The Effect of Lipopolysaccharides on the Electrostatic Properties of Gram-Negative General Porins from Enterobacteriaceae

We investigated, by using all-atom molecular dynamics simulations, the effect of the outer membrane of Gram-negative bacteria, composed in the outer leaflet by polar/charged lipopolysaccharides (LPS), on the electrostatic properties of general porins from the Enterobacteriaceae family. General porins constitute the main path for the facilitated diffusion of polar antibiotics through the outer membrane. As model system we selected OmpK36 from Klebsiella pneumoniae, the ortholog of OmpC from Escherichia coli. This species presents high variability of amino acid composition of porins, with the effect to increase its resistance to the penetration of antibiotics. The various properties we analyzed seem to indicate that LPS acts as an independent layer without affecting the internal electrostatic properties of OmpK36. The only apparent effect on the microsecond time scale we sampled is the appearance of calcium ions, when present at moderate concentration in solution, inside the pore. However, we noticed increased fluctuations of the polarization density and only minor changes on its average value.

External Electric Field Control of Exciton Motion in Porphyrin-Based Metal Organic Frameworks

Porphyrins are excellent light-harvesting complexes. Presently they are unsuitable for photovoltaic applications, as their excellent light absorbance is compensated to a large extent by their poor transport properties, where most excitons are lost by recombination. Arranging porphyrins in regular, strongly bound, lattices of surface-anchored metal-organic frameworks (PP-SURMOFs) may facilitate charge carrier dissociation, but does not significantly enhance the conductive properties. In most cases, photogenerated excitons traverse undirected, Brownian motion through a hopping process, resulting in a substantial diffusion length to reach electrodes, leading to significant exciton loss through recombination. Here, we propose to guide exciton diffusion indirectly by an external electric field. We show that electric fields, even as strong as 1 V nm-1, do not affect the HOMO-LUMO gap of the porphyrins. However, fields of 0.1 V nm-1 and even less demonstrate a notable Stark effect, with slight band gap reductions, for some PP-SURMOFs. When applied as an electric field gradient, for instance, via the substrate, it creates a unidirectional hopping pathway for the excitons. Consequently, we expect a significant reduction of exciton diffusion length leading to increased utilization of photogenerated excitons as they reach the electrodes. This strategy holds promise for integrating photoactive molecules in photovoltaic and photocatalytic applications.

Electric Field Enhanced Ammoxidation of Aldehydes Using Supported Fe Clusters Under Ambient Oxygen Pressure

Heterogeneous catalytic ammoxidation provides an eco-friendly route for the cyanide-free synthesis of nitrile compounds, which are important precursors for synthetic chemistry and pharmaceutical applications. However, in general such a process requires high pressures of molecular oxygen at elevated temperatures to accelerate the oxygen reduction and imine dehydrogenation steps, which is highly risky in practical applications. Here, we report an electric field enhanced ammoxidation system using a supported Fe clusters catalyst (Fe/NC), which enables efficient synthesis of nitriles from the corresponding aldehydes under ambient air pressure at room temperature (RT). A synergistic effect between the external electric field and the Fe/NC catalyst promotes the ammonia activation and the dehydrogenation of the generated imine intermediates and avoids the unwanted backwards reaction to aldehydes. This electric field enhanced ammoxidation system presents high efficiency and selectivity for the conversion of a series of aldehydes under mild conditions with high durability, rendering it an attractive process for the green synthesis of nitriles with fragile functional groups.

The Keto-Switched Photocatalysis of Reconstructed Covalent Organic Frameworks for Efficient Hydrogen Evolution

The keto-switched photocatalysis of covalent organic frameworks (COFs) for efficient H2 evolution was reported for the first time by engineering, at a molecular level, the local structure and component of the skeletal building blocks. A series of imine-linked BT-COFs were synthesized by the Schiff-base reaction of 1, 3, 5-benzenetrialdehyde with diamines to demonstrate the structural reconstruction of enol to keto configurations by alkaline catalysis. The keto groups of the skeletal building blocks served as active injectors, where hot π-electrons were provided to Pt nanoparticles (NPs) across a polyvinylpyrrolidone (PVP) insulting layer. The characterization results, together with density functional theory calculations, indicated clearly that the formation of keto-injectors not only made the conduction band level more negative, but also led to an inhomogeneous charge distribution in the donor-acceptor molecular building blocks to form a strong intramolecular built-in electric field. As a result, visible-light photocatalysis of TP-COFs-1 with one keto group in the skeletal building blocks was successfully enabled and achieved an impressive H2 evolution rate as high as 0.96 mmol g-1  h-1 . Also, the photocatalytic H2 evolution rates of the reconstructed BT-COFs-2 and -3 with two and three keto-injectors were significantly enhanced by alkaline post-treatment.

Spatiotemporally dynamic electric fields for brain cancer treatment

OBJECTIVE

The treatment of glioblastoma (GBM) using low intensity electric fields (~1 V/cm) is being investigated using multiple implanted bioelectrodes, which was termed intratumoral modulation therapy (IMT). Previous IMT studies theoretically optimized treatment parameters to maximize coverage with rotating fields, which required experimental investigation. In this study, we employed computer simulations to generate spatiotemporally dynamic electric fields, designed and purpose-built an IMT device for in vitro experiments, and evaluated the human GBM cellular responses to these fields. &#xD;Approach: After measuring the electrical conductivity of the in vitro culturing medium, we designed experiments to evaluate the efficacy of various spatiotemporally dynamic fields: (a) different rotating field magnitudes, (b) rotating vs. non-rotating fields, (c) 200 kHz vs. 10 kHz stimulation, and (d) constructive vs. destructive interference. A custom printed circuit board (PCB) was fabricated to enable four-electrode IMT in a 24-well plate. Patient-derived GBM cells were treated and analyzed for viability using bioluminescence imaging. &#xD;Main results: The optimal PCB design had electrodes placed 6.3 mm from the center. Spatiotemporally dynamic IMT fields at magnitudes of 1, 1.5, and 2 V/cm reduced GBM cell viability to 58%, 37% and 2% of sham controls respectively. Rotating vs. non-rotating, and 200 kHz vs. 10 kHz fields showed no statistical difference. The rotating configuration yielded a significant reduction (p<0.01) in cell viability (47±4%) compared to the voltage matched (99±2%) and power matched (66±3%) destructive interference cases.&#xD;Significance: We found the most important factors in GBM cell susceptibility to IMT are electric field strength and homogeneity. Spatiotemporally dynamic electric fields have been evaluated in this study, where improvements to electric field coverage with lower power consumption and minimal field cancellations has been demonstrated. The impact of this optimized paradigm on cell susceptibility justifies its future use in preclinical and clinical trial investigations.

Electric field assisted multicomponent reaction in a microfluidic reactor for superior conversion and yield

We explore the improvements in yield and conversion of a chemical reaction inside a two-phase microfluidic reactor when subjected to an externally applied alternating current (AC) electric field. A computational fluid dynamic (CFD) framework has been developed to incorporate the descriptions of the two-phase flow, multicomponent transport and reaction, and the Maxwell's stresses generated at oil-water interface owing to the presence of the externally applied electric field. The CFD model ensures that the reactants are flown into a microchannel together with the oil and water phases before the reaction takes place at the interface and products diffuse back to the bulk phases. The study unveils that the variation in the intensity of the AC field helps in converting a two-phase stratified flow into an oil-in-water microemulsion composed of oil slugs, plugs, or droplets. Importantly, the results also suggest that harnessing the vortices inside or outside these flow patterns helps in the improvement in mass transfer across the interface, which can be employed to improve the yield and conversion of a reaction. We have shown an example case of a pseudo-first order reaction for which the variation in frequency and intensity of AC field is found to form higher surface-to-volume-ratio flow patterns having a higher throughput. The convective recirculation in and around these miniaturized flow morphologies increase the rate of mass transfer, mixing of reactant and products, conversion of reactant, and yield of products. The results reported can be of significance in the design and development of future advanced-flow rector technologies.

Realistic Electric Field Mapping of Anisotropic Muscle During Electrical Stimulation Using a Combination of Water Diffusion Tensor and Electrical Conductivity

Purpose

To realistically map the electric fields of biological tissues using a diffusion tensor magnetic resonance electrical impedance tomography (DT-MREIT) method to estimate tissue response during electrical stimulation.

Methods

Imaging experiments were performed using chunks of bovine muscle. Two silver wire electrodes were positioned inside the muscle tissue for electrical stimulation. Electric pulses were applied with a 100-V amplitude and 100-μs width using a voltage stimulator. During electrical stimulation, we collected DT-MREIT data from a 3T magnetic resonance imaging scanner. We adopted the projected current density method to calculate the electric field. Based on the relation between the water diffusion tensor and the conductivity tensor, we computed the position-dependent scale factor using the measured magnetic flux density data. Then, a final conductivity tensor map was reconstructed using the multiplication of the water diffusion tensor and the scale factor.

Results

The current density images from DT-MREIT data represent the internal current flows that exist not only in the electrodes but also in surrounding regions. The reconstructed electric filed map from our anisotropic conductivity tensor with the projected current density shows coverage that is more than 2 times as wide, and higher signals in both the electrodes and surrounding tissues, than the previous isotropic method owing to the consideration of tissue anisotropy.

Conclusions

An electric field map obtained by an anisotropic reconstruction method showed different patterns from the results of the previous isotropic reconstruction method. Since accurate electric field mapping is important to correctly estimate the coverage of the electrical treatment, future studies should include more rigorous validations of the new method through in vivo and in situ experiments.

Shape Effect of Surface-Enhanced Raman Scattering-Active-Substrate-Based Nanoparticles on Local Electric Field for Biochemical Sensing Application

The metal nanoparticles exhibit different degrees of localized surface plasmon resonance which depends on different type nano-sized structures. In this work, in experiment, Au/TiO2/Ti/Si SERS-active substrate with spherical shape nanoparticles is fabricated by using a hydrothermal treatment process and applied to detect Rhodamine 6G sample. Based on experimental observation, a three-dimensional finite-difference time-domain simulation is utilized to explore the local field distributions. We examine the effect of surface roughness and shape of Au nanoparticles on the enhancement magnitude of local electric field of SERS-active substrates. Besides, different shapes of nanoparticles, nanocages and Au/Ag alloy nanoparticles are also modeled and discussed. The engineering findings of this study indicate that the substrate with roughened surface may exhibit large electric field enhancement; in particular, for the cubic shape of nanoparticles. The electric field enhancement of spherical and cubic nanoparticles could be further enlarged by Au/Ag alloy and Au nanocage structures. The results may benefit the design and fabrication of nanoparticles for various biochemical sensing applications.

Effects of Hydrostatic Pressure and Electric Field on the Electron-Related Optical Properties in GaAs Multiple Quantum Well

The properties of the electronic structure of a finite-barrier semiconductor multiple quantum well are investigated taking into account the effects of the application of a static electric field and hydrostatic pressure. With the information of the allowed quasi-stationary energy states, the coefficients of linear and nonlinear optical absorption and of the relative refractive index change associated to transitions between allowed subbands are calculated with the use of a two-level scheme for the density matrix equation of motion and the rotating wave approximation. It is noticed that the hydrostatic pressure enhances the amplitude of the nonlinear contribution to the optical response of the multiple quantum well, whilst the linear one becomes reduced. Besides, the calculated coefficients are blueshifted due to the increasing of the applied electric field, and shows systematically dependence upon the hydrostatic pressure. The comparison of these results with those related with the consideration of a stationary spectrum of states in the heterostructure-obtained by placing infinite confining barriers at a conveniently far distance-shows essential differences in the pressure-induced effects in the sense of resonant frequency shifting as well as in the variation of the amplitudes of the optical responses.

Heisenberg's Uncertainty Principle, Intense Electric Field, Heavily Doped Optoelectronic Quantized Structures and the Electron Statistics

In this paper we show that the direct application of Heisenberg’s uncertainty principle (HUP) leads to the expression of the electron statistics (ES) under extreme degeneracy and intense electric field in bulk, quantum wells, nano wires and in the presence of quantizing magnetic field in III–V, ternary and quaternary materials on the basis of a newly formulated electron dispersion laws without using the usual density-of-states (DOS) function approach for finding out the ES under different physical lattice matched to InP conditions. It appears taking HD InSb, InAs, Hg1−xCdxTe, In1−xGaxAsyP1−y as examples that the Fermi energy increases with increasing electron concentration and the surface electric field in all the cases. Besides the Fermi energy decreases with increasing alloy composition and film thickness in different manners which depend totally on the values of the energy band constants. The Fermi energy oscillates with inverse quantizing magnetic field due to SdH effect. We have also shown that under certain limiting conditions all our generalized results lead to the well known formulas as given in the literature.

Can Lucifer Yellow Indicate Correct Permeability of Biological Cell Membrane under An Electric and Magnetic Field?

The effect of external magnetic and electric fields, in the range of electroporation and magnetoporation, on Lucifer Yellow (LY) fluorescence in the absence of cells is studied. Electric-field-induced quenching and magnetic field-induced increase are observed for fluorescence intensity of LY. Regard to the fact that the variation of field-induced fluorescence, even in the absence of cells, can be observed, the application of LY, as a marker, is debatable in electroporation and magnetoporation techniques.