Solid-state Characterization Research Articles

Interface modulation of Pt/Al2O3 catalyst and their roles in thermal stability

Interfacial local environment of noble metal nanoparticles (NPs) and support is crucial for the development and design of thermally and chemically stable noble metal heterogeneous catalysts. The unique chemical environment can strengthen the NPs interaction with the support surface, which can effectively avoid the agglomeration of NPs. The strategy is developed to modulate the interfacial chemical environment of supported Pt NPs with the help of the unsaturated Al3+ in Al2O3N (nanobelt) support, resulting in a sintering-resistant Pt/Al2O3N catalyst. Al solid-state MAS NMR characterization shows that Al2O3N support contains a large amount of unsaturated Alpenta3+ (about 22.6%). XAS confirms that Pt NPs deposited on the surface of Al2O3 with rich unsaturated pentahedral coordinated Al3+ sites have a unique coordination structure at the interface (more Pt-O coordination). When catalyzing the CO oxidation as a probe reaction, the catalytic activity and the particle sizes of Pt NPs do not change significantly even after the reaction at 400 °C for 15 days, and the complete CO conversion temperature increases only by 40 °C when the catalyst is screened at 600 °C for 5 days. This work demonstrates a new strategy to develop stable large-scale anti-sintering noble metal-based heterogeneous catalysts for many important high-temperature industrial applications.

A Package of Established Analytical Tools to Investigate the Solid-State Alteration of Lipid-Based Excipients.

Lipid-based excipients (LBEs) are low-toxic, biocompatible, and natural-based, and their application supports the sustainability of pharmaceutical manufacturing. However, the major challenge is their unstable solid-state, affecting the stability of the pharmaceutical product. Critical physical properties of lipids for their processing-such as melt temperature and viscosity, rheology, etc.-are related to their molecular structure and their crystallinity. Additives, as well as thermal and mechanical stress involved in the manufacturing process, affect the solid-state of lipids and thus the performance of pharmaceutical products thereof. Therefore, understanding the alteration in the solid-state is crucial. In this work, the combination of powder x-ray diffraction and differential scanning calorimetry (DSC) is introduced as the gold standard for the characterization of lipids' solid state. X-ray diffraction is the most efficient method to screen polymorphism and crystal growth. The polymorphic arrangement and the lamella length are characterized in the wide- and small-angle regions of x-ray diffraction, respectively. The small-angle x-ray scattering (SAXS) region can be further used to investigate crystal growth. Phase transition and separation can be indicated. DSC is used to screen the thermal behavior of lipids, estimate the miscibility of additives and/or active pharmaceutical ingredients (API) in the lipid matrix, and provide phase diagrams. Four case studies are presented in which LBEs are either used as a coating material or as an encapsulation matrix to provide lipid-coated multiparticulate systems and lipid nanosuspensions, respectively. The lipid solid-state and its potential alteration during storage are investigated and correlated to the alteration in the API release. Qualitative microscopical methods such as polarized light microscopy and scanning electron microscopy are complementary tools to investigate micro-level crystallization. Further analytical methods should be added based on the selected manufacturing process. The structure-function-processability relationship should be understood carefully to design robust and stable lipid-based pharmaceutical products.

Electrospun MnCo2O4/carbon-nanofibers as oxygen electrode for alkaline zinc-air batteries

A MnCo2O4 catalyst supported on nitrogen-doped carbon nanofibers (CNF) obtained in a single-step electrospinning process is presented. MnCo2O4/CNF is investigated as bifunctional electrode for the electrocatalysis of oxygen in metal-air batteries. Crystallographic structure, morphology, and surface properties are analyzed using solid-state characterization techniques that reveal the presence of a 20 nm-particle-sized spinel and a large amount of oxidized metal species (Mn4+ and Co3+). These features are correlated with the electrochemical behavior for the oxygen reduction (ORR) and oxygen evolution (OER), showing good performances in particular for the OER compared with IrO2, benchmark catalyst for this reaction. Results revealed a synergistic effect of the catalytically active nitrogen-doped carbon nanofiber and the manganese and cobalt active species from the spinel, being responsible for the remarkable reversibility of this catalyst (ΔE = 799 mV), outperforming most of the previous works in the literature on this type of manganese/cobalt-based spinel materials. A preliminary test of an alkaline Zn-air battery equipped with this catalyst at the oxygen (positive) electrode confirms proper activity and stability during cycling operations typical of these rechargeable devices. Besides, the spinel-nanofiber-based catalyst has been produced by an easily-scalable electrospinning process, representing an advance of the current technology on positive electrodes for metal-air batteries. The curated synthesis of our MnCo-N-CNF spinel is fundamental to obtaining a catalyst with a high intrinsic catalytic activity (determined by rotating disk electrode) and an appropriate performance in a relevant environment (both gas diffusion electrode and Zn-air battery).

Pain Management with Topical Aceclofenac Nanosuspension In-Vitro/In- Vivo and Proof of Concept Studies

Introduction: Pain is one of the most common medical conditions and affects more than diabetes, heart disease, and cancer combined. Current pain treatments mainly rely on NSAIDs analgesics and remain unsatisfactory. Due to associated adverse effects such as gastrointestinal ulcers and bleeding and low solubility limits its uses. Objective: The present research focus on advance in the field of pain treatment by topical delivery of NSAIDs (aceclofenac) drugs via enhancing its solubility and diminishing related side effects. Materials and Methods: ACE-nanosuspension (ACE-NS) prepared by anti-solvent precipitation technique was characterized for particle size, PDI, zeta-potential, total drug content, DSC, FTIR, P-XRD and FESEM. Further spreadabilty, ex-vivo occlusivity, in-vitro release, ex-vivo skin permeation and retention and stability studies were performed. Dermal irritation and histopathological examinations were conducted in accordance to OECD guidelines. Proof of concept studies were accomplished using radiant tail flick and paw-licking animal model. Results: ACE-NS showed particle size of 148 ±15 nm with PDI: 0.170, zeta potential: 21.2 mV and total drug content of 86±0.23% respectively. DSC, FT-IR, P-XRD and FESEM studies revealed the thermal behavior, compatibility, solid state characterization and morphology of ACE-NS. ACE-NS loaded ointment showed a spreadability ratio of 0.23 and a drug content of 84±1.15%. In-vitro release of ACE from nano-ACE-ointment (88.07%) was higher than marketed formulation (70.55%) and free drug ointment (70.45%) after 24 hours. Release profile of nano-ACE-ointment fitted best for Higuchi model with r2 = 0.94 and n = 0.45 and its permeation flux was 9.2312 ± 0.8430 mg/cm2/h, which was significantly higher (p ≤0.05) than ACE marketed gel (2.6158 ± 0.4352 mg/cm2/h). Cutaneous irritation and histological studies revealed no inflammatory skin lesions post treatment with ACE-NS. Furthermore, ACE-NS-ointment showed better analgesic effect than marketed formulation in both radiant tail flick model (2.87 times) and paw-licking (2.73 times) animal model. Conclusion: Studies highlighted the potential of topical nano-ACE-ointment for pain management.

Building hybrid luminescent materials: Understanding stacking modes in aggregate structure to emission modulation

Two charge transfer (CT) complexes A1 and A2 with tunable emissions were explored by diluting anthracene functionalized stilbene as donors with 1,2,4,5-tetracyanobenzene (TCNB) as the acceptor unit. The effect of substituent tailoring on the supramolecular packing and optical properties of the two CT products was accomplished by various solid-state characterization and theoretical calculations. It was found that these binary CT cocrystals exhibit two types of alternatively sandwiched face-to-face patterns (A1 (DADA), A2 (DAD··DAD), and red-shifted emissions relative to their monomers through π-π interactions accompanied by hydrogen bonds as indicated by the structural analysis. The two crystalline aggregates feature molar ratios of 1:1 or 1:2 and molecular packing-dependent emissions, induced by different dihedral angles attributed to the substituent effect, thereby leading to diverse π-π interactions and charge transfer effects respectively, which further results in tunable photophysical properties. These results suggest that the marriage of substituent engineering and cocrystal engineering is a promising molecular design strategy that will help to understand the relationship between emission property and molecular packing with the aim to guide further the development of novel organic solid luminescent materials.

Development and exploration on flowability of solid self-nanoemulsifying drug delivery system of morin hydrate

• Solid SNEDDS of MH was prepared by physical adsorption method. • Flowability of solid SNEDDS was investigated by powder flow tester. • Solid state characterization confers transformation of crystalline to amorphous. • In vitro- In vivo studies revealed an improvement of dissolution & bioavailability. • The estimated shelf life of solid SNEDDS of MH was found to be 27.57 months. Morin hydrate (MH) is a promising flavonoid with diverse biological activities; unfortunately, it finds limited clinical application due to its low water solubility. Herein, we developed a liquid self nano-emulsifying drug delivery system ( l -SNEDDS) employing Labrafil M 1994 CS, Cremophor RH 40, and Transcutol HP. The l -SNEDDS has been solidified by physical adsorption using inert carriers, i.e., Neusilin US2 and Aerosil 200. The S-SNEDDS was thoroughly investigated for flow function (FF), effective angle of wall friction (EAWF), and effective angle of internal friction (EAIF) employing a powder flow tester (PFT). The solid-state characterizations of S-SNEDDS were performed using FTIR, DSC, PXRD, and SEM. Further, in vitro dissolution, in vivo pharmacokinetic, and shelf life estimation were performed on selected SOF-2 formulation. The SOF-2 reveals good emulsifying ability, particle size (52 ± 4.25 nm), and PDI (0.133 ± 0.06). The FF and Jenike’s classification suggests the “free-flowing” nature of S-SNEDDS prepared using Neusilin US2. Further, S-SNEDDS prepared using Neusilin US2 showed a low friction angle, i.e., EAWF and EAIF, than Aerosil 200, therefore, a better flowability. The solid-state characterization of SOF-2 demonstrated the transition of MH from crystalline to amorphous state and good compatibility between MH and Neusilin US2. Further, SOF-2 showed more dissolution than pure MH and subsequently 2.97-fold increments in its oral bioavailability. Moreover, the shelf life of SOF-2 was reported to be 27.57 months, suggesting its excellent physical and chemical stability. In brief, solidifying l -SNEDDS and investigating flow behaviors by PFT could find attention in the pharmaceutical and food industry for commercial purposes.

Mechanochemical synthesis, crystal structure analysis and solid-state characterization of quininium aspirinate, a drug–drug salt

Mechanochemical synthesis, crystal structure analysis and solid-state characterization of quininium aspirinate, a drug–drug salt

Solid-State synthesis, structural and magnetic characterization of ferromagnetic phases in 24Ga/76Fe(0 0 1), 40Ga/60Fe(0 0 1) and 60Ga/40Fe(0 0 1) bilayers

The A2, B2, D03 phases and dispersive nanoprecipitates play key roles in the nature of super-functional properties, such as the large and sensitive magnetostriction, in Fe100-xGax alloys. However, the temperature conditions for the occurrence of the chemical interaction between Fe and Ga, leading to the synthesis of these phases and nanoprecipitates, remain completely unexplored. Herein we first report results of the start of the chemical interaction at the Ga/Fe(001) interface and the structural and magnetic phase transformations in 24Ga/76Fe(001), 40Ga/60Fe(001) and 60Ga/40Fe(001) bilayers from room temperature to 800 °C.For all bilayers the magnetic ordered D03 phase is the first phase which is formed at the Ga/Fe(001) interface at ∼ 375 °C. When the annealing temperature is increased above 580 °C in 24Ga/76Fe(001) samples the epitaxial D03(001) layer begins to develop into the epitaxial magnetic ordered B2(001) layer, which remains after annealing to 800 °C. In 40Ga/60Fe(001) samples the epitaxial D03(001) layer evolves into the epitaxial B2(001) layer and a new epitaxial layer with interplanar spacing 0.1484 nm (L60ʹ), which has close reflections with L60 nanoprecipitates. The L60ʹ phase exhibits unique magnetic properties, including a large magnetic fourfold anisotropy constant of ∼ 7·105erg/cm3 and 8-fold anisotropy. The solid-state reactions in 60Ga/40Fe(001) samples start with the synthesis of D03 nanograins embedded in amorphous phases, whose peaks are centered on D03(004) and Fe(002) reflections. Above 700 °C the amorphous phases partially crystallize and the epitaxial magnetic L60ʹ and ordered B2(001) phases emerge. Dewetting and unidentified secondary precipitations are observed in all samples and their influence on the magnetic properties is discussed. Our results demonstrate not only the complex nature of initial stage Fe100-xGax alloy synthesis, but also predict the low-temperature transformation at ∼ 375 °C in the Fe - Ga phase diagram.

Solid-state synthesis, characterizations and luminescent properties of EuBO3 phosphors with various Gd3+ concentrations for X-ray screen material application

In the present work, EuBO3 phoshors doped with various Gd3+ ion concentration, Eu1-XGdXBO3; (x = 0.0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6 and 0.7), were synthesized by solid state reaction method at 900° for 18 h. Their crystal structure was determined by X-ray diffraction (XRD) technique showing triclinic EuBO3 (JCSD 01-089-7888) and hexagonal crystal EuBO3 (JCDD 00-013-0485). Structure dependence luminescence concentration quenching was observed. The photoluminescence behaviors of Eu3+ in the phosphor material were investigated by the excitation and emission spectra which show the charge-transfer band (CTB) of O2−→Eu3+. The excitation bands of Gd3+ ions were observed at 275 nm (8S7/2 → 6I9/2) and 313 (8S7/2 → 6D7/2). The emission spectra displayed two prominent peaks of magnetic dipole (5D0→7F1) and electric dipole (5D0→7F2) transitions which signify the symmetry of the lattice. The CIE chromaticity coordinates were reddish-orange emission (x = 0.6635, y = 0.364) which corresponds to excited by the UVGL-25 Compact UV Lamp at 365 nm and X-ray Cu target (40 kV, 30 mA).

Fabrication, In Vitro and In Vivo Evaluation of Non-Ordered Mesoporous Silica-Based Ternary Solid Dispersions for Enhanced Solubility of Flurbiprofen

The aim of this study was to improve the solubility and prevent the ulcerogenic effect of flurbiprofen. Initially, binary and ternary solid dispersions (BSDs and TSDs) of flurbiprofen were prepared by using non-ordered mesoporous silica and gelucire. After preformulation testing (solubility, flow properties, % yield, and entrapment efficiency), four formulations were selected for further detailed studies. Solid-state characterization of optimized formulations (S1, S6, S7, and S12) showed successful drug incorporation in the solid dispersion at the molecular state without any noticeable interactions. The in vitro solubility and release study showed an increase in solubility and 98–100% of drug release in 30–45 min. The in vivo gastro-protective effect of the optimized formulations containing flurbiprofen and silica (1:1) with 25% w/w gelucire (S6 and S12) showed a reduction in the gastric lesion index (GLI) after four days of treatment. Moreover, histological images of the stomach lining (S6 and S12) illustrated normal epithelial cells and a partially protected mucosal membrane. Thus, TSD exhibited a significant increase in solubility and the dissolution rate and reduced the gastric ulceration. Therefore, TSDs are dubbed as efficacious carriers to enhance the bioavailability of flurbiprofen while simultaneously reducing its side effects.

Insights into Cocrystallization and Coamorphization Engineering Techniques in the Delivery of Traditional Chinese Medicine: Formation Mechanism, Solid-State Characterization, and Improved Pharmaceutical Properties

Insights into Cocrystallization and Coamorphization Engineering Techniques in the Delivery of Traditional Chinese Medicine: Formation Mechanism, Solid-State Characterization, and Improved Pharmaceutical Properties

Acid-etched Halloysite nanotubes as superior carriers for ciprofloxacin

Clay minerals have opened new avenues in drug delivery, including antimicrobials, greatly enhancing the stability and efficacy of the active payloads. Among these clay mineral hosts, Halloysite nanotubes (HNT) have emerged as a prominent carrier owing to their intrinsic mesoporous tubular nanostructure and high adsorption capacity. The acidic etching of HNT increases their specific surface area and porosity, consequently enhancing their loading potential. In this work, we show for the first time, that etched HNT (E-HNT) are superior carriers of the potent antibiotic ciprofloxacin (CIP) compared to pristine HNT in terms of loading capacity and antibacterial effect. The loading conditions are optimized within near-physiological conditions to enable future combinations with biomolecules; where CIP loading and release are characterized by UV–Vis measurements and thermogravimetry. Solid-state characterization suggests an adsorptive loading mechanism, involving electrostatic attraction and possible tautomerism. Release experiments show that the loaded CIP exhibits a sustained release profile and maintains its antibacterial potency as confirmed by the broth microdilution (BMD) and zone of inhibition methods. Thus, the facile etching of HNT enhances the nanoclay properties rendering it suitable for future application in drug delivery formulations.

Photochemistry and Photophysics of Charge-Transfer Excited States in Emissive d10/d0 Heterobimetallic Titanocene Tweezer Complexes.

Transition-metal complexes that undergo ligand-to-metal charge transfer (LMCT) to d0 metals are of interest as possible photocatalysts due to the lack of deactivating d-d states. Herein, the synthesis and characterization of nine titanocene complexes of the formula Cp2Ti(C2Ar)2·MX (where Ar = phenyl, dimethylaniline, or triphenylamine; and MX = CuCl, CuBr, or AgCl) are presented. Solid-state structural characterization demonstrates that MX coordinates to the alkyne tweezers and CuX coordination has a greater structural impact than AgCl. All complexes, including the parent complexes without coordinated MX, are brightly emissive at 77 K (emission max between 575 and 767 nm), with the coordination of MX redshifting the emission in all cases except for the coordination of AgCl into Cp2Ti(C2Ph)2. TDDFT investigations suggest that emission is dominated by arylalkynyl-to-titanium 3LMCT in all cases except Cp2Ti(C2Ph)2·CuBr, which is dominated by CuBr-to-Ti charge transfer. In room-temperature fluid solution, only Cp2Ti(C2Ph)2 and Cp2Ti(C2Ph)2·AgCl are emissive, albeit with photoluminescent quantum yields ≤2 × 10-4. The parent complexes photodecompose in room-temperature solution with quantum yields, Φrxn, between 0.25 and 0.99. The coordination of MX decreases Φrxn by two to three orders of magnitude. There is a clear trend that Φrxn increases as the emission energy increases. This trend is consistent with a competition between energy-gap-law controlled nonradiative decay and thermally activated intersystem crossing between the 3LMCT state and the singlet transition state for decomposition.

Positive Cooperativity Induced by Interstrand Interactions in Silver(I) Complexes with α,α'-Diimine Ligands.

The allosteric positive cooperativity accompanying the formation of compact [CuI(α,α′‐diimine)2]+ building blocks contributed to the historically efficient synthesis of metal‐containing catenates and knotted assemblies. However, its limited magnitude can easily be overcome by the negative chelate cooperativity that controls the overall formation of related polymetallic multistranded helicates and grids. Despite the more abundant use of analogous dioxygen‐resistant [AgI(α,α′‐diimine)2]+ units in modern entangled metallo‐supramolecular assemblies, a related thermodynamic justification was absent. Solid‐state structural characterizations show the successive formation of [AgI(α,α′‐diimine)(CH3CN)][X] and [AgI(α,α′‐diimine)2][X] upon the stepwise reactions of α,α′‐diimine=2,2′‐bipyridine (bpy) or 1,10‐phenanthroline (phen) derivatives with AgX (X=BF4 −, ClO4 −, PF6 −). In room‐temperature, 5–10 mM acetonitrile solutions, these cationic complexes exist as mixtures in fast exchange on the NMR timescale. Spectrophotometric titrations using the unsubstituted bpy and phen ligands point to the statistical (=non‐cooperative) binding of two successive bidentate ligands around AgI, a mechanism probably driven by the formation of hydrophobic belts, that overcomes the unfavorable decrease in the positive charge borne by the metallic cation. Surprisingly, the addition of methyl groups adjacent to the nitrogen donors (6,6′ positions in dmbpy; 2,9 positions in dmphen) induces positive cooperativity for the formation of [Ag(dmbpy)2]+ and [Ag(dmphen)2]+, a trend assigned to additional stabilizing interligand interactions. Adding rigid and polarizable phenyl side arms in [Ag(Brdmbpy)2]+ further reinforces the positively cooperative process, while limiting the overall decrease in metal–ligand affinity.

Development and evaluation of nanocrystals loaded hydrogel for topical application

Our main aim in the present investigation, development and evaluation of the Niclosamide (NCL) based nanocrystals (NC) and hydrogel to provide effective anti-psoriatic activity. The prepared nanosuspension of NCL was stabilized by using poly-vinyl-pyrrolidone/vinyl acetate (PVP/VA) co-polymer with 1:1 ratio (drug/polymer-copolymer) to get stable nanocrystals, which were further modified using hyaluronic acid to provide CD-44 targeting. Central composite design of the experiment was applied in the study to screen out the various independent variables and their response surface graphs. The particle size and polydispersity index of the nanosuspension was measured 173.3 ± 10.2 nm and 0.221 ± 0.09. The solid-state characterization was performed using electron microscopy, Differential scanning calorimetry, powdered x-ray diffraction, and spectroscopic techniques of prepared nanocrystals. The NCL-hydrogel was shows the drug content 95.5% ± 0.12 to 96.5% ± 0.4 and delayed 8.25 ± 1.6% drug released in 12hr. The NCL-hydrogel was found stable at 25 ± 2 °C. The drug release pattern follows the Higuchi model with the highest regression coefficient (R2) and minimum Akaike Information Criteria value (AIC). Cytotoxicity assay in HaCaT cells showed an increase in inhibitory effect by all the formulations than coarse-NCL. The IC50 value NCL, F1 and F2 were found to be 1.25 μM (373 μg/ml), 0.017 μM (57 ng/ml) and 0.023 μM (74 ng/ml), respectively at 48hr using HaCaT cells.

Topologically Driven Pore/Surface Engineering in a Recyclable Microporous Metal-Organic Vessel Decorated with Hydrogen-Bond Acceptors for Solvent-Free Heterogeneous Catalysis.

The use of metal-organic frameworks (MOFs) comprising custom-designed linkers/ligands as efficient and recyclable heterogeneous catalysts is on the rise. However, the topologically driven bifunctional porous MOFs for showcasing a synergistic effect of two distinct activation pathways of substrates (e.g., involving hydrogen bonding and a Lewis acid) in multicomponent organic transformations are very challenging. In particular, the novelty of such studies lies in the proper pore and/or surface engineering in MOFs for bringing the substrates in close proximity to understand the mechanistic aspects at the molecular level. This work represents the topological design, solid-state structural characterization, and catalytic behavior of an oxadiazole tetracarboxylate-based microporous three-dimensional (3D) metal-organic framework (MOF), {[Zn2(oxdia)(4,4'-bpy)2]·8.5H2O}n (1), where the tetrapodal (4-connected) 5,5'-(1,3,4-oxadiazole-2,5-diyl)diisophthalate (oxdia4-), the tetrahedral metal vertex (Zn(II)), and a 2-connected pillar linker 4,4'-bipyridine (4,4'-bpy) are unique in their roles for the formation, stability, and function. As a proof of concept, the efficient utilization of both the oxadiazole moiety with an ability to provide H-bond acceptors and the coordinatively unsaturated Zn(II) centers in 1 is demonstrated for the catalytic process of the one-pot multicomponent Biginelli reaction under mild conditions and without a solvent. The key steps of substrate binding with the oxadiazole moiety are ascertained by a fluorescence experiment, demonstrating a decrease or increase in the emission intensity upon interaction with the substrates. Furthermore, the inherent polarizability of the oxadiazole moiety is exploited for CO2 capture and its size-selective chemical fixation to cyclic carbonates at room temperature and under solvent-free conditions. For both catalytic processes, the chemical stability, structural integrity, heterogeneity, versatility in terms of substrate scope, and mechanistic insights are discussed. Interestingly, the first catalytic process occurs on the surface, while the second reaction occurs inside the pore. This study opens new ways to catalyze different organic transformation reactions by utilizing this docking strategy to bring the multiple components close together by a microporous MOF.

Synthesis, Optical Characterization in Solution and Solid-State, and DFT Calculations of 3-Acetyl and 3-(1'-(2'-Phenylhydrazono)ethyl)-coumarin-(7)-substituted Derivatives.

Intramolecular charge transfer (ICT) effects are responsible for the photoluminescent properties of coumarins. Hence, optical properties with different applications can be obtained by ICT modulation. Herein, four 3-acetyl-2H-chromen-2-ones (1a–d) and their corresponding fluorescent hybrids 3- (phenylhydrazone)-chromen-2-ones (2a–d) were synthesized in 74–65% yields. The UV-Vis data were in the 295–428 nm range. The emission depends on the substituent in position C-7 bearing electron-donating groups. Compounds 1b–d showed good optical properties due to the D-π-A structural arrangement. In compounds 2a–d, there is a quenching effect of fluorescence in solution. However, in the solid, an increase is shown due to an aggregation-induced emission (AIE) effect given by the rotational restraints and stacking in the crystal. Computational calculations of the HOMO-LUMO orbitals indicate high absorbance and emission values of the molecules, and gap values represent the bathochromic effect and the electronic efficiency of the compounds. Compounds 1a–d and 2a–d are good candidates for optical applications, such as OLEDs, organic solar cells, or fluorescence markers.

Complementarity of mDSC, DMA, and DRS Techniques in the Study of Tg and Sub-Tg Transitions in Amorphous Solids: PVPVA, Indomethacin, and Amorphous Solid Dispersions Based on Indomethacin/PVPVA.

Recently, glasses, a subset of amorphous solids, have gained attention in various fields, such as polymer chemistry, optical fibers, and pharmaceuticals. One of their characteristic features, the glass transition temperature (Tg) which is absent in 100% crystalline materials, influences several material properties, such as free volume, enthalpy, viscosity, thermodynamic transitions, molecular motions, physical stability, mechanical properties, etc. In addition to Tg, there may be several other temperature-dependent transitions known as sub-Tg transitions (or β-, γ-, and δ-relaxations) which are identified by specific analytical techniques. The study of Tg and sub-Tg transitions occurring in amorphous solids has gained much attention because of its importance in understanding molecular kinetics, and it requires the combination of conventional and novel characterization techniques. In the present study, three different analytical techniques [modulated differential scanning calorimetry (mDSC), dynamic mechanical analysis (DMA), and dielectric relaxation spectroscopy (DRS)] were used to perform comprehensive qualitative/quantitative characterization of molecular relaxations, miscibility, and molecular interactions present in an amorphous polymer (PVPVA), a model drug (indomethacin, IND), and IND/PVPVA-based amorphous solid dispersions (ASDs). This is the first ever reported DMA study on PVPVA in its powder form, which avoids the contribution of solvent to the mechanical properties when a self-standing polymer film is used. A good correlation between the techniques in determining the Tg value of PVPVA, IND, and IND/PVPVA-based ASDs is established, and the negligible difference (within 10 °C) is attributed to the different material properties assessed in each technique. However, the overall Tg behavior, the decrease in Tg with increase in drug loading in ASDs, is universally observed in all the above-mentioned techniques, which reveals their complementarity. DMA and DRS techniques are used to study the different sub-Tg transitions present in PVPVA, amorphous IND, and IND/PVPVA-based ASDs because these transitions are normally too weak or too broad for mDSC to detect. For IND/PVPVA-based ASDs, both techniques show a shift of sub-Tg transitions (or secondary relaxation peaks) toward the high-temperature region from -140 to -45 °C. Thus, this paper outlines the usage of different solid-state characterization techniques in understanding the different molecular dynamics present in the polymer, drug, and their interactions in ASDs with the integrated information obtained from individual techniques.

Detecting Crystallinity Using Terahertz Spectroscopy in 3D Printed Amorphous Solid Dispersions

This study demonstrates the applicability of terahertz time-domain spectroscopy (THz-TDS) in evaluating the solid-state of the drug in selective laser sintering-based 3D printed dosage forms. Selective laser sintering is a powder bed-based 3D printing platform, which has recently demonstrated applicability in manufacturing amorphous solid dispersions (ASDs) through a layer-by-layer fusion process. When formulating ASDs, it is critical to confirm the final solid state of the drug as residual crystallinity can alter the performance of the formulation. Moreover, SLS 3D printing does not involve the mixing of the components during the process, which can lead to partially amorphous systems causing reproducibility and storage stability problems along with possibilities of unwanted polymorphism. In this study, a previously investigated SLS 3D printed ASD was characterized using THz-TDS and compared with traditionally used solid-state characterization techniques, including differential scanning calorimetry (DSC) and powder X-ray diffractometry (pXRD). THz-TDS provided deeper insights into the solid state of the dosage forms and their properties. Moreover, THz-TDS was able to detect residual crystallinity in granules prepared using twin-screw granulation for the 3D printing process, which was undetectable by the DSC and XRD. THz-TDS can prove to be a useful tool in gaining deeper insights into the solid-state properties and further aid in predicting the stability of amorphous solid dispersions.

Preparation of redispersible dry nanoemulsion using chitosan-octenyl succinic anhydride starch polyelectrolyte complex as stabilizer

In this study, chitosan-octenyl succinic anhydride (OSA) starch polyelectrolyte complex (PEC) was investigated as a stabilizer for redispersible dry nanoemulsion. Fenofibrate, a BCS class II lipid-lowering drug, with poor solubility was used as model drug. The dry nanoemulsions were prepared by spray drying of the formulation consisting of fenofibrate nanoemulsions with chitosan-OSA starch PEC as a stabilizer and lactose as a solid carrier. The effect of formulation variables such as type of emulsion stabilizer, starch to oil ratio, PEC formation method, and lactose amount were investigated. The results showed that the droplet size of liquid nanoemulsions remarkably decreased with an increasing starch to oil ratio. Solid-state characterizations (FTIR, Raman, DSC, and PXRD) revealed that fenofibrate was present in molecularly dispersed form in the spray-dried nanoemulsions. Higher lactose levels provided the spray-dried nanoemulsions with improved redispersibility and smaller droplet sizes. Interestingly, the high drug dissolution without pH effect was obtained at a high lactose level and a high molar charge ratio of chitosan- OSA starch PEC. These results revealed that the redispersible dry nanoemulsion prepared by spray drying could be utilized for improving the dissolution of fenofibrate. Therefore, chitosan-OSA starch PEC was a promising stabilizer for dry nanoemulsion.