| 1. |
- Argatov, Ivan, et al.
(författare)
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An empirical model for sorption by glassy polymers : An assessment of thermodynamic parameters
- 2021
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Ingår i: Polymer testing. - : Elsevier. - 0142-9418 .- 1873-2348. ; 99
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Tidskriftsartikel (refereegranskat)abstract
- A new fitting model for sorption by glassy polymers is suggested based on the Flory–Huggins (FH) equation with a composite formula for the FH interaction parameter, χ, which is applicable if sorption experimental data shows a single-maximum variation of the FH parameter. Namely, a power-like and a linear approximation is assumed for χ(φ1), as a function of solvent volume fraction φ1, before and after the point of its maximum. After determining the maximum point from a direct inspection of the sorption data, the three fitting parameters are evaluated by solving two independent least-square minimization problems. Several sorption studies of biopolymers taken from the literature show that the endset of the glass transition region is correlated with the position of the maximum of the FH interaction parameter. Based on this hypothesis and the Vrentas–Vrentas model for sorption of glassy polymers, a theoretical framework for the glass transition analysis is developed. In particular, the solvent-induced glass transition temperature variation can be estimated from the sorption isotherm as a function of the solvent content corresponding to temperatures above the temperature of sorption.
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| 2. |
- Argatov, Ivan, et al.
(författare)
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Analysis of the minimal model for the enthalpy relaxation and recovery in glass transition : application to constant-rate differential scanning calorimetry
- 2021
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Ingår i: Continuum Mechanics and Thermodynamics. - : Springer. - 0935-1175 .- 1432-0959. ; 33, s. 107-123
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Tidskriftsartikel (refereegranskat)abstract
- The so-called minimal model is formulated for describing the enthalpy relaxation and recovery in glass transition. The model is based on the Arrhenius law for the enthalpy relaxation, which uses two-dimensional parameters, namely the activation energy and the so-called pre-factor (relaxation time at relatively high temperature). A numerically effective exact analytical solution is obtained for the case of constant-rate differential scanning calorimetry. The developed model is analyzed according to the logic of the model itself without introducing additional simplifying assumptions of thermodynamic nature. For typical range of the model parameters, the resulting differential equation contains a large parameter, which offers an opportunity for the application of asymptotic and approximate techniques. A number of simple approximations have been provided for some thermodynamic quantities of interest.
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| 3. |
- Argatov, Ivan, et al.
(författare)
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Dynamics of post-occlusion water diffusion in stratum corneum
- 2022
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Ingår i: Scientific Reports. - : Nature Publishing Group. - 2045-2322. ; 12:1
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Tidskriftsartikel (refereegranskat)abstract
- Diffusion of water through membranes presents a considerable challenge, as the diffusivity often depends on the local concentration of water. One particular example with strong biological relevance is the stratum corneum (SC) as the primary permeability barrier for the skin. A simple alternative for the constant diffusivity model is provided by the Fujita's two-parameter rational approximation, which captures the experimentally observed fact that the SC diffusion constant for water increases with increasing the water concentration. Based on Fick's law of diffusion, a one-dimensional concentration-dependent diffusion model is developed and applied for the analysis of both the steady-state transepidermal water loss (TEWL) and the non-steady-state so-called skin surface water loss (SSWL) occurred after removal of an occlusion patch from the SC surface. It is shown that some of the age-related changes in the SSWL can be qualitatively explained by the variation of the dimensionless Fujita concentration-dependence parameter.
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| 4. |
- Argatov, Ivan, et al.
(författare)
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Modeling of composite sorption isotherm for stratum corneum
- 2022
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Ingår i: Biochimica et Biophysica Acta - Biomembranes. - : Elsevier. - 0005-2736 .- 1879-2642. ; 1864:7, s. 1-8
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Tidskriftsartikel (refereegranskat)abstract
- Equilibrium water sorption in stratum corneum (SC) is considered by treating it as a biocomposite with two main phases, namely, corneocytes and lipids. To validate the rule of mixtures for the individual phase sorption isotherms, a new flexible fitting model is introduced by accounting for characteristic features observed in the variations of the thermodynamic correction factors corresponding to the individual sorption isotherms. The comparison of the model fitting performance with that of the five-parameter Park's model shows a remarkably good ability to fit experimental data for different types of sorption isotherms. The effect of the lipids content on the variance of the composite sorption isotherm of stratum corneum is highlighted. The sensitivity analysis reveals that for the typical water content 20-30 wt%, which corresponds to the SC in a stable condition, the sensitivity of the composite sorption isotherm to the variation of the lipids content on dry basis is predominantly positive and sufficiently small. The good agreement observed between the experimental sorption isotherm for SC and the composite isotherm, which is based on the rule of mixtures for the individual phase sorption isotherms, yields a plausible conclusion (hypothesis) that the corneocytes-lipids mechanical interaction during unconstrained swelling of the SC membrane in the in vitro laboratory experiment is negligible.
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| 5. |
- Argatov, Ivan, et al.
(författare)
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Sedimentation of a starch microsphere : What is usually missed and why?
- 2023
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Ingår i: Heliyon. - : Cell Press. - 2405-8440. ; 9:10
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Tidskriftsartikel (refereegranskat)abstract
- Gravimetric sedimentation is known as a relatively simple method of determining density of spherical particles. When the method is applied to water-swollen starch microparticles of about submillimeter sizes, it becomes evident that a careful selection of the experimental setup parameters is needed for producing accurate testing results. The main reason for this is that the mean particle density is very close to the density of water, and therefore, a dynamic model accounting for the so-called Bassett history force should be employed for describing the unsteady accelerating particle settling. A main novelty of this study consists in deriving a priori estimates for the settling time and distance.
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| 6. |
- 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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| 7. |
- 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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| 8. |
- 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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| 9. |
- 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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| 10. |
- 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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| 11. |
- Cretella, Margherita, et al.
(författare)
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Determination of Density of Starch Hydrogel Microspheres from Sedimentation Experiments Using Non-Stokes Drag Coefficient
- 2024
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Ingår i: Gels. - 2310-2861. ; 10:4
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Tidskriftsartikel (refereegranskat)abstract
- Sedimentation is an important property of colloidal systems that should be considered when designing pharmaceutical formulations. In pharmaceutical applications, sedimentation is normally described using Stokes' law, which assumes laminar flow of fluid. In this work we studied swelling and hydration of spherical cross-linked amorphous starch microspheres in pure water, solutions of sodium chloride, and in pH-adjusted aqueous solutions. We demonstrated that Reynolds numbers obtained in these experiments correspond to the transition regime between the laminar flow and the turbulent flow and, hence, expressions based on the non-Stokes drag coefficient should be used for calculations of sedimentation velocity from known density or for assessment of density from observed sedimentation velocity. The density of starch microparticles hydrated in water was about 1050 kg/m3, while densities obtained from experiment with other liquids were dependent on the liquids' densities. The data indicate that the swelling of the cross-linked starch microparticles as characterized by their densities is not sensitive to pH and salt concentration in the studied range of these parameters.
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| 12. |
- Digaitis, Ramūnas, PhD, et al.
(författare)
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Hydration and dehydration induced changes in porosity of starch microspheres
- 2022
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Ingår i: Carbohydrate Polymers. - : Elsevier. - 0144-8617 .- 1879-1344. ; 291, s. 119542-119542
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Tidskriftsartikel (refereegranskat)abstract
- Characterization and tuning of the porosity of amorphous starch materials are important for many applications, including controlled release of encapsulated proteins. The porosities of these materials in dry and hydrated states can have different physicochemical origins and properties. Here, porosities of dry cross-linked starch microspheres and their hydration-induced transformations were characterized by small angle X-ray scattering, scanning electron and optical microscopies, thermogravimetric analysis, sorption calorimetry, nitrogen sorption, and helium-pycnometry. The analyses revealed that dry microspheres consist of porous cores with pore diameters below 100 nm and shells which appeared to be denser but contained wider pores (100–300 nm). The outer crust of the microspheres shell is non-porous, which restricts diffusion of nitrogen, water, and ethanol. Partial hydration triggered an irreversible collapse of dry porosity at 12 wt% water. Further hydration resulted in interfacial changes and promoted wet porosity, related to characteristic distances between polymer chains.
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| 13. |
- Engstedt, Jenni, et al.
(författare)
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Phase behavior of soybean phosphatidylcholine and glycerol dioleate in hydrated and dehydrated states studied by small-angle X-ray scattering
- 2023
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Ingår i: Soft Matter. - : Royal Society of Chemistry. - 1744-683X .- 1744-6848. ; 19:43, s. 8305-8317
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Tidskriftsartikel (refereegranskat)abstract
- Soybean phosphatidylcholine (SPC) and glycerol dioleate (GDO) form liquid crystal nanostructures in aqueous environments, and their mixtures can effectively encapsulate active pharmaceutical ingredients (API). When used in a subcutaneous environment, the liquid crystalline matrix gradually hydrates and degrades in the tissue whilst slowly releasing the API. Hydration dependent SPC/GDO phase behavior is complex, non-trivial, and still not fully understood. A deeper understanding of this system is important for controlling its function in drug delivery applications. The phase behavior of the mixture of SPC/GDO/water was studied as a function of hydration and lipid ratio. Small-angle X-ray scattering (SAXS) was used to identify space groups in liquid crystalline phases and to get detailed structural information on the isotropic reverse micellar phase. The reported pseudo ternary phase diagram includes eight different phases and numerous multiphase regions in a thermodynamically consistent way. For mixtures with SPC as the predominant component, the system presents a reverse hexagonal, lamellar and R3m phase. For mixtures with lower SPC concentrations, reverse cubic (Fd3m and Pm3n) as well as intermediate and isotropic micellar phases were identified. By modeling the SAXS data using a core–shell approach, the properties of the isotropic micellar phase were studied in detail as a function of concentration. Moreover, SAXS analysis of other phases revealed new structural features in relation to lipid–water interactions. The new improved ternary phase diagram offers valuable insight into the complex phase behavior of the SPC/GDO system. The detailed structural information is important for understanding what APIs can be incorporated in the liquid crystal structure.
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| 14. |
- Engstedt, Jenni, et al.
(författare)
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Swelling kinetics of mixtures of soybean phosphatidylcholine and glycerol dioleate
- 2024
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Ingår i: Colloids and Surfaces B. - : Elsevier. - 0927-7765 .- 1873-4367. ; 239
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Tidskriftsartikel (refereegranskat)abstract
- Lipid-based drug delivery systems offer the potential to enhance bioavailability, reduce dosing frequency, and improve patient adherence. In aqueous environment, initially dry lipid depots take up water and form liquid crystalline phases. Variation of lipid composition, depot size and hydration-induced phase transitions will plausibly affect the diffusion in and out of the depot. Lipid depots of soybean phosphatidylcholine (SPC) and glycerol dioleate (GDO) mixtures were hydrated for varying time durations in a phosphate-buffered saline (PBS) buffer and then analyzed with Karl Fischer titration, magnetic resonance imaging (MRI) and gravimetrically. Mathematical modeling of the swelling process using diffusion equations, was used to estimate the parameters of diffusion. Both composition of lipid mixture and depot size affect swelling kinetics… The diffusion parameters obtained in Karl Fischer titration and MRI (with temporal and spatial resolution respectively) are in good agreement. Remarkably, the MRI results show a gradient of water content within the depot even after the end of diffusion process. Apparently contradicting the first Fick's law in its classical form, these results find an explanation using the generalized Fick's law that considers the gradient of chemical potential rather than concentration as the driving force of diffusion.
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| 15. |
- Falk, Yana Znamenskaya, et al.
(författare)
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Interactions of Perfluorohexyloctane With Polyethylene and Polypropylene Pharmaceutical Packaging Materials.
- 2020
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Ingår i: Journal of Pharmaceutical Sciences. - : Elsevier. - 0022-3549 .- 1520-6017. ; 109:7, s. 2180-2188
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Tidskriftsartikel (refereegranskat)abstract
- Semifluorinated alkanes (SFAs) are aprotic solvents, which may be used as drug solvents for topical ocular applications, for instance, in dry eye syndrome. Their physical properties suggest that they might be prone to interaction with plastic materials, such as, polyethylene (PE) and polypropylene (PP), which are commonly used as packaging materials for pharmaceutical products. In this study, we investigate interactions of PE and PP with a liquid SFA perfluorohexyloctane (PFHO) using differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and cross-polarized light microscopy. Binary phase diagrams of PFHO-PE and PFHO-PP systems demonstrating interactions of PFHO with the polymeric materials were constructed based on DSC data. According to this data, PFHO tends to lower the melting temperatures of PE and PP. The equilibrium values of solubilities of the polymers in PFHO and PFHO in the polymers were obtained by extrapolation of melting enthalpy data. Absorption of PFHO by PE and PP materials at ambient conditions after four weeks of equilibration was also studied by TGA. From the presented results, it may be concluded that thorough studies of interactions of PE or PP with SFAs are required when these materials are used as packaging components in SFA-based formulations.
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| 16. |
- Genevskiy, Vladislav, et al.
(författare)
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Water sorption properties and nanostructures of airway mucus in patients with COPD and cystic fibrosis
- 2022
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Ingår i: European Respiratory Journal. - : EUROPEAN RESPIRATORY SOC JOURNALS LTD. - 0903-1936 .- 1399-3003. ; 60:Suppl 66
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- Background: Muco-obstructive diseases lead to hypersecretion, changing the airway mucus properties, and impairing mucociliary transport, resulting in mucostasis, and increasing infection likelihood. Mucin structure may determine the water sorption properties of mucus and play a role in chronic obstructive pulmonary disease (COPD) and cystic fibrosis (CF).Objectives: Investigate the sorption properties and mucin nanostructures in mucus collected from healthy, COPD and CF airways.Methods: To investigate mucin nanostructures, small-angle X-ray scattering (SAXS) and atomic force microscopy (AFM) were used. Sorption properties were determined by quartz crystal microbalance with dissipation (QCM-D). Cell-culture (cc) samples from healthy airway mucus (HAM), COPD and CF cultures, and patient HAM from endotracheal tubes and COPD from bronchoscopy were used. Patient mucus was oven-dried at 80°C for the solids content.Results: SAXS and AFM revealed mucin monomers with typical dumbbell structures and varying chain lengths, CF mucins having the shortest chain lengths. Dry-weight solids reached 11wt% in COPD mucus. From QCM-D analysis, cc-COPD and COPD mucus had the highest water content (67 and 75%) during sorption at 99% humidity compared with cc-HAM and HAM (63 and 56%). The overall sorption isotherm for cc-CF mucus was notably lower than HAM and COPD. In low-humidity environments, no hydration-induced glass transition was observed, suggesting mucus remains in a rubbery state.Conclusions: Mucin nanostructures observed in disease could explain the sorption properties where mucin chains affect water content in high humidity environments, which may play a role in protecting the epithelium.
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| 17. |
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| 18. |
- Kelly, Susyn J, et al.
(författare)
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Water Sorption and Structural Properties of Human Airway Mucus in Health and Muco-Obstructive Diseases.
- 2024
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Ingår i: Biomacromolecules. - : American Chemical Society (ACS). - 1525-7797 .- 1526-4602. ; 25:3, s. 1578-1591
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Tidskriftsartikel (refereegranskat)abstract
- Muco-obstructive diseases change airway mucus properties, impairing mucociliary transport and increasing the likelihood of infections. To investigate the sorption properties and nanostructures of mucus in health and disease, we investigated mucus samples from patients and cell cultures (cc) from healthy, chronic obstructive pulmonary disease (COPD), and cystic fibrosis (CF) airways. Atomic force microscopy (AFM) revealed mucin monomers with typical barbell structures, where the globule to spacer volume ratio was the highest for CF mucin. Accordingly, synchrotron small-angle X-ray scattering (SAXS) revealed more pronounced scattering from CF mucin globules and suggested shorter carbohydrate side chains in CF mucin and longer side chains in COPD mucin. Quartz crystal microbalance with dissipation (QCM-D) analysis presented water sorption isotherms of the three types of human airway mucus, where, at high relative humidity, COPD mucus had the highest water content compared to cc-CF and healthy airway mucus (HAM). The higher hydration of the COPD mucus is consistent with the observation of longer side chains of the COPD mucins. At low humidity, no dehydration-induced glass transition was observed in healthy and diseased mucus, suggesting mucus remained in a rubbery state. However, in dialyzed cc-HAM, a sorption-desorption hysteresis (typically observed in the glassy state) appeared, suggesting that small molecules present in mucus suppress the glass transition.
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| 19. |
- Kocherbitov, Vitaly
(författare)
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A model for water sorption isotherms and hydration forces in sugar surfactants
- 2023
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Ingår i: Journal of Colloid and Interface Science. - : Elsevier. - 0021-9797 .- 1095-7103. ; 633, s. 343-351
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Tidskriftsartikel (refereegranskat)abstract
- HYPOTHESIS: Hydration forces between surfactant bilayers can be assessed using water sorption isotherms of surfactants. For a quantitative description, a water sorption model that relates water activity to water content in surfactant-based systems should be proposed.THEORY AND SIMULATIONS: A water sorption model for nonionic surfactant systems based on the idea on partial solvent accessibility is proposed. The model contains only two parameters: one describes the strength of interactions, the other describes the fraction of surfactant available for water. For comparison, molecular dynamics simulations of bilayers of n-octyl β-d-glucoside with different water contents are presented.FINDINGS: The model provides an excellent fit of experimental data on water sorption isotherms of two sugar surfactants. The results of the fitting are compared with molecular dynamics simulations and show a good correlation between simulations and the theory proposed. Analysis of interaction energies shows weakly endothermic hydration both in the simulations and in the sorption model, which agrees with calorimetric data on hydration. The model also shows a non-exponential decay of hydration forces with respect to the distance between bilayers; an expression for the decay length is derived.
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| 20. |
- Kocherbitov, Vitaly, et al.
(författare)
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A thermodynamic theory of sorption in glassy polymers
- 2021
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Ingår i: Polymer. - : Elsevier. - 0032-3861 .- 1873-2291. ; 233
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Tidskriftsartikel (refereegranskat)abstract
- Sorption of vapors by glassy polymers is known to have properties that are different from those typical for sorption by rubbery polymers or liquids. Despite an importance for many practical applications, this difference is still not fully understood. We developed a thermodynamic theory for description of penetrant activity in the glassy state. The presented approach considers the glass transition in terms of a second order phase transition and utilizes heat capacity changes for calculation of thermodynamic activity. The formalism developed here explains a deviation of penetrant activity in the glassy state from equilibrium values. Moreover, the sorption-desorption hysteresis can be explained in thermodynamic terms as well. We demonstrate that not only the heat capacity change of the polymer, but also the heat capacity change of the penetrant should be considered to understand the difference between three cases: sorption by equilibrium liquid, absorption by glass and desorption from glass. The theory presented here is tested on experimental data on water sorption by maltodextrin and bovine submaxillary gland mucin. A very good fitting of the experimental data for both sorption and desorption cases is demonstrated. The values of heat capacity increments of the components obtained by fitting the penetrant activity data can be used to get new insights into the non-equilibrium properties of glassy materials.
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| 21. |
- Kocherbitov, Vitaly, et al.
(författare)
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Hydrogen bonding in glassy trehalose-water system : Insights from density functional theory and molecular dynamics simulations
- 2024
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Ingår i: Journal of Chemical Physics. - : American Institute of Physics (AIP). - 0021-9606 .- 1089-7690. ; 160:8
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Tidskriftsartikel (refereegranskat)abstract
- We report a detailed density functional theory and molecular dynamics study of hydrogen bonding between trehalose and water, with a special emphasis on interactions in the amorphous solid state. For comparison, water-water interactions in water dimers and tetramers are evaluated using quantum calculations. The results show that the hydrogen bonding energy is dependent not only on the geometry (bond length and angle) but also on the local environment of the hydrogen bond. This is seen in quantum calculations of complexes in vacuum as well as in amorphous solid states with periodic boundary conditions. The temperature-induced glass transition in the trehalose-water system was studied using molecular dynamics simulations with varying cooling and heating rates. The obtained parameters of the glass transition are in good agreement with the experiments. Moreover, the dehydration of trehalose in the glassy state was investigated through a gradual dehydration with multiple small steps under isothermal conditions. From these simulations, the values of water sorption energy at different temperatures were obtained. The partial molar enthalpy of mixing of water value of −18 kJ/mol found in calorimetric experiments was accurately reproduced in these simulations. These findings are discussed in light of the hydrogen bonding data in the system. We conclude that the observed exothermic effect is due to different responses of liquid and glassy matrices to perturbations associated with the addition or removal of water molecules.
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| 22. |
- Kocherbitov, Vitaly
(författare)
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On the calculation of thermodynamic parameters in sorption calorimetric experiments
- 2021
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Ingår i: Journal of Chemical Thermodynamics. - : Elsevier. - 0021-9614 .- 1096-3626. ; 152
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Tidskriftsartikel (refereegranskat)abstract
- The sorption calorimetry method developed by Wadso and co-workers is one of the most successful methods for studying the enthalpy of vapor sorption by solids and gels. A unique feature of this method is a simultaneous measurement of the water sorption isotherm and the sorption enthalpy. The accuracy of the enthalpy measurements in sorption calorimetric experiments can be affected by diffusion of water vapour through the injection channel tube and potentially through small leaks in the sorption cell. At high water activities this leads to an apparent drift of the measured enthalpies towards endothermic values. In this work we propose an improvement of the enthalpy calculation method, that eliminates these effects and substantially improves the accuracy of the enthalpy measurements. The new method is successfully tested on previously published sorption calorimetric data and can be recommended for use in future experiments. (C) 2020 The Author(s). Published by Elsevier Ltd.
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| 23. |
- Lind, Tania K., et al.
(författare)
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Effects of ethylene oxide chain length on crystallization of polysorbate 80 and its related compounds
- 2021
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Ingår i: Journal of Colloid and Interface Science. - : Elsevier. - 0021-9797 .- 1095-7103. ; 592, s. 468-484
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Tidskriftsartikel (refereegranskat)abstract
- As a result of the synthesis protocol polyoxyethylene sorbitan monooleate (polysorbate 80, PS80) is a highly complex mixture of compounds. PS80 was therefore separated into its main constituents, e.g. polyoxyethylene isosorbide esters and polyoxyethylene esters, as well as mono- di- and polyesters using preparative high-performance liquid chromatography. In this comprehensive study the individual components and their ethoxylation level were verified by matrix assisted laser desorption/ionization time-of-flight and their thermotropic behavior was analyzed using differential scanning calorimetry and X-ray diffraction. A distinct correlation was found between the average length of the ethylene oxide (EO) chains in the headgroup and the individual compounds' ability to crystallize. Importantly, a critical number of EO units required for crystallization of the headgroup was determined (6 EO units per chain or 24 per molecule). The investigation also revealed that the hydrocarbon tails only crystallize for polyoxyethylene sorbitan esters if saturated. PS80 is synthesized by reacting with approximately 20 mol of EO per mole of sorbitol, however, the number of EO units in the sorbitan ester in commercial PS80 products is higher than the expected 20 (5 EO units per chain). The complex behavior of all tested compounds revealed that if the amount of several of the linear by-products is reduced, the number of EO units in the chains will stay below the critical number and the product will not be able to crystallize by the EO chains.
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| 24. |
- Nilsson, Emelie J., et al.
(författare)
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Mechanisms of crystallisation in polysorbates and sorbitan esters
- 2020
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Ingår i: CrystEngComm. - : Royal Society of Chemistry. - 1466-8033. ; 22:22, s. 3840-3853
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Tidskriftsartikel (refereegranskat)abstract
- Polysorbates (PS), commonly known as Tween (TM), are some of the most extensively used excipients and protein stabilisers in biopharmaceutical products worldwide. It is stipulated in the pharmacopoeia specifications that these ethoxylated surfactants are complex mixtures comprised of a wealth of molecular species. While little is known about the propensity of PSs to crystallise, they are used in applications ranging from food products, cosmetics, different types of drug dosage forms like creams and oral products to parenteral applications. However, in recent years a range of issues and safety concerns have appeared when using them for stabilising biopharmaceutical products including precipitation, particle formation, and adverse biological effects. Therefore, the aim of this study was to thoroughly characterise the thermotropic behaviour and mechanism of crystallisation of polysorbates with different hydrocarbon tails and their non-ethoxylated sorbitan ester equivalents for comparison. A systematic and comprehensive product characterisation was carried out, taking advantage of a combination of complementary techniques such as differential scanning calorimetry, matrix assisted laser desorption ionisation time-of-flight and small- and wide-angle X-ray diffraction. We show that polysorbate 80, having an unsaturated hydrocarbon tail, crystallises by the ethylene oxide chains in the headgroup. Polysorbate 20, 40, and 60, containing saturated hydrocarbon esters tails, crystallise not only by the ethylene oxide chains but also by their hydrocarbon tails. An analogous behaviour was observed for the PS non-ethoxylated equivalents, the sorbitan esters. Sorbitan esters with saturated hydrocarbon tails displayed a crystallisation of the tail upon cooling, whereas the sorbitan ester with unsaturated hydrocarbon tail displayed no crystallisation.
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| 25. |
- 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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| 26. |
- 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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| 27. |
- Slaninova, Eva, et al.
(författare)
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On the bioprotective effects of 3-hydroxybutyrate : Thermodynamic study of binary 3HB-water systems.
- 2023
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Ingår i: Biophysical Journal. - : Elsevier. - 0006-3495 .- 1542-0086. ; 122:3, s. 460-469
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Tidskriftsartikel (refereegranskat)abstract
- Microorganisms must face various inconvenient conditions; therefore, they developed several approaches for protection. Such a strategy also involves the accumulation of compatible solutes, also called osmolytes. It has been proved that the monomer unit 3-hydroxybutyrate (3HB), which is present in sufficient concentration in poly(3-hydroxybutyrate) (PHB)-accumulating cells, serves as a chemical chaperone protecting enzymes against heat and oxidative stress and as a cryoprotectant for enzymes, bacterial cells, and yeast. The stress robustness of the cells is also strongly dependent on the behavior and state of intracellular water, especially during stress exposure. For a better understanding of the protective mechanism and effect of strongly hydrophilic 3HB in solutions at a wide range of temperatures, a binary phase diagram of system sodium 3HB (Na3HB)-water in equilibrium and the state diagrams showing the glass transitions in the system were constructed. To investigate the activity of water in various compositions of the Na3HB/water system, three experimental techniques have been used (dynamic water sorption analysis, water activity measurements, and sorption calorimetry). First, Na3HB proved its hydrophilic nature, which is very comparable with known compatible solutes (trehalose). Results of differential scanning calorimetry demonstrated that Na3HB is also highly effective in depressing the freezing point and generating a large amount of nonfrozen water (1.35 g of water per gram of Na3HB). Therefore, Na3HB represents a very effective cryoprotectant that can be widely used for numerous applications.
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| 28. |
- Tsompou, Andriani, et al.
(författare)
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Surface and bulk mechanisms in repeating treatment of solid surfaces by purified water
- 2023
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Ingår i: Heliyon. - : Cell Press. - 2405-8440. ; 9:6
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Tidskriftsartikel (refereegranskat)abstract
- To decrease the negative impact of surfactants, the idea of using purified water in washing has been proposed. Previous studies showed that purified water facilitates the roll-up mechanism by promoting electrostatic interactions between the surface and the soil. However, washing mech-anisms can be dependent on the amount of remaining soil.In this work we studied the removal of thin Vaseline films and thicker oil films from hydro-philic surfaces using multiple washing cycles at different temperatures. The Quartz Crystal Mi-crobalance with Dissipation monitoring (QCM-D) and gravimetric analysis were used for thin and thick films respectively. In QCM-D experiments most of the thin film was removed during the first two cycles, while following cycles did not substantially affect washing efficiency; increased temperature facilitated the washing process. Gravimetric analysis showed that the washing of thicker films can be divided into two regimes. During the first, exponential, regime the amount of oil on the surface is high and surface mechanisms, such as roll-up, dominate. Oil droplets are kinetically stabilized in purified water by electrostatic interactions. As the amount of oil on the surface decreases, the second, linear, regime is introduced. The removal of oil occurs by equi-librium bulk mechanisms, where electrostatic interactions are less important.
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| 29. |
- Tsompou, Andriani, et al.
(författare)
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The effects of water purity on removal of hydrophobic substances from solid surfaces without surfactants
- 2022
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Ingår i: Journal of Colloid and Interface Science. - : Elsevier. - 0021-9797 .- 1095-7103. ; 608, s. 1929-1941
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Tidskriftsartikel (refereegranskat)abstract
- Hypothesis: Detergents used in everyday life for cleaning and washing are a source of water pollution and can have a negative effect on human health and the environment. To reduce their negative impact, a new trend of using only purified water for washing and cleaning applications is emerging. A scientific basis of this method needs to be established, as its mechanisms and the efficiency should be better understood. Experiments: In this work, we investigate the effect of water purity on the removal of hydrophobic films from solid surfaces using quartz crystal microbalance with dissipation monitoring (QCM-D) and gravimetric experiments. We compared the cleaning efficiency of TAP water, two grades of purified water, NaCl solution and SDS solution. Findings: The QCM-D results show that both grades of purified water remove more than 90% of Vaseline deposited of the surface while tap water only 75%. SDS solution fully removes the deposited layer. Gravimetric experiments with removal of olive oil from hydrophilic and hydrophobic surfaces also indicate higher efficiency of purified water grades. Contact angle experiments show that pure water facilitates roll-up mechanism of cleaning. We suggest that due to lower ionic strength, purified water increases electrostatic repulsion and promotes the cleaning process.
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