Strong Charge Interaction Research Articles

Insight into the oxidation mechanism of MoSi2: Ab-initio calculations

Transition metal silicides (TMSis) are potential candidates for high-temperature applications. However, the improvement of oxidation resistance of TMSis is still a big challenge due to the formation of volatile oxides. To overcome the important problem, we use the ab-initio calculations to study the oxidation mechanism of MoSi2 and investigate the influence of Al and Cr on the oxidation resistance of MoSi2. Two possible O-doped sites: octahedral interstitial site and tetrahedral interstitial site are considered. We find that oxygen prefers to occupy the TI-2 site because of the strong charge interaction between Si and O. We further examine the alloying effect in MoSi2. Cr-doping is a thermodynamically stable in contrary to Al-doping is a thermodynamically instable. Importantly, alloying elements can effectively improve the oxidation resistance of MoSi2 because those alloying elements enhance the localized hybridization between Si and O. Finally, our work can open up a new path to improve the oxidation resistance of TMSis high-temperature materials.

The inhibition of acetylcholinesterase by a brain-targeting polylysine-ApoE peptide: biochemical and structural characterizations.

The in-trans delivery of protein therapeutics across the blood-brain barrier by K16ApoE peptide carrier has been demonstrated to improve the neurological symptoms and increase the life-span of late-infantile neuronal ceroid lipofuscinosis (LINCL) mice. However, acute toxicity of K16ApoE was observed in LINCL mice resulting in a narrow therapeutic index, limiting the potential of translating the K16ApoE into a viable drug delivery system. This study aims to unravel the toxic mechanism of action. We hypothesized that the toxic response towards the peptide was induced by inhibition of acetylcholinesterase (AChE) activity at neuro-muscular junction. Here, results from the dose-response study suggested that AChE activity was inhibited by K16ApoE at either low or high doses but not at the mid-dose where a significant increase in AChE activity was observed. Meanwhile, molecular docking simulations showed that the N-terminus of K16ApoE is capable of binding to the active site gorge of AChE. In addition to a favorable spatial orientation, this docking pose also revealed strong surface charge interactions which may account for the observed inhibitory effect. While statistical analysis of the dose response and survival ratio suggested that AChE is not the primary mechanism of action for the acute toxicity of K16ApoE, both biochemical evidence and structural analysis have assigned indirect but critical roles for AChE in the overall toxicity mechanism of this peptide carrier.

Nanocomposites Based on CoSe2-Decorated FeSe2 Nanoparticles Supported on Reduced Graphene Oxide as High-Performance Electrocatalysts toward Oxygen Evolution Reaction.

FeCo-based materials are promising candidates as efficient, affordable, and sustainable electrocatalysts for oxygen evolution reaction (OER). Herein, a composite based on FeSe2@CoSe2 particles supported on reduced graphene oxide (rGO) was successfully prepared as an OER catalyst. In the catalyst, the CoSe2 phase was located on the FeSe2 surface, forming a large number of exposed heterointerfaces with acidic iron sites because of strong charge interaction between CoSe2 and FeSe2. It is believed that the exposed heterointerfaces act as catalytic active sites for OER via a two-site mechanism, manifesting an overpotential as low as 260 mV to reach the current density of 10 mA cm-2 in 1 M KOH and excellent stability for at least 6 h, which is superior to those of CoSe2/rGO, FeSe2/rGO, as well as most of the FeNi- and FeCo-based electrocatalysts reported in recent literatures. It was demonstrated that the most optimal composite electrocatalysts release more Fe species into the electrolyte during the OER process, whereas the releasing of Co species is negligible. When the FeSe2@CoSe2/rGO catalysts were loaded on a α-Fe2O3 photoanode, the photocurrent density was increased by three times. These results may open up a promising avenue into the design and engineering of highly active and durable catalysts for water oxidation.

Electrically Controlled Dimensionality of Magnetic Systems in Organic Materials

Electrically controlling charge density in materials using electronic device structures shows various interesting phenomena, such as electrically induced ferromagnetism and superconductivity, owing to strong charge interactions. However, electrically controlled dimensionality of magnetic systems has not yet been fully investigated. Here we report electrically controlled magnetic interactions and dimensionality of magnetic systems in organic materials from a microscopic viewpoint, which were revealed by electron spin resonance (ESR) spectroscopy using ionic liquid-gated devices. The ESR investigation demonstrated that the magnetic systems’ dimensionality of electrically accumulated charges varied from zero dimensional to two dimensional in a regioregular polymer, regioregular poly(3-hexylthiophene) (RR-P3HT), by increasing charge densities. This phenomenon is in contrast to those in a small molecule pentacene and a regiorandom polymer, regiorandom poly(3-hexylthiophene) (RRa-P3HT), where it varied from zero to three dimensional when their charge densities increased. Moreover, the formation of the complete spinless states of electrically induced charges was observed. Our investigation demonstrates the novel magnetic systems based on electrically induced charges.

Insight into sulfur vacancy-induced insulator to metal transition of Li2S

Sulfur vacancy-induced charge carrier trap is quite important for improving the insulating characteristic of Li2S. In this work, we apply the first-principle calculations to investigate the influence of sulfur intrinsic vacancy and sulfur vacancy concentration on the structure and conductivity of Li2S. Sulfur intrinsic vacancy is dynamically stable. Importantly, sulfur vacancy reduces the band gap of Li2S. The calculated band gap of sulfur intrinsic vacancy is 0.700[Formula: see text]eV. We suggest that the removed sulfur atom leads to Li-2[Formula: see text] state shift from conduction band to Fermi level and improves the charge overlap between the top of valence band (VB) and the bottom of conduction band (CB). The strong charge interaction of Li pairing atoms forms the Li–Li metallic bond. Finally, we predict that sulfur vacancy gives rise to the insulator to metal transition of Li2S. Our works open up a new possibility for improving the conductivity of Li2S.

Surface‐Modified Mesh Filter for Direct Nucleic Acid Extraction and its Application to Gene Expression Analysis

Rapid and convenient isolation of nucleic acids (NAs) from cell lysate plays a key role for onsite gene expression analysis. Here, this study achieves one-step and efficient capture of NA directly from cell lysate by developing a cationic surface-modified mesh filter (SMF). By depositing cationic polymer via vapor-phase deposition process, strong charge interaction is introduced on the surface of the SMF to capture the negatively charged NAs. The NA capturing capability of SMF is confirmed by X-ray photoelectron spectroscopy, fluorescent microscopy, and zeta potential measurement. In addition, the genomic DNAs of Escherichia Coli O157:H7 can be extracted by the SMF from artificially infected food, and fluorescent signal is observed on the surface of SMF after amplification of target gene. The proposed SMF is able to provide a more simplified, convenient, and fast extraction method and can be applied to the fields of food safety testing, clinical diagnosis, or environmental pollutant monitoring.

Controlled co-release of doxorubicin and reactive oxygen species for synergistic therapy by NIR remote-triggered nanoimpellers

How to encapsulate and transport the payload of multiple therapeutic compounds avoiding premature leakage, and simultaneously co-release them rapidly at specific lesions still remains the major concern in clinic. Herein, we designed the UCN@mSiO2-(Azo+RB) (azobenzene groups and Rose Bengal) nanoimpellers, which used the multicolor-emission capability of the core-shell upconverting nanoparticles (UCNs) at a single excitation wavelength to co-release anticarcinogen doxorubicin (Dox) and reactive oxygen species (ROS) for combined chemotherapy and photodynamic therapy (PDT). The nanoimpeller was formed from UCN inner core, mesoporous silica shell, and light triggers Azo and RB molecules. The UCNs emitting UV/blue and green/red multiband light were used to activate the photoresponsive Azo and photosensitizer RB molecules; The mesoporous silica shell offered the possibilities to load anticancer drug and conjugate the light triggers; As there are strong charge interaction and hydrogen bonds between Dox and surface silanols of mesoporous silica, the azobenzene molecules worked as “gatekeeper” and “molecular stirrer” to precisely trap and propel the release of Dox under the external stimuli. The time-dependent drug release analysis, ROS production test and PDT test suggested that the nanoparticles may serve as a useful multifunctional nanoplatform for synergistic therapy and cancer diagnostic.

Substantial improvements of long-term stability in encapsulation-free WS2 using highly interacting graphene substrate

We report the novel role of graphene substrates in obstructing the aging propagation in both the basal planes and edges of two-dimensitional sheets of transition metal dichalcogenides (TMDs). Even after 300 d in ambient air conditions, the epitaxially grown WS2/graphene samples have a clean, uniform surface without any encapsulation. We show that high crystallinity is an effective factor that determines the excellent air stability of WS2/graphene, and we present impressive experimental evidence of the relation between defects and the aging phenomena. Moreover, we reveal the strong interlayer charge interaction as an additional factor for the enhanced air stability as a result of charge transfer-induced doping. This work not only proposes a simple method to create highly stable TMDs by the selection of a suitable substrate but also paves the way for the realization of practical TMDs-based applications.

IrGPU.proton.Net: Irregular strong charge interaction networks of protonatable groups in protein molecules--a GPU solver using the fast multipole method and statistical thermodynamics.

A cluster of strongly interacting ionization groups in protein molecules with irregular ionization behavior is suggestive for specific structure-function relationship. However, their computational treatment is unconventional (e.g., lack of convergence in naive self-consistent iterative algorithm). The stringent evaluation requires evaluation of Boltzmann averaged statistical mechanics sums and electrostatic energy estimation for each microstate. irGPU: Irregular strong interactions in proteins--a GPU solver is novel solution to a versatile problem in protein biophysics--atypical protonation behavior of coupled groups. The computational severity of the problem is alleviated by parallelization (via GPU kernels) which is applied for the electrostatic interaction evaluation (including explicit electrostatics via the fast multipole method) as well as statistical mechanics sums (partition function) estimation. Special attention is given to the ease of the service and encapsulation of theoretical details without sacrificing rigor of computational procedures. irGPU is not just a solution-in-principle but a promising practical application with potential to entice community into deeper understanding of principles governing biomolecule mechanisms.

Pd/transition metal oxides functionalized ZSM-5 single crystals with b-axis aligned mesopores: Efficient and long-lived catalysts for benzene combustion

A series of PdO/transition metal oxides functionalized mesoporous ZSM-5 single crystals with b-axis aligned mesopores (x%Pd/x%M-ZSM-5-OMs) have been successfully prepared from self-assembly of the designed cationic amphiphilic copolymer of polystyrene-co-poly4-vinylpyridine (C-PSt-co-P4VP) with ZSM-5 zeolite precursor based on their strong positive-negative charge interaction under high temperature hydrothermal conditions. Characterizations of XRD patterns showed that x%Pd/x%M-ZSM-5-OMs exhibit good crystallinity with typical MFI zeolite characters; N2 isotherms showed that x%Pd/x%M-ZSM-5-OMs have large BET surface areas and mesopore volumes. SEM images showed the single crystal structure of x%Pd/x%M-ZSM-5-OMs, which have abundant and b-axis aligned mesopores, running through the whole zeolite crystals. TEM images further confirmed b-axis aligned mesopores, and good dispersion of active sites with high degree of crystallinity in x%Pd/x%M-ZSM-5-OMs. XPS spectra showed that transition metal oxides and PdO active species have been successfully loaded into ZSM-5-OM support. H2–TPR curves showed the low reduction temperatures of PdO and transition metal species in x%Pd/x%M-ZSM-5-OMs, which was favorable for the enhancement of their abilities for VOCs combustion. Catalytic tests showed that x%Pd/x%M-ZSM-5-OMs exhibit good catalytic activities and long catalytic lives for benzene combustion under rather mild conditions in comparison with that of x%Pd/x%M-ZSM-5, which would be very important for the wide applications of zeolites with controlled mesopores in the areas of VOCs oxidation.

Enhanced photocatalytic activity and structural stability by hybridizing Ag3PO4 nanospheres with graphene oxide sheets

Graphene oxide (GO)-Ag(3)PO(4) nanocomposites synthesized through a facile solution approach via electrostatic interaction were investigated as excellent photocatalysts for the degradation of rhodamine B (RhB) under visible light irradiation. SEM and TEM observations indicate that Ag(3)PO(4) nanospheres of ~120 nm in diameter were well dispersed and anchored onto the exfoliated GO sheets. The characterizations of FTIR and Raman demonstrated the existence of strong charge interactions between GO sheets and Ag(3)PO(4) nanospheres. As compared to Ag(3)PO(4) nanospheres alone, the attachments of GO sheets led to a band gap narrowing (2.10 eV) and a strong absorbance in the near infrared region (NIR). The photoluminescence (PL) analysis indicates a more efficient separation of electron-hole pairs in the GO-Ag(3)PO(4) nanocomposites. Notably, the incorporation of GO sheets not only significantly enhances the photocatalytic activity but also improves the structural stability of Ag(3)PO(4). The positive synergistic effects between Ag(3)PO(4) nanospheres and GO sheets are proposed to contribute to the improved photocatalytic properties. A possible photocatalytic mechanism of the GO-Ag(3)PO(4) nanocomposites was assumed as well. The integration of these advantages enables such GO-Ag(3)PO(4) hybrid material to be a nice photocatalyst for broad applications in a sewage treatment system.

Screw Motion Regulates Multiple Functions of T4 Phage Protein Gene Product 5 during Cell Puncturing

Bacteriophage T4 penetrates the outer membrane of Escherichia coli using a multifunctional device composed of a gene product 5 (gp5) protein trimer. We report that gp5 sequentially exerts distinct functions along the course of penetration stages induced by screw motion. A triple-stranded β-helix of gp5 acts as a cell-puncturing drill bit to make a hole on the membrane and then send the lipids upward efficiently by strong charge interactions. The gp5 lysozyme domains, which degrade the peptidoglycan layer later, are shown to play novel roles to enlarge the hole and control the release of the β-helix. The lysozyme active site is protected from lipid binding during the penetration and is exposed after the β-helix release. Intrinsic multiple functions of gp5 are shown to be served in turn regulated by gradual change of interdomain interactions, which enables the initial infection process with single protein trimer by continuous screw motion. The results of lysozyme domain should be understood as the case where a single-function protein acquired multiple chemical functions through interplay with other domains in a multidomain protein.

Identification of biologically active conformations in flexible drug molecules

Small perturbations to the conformation of a flexible drug molecule due to substituent changes allow scope for exploring the effect of population shifts in the conformation without necessarily perturbing the basic mode of binding to the receptor. The correlation of the biological effect with a conformer fraction in a series of compounds may thus permit identification of the biologically active con former. A review of the difficulties in extracting such information from data on drug-receptor complexes is made. The phase environment of the drug-receptor complex, the effects of charge redistribution on binding due to strong charge interactions, and the possible poor alignment of bonds in a gross free-energy effect are considered in the development of a precise model for identifying the protonated form of a drug acting on a receptor in a nonaqueous phase. When counterions are employed to mimic the effects of charge reorganization on drug-receptor interaction, difficulties arise in relating the fraction of the relevant charged conformer in the nonaqueous phase to the reference aqueous concentration. It is shown that this problem can be circumvented by the use of conformer acidity constants which link the concentration of a protonated conformer to that of the unprotonated form. The advantage of their use lies in the similar entropies associated with protonation on surfaces of a given shape. Computation is greatly aided since for any given conformation the problem reduces to a single calculation involving the energetics of strong charge interaction, while the conformer statistics may be performed on the unprotonated molecule. The effect of a-methyl substitution on the flexible side chain of a phenoxypropanolamine molecule is used as an example of the potential use of the model.

Turning calcium carbonate into a cost-effective wastewater-sorbing material by occluding waste dye

Background, aim, and scope Over the years, organic pollution in the environment has aroused people’s concern worldwide, especially persistent organic pollutants (POPs). Particularly in developing countries, plenty of concentrated organic wastewaters treated noneffectively are discharged into aquatic environments from chemical, textile, paper-making, and other industries to seriously threaten the surface and drinking water. The conventional wastewater treatment techniques are often helpless due to high cost with multilevel processing. Adsorption as an efficient method is often applied to the treatment of wastewater. The aim of this work is to develop an eco-friendly and cost-effective wastewater-sorbing material with weak acidic pink red B (APRB) and calcium carbonate (CaCO3) by reusing highly concentrated dye wastewater.

Tryptophan Phosphorescence Studies of the d-Galactose/d-Glucose-Binding Protein from Escherichia coli Provide a Molecular Portrait with Structural and Dynamics Features of the Protein

The D-galactose/D-glucose-binding protein (GGBP) from E. coli serves as an initial component for both chemotaxis toward glucose and high-affinity active transport of the sugar. In this work, we have used phosphorescence spectroscopy to investigate the effects of glucose and calcium on the dynamics and stability of GGBP. We found that GGBP exhibits a phosphorescence spectrum composed of two energetically distinct 0,0-vibrational bands centered at 404.43 and 409.61 nm; the large energy separation between them indicates two classes of chromophores making distinct dipolar interactions with their surrounding. Interestingly, the high-energy spectral component (404.43 nm) is one of the bluest spectra reported to date in proteins. Considering the ground state dipole direction, low-energy configurations for the indole side chain in proteins leading to blue-shifted spectra can arise from negative charges in proximity to the imidazole-ring nitrogen and/or positive charges near C4-C5 of the benzene ring. Among the five tryptophan residues of GGBP, Trp-284, located at the N-terminal domain of the protein, and Trp-183, located in the protein hinge region, make strong attractive charge interactions with surrounding side chains. Regarding Trp-284, the indole ring nitrogen is in contact with the negative charge of the Asp-267, whereas Trp-183 is next to the Glu-149 residue. In the latter, the ground state energy is further lowered by the proximity of the Arg-158 to the negative end (near C6) of the indole dipole. Regarding the red spectral component (409.61 nm), it is more intense than the blue component, presumably because more residues contribute to it. lambda 0,0 is typical of environments that are weakly polar or characterized by charges positioned near 90 degrees from the ground state dipole direction (the case of W195 and W127). The binding of glucose modifies the phosphorescence lifetime values as well as the spectrum of GGBP, shifting the blue band 0.54 nm to the blue and the red band 1 nm to the red. Finally, the removal of the calcium from GGBP structure causes variations in lifetime values and spectral shifts similar to those induced by glucose binding to the native protein. Aided by a detailed inspection of the three-dimensional structure of GGBP, these results contribute to a better understanding of the structure/function relationship of this protein.

Elimination of metformin–croscarmellose sodium interaction by competition

During analytical method development and validation, a strong charge interaction between metformin and croscarmellose sodium was observed when the aqueous solution containing metformin was spiked with croscarmellose sodium. The charge interaction resulted in the retention of metformin in croscarmellose sodium and caused a serious drug recovery problem. The percent recovery of metformin in the solution was much lower than its theoretical values, especially in the low metformin concentration range. To overcome the metformin–croscarmellose interaction, arginine was selected as a competitor for the binding sites on croscarmellose sodium. Because of the competition and stronger interaction between arginine and croscarmellose sodium than metformin and croscarmellose sodium, a complete recovery of metformin in presence of arginine in both low and high concentration ranges was achieved. The effect of arginine on the recovery of metformin and the competition mechanism are discussed in this paper.

Spontaneous Immobilization of Liposomes on Electron-Beam Exposed Resist Surfaces

We have found an interesting immobilization technique of liposomes on electron-beam exposed resist surfaces. The immobilized liposomes have been visualized by the atomic force microscope and have shown well-organized three-dimensional physical structures, in which the liposomes maintain their shapes and sizes similar to those of the original design in prepared solution. The immobilization is based on a strong static charge interaction between the resist surface and the liposomes. Further experiments show that very strong charge in the surfaces produces the firm immobilization of the liposome. We believe these findings can be related to various liposome applications such as drug delivery system, electrochemical or biosensors, and nanoscale membrane function studies.

Dielectric Properties of a Nematic Binary Mixture

In this paper, a phase diagram is developed for the molar mixtures of nematic liquid crystals of 5CB and MBBA. In order to understand the interaction of the two systems, dielectric permittivities ˜‖ and ˜⊥ were measured for mixtures of various concentrations. The usual assumption is that in the absence of chemical reactions the bulk physical properties add up as a weighted sum of the individual properties. Our dielectric permittivity data clearly show a correlation to the phase diagram and the existence of the induced phase. In order to understand the interactions from a fundamental level, we modeled the 5CB and MBBA molecules using a Silicon Graphics O2 workstation running the software Spartan 5.1. Different electrical surfaces were calculated for a geometrically optimized molecule. Our investigations support the idea of strong charge interactions between the nematic systems.

모세관 전기 영동을 이용한 퀴놀린계 항생제의 광학 이성질체 분석

(+)(18crown6)-tetracarboxylic acid (<TEX>$18C6H_4$</TEX>)를 퀴놀린계 항생제인 gemifloxacin을 모세관 전기영동법으로 키랄 분리하였다. Body fluid에서 퀴놀린계 항생제인 gemifloxacin의 직접적인 분석은 빠른 분석 시간, 다성분 분석등의 여러 가지 장점을 가진다. 그러나 Body fluid내의 높은 농도의 나트륨 이온은 <TEX>$18C6H_4$</TEX>와 강한 전하 상호작용으로 인하여 gemifoxacin과 <TEX>$18C6H_4$</TEX>의 상호작용을 방해한다. 키랄 선택제와 나트륨 이온 사이의 상호 작용을 줄이기 위해 완충 용액에 킬레이트 리간드 EDTA를 첨가하였다. 시료 용액에 150mM의 나트륨 이온이 존재 할 때에도 분리 효율의 향상과 이동 시간의 감소를 관찰 할 수 이었다. Chiral separation of gemifloxacin, an quinolone antibacterial agent, using (+)-(18-crown-6)-tetracar-boxylic acid <TEX>$(18C6H_4)$</TEX> as a chiral selector was performed by capillary electrophoresis (CE). Direct analysis of quinolone antibacterial agent in body fluid is beneficial in terms of fast analysis time, multicomponent analysis. However, high con-centration of sodium ion in body fluid can prevent gemifloxacin from interacting with <TEX>$18C6H_4$</TEX> since sodium ion has high affinity with <TEX>$18C6H_4$</TEX> due to the strong charge interaction. Ethylenediaminetetraacetic acid (EDTA), as a chelating ligand, was added in the running buffer in order to reduce the interaction between sodium ion and the chiral selector. Increased separation efficiency and reduced migration time were observed while sodium ion exists in the sample solution at the concentration up to 150 mM.

Genetically engineered charge modifications to enhance protein separation in aqueous two‐phase systems: Charge directed partitioning

This report continues or examination of the effect of genetically engineered charge modifications on the partitioning behavior of proteins in aqueous two-phase extration. The genetic modifications consisted of the fusion of charged peptide tails to beta-galactosidase and charge-change point mutations to T4 lysozyme. Our previous article examined the influence of these charge modifications on partitioning as a function of interfacial potential difference. In this study, we examined charge directed partitioning behavior in PEG/dextran systems containing small amounts of the charged polymers diethylaminoethyl-dextran (DEAE-dextran) or dextran sulfate. The best results were obtained when attractive forces between the protein and polymer were present. Nearly 100% of the beta-galactosidase, which carries a net negative charge, partitioned to the DEAE-dextran-rich phase regardless of whether the phase was dextran or PEG. In these cases, cloudiness of the protein-rich phases suggest that strong charge interactions resulted in protein/polymer aggregation, which may have contributed to the extreme partitioning. Unlike the potentialdriven partitioning reported previously, consistent partitioning trends were observed as a result of the fusion tails, with observed shifts in partition coefficient (K(p)) of up to 37-fold. However, these changes could not be solely attributed to charge-based interactions. Similarly, T4 lysozyme, carrying a net positive charge, partitioned to the dextran sulfate-containing phase, and displayed four- to sevenfold shifts in K(p) as a result of the point mutations. These shifts were two to four times stronger than those observed for potential driven partitioning. Little effect on partitioning was observed when the protein and polymer had the same charge, with the exception of beta-galactosidase with polyarginine tails. The high positive charge density of these tails provided for a localized interaction with the dextran sulfate, and resulted in 2- to 15-fold shifts in K(p). (c) 1995 John Wiley & Sons, Inc.