Combined Theoretical and Experimental Study of the Complexation of a Hexaarylbenzene-Based Receptor with the Potassium Cation

In this study, non-covalent binding interactions of the hexaarylbenzene-based receptor (R) with the potassium cation have been investigated. Employing quantum mechanical density functional theory calculations, the most probable structure of the KR ⁺ complex species was predicted. In this complex, the K⁺ cation synergistically interacts with the polar ethereal oxygen fence and with the central hydrophobic benzene bottom via cation?C?? interaction. The strength of the KR ⁺ complex was evaluated experimentally by affinity capillary electrophoresis. From the dependence of the effective electrophoretic mobility of the receptor R on the concentration of the potassium ion in the background electrolyte, the thermodynamic binding (stability, association) constant (K _KR) of the KR ⁺ complex in methanol was evaluated as log₁₀?K _KR?=?3.20?±?0.22.     

A polyaromatic receptor with an ethereal fence that directs K+ for effective cation-pi interaction

We have designed and synthesized a HAB-based receptor with six ethereal oxygens on one face of the central benzene ring by a trimerization of a diarylacetylene in which the ethereal oxygens are tied together with a tetramethylene bridge. This unique amphiphilic receptor allows an efficient binding of a single potassium cation by a synergistic interaction with the polar ethereal fence and with the central benzene ring via cation-pi interaction. Furthermore, the ready accessibility of this unique receptor with a bipolar binding pocket will allow the exploration of its usage for developing efficient sensing devices for various metal cations.     

Extraction and DFT study on the complexation of the cesium cation with a hexaarylbenzene-based receptor

From extraction experiments and γ-activity measurements, the extraction constant corresponding to the equilibrium Cs⁺(aq) + A⁻(aq) + 1(nb) ⇆ 1·Cs⁺(nb) + A⁻ (nb) taking part in the two-phase water–nitrobenzene system (A⁻ = picrate, 1 = hexaarylbenzene-based receptor; aq = aqueous phase, nb = nitrobenzene phase) was evaluated as log K _ex (1·Cs⁺, A⁻) = 2.8 ± 0.1. Further, the stability constant of the hexaarylbenzene-based receptor·Cs⁺ complex (abbrev. 1·Cs⁺) in nitrobenzene saturated with water was calculated for a temperature of 25 °C: log β _nb (1·Cs⁺) = 4.7 ± 0.1. By using quantum mechanical DFT calculations, the most probable structure of the 1·Cs⁺ complex species was solved. In this complex having C ₃ symmetry, the cation Cs⁺ synergistically interacts with the polar ethereal oxygen fence and with the central hydrophobic benzene bottom via cation–π interaction. Finally, the calculated binding energy of the resulting complex 1·Cs⁺ is −220.0 kJ/mol, confirming relatively high stability of the considered cationic complex species.     

Structural and polarization properties of polyimide/TiO2 nanocomposites

Polyimide (PI)/titanium dioxide (TiO₂) nanocomposite films were prepared by a solution mixing method with different contents of TiO₂ nanoparticles. The structural and thermal properties of pure PI and PI/TiO₂ nanocomposite films were studied by several techniques such as scanning electron microscopy (SEM), atomic force microscopy (AFM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and thermally stimulated depolarization current (TSDC). The SEM and AFM measurements show the uniform dispersion of TiO₂ nanoparticles in PI matrix, and it is also observed that the value of average roughness increases with increasing the contents of TiO₂ nanoparticles. The XRD pattern shows the presence of TiO₂ nanoparticles in PI matrix. It has been observed that the average crystallite size and percentage of crystallinity increase with content of the TiO₂ nanoparticles. FTIR spectra depict the position of different bonds in PI and nanocomposite samples. The TSDC results represent the modification of polarization phenomenon after filling of PI by titania nanoparticles.     

Understanding changes in DTI metrics in patients with different stages of neurocysticercosis

Diffusion tensor imaging (DTI) was performed on 25 patients with neurocysticercosis (NCC). The aim of this study was to investigate the changes in DTI measures during the evolutionary course of NCC lesions from vesicular to calcified stage in the brain. DTI measures were quantified from the NCC lesions of all patients. On the basis of conventional imaging findings, NCC lesions were classified into vesicular, vesicular colloidal, granular nodular and calcified stages. Significant inverse correlation was observed between the evolutionary stage of NCC lesion and mean diffusivity (MD; r=−0.748, P<0.001) and spherical anisotropy (CS; r=−0.585, P<.001) values. Significant direct correlations were observed between evolutionary stages of NCC lesion and mean fractional anisotropy (FA; r=0.575, P<0.001), linear anisotropy (CL; r=0.478, p<0.001) and planar anisotropy (CP; r=0.561, p<0.001) values. Successive decrease in MD values calculated from NCC lesions was observed, moving from vesicular to granular nodular stage. On FA, CL and CP maps, a significant increase in signal intensity value was observed in calcified as compared to other stages. We conclude that DTI measures may indicate the evolutionary changes in NCC from vesicular to calcified stage.     

The anomalous penetration of intense circularly polarized electromagnetic beam through overdense magnetized plasma

The steady state nonlinear propagation of an intense, circularly polarized electromagnetic beam in an inhomogeneous magnetized plasma has been investigated in paraxial approximation. The laser induces a large oscillatory velocity on electrons, raising their mass and lowering the plasma frequency. Further, rising due to cyclotron resonance effect. The propagation of the electromagnetic waves in magnetized plasma in both the extraordinary and ordinary mode is analyzed. The nonlinearity in dielectric function is considered in presence of external magnetic field due to saturation effects for arbitrary large intensity, which leads to focusing/defocusing of the beam. The focusing effect along with magnetic field helps in the process of anomalous penetration of the beam by enhancing the depletion of the plasma from the axial region. The penetration increases with the incident beam power up to some critical value beyond which it rises abruptly when all electrons have been driven out of the axis. The cyclotron resonance effect awfully supports the laser beam to propagate inside the overdense plasma region. Numerical computations are performed for typical parameters of relativistic laser–plasma interaction applicable for underdense and overdense plasma.     

High-throughput capillary electrophoresis analysis of biopharmaceuticals utilizing sequential injections

The complexity of biotherapeutic products implies an ever-increasing list of product quality attributes that need to be monitored and characterized. In addition, the growing interest in implementing process analytical technology in biopharmaceutical production has further increased the testing burden, together with the need for rapid testing that can facilitate real-time or near-real-time decision-making. Capillary electrophoresis (CE) has made a place in biopharmaceutical analysis but is regarded as a low-throughput method, with the instrument dead time constituting more than 80% of the total time of analysis. In this study, the dead time of CE was utilized to analyse 3 mAb samples in a single-CE run. This approach resulted in an up to 77% reduction in the total analysis time and increased the productivity by up to 300%, compared to traditional single CE-ultraviolet runs, without compromising resolution or relative peak areas. Additionally, good method reproducibility was observed. The compatibility of the method has been demonstrated with protein A eluate and cation exchange chromatography fractions. We, thus, propose that sequential injections can be applied for fast and robust CE analysis of biopharmaceuticals.