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978 results on '"Stepanov, Alexander A."'

253. Hydrogen Bonding Between Ions of Like Charge in Ionic Liquids Characterized by NMR Deuteron Quadrupole Coupling Constants—Comparison with Salt Bridges and Molecular Systems

Author

Khudozhitkov, Alexander E., primary, Neumann, Jan, additional, Niemann, Thomas, additional, Zaitsau, Dzmitry, additional, Stange, Peter, additional, Paschek, Dietmar, additional, Stepanov, Alexander G., additional, Kolokolov, Daniil I., additional, and Ludwig, Ralf, additional

Published
2019
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256. Acousto-optic spectrometer ISEM for ExoMars-2020 space mission: ground measurements and calibrations

Author

Dobrolenskiy, Yury S., primary, Mantsevich, Sergey, additional, Evdokimova, Nadezhda, additional, Korablev, Oleg, additional, Fedorova, Anna, additional, Kalinnikov, Yuri, additional, Vyazovetskiy, Nikita, additional, Titov, Andrei, additional, Stepanov, Alexander, additional, Sapgir, Alexander, additional, Dzyuban, Ilya, additional, Kuzmin, Ruslan, additional, Ivanov, Yuriy, additional, Syniavskyi, Ivan, additional, Petrov, Vladislav, additional, Smol'yaninova, Vera, additional, and Dokuchaev, Alexander, additional

Published
2019
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265. Dissecting the effects of water guest adsorption and framework breathing on the AlO4(OH)2 centres of metal–organic framework MIL-53 (Al) by solid state NMR and structural analysis.

Author

Khudozhitkov, Alexander E., Arzumanov, Sergei S., Toktarev, Alexander V., Cherepanova, Svetlana V., Gabrienko, Anton A., Kolokolov, Daniil I., and Stepanov, Alexander G.

Abstract

The relationship between the adsorption of water on MIL-53 (Al) MOF, the structural phase of MIL-53 (Al), and the quadrupole coupling constant of 27Al framework aluminium atom (QCC) of the MOF AlO4(OH)2 centres (Al-sites) has been investigated by combining solid-state 27Al MAS NMR spectroscopy with XRD analysis and DFT calculations. It is established that 27Al QCC is primarily sensitive to water adsorption to the Al-sites and by a minor extent to the framework contraction/expansion interconversions. We thus conclude that the 27Al MAS NMR method is sensitive enough to differentiate the effects of pore contractions and water adsorption to Al-sites basing on the changes of the QCC value. [ABSTRACT FROM AUTHOR]

Published
2021
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267. Double Ended Lists Package

Author

Musser, David R., Stepanov, Alexander A., Muchnick, Steven S., editor, Schnupp, Peter, editor, Musser, David R., and Stepanov, Alexander A.

Published
1989
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268. Using the Packages

Author

Musser, David R., Stepanov, Alexander A., Muchnick, Steven S., editor, Schnupp, Peter, editor, Musser, David R., and Stepanov, Alexander A.

Published
1989
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269. Stacks Package

Author

Musser, David R., Stepanov, Alexander A., Muchnick, Steven S., editor, Schnupp, Peter, editor, Musser, David R., and Stepanov, Alexander A.

Published
1989
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272. Singly Linked Lists Package

Author

Musser, David R., Stepanov, Alexander A., Muchnick, Steven S., editor, Schnupp, Peter, editor, Musser, David R., and Stepanov, Alexander A.

Published
1989
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276. Introduction

Author

Musser, David R., Stepanov, Alexander A., Muchnick, Steven S., editor, Schnupp, Peter, editor, Musser, David R., and Stepanov, Alexander A.

Published
1989
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277. Linear Data Structures

Author

Musser, David R., Stepanov, Alexander A., Muchnick, Steven S., editor, Schnupp, Peter, editor, Musser, David R., and Stepanov, Alexander A.

Published
1989
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280. Porous metal–organic polyhedral frameworks with optimal molecular dynamics and pore geometry for methane storage

Author

Yan, Yong, Kolokolov, Daniil I., da Silva, Ivan, Stepanov, Alexander G., Blake, Alexander J., Dailly, Anne, Manuel, Pascal, Tang, Chiu C., and Yang, Sihai

Abstract

Natural gas (methane, CH4) is widely considered as a promising energy carrier for mobile applications. Maximising the storage capacity is the primary goal for the design of future storage media. Here we report the CH4 storage properties in a family of isostructural (3,24)-connected porous materials, MFM-112a, MFM-115a and MFM-132a with different linker backbone functionalisation. Both MFM-112a and MFM-115a show excellent CH4 uptakes of 236 and 256 cm3 (STP) cm–3 (v/v) at 80 bar and room temperature, respectively. Significantly, MFM-115a displays an exceptionally high deliverable CH4 capacity of 208 v/v between 5 and 80 bar at room temperature, making it among the best performing MOFs for methane storage. We also synthesized the partially deuterated versions of the above materials and applied solid-state 2H NMR spectroscopy to show that these three frameworks contain molecular rotors which exhibit motion in fast, medium and slow regimes, respectively. In situ neutron powder diffraction studies on the binding sites for CD4 within MFM-132a and MFM-115a reveal that the primary binding site is located within the small pocket enclosed by the [(Cu2)3(isophthalate)3] window and three anthracene/phenyl panels. The open Cu(II) sites are the secondary/tertiary adsorption sites in these structures. Thus, we obtained direct experimental evidence showing that a tight cavity can generate a stronger binding affinity to gas molecules than open metal sites. Thus, solid-state 2H NMR and neutron diffraction studies revealed that it is the combination of optimal molecular dynamics, pore geometry and size, and favourable binding sites that leads to the exceptional and different methane uptakes in these materials.

Published
2017

283. Post-synthetic modulation of the charge distribution in a metal–organic framework for optimal binding of carbon dioxide and sulfur dioxide

Author

Li, Lei, primary, da Silva, Ivan, additional, Kolokolov, Daniil I., additional, Han, Xue, additional, Li, Jiangnan, additional, Smith, Gemma, additional, Cheng, Yongqiang, additional, Daemen, Luke L., additional, Morris, Christopher G., additional, Godfrey, Harry G. W., additional, Jacques, Nicholas M., additional, Zhang, Xinran, additional, Manuel, Pascal, additional, Frogley, Mark D., additional, Murray, Claire A., additional, Ramirez-Cuesta, Anibal J., additional, Cinque, Gianfelice, additional, Tang, Chiu C., additional, Stepanov, Alexander G., additional, Yang, Sihai, additional, and Schroder, Martin, additional

Published
2019
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285. The accuracy challenge of the DFT-based molecular assignment of 13C MAS NMR characterization of surface intermediates in zeolite catalysis.

Author

Kolganov, Alexander A., Gabrienko, Anton A., Chernyshov, Ivan Yu., Stepanov, Alexander G., and Pidko, Evgeny A.

Abstract

The influence of the model and method choice on the DFT predicted 13C NMR chemical shifts of zeolite surface methoxide species has been systematically analyzed. Twelve 13C NMR chemical shift calculation protocols on full periodic and hybrid periodic–cluster DFT calculations with varied structural relaxation procedures are examined. The primary assessment of the accuracy of the computational protocols has been carried out for the Si–O(CH3)–Al surface methoxide species in ZSM-5 zeolite with well-defined experimental NMR parameters (chemical shift, δ(13C) value) as a reference. Different configurations of these surface intermediates and their location inside the ZSM-5 pores are considered explicitly. The predicted δ value deviates by up to ±0.8 ppm from the experimental value of 59 ppm due to the varied confinement of the methoxide species at different zeolite sites (model accuracy). The choice of the exchange–correlation functional (method accuracy) introduces ±1.5 ppm uncertainty in the computed chemical shifts. The accuracy of the predicted 13C NMR chemical shifts for the computational assignment of spectral characteristics of zeolite intermediates has been further analyzed by considering the potential intermediate species formed upon methane activation by Cu/ZSM-5 zeolite. The presence of Cu species in the vicinity of surface methoxide increases the prediction uncertainty to ±2.5 ppm. The full geometry relaxation of the local environment of an active site at an appropriate level of theory is critical to ensure a good agreement between the experimental and computed NMR data. Chemical shifts (δ) calculated via full geometry relaxation of a cluster model of a relevant portion of the zeolite lattice site are in the best agreement with the experimental values. Our analysis indicates that the full geometry optimization of a cluster model at the PBE0-D3/6-311G(d,p) level of theory followed by GIAO/PBE0-D3/aug-cc-pVDZ calculations is the most suitable approach for the calculation of 13C chemical shifts of zeolite surface intermediates. [ABSTRACT FROM AUTHOR]

Published
2020
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287. Determination of Hyperfine Coupling Constants of Fluorinated Diphenylacetylene Radical Anions by Magnetic Field-Affected Reaction Yield Spectroscopy

Author

Sannikova, Victoria A., primary, Davydova, Maria P., additional, Sherin, Peter S., additional, Babenko, Simon V., additional, Korolev, Valeri V., additional, Stepanov, Alexander A., additional, Nikul’shin, Pavel V., additional, Kalneus, Evgeny V., additional, Vasilevsky, Sergei F., additional, Benassi, Enrico, additional, and Melnikov, Anatoly R., additional

Published
2018
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289. Ammonia as Proton Conducting Medium Confined in Porous Materials

Author

Lim, Dae-Woon, primary, Tsukada, Hiromu, primary, Shigematsu, Akihito, primary, Yamada, Teppei, primary, Otsubo, Kazuya, primary, Khudozhitkov, Alexander E., primary, Stepanov, Alexander G., primary, Kolokolov, Daniil I., primary, Maesato, Mitsuhiko, primary, and Kitagawa, Hiroshi, primary

Published
2018
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292. Enhancement of Proton Conductivity in Nonporous Metal–Organic Frameworks: The Role of Framework Proton Density and Humidity

Author

Pili, Simona, primary, Rought, Peter, additional, Kolokolov, Daniil I., additional, Lin, Longfei, additional, da Silva, Ivan, additional, Cheng, Yongqiang, additional, Marsh, Christopher, additional, Silverwood, Ian P., additional, García Sakai, Victoria, additional, Li, Ming, additional, Titman, Jeremy J., additional, Knight, Lyndsey, additional, Daemen, Luke L., additional, Ramirez-Cuesta, Anibal J., additional, Tang, Chiu C., additional, Stepanov, Alexander G., additional, Yang, Sihai, additional, and Schröder, Martin, additional

Published
2018
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297. Generic programming

Author

Musser, David R., Stepanov, Alexander A., Goos, G., editor, Hartmanis, J., editor, Barstow, D., editor, Brauer, W., editor, Brinch Hansen, P., editor, Gries, D., editor, Luckham, D., editor, Moler, C., editor, Pnueli, A., editor, Seegmüller, G., editor, Stoer, J., editor, Wirth, N., editor, and Gianni, P., editor

Published
1989
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298. Tecton: A language for manipulating generic objects

Author

Kapur, Deepak, Musser, David R., Stepanov, Alexander A., Goos, G., editor, Hartmanis, J., editor, Brauer, W., editor, Brinch Hansen, P., editor, Gries, D., editor, Moler, C., editor, Seegmüller, G., editor, Stoer, J., editor, Wirth, N., editor, and Staunstrup, Jørgen, editor

Published
1982
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299. Tailoring porosity and rotational dynamics in a series of octacarboxylate metal-organic frameworks

Author

Moreau, Florian, Kolokolov, Daniil L., Stepanov, Alexander G., Easun, Timothy L., Dailly, Anne, Lewis, William, Blake, Alexander J., Nowell, Harriett, Lennox, Matthew J., Besley, Elena, and Yang, Sihai

Subjects
metal organic framework, crystal engineering, methane, 2H NMR, molecular dynamics
Abstract

Modulation and precise control of porosity of metal-organic frameworks (MOFs) are of critical importance to their materials function. Here we report the first modulation of porosity for a series of isoreticular octacarboxylate MOFs, denoted MFM-180 to MFM-185, via a strategy of selective elongation of metal-organic cages. Owing to the high ligand connectivity, these MOFs show absence of network interpenetration, robust structures and permanent porosity. Interestingly, activated MFM-185a shows a record high BET surface area of 4734 m2 g-1 for an octacarboxylate MOF. These MOFs show remarkable CH4 and CO2 adsorption properties, notably with simultaneously high gravimetric and volumetric deliverable CH4 capacities of 0.24 g g-1 and 163 v/v (298 K, 5-65 bar) recorded for MFM-185a due to selective elongation of tubular cages. Dynamics of molecular rotors in deuterated MFM-180a-d16 and MFM-181a-d16 were investigated by variable-temperature 2H solid state NMR spectroscopy to reveal the reorientation mechanisms within these materials. Analysis of the flipping modes of the mobile phenyl groups on the linkers, their rotational rates and transition temperatures, paves the way to controlling and understanding the role of molecular rotors through organic linker design within porous MOF materials.

Published
2017

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