Oxacillin is a penicillinase-resistant, narrow-spectrum beta-lactam crystalline antibiotic of the penicillin class, resistant to beta-lactamases. The main purpose of this paper was to develop and apply a new spectrophotometric method in the visible (VIS) field for the analysis of pure Oxacillin from various pharmaceutical samples. Oxacillin reacted completely with 1.10 Phenanthroline 0.2% alcoholic solution in the presence of an aqueous solution of ferric chloride (FeCl₃, 6%), which led to the quantitative formation of a intense bright yellow complex with a faint orange tint, after heating the solutions for 20 minutes at 70 ºC constant temperature. The intense bright yellow colored synthetized complex was then spectrophotometrically determined at λ = 420 nm corresponding to its absorption maximum, in relation to double-distilled water as a blank. One solid pharmaceutical capsule officially contained 500 mg pure Oxacillin, as reference value. As a result of the experiment, 491.308 mg of pure Oxacillin/solid capsule was obtained. This amount corresponded to a percentage content of 98.262 % determined by pure sodium Oxacillin and calculated per solid capsule of pharmaceutical product. The obtained result was very close to the reference value which was 500 mg of pure Oxacillin. The relative percentage deviation (relative percentage procedural error) was only E = 1.738 % to the official value and it fit perfectly within the official normal limits of values indicated by the Romanian Pharmacopoeia, 10th Edition, and by the European Pharmacopoeia Rules (± 5 %). Statistical analysis revealed a very good linearity of the visible spectrophotometric method for pure standard analyzed solutions in a large concentration range, from 1,20 μg/mL to 36,00 μg/mL. The linear regression coefficient R² was 0,999504 and the correlation coefficient R was 0,999752; as R² ≥ 0.9990 and R > 0.9990, they were found to be within the normal official range of values.

Introduction

Metal–Organic Frameworks (MOFs), porous materials self-assembled by metal ions and organic ligands, are attracting ever-growing interest in material chemistry. Their high porosity, tunable pore size and large surface area make MOFs promising candidates to separate CO₂. Ultramicroporosity (pore size < 0,7 nm) and the presence of nitrogen atoms are crucial requirements in the design of MOFs for CO₂ uptake._{. Based on this,} by combining 3 6-N-ditriazolyl-2,5-dihydroxy-1,4-benzoquinone (trz₂An), as the organic linker, with Co^II or Cu^II, two new ultramicroporous MOFs, formulated as [Co(trz₂An)]n·3H₂O (1) and[Cu(trz₂An)]·(H₂O)_2.5(2), have been obtained.

Material and Methods

MOFs 1 and 2 were synthesized by optimizing the synthetic procedure reported in literature. A solution of CoCl₂·6H₂O or CuCl₂·2H₂O was slowly added to a mixture of trz₂An, NaOH and water and heated in autoclave at 130 °C for 48 hours. The rectangular crystals, suitable for a single X-ray diffraction study, were washed three times using an acid aqueous solution in order to solubilize and remove the Co(OH)₂ and Cu(OH)₂ obtained during the reaction.

Results

In 1, Co^II ions are equatorially coordinated to four oxygen atoms of two bis(bidentate) trz₂An ligands. The distorted octahedral coordination sphere of Co^II ions is completed with two nitrogen atoms from the N4 atoms of the 1,2,4-triazole substituted pendant rings of trz₂An ligands. Two voids of 90.4 ų were found in the unit cell of the crystals, giving a void volume of 23.5%. MOF 2 is characterized by cubic cavities with a volume void of 28 % due to the coordination to the N atom at the 4-position of the triazole ring, which induces an alternate orientation of Cu-anilate chains.

Conclusions

The same trz₂An linker has been employed to obtain, in combination with Co^II and Cu^II, two robust, isomorphous and ultramicroporous MOFs, suitable for CO₂uptake and separation.

Investigation of the phases and the nature of the corresponding phase transition of a chiral ferroelectric liquid crystalline compound

Barnali Barman

Department of Physics, Seva Bharati Mahavidyalaya, Jhargram, West Bengal, India, 721507

Abstract

Liquid crystals offer an excellent platform for studying the nature of phase transitions by providing a rich variety of mesophase orderings [1]. In many cases, they occur in narrow temperature ranges, and the phase transitions between different mesophases can be either continuous or weakly first-order. The most commonly studied mesophases are nematic (N), smectic-A (SmA), smectic-C (SmC), and their chiral analogue,s such as N*, SmA*, and SmC* phases. This work mainly focuses on the characteristics of the N* to SmC* phase transition of a pure ferroelectric liquid crystalline (FLC) compound, namely QVE 8/5 [2, 3]. The textures are characteristics of the different phases. For the studied compound, the characteristic textures corresponding to the N* and SmC* phases have been detected. The optical transmission method [ 4, 5] has been used in order to investigate the N* to SmC* phase transition. The temperature variation of the transmitted intensity for the compounds QVE 8/5 have been measured for both planar and homeotropic alignments of the molecules. The critical behaviour of the N* to SmC* phase transition has also been investigated. The extracted critical exponent (α') of the investigated compound was found to be less than 0.5, which implies the second-order nature of the N*-SmC* phase transition corresponding to the studied FLC compound.

References

1. A. Clark, S. T. Lagerwall; Ferroelectrics Appl. Phys, 59, 25 (1984).
2. Pakhomov, M. Kaspar, V. Hamplova, A.M. Bubnov, H. Sverenyak, M. Glogarova, I. Stibor; Ferroelectrics, 212, 341 (1998).
3. Vajda, M. Kaspar, V. Hamplova, S. A. Pakhomov, P. Vanek, A. Bubnov, K. Fodor-Csorba and Nandor Eber; Mol Cry. and Liq. Cry., 365, 569 (2001).
4. Prasad and M. K. Das; J. Phys. Condens. Matter., 22, 195106 (2010).
5. Barman, S.K. Sarkar, M. K. Das; Phase Transit., 91, 58 (2018).

This study demonstrates the enhancement in photoluminescence (PL) of nematic liquid crystals (NLCs) doped with CsPbBr3 (perovskite) quantum dots (QDs). These perovskite QDs significantly boost the PL intensity by improving the anisotropic nature of NLC molecules, thereby reducing light leakage centers and intrinsic defects. Two different sizes of QDs were synthesized using a wet chemical method. X-ray Diffraction (XRD) confirmed the orthorhombic crystallite structure of the QDs, while Transmission Electron Microscopy (TEM) determined their size as 5.5 (±0.98) nm and 10 (±1.8) nm. The optical features of QDs were investigated by recording absorption and emission spectra at room temperature, which revealed unique excitonic peaks at 479 and 513 nm, whereas emission was seen at 503 and 518 nm for two different sizes, respectively. These highly luminescent QDs were further used to enhance the emission of NLC. Initially, liquid crystal (LC) sample cells were fabricated using the conventional polyimide technique, followed by the incorporation of NLC-QD composites via capillary action. The prepared sample cells were then characterized using polarizing optical microscope (POM) images and PL spectra measurements. The intensified dark state and brightened bright state POM images demonstrate improved unidirectional alignment along with a homogeneous texture of the NLC-QD composite. This improvement in molecular alignment, coupled with the reduction in light leakage centres and defects, is reflected in the PL spectra, showing an increased emission intensity of 18 % for the 10 nm sized sample. The enhanced emission of NLCs is attributed to the modified dielectric anisotropy in the presence of QDs. Conversely, 5.5 nm NLC–QD composites led to increased light leakage centres in the POM dark state and a subsequent reduction in PL intensity. The results indicate that these QDs are ideal for fabricating QD-based display devices with enhanced optical contrast, making them a promising choice for next-generation display technologies.

Liquid crystals (LCs) have a wide variety of applications, propelling them to the forefront of electro-optics and displays. In many more recent applications, the behaviour of liquid crystals have reliedon particles suspended within them. Yet, particle behaviour and distribution can be significantly influenced by the application of an electric field. As a result, particles dispersed in the liquid crystal experience forces that can induce motion, change their translational direction, and even alter spatial organization^[1]. Polarizing microscopy enables the examination of alignment quality and facilitates the identification of the electric field frequency stability regimes where particular particle behaviors are observable^[2].

Investigating micro-rods with different aspect ratios leads to a wealth of additional degrees of freedom for motion as compared to the translation observed for spherical particles ^[3]. Insight into their behaviour is crucial for engineering novel materials and devices with specific features to diverse applications. The significance of aspect ratios in influencing the dynamic behavior of micromaterials in various settings is investigated in this work. Our experiments have unveiled novel modes of motion, encompassing both linear and nonlinear dynamics, for rod-shaped particles in a nematic liquid crystal under the influence of an electric field. The observed behaviors included linear translation, circular motion, and a newly characterized pattern involving rotation around both the long and short axes of the rods, obviously absent for spherical microparticles. Additionally, we identified novel macroscopic modes of motion, such as looping and logarithmic spiral trajectories.

The dynamic behaviour depends on particle size, confining cell gap, viscosity via temperature change, and electric field amplitude and frequency. The molecular boundary conditions produced by various cell gaps can alter how the particle in the liquid crystal reacts to outside stimuli, i.e., electric fields in our case. The results are of importance to fundamentally understand the motion of particles of different shape.

Lanthanide-based MOFs are promising candidates for the creation of luminescent materials, since REE(III) ions possess predictable, multicolored, narrow-band luminescence with long excited state lifetimes and high quantum yields.

In this research, the structure and properties of coordination compounds of various dimensions based on 1,4-diazabicyclo[2.2.2]octane-N,N’-dioxide (odabco) and Ln³⁺ (Ln³⁺ = Tb³⁺ and Eu³⁺) cations were studied. Their formulas are as follows: [Ln(odabco)₃](NO₃)₃∙4.5H₂O (1_Tb; 1_Eu); (Hodabco)₃[Ln(H₂O)₂(NO₃)₄](NO₃)₂ (2_Tb; 2_Eu); [Ln(odabco)₃]₂[Ln(NO₃)₆](NO₃)₃∙3H₂O (3_Tb; 3_Eu).

1_Ln contain a three-dimensional porous cell [Ln(odabco)₃]³⁺ with a mononuclear octahedral metal center and disordered nitrate anions in the pores. 2_Ln contain polymeric organic cations (Hodabco)⁺ interconnected by hydrogen bonds into chains. Aquanitrate complexes and free nitrates are located in the interchain space as counterions. 3_Ln contain a coordination framework close to 2_Ln, but they also contain large hexanitrate complexes of lanthanides in their voids. The crystal structures of all compounds were determined by means of single-crystal XRD analysis, and their phase purity and stability were confirmed by means of PXRD, CHNS analysis, thermogravimetric analysis and IR spectroscopy.

Excitation and emission spectra and kinetic decay curves of luminescence were studied for all samples. Sensing properties were revealed for 3_Eu, quenching the luminescence of a suspension in ethanol solutions of chromate or dichromate. For the last, LOD was 2.4·10^-6 M for a 270 nm excitation wavelength and 2.1·10^-7 M for a 395 nm excitation wavelength. 3_Tb were also found to be quenching the luminescence for an ethanol solution of chromate and dichromate. LODs were 6.6·10^-7 M and 1.1·10^-5 M, respectively. The luminescence response at the micromolar concentration range was also found to be fast, with an equilibrium time no longer than 20 min. Therefore, porous MOFs 3_Ln with a cationic polymeric structure were found to be effective luminescent sensors for toxic Cr(VI) anions.

The advanced synthesis of coordination polymers is fascinating due to its resulting structural diversity and vast opportunities to design new functional magnetic materials.

The physicochemical properties of coordination polymers result from a combination of synthesis conditions and properties of simple, well-known precursors [1,2,3]. This generates the possibility to model the electrical, magnetic, and optical properties of coordination polymers. These could find application as luminescent materials, catalysts, sensors, ion exchangers, and as magnetic materials. An important research topic in recent years is the luminescent properties of these materials. In comparison with organic compounds that are used, e.g., in the manufacturing of OLED-type diodes, inorganic coordination compounds prevail as they possess a much higher thermal stability, widening the operational temperature range.

Depending on the valence electrons' configuration, the luminescent properties of coordination polymers are governed by MLCT (metal–ligand charge transfer), LMCT (ang. ligand–metal charge transfer), LLCT (ang. ligand–ligand charge transfer), or IL (ang. inter-ligand charge transfer) states.

Herein, we present novel coordination polymers based on copper ions and organic aminocarboxylate ligands. For these compounds, the complexation of copper ions results in the amplification of emissions and an increase in the maximum emission shift.

Literature

[1] S.R. Batten, S.M. Neville, D.R. Turner, Coordination Polymers: Design, Analysis and Application, School of Chemistry, Monash University, Victoria, Australia, (2009)

[2] B. Moulton, M. J. Zaworotko, Chem. Rev. 101, 1629 (2001)

[3] . A. Kochel, M. Hołyńska, K. Twaróg, A. Jezierska, J. J. Panek and J. Wojaczyński Acta Cryst. C78, 405 (2022)

The detection of organic and inorganic compounds using electrochemical sensors has garnered attention due to their low-cost fabrication and excellent sensitivity. To enhance the sensitivity of the sensor using metal oxides as active materials, defect states such as oxygen vacancies have been studied. These defects operate as donor levels near the conduction band of the metal oxide. In this study, we present the synthesis of TiO2 nanotubes decorated with Ag spheres, along with an investigation into their chemical, structural, and optical properties for electrochemical sensing applications. TiO2 nanotubes were synthesized through a three-step anodization process, while Ag spheres were deposited using electrochemical deposition. The electrolyte solution for the growth of TiO2 nanotubes consisted of ammonium fluoride and ethylene glycol, while silver nitrate and citric acid were employed as the electrolyte solution for Ag sphere deposition. FE-SEM analysis revealed the successful deposition of Ag spheres with a spherical morphology over TiO2 nanotubes, with the morphology being significantly influenced by the concentration of organic acid in the electrolyte solution. Stoichiometry analysis was performed on both the TiO2 nanotube film and on the film decorated with Ag spheres. Additionally, the band gap energy was calculated from the diffuse reflectance spectroscopy (DRS) spectrum. According to photoluminescence analysis, a larger area associated with oxygen vacancies in TiO2 nanotubes decorated with Ag spheres was identified. The presence of localized energy levels within the band gap resulting from oxygen vacancies and Ag spheres led to a reduction in the band gap energy of the semiconductor. This phenomenon is particularly relevant for creating more active sites suitable for the adsorption of compounds in electrochemical sensing applications.^1,2

References

[1] A. Arenas-Hernandez, C. Zuñiga Islas, M. Moreno. Appl. Sci., (2022) 12, 3690.

[2] Singh, K.; Maurya, K. K.; Malviya M. J. Anal. Test., (2023) 8, 143.

High-energy ball milling is a simple and eco-friendly technique that has gained increasing popularity in recent years. This one-pot method of synthesis allows for the preparation of solid materials from a green perspective, avoiding multiple and complex steps, the use of solvents and the extreme pressure and temperature conditions commonly employed. Due to its multiple advantages, high-energy ball milling can make structural and surface modifications within the solid matrix according to the physicochemical properties needed, such as defect accumulation, polymorphic transformations, grain boundaries, amorphization, particle refinement and increases in specific surface area and ion mobility. In this regard, ceria–titania mixtures were obtained using several high-energy ball milling conditions (varying the metal oxide concentration, ball-to-powder ratio, time and rotational speed). The crystal structures created by the milling process were studied by means of X-ray Powder Diffraction (XRPD), including cerianite, anatase, rutile and high-pressure TiO₂ (II) formation. Moreover, the crystallite sizes and the specific surface area (S_BET) values were estimated using the Scherrer equation and N₂ physisorption (BET method), respectively. According to this preliminary study, the materials generated through this sustainable, cost-effective and easy-to-scale technique could be useful as catalyst supports for different metal nanoparticles or could act as catalysts in a variety of applications, e.g., oxidation and photocatalytic reactions in both the liquid and gas phases.

In industry, cyclohexane is obtained exclusively through the hydrogenation of benzene, but the subsequent complete separation of these liquids is very difficult, since they have similar boiling points and form an azeotrope. Their selective adsorptive separation using metal–organic frameworks (MOFs) is one of the promising approaches. Two- and three-dimensional MOFs contain cavities, the size, geometry and chemical nature of which enable the isolation of the desired component from a difficult-to-separate mixture. Combining various organic ligands and metal ions provides almost unlimited design possibilities for MOFs.

The present study considers the sorption of benzene and cyclohexane for five previously reported MOFs based on trans-1,4-cyclohexanedicarboxylic acid acting as an example of a ligand with a saturated carbon skeleton: [Ga(OH)(C₈H₁₀O₄)] (1), [Ca(H₂O)₂(C₈H₁₀O₄)]·H₂O (2), [Zr₆O₄(OH)₄(C₈H₁₀O₄)₆] (3) [1], [Cu₂(C₈H₁₀O₄)₂] (4) [2], [Al(OH)(C₈H₁₀O₄)]·H₂O (5). The adsorption of individual compounds from the liquid and gas phase and competitive adsorption from mixtures were investigated.

For MOFs 3 and 4, the high selectivity of benzene sorption over cyclohexane was determined, with volume-by-volume selectivity up to ~13. Further, benzene/cyclohexane adsorption selectivities were calculated from the adsorption data using two methods. According to the Henry method, the C₆H₆/C₆H₁₂ Henry constant ratios at low pressures were 7105 for [Zr₆O₄(OH)₄(chdc)₆] and 3.63 for [Cu₂(chdc)₂]. According to the ideal adsorbed solution theory (IAST) for near-atmosphere pressures, the corresponding selectivity coefficients were 23.6 for [Zr₆O₄(OH)₄(chdc)₆] and 1.23 for [Cu₂(chdc)₂].

These results indicate the promising potential of using metal–organic frameworks 3 and 4 with an alicyclic ligand as highly effective sorbents for the separation of the industrial mixtures of benzene and cyclohexane.

[1] Bueken B. et al., Chemistry–A European Journal, 2016, 22, 3264.

[2] Lannoeye J et al., Microporous and Mesoporous Materials, 2016, 226, 292.