pH Dependence Research Articles

DNA Release from Polyaziridine Polyplexes Aided by Biomacromolecules: Effect of pH

The pH dependence of heparin and dextran sulfate aided release of DNA from its polyplexes with polyaziridine (PA) has been investigated using Quartz crystal microbalance with dissipation monitoring (QCM-D). The acoustic behavior of ternary systems indicated that the DNA decondensation was favored at physiological pH. When pH < 7.4, PA was significantly positively charged and ternary complexation occurred. When pH exceeded 7.4, very small proportion of DNA was released upon heparin addition due to marked reduction in cationic nature of PA. An increase in thickness at the interface due to adsorbed material at pH 9.0 showed the retention of heparin on the surface despite of negligible release of DNA. In terms of PA binding, heparin proved to be a better competitor than dextran sulfate.

Interfacial interaction of amorphous NiFe hydroxide/graphene composites elevating the oxygen evolution catalytic performance

Ni-based amorphous transition metal catalysts have gained considerable research attention owing to their superior alkaline oxygen evolution performance compared to their crystalline counterparts. In this work, we prepared amorphous NiFe/graphene composites via the solvothermal method. By regulating the ratio of components, the composite catalyst exhibited an exceptionally low overpotential of 231 mV at a current density of 10 mA cm−2 and maintained stable catalytic behavior for 100 h at this current density. Electrochemical analysis and differential charge density diagrams revealed the presence of charge transport at the interface of the heterogeneous structure, greatly increasing the intrinsic activity of the material. Additionally, pH dependence on the catalytic activity suggested a decoupled proton-electron transfer (PT/ET) pathway, and chemical deprotonation is identified as the rate-limiting step in the catalytic reaction. These findings provide critical insights and reliable data to facilitate future research on improving the oxygen evolution performance of NiFe-based amorphous catalysts.

GDGT distribution in tropical soils and its potential as a terrestrial paleothermometer revealed by Bayesian deep-learning models

Branched and isoprenoidal glycerol dialkyl glycerol tetraethers (br- and isoGDGTs) are membrane lipids produced by bacteria and archaea, respectively. These lipids form the basis of several frequently used paleoclimatic proxies. For example, the degree of methylation of brGDGTs (MBT’5Me) preserved in mineral soils (as well as peats and lakes) is one of the most important terrestrial paleothermometers, but features substantial variability that is so far insufficiently constrained. The distribution of isoGDGTs in mineral soils has received less attention and applications have focused on the use of the relative abundance of the isoGDGT crenarchaeol versus brGDGTs (BIT index) as an indicator of aridity. To expand our knowledge of the factors that can impact the br- and isoGDGT distribution in mineral soils, including the MBT’5Me index, and to improve isoGDGT-based precipitation reconstructions, we surveyed the GDGT distribution in a large collection of mineral surface soils (n = 229) and soil profiles (n = 22) across tropical South America. We find that the MBT’5Me index is significantly higher in grassland compared to forest soils, even among sites with the same mean annual air temperature. This is likely a result of a lack of shading in grasslands, leading to warmer soils. We also find a relationship between MBT’5Me and soil pH in tropical soils. Together with existing data from arid areas in mid-latitudes, we confirm the relationship between the BIT-index and aridity, but also find that the isoGDGT distribution alone is aridity dependent. The combined use of the BIT-index and isoGDGTs can strengthen reconstructions of past precipitation in terrestrial archives. In terms of site-specific variations, we find that the variability in BIT and MBT’5Me is larger at sites that show on average lower BIT and MBT’5Me values. In combination with modelling results, we suggest that this pattern arises from the mathematical formulation of these proxies that amplifies variability for intermediate values and mutes it for values close to saturation (value of 1). Soil profiles show relatively little variation with depth for the brGDGT indices. On the other hand, the isoGDGT distribution changes significantly with depth as does the relative abundance of br- versus isoGDGTs. This pattern is especially pronounced for the isoGDGTIsomerIndex where deeper soil horizons show a near absence of isoGDGT isomers. This might be driven by archaeal community changes in different soil horizons, potentially driven by the difference between aerobic and anaerobic archaeal communities. Finally, we use our extensive new dataset and Bayesian neural networks (BNNs) to establish new brGDGT-based temperature models. We provide a tropical soil calibration that removes the pH dependence of tropical soils (n = 404; RMSE = 2.0 °C) and global peat and soil models calibrated against the temperature of the months above freezing (n = 1740; RMSE = 2.4) and mean annual air temperature (n = 1740; RMSE = 3.6). All models correct for the bias found in arid samples. We also successfully test the new calibrations on Chinese loess records and tropical river sediments. Overall, the new calibrations provide improved temperature reconstructions for terrestrial archives.

A novel in vitro system of supported planar endosomal membranes (SPEMs) reveals an enhancing role for cathepsin B in the final stage of Ebola virus fusion and entry.

Ebola virus (EBOV) causes a hemorrhagic fever with fatality rates up to 90%. The EBOV entry process is complex and incompletely understood. Following attachment to host cells, EBOV is trafficked to late endosomes/lysosomes where its glycoprotein (GP) is processed to a 19-kDa form, which binds to the EBOV intracellular receptor Niemann-Pick type C1. We previously showed that the cathepsin protease inhibitor, E-64d, blocks infection by pseudovirus particles bearing 19-kDa GP, suggesting that further cathepsin action is needed to trigger fusion. This, however, has not been demonstrated directly. Since 19-kDa Ebola GP fusion occurs in late endosomes, we devised a system in which enriched late endosomes are used to prepare supported planar endosomal membranes (SPEMs), and fusion of fluorescent (pseudo)virus particles is monitored by total internal reflection fluorescence microscopy. We validated the system by demonstrating the pH dependencies of influenza virus hemagglutinin (HA)-mediated and Lassa virus (LASV) GP-mediated fusion. Using SPEMs, we showed that fusion mediated by 19-kDa Ebola GP is dependent on low pH, enhanced by Ca2+, and augmented by the addition of cathepsins. Subsequently, we found that E-64d inhibits full fusion, but not lipid mixing, mediated by 19-kDa GP, which we corroborated with the reversible cathepsin inhibitor VBY-825. Hence, we provide both gain- and loss-of-function evidence that further cathepsin action enhances the fusion activity of 19-kDa Ebola GP. In addition to providing new insights into how Ebola GP mediates fusion, the approach we developed employing SPEMs can now be broadly used for studies of virus and toxin entry through endosomes. IMPORTANCE Ebola virus is the causative agent of Ebola virus disease, which is severe and frequently lethal. EBOV gains entry into cells via late endosomes/lysosomes. The events immediately preceding fusion of the viral and endosomal membranes are incompletely understood. In this study, we report a novel in vitro system for studying virus fusion with endosomal membranes. We validated the system by demonstrating the low pH dependencies of influenza and Lassa virus fusion. Moreover, we show that further cathepsin B action enhances the fusion activity of the primed Ebola virus glycoprotein. Finally, this model endosomal membrane system should be useful in studying the mechanisms of bilayer breaching by other enveloped viruses, by non-enveloped viruses, and by acid-activated bacterial toxins.

Metallothionein-3 and carbonic anhydrase metalation properties with Zn(II) and Cd(II) change as a result of protein-protein interactions.

Metallothioneins (MT) are regulators of the metals Zn(II) and Cu(I) and act as antioxidants in many organisms, including in humans. Isoform 3 (MT3) is expressed constitutively in central nervous tissue and has been shown to have additional biological functions, including the inhibition of neuronal growth, the regulation of apoptosis, and cytoskeleton modulation. To facilitate these functions, protein-protein interactions likely occur. These interactions may then impact the metalation status of the MT and the recipient metalloprotein. Using electrospray ionization mass spectrometry and circular dichroism spectroscopy, we report that the interaction between the zinc metalloenzyme, carbonic anhydrase (CA), and MT3, impacts the metalation profiles of both apo-MT3 and apo-CA with Cd(II) and Zn(II). We observe two phases in the metalation of the apo-CA, the first of which is associated with an increased binding affinity of apo-CA for Cd/Zn(II) and the second pathway is associated with apo-CA metalated without a change in binding affinity. The weak interactions that result in this change of binding affinity are not detectable as a protein complex in the ESI-mass spectral data or in the circular dichroism spectra. These unusual metalation properties of apo-CA in the presence of apo-MT3 are evidence of the effects of protein-protein interactions. With adjustment to take into account the interaction of both proteins, we report the complete Cd(II) and Zn(II) binding constants of MT3 under physiological conditions, as well as the pH dependence of these binding pathways.

Effectiveness of Anthocyanin-Rich Sour Cherry Extract on Gliadin-Induced Caco-2 Barrier Damage.

Several types of gluten-related disorders are known, in which the common starting point is gluten-induced zonulin release. Zonulin results in varying degrees of increased permeability in certain gluten-related disorders but is largely responsible for the development of further pathogenic processes and symptoms. Therefore, it is important to know the barrier-modulating role of individual nutritional components and to what extent the antioxidant substance supports the protection of gliadin-induced membrane damage with its radical scavenging capacity. We investigated the pH dependence of the gliadin-anthocyanin interaction using UV photometry, during which a concentration-dependent interaction was observed at pH 6.8. The barrier modulatory effect of the anthocyanin-rich sour cherry extract (AC) was analyzed on Caco-2 cell culture with pepsin-trypsin-resistant gliadin (PT-gliadin) exposure by TEER measurement, zonula occludens-1 (ZO-1), and Occludin immunohistochemistry. In addition to the TEER-reducing and TJ-rearranging effects of PT-gliadin, NF-κB activation, an increase in cytokine (TNF-α, IFN-γ, and IL-8) release, and mitochondrial ROS levels were observed. We confirmed the anti-inflammatory, stabilizing, and restoring roles of AC extract during gliadin treatment on the Caco-2 monolayer. The extract was able to significantly reduce cytokine and ROS levels despite the known interaction of the main components of the extract with PT-gliadin.

Unraveling the kinetics and pharmacology of human PepT1 using solid supported membrane-based electrophysiology

The human Peptide Transporter 1 (hPepT1) is known for its broad substrate specificity and its ability to transport (pro-)drugs. Here, we present an in-depth comprehensive study of hPepT1 and its interactions with various substrates via solid supported membrane-based electrophysiology (SSME). Using hPepT1-containing vesicles, we could not identify any peptide induced pre-steady-state currents, indicating that the recorded peak currents reflect steady-state transport. Electrogenic co-transport of H+/glycylglycine (GlyGly) was observed across a pH range of 5.0 to 9.0. The pH dependence is described by a bell-shaped activity curve and two pK values. KM and relative Vmax values of various canonical and non-canonical peptide substrates were contextualized with current mechanistic understandings of hPepT1. Finally, specific inhibition was observed for various inhibitors in a high throughput format, and IC50 values are reported. Taken together, these findings contribute to promoting the design and analysis of pharmacologically relevant substances.

The formation of Fe3+-doxycycline complex is pH dependent: implications to doxycycline bioavailability.

The interactions of drugs with iron are of interest in relation to the potential effects of iron-rich foods and iron supplements on sorption and bioavailability. Doxycycline (DOX), a member of the tetracycline class of broad-spectrum antibiotics, is frequently administered by oral route. In the digestive tract, DOX can be exposed to iron at different pH values (stomach pH 1.5-4, duodenum pH 5-6, distal jejunum and ileum pH 7-8). In relation to this, we analyzed the impact of pH on Fe3+-DOX complex formation. The optimal conditions for Fe3+-DOX complex formation are pH = 4 and [Fe3+]/[DOX] = 6 molar ratio. HESI-MS showed that Fe3+-DOX complex has 1:1 stoichiometry. Raman spectra of Fe3+-DOX complex indicate the presence of two Fe3+-binding sites in DOX structure: tricarbonylamide group of ring A and phenolic-diketone oxygens of BCD rings. The Fe3+-DOX complex formed at pH = 4 is less susceptible to oxidation than DOX at this pH. The increase of pH induces the decomposition of Fe3+-DOX complex without oxidative degradation of DOX. The pH dependence of Fe3+-DOX complex formation may promote unwanted effects of DOX, impeding the absorption that mainly takes place in duodenum. This could further result in higher concentrations in the digestive tract and to pronounced impact on gut microbiota.

Bifunctional Oxygen Electrocatalysis on Manganese Oxide

Limited supply of precious metals impedes the scale up of electrolyzer production. To enable 100s of GWs of PEM electrolyzer capacity by 2030, iridium supply must grow by more than 10x.[1] Alternatively, catalysts made of cheaper, more abundant manganese could relieve these constraints, if engineered to have comparable activity and stability. The unique bifunctional OER/ORR activity of Mn oxide could also enable electrolyzers that both produce and consume fuel with a single catalyst. Yet rational design of Mn oxide catalysts requires a better understanding of the structural and chemical motifs that lead to high bifunctional performance.In this talk, we will discuss our investigation of the bifunctional OER & ORR activity of Mn oxide and its unusual pH dependence. Our model system, 𝛼-KxMnO2, is among the best reported Mn oxide catalysts for both the OER and the ORR, with ORR activity matching that of Pt.[2] While the OER activity of Mn oxide has been shown to increase at higher pH,[3] we will show that its ORR activity improves as well. We will discuss our attempts to understand this phenomenon with operando scanning transmission x-ray microscopy (STXM), which enables spectroscopic investigation of single catalyst particles during reaction with spatial resolution down to 25 nm. Complementary surface DFT calculations provide further evidence for identification of the active crystal facets and insights into the pH-dependency of the OER & ORR mechanisms. We will discuss the implications of this work on the design of bidirectional electrolyzers with low-cost, non-precious metal catalysts.[1] IRENA. Green Hydrogen Cost Reduction. 2020 [2] Meng, Y. et al. J. Am. Chem. Soc. 2014, 136 (32), 11452–11464.[3] Takashima, T. et al. J. Am. Chem. Soc. 2012, 134 (3), 1519–1527.

The Mechanism of Hydrogen Evolution Reaction at the Buried Interface of Silica-Coated Electrocatalysts

Semipermeable oxide coatings can protect electrocatalysts in harsh environments without reducing the catalytic performance (Labrador, Esposito et al. ACS Catal. 8, 2018, 1767–1778), making them attractive for direct seawater electrolysis. We recently showed that the buried SiO2/Pt interface of silica-coated platinum electrocatalysts is environment-dependent and changes with the pH value of the electrolyte and the electrode potential (Qu and Urban, ACS Appl. Mater. Interfaces 12, 2020, 52125–52135). Here, we discuss the impact of silica membrane coatings on the hydrogen evolution reaction (HER) mechanism at the interface with different transition-metal surfaces. Stable configurations of the buried SiO2/TM interface at HER conditions were determined using density-functional theory (DFT) calculations. Computed Pourbaix diagrams for different transition-metal substrates show the pH and potential dependence of reaction intermediates and the hydrogen coverage on the metal surface. Our results indicate that the HER mechanism at the buried SiO2/catalyst interfaces may involve the silica membrane. Hence, besides the protective quality of silica membranes, this also points to the possibility of designing synergistic membrane-coated electrocatalysts that surpass the bare surfaces of earth-abundant transition metals in terms of catalytic performance (stability, activity, and/or selectivity).

Re-Structuring of Interfacial Water into Strongly Hydrogen Bonded “Ice-like” Structures as the Unifying Descriptor for Improving Sluggish HOR/HER in Alkaline Electrolyte

The 2 orders of magnitude loss of Platinum Group Metal (PGM) activity toward Hydrogen Oxidation and Reduction reactions (HOR/HER) has hindered implementation of alkaline based electrolyzers and fuel cells and demonstrated a significant knowledge gap in our fundamental understanding of electrochemical interfaces.1 Beneath the seemingly simple reaction lies a potentially convoluted mechanism, with various researchers assigning the activity loss to shifts in electrode potential of zero free charge,2 changed binding energies of adsorbates and reactive intermediates,3,4 and the re-arrangement of interfacial water.5 Recently, Monteiro et al. showed an activity dependence on interfacial cation concentration and identity, suggesting that charge dense cations are able to better stabilize the OH- produced from the unfavorable but necessary water splitting in the HER direction near the negatively charged surface.6,7 In this work, we challenge this notion by demonstrating that competition for water molecules between Outer Helmholtz Plane (OHP) cations and the interfacial water structure is responsible for the activity loss. Through the use of traditional Rotating Disk Electrode, in situ Attenuated Total Reflection-Surface Enhanced Infrared Reflection Absorption Spectroscopy (ATR-SEIRAS) and judicious choice of crown ether additives to hinder the water-interfacial cation interaction, we show a positive correlation between the strength and number of interfacial water-water hydrogen bonds and platinum’s HOR/HER activity.The typical double layer structure in an aqueous electrochemical system consists of specifically adsorbed species in the Inner Helmholtz Plane (IHP), the first layer of non-adsorbates at the OHP, and water hydrating the charged species. ATR-SEIRAS has previously been used to analyze the structure of these hydration shells on a CO covered Pt surface, demonstrating hydrating waters interacting mainly with alkali metal cations through the increase of a 3600 cm-1 ν(O-H) stretch and weak interactions with surrounding interfacial water.8 Through chelation with crown ether, these hydration shells convert from strongly to weakly cation interacting, favoring instead hydrogen bonding with other water molecules, shown with increasing absorption bands at lower wavenumbers (3400 cm-1). This transition is accompanied by an increase in 3000 cm-1 on the CO-free Pt surface, previously assigned to strongly hydrogen bonded “ice-like” interfacial water.9 We further show a similar increase in the 3000 cm-1 band for other kinetic enhancing additives recently reported in the literature, supporting the notion that increasing water-water hydrogen bonding is the unifying descriptor for promoting a rigid interfacial “ice-like” structure and improving PGM HOR/HER activity. Durst, J. et al. New insights into the electrochemical hydrogen oxidation and evolution reaction mechanism. Energy Environ. Sci. 7, 2255–2260 (2014).Sarabia, F. J., Sebastián-Pascual, P., Koper, M. T. M., Climent, V. & Feliu, J. M. Effect of the Interfacial Water Structure on the Hydrogen Evolution Reaction on Pt(111) Modified with Different Nickel Hydroxide Coverages in Alkaline Media. ACS Appl. Mater. Interfaces 11, 613–623 (2019).McCrum, I. T. & Koper, M. T. M. The role of adsorbed hydroxide in hydrogen evolution reaction kinetics on modified platinum. Nat. Energy 5, 891–899 (2020).Yang, X., Nash, J., Oliveira, N. J., Yan, Y. & Xu, B. Understanding the pH Dependence of Underpotential Deposited Hydrogen on Platinum. Angew. Chemie - Int. Ed. 58, 17718–17723 (2019).Zhao, K. et al. Enhancing Hydrogen Oxidation and Evolution Kinetics by Tuning the Interfacial Hydrogen-Bonding Environment on Functionalized Platinum Surfaces. Angew. Chemie - Int. Ed. 61, (2022).Monteiro, M. C. O., Goyal, A., Moerland, P. & Koper, M. T. M. Understanding Cation Trends for Hydrogen Evolution on Platinum and Gold Electrodes in Alkaline Media. ACS Catal. 11, 14328–14335 (2021).Goyal, A. & Koper, M. T. M. The Interrelated Effect of Cations and Electrolyte pH on the Hydrogen Evolution Reaction on Gold Electrodes in Alkaline Media. Angew. Chemie - Int. Ed. 60, 13452–13462 (2021).Yamakata, A. & Osawa, M. Cation-dependent restructure of the electric double layer on CO-covered Pt electrodes: Difference between hydrophilic and hydrophobic cations. J. Electroanal. Chem. 800, 19–24 (2017).Osawa, M., Tsushima, M., Mogami, H., Samjeské, G. & Yamakata, A. Structure of water at the electrified platinum-water interface: A study by surface-enhanced infrared absorption spectroscopy. J. Phys. Chem. C 112, 4248–4256 (2008). Figure 1

Explorations of Fluorescence Modulation of DNA Functionalized Single Wall Carbon Nanotubes by Catechol-Bearing Compounds

This work describes explorations into analyte-mediated modulation of the fluorescence of single-stranded DNA functionalized single wall carbon nanotubes (SWCNT). SWCNTs have several photophysical properties that make them attractive for imaging in biology. They fluoresce in the near-infrared (NIR) region of the spectrum (900 – 1300 nm), which is suitable for imaging in thick biological specimens because of reduced scattering of NIR photons and minimal tissue autofluorescence. SWCNTs exhibit superior photostability and can be considered to be non-photobleaching on time scales of interest to biological imaging. In addition to these advantageous photophysical properties, SWCNT fluorescence can be selectively sensitized to local chemical environments, which has served as a basis for the synthesis and application of SWCNT-based optical biosensors for a variety of biologically relevant compounds including dopamine, norepinephrine, serotonin, and oxytocin, among others. However, the mechanistic basis for fluorescence modulation of functionalized nanotubes by various classes of analytes remains incompletely understood. One class of optical biosensors that have been particularly successful in biological research includes (GT)N oligonucleotide functionalized SWCNTs that exhibit exquisite turn-on response to compounds that contain catechol-like motifs. In this work, we offer new insights into the mechanism of molecular recognition and fluorescence modulation of this sensor class by catechol-like compounds. We first carried out a fragment-based structure activity relationship study to establish how the structural and electronic properties of these compounds correlated with their ability to modulate SWCNT-fluorescence. This helped us establish a spectrum of substrate functionalities that are detectable by this sensor class. Intriguingly however, our experiments revealed that solution phase fluorescence turn-on events are critically influenced by factors that are not intrinsic to the analytes, including solution pH. We will present the pH dependence of fluorescence turn-on events and establish structural and electronic correlates for these dependencies. As a results of these explorations, we have been able to achieve an improved understanding of sensor dynamics and sensing mechanism. We expect that the insights gleaned from this work will contribute to the body of knowledge that underpins SWCNT-based optical sensors.

Electrocatalytic and Spectroscopic Studies on Cytochrome Bd Oxidase, a Highly Diverse Bacterial Defense Factor

The selective reduction of oxygen to water is crucial to life and a central process in aerobic organisms. It is catalyzed by several different enzymes, including cytochrome bd oxidases that are solely present in prokaryotes, including several pathogens. In addition, these enzymes play a crucial role in protection against oxidative stress, in virulence, adaptability and antibiotics resistance. The reduction of O2 occurs at the high spin D-type heme in all cytochrome bd oxidases, that is also the binding site for several ligands from signaling processes, including NO, H2S and CO.Here we present the electrocatalytic study of the cytochrome bd I and bd II oxidases from Escherichia coli (1,2) as well on other related bd oxidases. Structural parameters that are crucial for the reactivity towards oxygen are analyzed. The pH dependency of the binding and release of NO, an important signaling factor is presented. The influence of mutants in the proton channel on the NO release is discussed.(1) Grauel, A. Kägi, J. Rasmussen, T. Makarchuk, I. Oppermann, S. Moumbock, A., Wohlwend, D., Müller, R., Melin, F., Günther, S., Hellwig, P., Böttcher, B., and Friedrich, T., ‘Structure of Escherichia coli cytochrome bd-II type oxidase with bound aurachin D’ (2021) Nat. Commun., 12:6498.(2) Nikolaev, A., Safarian, S., Thesseling, A., Wohlwend, D., Friedrich, T., Michel, H., Kusumoto, T., Sakamoto, J., Melin, F., Hellwig P. ‘Electrocatalytic evidence of the diversity of the oxygen reaction in the bacterial bd oxidase from different organisms’ (2021) Biochim. Biophys. Acta 1862, 148436.

Promoting Hydrogen Evolution and Oxidation by Reconstructing Hydrogen-Bonding Network of Interfacial Water

The hydrogen evolution and oxidation reactions (HER/HOR) at the electrode-water control the performance of water electrolyzers and hydrogen fuel cells, two important devices for deep decarbonization of our economy (1). Platinum (Pt) catalyzes the HER/HOR with exceptional activity and stability across a wide pH range. However, its activity progressively decreases by about two orders of magnitude as the pH increases from 0 to 13 (2, 3). The lack of understanding of this pH dependence reflects our fundamental knowledge gaps in electrochemistry and has hindered the advancement of alkaline electrolyzers and fuel cells.Herein, we promoted the HER/HOR of Pt in base by introducing N-methylimidazoles in the Pt-water interface. In situ spectroscopic characterization of the interface together with computations showed that the N-methylimidazoles form strong hydrogen-bonding with neighboring water molecules thereby reconstructing the H-bond network of interfacial water. We accordingly established a unified mechanism by which the HER/HOR in acid and base proceeds via diffusion of protons and hydroxides, respectively through the H-bond network of interfacial water by the Grotthuss mechanism. This mechanism accounts for the pH-dependent HER/HOR kinetics of platinum, a long-standing puzzle. Utilization of N-methylimidazoles as the HER/HOR probes and promoters not only leads to the elucidation of the HER/HOR mechanism but also holds great promise for applications. We have demonstrated 40% performance improvement of an anion exchange membrane water electrolyzer by adding 10-5 M 1,2-dimethylimidazole into the 0.1 M potassium hydroxide solution fed into its Pt cathode. Acknowledgements This work was supported by the Office of Naval Research (ONR) grant N000141712608 (Q.J.)This research used beamline 7-BM (QAS) of the National Synchrotron Light Source II, a U.S. Department of Energy (DOE) Office of Science User Facility operated for the DOE Office of Science by Brookhaven National Laboratory Contract DE-SC0012704. Beamline operations were supported in part by the Synchrotron Catalysis Consortium Grant DE-SC0012335. V. R. Stamenkovic, D. Strmcnik, P. P. Lopes and N. M. Markovic, Nat. Mater., 16, 57 (2017). J. Durst, A. Siebel, C. Simon, F. Hasché, J. Herranz and H. A. Gasteiger, Energy Environ. Sci., 7, 2255 (2014). W. Sheng, Z. Zhuang, M. Gao, J. Zheng, J. G. Chen and Y. Yan, Nat. Commun., 6 (2015). Figure 1

Investigations of Charge Transfer Processes on Plasmonic Cathode Electrodes

The establishment of efficient light energy conversion system is an important issue in the field of photoelectrochemical region. For the realization of it, the wide-band semiconductor electrode could be the good candidate. However, semiconductor electrodes often have the limitation to the ultraviolet region because of their band gap energy. Because the sunlight energy mainly consists of visible light, the visible-light induced photoenergy conversion is a challenging issue. As the breakthrough for it, recently, the combination of the plasmonic metal nanostructures with wide semiconductor electrodes has been received much attention because of the addition of visible light response characters. Up to now, the various systems of the anodic reaction controls have been established. Recently, the cathode system which can control the reduction reactions at metal semiconductor interfaces have been reported via the introduction of plasmonic metal nanostructures into the p-type semiconductor electrodes. In our previous study, we have established the plasmonic photocathode by using the Ag nanostructures with the p-type GaP electrode [1]. In this system, it can be considered as the holes excited in the metal structures injected into the valence band of the p-type semiconductor and the remained electron are consumed in the hydrogen evolution reaction. In addition, we have observed the unique pH dependence on the hydrogen evolution which could not be observed on conventional metal electrodes. For understanding the unique reaction selectivity on the plasmonic cathode electrode, the detail understanding about both the charge transfer process and absolute electrochemical potential of generated electrons. In this study, we have attempted to obtain such information through the various chemical reactions using the various types of plasmonic structures. Through the various photoelectrochemical measurements, we have confirmed the changes in the electrochemical potential of excited electrons depending on the optical characters of plasmonic structures. The unique molecular selectivity was also observed. Our current research would provide the novel insight for the accurate design of the high efficient visible light conversion device.[1] H. Minamimoto et al., Chem. Lett., 2020, 49, 806.

Oxidation of the N-containing phosphonate antiscalants NTMP and DTPMP in reverse osmosis concentrates: Reaction kinetics and degradation rate

N-containing organophosphonate antiscalants such as Aminotris (methylene phosphonic acid) (NTMP/ATMP) and Diethylenetriamine penta(methylene phosphonic acid) (DTPMP) are commonly used in reverse osmosis (RO) to prevent scaling, as well as to increase permeate yields. However, the concentrate in RO still contains antiscalants which can cause adverse effects in the environment such as mobilization of heavy metals. The abatement of antiscalants from RO concentrate can promote the precipitation of oversaturated scale-forming substances and reduce the risk of adverse environmental effects. In the present study, the degradation of NTMP and DTPMP as representatives for N-containing organophosphonate by ozone, hydroxyl radicals (•OH), and sulfate radicals (SO4•-) are studied regarding reaction kinetics and degradation in different matrices. The results show that NTMP and DTPMP react fast with ozone and sulfate radicals (formed in UV/persulfate). Reaction rate constants of ozone showed a strong pH dependency due to the dissociation of the amine. The apparent reaction rates for pH 7 have been determined to be kapp(NTMP + ozone) = 1.44 × 105 M−1 s−1 and kapp(DTPMP + ozone) = 1.16 × 106 M−1 s−1. Reaction kinetics of •OH and SO4•- did not play a distinctive pH dependency (k(•OH) = 109-1010 M−1 s−1 and k(SO4•-) = 107-108 M−1 s−1). Furthermore, real water experiments have shown that ozonation and UV/persulfate are effective tools to abate organophosphonates in RO concentrates. The formation of carcinogenic bromate in ozonation is minimized by the presence of N-containing organophosphonates presumably due to enhanced ozone consumption and scavenging of free bromine.

Динамика кислотно-щелочных и окислительно-восстановительных условий в аллювиальных техногенно засоленных почвах таежно-лесной зоны

The alluvial technogenically saline soils on the territory of the Verkhnekamsk salt deposit in the Perm Region were examined. It was found that in the studied part of the valleys of small rivers, alluvial saline soils occupy tens of hectares. During the summer-autumn observation period in alluvial humus gley saline saturated soil (Gleyic Fluvisol (Loamic, Salic)) at a depth of 10-40 cm, reducing conditions prevailed (Eh from +200 mV to -250 mV), favoring the biochemical recovery of iron and sulfur. The reaction of the soil medium ranged from 6,5–7,8 pH. In alluvial gley salt marsh unsaturated soils during the summer-autumn period in a layer of 10-40 cm, an alternation of anaerobic and aerobic conditions (Eh from -50 mV to +550 mV) was noted; the reaction of the soil medium at a depth of about 10-20 cm ranged from 2,5–4,1 pH. The regression dependence of pH on the value of Eh has been established with a correlation coefficient of R = -0,84. Apparently, technogenically saline alluvial soils have the potential for the formation of sulfide compounds and their subsequent oxidation with the appearance of a sharp acid reaction of the soil medium. Keywords: TECHNOGENIC SALINIZATION, EH, PH, GLEYIC FLUVISOL (LOAMIC, SALIC)

Molecular characterisation of Entamoeba histolytica UDP-glucose 4-epimerase, an enzyme able to provide building blocks for cyst wall formation.

In the human host, the protozoan parasite Entamoeba histolytica is adapted to a non-invasive lifestyle in the colon as well as to an invasive lifestyle in the mesenterial blood vessels and the liver. This means to cope with bacteria and human cells as well as various metabolic challenges. Galactose and N-acetylgalactosamine (GalNAc) are sugars of great importance for the amoebae, they attach to the host mucus and enterocytes via their well-studied Gal/GalNAc specific lectin, they carry galactose residues in their surface glycans, and they cleave GalNAc from host mucins. The enzyme UDP-glucose 4-epimerase (GalE) works as a bridge between the galactose and glucose worlds, it can help to generate glucose for glycolysis from phagocytosis products containing galactose as well as providing UDP-galactose necessary for the biosynthesis of galactose-containing surface components. E. histolytica contains a single galE gene. We recombinantly expressed the enzyme in Escherichia coli and used a spectrophotometric assay to determine its temperature and pH dependency (37°C, pH 8.5), its kinetics for UDP-glucose (Km = 31.82 μM, Vmax = 4.31 U/mg) and substrate spectrum. As observed via RP-HPLC, the enzyme acts on UDP-Glc/Gal as well as UDP-GlcNAc/GalNAc. Previously, Trypanosoma brucei GalE and the bloodstream form of the parasite were shown to be susceptible to the three compounds ebselen, a selenoorganic drug with antioxidant properties, diethylstilbestrol, a mimic of oestrogen with anti-inflammatory properties, and ethacrynic acid, a loop diuretic used to treat oedema. In this study, the three compounds had cytotoxic activity against E. histolytica, but only ebselen inhibited the recombinant GalE with an IC50 of 1.79 μM (UDP-Gal) and 1.2 μM (UDP-GalNAc), suggesting that the two other compounds are active against other targets in the parasite. The importance of the ability of GalE to interconvert UDP-GalNAc and UDP-GlcNAc may be that the trophozoites can generate precursors for their own cyst wall from the sugar subunits cleaved from host mucins. This finding advances our understanding of the biochemical interactions of E. histolytica in its colonic environment.

Structural Analyses of Substrate-pH Activity Pairing Observed across Diverse Polysaccharide Lyases.

Anionic polysaccharides found in nature are functionally and structurally diverse, and so are the polysaccharide lyases (PLs) that catalyze their degradation. Atomic superposition of various PL folds according to their cleavable substrate structure confirms the occurrence of structural convergence at PL active sites. This suggests that various PL folds have emerged to cleave a particular class of anionic polysaccharide during the course of evolution. Whereas the structural and mechanistic similarity of PL active site has been highlighted in earlier studies, a detailed understanding regarding functional properties of this catalytic convergence remains an open question, especially the role of extrinsic factors such as pH in the context of substrate binding and catalysis. Our earlier structural and functional work on pH directed multisubstrate specificity of Smlt1473 inspired us to regroup PLs according to substrate type to analyze the pH dependence of their catalytic activity. Interestingly, we find that particular groups of substrates are cleaved in a particular pH range (acidic/neutral/basic) irrespective of PL fold, boosting the idea of functional convergence as well. On the basis of this observation, we set out to define structurally and computationally the key constituents of an active site among PL families. This study delineates the structural determinants of conserved "substrate-pH activity pairing" within and between PL families.

General Kinetic Model for pH Dependence of Proton-Coupled Electron Transfer: Application to an Electrochemical Water Oxidation System.

The pH dependence of proton-coupled electron transfer (PCET) reactions, which are critical to many chemical and biological processes, is a powerful probe for elucidating their fundamental mechanisms. Herein, a general, multichannel kinetic model is introduced to describe the pH dependence of both homogeneous and electrochemical PCET reactions. According to this model, a weak pH dependence can arise from the competition among multiple sequential and concerted PCET channels involving different forms of the redox species, such as protonated and deprotonated forms, as well as different proton donors and acceptors. The contribution of each channel is influenced by the relative populations of the reactant species, which often depend strongly on pH, leading to complex pH dependence of PCET apparent rate constants. This model is used to explain the origins of the experimentally observed weak pH dependence of the electrochemical PCET apparent rate constant for a ruthenium-based water oxidation catalyst attached to a tin-doped In2O3 (ITO) surface. The weak pH dependence is found to arise from the intrinsic differences in the rate constants of participating channels and the dependence of their relative contributions on pH. This model predicts that the apparent maximum rate constant will become pH-independent at higher pH, which is confirmed by experimental measurements. Our analysis also suggests that the dominant channels are electron transfer at lower pH and sequential PCET via electron transfer followed by fast proton transfer at higher pH. This work highlights the importance of considering multiple competing channels simultaneously for PCET processes.