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S. V. Bhat - One of the best experts on this subject based on the ideXlab platform.
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Spin Probe EsR Studies on Nanocomposite Polymer Electrolytes
Applied Magnetic Resonance, 2009Co-Authors: Madhurjya Modhur Borgohain, D. Banerjee, L. Korecz, S. V. BhatAbstract:The possibility of using Spin-Probe electron Spin resonance (ESR) as a tool to study glass transition temperature, T g, of polymer electrolytes is explored in 4-hydroxy-2,2,6,6-tetramethylpiperidine-N-oxyl (TEMPOL)-doped composite polymer electrolyte (PEG)46LiClO4 dispersed with nanoparticles of hydrotalcite. The T g is estimated from the measured values of T 50G, the temperature at which the extrema separation 2A zz of the broad powder spectrum decreases to 50 G. In another method, the correlation time τc for the Spin Probe dynamics was determined by computer simulation of the ESR spectra and T g has been identified as the temperature at which τc begins to show temperature dependence. While both methods give values of T g close to those obtained from differential scanning calorimetry, it is concluded that more work is required to establish Spin-Probe ESR as a reliable technique for the determination of T g.
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Spin Probe ESR Signature of Freezing in Water: Is it Global or Local?
arXiv: Soft Condensed Matter, 2008Co-Authors: Debamalya Banerjee, S. V. BhatAbstract:First systematic Spin Probe ESR study of water freezing has been conducted using TEMPOL and TEMPO as the Probes. The Spin Probe signature of the water freezing has been described in terms of the collapse of narrow triplet spectrum into a single broad line. This Spin Probe signature of freezing has been observed at an anomalously low temperature when a milimoler solution of TEMPOL is slowly cooled from room temperature. A systematic observation has revealed a Spin Probe concentration dependence of these freezing and respective melting points. These results can be explained in terms of localization of Spin Probe and liquid water, most probably in the interstices of ice grains, in an ice matrix. The lowering of Spin Probe freezing point, along with the secondary evidences, like Spin Probe concentration dependence of peak-to-peak width in frozen limit signal, indicates a possible size dependence of these localizations/entrapments with Spin Probe concentration. A weak concentration dependence of Spin Probe assisted freezing and melting points, which has been observed for TEMPO in comparison to TEMPOL, indicates different natures of interactions with water of these two Probes. This view is also supported by the relaxation behavior of the two Probes.
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Spin Probe Signature of Freezing in Water Slow Cooling Experiment: Our Observation is Global or Local?
2008Co-Authors: Debamalya Banerjee, S. V. BhatAbstract:First systematic Spin Probe ESR study of water freezing has been conducted using TEMPOL and TEMPO as the Probes. The Spin Probe signature of the water freezing has been described in terms of the collapse of narrow triplet spectrum into a single broad line. This Spin Probe signature of freezing has been observed at an anomalously low temperature when a milimoler solution of TEMPOL is slowly cooled from room temperature. A systematic observation has revealed a Spin Probe concentration dependence of these freezing and respective melting points. These results can be explained in terms of localization of Spin Probe and liquid water,most probably in the interstices of ice grains, in an ice matrix. The lowering of Spin Probe freezing point, along with the secondary evidences, like Spin Probe concentration dependence of peak-to-peak width in frozen limit signal, indicates a possible size dependence of these localizations/entrapments with Spin Probe concentration. A weak concentration dependence of Spin Probe assisted freezing and melting points, which has been observed for TEMPO in comparison to TEMPOL, indicates different natures of interactions with water of these two Probes. This view is also supported by the relaxation behavior of the two Probes.
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vitrification and glass transition of water insights from Spin Probe esr
Physical Review Letters, 2005Co-Authors: Shrivalli N Bhat, Ajay Sharma, S. V. BhatAbstract:Three long-standing problems related to the physics of water, viz., the possibility of vitrifying bulk water by rapid quenching, its glass transition, and the supposed impossibility of obtaining supercooled water between 150 and 233 K, the so-called "no man's land" of its phase diagram, are studied using the highly sensitive technique of Spin Probe ESR. Our results suggest that water can indeed be vitrified by rapid quenching; it undergoes a glass transition at approximately 135 K, and the relaxation behavior studied using this method between 165 K and 233 K closely follows the predictions of the Adam-Gibbs model.
C. J. Rhodes - One of the best experts on this subject based on the ideXlab platform.
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Monitoring the Tetraethyl Orthosilicate (TEOS)-Based Sol–Gel Process with Cu(II) Ions as a Spin Probe
Applied Magnetic Resonance, 2016Co-Authors: M. Mazúr, L. Husáriková, M. Valko, C. J. RhodesAbstract:The various stages of the tetraethyl orthosilicate-based sol–gel process were investigated using electron paramagnetic resonance (EPR) spectroscopy with Cu(II) cations as a Spin Probe. The latter were introduced to the starting reaction mixture in the form of various copper(II) salts containing anions of different basicity (CuCl_2, Cu(ac)_2, or CuSO_4). At the various defined stages of the sol–gel process, the experimental EPR spectra, recorded at both ambient and liquid nitrogen temperature, were found to be a superimposition of three main types of individual subspectra ( Γ _1, Γ _2, and Φ ), which reflect the different local environment in which the Cu(II) ions were located. The Spin Hamiltonian parameters of each individual subspectrum remained identical, within experimental error, throughout the various stages of the sol–gel process. In contrast, the relative proportion of the individual subspectra varied significantly as the sol–gel process proceeded, from which the liquid-state to solid-state transition could be monitored as it occurred in the sol–gel reaction medium. Identical results were obtained, irrespective of the nature of the copper(II) salt employed. The results demonstrate that the EPR method provides an effective means with which to monitor the sol-to-gel transition from the viscous, colloid suspension to the final viscoelastic gel.
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Monitoring the Tetraethyl Orthosilicate (TEOS)-Based Sol–Gel Process with Cu(II) Ions as a Spin Probe
Applied Magnetic Resonance, 2016Co-Authors: M. Mazúr, L. Husáriková, M. Valko, C. J. RhodesAbstract:The various stages of the tetraethyl orthosilicate-based sol–gel process were investigated using electron paramagnetic resonance (EPR) spectroscopy with Cu(II) cations as a Spin Probe. The latter were introduced to the starting reaction mixture in the form of various copper(II) salts containing anions of different basicity (CuCl_2, Cu(ac)_2, or CuSO_4). At the various defined stages of the sol–gel process, the experimental EPR spectra, recorded at both ambient and liquid nitrogen temperature, were found to be a superimposition of three main types of individual subspectra ( Γ _1, Γ _2, and Φ ), which reflect the different local environment in which the Cu(II) ions were located. The Spin Hamiltonian parameters of each individual subspectrum remained identical, within experimental error, throughout the various stages of the sol–gel process. In contrast, the relative proportion of the individual subspectra varied significantly as the sol–gel process proceeded, from which the liquid-state to solid-state transition could be monitored as it occurred in the sol–gel reaction medium. Identical results were obtained, irrespective of the nature of the copper(II) salt employed. The results demonstrate that the EPR method provides an effective means with which to monitor the sol-to-gel transition from the viscous, colloid suspension to the final viscoelastic gel.
M. A. Hemminga - One of the best experts on this subject based on the ideXlab platform.
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Molecular mobility in the cytoplasm: an approach to describe and predict lifespan of dry germplasm.
Proceedings of the National Academy of Sciences of the United States of America, 2000Co-Authors: J Buitink, M. A. Hemminga, O Leprince, F A HoekstraAbstract:Molecular mobility is increasingly considered a key factor influencing storage stability of biomolecular substances, because it is thought to control the rate of detrimental reactions responsible for reducing the shelf life of, for instance, pharmaceuticals, food, and germplasm. We investigated the relationship between aging rates of germplasm and the rotational motion of a polar Spin Probe in the cytoplasm under different storage conditions using saturation transfer electron paramagnetic resonance spectroscopy. Rotational motion of the Spin Probe in the cytoplasm of seed and pollen of various plant species changed as a function of moisture content and temperature in a manner similar to aging rates or longevity. A linear relationship was established between the logarithms of rotational motion and aging rates or longevity. This linearity suggests that detrimental aging rates are associated with molecular mobility in the cytoplasm. By measuring the rotational correlation times at low temperatures at which experimental determination of longevity is practically impossible, this linearity enabled us to predict vigor loss or longevity. At subzero temperatures, moisture contents for maximum life span were predicted to be higher than those hitherto used in genebanks, urging for a reexamination of seed storage protocols.
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Is there a role for oligosaccharides in seed longevity? An assessment of intracellular glass stability.
Plant Physiology, 2000Co-Authors: J Buitink, M. A. Hemminga, F A HoekstraAbstract:We examined whether oligosaccharides extend seed longevity by increasing the intracellular glass stability. For that purpose, we used a Spin Probe technique to measure the molecular mobility and glass transition temperature of the cytoplasm of impatiens (Impatiens walleriana) and bell pepper (Capsicum annuum) seeds that were osmo-primed to change oligosaccharide content and longevity. Using saturation transfer electron paramagnetic resonance spectroscopy, we found that the rotational correlation time of the polar Spin Probe 3-carboxy-proxyl in the cytoplasm decreased, together with longevity, as a function of increasing seed water content, suggesting that longevity may indeed be regulated by cytoplasmic mobility. Osmo-priming of the seeds resulted in considerable decreases in longevity and oligosaccharide content, while the sucrose content increased. No difference in the glass transition temperature was found between control and primed impatiens seeds at the same temperature and water content. Similarly, there was no difference in the rotational motion of the Spin Probe in the cytoplasm between control and primed impatiens and bell pepper seeds. We therefore conclude that oligosaccharides in seeds do not affect the stability of the intracellular glassy state, and that the reduced longevity after priming is not the result of increased molecular mobility in the cytoplasm.
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A Spin Probe ESR study of sugar water mixtures in the liquid and glassy state.
Electron Spin Resonance (ESR) Applications in Organic and Bioorganic Materials, 1992Co-Authors: M. J. G. W. Roozen, P. Walstra, T. Van Vliet, M. A. HemmingaAbstract:Conventional and saturation transfer ESR spectroscopy are used to study the rotational behaviour of two different nitroxide Spin Probes: 4-hydroxy, 2,2,6,6-tetra-methylpiperidino-oxyl (TEMPOL) and 3-maleimido-2,2,5,5,tetra-methyl-1pyrrolodinyloxyl in glycerol water, sucrose water and dextrin water mixtures as a function of temperature. In the liquid state the results are discussed in terms of slip and stickiness of the Spin Probes, which depend on the strength of the hydrogen bonds between the Spin Probe and the solvent. Except for the malemeimido Spin Probe in anhydrous glycerol, which can form an extended solvation shell, the slip increases as the water content of the mixture decreases. This is explained by a decrease of hydrogen bonds between the Spin Probe and the solvent. In sucrose water mixtures above 70% by weight sucrose and in sucrose water mixtures in the glassy state the Spin Probes are presumably present in cavities. At the temperature at which the transition from glassy state to solution takes place an extreme increase in rotational mobility of the Spin Probes can be observed. The temperature at which this increase is observed agrees reasonably well with the glass transition temperature as determined by differential scanning calorimetry experiments. The apparent activation energy for rotation in glassy maltodextrin increases as the molecular weight becomes larger, presumably due to a decrease in the free volume of the sample. No influence of the water content of the glassy samples at temperatures above the freezing point of water on the apparent activation energy is observed.
Gunter Grampp - One of the best experts on this subject based on the ideXlab platform.
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room temperature ionic liquids discerned via nitroxyl Spin Probe dynamics
Journal of Physical Chemistry B, 2011Co-Authors: Boryana Mladenova, Daniel R Kattnig, Gunter GramppAbstract:The temperature dependence of the rotational correlation times, τ(c), of the nitroxide Spin Probes TEMPO, TEMPOL, TEMPAMINE, and Fremy's salt in the ionic liquids 1-ethyl-3-methylimidazolium ethylsulfate, 1-butyl-3-methylimidazolium hexafluorophosphate, 1-ethyl-3-methylimidazolium tetrafluoroborate, and 1-butyl-3-methylimidazolium tetrafluoroborate is scrutinized. The rotation correlation times vary between 54 and 1470 ps at 300 K. Within a temperature range of 280-380 K, the rotational tumbling is well described by the extended Debye-Stokes-Einstein law. The hydrodynamic radii are smaller than the geometrical radii though. This discrepancy can partly be accounted for by microviscosity effects and deviations from the spherical shape. This study is distinguished from similar studies by the fact that proton superhyperfine coupling constants could be resolved for all nitroxides in the ionic liquids by carefully optimizing the experimental protocol. As a consequence, many rotational correlation times reported here are smaller than those found previously. Furthermore, the temperature dependence of the nitrogen ESR coupling constants is reported and discussed in detail. A surprising effect of adventitious water is reported for TEMPAMINE.
Elisa Riedo - One of the best experts on this subject based on the ideXlab platform.
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imaging thermal conductivity with nanoscale resolution using a scanning Spin Probe
Nature Communications, 2015Co-Authors: Abdelghani Laraoui, Halley Aycockrizzo, Yang Gao, Elisa Riedo, Carlos A MerilesAbstract:The ability to Probe nanoscale heat flow in a material is often limited by lack of spatial resolution. Here, we use a diamond-nanocrystal-hosted nitrogen-vacancy centre attached to the apex of a silicon thermal tip as a local temperature sensor. We apply an electrical current to heat up the tip and rely on the nitrogen vacancy to monitor the thermal changes the tip experiences as it is brought into contact with surfaces of varying thermal conductivity. By combining atomic force and confocal microscopy, we image phantom microstructures with nanoscale resolution, and attain excellent agreement between the thermal conductivity and topographic maps. The small mass and high thermal conductivity of the diamond host make the time response of our technique short, which we demonstrate by monitoring the tip temperature upon application of a heat pulse. Our approach promises multiple applications, from the investigation of phonon dynamics in nanostructures to the characterization of heterogeneous phase transitions and chemical reactions in various solid-state systems.
