Kinetics and mechanisms of enhanced ammonia abatement under synchronous process of electrochemistry and adsorption.

As a kind of common nitrogen pollutants, ammonia seriously pollutes water and soil environments and threatens human health. The treatment of water contaminated with ammonia was carried out in an electrochemical-adsorption system (ECAS). This paper discusses the capacity, kinetics, and mechanism of ammonia electrosorption, which is accurately described by a pseudo-first-order model, indicating that physical adsorption is the dominating mechanism. A high adsorption capacity of 4.086 mg N/g was attributed to the formation of a large number of adsorption sites and the highly acidic nature of dealumination of zeolites during electrolysis. Fast directional migration of ammonia in the electric field weakened the negative effect of boundary layer on adsorption and accelerated adsorption procedure. Brunauer, Emmett, and Teller measurements and scanning electron microscopy indicated that the formation of new channels and surface erosion, which resulted in a large surface area and pore volume of zeolites and a low resistance towards ion migration. As a whole, this study achieved efficient ammonia removal without the addition of chemical reagents to avoid secondary pollution.

Cell wall channels of Rhodococcus species: identification and characterization of the cell wall channels of Rhodococcus corynebacteroides and Rhodococcus ruber.

The cell wall of Rhodococcus corynebacteroides formerly known as Nocardia corynebacteroides contains cell wall channels that are responsible for the cell wall permeability of this bacterium. Based on partial sequencing of the polypeptide subunits and a BLAST search, we identified one polypeptide of R. corynebacteroides (PorARc) and two polypeptides (PorARr and PorBRr) from the closely related bacterium Rhodococcus ruber. The corresponding genes, porARc (606 bp), porARr (702 bp), and porBRr (540 bp) are constituents of the known genome of R. corynebacteroides DSM-20151 and R. ruber DSM-43338, respectively. porARr and porBRr of R. ruber are possibly forming a common operon coding for the polypeptide subunits of the cell wall channel. The genes coding for PorARc and for PorARr and PorBRr without signal peptide were separately expressed in the porin-deficient Escherichia coli BL21DE3Omp8 strain and the proteins were purified to homogeneity. All proteins were checked for channel formation in lipid bilayers. PorARc formed channels with characteristics that were very similar to those of a previous study. The proteins PorARr and PorBRr expressed in E. coli could alone create channels in lipid bilayer membranes, despite the possibility that the two corresponding genes form a porin operon and that both subunits possibly form the cell wall channels in vivo. Based on amino acid sequence comparison of a variety of proteins forming cell wall channels in bacteria of the suborder Corynebacterineae, it seems very likely that PorARc, PorARr, and PorBRr are members of a huge family of proteins (PF09203) that form MspA-like cell wall channels.

Clostridium perfringens Beta2 toxin forms highly cation-selective channels in lipid bilayers.

Clostridium perfringens is a potent producer of a variety of toxins. Well studied from these are five toxins (alpha, Beta (CPB), epsilon, iota and CPE) that are produced by seven toxinotype strains (A-G) of C. perfringens. Besides these toxins, C. perfringens produces also another toxin that causes necrotizing enterocolitis in piglets. This toxin termed consensus Beta2 toxin (cCPB2) has a molecular mass of 27,620 Da and shows only little homology to CPB and no one to the other toxins of C. perfringens. Its primary action on cells remained unknown to date. cCPB2 was heterogeneously expressed as fusion protein with GST in Escherichia coli and purified to homogeneity. Although cCPB2 does not exhibit the typical structure of beta-stranded pore-forming proteins and contains no indication for the presence of amphipathic alpha-helices we could demonstrate that cCPB2 is a pore-forming component with an extremely high activity in lipid bilayers. The channels have a single-channel conductance of about 700 pS in 1 M KCl and are highly cation-selective as judged from selectivity measurements in the presence of salt gradients. The high cation selectivity is caused by the presence of net negative charges in or near the channel that allowed an estimate of the channel size being about 1.4 nm wide. Our measurements suggest that the primary effect of cCPB2 is the formation of cation-selective channels followed by necrotic enteritis in humans and animals. We searched in databases for homologs of cCPB2 and constructed a cladogram representing the phylogenetic relationship to the next relatives of cCPB2.

Role of Oxygen Vacancy Ordering and Channel Formation in Tuning Intercalation Pseudocapacitance in Mo Single-Ion-Implanted CeO2-x Nanoflakes.

Metal oxide pseudocapacitors are limited by low electrical and ionic conductivities. The present work integrates defect engineering and architectural design to exhibit, for the first time, intercalation pseudocapacitance in CeO2-x. An engineered chronoamperometric electrochemical deposition is used to synthesize 2D CeO2-x nanoflakes as thin as ∼12 nm. Through simultaneous regulation of intrinsic and extrinsic defect concentrations, charge transfer and charge-discharge kinetics with redox and intercalation capacitances together are optimized, where reduction increases the gravimetric capacitance by 77% to 583 F g-1, exceeding the theoretical capacitance (562 F g-1). Mo ion implantation and reduction processes increase the specific capacitance by 133%, while the capacitance retention increases from 89 to 95%. The role of ion-implanted Mo6+ is critical through its interstitial solid solubility, which is not to alter the energy band diagram but to facilitate the generation of electrons and to establish the midgap states for color centers, which facilitate electron transfer across the band gap, thus enhancing n-type semiconductivity. Critically, density functional theory simulations reveal, for the first time, that the reduction causes the formation of ordered oxygen vacancies that provide an atomic channel for ion intercalation. These channels enable intercalation pseudocapacitance but also increase electrical and ionic conductivities. In addition, the associated increased active site density enhances the redox such that the 10% of the Ce3+ available for redox (surface only) increases to 35% by oxygen vacancy channels. These findings are critical for any oxide system used for energy storage systems, as they offer both architectural design and structural engineering of materials to maximize the capacitance performance by achieving accumulative surface redox and intercalation-based redox reactions during the charge/discharge process.

Viroporins vs. Other Pore-Forming Proteins: What Lessons Can We Take?

Pore-forming proteins (PFPs) exist in virtually all domains of life, and by disrupting cellular membranes, depending on the pore size, they cause ion dis-balance, small substances, or even protein efflux/influx, influencing cell's signaling routes and fate. Such pore-forming proteins exist from bacteria to viruses and also shape host defense systems, including innate immunity. There is strong evidence that amyloid toxicity is also caused by prefibrillar oligomers making "amyloid pores" into cellular membranes. For most of the PFPs, a 2-step mechanism of protein-membrane interaction takes place on the "lipid rafts," membrane microdomains rich in gangliosides and cholesterol. In this mini-review paper, common traits of different PFPs are looked at. Possible ways for therapy of channelopathies and/or modulating immunity relevant to the new threat of SARS-CoV-2 infections could be learnt from such comparisons.

Channel Formation by LktA of Mannheimia (Pasteurella) haemolytica in Lipid Bilayer Membranes and Comparison of Channel Properties with Other RTX-Cytolysins.

Cytolysin LktA is one of the major pathogenicity factors of Mannheimia haemolytica (formerly Pasteurella haemolytica) that is the cause of pasteurellosis, also known as shipping fever pneumonia, causing substantial loss of sheep and cattle during transport. LktA belongs to the family of RTX-toxins (Repeats in ToXins) that are produced as pathogenicity factors by a variety of Gram-negative bacteria. Sublytic concentrations of LktA cause inflammatory responses of ovine leukocytes. Higher concentrations result in formation of transmembrane channels in target cells that may cause cell lysis and apoptosis. In this study we investigated channel formation by LktA in artificial lipid bilayer membranes made of different lipids. LktA purified from culture supernatants by polyethylene glycol 4000 precipitation and lyophilization had to be activated to frequently form channels by solution in 6 M urea. The LktA channels had a single-channel conductance of about 60 pS in 0.1 M KCl, which is about one tenth of the conductance of most RTX-toxins with the exception of adenylate cyclase toxin of Bordetella pertussis. The LktA channels are highly cation-selective caused by negative net charges. The theoretical treatment of the conductance of LktA as a function of the bulk aqueous concentration allowed a rough estimate of the channel diameter, which is around 1.5 nm. The size of the LktA channel is discussed with respect to channels formed by other RTX-toxins. We present here the first investigation of LktA in a reconstituted system.

Clostridium perfringens Enterotoxin: The Toxin Forms Highly Cation-Selective Channels in Lipid Bilayers.

One of the numerous toxins produced by Clostridium perfringens is Clostridium perfringens enterotoxin (CPE), a polypeptide with a molecular mass of 35.5 kDa exhibiting three different domains. Domain one is responsible for receptor binding, domain two is involved in hexamer formation and domain three has to do with channel formation in membranes. CPE is the major virulence factor of this bacterium and acts on the claudin-receptor containing tight junctions between epithelial cells resulting in various gastrointestinal diseases. The activity of CPE on Vero cells was demonstrated by the entry of propidium iodide (PI) in the cells. The entry of propidium iodide caused by CPE was well correlated with the loss of cell viability monitored by the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) test. CPE formed ion-permeable channels in artificial lipid bilayer membranes with a single-channel conductance of 620 pS in 1 M KCl. The single-channel conductance was not a linear function of the bulk aqueous salt concentration indicating that point-negative charges at the CPE channel controlled ion transport. This resulted in the high cation selectivity of the CPE channels, which suggested that anions are presumably not permeable through the CPE channels. The possible role of cation transport by CPE channels in disease caused by C. perfringens is discussed.

Three-Dimensional Visualization of Gas Evolution and Channel Formation inside a Lithium-Ion Battery.

Gas generation within lithium ion batteries (LIBs) gives rise to safety concerns that question their applicability. By employing synchrotron X-ray imaging, the gas and channel evolution occurring in an operating LIB have been directly visualized in their inherent 3D state as a function of discharge and charge. Using the spatial 3D distribution of gas bubbles and channels, the active particles that dictate the performance of a functional LIB were identified and visualized in 3D. Delithiation and lithiation are interpreted as the process of activating particles continuously in a step-by-step way. The present work not only demonstrates the generation and evolution of gas within LIB in 3D, but also reveals the distribution of active particles for the first time. These fundamentally findings presented here shed light on a range of processes that could not previously be characterized in 3D and can provide practical guidance for the design of next-generation LIBs with improved safety.