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Romanini M, Macovez R, Valenti S, Noor W, Tamarit JL. Dielectric Spectroscopy Studies of Conformational Relaxation Dynamics in Molecular Glass-Forming Liquids. Int J Mol Sci 2023; 24:17189. [PMID: 38139017 PMCID: PMC10743228 DOI: 10.3390/ijms242417189] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/19/2023] [Revised: 11/29/2023] [Accepted: 12/04/2023] [Indexed: 12/24/2023] Open
Abstract
We review experimental results obtained with broadband dielectric spectroscopy concerning the relaxation times and activation energies of intramolecular conformational relaxation processes in small-molecule glass-formers. Such processes are due to the interconversion between different conformers of relatively flexible molecules, and generally involve conformational changes of flexible chain or ring moieties, or else the rigid rotation of planar groups, such as conjugated phenyl rings. Comparative analysis of molecules possessing the same (type of) functional group is carried out in order to test the possibility of assigning the dynamic conformational isomerism of given families of organic compounds to the motion of specific molecular subunits. These range from terminal halomethyl and acetyl/acetoxy groups to both rigid and flexible ring structures, such as the planar halobenzene cycles or the buckled saccharide and diazepine rings. A short section on polyesters provides a generalisation of these findings to synthetic macromolecules.
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Affiliation(s)
| | | | | | | | - Josep Lluís Tamarit
- Grup de Caracterització de Materials, Departament de Física and Barcelona Research Center in Multiscale Science and Engineering, Universitat Politècnica de Catalunya, Barcelona East School of Engineering (EEBE), Av. Eduard Maristany 10-14, E-08019 Barcelona, Spain; (M.R.); (R.M.); (S.V.); (W.N.)
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Svoboda R, Pakosta M, Doležel P. How the Presence of Crystalline Phase Affects Structural Relaxation in Molecular Liquids: The Case of Amorphous Indomethacin. Int J Mol Sci 2023; 24:16275. [PMID: 38003465 PMCID: PMC10671508 DOI: 10.3390/ijms242216275] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/30/2023] [Revised: 11/10/2023] [Accepted: 11/12/2023] [Indexed: 11/26/2023] Open
Abstract
The influence of partial crystallinity on the structural relaxation behavior of low-molecular organic glasses is, contrary to, e.g., polymeric materials, a largely unexplored territory. In the present study, differential scanning calorimetry was used to prepare a series of amorphous indomethacin powders crystallized to various extents. The preparations stemmed from the two distinct particle size fractions: 50-125 µm and 300-500 µm. The structural relaxation data from the cyclic calorimetric measurements were described in terms of the phenomenological Tool-Narayanaswamy-Moynihan model. For the 300-500 µm powder, the crystalline phase forming dominantly on the surface led to a monotonous decrease in the glass transition by ~6 °C in the 0-70% crystallinity range. The activation energy of the relaxation motions and the degree of heterogeneity within the relaxing matrix were not influenced by the increasing crystallinity, while the interconnectivity slightly increased. This behavior was attributed to the release of the quenched-in stresses and to the consequent slight increase in the structural interconnectivity. For the 50-125 µm powder, distinctly different relaxation dynamics were observed. This leads to a conclusion that the crystalline phase grows throughout the bulk glassy matrix along the internal micro-cracks. At higher crystallinity, a sharp increase in Tg, an increase in interconnectivity, and an increase in the variability of structural units engaged in the relaxation motions were observed.
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Affiliation(s)
- Roman Svoboda
- Department of Physical Chemistry, Faculty of Chemical Technology, University of Pardubice, Studentská 573, 532 10 Pardubice, Czech Republic
| | - Marek Pakosta
- Faculty of Electrical Engineering and Informatics, University of Pardubice, nam. Cs. legii 565, 530 02 Pardubice, Czech Republic; (M.P.); (P.D.)
| | - Petr Doležel
- Faculty of Electrical Engineering and Informatics, University of Pardubice, nam. Cs. legii 565, 530 02 Pardubice, Czech Republic; (M.P.); (P.D.)
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Valenti S, Arioli M, Jamett A, Tamarit JL, Puiggalí J, Macovez R. Amorphous solid dispersions of curcumin in a poly(ester amide): Antiplasticizing effect on the glass transition and macromolecular relaxation dynamics, and controlled release. Int J Pharm 2023; 644:123333. [PMID: 37597594 DOI: 10.1016/j.ijpharm.2023.123333] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/24/2023] [Revised: 07/20/2023] [Accepted: 08/17/2023] [Indexed: 08/21/2023]
Abstract
In order to exploit the pharmacological potential of natural bioactive molecules with low water solubility, such as curcumin, it is necessary to develop formulations, such as amorphous polymer dispersions, which allow a constant release rate and at the same time avoid possible toxicity effects of the crystalline form of the molecule under scrutiny. In this study, polymer dispersions of curcumin were obtained in PADAS, a biodegradable semicrystalline copolymer based on 1,12-dodecanediol, sebacic acid and alanine. The dispersions were fully characterized by means of differential scanning calorimetry and broadband dielectric spectroscopy, and the drug release profile was measured in a simulated body fluid. Amorphous homogeneous binary dispersions were obtained for curcumin mass fraction between 30 and 50%. Curcumin has significantly higher glass transition temperature Tg (≈ 347 K) than the polymer matrix (≈274-277 K depending on the molecular weight), and dispersions displayed Tg's intermediate between those of the pure amorphous components, implying that curcumin acts as an effective antiplasticizer for PADAS. Dielectric spectroscopy was employed to assess the relaxation dynamics of the binary dispersion with 30 wt% curcumin, as well as that of each (amorphous) component separately. The binary dispersion was characterized by a single structural relaxation, a single Johari-Goldstein process, and two local intramolecular processes, one for each component. Interestingly, the latter processes scaled with the Tg of the sample, indicating that they are viscosity-sensitive. In addition, both the pristine polymer and the dispersion exhibited an interfacial Maxwell-Wagner relaxation, likely due to spatial heterogeneities associated with phase disproportionation in this polymer. The release of curcumin from the dispersion in a simulated body fluid followed a Fickian diffusion profile, and 51% of the initial curcumin content was released in 48 h.
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Affiliation(s)
- Sofia Valenti
- Barcelona Research Center in Multiscale Science and Engineering, Universitat Politècnica de Catalunya, Campus Diagonal-Besòs, Av. Eduard Maristany 10-14, E-08019 Barcelona, Catalonia, Spain; Synthetic Polymers: Structure and Properties. Biodegradable Polymers, Departament de Enginyeria Química, Universitat Politècnica de Catalunya, EEBE, Av. Eduard Maristany 10-14, E-08019 Barcelona, Catalonia, Spain; Grup de Caracterització de Materials, Departament de Física, Universitat Politècnica de Catalunya, EEBE, Av. Eduard Maristany 10-14, E-08019 Barcelona, Catalonia, Spain
| | - Matteo Arioli
- Synthetic Polymers: Structure and Properties. Biodegradable Polymers, Departament de Enginyeria Química, Universitat Politècnica de Catalunya, EEBE, Av. Eduard Maristany 10-14, E-08019 Barcelona, Catalonia, Spain
| | - Alex Jamett
- Grup de Caracterització de Materials, Departament de Física, Universitat Politècnica de Catalunya, EEBE, Av. Eduard Maristany 10-14, E-08019 Barcelona, Catalonia, Spain
| | - Josep Lluís Tamarit
- Barcelona Research Center in Multiscale Science and Engineering, Universitat Politècnica de Catalunya, Campus Diagonal-Besòs, Av. Eduard Maristany 10-14, E-08019 Barcelona, Catalonia, Spain; Grup de Caracterització de Materials, Departament de Física, Universitat Politècnica de Catalunya, EEBE, Av. Eduard Maristany 10-14, E-08019 Barcelona, Catalonia, Spain
| | - Jordi Puiggalí
- Barcelona Research Center in Multiscale Science and Engineering, Universitat Politècnica de Catalunya, Campus Diagonal-Besòs, Av. Eduard Maristany 10-14, E-08019 Barcelona, Catalonia, Spain; Synthetic Polymers: Structure and Properties. Biodegradable Polymers, Departament de Enginyeria Química, Universitat Politècnica de Catalunya, EEBE, Av. Eduard Maristany 10-14, E-08019 Barcelona, Catalonia, Spain; Institute for Bioengineering of Catalonia (IBEC), The Barcelona Institute of Science and Technology (BIST), Carrer Baldiri i Reixac 11-15, E-08028 Barcelona, Catalonia, Spain
| | - Roberto Macovez
- Barcelona Research Center in Multiscale Science and Engineering, Universitat Politècnica de Catalunya, Campus Diagonal-Besòs, Av. Eduard Maristany 10-14, E-08019 Barcelona, Catalonia, Spain; Grup de Caracterització de Materials, Departament de Física, Universitat Politècnica de Catalunya, EEBE, Av. Eduard Maristany 10-14, E-08019 Barcelona, Catalonia, Spain.
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Grzybowski A. Glass Transition and Related Phenomena. Int J Mol Sci 2023; 24:ijms24108685. [PMID: 37240021 DOI: 10.3390/ijms24108685] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/02/2023] [Accepted: 05/08/2023] [Indexed: 05/28/2023] Open
Abstract
Despite recent advances in the study of complex systems, which were recognized by the Nobel Prize in Physics in 2021, glass transition and the physicochemical phenomena that occur in the supercooled liquid and glassy states have remained shrouded, at least partially, in mystery for various material groups [...].
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Affiliation(s)
- Andrzej Grzybowski
- Institute of Physics, University of Silesia in Katowice, ul. 75 Pułku Piechoty 1, 41-500 Chorzów, Poland
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Valenti S, Cazorla C, Romanini M, Tamarit JL, Macovez R. Eutectic Mixture Formation and Relaxation Dynamics of Coamorphous Mixtures of Two Benzodiazepine Drugs. Pharmaceutics 2023; 15:pharmaceutics15010196. [PMID: 36678825 PMCID: PMC9861849 DOI: 10.3390/pharmaceutics15010196] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/02/2022] [Revised: 12/27/2022] [Accepted: 12/30/2022] [Indexed: 01/09/2023] Open
Abstract
The formation of coamorphous mixtures of pharmaceuticals is an interesting strategy to improve the solubility and bioavailability of drugs, while at the same time enhancing the kinetic stability of the resulting binary glass and allowing the simultaneous administration of two active principles. In this contribution, we describe kinetically stable amorphous binary mixtures of two commercial active pharmaceutical ingredients, diazepam and nordazepam, of which the latter, besides being administered as a drug on its own, is also the main active metabolite of the other in the human body. We report the eutectic equilibrium-phase diagram of the binary mixture, which is found to be characterized by an experimental eutectic composition of 0.18 molar fraction of nordazepam, with a eutectic melting point of Te = 395.4 ± 1.2 K. The two compounds are barely miscible in the crystalline phase. The mechanically obtained mixtures were melted and supercooled to study the glass-transition and molecular-relaxation dynamics of amorphous mixtures at the corresponding concentration. The glass-transition temperature was always higher than room temperature and varied linearly with composition. The Te was lower than the onset of thermal decomposition of either compound (pure nordazepam decomposes upon melting and pure diazepam well above its melting point), thus implying that the eutectic liquid and glass can be obtained without any degradation of the drugs. The eutectic glass was kinetically stable against crystallization for at least a few months. The relaxation processes of the amorphous mixtures were studied by dielectric spectroscopy, which provided evidence for a single structural (α) relaxation, a single Johari-Goldstein (β) relaxation, and a ring-inversion conformational relaxation of the diazepinic ring, occurring on the same timescale in both drugs. We further characterized both the binary mixtures and pure compounds by FTIR spectroscopy and first-principles density functional theory (DFT) simulations to analyze intermolecular interactions. The DFT calculations confirm the presence of strong attractive forces within the heteromolecular dimer, leading to large dimer interaction energies of the order of -0.1 eV.
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Study of Thermal Properties, Molecular Dynamics, and Physical Stability of Etoricoxib Mixtures with Octaacetylmaltose near the Glass Transition. Int J Mol Sci 2022; 23:ijms23179794. [PMID: 36077212 PMCID: PMC9456116 DOI: 10.3390/ijms23179794] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/08/2022] [Revised: 08/24/2022] [Accepted: 08/26/2022] [Indexed: 11/16/2022] Open
Abstract
In this paper, we thoroughly investigated the physical stability of the anti-inflammatory drug etoricoxib, which has been reported earlier to be resistant to recrystallization in its glassy and supercooled states at ambient pressure. Our unique application of the standard refractometry technique showed that the supercooled liquid of the drug was able to recrystallize during isothermal experiments in atmospheric conditions. This enabled us to determine the crystallization onset timescale and nucleation energy barrier of etoricoxib for the first time. As the physical instability of etoricoxib requires working out an efficient method for improving the drug’s resistance to recrystallization to maintain its amorphous form utility in potential pharmaceutical applications, we focused on finding a solution to this problem, and successfully achieved this purpose by preparing binary mixtures of etoricoxib with octaacetylmaltose. Our detailed thermal, refractometry, and molecular dynamics studies of the binary compositions near the glass transition revealed a peculiar behavior of the glass transition temperatures when changing the acetylated disaccharide concentration in the mixtures. Consequently, the anti-plasticization effect on the enhancement of physical stability could be excluded, and a key role for specific interactions in the improved resistance to recrystallization was expected. Invoking our previous results obtained for etoricoxib, the chemically similar drug celecoxib, and octaacetylmaltose, we formulated a hypothesis about the molecular mechanisms that may cause an impediment to crystal nuclei formation in the amorphous mixtures of etoricoxib with octaacetylmaltose. The most plausible scenario may rely on the formation of hydrogen-bonded heterodimers of the drug and excipient molecules, and the related drop in the population of the etoricoxib homodimers, which disables the nucleation. Nevertheless, this hypothesis requires further investigation. Additionally, we tested some widely discussed correlations between molecular mobility and crystallization properties, which turned out to be only partially satisfied for the examined mixtures. Our findings constitute not only a warning against manufacturing the amorphous form of pure etoricoxib, but also evidence for a promising outcome for the pharmaceutical application of the amorphous compositions with octaacetylmaltose.
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