Nanoconfinement Effects on the Glass Transition and Crystallization Behaviors of Nifedipine

Unprecedented Packing Polymorphism of Oxindole: An Exploration Inspired by Crystal Structure Prediction

Crystal polymorphism, characterized by different packing arrangements of the same compound, strongly ties to the physical properties of a molecule. Determining the polymorphic landscape is complex and time-consuming, with the number of experimentally observed polymorphs varying widely from molecule to molecule. Furthermore, disappearing polymorphs, the phenomenon whereby experimentally observed forms cannot be reproduced, pose a significant challenge for the pharmaceutical industry. Herein, we focused on oxindole (OX), a small rigid molecule with four known polymorphs, including a reported disappearing form. Using crystal structure prediction (CSP), we assessed OX solid-state landscape and thermodynamic stability by comparing predicted structures with experimentally known forms. We then performed melt and solution crystallization in bulk and nanoconfinement to validate our predictions. These experiments successfully reproduced the known forms and led to the discovery of four novel polymorphs. Our approach provided insights into reconstructing disappearing polymorphs and building more comprehensive polymorph landscapes. These results also establish a new record of packing polymorphism for rigid molecules.

Effect of Aerosol Size on Glass Transition Temperature

The amorphous phase state of suspended nanoparticles affects their atmospheric lifetimes and environmental impact. Influence of relative humidity and chemical composition on the glass-to-liquid transition is well-known. However, the influence of the particle size on the phase transition remains uncertain. Here we show experimental data that probe the amorphous phase transition of suspended sucrose particles as a function of particle size. The depression in glass-transition temperature follows the Gibbs-Thomson or Keesom-Laplace predicted proportionality of ΔTg ∝ D-1 for particles 100-700 nm in diameter, but the proportionality changes to ΔTg ∝ D-1/2 for smaller sizes. Literature data for glass-transition temperature depression in thin films and nanoconfined compounds show similar and strong deviations from the expected D-1 behavior. While the observed proportionalities remain incompletely understood, the results here provide evidence that the deviation from ΔTg ∝ D-1 is not attributable to substrate effects.

Drug-Coformer Loaded-Mesoporous Silica Nanoparticles: A Review of the Preparation, Characterization, and Mechanism of Drug Release

Drug-coformer systems, such as coamorphous and cocrystal, are gaining recognition as highly effective strategies for enhancing the stability, solubility, and dissolution of drugs. These systems depend on the interactions between drug and coformer to prevent the conversion of amorphous drugs into the crystalline form and improve the solubility. Furthermore, mesoporous silica (MPS) is also a promising carrier commonly used for stabilization, leading to solubility improvement of poorly water-soluble drugs. The surface interaction of drug-MPS and the nanoconfinement effect prevent amorphous drugs from crystallizing. A novel method has been developed recently, which entails the loading of drug-coformer into MPS to improve the solubility, dissolution, and physical stability of the amorphous drug. This method uses the synergistic effects of drug-coformer interactions and the nanoconfinement effect within MPS. Several studies have reported successful incorporation of drug-coformer into MPS, indicating the potential for significant improvement in dissolution characteristics and physical stability of the drug. Therefore, this study aimed to discuss the preparation and characterization of drug-coformer within MPS, particularly the interaction in the nanoconfinement, as well as the impact on drug release and physical stability.

The step-wise dissolution method: An efficient DSC-based protocol for verification of predicted API-polymer compatibility

The development of an amorphous solid dispersion (ASD) is a promising strategy for improving the low bioavailability of many poorly water-soluble active pharmaceutical ingredients (APIs). The construction of a temperature-composition (T-C) phase diagram for an API-polymer combination is imperative as it can provide critical information that is essential for formulating stable ASDs. However, the currently followed differential scanning calorimetry (DSC)-based strategies for API solubility determination in a polymer at elevated temperatures are inefficient and, on occasions, unreliable, which may lead to an inaccurate prediction at lower temperatures of interest (i.e., T = 25 °C). Recently, we proposed a novel DSC-based protocol called the "step-wise dissolution" (S-WD) method, which is both cost- and time-effective. The objective of this study was to test the applicability of the S-WD method regarding expeditious verification of the purely-predicted API-polymer compatibility via the perturbed chain-statistical associating fluid theory (PC-SAFT) equation of state (EOS). Fifteen API-polymer T-C phase diagrams were reliably constructed, with three distinct API-polymer case types being identified regarding the approach used for the S-WD method. Overall, the PC-SAFT EOS provided satisfactory qualitative descriptions of the API-polymer compatibility, but not necessarily accurate quantitative predictions of the API solubility in the polymer at T = 25 °C. The S-WD method was subsequently modified and an optimal protocol was proposed, which can significantly reduce the required experimental effort.

Mesoporous Matrices as a Promising New Generation of Carriers for Multipolymorphic Active Pharmaceutical Ingredient Aripiprazole

The enhancement of the properties (i.e., poor solubility and low bioavailability) of currently available active pharmaceutical ingredients (APIs) is one of the major goals of modern pharmaceutical sciences. Among different strategies, a novel and innovative route to reach this milestone seems to be the application of nanotechnology, especially the incorporation of APIs into porous membranes composed of pores of nanometric size and made of nontoxic materials. Therefore, in this work, taking the antipsychotic API aripiprazole (APZ) infiltrated into various types of mesoporous matrices (anodic aluminum oxide, native, and silanized silica) characterized by similar pore diameters (d = 8-10 nm) as an example, we showed the advantage of incorporated systems in comparison to the bulk substance considering the crystallization kinetics, molecular dynamics, and physical stability. Calorimetric investigations supported by the temperature-dependent X-ray diffraction measurements revealed that in the bulk system the recrystallization of polymorph III, which next is converted to the mixture of forms IV and I, is visible, while in the case of confined samples polymorphic forms I and III of APZ are produced upon heating of the molten API with different rates. Importantly, the two-step crystallization observed in thermograms obtained for the API infiltrated into native silica templates may suggest crystal formation by the interfacial and core molecules. Furthermore, dielectric studies enabled us to conclude that there is no trace of crystallization of spatially restricted API during one month of storage at T = 298 K. Finally, we found that in contrast to the crystalline and amorphous bulk samples, all examined confined systems show a logarithmic increase in API dissolution over time (very close to a prolonged release effect) without any sign of precipitation. Our data demonstrated that mesoporous matrices appear to be interesting candidates as carriers for unstable amorphous APIs, like APZ. In addition to protecting them against crystallization, they can provide the desired prolonged release effect, which may increase the drug concentration in the blood (resulting in higher bioavailability). We believe that the "nanostructirization" in terms of the application of porous membranes as a novel generation of drug carriers might open unique perspectives in the further development of drugs characterized by prolonged release.

Probing fluconazole deposition inside mesoporous silica using solid-state NMR spectroscopy: Crystallization of a confined metastable form and phase transformations under storage conditions

Encapsulation of molecules into mesoporous silica carriers continues to attract considerable interest in the area of drug delivery and crystal engineering. Here, MCM-41, SBA-15 and MCF silica matrices were used to encapsulate fluconazole (FLU), a pharmaceutically relevant molecule with known conformational flexibility, using the melting method. The composites have been characterized using 1H, 13C and 19F NMR spectroscopy, nitrogen adsorption, PXRD and thermal analysis (DSC, TGA). Drug loading up to 50 wt% allowed us to probe the crystallization process and to detect different local environments of confined FLU molecules. 19F NMR spectroscopy enabled us to detect the gradual pore filling of silica with FLU and differentiate the amorphous domains and surface species. The use of the complementary structural and thermal techniques enabled us to monitor crystallization of the metastable FLU form II in MCF. Using 1H and 19F NMR spectroscopy we observed pore-size dependent reversible dehydration/hydration behaviour in the MCM and SBA composites. As water content has considerable importance in understanding of physicochemical stability and shelf-life of pharmaceutical formulations, experimental evidence of the effect of API-water-carrier interactions on the API adsorption mechanism on silica surface is highlighted.

Rigid Nuclei and Flexible Nuclei: Appearance and Disappearance of Nuclei in Indomethacin Glass Revealed by a Long-Term Annealing Study

In this study, nucleation/crystallization behaviors of indomethacin glass are discussed with emphasis on the fate of nuclei, which is explained using a notion of "rigid" and "flexible" nuclei. The observation was made mainly by thermal analysis of indomethacin glass after long-term annealing at various temperatures. Formation of nuclei was evaluated by observing cold crystallization behaviors of the annealed glasses, as they should be dominated by the "nuclei form" produced in the glass. Nuclei of forms α and γ, which have opposite stability trends, were found to appear over a wide temperature range. The nuclei of form α were stable even in the presence of other crystal forms, whereas those of form γ were likely to be easily integrated into other crystals during their growth, which was explained by a notion of rigid and flexible nuclei. Moreover, unconventionally fast crystallization in the glass-transition region and the finding of a new crystal form are also reported.

Mesoporous Drug Delivery System: From Physical Properties of Drug in Solid State to Controlled Release

Mesoporous materials, which exhibit great potential in the control of polymorphs and delivery of poorly water-soluble drugs, have obtained considerable attention in the field of pharmaceutical science. The physical properties and release behaviors of amorphous or crystalline drugs may be affected by formulating them into mesoporous drug delivery systems. In the past few decades, an increasing amount of papers have been written about mesoporous drug delivery systems, which play a crucial role in improving the properties of drugs. Herein, mesoporous drug delivery systems are comprehensively reviewed in terms of their physicochemical characteristics, control of polymorphic forms, physical stability, in vitro performance, and in vivo performance. Moreover, the challenges and strategies of developing robust mesoporous drug delivery systems are also discussed.

Physical Aging of Polystyrene Confined in Anodic Aluminum Oxide Nanopores

We investigated the glassy dynamics of polystyrene (PS) confined in anodic aluminum oxide (AAO) nanopores by differential scanning calorimetry. Based on the outcome of our experiments, we show that the cooling rate applied to process the 2D confined PS melt has a significant impact on both the glass transition and the structural relaxation in the glassy state. A single glass transition temperature (T_g) is observed in quenched samples, while slow-cooled PS chains show two T_gs corresponding to a core-shell structure. The former phenomenon resembles what is observed in freestanding structures, while the latter is imputed to the adsorption of PS onto AAO walls. A more complex picture was drawn for physical aging. In the case of quenched samples, we observed a non-monotonic trend of the apparent aging rate that in 400 nm pores, reaches a value almost twice as larger than what is measured in bulk and decreases upon further confinement in smaller nanopores. For slow-cooled samples, by adequately varying the aging conditions, we were able to control the equilibration kinetics and either separate the two aging processes or induce an intermediate aging regime. We propose a possible explanation of these findings in terms of distribution in free volume and the presence of different aging mechanisms.

Selecting Counterions to Improve Ionized Hydrophilic Drug Encapsulation in Polymeric Nanoparticles

Hydrophobic ion pairing (HIP) can successfully increase the drug loading and control the release kinetics of ionizable hydrophilic drugs, addressing challenges that prevent these molecules from reaching the clinic. Nevertheless, polymeric nanoparticle (PNP) formulation development requires trial-and-error experimentation to meet the target product profile, which is laborious and costly. Herein, we design a preformulation framework (solid-state screening, computational approach, and solubility in PNP-forming emulsion) to understand counterion-drug-polymer interactions and accelerate the PNP formulation development for HIP systems. The HIP interactions between a small hydrophilic molecule, AZD2811, and counterions with different molecular structures were investigated. Cyclic counterions formed amorphous ion pairs with AZD2811; the 0.7 pamoic acid/1.0 AZD2811 complex had the highest glass transition temperature (T_g; 162 °C) and the greatest drug loading (22%) and remained as phase-separated amorphous nanosized domains inside the polymer matrix. Palmitic acid (linear counterion) showed negligible interactions with AZD2811 (crystalline-free drug/counterion forms), leading to a significantly lower drug loading despite having similar log P and pK_a with pamoic acid. Computational calculations illustrated that cyclic counterions interact more strongly with AZD2811 than linear counterions through dispersive interactions (offset π-π interactions). Solubility data indicated that the pamoic acid/AZD2811 complex has a lower organic phase solubility than AZD2811-free base; hence, it may be expected to precipitate more rapidly in the nanodroplets, thus increasing drug loading. Our work provides a generalizable preformulation framework, complementing traditional performance-indicating parameters, to identify optimal counterions rapidly and accelerate the development of hydrophilic drug PNP formulations while achieving high drug loading without laborious trial-and-error experimentation.

Formulation Approaches to Crystalline Status Modification for Carotenoids: Impacts on Dissolution, Stability, Bioavailability, and Bioactivities

Carotenoids, including carotenes and xanthophylls, have been identified as bioactive ingredients in foods and are considered to possess health-promoting effects. From a biopharmaceutical perspective, several physicochemical characteristics, such as scanty water solubility, restricted dissolution, and susceptibility to oxidation may influence their oral bioavailability and eventually, their effectiveness. In this review, we have summarized various formulation approaches that deal with the modification of crystalline status for carotenoids, which may improve their physicochemical properties, oral absorption, and biological effects. The mechanisms involving crystalline alteration and the typical methods for examining crystalline states in the pharmaceutical field have been included, and representative formulation approaches are introduced to unriddle the mechanisms and effects more clearly.

Studying the Intermolecular Interactions, Structural Dynamics, and Non-Equilibrium Kinetics of Cilnidipine Infiltrated into Alumina and Silica Pores

In the present study, the behavior of the calcium channel blocker cilnidipine (CLN) infiltrated into silica (SiO₂) and anodic aluminum oxide (AAO) porous membranes characterized by a similar pore size (d = 8 nm and d = 10 nm, respectively) as well as the bulk sample has been investigated using differential scanning calorimetry, broadband dielectric spectroscopy (BDS), and Fourier-transform infrared spectroscopy (FTIR) techniques. The obtained data suggested the existence of two sets of CLN molecules in both confined systems (core and interfacial). They also revealed the lack of substantial differences in inter- and intramolecular dynamics of nanospatially restricted samples independently of the applied porous membranes. Moreover, the annealing experiments (isothermal time-dependent measurements) performed on the confined CLN clearly indicated that the whole equilibration process under confinement is governed by structural relaxation. It was also found that the β_anneal parameters obtained from BDS and FTIR data upon equilibration of both confined samples are comparable (within 10%) to each other, while the equilibration constants are significantly different. This finding strongly emphasizes that there is a close connection between the inter- and intramolecular dynamics under nanospatial restriction.

Polymorph control by designed ultrasound application strategy: The role of molecular self-assembly

Molecular self-assembly plays a vital role in the nucleation process and sometimes determines the nucleation outcomes. In this study, ultrasound technology was applied to control polymorph nucleation. For the first time, different ultrasonic application methods based on the nucleation mechanisms have been proposed. For PZA-water and DHB-toluene systems that the molecular self-assembly in solution resembles the synthon in crystal structure, ultrasound pretreatment strategy was conducted to break the original molecular interactions to alter the nucleated form. When the solute molecular self-associates can't give sufficient information to predict the nucleated polymorph like INA-ethanol system, the method of introducing continuous ultrasonic irradiation in the nucleation stage was applied. The induction of ultrasound during nucleation process can break the original interactions firstly by shear forces and accelerate the occurrence of nucleation to avoid the reorientation and rearrangement of solute molecules. These strategies were proved to be effective in polymorph control and have a degree of applicability.

A Comparative Study of the Pharmaceutical Properties between Amorphous Drugs Loaded-Mesoporous Silica and Pure Amorphous Drugs Prepared by Solvent Evaporation

The formulation of poorly water-soluble drugs is one of the main challenges in the pharmaceutical industry, especially in the development of oral dosage forms. Meanwhile, there is an increase in the number of poorly soluble drugs that have been discovered as new chemical entities. It was also reported that the physical transformation of a drug from a crystalline form into an amorphous state could be used to increase its solubility. Therefore, this study aims to evaluate the pharmaceutical properties of amorphous drug loaded-mesoporous silica (MPS) and pure amorphous drugs. Ritonavir (RTV) was used as a model of a poorly water-soluble drug due to its low recrystallization tendency. RTV loaded-MPS (RTV/MPS) and RTV amorphous were prepared using the solvent evaporation method. Based on observation, a halo pattern in the powder X-ray diffraction pattern and a single glass transition (T_g) in the modulated differential scanning calorimetry (MDSC) curve was discovered in RTV amorphous, indicating its amorphization. The T_g was not detected in RTV/MPS, which showed that the loading RTV was completed. The solid-state NMR and FT-IR spectroscopy also showed the interaction between RTV and the surface of MPS in the mesopores. The high supersaturation of RTV was not achieved for both RTV/MPS and the amorphous state due to its strong interaction with the surface of MPS and was not properly dispersed in the medium, respectively. In the dissolution test, the molecular dispersion of RTV within MPS caused rapid dissolution at the beginning, while the amorphous showed a low rate due to its agglomeration. The stability examination showed that the loading process significantly improved the physical and chemical stability of RTV amorphous. These results indicated that the pharmaceutical properties of amorphous drugs could be improved by loaded-MPS.

Polymorphic selectivity in crystal nucleation

Crystal nucleation rates have been measured in the supercooled melts of two richly polymorphic glass-forming liquids: ROY and nifedipine (NIF). ROY or 5-methyl-2-[(2-nitrophenyl)amino]-3-thiophenecarbonitrile is known for its crystals of red, orange, and yellow colors and many polymorphs of solved structures (12). Of the many polymorphs, ON (orange needles) nucleates the fastest with the runner up (Y04) trailing by a factor of 103 when compared under the same mobility-limited condition, while the other unobserved polymorphs are slower yet by at least 5 orders of magnitude. Similarly, of the six polymorphs of NIF, [Formula: see text]′ nucleates the fastest, [Formula: see text]′ is slower by a factor of 10, and the rest are slower yet by at least 5 decades. In both systems, the faster-nucleating polymorphs are not built from the lowest-energy conformers, while they tend to have higher energies and lower densities and thus greater similarity to the liquid phase by these measures. The temperature ranges of this study covered the glass transition temperature Tg of each system, and we find no evidence that the nucleation rate is sensitive to the passage of Tg. At the lowest temperatures investigated, the rates of nucleation and growth are proportional to each other, indicating that a similar kinetic barrier controls both processes. The classical nucleation theory provides an accurate description of the observed nucleation rates if the crystal growth rate is used to describe the kinetic barrier for nucleation. The quantitative rates of both nucleation and growth for the competing polymorphs enable prediction of the overall rate of crystallization and its polymorphic outcome.

Characterization of Drugs with Good Glass Formers in Loaded-Mesoporous Silica and Its Theoretical Value Relevance with Mesopores Surface and Pore-Filling Capacity

The incorporation of a drug into mesoporous silica (MPS) is a promising strategy to stabilize its amorphous form. However, the drug within MPS has shown incomplete release, despite a supersaturated solution being generated. This indicates the determination of maximum drug loading in MPS below what is experimentally necessary to maximize the drug doses in the system. Therefore, this study aimed to characterize the drugs with good glass former loaded-mesoporous silica, determine the maximum drug loading, and compare its theoretical value relevance to monolayer covering the mesoporous (MCM) surface, as well as pore-filling capacity (PFC). Solvent evaporation and melt methods were used to load each drug into MPS. In addition, the glass transition of ritonavir (RTV) and cyclosporine A (CYP), as well as the melting peak of indomethacin (IDM) and saccharin (SAC) in mesoporous silica, were not discovered in the modulated differential scanning calorimetry (MDSC) curve, demonstrating that each drug was successfully incorporated into the mesopores. The amorphization of RTV-loaded MPS (RTV/MPS), CYP-loaded MPS (CYP/MPS), and IDM-loaded MPS (IDM/MPS) were confirmed as a halo pattern in powder X-ray diffraction measurements and a single glass transition event in the MDSC curve. Additionally, the good glass formers, nanoconfinement effect of MPS and silica surface interaction contributed to the amorphization of RTV, CYP and IDM within MPS. Meanwhile, the crystallization of SAC was observed in SAC-loaded MPS (SAC/MPS) due to its weak silica surface interaction and high recrystallization tendency. The maximum loading amount of RTV/MPS was experimentally close to the theoretical amount of MCM, showing monomolecular adsorption of RTV on the silica surface. On the other hand, the maximum loading amount of CYP/MPS and IDM/MPS was experimentally lower than the theoretical amount of MCM due to the lack of surface interaction. However, neither CYP or IDM occupied the entire silica surface, even though some drugs were adsorbed on the MPS surface. Moreover, the maximum loading amount of SAC/MPS was experimentally close to the theoretical amount of PFC, suggesting the multilayers of SAC within the MPS. Therefore, this study demonstrates that the characterization of drugs within MPS, such as molecular size and interaction of drug-silica surface, affects the loading efficiency of drugs within MPS that influence its relevance with the theoretical value of drugs.

Nanoconfinement of a Pharmaceutical Cocrystal with Praziquantel in Mesoporous Silica: The Influence of the Solid Form on Dissolution Enhancement

Nanoconfinement is a recent strategy to enhance solubility and dissolution of active pharmaceutical ingredients (APIs) with poor biopharmaceutical properties. In this work, we combine the advantage of cocrystals of racemic praziquantel (PZQ) containing a water-soluble coformer (i.e., increased solubility and supersaturation) and its confinement in a mesoporous silica material (i.e., increased dissolution rate). Among various potential cocrystalline phases of PZQ with dicarboxylic acid coformers, the cocrystal with glutaric acid (PZQ-GLU) was selected and successfully loaded by the melting method into nanopores of SBA-15 (experimental pore size of 5.6 nm) as suggested by physical and spectroscopic characterization using various complementary techniques like N₂ adsorption, powder X-ray diffraction (PXRD), infrared spectroscopy (IR), solid-state NMR (ss-NMR), differential scanning calorimetry (DSC), and field emission-scanning electron microscopy (FE-SEM) analysis. The PZQ-GLU phase confined in SBA-15 presents more mobility according to ss-NMR studies but still retains its cocrystal-like features in the IR spectra, and it also shows depression of the melting transition temperature in DSC. On the contrary, pristine PZQ loaded into SBA-15 was found only in the amorphous state, according to the aforementioned studies. This dissimilar behavior of the composites was attributed to the larger crystal lattice of PZQ over the PZQ-GLU cocrystal (3320.1 vs 1167.9 ų) and to stronger intermolecular interactions between PZQ and GLU, facilitating the confinement of a more mobile solid-like phase in the constrained channels. Powder dissolution studies under extremely nonsink conditions (SI = 0.014) of the confined PZQ-GLU and amorphous PZQ phases embedded in mesoporous silica showed transient supersaturation behavior when dissolving in simulated gastric fluid (HCl pH 1.2 at 37 ± 0.5 °C) in a similar fashion to the bare cocrystal PZQ-GLU. A comparison of the area under the curve (AUC_0-90 min) of the dissolution profiles afforded a dissolution advantage of 2-fold (p < 0.05) of the new solid phases over pristine racemic PZQ after 90 min; under these conditions, the solubilized API reprecipitated as the recently discovered PZQ hemihydrate (PZQ-HH). In the presence of a cellulosic polymer, sustained solubilization of PZQ from composites SBA-15/PZQ or SBA-15/PZQ-GLU was observed, increasing AUC_0-90 min up to 5.1-fold in comparison to pristine PZQ. The combination of a confined solid phase in mesoporous silica and a methylcellulose polymer in the dissolution medium effectively maintained the drug solubilized during times significant to promote absorption. Finally, powder dissolution studies under intermediate nonsink conditions (SI = 1.99) showed a fast release profile from the nanoconfined PZQ-GLU phase in SBA-15, which reached rapid saturation (95% drug dissolved at 30 min); the amorphous PZQ composite and bare PZQ-GLU also displayed an immediate release of the API but at a lower rate (69% drug dissolved at 30 min). In all of these cases, a large dissolution advantage was observed from any of the novel solid phases over PZQ.

Encapsulation of drug into mesoporous silica by solvent evaporation: A comparative study of drug characterization in mesoporous silica with various molecular weights

Mesoporous silica (MS) is a promising material as a drug carrier that is used in pharmaceutical applications. It was discovered that the incorporation of drugs into MS has the potential to improve their dissolution and bioavailability due to the large specific surface area. This study aimed to characterize the drugs with various molecular weights in MS as well as to elucidate their impact on the loading amount and the amorphization within MS. The solvent evaporation method was used to encapsulate itraconazole (ITZ), nifedipine (NIF), and nicotinamide (NIC), respectively, into MS. The result shows the absence of glass transition and the melting peak of ITZ, NIF, and SAC within MS signifying the successful encapsulation. A hallo pattern was found in ITZ and NIF within MS indicating the amorphization. The high molecular weight and the interaction between the drug with the silica surface is reportedly contributed to the formation of the amorphous state. Meanwhile, the characteristic diffraction peaks of NIC crystal were observed for NIC within MS. In conclusion, the molecular weight of the drug has a significant effect on the loading amount and the amorphization of the drug within MS.

Thermal properties and cold crystallization kinetics of deep eutectic solvents confined in nanopores

Herein, the phase behaviors of both bulk and confined deep eutectic solvents in controlled pore glasses were first investigated. Glass transition, cold crystallization and melting behaviors alter significantly in the nanopores due to the size effect and interfacial interactions. Kinetic analysis of the crystallization reveals increased effective activation energies and pre-exponential factors under nanoconfinement.

Influence of Adsorption State and Molecular Interaction on Physical Stability of Confined Amorphous Vortioxetine

The composites of amorphous vortioxetine (VXT) and ordered mesoporous silica were prepared. Three silica matrixes with different pore sizes were used here: Mobil Composition of Matter No.41 (MCM), Santa Barbara Amorphous No.15 (SBA), and mesostructured cellular foam (MCF). The amorphous composites behaved enhanced physical stability (303.15 K, 56.0 ± 0.4% RH) compared to bulk VXT amorphism. Interestingly, the physical stability of these amorphous composites showed a great difference. Amorphous VXT loaded in MCF crystallized within 1 week, while VXT-SBA composites could be stable over 3 months. The stability of VXT-MCM composites were somewhere in between. In addition, with VXT loading decreasing, the physical stability of confined amorphous VXT became better. Nitrogen adsorption measurements indicated that VXT molecules were adsorbed in SBA in a dispersive state while aggregated in MCM and MCF. VXT-VXT interactions in MCM could be stronger than that in SBA. ¹H-¹³C solid-state nuclear magnetic resonance experiments demonstrated the weaker VXT-VXT interactions in SBA. The dispersive adsorption state and weak VXT-VXT interactions were benefit to the physical stability of amorphous VXT in SBA channels. In addition, dissolution profiles of confined amorphous VXT and bulk crystalline VXT were determined and the dissolution rate of VXT loaded in nanopores was faster than the latter.

Isothermal Crystallization and Time-Temperature Transformation of Amorphous Nifedipine: A Case of Polymorphism Formation and Conversion

Crystallization of active pharmaceutical ingredients (APIs) from the supercooled liquid state is an important issue in determining the stability of amorphous pharmaceutical dispersions. In the present study, the isothermal crystallization from the supercooled liquid state of the pharmaceutical compound nifedipine was investigated by both rheological and differential scanning calorimetry (DSC) measurements, and the crystallization kinetics was fitted to the Johnson-Mehl-Avrami (JMA) equation. Both the crystallization induction time and completion time from the two methods were used to construct the time-temperature-transformation (TTT) diagram for nifedipine. A model based on a modification of classical homogeneous nucleation and crystal growth theory was employed to fit the induction and completion time curves. Both DSC and rheological methods give similar results for the crystallization kinetics of the nifedipine. From the crystallization kinetics modeling, the solid-liquid interfacial surface tension σ_SL of nifedipine was estimated and the value was found to be consistent with prior results obtained from melting point depression measurements as a function of crystal size. Evidence is shown that for temperatures below 110 °C, at the early stage of nucleation, NIF first nucleates into the metastable β'-form and later converts into the stable α-form during the isothermal crystallization. We are also able to report the heat of fusion of the γ'-NIF based on the calorimetric experiments.

Monitoring Crystallization Processes in Confined Porous Materials by Dynamic Nuclear Polarization Solid-State Nuclear Magnetic Resonance

Establishing mechanistic understanding of crystallization processes at the molecular level is challenging, as it requires both the detection of transient solid phases and monitoring the evolution of both liquid and solid phases as a function of time. Here, we demonstrate the application of dynamic nuclear polarization (DNP) enhanced NMR spectroscopy to study crystallization under nanoscopic confinement, revealing a viable approach to interrogate different stages of crystallization processes. We focus on crystallization of glycine within the nanometric pores (7-8 nm) of a tailored mesoporous SBA-15 silica material with wall-embedded TEMPO radicals. The results show that the early stages of crystallization, characterized by the transition from the solution phase to the first crystalline phase, are straightforwardly observed using this experimental strategy. Importantly, the NMR sensitivity enhancement provided by DNP allows the detection of intermediate phases that would not be observable using standard solid-state NMR experiments. Our results also show that the metastable β polymorph of glycine, which has only transient existence under bulk crystallization conditions, remains trapped within the pores of the mesoporous SBA-15 silica material for more than 200 days.

Effect of drug-coformer interactions on drug dissolution from a coamorphous in mesoporous silica

In this study, the molecular state of ritonavir (RTN)-saccharin (SAC) coamorphous incorporated into mesoporous silica by solvent evaporation and the effect of SAC on the RTN dissolution from mesopores were investigated. The amorphization of RTN-SAC was confirmed as a halo pattern in powder X-ray diffraction measurements and a single glass transition event in the modulated differential scanning calorimetry (MDSC) curve. ¹³C solid-state NMR spectroscopy revealed a hydrogen bond between the thiazole nitrogen of RTN and the amine proton of SAC. The glass transition of the RTN-SAC coamorphous in mesoporous silica was not found in the MDSC curve, indicating that RTN and SAC were monomolecularly incorporated into the mesopores. Solid-state NMR measurements suggested that the co-incorporation of SAC into the mesopores decreased the local mobility of the thiazole group of RTN via hydrogen bond formation. The RTN-SAC 1:1 coamorphous in mesoporous silica retained the X-ray halo-patterns after 30 d of storage, even under high temperature and humidity conditions. In the dissolution test, the RTN-SAC 1:1 coamorphous in mesoporous silica maintained RTN supersaturation for a longer time than the RTN amorphous in mesoporous silica. This study demonstrated that the drug-coformer interaction within mesoporous silica can significantly improve drug dissolution.

Effect of Nanopore Geometry in the Conformation and Vibrational Dynamics of a Highly Confined Molecular Glass

The effect of nanoporous confinement on the glass transition temperature (T_g) strongly depends on the type of porous media. Here, we study the molecular origins of this effect in a molecular glass, N,N'-bis(3-methylphenyl)-N,N'-diphenylbenzidine (TPD), highly confined in concave and convex geometries. When confined in controlled pore glass (CPG) with convex pores, TPD's vibrational spectra remained unchanged and two T_g's were observed, consistent with previous studies. In contrast, when confined in silica nanoparticle packings with concave pores, the vibrational peaks were shifted due to more planar conformations and T_g increased, as the pore size was decreased. The strong T_g increases in concave pores indicate significantly slower relaxation dynamics compared to CPG. Given TPD's weak interaction with silica, these effects are entropic in nature and are due to conformational changes at molecular level. The results highlight the role of intramolecular degrees of freedom in the glass transition, which have not been extensively explored.

Manipulating the physical states of confined ibuprofen in SBA-15 based drug delivery systems obtained by solid-state loading: Impact of the loading degree

Using the Milling-Assisted Loading (MAL) solid-state method for loading a poorly water-soluble drug (ibuprofen, IBP) within the SBA-15 matrix has given the opportunity to manipulate the physical state of drugs for optimizing bioavailability. The MAL method makes it easy to control and analyze the influence of the degree of loading on the physical state of IBP inside the SBA-15 matrix with an average pore diameter of 9.4 nm. It was found that the density of IBP molecules in an average pore size has a direct influence on both the glass transition and the mechanism of crystallization. Detailed analyzes of the crystallite distribution and melting by Raman mapping, x-ray diffraction, and differential scanning calorimetry have shown that the crystals are localized in the core of the channel and surrounded by a liquid monolayer. The results of these complementary investigations have been used for determining the relevant parameters (related to the SBA-15 matrix and to the IBP molecule) and the nature of the physical state of the confined matter.

Influence of Drug-Silica Electrostatic Interactions on Drug Release from Mesoporous Silica-Based Oral Delivery Systems

Mesoporous silica particles are attractive carriers for poorly soluble drugs whereby confinement of drugs in the mesopores leads to amorphization, which makes them potential carriers for enhanced oral delivery. However, interactions between the drug molecules and the silica surface can lead to incomplete drug release. The strength of the interaction depends on the silica surface chemistry, which varies as a function of pH, as well as on drug chemistry and ionization states. Herein, the adsorption and dissolution behavior of weakly basic drugs were evaluated as a function of pH to understand the impact of electrostatic interactions on the performance of mesoporous silica-based formulations. A higher adsorption was noted when the drug interacted with the silica surface via electrostatic interactions compared to hydrogen bonding. Higher adsorption, in turn, led to a lower extent of drug release. In two-stage release studies of drugs with pK_a values close to the intestinal pH, a shift from low to higher pH solutions resulted in a decrease in the solution concentration. Further investigations demonstrated that this was due to readsorption of the drug, initially released in the acidic medium when the pH was increased. Two-stage release studies were also coupled with mass transport measurements. Only a slight improvement in drug release due to simultaneous absorption across a membrane was observed, suggesting strong drug adsorption to the silica surface arising from favorable electrostatic interactions, which diminishes the effect of sink conditions provided by the absorptive environment. This study highlights that physiological parameters, such as solution pH, are important considerations when designing mesoporous silica-based formulations for poorly soluble drugs. It also underscores the importance of incorporating in vivo-relevant conditions in in vitro testing to better evaluate these complex formulations due to the notable effect of dissolution media on the release behavior.

Structure and thermodynamics of mixed polymeric micelles with crystalline cores: tuning properties via co-assembly

We investigate micelles formed by mixtures of n-alkyl-poly(ethylene oxide) block copolymers, Cn-PEO, with different alkyl block lengths in aqueous solution. This model system has previously been used to shed light on the interplay between exchange kinetics and crystallinity in self-assembling systems [König et al., Phys. Rev. Lett., 2019, 122, 078001]. Now we report on the structure and thermodynamics of these micelles by combining results from small-angle X-ray scattering, differential scanning calorimetry and volumetric measurements. We show that mixed micelles are formed despite the fact that length-mismatched n-alkanes of similar weights in bulk tend to demix below the crystallization temperature. Instead, the system exhibits similar properties as single-component micelles but with a modulated melting region. Interestingly, the melting point depression due to self-confinement within the micellar core can be approximately described by a generalized Gibbs-Thomson equation, similar to single-component micelles [Zinn et al. Phys. Rev. Lett., 2014, 113, 238305]. Furthermore, we find a novel scaling law for these micelles where, at least for larger n, the aggregation number scales with the third power of the length of the hydrophobic block, Nagg ∝ n3. Possibly, there might be a cross-over from the conventional Nagg ∝ n2 behaviour around n ≈ 19. However, the reason for such a transition as well as the strong n dependence remains a challenge and requires more theoretical work.