dynamic simulations we determined that protons move by surprisingly short jumps of only ~0.5–0.7 Å, much smaller than the typical ion jump length in ionic liquids. Our analysis confirms the existence of correlations in these proton jumps. However, these correlations actually reduce the conductivity, in contrast to a desirable enhancement, as is usually assumed by a Grotthuss mechanism. Furthermore, our analysis suggests that the expected Grotthuss-like enhancement of conductivity cannot be realized in bulk liquids where ionic correlations always decrease conductivity. Although the Grotthuss mechanism of proton transfer is generally considered to be the most efficient means of proton transport, the search for experimental evidence of the mechanism has remained elusive and in certain cases confusing. Here, dielectric spectroscopy, quasieleastic neutron and light scattering, along with ab initio molecular dynamics simulations have been utilized to elucidate the mechanism of proton transfer in pure and 85% aqueous phosphoric acid. [ABSTRACT FROM AUTHOR]
- Published
- 2023
- Full Text
- View/download PDF
4. Broadband Wide-Angle VElocity Selector (BWAVES) neutron spectrometer designed for the SNS Second Target Station.
- Author
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Mamontov, Eugene, Bordallo, Heloisa N., Delaire, Olivier, Nickels, Jonathan, Peters, Judith, Schneider, Gerald J., Smith, Jeremy C., and Sokolov, Alexei P.
- Subjects
NEUTRON scattering ,ENERGY transfer ,MOMENTUM transfer ,WAVELENGTHS ,VELOCITY - Abstract
A recently proposed wide-angle velocity selector (WAVES) device for choosing the velocity of detected neutrons after they have been scattered by the sample paves the way for inverted geometry neutron spectrometers with continuously adjustable final neutron wavelength. BWAVES broadband inverted geometry spectrometer proposed for the Second Target Station at the Spallation Neutron Source at Oak Ridge National Laboratory is designed using WAVES to simultaneously probe dynamic processes spanning 4.5 decades in time (energy transfer). This makes BWAVES a uniquely flexible instrument which can be viewed as either a quasielasitc neutron scattering (QENS) spectrometer with a practically unlimited (overlapping with the vibrational excitations) range of energy transfers, or a broadband inelastic vibrational neutron spectrometer with QENS capabilities, including a range of accessible momentum transfer (Q) and a sufficiently high energy resolution at the elastic line. The new capabilities offered by BWAVES will expand the application of neutron scattering in ways not possible with existing neutron spectrometers. [ABSTRACT FROM AUTHOR]
- Published
- 2022
- Full Text
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5. Engineering the Interlayer Spacing by Pre‐Intercalation for High Performance Supercapacitor MXene Electrodes in Room Temperature Ionic Liquid.
- Author
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Liang, Kun, Matsumoto, Ray A., Zhao, Wei, Osti, Naresh C., Popov, Ivan, Thapaliya, Bishnu P., Fleischmann, Simon, Misra, Sudhajit, Prenger, Kaitlyn, Tyagi, Madhusudan, Mamontov, Eugene, Augustyn, Veronica, Unocic, Raymond R., Sokolov, Alexei P., Dai, Sheng, Cummings, Peter T., and Naguib, Michael
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IONIC liquids ,SUPERCAPACITOR performance ,SUPERCAPACITOR electrodes ,ENERGY density ,NEUTRON scattering ,AQUEOUS electrolytes - Abstract
MXenes exhibit excellent capacitance at high scan rates in sulfuric acid aqueous electrolytes, but the narrow potential window of aqueous electrolytes limits the energy density. Organic electrolytes and room‐temperature ionic liquids (RTILs) can provide higher potential windows, leading to higher energy density. The large cation size of RTIL hinders its intercalation in‐between the layers of MXene limiting the specific capacitance in comparison to aqueous electrolytes. In this work, different chain lengths alkylammonium (AA) cations are intercalated into Ti3C2Tx, producing variation of MXene interlayer spacings (d‐spacing). AA‐cation‐intercalated Ti3C2Tx (AA‐Ti3C2), exhibits higher specific capacitances, and cycling stabilities than pristine Ti3C2Tx in 1 m 1‐ethly‐3‐methylimidazolium bis‐(trifluoromethylsulfonyl)‐imide (EMIMTFSI) in acetonitrile and neat EMIMTFSI RTIL electrolytes. Pre‐intercalated MXene with an interlayer spacing of ≈2.2 nm, can deliver a large specific capacitance of 257 F g−1 (1428 mF cm−2 and 492 F cm−3) in neat EMIMTFSI electrolyte leading to high energy density. Quasi elastic neutron scattering and electrochemical impedance spectroscopy are used to study the dynamics of confined RTIL in pre‐intercalated MXene. Molecular dynamics simulations suggest significant differences in the structures of RTIL ions and AA cations inside the Ti3C2Tx interlayer, providing insights into the differences in the observed electrochemical behavior. [ABSTRACT FROM AUTHOR]
- Published
- 2021
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6. Atomistic details of protein dynamics and the role of hydration water.
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Khodadadi, Sheila and Sokolov, Alexei P.
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PROTEINS , *HYDRATION , *NEUTRON scattering , *MOLECULAR dynamics , *SIMULATION methods & models - Abstract
Background The importance of protein dynamics for their biological activity is now well recognized. Different experimental and computational techniques have been employed to study protein dynamics, hierarchy of different processes and the coupling between protein and hydration water dynamics. Yet, understanding the atomistic details of protein dynamics and the role of hydration water remains rather limited. Scoop of review Based on overview of neutron scattering, molecular dynamic simulations, NMR and dielectric spectroscopy results we present a general picture of protein dynamics covering time scales from faster than ps to microseconds and the influence of hydration water on different relaxation processes. Major conclusions Internal protein dynamics spread over a wide time range from faster than picosecond to longer than microseconds. We suggest that the structural relaxation in hydrated proteins appears on the microsecond time scale, while faster processes present mostly motion of side groups and some domains. Hydration water plays a crucial role in protein dynamics on all time scales. It controls the coupled protein-hydration water relaxation on 10–100 ps time scale. This process defines the friction for slower protein dynamics. Analysis suggests that changes in amount of hydration water affect not only general friction, but also influence significantly the protein's energy landscape. General significance The proposed atomistic picture of protein dynamics provides deeper understanding of various relaxation processes and their hierarchy, similarity and differences between various biological macromolecules, including proteins, DNA and RNA. This article is part of a Special Issue entitled “Science for Life” Guest Editor: Dr. Austen Angell, Dr. Salvatore Magazù and Dr. Federica Migliardo”. [ABSTRACT FROM AUTHOR]
- Published
- 2017
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7. Influence of Ions on Water DiffusionA NeutronScattering Study.
- Author
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Ben Ishai, Paul, Mamontov, Eugene, Nickels, Jonathan D., and Sokolov, Alexei P.
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NEUTRON scattering , *SPECTRUM analysis , *POTASSIUM ions , *MOLECULAR structure , *QUASIELASTIC neutron scattering , *TRANSLATIONAL spectroscopy - Abstract
Using quasielastic neutron scatteringspectroscopy, we measuredthe averaged translational diffusion of water in solutions of biologicallyrelevant salts, NaCl, a kosmotrope, and KCl, a chaotrope. The analysisrevealed the striking difference in the influence of these ions onwater dynamics. While the averaged water diffusion slows down in thepresence of the structure making (kosmotrope) Na+ion,the diffusion becomes faster in the presence of the structure breaking(chaotrope) K+ion. The latter means that, despite strongCoulombic interactions introduced by the K+ions, theirdisruption of the hydrogen-bonding network is so significant thatit leads to faster diffusion of the water molecules. [ABSTRACT FROM AUTHOR]
- Published
- 2013
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8. Elastic and Conformational Softness of a Globular Protein.
- Author
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Liang Hong, Glass, Dennis C., Nickels, Jonathan D., Perticaroli, Stefania, Zheng Yi, Madhusudan, Tyagi, O'Neill, Hugh, Qiu Zhang, Sokolov, Alexei P., and Smith, Jeremy C.
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GLOBULAR proteins , *PROTEIN analysis , *GREEN fluorescent protein , *FLUOROPHORES spectra , *NEUTRON scattering , *MOLECULAR dynamics - Abstract
Flexibility, or softness, is crucial for protein function and consists of a conformational component, involving jumps between potential wells, and an elastic component, involving fluctuations within the wells. Combining molecular dynamics simulation with incoherent neutron scattering and light scattering measurements on green fluorescent protein, we reveal a relationship between the intrawell fluctuations and elastic moduli of the protein. This finding leads to a simple means of experimentally separating the conformational from the elastic atomic displacements. [ABSTRACT FROM AUTHOR]
- Published
- 2013
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9. Three Classes of Motion in the Dynamic Neutron-Scattering Susceptibility of a Globular Protein.
- Author
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Liang Hong, Smolin, Nikolai, Lindner, Benjamin, Sokolov, Alexei P., and Smith, Jeremy C.
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NEUTRON scattering , *LYSOZYMES , *MOLECULAR dynamics , *HYDRATION , *GLOBULAR proteins - Abstract
A simplified description of the 295 K dynamics of a globular protein over a wide frequency range (1-1000 GHz) is obtained by combining neutron scattering of lysozyme with molecular dynamics simulation. The molecular dynamics simulation agrees quantitatively with experiment for both the protein and the hydration water and shows that, whereas the hydration water molecules subdiffuse, the protein atoms undergo confined motion decomposable into three distinct classes: localized diffusion, methyl group rotations, and jumps. Each of the three classes gives rise to a characteristic neutron susceptibility signal. [ABSTRACT FROM AUTHOR]
- Published
- 2011
- Full Text
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