In this work, we investigated the influence of positional isomerism on the packing arrangements and the hydrogen bond network in multicomponent crystals of the drug riluzole with hydroxybenzoic acids. A combined theoretical/experimental study, including virtual screening, X-ray diffraction, IR/Raman spectroscopy, thermal analysis and periodic DFT computations, was conducted to isolate and identify the novel crystal forms. By surveying multicomponent crystals of riluzole deposited in the Cambridge Structural Database, we found that salicylic acid derivatives with pKa < 3.8 form salts with riluzole, while benzoic acid derivatives without ortho-hydroxyl groups form cocrystals. New multicomponent crystals of riluzole with salicylic, 4-hydroxybenzoic, 2,3-, 2,4- and 2,6-dihydroxybenzoic acid were obtained and structurally characterized. Varying the experimental conditions allowed us to isolate samples of metastable polymorphs of salts with salicylic, 2,4- and 2,6-dihydroxybenzoic acids. For Form II of the riluzole + 2,6-dihydroxybenzoic acid salt, the crystal structure was determined based on data on powder diffraction of high-energy synchrotron radiation. The hydrogen bond network was found to be identical in riluzole 2,6-dihydroxybenzoate Form I and Form II, and the difference was limited to the mutual orientation of hydrogen-bonded layers, which is a rare example of packing polymorphism. The metastable form was found to undergo an irreversible phase transition at about 120°C, visible as an exothermal event on the thermogram. For riluzole salicylate, two polymorphic modifications were discovered in addition to the already reported form, and the stability relationship between them was studied based on DSC, HSM and dissolution studies. In addition, solvated salt forms were found in the systems with 2,4- and 2,6-dihydroxybenzoic acids during slurry experiments in water, dioxane and DMSO. For the newly obtained phases and pure components, their solubility was determined in aqueous buffer solutions at different pHs and organic solvents, and salt formation thermodynamic functions were obtained from the thermodynamic cycle.

Magnetic memory systems are one of the recently strongly investigated topics in the research area of spintronics. Amongst the different data storage systems, magnetic nanoparticles are of high interest since they can often store large amounts of data on small scales. Such magnetic nanoparticles, however, pose new challenges, such as oxidation and agglomeration. Here, we show micromagnetic simulations using MagPar, which solves the Landau–Lifshitz–Gilbert equation using finite elements, to analyze the energy density of iron nano-spheres. For spheres of 10 nm or 25 nm and different oxide shell thicknesses, 3D energy maps were calculated. Interestingly, the cubic magneto-crystalline anisotropy led to a non-uniform energy distribution of the magnetic nano-spheres, with the number of extrema decreasing for larger oxide layer thicknesses. In the case of the agglomeration of four nano-spheres, the distances between the nano-spheres strongly modified the system’s magnetic properties, where an oxide shell enabled bringing the nano-spheres closer together before they start influencing each other, which was evaluated by comparing the magnetic properties of these agglomerates with the single nano-spheres. For the oxide coated system, the maximum packing density could be increased by about 12%, as compared to the non-coated system, indicating that a higher data density can be reached by preparing a matrix of magnetic nano-spheres with oxide shells.

The original purpose of polymer stabilisation of liquid crystals was the exploitation of scattering devices in electronic paper/eBook readers, but advancements in other technologies have replaced their initial purpose. However, novel uses continue to emerge, such as intelligent privacy windows, smart glass, reflective displays, broadband reflective cholesteric devices, uses in lasing or holography, and blue-phase displays. Motivated by the need to enhance the performance of smart windows, polymer-stabilised cholesteric liquid crystals (PSCLCs) are applied in this technology. This study investigated the morphology and spectroscopic characteristics of refilled polymer-stabilised liquid crystals. The polymer network is fabricated by introducing a small amount of bifunction monomer into a nematic or chiral nematic liquid crystal. This is then photo-polymerised to form a network which templates the liquid crystal structure it was formed in. The system formed is a bi-continuous material with a continuous polymer network within a continuous liquid crystal. Washing out the liquid crystal leaves a long-range orientationally ordered network for polymerization in the nematic phase and a helical network for the chiral nematic phase.

The primary aims of this research are the utilisation of different types of polymer networks, refilled with various liquid crystal phases. Different lyotropic or cholesteric liquid crystals with opposite handedness and varying pitch are refilled into a specific polymer network, and the interaction between network and liquid crystal characterized by polarizing microscopy and spectroscopy as well as scattering measurements is observed. We demonstrate significantly enhanced orientation of lyotropic LCs, low pitch limits of helical transfer, and induced twist grain boundary-like structures.

Contamination by heavy metals is a pressing issue due to its numerous hazardous effects on human health. One of the main challenges associated with this type of contamination is the resistance of heavy metals to degradation and their accumulation in living organisms. However, a wide variety of methods, including ion exchange, membrane filtration, flotation, electrolytic methods, and adsorption, can be employed to eliminate heavy metals from water. To achieve the efficient removal of heavy metals from water, a high-surface-area absorbent is necessary. This enhances contact and interaction with heavy metal ions, and the use of nanoparticles significantly improves this aspect. This study investigates the preparation of Fe₃O₄ nanoparticles using a solvothermal method. This method allows to produce ultrafine magnetite powders with homogeneous particles, a narrow size distribution, and consistent morphology, free from other crystalline phases that could hinder heavy metal ion absorption. The experiments involved varying temperatures (180-220 °C) and reaction times (4-12 h) and utilized FeCl₃ as the iron ion precursor. Following the solvothermal treatments, the precipitated particles were magnetically separated from the hydrothermal solution. The magnetic particles were then analyzed using XRD, SEM, and FTIR. Structural characterization via SEM confirmed that the obtained particles were magnetite in the form of homogeneous spherical particles with an average size of 450 nm, composed of smaller agglomerated nanoparticles with an average size of 8.4 nm. Microstructural characterization using the XRD and FTIR techniques also confirmed the magnetite structure, exhibiting defined reflections without any secondary crystalline phases. Kinetic and isotherm data from a preliminary study fit well with established models, indicating efficient fluoride capture. Additionally, the maximum adsorption capacity reached 39.44 mg/g F^- within 30 minutes, remaining stable thereafter. These findings suggest that the synthesized magnetite nanoparticles are ideal candidates for heavy metal and fluoride removal from water.

Azo-dye layers have shown great promise due to the possibility of obtaining noncontact photoalignment layers of high quality. In this study, we investigate a structure that consists of a nematic liquid crystal (NLC) cell, in which one of the substrates is covered with a photosensitive azo-dye layer. The NLC has an initial planar director orientation. The linearly polarized light falls normally on the surface of the cell and propagates through the liquid crystal, reaching the azo-dye layer and interacting with it. The interaction of the light with the azo-dye leads to reorientation of the molecules of the azo-dye perpendicular to the light polarization. This changes the boundary condition for the NLC director and can result in its reorientation to a twisted state. Considering the NLC cell parameters that facilitate the Mauguin regime, the same photoalignment mechanism then kicks in in a perpendicular direction, leading to oscillations of the boundary conditions for the director and of the NLC director profile.
The dynamics of the NLC director reorientation is modeled using the free energy formalism, and the reorientation of the azo-dye molecules is modeled within the 2D Brownian orientation diffusion model. It was established that when the incident light intensity reaches a threshold value, the induced photo-alignment of the azo-dye becomes sufficient to start the NLC director reorientation toward a π⁄2 twist state. The threshold intensity increases with the Frank elastic constant and decreases with the anchoring energy. An increase in the light intensity and the azo-dye intermolecular interaction coefficient and the decrease in the viscosity of the NLC director lead to faster transitions between states and a lower period of oscillations.

The concept of random walk (RW) [1] and its variation in the form of the self-avoiding random walks (SAWs) [2] are important tools in studying complex processes in a wide variety of fields, including, among others, polymer physics. Recent molecular simulations on extremely confined, monolayer films made of athermal semi-flexible polymers have revealed a wealth of structural behavior as a function of surface coverage chain stiffness, in the form of equilibrium bending angle [3]. Inspired by this and to quantify the thermodynamic stability of the two-dimensional polymer crystals, we map them into self-avoiding rotating walks (SARWs), restricted to follow the geometric constraints of the corresponding lattices. For a reference crystal, and by selecting a compatible equilibrium bending angle, we enumerate all possible configurations of single-chain crystals and calculate the corresponding size distribution as a function of the number of steps. SARW enumeration has been performed on honeycomb, square, and triangular lattices, all being characterized by different coordination numbers and lattice connectivity. The scaling of the number of SARWs, as well as their average size, as a function of steps are fitted using exponential-power-law asymptotic expressions and critical amplitudes; the connective constant and the critical exponents are compared against the analogous ones for conventional SAWs, corresponding to freely jointed polymers, under the same conditions [4,5].

[1] R. Bhattacharya, and E. C. Waymire, Random Walk, Brownian Motion and Martingales, Springer-Verlag (2021).

[2] N. Madras, and G. Slade, The Self-Avoiding Walk; Birkhauser: Boston (1996).

[3] D. Martínez-Fernández et al., J. Chem. Phys. (2024, under review).

[4] N. Clisby, Phys. Rev. Lett. 104, 055702 (2010).

[5] O. Parreño et al., Polymers 12, 799 (2020).

Aqueous lyotropic chromonic liquid crystals (LCLCs) constitute a class of anisotropic fluids valuable for self-assembly at the microscale. Disodium cromoglycate (DSCG) (commonly used commercially as an anti-asthmatic drug), is of particular interest to explore the behavior of microscopic biological organisms (such as rod-like bacteria and mammalian cells) in an environment where local rotational symmetry is broken. The fabrication of LCLC-based devices critically depends on the well-controlled molecular orientation/alignment of LCLC assemblies. This, however, has traditionally been difficult compared to more traditional thermotropic LC phases due to the low surface anchoring energy provided by conventional-rubbed alignment layers. Uniform alignment and spatially non-uniform patterned LCLCs facilitate emerging applications. In the proposed project, we present the planar alignment of DSCG LCs by modifying the surface anchoring strength using a UV-cured polymer layer (SU-8) for alignment. Furthermore, we demonstrate the controlled topological defects by patterning the DSCG LCs into micro-patterned arrays (prepared via photolithography) using square air pillars. The primary objective of the project is to direct distributions and trajectories of active and passive matter using pre-engineered LCLC director arrangements. The primary objective of the project is to direct distributions and trajectories of active and passive matter using pre-engineered LCLC director arrangements.

Abstract

Literature reports of zinc(II) 2,2’-bipyridine crystal in chemistry journals by different researchers call for urgent attention because of its significance in catalysis, drug delivery, electrochemistry, materials chemistry, nanomedicine, and nanotechnology. Here, different coordination geometries reported include distorted tetrahedral, distorted octahedral, tetrahedral, octahedral, and square pyramidal geometries. Outside other forms of characterization, there are techniques of bite angle, such as computational chemistry and nuclear magnetic resonance (NMR); this study considered the concept of bite angle determined experimentally from X-ray crystallography. This led to the following research question: “how does the bite angle assess the different coordination geometries of zinc (II) 2,2’crystal reported in the literature of Chemistry journals?". In response to this question, qualitative research was used as the methodological approach to explore how the ligand field theory (LFT) supports the bite angle’s assessment of the coordination geometry of zinc(II) 2, 2’crystal using X-ray crystallography from recently reported literature in top-rated chemistry journals. Results showed how bite angles of similar zinc(II) 2,2’crystal compared with LFT to validate the reported coordination geometry of zinc(II) 2,2’-bipyridine crystal. The implication of this study is to enhance the relevance and importance of bite angle in zinc(II) 2, 2’crystal.

TCID is a method used for obtaining enantiopure solids from racemic mixtures in the crystalline phase, while fast racemization occurs in solution, with solubility affected by temperature swings. Although TCID theoretically doubles the yield compared to chiral separation methods due to the conversion of the counter enantiomer, the experimental yield remains unproven. One setback is the extraction of the dissolved solute while maintaining chiral purity. Furthermore, due to the slow induction time and the stochasticity of deracemization, an initial suspension with 20% c.e.e. (crystal enantiomeric excess) is commonly imposed to bias the deracemization, but this investment may be undesirable for industrial applications.

Herein, we applied TCID to (1-(4-chlorophenyl)-4,4-dimethyl-2-(1H-1,2,4-triazol-1-yl) pentan-3-one), employing a cooling step at the end of the process to overcome the issue of yield, and a washing step to further improve the c.e.e. This adjustment produced a mass yield of 92% with 99.9% c.e.e. within 24 hours on an 8.6 g scale. The final cooling step removes the majority of dissolved solute, enhancing the yield without significantly prolonging the process, and the washing step improves the enantiopurity.

Additionally, we investigate the stochasticity of deracemization during the initial stages, focusing on the development of c.e.e. from low initial values (1-5% c.e.e.) at a 2.5-gram scale. By assessing the kinetics, we determine that an initial c.e.e. of 2% for this system is adequate without significant risk of chiral flipping and to avoid the induction time. Our findings show the suitability of TCID to be performed on the industrial scale, with reduced initial c.e.e. to direct and overcome the induction time and a simple method to optimize the final yield and purity.

Double perovskite (DP) compounds have been reported to possess many valuable properties and are considered excellent candidates for magnetocaloric applications, high-performing semiconductivity in optoelectronic devices, and photo(electro)chemical energy storage systems [1-4]. To explore the physical properties of double perovskite Ba₂TiMnO₆, we examined its optical and pressure dependence utilizing PBE-GGA and PBE-GGA+U exchange—correlation energy functionals. Following previous findings, DFT calculations revealed direct semiconducting band-gaps of 0.82, 0.98, and 1.27 eV, respectively [5]. Moreover, the optical properties show high dielectric constants, a robust light absorption coefficient in the UV energy range, and a significant optical conductivity of 6.53 × 105 cm−1, making Ba₂TiMnO₆ a promising candidate for high-performance perovskite solar cells in optoelectric applications. We identified that optical properties below 10 eV are mostly due to intraband and interband transitions of Mn-3d electrons. Employing the Projected Augmented Wave (PAW) method, we also studied the impact of pressure on crystal structure and density of states. Notably, near 8 GPa, there appears to be a structural distortion, accompanied by a sharp increase in the semiconducting gap.

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