CaptureSelect FcXP affinity medium exhibits strong aggregate separation capability

Protein A affinity chromatography has been widely used for initial product capture in recombinant antibody/Fc-fusion purification. However, in general Protein A lacks the capability of separating aggregates (unless the aggregates are too large to enter the pores of resin beads or have their Protein A binding sites buried, in which case the aggregates do not bind). In the current work, we demonstrated that CaptureSelect FcXP affinity medium exhibited strong aggregate separation capability and effectively removed aggregates under pH or conductivity gradient elution in two bispecific antibody (bsAb) cases. For these two cases, aggregate contents were reduced from >16% and >22% (in the feed) to <1% and <5% (in the eluate) for the first and second bsAbs, respectively. While more case studies are required to further demonstrate FcXP's superiority in aggregate removal, findings from the current study suggest that FcXP can potentially be a better alternative than Protein A for product capture in cases where aggregate content is high.

PETR: A novel peristaltic mixed tubular bioreactor simulating human colonic conditions

A novel bioreactor simulating human colonic conditions for in vitro cultivation of intestinal microbiota is presented. The PEristaltic mixed Tubular bioReactor (PETR) is modular designed and periodically kneaded to simulate intestinal peristalsis. The reactor is introduced, characterized from a bioprocess engineer's perspective and discussed in its ability to mimic colon conditions. PETR provides physiological temperature and appropriate anaerobic conditions, simulates intestinal peristalsis, and has a mean residence time of 32.8 ± 0.8 h comparable to the adult human colon. The single-tube design enables a time-constant and longitudinally progressive pH gradient from 5.5 to 7.0. Using a dialysis liquid containing high molecular weight polyethylene glycol, the integrated dialysis system efficiently absorbs short chain fatty acids (up to 60%) and water (on average 850 mL d-1 ). Cultivation of a typical gut bacterium (Bifidobacterium animalis) was performed to demonstrate the applicability for controlled microbiota cultivation. PETR is unique in combining simulation of the entire colon, peristaltic mixing, dialytic water and metabolite absorption, and a progressive pH gradient in a single-tube design. PETR is a further step to precise replication of colonic conditions in vitro for reliable and reproducible microbiota research, such as studying the effect of food compounds, prebiotics or probiotics, or the development and treatment of infections with enteric pathogens, but also for further medical applications such as drug delivery studies or to study the effect of drugs on and their degradation by the microbiota.

A model for collagen secretion by intercompartmental continuities

Newly synthesized secretory proteins are exported from the endoplasmic reticulum (ER) at specialized subcompartments called exit sites (ERES). Cargoes like procollagen are too large for export by the standard COPII-coated vesicle of 60 nm average diameter. We have previously suggested that procollagen is transported from the ER to the next secretory organelle, the ER-Golgi intermediate compartment (ERGIC), in TANGO1-dependent interorganelle tunnels. In the theoretical model presented here, we suggest that intrinsically disordered domains of TANGO1 in the ER lumen induce an entropic contraction, which exerts a force that draws procollagen toward the ERES. Within this framework, molecular gradients of pH and/or HSP47 between the ER and ERGIC create a force in the order of tens of femto-Newtons. This force is substantial enough to propel procollagen from the ER at a speed of approximately 1 nm · s-1. This calculated speed and the quantities of collagen secreted are similar to its observed physiological secretion rate in fibroblasts, consistent with the proposal that ER export is the rate-limiting step for procollagen secretion. Hence, the mechanism we propose is theoretically adequate to explain how cells can utilize molecular gradients and export procollagens at a rate commensurate with physiological needs.

How chloride functions to enable proton conduction in photosynthetic water oxidation: Time-resolved kinetics of intermediates (S-states) in vivo and bromide substitution

Chloride (Cl-) is essential for O2 evolution during photosynthetic water oxidation. Two chlorides near the water-oxidizing complex (WOC) in Photosystem II (PSII) structures from Thermosynechococcus elongatus (and T. vulcanus) have been postulated to transfer protons generated from water oxidation. We monitored four criteria: primary charge separation flash yield (P* → P+QA-), rates of water oxidation steps (S-states), rate of proton evolution, and flash O2 yield oscillations by measuring chlorophyll variable fluorescence (P* quenching), pH-sensitive dye changes, and oximetry. Br-substitution slows and destabilizes cellular growth, resulting from lower light-saturated O2 evolution rate (-20 %) and proton release (-36 % ΔpH gradient). The latter implies less ATP production. In Br- cultures, protonogenic S-state transitions (S2 → S3 → S0') slow with increasing light intensity and during O2/water exchange (S0' → S0 → S1), while the non-protonogenic S1 → S2 transition is kinetically unaffected. As flash rate increases in Cl- cultures, both rate and extent of acidification of the lumen increase, while charge recombination is suppressed relative to Br-. The Cl- advantage in rapid proton escape from the WOC to lumen is attributed to correlated ion-pair movement of H3O+Cl- in dry water channels vs. separated Br- and H+ ion movement through different regions (>200-fold difference in Bronsted acidities). By contrast, at low flash rates a previously unreported reversal occurs that favors Br- cultures for both proton evolution and less PSII charge recombination. In Br- cultures, slower proton transfer rate is attributed to stronger ion-pairing of Br- with AA residues lining the water channels. Both anions charge-neutralize protons and shepherd them to the lumen using dry aqueous channels.

pH Gradients in Spatially Non-Uniform AC Electric Fields around the Charging Frequency; A Study of Two Different Geometries and Electrode Passivation

Dielectrophoresis (DEP), a precision nonlinear electrokinetic tool utilized within microfluidic devices, can induce bioparticle polarization that manifests as motion in the electric field; this phenomenon has been leveraged for phenotypic cellular and biomolecular detection, making DEP invaluable for diagnostic applications. As device operation times lengthen, reproducibility and precision decrease, which has been postulated to be caused by ion gradients within the supporting electrolyte medium. This research focuses on characterizing pH gradients above, at, and below the electrode charging frequency (0.2-1.4 times charging frequency) in an aqueous electrolyte solution in order to extend the parameter space for which microdevice-imposed artifacts on cells in clinical diagnostic devices have been characterized. The nonlinear alternating current (AC) electric fields (0.07 Vpp/μm) required for DEP were generated via planar T-shaped and star-shaped microelectrodes overlaid by a 70 μm high microfluidic chamber. The experiments were designed to quantify pH changes temporally and spatially in the two microelectrode geometries. In parallel, a 50 nm hafnium oxide (HfO2) thin film on the microelectrodes was tested to provide insights into the role of Faradaic surface reactions on the pH. Electric field simulations were conducted to provide insights into the gradient shape within the microelectrode geometries. Frequency dependence was also examined to ascertain ion electromigration effects above, at, and below the electrode charging frequency. The results revealed Faradaic reactions above, at, and below the electrode charging frequency. Comparison experiments further demonstrated that pH changes caused by Faradaic reactions increased inversely with frequency and were more pronounced in the star-shaped geometry. Finally, HfO2 films demonstrated frequency-dependent properties, impeding Faradaic reactions.

Field development of Posidonia oceanica seedlings changes under predicted acidification conditions

Ocean acidification has been consistently evidenced to have profound and lasting impacts on marine species. Observations have shown seagrasses to be highly susceptible to future increased pCO₂ conditions, but the responses of early life stages as seedlings are poorly understood. This study aimed at evaluating how projected Mediterranean Sea acidification affects the survival, morphological and biochemical development of Posidonia oceanica seedlings through a long-term field experiment along a natural low pH gradient. Future ocean conditions seem to constrain the morphological development of seedlings. However, high pCO₂ exposures caused an initial increase in the degree of saturation of fatty acids in leaves and then improved the fatty acid adjustment increasing unsaturation levels in leaves (but not in seeds), suggesting a nutritional compound translocation. Results also suggested a P. oceanica structural components remodelling which may counteract the effects of ocean acidification but would not enhance seagrass seedling productivity.

Revealing charge heterogeneity of stressed trastuzumab at the subunit level

Trastuzumab is known to be heterogeneous in terms of charge. Stressing trastuzumab under physiological conditions (pH 7.4 and 37 °C) increases charge heterogeneity further. Separation of charge variants of stressed trastuzumab at the intact protein level is challenging due to increasing complexity making it difficult to obtain pure charge variants for further characterization. Here we report an approach for revealing charge heterogeneity of stressed trastuzumab at the subunit level by pH gradient cation-exchange chromatography. Trastuzumab subunits were generated after limited proteolytic cleavage with papain, IdeS, and GingisKHAN®. The basic pI of Fab and F(ab)₂ fragments allowed to use the same pH gradient for intact protein and subunit level analysis. Baseline separation of Fab subunits was obtained after GingisKHAN® and papain digestion and the corresponding modifications were determined by LC-MS/MS peptide mapping and middle-down MALDI-ISD FT-ICR MS. The described approach allows a comprehensive charge variant analysis of therapeutic antibodies that have two or more modification sites in the Fab region.

Enhancing the selective synthesis of butyrate in microbial electrosynthesis system by gas diffusion membrane composite biocathode

The reduction of carbon dioxide (CO₂) to high value-added multi-carbon compounds at the cathode is an emerging application of microbial electrosynthesis system (MES). In this study, a composite cathode consisting of hollow fiber membrane (HFM) and the carbon felt is designed to enhance the CO₂ mass transfer of the cathode. The result shows that the main products are acetate and butyrate without other substances. The electrochemical performance of the electrode is significantly improved after biofilm becomes matures. The composite cathode significantly reduces the "threshold" for the synthesis of butyrate. Moreover, CO₂ is dissolved and protons are consumed by synthesizing volatile fatty acids (VFAs) to maintain a stable pH inside the composite electrode. The synthesis mechanism of butyrate is that CO₂ is converted sequentially into acetate and butyrate. The microenvironment of the composite electrode enriches Firmicute. This composite electrode provides a novel strategy for regulating the microenvironment.

Time and charge/pH-dependent activation of K+ channel-mediated K+ influx and K+/H+ exchange in guinea pig heart isolated mitochondria; role in bioenergetic stability

Mitochondria play an important role not only in producing energy for the cell but also for regulating mitochondrial and cell function depending on the cell's needs and environment. Uptake of cations, anions, and substrates requires a stable, polarized transmembrane charge potential (ΔΨ_m). Chemiosmosis requires ion exchangers to remove Na⁺, K⁺, Ca²⁺, PO₄^3-, and other charged species that enter mitochondria. Knowledge of the kinetics of mitochondrial (m) cation channels and exchangers is important in understanding their roles in regulating mitochondrial chemiosmosis and bioenergetics. The influx/efflux of K⁺, the most abundant mitochondrial cation, alters mitochondrial volume and shape by bringing in anions and H₂O by osmosis. The effects of K⁺ uptake through ligand-specific mK⁺ channels stimulated/inhibited by agonists/antagonists on mitochondrial volume (swelling/contraction) are well known. However, a more important role for K⁺ influx is likely its effects on H⁺ cycling and bioenergetics facilitated by mitochondrial (m) K⁺/H⁺ exchange (mKHE), though the kinetics and consequences of K⁺ efflux by KHE are not well described. We hypothesized that a major role of K⁺ influx/efflux is stimulation of respiration via the influx of H⁺ by KHE. We proposed to modulate KHE activity by energizing guinea pig heart isolated mitochondria and by altering the mK⁺ cycle to capture changes in mitochondrial volume, pH_m, ΔΨ_m, and respiration that would reflect a role for H⁺ influx via KHE to regulate bioenergetics. To test this, mitochondria were suspended in a 150 mM K⁺ buffer at pH 6.9, or in a 140 mM Cs⁺ buffer at pH 7.6 or 6.9 with added 10 mM K⁺, minimal Ca²⁺ and free of Na⁺. O₂ content was measured by a Clark electrode, and pH_m, ΔΨ_m, and volume, were measured by fluorescence spectrophotometry and light-scattering. Adding pyruvic acid (PA) alone caused increases in volume and respiration and a rapid decrease in the transmembrane pH gradient (ΔpH_m = pH_in-pH_ext) at pH_ext 6.9> > 7.6, so that ΔΨ_m was charged and maintained. BK_Ca agonist NS1619 and antagonist paxilline modified these effects, and KHE inhibitor quinine and K⁺ ionophore valinomycin depolarized ΔΨ_m. We postulate that K⁺ efflux-induced H⁺ influx via KHE causes an inward H⁺ leak that stimulates respiration, but at buffer pH 6.9 also utilizes the energy of ΔpH_m, the smaller component of the overall proton motive force, ΔμH⁺. Thus ΔpH_m establishes and maintains the ΔΨ_m required for utilization of substrates, entry of all cations, and for oxidative phosphorylation. Thus, K⁺ influx/efflux appears to play a pivotal role in regulating energetics while maintaining mitochondrial ionic balance and volume homeostasis.

pH-Sensitive Controlled Motion of Micrometer-sized Oil Droplets in a Solution of Surfactants Containing Fumaric Acid Derivatives

Self-propelled droplets are of considerable interest as an appropriate model for understanding the self-propulsion of objects in the fields of nonequilibrium physics and nonlinear science. Several research groups have reported the monodirectional motion of droplets, that is, chemotaxis, using stimuli-responsive materials. However, the precise control of chemotaxis remains challenging from the perspective of synthetic chemistry because chemotactic motion is primarily induced by the consumption of reactive oil or surfactants. Herein, we report a chemical system containing pH-responsive fumaric acid derivatives, in which the oil droplet exhibited positive chemotaxis over a wide pH range-from basic to acidic conditions. From the measurements of the interfacial tension between the oil and aqueous phases, it was deduced that the positive chemotaxis was due to heterogeneity in the interfacial tension of the droplet surface, which was accompanied by the production of surface-active compounds in the pH gradient in a linear-type channel.

Anagliptin promotes apoptosis in mouse colon carcinoma cells via MCT-4/lactate-mediated intracellular acidosis

Cancer cells frequently exhibit an acidic extracellular microenvironment, where inversion of the transmembrane pH gradient is associated with tumor proliferation and metastasis. To elucidate a new therapeutic target against cancer, the current study aimed to determine the mechanism by which the dipeptidyl peptidase-4 inhibitor anagliptin regulates the cellular pH gradient and concomitant extracellular acidosis during cancer progression. A total of 5x10⁵ CT-26 cells (resuspended in phosphate buffer saline) were injected subcutaneously in the right flank of male BALB/c mice (weighing 25-28 g). The tumor samples were harvested, and lactate was detected using a lactate assay kit. Immunohistochemistry was used to detect the Ki67 and PCNA. MTT assay and flow cytometric were used to detect cell viability. Intracellular pH was detected by fluorescence pH indicator. The results revealed that anagliptin effectively reduced tumor growth, but did not affect the body weight of treated mice. Anagliptin reduced the accumulation of lactate in tumor sample. Treatment with anagliptin stimulated the apoptosis of CT-26 cells. And lactate excretion inhibition is accompanied by an increase in extracellular pH (pHe) after treatment with anagliptin. Furthermore, anagliptin induced intracellular acidification and reversed the low pHe gradient via monocarboxylate transporter-4 (MCT-4)-mediated lactate excretion. Additionally, anagliptin reversed the aberrant transmembrane extracellular/intracellular pH gradient by suppressing MCT-4-mediated lactate excretion, while also reducing mitochondrial membrane potential and inducing apoptosis. These data revealed a novel function of anagliptin in regulating lactate excretion from cancer cells, suggesting that anagliptin may be used as a potential treatment for cancer.

Insight into Hydrogenation Selectivity of the Electrocatalytic Nitrate-to-Ammonia Reduction Reaction via Enhancing the Proton Transport

The electrocatalytic nitrate-to-ammonia reduction reaction route (NARR) is one of the emerging routes toward green ammonia synthesis, and its conversion efficiency is controlled mainly by the hydrogenation selectivity. This study proposed a likely NARR route feasible and effective even in a neutral condition. Its high catalytic selectivity and efficiency were achieved by a switch of the sulfate solution to the phosphate buffer solution (PBS), while conditions of NO₃ ^- concentration, pH, and applied potential were maintained unchanged. Specifically, the faradaic efficiencies toward NH₃ (FE NH 3 ) in Na₂ SO₄ were as low as 9.8, 19.8, and 11.4 % versus remarkably jumping to 82.8, 90.5, and 89.5 % in PBS under -0.75, -1.0, and -1.25 V, respectively. The corresponding faradaic efficiencies toward NO₂ ^- (FE NO 2 - ), 77.0, 69.2, and 73.7 % in Na₂ SO₄ , significantly dropped to10.8, 7.4, and 4.4 % in PBS, evidencing an unexpected selectivity reversal of the nitrate reduction from NO₂ ^- to NH₃ . This insight was further revealed by the visualization of the pH gradient near the electrode surface during NARR and confirmed by density functional theory calculations; PBS notably facilitated the proton transport and active mitigation over the proton transfer barrier. The use of PBS resulted in a maximal partial current density toward NH₃ (J NH 3 ) and NH₃ formation rate (r NH 3 ) up to 133.5 mA cm^-2 and 1.74×10^-7  mol s^-1  cm^-2 in 1.0 m KNO₃ at -1.25 V.

Separation of charge variants of a monoclonal antibody by overloaded ion exchange chromatography

A procedure for adjusting the content of charge variants of monoclonal antibody by ion exchange chromatography has been developed. The band splitting phenomenon was utilized to split the protein load into two parts, i.e., the flowthrough and bound fractions, which were either enriched or depleted with some of variants. The phenomenon was triggered by thermodynamic effects resulting from oversaturation of the resin binding sites at high column loadings as well as from kinetic effects arising from limited rates of mass transport. Cation exchange chromatography (CEX) and anion exchange chromatography (AEX) separations were examined, with the reverse order of the variant elution: acidic, main, basic in CEX, and basic, main, acidic in AEX, and the corresponding reverse enrichment tendency in the collected fractions. The separations were performed by pH gradient, whose course was simplified to two stages: isocratic loading and washing at mild pH to load and partly elute the protein, followed by a rapid pH change towards non-binding conditions to desorb the remains of the protein load. To improve yield of the operation, possibility of recycling of waste fractions was considered. To predict the process performance, a dynamic model was developed, which accounted for both adsorption kinetics and thermodynamics.

Purification of N-acetylgalactosamine-modified-oligonucleotides using orthogonal anion-exchange and mixed-mode chromatography approaches

N-acetylgalactosamine (GalNAc)-modified small interfering ribonucleic acids (siRNA) have shown promising outcomes for targeted siRNA delivery resulting in gene silencing in vivo; however, their structural complexity requires development of new purification methods to address high purity and recovery requirements. The current study evaluates complementary purification approaches using a mixed-mode Scherzo SS-C18 and anion-exchange (AEX) TSK-gel SuperQ-5PW for a range of single-stranded triantennary GalNAc-oligonucleotides. Initially, the semi-preparative mixed-mode support (10 × 250 mm, 3 µm) was compared against the preparative AEX analogue (21.5 × 300 mm, 13 µm), with the former affording double the recovery and higher purity of 95% over its AEX counterpart displaying 91% for a selected siRNA conjugate. An assortment of GalNAc-modified oligonucleotides was later purified using the mixed-mode resin revealing good recoveries (∼30-60%) and high purities of 90-94% ranging from straightforward to more challenging purifications. High sample loading in the 20 mg range was achieved, which was comparable with the larger preparative TSKgel SuperQ-5PW support. The Scherzo-SS-C18 resin also afforded some degree of resolution between diastereomers containing phosphorothioate functionalities. The TSKgel SuperQ-5PW support was later investigated to provide orthogonal separation selectivity to the Scherzo-SS-C18 column enabling purification of a selected, GalNAc-siRNA conjugate. The developed pH (8.5-11) and salt (0.3-0.7 M) gradients method provided enhanced separation selectivity between the free and conjugated siRNA, while minimizing formation of secondary structures and highlighting a complementary approach to deal with challenging purifications of oligonucleotide-GalNAc conjugates. Together, the use of AEX and mixed-mode columns provide much needed orthogonality to deal with complex GalNAc-modified oligonucleotides and potentially other upcoming modalities.

Change of charge variant composition of trastuzumab upon stressing at physiological conditions

Cation-exchange chromatography is a widely used approach to study charge heterogeneity of monoclonal antibodies. Heterogeneity may arise both in vitro and in vivo because of the susceptibility of monoclonal antibodies to undergo chemical modifications. Modifications may adversely affect the potency of the drug, induce immunogenicity or affect pharmacokinetics. In this study, we evaluated the application of optimized pH gradient systems for the separation of charge variants of trastuzumab after forced degradation study. pH gradient-based elution resulted in high-resolution separation of some 20 charge variants after 3 weeks at 37°C under physiological conditions. The charge variants were further characterized by LC-MS-based peptide mapping. There was no significant difference in the binding properties to HER2 or a range of Fcγ receptors between non-stressed and stressed trastuzumab.

Hydrophilic porous materials provide efficient gas-liquid separation to advance hydrogen production in microbial electrolysis cells

Preventing methane evolution is a key issue to guarantee stable hydrogen production in microbial electrolysis cell (MEC). In this study, low-cost hydrophilic porous materials, such as non-woven cloth (NWC) and polyvinylidenedifluoride (PVDF), were investigated as alternatives to proton exchange membrane (PEM) in MEC. The MEC with a NWC (NWC-MEC) improved the current density and hydrogen production rate (HPR) of 262.5±10 A m^-3 and 2.5±0.2 m³ m^-3 d^-1, respectively, due to its lower pH gradient (0.37) and ion transport resistance (0.9±0.1 mΩ m²). Hydrogen production in NWC-MEC (from 2.5 to 2.1 m³ m^-3 d^-1) and PVDF-MEC (from 2.2 to 2.0 m³ m^-3 d^-1) showed more stable performance compared to PEM-MECs (from 2.2 to 1.6 m³ m^-3 d^-1) during 30 days of operation. Moreover, results of anodic microbial community analysis indicate that the growth of methanogens of NWC-MEC and PVDF-MEC was effectively inhibited in 30 days.

Simultaneous Monitoring of Monoclonal Antibody Variants by Strong Cation-Exchange Chromatography Hyphenated to Mass Spectrometry to Assess Quality Attributes of Rituximab-Based Biotherapeutics

Different manufacturing processes and storage conditions of biotherapeutics can lead to a significant variability in drug products arising from chemical and enzymatic post-translational modifications (PTMs), resulting in the co-existence of a plethora of proteoforms with different physicochemical properties. To unravel the heterogeneity of these proteoforms, novel approaches employing strong cation-exchange (SCX) high-performance liquid chromatography (HPLC) hyphenated to mass spectrometry (MS) using a pH gradient of volatile salts have been developed in recent years. Here, we apply an established SCX-HPLC-MS method to characterize and compare two rituximab-based biotherapeutics, the originator MabThera® and its Indian copy product Reditux™. The study assessed molecular differences between the two drug products in terms of C-terminal lysine variants, glycosylation patterns, and other basic and acidic variants. Overall, MabThera® and Reditux™ displayed differences at the molecular level. MabThera® showed a higher degree of galactosylated and sialylated glycoforms, while Reditux™ showed increased levels of oligomannose and afucosylated glycoforms. Moreover, the two drug products showed differences in terms of basic variants such as C-terminal lysine and N-terminal truncation, present in Reditux™ but not in MabThera®. This study demonstrates the capability of this fast SCX-HPLC-MS approach to compare different drug products and simultaneously assess some of their quality attributes.

Analysis of complex protein elution behavior in preparative ion exchange processes using a colloidal particle adsorption model

A fundamental understanding of the protein retention mechanism in preparative ion exchange (IEX) chromatography columns is essential for a model-based process development approach. For the past three decades, the mechanistic description of protein retention has been based predominantly on the steric mass action (SMA) model. In recent years, however, retention profiles of proteins have been reported more frequently for preparative processes that are not consistent with the mechanistic understanding relying on the SMA model. In this work, complex elution behavior of proteins in preparative IEX processes is analyzed using a colloidal particle adsorption (CPA) model. The CPA model is found to be capable of reproducing elution profiles that cannot be described by the traditional SMA model. According to the CPA model, the reported complex behavior can be ascribed to a strong compression and concentration of the elution front in the lower unsaturated part of the chromatography column. As the unsaturated part of the column decreases with increasing protein load density, exceeding a critical load density can lead to the formation of a shoulder in the peak front. The general applicability of the model in describing preparative IEX processes is demonstrated using several industrial case studies including multiple monoclonal antibodies on different IEX adsorber systems. In this context, the work covers both salt controlled and pH-controlled protein elution.

Empirical correction of non-linear pH gradients and a tool for application to protein ion exchange chromatography

This concept article reports a practical solution to improve the linearity of effluent pH response as observed in pH gradient cation exchange chromatography (CEX). When performing pH gradient CEX, it is not easy to develop buffer systems that will universally provide pH response proportional with the mobile phase (buffer) composition. It is an especially challenging pursuit when exploring MS compatible buffers (e.g. ammonium-acetate, ammonium-carbonate). In addition to "non-proportional" behavior from the mobile phase composition, the chromatographic column itself will sometimes impose an unpredictable impact on the effluent pH. Here, we propose a simple approach based on the on-line measurement of effluent pH response, conversion of pH to mobile phase volume fraction (φ) and then generation of the inverse response function in the time domain. In the end, when setting the inverse function as the gradient program instead of a linear gradient, an improved - ideally linear - pH response can be produced. A simple Excel tool was developed to assist analysts with this correction procedure, and it has been made available by download for public use.

Cooperative Chemotaxis of Magnesium Microswimmers for Corrosion Spotting

Numerous artificial micro- and nanomotors, as well as various swimmers have been inspired by living organisms that are able to move in a coordinated manner. Their cooperation has also gained a lot of attention because the resulting clusters are able to adapt to changes in their environment and to perform complex tasks. However, mimicking such a collective behavior remains a challenge. In the present work, magnesium microparticles are used as chemotactic swimmers with pronounced collective features, allowing the gradual formation of macroscopic agglomerates. The formed clusters act like a single swimmer able to follow pH gradients. This dynamic behavior can be used to spot localized corrosion events in a straightforward way. The autonomous docking of the swimmers to the corrosion site leads to the formation of a local protection layer, thus increasing corrosion resistance and triggering partial self-healing.

Total Matrix Ca2+ Modulates Ca2+ Efflux via the Ca2+/H+ Exchanger in Cardiac Mitochondria

Mitochondrial Ca²⁺ handling is accomplished by balancing Ca²⁺ uptake, primarily via the Ru360-sensitive mitochondrial calcium uniporter (MCU), Ca²⁺ buffering in the matrix and Ca²⁺ efflux mainly via Ca²⁺ ion exchangers, such as the Na⁺/Ca²⁺ exchanger (NCLX) and the Ca²⁺/H⁺ exchanger (CHE). The mechanism of CHE in cardiac mitochondria is not well-understood and its contribution to matrix Ca²⁺ regulation is thought to be negligible, despite higher expression of the putative CHE protein, LETM1, compared to hepatic mitochondria. In this study, Ca²⁺ efflux via the CHE was investigated in isolated rat cardiac mitochondria and permeabilized H9c2 cells. Mitochondria were exposed to (a) increasing matrix Ca²⁺ load via repetitive application of a finite CaCl₂ bolus to the external medium and (b) change in the pH gradient across the inner mitochondrial membrane (IMM). Ca²⁺ efflux at different matrix Ca²⁺ loads was revealed by inhibiting Ca²⁺ uptake or reuptake with Ru360 after increasing number of CaCl₂ boluses. In Na⁺-free experimental buffer and with Ca²⁺ uptake inhibited, the rate of Ca²⁺ efflux and steady-state free matrix Ca²⁺ [mCa²⁺]_ss increased as the number of administered CaCl₂ boluses increased. ADP and cyclosporine A (CsA), which are known to increase Ca²⁺ buffering while maintaining a constant [mCa²⁺]_ss, decreased the rate of Ca²⁺ efflux via the CHE, with a significantly greater decrease in the presence of ADP. ADP also increased Ca²⁺ buffering rate and decreased [mCa²⁺]_ss. A change in the pH of the external medium to a more acidic value from 7.15 to 6.8∼6.9 caused a twofold increase in the Ca²⁺ efflux rate, while an alkaline change in pH from 7.15 to 7.4∼7.5 did not change the Ca²⁺ efflux rate. In addition, CHE activation was associated with membrane depolarization. Targeted transient knockdown of LETM1 in permeabilized H9c2 cells modulated Ca²⁺ efflux. The results indicate that Ca²⁺ efflux via the CHE in cardiac mitochondria is modulated by acidic buffer pH and by total matrix Ca²⁺. A mechanism is proposed whereby activation of CHE is sensitive to changes in both the matrix Ca²⁺ buffering system and the matrix free Ca²⁺ concentration.

Enhancing the Mitochondrial Uptake of Phosphonium Cations by Carboxylic Acid Incorporation

There is considerable interest in developing drugs and probes targeted to mitochondria in order to understand and treat the many pathologies associated with mitochondrial dysfunction. The large membrane potential, negative inside, across the mitochondrial inner membrane enables delivery of molecules conjugated to lipophilic phosphonium cations to the organelle. Due to their combination of charge and hydrophobicity, quaternary triarylphosphonium cations rapidly cross biological membranes without the requirement for a carrier. Their extent of uptake is determined by the magnitude of the mitochondrial membrane potential, as described by the Nernst equation. To further enhance this uptake here we explored whether incorporation of a carboxylic acid into a quaternary triarylphosphonium cation would enhance its mitochondrial uptake in response to both the membrane potential and the mitochondrial pH gradient (alkaline inside). Accumulation of arylpropionic acid derivatives depended on both the membrane potential and the pH gradient. However, acetic or benzoic derivatives did not accumulate, due to their lowered pKa. Surprisingly, despite not being taken up by mitochondria, the phenylacetic or phenylbenzoic derivatives were not retained within mitochondria when generated within the mitochondrial matrix by hydrolysis of their cognate esters. Computational studies, supported by crystallography, showed that these molecules passed through the hydrophobic core of mitochondrial inner membrane as a neutral dimer. This finding extends our understanding of the mechanisms of membrane permeation of lipophilic cations and suggests future strategies to enhance drug and probe delivery to mitochondria.

Dynamics of the dissolved organic matter in a stream-lake system within an extremely acid to neutral pH range: Agrio-Caviahue watershed

The Agrio-Caviahue is a natural stream-lake system composed of the Upper Agrio River (UAR) -Lake Caviahue-Lower Agrio River (LAR). The system has a broad pH gradient from extremely acid in the hot spring to almost neutral pH only 60 km downstream the source, and varies as a function of the distance. The aim of this study was to analyze the dynamics of the dissolved organic matter (DOM) of this extreme system. For that matter, an absorbance and fluorescence-based characterization was performed on natural water samples and hydrophobic resin DOM extracts during different seasons in nine sampling stations. Between August and December, the hydrological connectivity is maximum due to precipitation and snowmelt, respectively. During these months, the stream that exits the lake governs the chemical characteristics downstream mainly in the period of high connectivity. In contrast, in the dry season when the flow of LAR is minimum, the two major affluents of this river influence its pH and DOM features, and deliver inputs of humified DOM from the wetlands where the tributaries are born. DOM was characterized by having low absorbance. The PARAFAC analysis of the fluorescent DOM (FDOM) validated three fluorescent components in the natural samples (with humic and non-humic features), two of which were also recorded in the extracts, meaning that no additional hydrophobic components were missed under the limit of detection of the fluorometer. The unique features of Agrio-Caviahue DOM resemble those found in DOM from Yellowstone hot springs, both acid and alkaline.

Impact of the column on effluent pH in cation exchange pH gradient chromatography, a practical study

In ionexchange chromatography, the pH gradient mode becomes more and more popular today for the analysis of therapeutic proteins as this mode can provide higher or alternative selectivity to the commonly used salt gradient mode. Ideally, a linear pH response is expected when performing linear gradients. However up to now, only a very few buffer systems have been developed and are commercially available which can perform nearly linear pH responses when flowing through a given column. It is also known that a selected buffer system (mobile phase) can work well on one column but can fail on other column. The goal of this study was to practically evaluate the effects that ionexchange columns (weak and strong exchangers) might have on effluent pH, when performing linear pH gradient separations of therapeutic monoclonal antibodies. To attain this objective, the pH was monitored on-line at the column outlet using a specific setup. To make comprehensive observations of the phenomenon, four different mobile phase conditions and five cation exchange columns (weak and strong exchangers) were employed. The obtained pH responses were systematically compared to responses measured in the absence of the columns. From this work, it has become clear that both the column and mobile phase can have significant effects on pH gradient chromatography and that their combination must be considered when developing a new method. Phase systems (column + mobile phase) providing linear pH responses are indeed the most suitable for separating mAbs with different isoelectric points and, with them, it is possible to elute mAbs across wide retention time ranges and with high selectivity.

Gene swamping alters evolution during range expansions in the protist Tetrahymena thermophila

At species' range edges, individuals often face novel environmental conditions that may limit range expansion until populations adapt. The potential to adapt depends on genetic variation upon which selection can act. However, populations at species' range edges are often genetically depauperate. One mechanism increasing genetic variation is reshuffling existing variation through sex. Sex, however, can potentially limit adaptation by breaking up existing beneficial allele combinations (recombination load). The gene swamping hypothesis predicts this is specifically the case when populations expand along an abiotic gradient and asymmetric dispersal leads to numerous maladapted dispersers from the range core swamping the range edge. We used the ciliate Tetrahymena thermophila as a model for testing the gene swamping hypothesis. We performed replicated range expansions in landscapes with or without a pH-gradient, while simultaneously manipulating the occurrence of gene flow and sexual versus asexual reproduction. We show that sex accelerated evolution of local adaptation in the absence of gene flow, but hindered it in the presence of gene flow. However, sex affected adaptation independently of the pH-gradient, indicating that both abiotic gradients and the biotic gradient in population density lead to gene swamping. Overall, our results show that gene swamping alters adaptation in life-history strategies.

A Relatively Small Gradient of Extracellular pH Directs Migration of MDA-MB-231 Cells In Vitro

Hematogenous tumor metastasis begins with the invasion and spread of primary tumor cells in the local tissue leading to intravasation. We hypothesized that tumor cells might actively migrate toward intratumor vessels with the extracellular metabolic gradient acting as a guiding cue. Here, we determined in vitro whether the extracellular gradient of pH can act as a cue for directional migration in MDA-MB-231 cells. Cell migration was determined by the wound-healing assay under gradients of extracellular pH (~0.2 units/mm) and oxygen concentration (~6% O₂/mm) that were produced by a microfluidic device, gap cover glass (GCG). Without GCG, the migration of cells was spatially homogeneous; the same number of cells migrated to the rectangular wound space from the left and right boundaries. In contrast, when GCG generated pH/O₂ gradients across the wound space, the number of cells migrating to the wound space from the boundary with higher pH/O₂ values was considerably decreased, indicating a preferential movement of cells toward the region of higher pH/O₂ in the gradient. The addition of hepes in the extracellular medium abolished both the extracellular pH gradient and the directional cell migration under GCG. We conclude that relatively small gradients of pH in the extracellular medium compared to those found in Na⁺/H⁺ exchanger-driven cell migration were sufficient to guide MDA-MB-231 cells. The directional cell migration as guided by the metabolic gradient could effectively elevate the probability of intravasation and, ultimately, hematogenous metastasis.

Cellular and extracellular matrix of bone, with principles of synthesis and dependency of mineral deposition on cell membrane transport

Bone differs from other connective tissues; it is isolated by a layer of osteoblasts that are connected by tight and gap junctions. This allows bone to create dense lamellar type I collagen, control pH, mineral deposition, and regulate water content forming a compact and strong structure. New woven bone formed after degradation of mineralized cartilage is rapidly degraded and resynthesized to impart structural order for local bone strength. Ossification is regulated by thickness of bone units and by patterning via bone morphogenetic receptors including activin, other bone morphogenetic protein receptors, transforming growth factor-β receptors, all part of a receptor superfamily. This superfamily interacts with receptors for additional signals in bone differentiation. Important features of the osteoblast environment were established using recent tools including osteoblast differentiation in vitro. Osteoblasts deposit matrix protein, over 90% type I collagen, in lamellae with orientation alternating parallel or orthogonal to the main stress axis of the bone. Into this organic matrix, mineral is deposited as hydroxyapatite. Mineral matrix matures from amorphous to crystalline hydroxyapatite. This process includes at least two-phase changes of the calcium-phosphate mineral as well as intermediates involving tropocollagen fibrils to form the bone composite. Beginning with initiation of mineral deposition, there is uncertainty regarding cardinal processes, but the driving force is not merely exceeding the calcium-phosphate solubility product. It occurs behind a epithelial-like layer of osteoblasts, which generate phosphate and remove protons liberated during calcium-phosphate salt deposition. The forming bone matrix is discontinuous from the general extracellular fluid. Required adjustment of ionic concentrations and water removal from bone matrix are important details remaining to be addressed.

Interfacial water and its potential role in the function of sericin against biofouling

Silk sericin is a globular protein whose resistance against fouling is important for applications in biomaterials and water-purification membranes. Here it is shown how sericin generates a water-exclusion zone that may facilitate antifouling behavior. Negatively charged microspheres were used to mimic the surface charge and hydrophobic domains in bacteria. Immersed in water, regenerated silk sericin formed a 100-µm-sized exclusion zone (for micron-size foulants), along with a proton gradient with a decrease of >2 pH-units. Thus, when in contact with sericin, water molecules near the surface restructure to form a physical exclusionary barrier that might prevent biofouling. The decreased pH turns the aqueous medium unviable for neutrophilic bacteria. Therefore, resistance to biofouling seems explainable, among other factors, on the basis of water-exclusionary phenomena. Furthermore, sericin may play a role in triggering the fibroin assembly process by lowering the pH to the required value.

A simple and rapid direct injection method for the determination of glyphosate and AMPA in environmental water samples

Glyphosate is currently the most widely used herbicide in the world, yet screening of environmental waters for this chemical is limited by the need for specialized derivatization and measurement methods that can be tedious and time-consuming. In this work, we present a novel method for the detection and quantification at trace levels of glyphosate and aminomethylphosphonic acid (AMPA) in environmental water samples. The detection and quantification of the analytes was performed by liquid chromatography (LC) coupled with tandem mass spectrometry (MS/MS). Chromatographic separation was achieved with an ion-exchange column and a pH-gradient elution of a solution of ammonium hydroxide and ammonium acetate. The limit of detection for glyphosate and AMPA was 0.25 μg L^-1 and the limit of quantification was 0.5 μg L^-1with a 20-μL injection. The method was used to investigate the levels of glyphosate and AMPA in surface water samples from the Yarra River catchment area and urban constructed stormwater wetlands. The results indicate that at the time of sampling, no glyphosate or AMPA was present in the samples from the Yarra River catchment area (n = 10). However, glyphosate was detected above the limit of quantification in 33% of the wetland samples (n = 12), with concentrations ranging from 1.95 to 2.96 μg L^-1. Similarly, AMPA was quantified in 83% of the wetland samples, with concentrations ranging from 0.55 to 2.42 μg L^-1. To our knowledge, this is the first report of a pH-gradient LC-MS/MS method for glyphosate and AMPA analysis at ultratrace levels, with minimal sample processing, avoiding costly, time-consuming derivatization and preconcentration steps. Graphical abstract ᅟ.

The flip side of the Arabidopsis type I proton-pumping pyrophosphatase (AVP1): Using a transmembrane H+ gradient to synthesize pyrophosphate

Energy partitioning and plant growth are mediated in part by a type I H⁺-pumping pyrophosphatase (H⁺-PPase). A canonical role for this transporter has been demonstrated at the tonoplast where it serves a job-sharing role with V-ATPase in vacuolar acidification. Here, we investigated whether the plant H⁺-PPase from Arabidopsis also functions in "reverse mode" to synthesize PP_i using the transmembrane H⁺ gradient. Using patch-clamp recordings on Arabidopsis vacuoles, we observed inward currents upon P_i application on the cytosolic side. These currents were strongly reduced in vacuoles from two independent H⁺-PPase mutant lines (vhp1-1 and fugu5-1) lacking the classical PP_i-induced outward currents related to H⁺ pumping, whereas they were significantly larger in vacuoles with engineered heightened expression of the H⁺-PPase. Current amplitudes related to reverse-mode H⁺ transport depended on the membrane potential, cytosolic P_i concentration, and magnitude of the pH gradient across the tonoplast. Of note, experiments on vacuolar membrane-enriched vesicles isolated from yeast expressing the Arabidopsis H⁺-PPase (AVP1) demonstrated P_i-dependent PP_i synthase activity in the presence of a pH gradient. Our work establishes that a plant H⁺-PPase can operate as a PP_i synthase beyond its canonical role in vacuolar acidification and cytosolic PP_i scavenging. We propose that the PP_i synthase activity of H⁺-PPase contributes to a cascade of events that energize plant growth.

Nanochannel Gradient Separations

Gradient-based electrophoretic separations enable simultaneous separation and concentration of molecules. Compared with conventional injection-based separations, they enable enrichment of low-concentration analytes from larger sample volumes that are not limited by an injection volume. We have demonstrated that a nanochannel, connecting two chemically different reservoirs, can maintain a stationary chemical gradient while trapping biomolecules and effectively averaging out many of the complex physicochemical hydrodynamics that would broaden the bands in a meso- or microscale capillary. Here we describe chemical and physical methods that enable this work.

The Importance of Natural Acidified Systems in the Study of Ocean Acidification: What Have We Learned?

Human activity is generating an excess of atmospheric CO₂, resulting in what we know as ocean acidification, which produces changes in marine ecosystems. Until recently, most of the research in this area had been done under small-scale, laboratory conditions, using few variables, few species and few life cycle stages. These limitations raise questions about the reproducibility of the environment and about the importance of indirect effects and synergies in the final results of these experiments. One way to address these experimental problems is by conducting studies in situ, in natural areas where expected future pH conditions already occur, such as CO₂ vent systems. In the present work, we compile and discuss the latest research carried out in these natural laboratories, with the objective to summarize their advantages and disadvantages for research to improve these investigations so they can better help us understand how the oceans of the future will change.

Longitudinal Measurements of Intra- and Extracellular pH Gradient in a Rat Model of Glioma

This study presents the first longitudinal measurement of the intracellular/extracellular pH gradient in a rat glioma model using noninvasive magnetic resonance imaging. The acid–base balance in the brain is tightly controlled by endogenous buffers. Tumors often express a positive pH gradient (pH_i – pH_e) compared with normal tissue that expresses a negative gradient. Alkaline pH_i in tumor cells increases activity of several enzymes that drive cellular proliferation. In contrast, acidic pH_e is established because of increased lactic acid production and subsequent active transport of protons out of the cell. pH_i was mapped using chemical exchange saturation transfer, whereas regional pH_e was determined using hyperpolarized ¹³C bicarbonate magnetic resonance spectroscopic imaging. pH_i and pH_e were measured at days 8, 12, and 15 postimplantation of C6 glioma cells into rat brains. Measurements were made in tumors and compared to brain tissue without tumor. Overall, average pH gradient in the tumor changed from −0.02 ± 0.12 to 0.10 ± 0.21 and then 0.19 ± 0.16. Conversely, the pH gradient of contralateral brain tissue changed from −0.45 ± 0.16 to −0.25 ± 0.21 and then −0.34 ± 0.25 (average pH ± 1 SD) Spatial heterogeneity of tumor pH gradient was apparent at later time points and may be useful to predict local areas of treatment resistance. Overall, the intracellular/extracellular pH gradients in this rat glioma model were noninvasively measured to a precision of ∼0.1 pH units at 3 time points. Because most therapeutic agents are weak acids or bases, a priori knowledge of the pH gradient may help guide choice of therapeutic agent for precision medicine.

A physics-based model for maintenance of the pH gradient in the gastric mucus layer

It is generally accepted that the gastric mucus layer provides a protective barrier between the lumen and the mucosa, shielding the mucosa from acid and digestive enzymes and preventing autodigestion of the stomach epithelium. However, the precise mechanisms that contribute to this protective function are still up for debate. In particular, it is not clear what physical processes are responsible for transporting hydrogen protons, secreted within the gastric pits, across the mucus layer to the lumen without acidifying the environment adjacent to the epithelium. One hypothesis is that hydrogen may be bound to the mucin polymers themselves as they are convected away from the mucosal surface and eventually degraded in the stomach lumen. It is also not clear what mechanisms prevent hydrogen from diffusing back toward the mucosal surface, thereby lowering the local pH. In this work we investigate a physics-based model of ion transport within the mucosal layer based on a Nernst-Planck-like equation. Analysis of this model shows that the mechanism of transporting protons bound to the mucus gel is capable of reproducing the trans-mucus pH gradients reported in the literature. Furthermore, when coupled with ion exchange at the epithelial surface, our analysis shows that bicarbonate secretion alone is capable of neutralizing the epithelial pH, even in the face of enormous diffusive gradients of hydrogen. Maintenance of the pH gradient is found to be robust to a wide array of perturbations in both physiological and phenomenological model parameters, suggesting a robust physiological control mechanism.NEW & NOTEWORTHY This work combines modeling techniques based on physical principles, as well as novel numerical simulations to test the plausibility of one hypothesized mechanism for proton transport across the gastric mucus layer. Results show that this mechanism is able to maintain the extreme pH gradient seen in in vivo experiments and suggests a highly robust regulation mechanism to maintain this gradient in the face of dynamic lumen composition.

Aspect has a greater impact on alpine soil bacterial community structure than elevation

Gradients in environmental conditions, including climate factors and resource availability, occur along mountain inclines, providing a 'natural laboratory' to explore their combined impacts on microbial distributions. Conflicting spatial patterns observed across elevation gradients in soil bacterial community structure suggest that they are driven by various interacting factors at different spatial scales. Here, we investigated the relative impacts of non-resource (e.g. soil temperature, pH) and resource conditions (e.g. soil carbon and nitrogen) on the biogeography of soil bacterial communities across broad (i.e. along a 1500 m mountain elevation gradient) and fine sampling scales (i.e. along sunny and shady aspects of a mountain ridge). Our analysis of 16S rRNA gene data confirmed that when sampling across distances of < 1000 m, bacterial community composition was more closely related to the aspect of a site than its elevation. However, despite large differences in climate and resource-availability factors across elevation- and aspect-related gradients, bacterial community composition and richness were most strongly correlated with soil pH. These findings highlight the need to incorporate knowledge of multiple factors, including site aspect and soil pH for the appropriate use of elevation gradients as a proxy to explore the impacts of climate change on microbial community composition.

Light-Induced Proton Pumping with a Semiconductor: Vision for Photoproton Lateral Separation and Robust Manipulation

Energy-transfer reactions are the key for living open systems, biological chemical networking, and the development of life-inspired nanoscale machineries. It is a challenge to find simple reliable synthetic chemical networks providing a localization of the time-dependent flux of matter. In this paper, we look to photocatalytic reaction on TiO₂ from different angles, focusing on proton generation and introducing a reliable, minimal-reagent-consuming, stable inorganic light-promoted proton pump. Localized illumination was applied to a TiO₂ surface in solution for reversible spatially controlled "inorganic photoproton" isometric cycling, the lateral separation of water-splitting reactions. The proton flux is pumped during the irradiation of the surface of TiO₂ and dynamically maintained at the irradiated surface area in the absence of any membrane or predetermined material structure. Moreover, we spatially predetermine a transient acidic pH value on the TiO₂ surface in the irradiated area with the feedback-driven generation of a base as deactivator. Importantly we describe how to effectively monitor the spatial localization of the process by the in situ scanning ion-selective electrode technique (SIET) measurements for pH and the scanning vibrating electrode technique (SVET) for local photoelectrochemical studies without additional pH-sensitive dye markers. This work shows the great potential for time- and space-resolved water-splitting reactions for following the investigation of pH-stimulated processes in open systems with their flexible localization on a surface.

A benign alternative process for efficient separation of pure commercially important flavonoid nutraceuticals from edible plants

The present study signifies the development of a unique, optimized procedure for both selective determination and separation of different flavonoid nutraceuticals from edible plants. Totally ten different flavonoids were determined (HPLC-DAD) and isolated from five different plants using the developed process with a remarkable purity of 91-98% and recovery of 88-95%. Box-Behnken experimental design model yielded a optimized amount of 40.36 mg/g of AI extract (Pinostrobin) and 28.95 mg/g of AI extract (Baicalein) with a high correlation coefficient (0.98-0.99), indicating a good fit between the second order regression model and the experimental observations. The final purity of compounds through optimized process is 97.1% (Pinostrobin) and 93.5% (Baicalein) respectively. The optimized yields depicted a total recovery of 92% for pinostrobin, and 89% for Baicalein respectively. Thus, the developed process worked as a potential alternative which when statistically optimized results in a remarkable recovery of flavonoids from various plants. Being an environmentally friendly protocol the process could be useful in industrial separation of commercially important flavonoids widely applied in food industry.

Impairment of pH gradient and membrane potential mediates redox dysfunction in the mitochondria of the post-ischemic heart

The mitochondrial electrochemical gradient (Δp), which comprises the pH gradient (ΔpH) and the membrane potential (ΔΨ), is crucial in controlling energy transduction. During myocardial ischemia and reperfusion (IR), mitochondrial dysfunction mediates superoxide (^·O₂^-) and H₂O₂ overproduction leading to oxidative injury. However, the role of ΔpH and ΔΨ in post-ischemic injury is not fully established. Here we studied mitochondria from the risk region of rat hearts subjected to 30 min of coronary ligation and 24 h of reperfusion in vivo. In the presence of glutamate, malate and ADP, normal mitochondria (mitochondria of non-ischemic region, NR) exhibited a heightened state 3 oxygen consumption rate (OCR) and reduced ^·O₂^- and H₂O₂ production when compared to state 2 conditions. Oligomycin (increases ΔpH by inhibiting ATP synthase) increased ^·O₂^- and H₂O₂ production in normal mitochondria, but not significantly in the mitochondria of the risk region (IR mitochondria or post-ischemic mitochondria), indicating that normal mitochondrial ^·O₂^- and H₂O₂ generation is dependent on ΔpH and that IR impaired the ΔpH of normal mitochondria. Conversely, nigericin (dissipates ΔpH) dramatically reduced ^·O₂^- and H₂O₂ generation by normal mitochondria under state 4 conditions, and this nigericin quenching effect was less pronounced in IR mitochondria. Nigericin also increased mitochondrial OCR, and predisposed normal mitochondria to a more oxidized redox status assessed by increased oxidation of cyclic hydroxylamine, CM-H. IR mitochondria, although more oxidized than normal mitochondria, were not responsive to nigericin-induced CM-H oxidation, which is consistent with the result that IR induced ΔpH impairment in normal mitochondria. Valinomycin, a K⁺ ionophore used to dissipate ΔΨ, drastically diminished ^·O₂^- and H₂O₂ generation by normal mitochondria, but less pronounced effect on IR mitochondria under state 4 conditions, indicating that ΔΨ also contributed to ^·O₂^- generation by normal mitochondria and that IR mediated ΔΨ impairment. However, there was no significant difference in valinomycin-induced CM-H oxidation between normal and IR mitochondria. In conclusion, under normal conditions the proton backpressure imposed by ΔpH restricts electron flow, controls a limited amount of ^·O₂^- generation, and results in a more reduced myocardium; however, IR causes ΔpH impairment and prompts a more oxidized myocardium.

Proton gradients at the origin of life

Chemiosmotic coupling - the harnessing of electrochemical ion gradients across membranes to drive metabolism - is as universally conserved as the genetic code. As argued previously in these pages, such deep conservation suggests that ion gradients arose early in evolution, and might have played a role in the origin of life. Alkaline hydrothermal vents harbour pH gradients of similar polarity and magnitude to those employed by modern cells, one of many properties that make them attractive models for life's origin. Their congruence with the physiology of anaerobic autotrophs that use the acetyl CoA pathway to fix CO₂ gives the alkaline vent model broad appeal to biologists. Recently, however, a paper by Baz Jackson criticized the hypothesis, concluding that natural pH gradients were unlikely to have played any role in the origin of life. Unfortunately, Jackson mainly criticized his own interpretations of the theory, not what the literature says. This counterpoint is intended to set the record straight.

A Hydrogen-Evolving Hybrid-Electrolyte Battery with Electrochemical/Photoelectrochemical Charging from Water Oxidation

Decoupled hydrogen and oxygen production were successfully embedded into an aqueous dual-electrolyte (acid-base) battery for simultaneous energy storage and conversion. A three-electrode configuration was adopted, involving an electrocatalytic hydrogen-evolving electrode as cathode, an alkaline battery-type or capacitor-type anode as shuttle, and a charging-assisting electrode for electro-/photoelectrochemically catalyzing water oxidation. The conceptual battery not only synergistically outputs electricity and chemical fuels with tremendous specific energy and power densities, but also supports various approaches to be charged by pure or solar-assisted electricity.

Triple-edged therapy targeting intracellular alkalosis and extracellular acidosis in cancer

Extracellular acidity and intracellular alkalinity are two of the characteristics hallmarks of malignant cells and their environment. This involves an inversion of the extracellular/intracellular pH gradient when compared with normal cells and it gives malignant cells proliferative and invasive advantages. Thus, the reversal of the pH gradient is a legitimate objective in the treatment of cancer and may be accomplished with drugs already used for other purposes and/or with specific new drugs that are currently being studied. The aim of this review is to describe a triple approach for reversing this gradient inversion using the concerted utilization of proton extrusion inhibitors, mitochondrial poisons and lysosomal poisons that should act synergistically through different mechanisms. The scheme presented here is compatible with almost all the chemotherapeutic protocols currently being used.

Effects of the residual ammonium concentration on NOB repression during partial nitritation with granular sludge

Partial nitritation was stably achieved in a bench-scale airlift reactor (1.5L) containing granular sludge. Continuous operation at 20 °C treating low-strength synthetic wastewater (50 mg N-NH₄⁺/L and no COD) achieved nitrogen loading rates of 0.8 g N-NH₄⁺/(L·d) during partial nitritation. The switch between nitrite-oxidizing bacteria (NOB) repression and NOB proliferation was observed when ammonium concentrations in the reactor were below 2-5 mg N-NH₄⁺/L for DO concentrations lower than 4 mg O₂/L at 20 °C. Nitrospira spp. were detected to be the dominant NOB population during the entire reactor operation, whereas Nitrobacter spp. were found to be increasing in numbers over time. Stratification of the granule structure, with ammonia-oxidizing bacteria (AOB) occupying the outer shell, was found to be highly important in the repression of NOB in the long term. The pH gradient in the granule, containing a pH difference of ca. 0.4 between the granule surface and the granule centre, creates a decreasing gradient of ammonia towards the centre of the granule. Higher residual ammonium concentration enhances the ammonium oxidation rate of those cells located further away from the granule surface, where the competition for oxygen between AOB and NOB is more important, and it contributes to the stratification of both populations in the biofilm.

Silk Spinning in Silkworms and Spiders

Spiders and silkworms spin silks that outcompete the toughness of all natural and manmade fibers. Herein, we compare and contrast the spinning of silk in silkworms and spiders, with the aim of identifying features that are important for fiber formation. Although spiders and silkworms are very distantly related, some features of spinning silk seem to be universal. Both spiders and silkworms produce large silk proteins that are highly repetitive and extremely soluble at high pH, likely due to the globular terminal domains that flank an intermediate repetitive region. The silk proteins are produced and stored at a very high concentration in glands, and then transported along a narrowing tube in which they change conformation in response primarily to a pH gradient generated by carbonic anhydrase and proton pumps, as well as to ions and shear forces. The silk proteins thereby convert from random coil and alpha helical soluble conformations to beta sheet fibers. We suggest that factors that need to be optimized for successful production of artificial silk proteins capable of forming tough fibers include protein solubility, pH sensitivity, and preservation of natively folded proteins throughout the purification and initial spinning processes.

Quality assessment of the saffron samples using second-order spectrophotometric data assisted by three-way chemometric methods via quantitative analysis of synthetic colorants in adulterated saffron

Saffron is a valuable culinary spice that can be used not only for dyes and cooking, but also for many medical purposes. Due to its high price and restriction of its production, various fraud manners in its production have been growing. Addition of synthetic colorants to saffron is the most common way for adulteration. In this work, chemometric methods are proposed to resolve the three-dimensional absorbance spectra-pH data for simultaneous determination of the two colorants Tartrazin and Sunset yellow, in adulterated saffron. The rank deficiency in the concentration mode impaired the system. Therefore, to extirpate the ambiguity, which results from rank deficiency, three-way variation array V was generated by subtracting the first pH spectrum from each spectrum at each pH. This allows the extraction of extent reaction profile and mixture reaction spectral profiles, as well as the relative concentrations of the analytes.

A chemometric-assisted method for the simultaneous determination of malachite green and crystal violet in water based on absorbance-pH data generated by a homemade pH gradient apparatus

An attractive method of generating second-order data was developed by a dropping technique to generate pH gradient simultaneously coupled with diode-array spectrophotometer scanning. A homemade apparatus designed for the pH gradient. The method and the homemade apparatus were used to simultaneously determine malachite green (MG) and crystal violet (CV) in water samples. The absorbance-pH second-order data of MG or CV were obtained from the spectra of MG or CV in a series of pH values of HCl-KCl solution. The second-order data of mixtures containing MG and CV that coexisted with interferents were analyzed using multidimensional partial least-squares with residual bilinearization. The method and homemade apparatus were used to simultaneously determine MG and CV in fish farming water samples and in river ones with satisfactory results. The presented method and the homemade apparatus could serve as an alternative tool to handle some analysis problems.

Targeting molecular hydrogen to mitochondria: barriers and gateways

Although the administration of molecular hydrogen (H2, dihydrogen) has been recognized as an effective innovative therapeutic procedure in biomedicine, H2 cellular kinetics and utilization seems to be less understood. In particular, mitochondrial barriers might impact on H2 use in mitochondria-related diseases and conditions. Double-membrane organization of mitochondria and large membrane potential are important elements of mitochondrial stability that control the transport of the molecule into and out of the organelle. In this perspective paper, we advanced possible obstacles and advantages for H2 delivery to mitochondria.

Highly linear pH gradients for analyzing monoclonal antibody charge heterogeneity in the alkaline range: Validation of the method parameters

Cation exchange chromatography has been routinely used for the quantification of monoclonal antibody (mAb) charge heterogeneity. A previously developed method utilizing pH gradients for the elution instead of salt gradients was validated according to current guidelines proposed by the ICH. The linearity, stability, accuracy, precision and the lower limit of quantification have been determined, using pure charge variant standards. The method is valid for the quantification of mAb samples with a charge heterogeneity between 1% and 50%. Three different approaches to obtaining pure standard material for the validation of bio-analytical methods for the quantification of charge heterogeneity of IgG are presented. These methods are based on salt gradient elution, pH gradient elution and displacement in cation exchange chromatography.

Assessing the utility of bipolar membranes for use in photoelectrochemical water-splitting cells

Membranes are important in water-splitting solar cells because they prevent crossover of hydrogen and oxygen. Here, bipolar membranes (BPMs) were tested as separators in water electrolysis cells. Steady-state membrane and solution resistances, electrode overpotentials, and pH gradients were measured at current densities relevant to solar photoelectrolysis. Under forward bias conditions, electrodialysis of phosphate buffer ions creates a pH gradient across a BPM. Under reverse bias, the BPM can maintain a constant buffer pH on both sides of the cell, but a large membrane potential develops. Thus, the BPM does not present a viable solution for electrolysis in buffered electrolytes. However, the membrane potential is minimized when the anode and cathode compartments of the cell contain strongly basic and acidic electrolytes, respectively.

A novel approach to investigate the effect of methionine oxidation on pharmacokinetic properties of therapeutic antibodies

Preserving the chemical and structural integrity of therapeutic antibodies during manufacturing and storage is a major challenge during pharmaceutical development. Oxidation of Fc methionines Met252 and Met428 is frequently observed, which leads to reduced affinity to FcRn and faster plasma clearance if present at high levels. Because oxidation occurs in both positions simultaneously, their individual contribution to the concomitant changes in pharmacokinetic properties has not been clearly established. A novel pH-gradient FcRn affinity chromatography method was applied to isolate three antibody oxidation variants from an oxidized IgG1 preparation based on their FcRn binding properties. Physico-chemical characterization revealed that the three oxidation variants differed predominantly in the number of oxMet252 per IgG (0, 1, or 2), but not significantly in the content of oxMet428. Corresponding to the increase in oxMet252 content, stepwise reduction of FcRn affinity in vitro, as well as faster clearance and shorter terminal half-life, in huFcRn-transgenic mice were observed. A single Met252 oxidation per antibody had no significant effect on pharmacokinetics (PK) compared with unmodified IgG. Importantly, only molecules with both heavy chains oxidized at Met252 exhibited significantly faster clearance. In contrast, Met428 oxidation had no apparent negative effect on PK and even led to somewhat improved FcRn binding and slower clearance. This minor effect, however, seemed to be abrogated by the dominant effect of Met252 oxidation. The novel approach of functional chromatographic separation of IgG oxidation variants followed by physico-chemical and biological characterization has yielded the first experimentally-backed explanation for the unaltered PK properties of antibody preparations containing relatively high Met252 and Met428 oxidation levels.

Highly linear pH gradients for analyzing monoclonal antibody charge heterogeneity in the alkaline range

Recombinant antibodies with high isoelectric point are frequent since most of them are constructed from the same framework. Classically, cation exchange chromatography is used as a standard method for the determination of antibody charge heterogeneity. In contrast, in this study highly linear pH gradients were achieved by keeping the buffering capacity over the length of the gradient constant. The buffering compounds were selected to be unretained on the column and their respective concentration was adjusted in the start and end buffer of the pH gradient to achieve constant buffering capacity. This helps conserve linearity and stability of the gradient. The method allows quantification of charge variant distribution and the determination of chromatographic isoelectric point. To demonstrate the effectiveness of this novel method, a ProPac WCX-10 column was used to separate isoforms of trastuzumab biosimilar antibodies. Effects of pH gradient linearity and of varying the analytical amount of sample on the separation are shown.