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| 3. |
- Bergman, Rikard, 1966, et al.
(författare)
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Slow Debye-type peak observed in the dielectric response of polyalcohols
- 2010
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 1089-7690 .- 0021-9606. ; 132:4
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Tidskriftsartikel (refereegranskat)abstract
- Dielectric relaxation spectroscopy of glass forming liquids normally exhibits a relaxation scenario that seems to be surprisingly general. However, the relaxation dynamics is more complicated for hydrogen bonded liquids. For instance, the dielectric response of monoalcohols is dominated by a mysterious Debye-like process at lower frequencies than the structural alpha-relaxation that is normally dominating the spectra of glass formers. For polyalcohols this process has been thought to be absent or possibly obscured by a strong contribution from conductivity and polarization effects at low frequencies. We here show that the Debye-like process, although much less prominent, is also present in the response of polyalcohols. It can be observed in the derivative of the real part of the susceptibility or directly in the imaginary part if the conductivity contribution is reduced by covering the upper electrode with a thin Teflon layer. We report on results from broadband dielectric spectroscopy studies of several polyalcohols: glycerol, xylitol, and sorbitol. The findings are discussed in relation to other experimental observations of ultraslow (i.e., slower than the viscosity related alpha-relaxation) dynamics in glass formers.
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| 4. |
- Berntsen, Peter, 1974, et al.
(författare)
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Dielectric and calorimetric studies of hydrated purple membrane
- 2005
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Ingår i: Biophysical Journal. - : Elsevier BV. - 0006-3495 .- 1542-0086. ; 89:5, s. 3111-3128
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Tidskriftsartikel (refereegranskat)abstract
- Purple membranes (PM) from halobacteria were hydrated to ∼0.4 and ∼0.2 g H 2 O/g of PM and studied by dielectric spectroscopy and differential scanning calorimetry between 120 and 300 K. The dielectric process, attributed to a local (β) relaxation of the confined supercooled water, shows an Arrhenius temperature behavior at low temperatures. In the case of the most hydrated PM a small deviation from the Arrhenius behavior occurs at 190-200 K together with a pronounced endothermic process and an increased activation energy. The observed crossover is accompanied by a reduction of the interlayer spacing due to the partial loss of the intermembrane water. All these effects at ∼200 K are consistent with a scenario where the local relaxation process merges with a nonobservable α-relaxation of the interlayer water, giving rise to a more liquid-like behavior of the interfacial water. For the less hydrated sample the effects are less pronounced and shift to a slightly higher temperature. © 2005 by the Biophysical Society.
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| 13. |
- Jansson, Helen, 1964, et al.
(författare)
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Hidden Slow Dynamics in Water
- 2010
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Ingår i: Physical Review Letters. - 1079-7114 .- 0031-9007. ; 104:1
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Tidskriftsartikel (refereegranskat)abstract
- It is well known that the structural and dynamical properties of water are of central importance for life on our planet. However, despite this knowledge its structural and dynamical properties are still far from fully understood. In this Letter we show for the first time that water exhibits an anomalously slow relaxation process, which is about 4 orders of magnitude slower than the viscosity-related structural main relaxation. This slow Debye-like process has previously only been observed in monoalcohols and more recently also in polyalcohols, and due to its slowness it is generally believed to be caused by some kind of collective motion of hydrogen-bonded structures. The new finding has important structural and dynamical implications for water.
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| 15. |
- Jansson, Helen, 1964, et al.
(författare)
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Role of Solvent for the Dynamics and the Glass Transition of Proteins
- 2011
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Ingår i: Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1520-5207 .- 1520-6106. ; 115:14, s. 4099-4109
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Tidskriftsartikel (refereegranskat)abstract
- For the first time, a systematic investigation of the glass transition and its related dynamics of myoglobin in water-glycerol solvent mixtures of different water contents is presented. By a combination of broadband dielectric spectroscopy and differential scanning calorimetry (DSC), we have studied the relation between the protein and solvent dynamics with the aim to better understand the calorimetric glass transition, T-g, of proteins and the role of solvent for protein dynamics. The results show that both the viscosity related alpha-relaxation in the solvent as well as several different protein relaxations are involved in the calorimetric glass transition, and that the broadness (Delta T-g) of the transition depends strongly on the total amount of solvent. The main reason for this seems to be that the protein relaxation processes become more separated in time with decreasing solvent level. The results are compared to that of hydrated myoglobin where the hydration water does not give any direct contribution to the calorimetric T-g. However, the large-scale a-like relaxation in the hydration water is still responsible for the protein dynamics that freeze-in at T-g. Finally, the dielectric data show clearly that the protein relaxation processes exhibit similar temperature dependences as the alpha-relaxation in the solvent, as suggested for solvent-slaved protein motions.
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| 16. |
- Jansson, Helen, 1964, et al.
(författare)
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Slow dielectric response of Debye-type in water and other hydrogen bonded liquids
- 2010
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Ingår i: Journal of Molecular Structure. - : Elsevier BV. - 0022-2860. ; 972:1-3, s. 92-98
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Tidskriftsartikel (refereegranskat)abstract
- The slow dynamics of some hydrogen bonded glass-forming liquids has been investigated by broadband dielectric spectroscopy. We show that the polyalcohols glycerol, xylitol, and sorbitol, and mixtures of glycerol and water, and in fact, even pure water exhibit a process of Debye character at longer time-scales than the glass transition and viscosity related alpha-relaxation. Even if it is less pronounced, this process displays many similarities to the well-studied Debye-like process in monoalcohols. It can be observed in both the negative derivative of the real part of the permittivity or in the imaginary part of the permittivity, if the conductivity contribution is reduced. In the present study the conductivity contribution has been suppressed by use of a thin Teflon film placed between the sample and one of the electrodes. The new findings might have important implications for the structure and dynamics of hydrogen bonded liquids in general, and for water in particular. (c) 2010 Elsevier B.V. All rights reserved.
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| 17. |
- Sjöström, Johan, 1978, et al.
(författare)
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Dielectric secondary relaxation of water in aqueous binary glass-formers
- 2010
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Ingår i: Physical Chemistry Chemical Physics. - : Royal Society of Chemistry (RSC). - 1463-9084 .- 1463-9076. ; 12:35, s. 10452-10456
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Tidskriftsartikel (refereegranskat)abstract
- Glassy aqueous binary mixtures generally exhibit a water induced dielectric relaxation. The characteristic time-scale of this relaxation follows an Arrhenius temperature dependence with a nearly universal activation energy. We here demonstrate for a series of model aqueous mixtures that the relaxation time also follows a remarkably general exponential dependence on the weight fraction of water. By comparison to literature data we show that this behaviour is shared by a wide range of molecular systems. Neither the detailed nature of the water molecules' glassy environment nor the details of the route of formation of the glassy state has a significant effect on the observed behaviour.
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| 18. |
- Sjöström, Johan, 1978, et al.
(författare)
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Effects of Water Contamination on the Supercooled Dynamics of a Hydrogen-Bonded Model Glass Former
- 2011
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Ingår i: Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1520-5207 .- 1520-6106. ; 115:8, s. 1842-1847
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Tidskriftsartikel (refereegranskat)abstract
- Broad-band dielectric spectroscopy is a commonly used tool in the study of glass-forming liquids. The high sensitivity of the technique together with the wide range of probed time scales makes it a powerful method for investigating the relaxation spectra of liquids. One particularly important class of glass-forming liquids that is often studied using this technique consists of liquids dominated by hydrogen (H) bond interactions. When investigating such liquids, particular caution has to be taken during sample preparation due to their often highly hygroscopic nature. Water can easily be absorbed from the atmosphere, and dielectric spectroscopy is a very sensitive probe of such contamination due to the large dipole moment of water. Our knowledge concerning the effects of small quantities of water on the dielectric properties of these commonly investigated liquids is limited. We here demonstrate the effects due to the presence of small amounts of water on the dielectric response of a typical H-bonded model glass former, tripropylene glycol. We show how the relaxation processes present in the pure liquid are affected by addition of water, and we find that a characteristic water induced relaxation response is observed for water contents as low as 0.15 wt %. We stress the importance of careful purification of hygroscopic liquids before experiments and quantify what the effects are if such procedures are not undertaken.
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| 19. |
- Sjöström, Johan, 1978, et al.
(författare)
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Hydrogen Bond Induced Nonmonotonic Composition Behavior of the Glass Transition in Aqueous Binary Mixtures
- 2011
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Ingår i: Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1520-5207 .- 1520-6106. ; 115:33, s. 10013-10017
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Tidskriftsartikel (refereegranskat)abstract
- The glass transition temperature, T(g), of a binary mixture commonly varies monotonically between the T(g)s of its two components. However, mixtures of strongly associating liquids can instead exhibit a nonmonotonic T(g) variation. The origins of such nonideal mixing behavior have often been correlated with composition dependent structural variations. For binary mixtures between a hydrogen- (H-) bonded liquid and water, however, such behavior is generally not well understood. The ubiquity and importance of aqueous mixtures both in nature and in man-made applications stresses the needed for a better understanding. We here demonstrate nonmonotonic T(g) variations in binary mixtures of n-propylene glycol monomethyl ethers (nPGMEs) and water, where the composition dependent T(g) show maxima within an intermediate composition range. We show that these T(g) maxima correspond to crossovers in the composition dependence of the step amplitude in the isobaric heat capacity at T(g). We further demonstrate that the observed effects are caused by H-bond interactions involving the nPGME hydroxyl group. We can account for our obervations using a simple model based on two effects due to the added water: (i) an H-bond induced formation of effective relaxing entities and (ii) a plasticizing effect at high water contents.
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| 20. |
- Sjöström, Johan, 1978, et al.
(författare)
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Investigating hydration dependence of dynamics of confined water: Monolayer, hydration water and Maxwell-Wagner processes
- 2008
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 1089-7690 .- 0021-9606. ; 128:15, s. art. nr. 154503-
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Tidskriftsartikel (refereegranskat)abstract
- The dynamics of water confined in silica matrices MCM-41 C10 and C18, with pore diameter of 21 and 36 Å, respectively, is examined by broadband dielectric spectroscopy (10-2 - 109 Hz) and differential scanning calorimetry for a wide temperature interval (110-340 K). The dynamics from capillary condensed hydration water and surface monolayer of water are separated in the analysis. Contrary to previous reports, the rotational dynamics are shown to be virtually independent on the hydration level and pore size. Moreover, a third process, also reported for other systems, and exhibiting a saddlelike temperature dependence is investigated. We argue that this process is due to a Maxwell-Wagner process and not to strongly bound surface water as previously suggested in the literature. The dynamics of this process is strongly dependent on the amount of hydration water in the pores. The anomalous temperature dependence can then easily be explained by a loss of hydration water at high temperatures in contradiction to previous explanations. © 2008 American Institute of Physics.
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| 21. |
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| 22. |
- Swenson, Jan, 1966, et al.
(författare)
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Anomalous behaviour of supercooled water and its implication for protein dymamics
- 2008
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Ingår i: Lecture Notes in Physics; Aspects of Physical Biology: Biological water, Protein solutions,Transport and Replication. - Berlin : Springer-Verlag Berlin. - 9783540787648 ; , s. 23-42
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Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- Water is the foundation of life, and without it life as we know it would not exist. An organism consists to a large extent of water and, apart from a few larger reservoirs, almost all water in a living organism is closely associated with surfaces of biomolecules of different kinds. This so-called biological water is known to affect the dynamics of biomaterials such as proteins, which. in turn is crucial for its functions. However, how and why the surrounding environment affects the dynamics of proteins and other biomolecules is still not fully understood. Recently, it was suggested [Fenimore et al. PNAS 2004, 101 14408] that local and more global protein motions are slaved (or driven) by the local beta-relaxation and the more large-scale cooperative a-relaxation in the surrounding solvent, respectively. In this chapter we present results from dielectric measurements on myoglobin in water-glycerol mixtures that support this slaving idea. Moreover, we show how confined supercooled water changes its dynamical behaviour from a low temperature Arrhenius behaviour to a high temperature non-Arrhenius behaviour at a certain temperature (around 200 K), and then we discuss likely explanations for the crossover and its consequence for protein dynamics.
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| 30. |
- Mattsson, Johan, 1969, et al.
(författare)
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Effects of hydrogen bonding on supercooled liquid dynamics and the implications for supercooled water
- 2009
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Ingår i: Physical Review B - Condensed Matter and Materials Physics. - 2469-9950 .- 2469-9969. ; 79:17, s. 174205-
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Tidskriftsartikel (refereegranskat)abstract
- The supercooled state of bulk water is largely hidden by unavoidable crystallization, which creates an experimentally inaccessible temperature regime - a "no man's land." We address this, and circumvent the crystallization problem by systematically studying the supercooled dynamics of hydrogen bonded oligomeric liquids (glycols), where water corresponds to the chain ends alone. This approach permits a "dilution of water" by altering the hydrogen bond concentration via variations in chain length. We observe a dynamic crossover in the temperature dependence of the structural relaxation time for all glycols, consistent with the common behavior of most supercooled liquids. We find that the crossover becomes more pronounced for increasing hydrogen bond concentrations, which leads to the prediction of a marked dynamic transition for water within "no man's land" at T similar to 220 K. Interestingly, the predicted transition thus takes place at a temperature where a so called "strong-fragile" transition has previously been suggested. Our results, however, imply that the dynamic transition of supercooled water is analogous to that commonly observed in supercooled liquids. Moreover, we find support also for the existence of a secondary relaxation of water with behavior analogous to that of the secondary relaxation observed for the glycols.
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| 37. |
- Svanberg, Christer, 1970, et al.
(författare)
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Secondary relaxation in confined and bulk propylene carbonate
- 2003
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Ingår i: Europhysics Letters. - : IOP Publishing. - 0295-5075 .- 1286-4854. ; 64:3, s. 358-363
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Tidskriftsartikel (refereegranskat)abstract
- Dielectric loss spectra of propylene carbonate in bulk and dissolved in a polymer matrix are investigated with focus on the currently debated excess wing. The spatial restrictions caused by the polymer matrix slow down the main structural (α) relaxation, while the excess wing continuously transforms towards a shoulder with increasing spatial restrictions. We show that the excess wing in a consistent manner can be described by a secondary relaxation with only a weak dependence of the concentration of polymer. Thus the results imply that the excess wing is due to a secondary relaxation submerged in the α-relaxation.
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