| 1. |
- Bogdanova, Ekaterina, et al.
(författare)
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Assessment of activation energy of enthalpy relaxation in sucrose-water system : effects of DSC cycle type and sample thermal history
- 2022
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Ingår i: Journal of thermal analysis and calorimetry (Print). - : Springer. - 1388-6150 .- 1588-2926. ; 147, s. 9695-9709
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Tidskriftsartikel (refereegranskat)abstract
- The purpose of this study is to critically analyze different methods of calculation of activation energy of relaxation in sucrose-water system from differential scanning calorimetry data. We consider the use of different thermal cycles for calculations together with Moynihan and Kissinger equations. We study the effect of two methods of glass transition temperature determination (half-step and inflection point) on the activation energy values. Along with experimental DSC data, we use the data simulated using Tool-Narayanaswamy-Moynihan model to validate the use of cooling and heating curves and to check the reproducibility of the activation energy calculations. The obtained results show that the thermal cycle with equal cooling and heating rates provides the most reliable data set and the glass transition temperature definition using inflection point rather than half step can be recommended for calculations. Moreover, due to technical reasons, heating rather than cooling scans provide the most reliable results of activation energy calculations. Furthermore, a simple method based on the width of the glass transition region shows reasonable results for single scan experiments. The activation energies of the glass transition in sucrose-water system with different water contents and different thermal histories were studied. Since it is impossible to apply traditional methods based on Moynihan equation for the activation energy evaluation for freeze-dried samples, we propose using another method based on the properties of the recovery peak. Combining the results obtained by different methods, we present a dependence of activation energy in sucrose-water system on water content. The results show that water decreases the activation energy of relaxation process in sucrose matrix.
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| 2. |
- Bogdanova, Ekaterina
(författare)
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Effect of water on the glass transition and properties of solid-state pharmaceutical formulations
- 2022
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The aim of this thesis was to increase our knowledge of the glassy state and the glass transition phenomenon and to evaluate the effect of water on the glassy state. To accomplish this, investigations were focused on the amorphous sucrose-water (paper I, II, III), trehalose-water (paper I), maltodextrin-water (paper I), and lysozyme-sucrose-water (paper IV) systems.We studied temperature-induced and isothermal glass transition (I, II, III, IV), as well as the impact of water on the activation energy of the relaxation process (II). It has been shown that water undergoes glass transition with disaccharides, but in polysaccharides water dynamics is uncoupled from the polymer matrix. This results in differences in the water diffusion coefficient: water moves several orders of magnitude faster in the polymers than in disaccharides (I). Water reduces the activation energy of the relaxation process in the sucrose-water system (II). Attenuated water diffusion at sub-zero temperatures leads to a delay in water crystallization/melting in the sucrose-water system, which does not happen in a polysaccharide - water system (III). The Tg of the lysozyme-sucrose system increases with increasing lysozyme concentration, i.e., the DCp of the mixtures does not follow the prediction based on the properties of the pure components. Consequently, lysozyme does not modulate the glass transition of the sucrose matrix and the increase of the Tg of the mixtures is a result of the confinement of amorphous sucrose in the space between lysozyme molecules. The amorphous structure and unfolding of lysozyme in the presence of sucrose was investigated by DSC and SAXS. These data revealed an increase of the protein-protein distance upon addition of sucrose and upon heating, as a result of lysozyme unfolding (IV).
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| 3. |
- Bogdanova, Ekaterina, et al.
(författare)
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Hydration enthalpies of amorphous sucrose, trehalose and maltodextrins and their relationship with heat capacities.
- 2021
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Ingår i: Physical Chemistry, Chemical Physics - PCCP. - : Royal Society of Chemistry (RSC). - 1463-9076 .- 1463-9084. ; 23:26, s. 14433-14448
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Tidskriftsartikel (refereegranskat)abstract
- The mechanisms of glass transitions and the behavior of small solute molecules in a glassy matrix are some of the most important topics of modern thermodynamics. Water plays an important role in the physical and chemical stability of lyophilized biologics formulations, in which glassy carbohydrates act as cryoprotectants and stabilizers. In this study, sorption calorimetry was used for simultaneous measurements of water activity and the enthalpy of water sorption by amorphous sucrose, trehalose and maltodextrins. Moreover, the heat capacity of these carbohydrates in mixtures with water was measured by DSC in a broad range of water contents. The hydration enthalpies of glassy sucrose, trehalose and maltodextrins are exothermic, and the enthalpy change of water-induced isothermal glass transitions is higher for small molecules. The partial molar enthalpy of mixing of water in slow experiments is about -18 kJ mol-1, but less exothermic in the case of small molecules at fast hydration scan rates. By measuring the heat capacities of disaccharides and maltodextrins as a function of water content, we separated the contributions of carbohydrates and water to the total heat capacities of the mixtures. The combination of these data allowed testing of thermodynamic models describing the hydration-induced glass transitions. The heat capacity changes calculated by the fitting of the hydration enthalpy data for disaccharides are in good agreement with the heat capacity data obtained by DSC, while for maltodextrins, the effect of sub-Tg transitions should be taken into account. Combining the data obtained by different techniques, we found a distinct difference in the behavior of water in glassy polymers compared to that in glassy disaccharides. By understanding the behavior of water in glassy carbohydrates, these results can be used to improve the design of freeze-dried formulations of proteins and probiotics.
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| 4. |
- Bogdanova, Ekaterina, et al.
(författare)
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Influence of Cooling Rate on Ice Crystallization and Melting in Sucrose-Water System
- 2022
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Ingår i: Journal of Pharmaceutical Sciences. - : Elsevier B.V.. - 0022-3549 .- 1520-6017. ; 111:7, s. 2030-2037
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Tidskriftsartikel (refereegranskat)abstract
- The ice crystallization and melting in systems where the equilibrium state is difficult to reach is one of the growing areas in pharmaceutical freeze-drying research. The quality of the final freeze-dried product depends on the parameters of the cooling step, which affect the ice nucleation and growth. In this paper, we present a DSC study of ice crystallization and melting in a sucrose-water system. Using two different types of thermal cycles, we examine the influence of cooling and heating rates on the thermal behavior of sucrose-water solutions with water contents between 50 and 100 wt%. The DSC results show that low cooling rates provide crystallization at higher temperatures and lead to lower amount of non-freezing water. Consequently, the glass transition and ice melting properties observed upon heating depend on the cooling conditions in the preceding step. Based on the experimental results, we investigate the reasons for the existence of the two steps on DSC heating curves in sucrose-water systems: the glass transition step and the onset of ice melting. We show that diffusion of water can be the limiting factor for ice growth and melting in the sucrose-water system when the amorphous phase is in a liquid state. In particular, when the diffusion coefficient drops below 10−14 m2/sec, the ice crystals growth or melting becomes strongly suppressed even above the glass transition temperature. Understanding the diffusion limitations in the sucrose-water system can be used for the optimization of the freeze-drying protocols for proteins and probiotics. © 2022 The Authors
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| 5. |
- Bogdanova, Ekaterina, et al.
(författare)
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Lysozyme-Sucrose Interactions in the Solid State : Glass Transition, Denaturation, and the Effect of Residual Water
- 2023
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Ingår i: Molecular Pharmaceutics. - : American Chemical Society. - 1543-8384 .- 1543-8392. ; 20:9, s. 4664-
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Tidskriftsartikel (refereegranskat)abstract
- The freeze-drying of proteins, along with excipients, offers a solution for increasing the shelf-life of protein pharmaceuticals. Using differential scanning calorimetry, thermogravimetric analysis, sorption calorimetry, and synchrotron small-angle X-ray scattering (SAXS), we have characterized the properties at low (re)hydration levels of the protein lysozyme, which was freeze-dried together with the excipient sucrose. We observe that the residual moisture content in these samples increases with the addition of lysozyme. This results from an increase in equilibrium water content with lysozyme concentration at constant water activity. Furthermore, we also observed an increase in the glass transition temperature (Tg) of the mixtures with increasing lysozyme concentration. Analysis of the heat capacity step of the mixtures indicates that lysozyme does not participate in the glass transition of the sucrose matrix; as a result, the observed increase in the Tg of the mixtures is the consequence of the confinement of the amorphous sucrose domains in the interstitial space between the lysozyme molecules. Sorption calorimetry experiments demonstrate that the hydration behavior of this formulation is similar to that of the pure amorphous sucrose, while the presence of lysozyme only shifts the sucrose transitions. SAXS analysis of amorphous lysozyme-sucrose mixtures and unfolding of lysozyme in this environment show that prior to unfolding, the size and shape of lysozyme in a solid sucrose matrix are consistent with its native state in an aqueous solution. The results obtained from our study will provide a better understanding of the low hydration behavior of protein-excipient mixtures and support the improved formulation of biologics. © 2023 The Authors.
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| 6. |
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| 7. |
- Phan-Xuan, Tuan, et al.
(författare)
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Hydration-Induced Structural Changes in the Solid State of Protein : A SAXS/WAXS Study on Lysozyme
- 2020
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Ingår i: Molecular Pharmaceutics. - : American Chemical Society. - 1543-8384 .- 1543-8392. ; 17:9, s. 3246-3258
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Tidskriftsartikel (refereegranskat)abstract
- The stability of biol. produced pharmaceuticals is the limiting factor to various applications, which can be improved by formulation in solid-state forms, mostly via lyophilization. Knowledge about the protein structure at the mol. level in the solid state and its transition upon rehydration is however scarce, and yet it most likely affects the phys. and chem. stability of the biol. drug. In this work, synchrotron small- and wide-angle X-ray scattering (SWAXS) are used to characterize the structure of a model protein, lysozyme, in the solid state and its structural transition upon rehydration to the liquid state. The results show that the protein undergoes distortion upon drying to adopt structures that can continuously fill the space to remove the protein-air interface that may be formed upon dehydration. Above a hydration threshold of 35 wt %, the native structure of the protein is recovered. The evolution of SWAXS peaks as a function of water content in a broad range of concentrations is discussed in relation to the structural changes in the protein. The findings presented here can be used for the design and optimization of solid-state formulations of proteins with improved stability.
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| 8. |
- Phan-Xuan, Tuan, et al.
(författare)
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The role of water in the reversibility of thermal denaturation of lysozyme in solid and liquid states
- 2021
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Ingår i: Biochemistry and Biophysics Reports. - : Elsevier B.V.. - 2405-5808. ; 28
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Tidskriftsartikel (refereegranskat)abstract
- Although unfolding of protein in the liquid state is relatively well studied, its mechanisms in the solid state, are much less understood. We evaluated the reversibility of thermal unfolding of lysozyme with respect to the water content using a combination of thermodynamic and structural techniques such as differential scanning calorimetry, synchrotron small and wide-angle X-ray scattering (SWAXS) and Raman spectroscopy. Analysis of the endothermic thermal transition obtained by DSC scans showed three distinct unfolding behaviors at different water contents. Using SWAXS and Raman spectroscopy, we investigated reversibility of the unfolding for each hydration regime for various structural levels including overall molecular shape, secondary structure, hydrophobic and hydrogen bonding interactions. In the substantially dehydrated state below 37 wt% of water the unfolding is an irreversible process and can be described by a kinetic approach; above 60 wt% the process is reversible, and the thermodynamic equilibrium approach is applied. In the intermediate range of water contents between 37 wt% and 60 wt%, the system is phase separated and the thermal denaturation involves two processes: melting of protein crystals and unfolding of protein molecules. A phase diagram of thermal unfolding/denaturation in lysozyme - water system was constructed based on the experimental data. © 2021 The Authors
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| 9. |
- Vejelyte, Irma, et al.
(författare)
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Timing of ductile shearing within the Druksiai-Polotsk Deformation Zone, Lithuania: a U-Pb titanite age
- 2010
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Ingår i: Estonian Journal of Earth Sciences. - : Estonian Academy Publishers. - 1736-7557 .- 1736-4728. ; 59:4, s. 256-262
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Tidskriftsartikel (refereegranskat)abstract
- A U-Pb dating of titanite from an augen granitoid mylonite in the Druksiai-Polotsk Deformation Zone has yielded a concordant age of 1534 +/- 9 Ma. This light brown titanite follows the foliation in the host rock and was obviously formed during retrogression from amphibolite to epidote-amphibolite facies and coeval mylonitization. Shear zones of the same age are known in southern and central Sweden and in NE Poland. These E-W trending deformation zones accommodate both mafic and granitoid intrusions and are probably related to an extensional period in the Mesoproterozoic evolution in the western part of the East European Craton prior to the 1.50-1.45 Ga Danopolonian orogeny.
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