Protonation Of Species Research Articles

Cooperation between an alcoholic proton and boryl species in the catalytic gem-hydrodiborylation of carboxylic esters to access 1,1-diborylalkanes

Cooperation between an alcoholic proton and boryl species in the selective gem-hydrodiborylation of carboxylic esters is described.

NMR controlled titrations characterizing organophosphorus compounds

1-Phosphonopropane-1,2,3-tricarboxylic acid (PPTC) was characterized by NMR controlled titrations. Specific dissociation constants pKi and specific chemical shifts δP [ppm] of protonation species HiLi-5 from diastereomers RS/SR and RR/SS of PPTC were obtained.

Tropylium and Porphyrinoid Character in Carbaporphyrinoid Systems. Relative Stability and Aromatic Characteristics of Azuliporphyrin and Tropiporphyrin Tautomers, Protonated Species, and Related Structures

DFT studies have been carried out on 46 azuliporphyrin (AzP) and tropiporphyrin (TrP) tautomers, cations, and dications. The structures were minimized using DFT-B3LYP/6-311++G(d,p), and the relative stabilities of the tautomers for each series were computed with M06-2X and B3LYP-D3 functionals. Nucleus independent chemical shifts, both NICS(0) and NICS(1) zz, were calculated for both the center of the macrocycles and the individual pyrrolic and carbocyclic subunits. In addition, anisotropy of induced current density (AICD) plots were generated for all of the species under investigation. The results provided insights into the favored conjugation pathways and aromatic properties of these important carbaporphyrinoid systems. The π delocalization pathways for AzP were complex, and contrary to previous speculations, there was no evidence for tropylium characteristics in the favored free base structure. The global diatropicity of AzP was found to increase with increasing solvent polarity, in agreement with experimental observations. TrP was shown to be planar and to possess a large global diamagnetic ring current. However, NICS calculations and AICD plots indicated that the cycloheptatrienyl components of the two most favored TrP tautomers have paratropic characteristics. These results are not fully consistent with the proton NMR spectra for TrPs. A dihydroTrP and a Diels-Alder adduct were investigated, and these showed exceptionally large shielding effects with NICS(1) zz values of -36.53 and -36.92 ppm, respectively, in agreement with experimental results. A silver(III) complex of tropiporphyrin was also examined, and this showed no paratropic character for the seven-membered ring, although in this case, the system was found to be severely twisted. Overall, the results provide important information about the electronic properties of AzP and TrP tautomers, as well as for related protonated species, and complement the extensive experimental studies that have been conducted on these systems.

HSCO+ and DSCO+: a multi-technique approach in the laboratory for the spectroscopy of interstellar ions

Context. Protonated molecular species have been proven to be abundant in the interstellar gas. This class of molecules is also pivotal for the determination of important physical parameters for the evolution of the interstellar medium (e.g. gas ionisation fraction) or as tracers of non-polar species which are not directly observable. The identification of these molecular species through radioastronomical observations is directly linked to precise laboratory spectral characterisation. Aims. The goal of the present work is to extend the laboratory measurements of the pure rotational spectrum of the ground electronic state of protonated carbonyl sulfide (HSCO+) and its deuterium substituted isotopomer (DSCO+). At the same time, we show how implementing different laboratory techniques allows for the determination of different spectroscopical properties of asymmetric-top protonated species. Methods. Three different high-resolution experiments were used in conjunction to detect for the first time the b-type rotational spectrum of HSCO+, and to extend, well into the sub-millimetre region, the a-type spectrum of the same molecular species and DSCO+. The electronic ground-state of both ions was investigated in the 273–405 GHz frequency range, allowing for the detection of 60 and 50 new rotational transitions for HSCO+ and DSCO+, respectively. Results. The combination of our new measurements with the three rotational transitions previously observed in the microwave region permits the rest frequencies of the most astronomically relevant transitions to be predicted to better than 100 kHz for both HSCO+ and DSCO+ up to 500 GHz, equivalent to better than 60 m s−1 in terms of equivalent radial velocity. Conclusions. The present work illustrates the importance of using different laboratory techniques to spectroscopically characterise a protonated species at high frequency. Each instrument addressed a complementary part of the same spectroscopic challenge, demonstrating the potential of such an approach for future studies of similar reactive species.

CEST imaging at 9.4 T using adjusted adiabatic spin‐lock pulses for on‐ and off‐resonant T1⍴‐dominated Z‐spectrum acquisition

The CEST experiment, with its correlation to rare proton species that are in exchange with the water pool, is very similar to the off-resonant water spin-lock (SL) experiment. In particular, low-power SL Z-spectrum acquisition allows insight into T1ρ and exchange effects with decreased direct water saturation. Because the available SL methods either require high B1 power or are instable in the presence of strong B1 and B0 inhomogeneity present at ultra-high fields, the goal of this study was to find a robust adiabatic SL pulse for on- and off-resonant application in the human brain at 9.4T. A series of Bloch simulations were used to find optimal pulse shape parameters of an adjusted hyperbolic secant pulse applicable in the low power regime typically used for exchange-weighted SL experiments. The optimized pulse was implemented and tested in phantom and in vivo experiments on a 9.4T human scanner for on- and off-resonant T1ρ - and Z-spectrum measurements. The simulation yielded a feasible pulse shape, which yielded robust images, less sensitivity to B1 and B0 inhomogeneity compared with previous SL approaches and less direct water saturation, as well as a higher chemical exchange weighting compared with conventional CEST approaches. By adapting a pulse shape for low-power SL experiments, we were able to acquire robust on- and off-resonant adiabatic SL prepared images in vivo at 9.4T. This development leads directly to SL Z-spectrum acquisition, beneficial for chemical-exchange-weighted MRI.

An integrated theoretical-experimental approach to understand facilitated proton transfer-electron transfer coupled reactions at thick-film modified electrodes

The main purpose of the current work is to generalize the analytical model for the facilitated proton transfer-electron transfer coupled reactions at thick organic film-modified electrodes, including ion pairing in the organic phase and considering non-ideal electrolyte solutions in both phases. The main equations to calculate half-wave potentials developed in this model allow the simulation of different chemical systems, comprising hydrophilic and hydrophobic neutral weak bases, at different experimental conditions such as pH, organic phase to aqueous phase volume ratio, and concentration ratios between the redox probe and the transferring protonated species. The model was checked against experimental voltammetric responses measured with the transfer of Tylosin A at the water|1,2-dichloroethene interface. Consequently, we present here an integrated theoretical-experimental approach in order to compare the results of our previous model [Zanotto et al. Electrochim. Acta 258 (2017) 727–734] with experimental data from Tylosin A and predicted half-wave potentials.

Ni/SIRAL-30 as a heterogeneous catalyst for ethylene oligomerization

The oligomerization of ethylene is an important catalytic process for the production of higher olefins, and is also a key step for jet-fuel production from bioethanol. We herein investigated the use of Ni/SIRAL-30 as a heterogeneous catalyst for ethylene oligomerization, as it can be prepared easily and cheaply by the simple impregnation of a Ni precursor on a commercial SIRAL-30 support with a high Brønsted acid site (BAS) density. Pyridine-infrared spectroscopy confirmed that proton species in the bridge-type Si-OH-Al frameworks of SIRAL-30 were partially exchanged with Ni2+ cations without interfering with the Al3+ sites. In addition, the Ni species following catalyst calcination under air and pretreatment with N2 was identified to be the isolated Ni2+ by XPS, EXAFS and CO adsorption. The Ni/SIRAL-30 catalyst gave almost complete ethylene conversion and stability over 100 h at 200 °C, 10 bar pressure, and at a weight hourly space velocity of 0.375 h−1 during continuous ethylene oligomerization. A Ni loading of 4 wt% on SIRAL-30 was optimal for both ethylene conversion and for maximizing the proportion of C10+ products formed, while the pretreatment of Ni(4 wt%)/SIRAL-30 at 550 °C under N2 resulted in the best catalytic activity. Although a degree of deactivation was observed due to the adsorption of heavy oligomers, the initial catalytic activity was restored by heating the used catalyst at 550 °C under air. These results confirm that the Ni(4 wt%)/SIRAL-30 catalyst is both recyclable and an efficient heterogeneous catalyst for continuous ethylene oligomerization.

The Nature of Hydrated Protons on Platinum Surface

The nature of hydrated protons formed at water/metal interfaces is one of the most intriguing research questions in the field of interfacial chemistry. We coadsorbed hydrogen and water on a Pt(111) surface in ultrahigh vacuum and studied the ionization of adsorbed hydrogen atoms to H+ ions by employing a combined experimental and theoretical approach. Spectroscopic evidence obtained by mass spectrometry and reflection absorption infrared spectroscopy as well as corresponding density functional theory calculations consistently show that adsorbed hydrogen atoms ionize into multiply hydrated proton species (H5O2 +, H7O3 +, and H9O4 +) on the surface, rather than H3O+. Then, upon addition of a water overlayer, the metal-bound hydrated protons spontaneously evolve into three-dimensional fully hydrated proton structures via proton transfer along the water overlayer. The stability of hydrated protons on Pt surface and their bulk dissolution behavior suggest the possibility that surface hydrated protons are a key intermediate in electrochemical interconversion between adsorbed H atoms and H+(aq) in water electrolysis and hydrogen evolution reactions.

Contributions of Magnetic Resonance Imaging to Gastroenterological Practice: MRIs for GIs.

MRI has transformed from the theoretical, investigative realm to mainstream clinical medicine over the past four decades and has become a core component of the diagnostic toolbox in the practice of gastroenterology (GI). Its success is attributable to exquisite contrast and the ability to isolate specific proton species through the use of different pulse sequences (i.e., T1-weighted, T2-weighted, diffusion-weighted) and exploiting extracellular and hepatobiliary contrast agents. Consequently, MRI has gained preeminence in various GI clinical applications: liver and pancreatic lesion evaluation and detection, liver transplantation evaluation, pancreatitis evaluation, Crohn's disease evaluation (using MR enterography) rectal cancer staging and perianal fistula evaluation. MR elastography, in concert with technical innovations allowing for fat and iron quantification, provides a noninvasive approach, or "MRI virtual liver biopsy" for diagnosis and management of chronic liver diseases. In the future, the arrival of ultra-high-field MR systems (7T) and the ability to perform magnetic resonance spectroscopy in the abdomen promise even greater diagnostic insight into chronic liver disease.

Picosecond Proton Transfer Kinetics in Water Revealed with Ultrafast IR Spectroscopy.

Aqueous proton transport involves the ultrafast interconversion of hydrated proton species that are closely linked to the hydrogen bond dynamics of water, which has been a long-standing challenge to experiments. In this study, we use ultrafast IR spectroscopy to investigate the distinct vibrational transition centered at 1750 cm-1 in strong acid solutions, which arises from bending vibrations of the hydrated proton complex. Broadband ultrafast two-dimensional IR spectroscopy and transient absorption are used to measure vibrational relaxation, spectral diffusion, and orientational relaxation dynamics. The hydrated proton bend displays fast vibrational relaxation and spectral diffusion timescales of 200-300 fs; however, the transient absorption anisotropy decays on a remarkably long 2.5 ps timescale, which matches the timescale for hydrogen bond reorganization in liquid water. These observations are indications that the bending vibration of the aqueous proton complex is relatively localized, with an orientation that is insensitive to fast hydrogen bonding fluctuations and dependent on collective structural relaxation of the liquid to reorient. We conclude that the orientational relaxation is a result of proton transfer between configurations that are well described by a Zundel-like proton shared between two flanking water molecules.

Novel arrangement for an electro-Fenton reactor that does not require addition of iron, acid and a final neutralization stage. Towards the development of a cost-effective technology for the treatment of wastewater

A novel arrangement for an electro-Fenton reactor aimed to treat neutral wastewater is presented. The arrangement consists on three-compartments in series, two of them packed with a cation exchange resin and one positioned between these, containing a polarized activated carbon column where the electrochemical generation of the Fenton reagent takes place. While the hydroxyl radicals electrochemically produced in-situ, react with the pollutant species adsorbed on the activated carbon cathode, the resin compartments administrate and collect the iron cation and the hydrated proton species in alternating flow direction cycles. The resulting process is a system that does not require acid or iron chemical addition to the process while at the same time, renders decontaminated water free of iron-dissolved species at neutral pH. The proposed electrochemical reactor arrangement is therefore the basis for the design of commercially viable electro-Fenton reactors in which the addition and subsequent removal of acid and iron chemicals is avoided; two of the currently most limiting features for the development of electro-Fenton technology for treating wastewater.

Galactic cosmic-ray model in the light of AMS-02 nuclei data

Cosmic ray (CR) physics has entered a precision-driven era. With the latest AMS-02 nuclei data (boron-to-carbon ratio, proton flux, helium flux and antiproton-to-proton ratio), we perform a global fitting and constrain the primary source and propagation parameters of cosmic rays in the Milky Way by considering 3 schemes with different data sets (with and without $\bar{\mathrm{p}}/\mathrm{p}$ data) and different propagation models (diffusion-reacceleration and diffusion-reacceleration-convection models). We find that the data set with $\bar{\mathrm{p}}/\mathrm{p}$ data can remove the degeneracy between the propagation parameters effectively and it favors the model with a very small value of convection (or disfavors the model with convection). The separated injection spectrum parameters are used for proton and other nucleus species, which reveal the different breaks and slopes among them. Moreover, the helium abundance, antiproton production cross sections and solar modulation are parametrized in our global fitting. Benefited from the self-consistence of the new data set, the fitting results show a little bias, and thus the disadvantages and limitations of the existed propagation models appear. Comparing to the best fit results for the local interstellar spectra ($\phi = 0$) with the VOYAGER-1 data, we find that the primary sources or propagation mechanisms should be different between proton and helium (or other heavier nucleus species). Thus, how to explain these results properly is an interesting and challenging question.

Direct Detection of Multiple Acidic Proton Sites in Zeolite HZSM-5.

Direct observation of multiple reactive sites in the zeolite HZSM-5, a member of the MFI family of zeolite structures, contradicts the traditional view of only one type of active protonic species in industrially important zeolites. In addition to the well-known Brönsted acid site proton, two other protonic species undergo room-temperature hydrogen-deuterium exchange with an alkane hydrocarbon reagent, including one zeolite moiety characterized by a broad 1H chemical shift at ca. 12-15 ppm that is reported here for the first time. Although the ca. 13 ppm chemical shift value is consistent with computational predictions from the literature for a surface-stabilized hydroxonium ion in a zeolite, data suggest that the signal does not arise from hydroxonium species but rather from hydroxyls on extra-lattice aluminol species proximate to Brönsted lattice sites, i.e., a small population of highly deshielded acid sites. Double-resonance experiments show that this species is proximate to Al atoms, similar to the Brönsted acid site proton. These sites can be removed by appropriate postsynthesis chemical treatment, yielding a catalyst with reduced activity for isotopic H/D exchange reactions. Additionally, other extra-lattice aluminum hydroxyl groups previously discussed in the literature but whose protons were considered unreactive are also shown for the first time to react with hydrocarbon probe molecules. Two-dimensional exchange NMR reveals direct proton exchange between the Brönsted site and these two types of extra-lattice Al-OH species, and it also reveals unexpected proton exchange between extra-lattice Al-OH species and an alkane reagent.

Facilitated proton transfer-electron transfer coupled reactions at thick-film modified electrodes

The theory of cyclic voltammetry of facilitated proton transfer-electron transfer coupled reactions (FPT-ET reactions) in a thick organic film modified electrode is developed. It is shown that the coupling between the facilitated proton transfer-electron transfer processes has a marked effect on the shape of the current-potential profiles. The model allows the analysis of the system in different experimental conditions, such as pH and concentration ratios between the redox probe and the transferring protonated species. This model for proton transfer assisted by different neutral weak bases in a two polarized interfaces system is compared to our previous results for a single polarizable interface. Finally, considerations regarding the application of the thick-film setup are discussed.

The Nature of Hydrated Protons on Platinum Surfaces.

The nature of hydrated protons formed at water/metal interfaces is one of the most intriguing research questions in the field of interfacial chemistry. We prepared coadsorption layers of hydrogen and water on a Pt(111) surface in ultrahigh vacuum and studied the ionization of adsorbed hydrogen atoms to H+ ions by employing a combined experimental and theoretical approach. Spectroscopic evidence obtained by mass spectrometry and reflection absorption infrared spectroscopy as well as corresponding density functional theory calculations consistently show that adsorbed hydrogen atoms ionize into multiply hydrated proton species (H5 O2+ , H7 O3+ , and H9 O4+ ) on the surface, rather than H3 O+ . Then, upon addition of a water overlayer, the metal-bound hydrated protons spontaneously evolve into three-dimensional fully hydrated proton structures through proton transfer along the water overlayer. The stability of hydrated protons on the Pt surface and their bulk dissolution behavior suggest the possibility that surface hydrated protons are a key intermediate in electrochemical interconversion between adsorbed H atoms and H+ (aq) in water electrolysis and hydrogen evolution reactions.

Bi-Functional Oxygen Electrodes for a Rechargeable Zinc/Air Battery with Choline Acetate Electrolyte

The primary alkaline zinc/air battery is known for its high energy density and is commonly used as energy supply for hearing aids devices with practical energy density values in the range of 700-850 mWh gzinc -1. However, recharging process is very challenging because of its low energy efficiency (<60%) due to high overpotential and poor cycling ability of the air electrode as well as dendrite and carbonate formation in alkaline solution. To overcome some drawbacks, alternative electrolytes such as ionic liquids (IL´s) are promising candidates.1 Room Temperature Ionic liquids (RTILs) are low temperature (<100°C) molten salts composed of organic cations and anions characterized by extremely low vapor pressure, high decomposition temperature, but also by high viscosity and poor/moderate conductivity. For electrochemical applications, and more especially for metal/air battery in which oxygen reactions occur, presence of proton species in ionic liquid is preferred since aprotic ones allow “only” 1e- oxygen reduction reaction (ORR) step.2 High surface tension is also a prerequisite for triple-phase boundary formation in the gas diffusion electrode (GDE). In this work, feasibility of choline acetate (ChAcO) with zinc salt as electrolyte mixture and AB2O4structured materials as bifunctional cathode catalyst was investigated. In this work, precious metal and spinel oxide bifunctional catalyst were prepared. 20 wt% Pt was deposited on commercial carbon (C65) by chemical reduction of hexachloro-platinic acid in formaldehyde at 80°C for 1 h. MnCo2O4 (MCO) and NiCo2O4 (NCO) Spinel were synthesized by hydrothermal (HT) and hard template (SS) methods. The structural characterization of the as-prepared catalysts was performed by means of XRD, SEM/EDX and TEM. Average size of as-prepared oxide particles was estimated to approximately 28, 100, 300 and 500 nm for HT-MCO, HT-NCO, SS-MCO and SS-NCO catalysts, respectively. Gas diffusion electrodes (GDE) with catalyst loading of 1 mgcat cm-2 were fabricated by airbrush spraying. Contact angle of electrode/electrolyte interface was measured for 100 h at room temperature and 30% RH. The electrochemical activity of commercial Pt/C and spinel-based GDE for ORR and OER were studied by cyclic voltammetry (CV) under half cell condition. The EL-Cell (ECC-Air) and coin cell (CR2032) were manufactured by assembling a Zn foil as active electrode, a glass fibre separator and a GDE. The cell performance was evaluated by U-I polarization at 1-100 µA cm-2 for 1-3 h charge/discharge cycle. A preliminary screening of catalysts in terms of activity and stability was conducted in EL-Cell with dry air at RT. At 50 µA cm-2, comparison of charge/discharge kinetics of the different catalysts over 5 h/cycle is shown in fig.1a. An effect of addition of water in the IL was studied at 100 µA cm-2 in ambient air (30% RH at 22°C), 24 h/cycle for one month (fig.1b). The best system was HT-MCO that was further investigated under coin cell (CR2032) condition (Zn || ChAcO + 30 wt% H2O + 0.01 M Zn AcO || MnCo2O4/C65). At 100 µA cm-2, an energy and columbic efficiency of 50 and 100% was calculated for the 3 h cycle, respectively. The same cell was successfully tested in ambient air (RT, 30% RH) for 700 h (140 cycles) at 50 µA cm-2. Average cell voltage was 0.75 V (discharge) and 1.9 V (charge). A discharge specific capacity of 725 mAh gZn -1 was achieved at 100 µA cm-2.

New DTPA-derived bis-naphthalenophanes: fluorescence, protonation, and complexation with aromatic amines

Two fluorescent, water-soluble bis-naphthalenophane isomers with six carboxylate arms, abbreviated as (bis-dtpa14nap)H6 and (bis-dtpa15nap)H6, were synthesized, which consist of two 1,4- or 1,5-substituted naphthalene rings interlinked by two diethylenetriaminepentaacetic (DTPA) chains through amide-linkages. Both DTPA-based macrocycles exhibit intense excimer and monomer emission bands, which sensitively respond to pH in three protonation steps; more sensitive is the 1,4-naphthyl isomer. The full pH-emission profiles have confirmed that the mono-protonated anion (bis-dtpanap)H5 − is the major protonation species at the physiological pH. Fluorometric titrations at pH 7.2 have proven that the 1,4-naphthalenophane anion forms 1:1-complexes with cationic phenethylamine (formation constant, 5700 M−1) and histamine (3000 M−1), excluding tryptamine cation, whereas the 1,5-isomer does not react with any of the three amines. The primary binding forces are electrostatic interactions between the CH2CO2 − arms of 1,4-naphthalenophane and the CH2CH2NH3 + chain of an aromatic amine. The resulting ion-pair is stabilized by encapsulation of the guest molecule in 1,4-napthalenophane cavity, while the 1,5-isomer cannot encapsulate. NMR studies have demonstrated that 1,4-napthalenophane has a higher freedom in reorientation of naphthalene rings. Such geometrical properties controlled by selection of naphthalene units are the feature of the new naphthalenophanes, and are responsible for the pH‒emission profiles and the complexation.

Structure and Electrical-Transport Relations in Ba(Zr,Pr)O3-δ Perovskites.

Members of the perovskite solid solution BaZr1-xPrxO3-δ (0.2 ≤ x ≤ 0.8) with potential high-temperature electrochemical applications were synthesized via mechanical activation and high-temperature annealing at 1250 °C. Structural properties were examined by Rietveld analysis of neutron powder diffraction and Raman spectroscopy at room temperature, indicating rhombohedral symmetry (space group R3̅c) for members x = 0.2 and 0.4 and orthorhombic symmetry (Imma) for x = 0.6 and 0.8. The sequence of phase transitions for the complete solid solution from BaZrO3 to BaPrO3 is Pm3̅m → R3̅c → Imma → Pnma. The structural data indicate that Pr principally exists as Pr4+ on the B site and that oxygen content increases with higher Pr content. Electrical-conductivity measurements in the temperature range of 250-900 °C in dry and humidified (pH2O ≈ 0.03 atm) N2 and O2 atmospheres revealed an increase of total conductivity by over 2 orders of magnitude in dry conditions from x = 0.2 to x = 0.8 (σ ≈ 0.08 S cm-1 at 920 °C in dry O2 for x = 0.8). The conductivity for Pr contents x > 0.2 is attributable to positively charged electronic carriers, whereas for x = 0.2 transport in dry conditions is n-type. The change in conduction mechanism with composition is proposed to arise from the compensation regime for minor amounts of BaO loss changing from predominantly partitioning of Pr on the A site to vacancy formation with increasing Pr content. Conductivity is lower in wet conditions for x > 0.2 indicating that the positive defects are, to a large extent, charge compensated by less mobile protonic species. In contrast, the transport mechanism of the Zr-rich composition (x = 0.2), with much lower electronic conductivity, is essentially independent of moisture content.

Bulk Defect Chemistry of PCFC Cathode Materials: Discussion of Defect Interactions

In order to extend the reactive zone for oxygen reduction to water beyond the gas/electrode/electrolyte three phase boundary, cathode materials for proton conducting ceramic fuel cells should exhibit a certain proton conductivity, exceeding 10-5 S/cm [1]. Proton uptake into (Ba,Sr,La)(Mn,Fe,Co)O3- d perovskites considered as cathode material can occur by incorporation of H2O (for ) or by incorporation of only H (for ) assuming ideally dilute defect concentrations [2,3]. These two regimes can be identified by thermogravimetric investigations over an extended range of pO2, pH2O and temperature. Independent of the actual proton incorporation regime the proton concentrations in (Ba,Sr,La)(Fe,Co)O3- d cathode materials amount to less than 3% [3]. They are much lower than for acceptor-doped Ba(Zr,Ce)O3-xelectrolytes, which remain completely hydrated (10-20% protons) up to about 400-500 °C. Correlations between cation composition and proton uptake will be explored [6]. The basicity of the oxide ions is known to favour proton uptake in electrolyte materials. In p-type conducting and redox-active cathode materials, additional defect interactions between protons and electron holes lead to a perceptible decrease of proton uptake already for low hole concentrations. This is probably related to the partially covalent bonding between the transition metal and oxygen, by which one localized hole affects the basicity of six adjacent oxide ions. Proton mobility in cathode materials has so far only been measured for Ba0.5Sr0.5Fe0.8Zn0.2O3- d [4], where it is comparable to that in Y-doped BaZrO3-x electrolytes. The estimated proton conductivity of » 10-3 S/cm at 350-450 °C [1] suffices to transport protons from the electrolyte through the dense cathode film to the gas interface, as evidenced from the diameter dependence of microelectrode resistances. The reduction of O2 to water can in principle proceed without oxygen incorporation into the cathode material. The measured pO2 dependence of the effective rate constant indicates that molecular oxygen species participate in the rate determining step. From the pH2O dependence for Ba0.5Sr0.5Co0.8Fe0.2O3- d microelectrodes we conclude that protonated oxygen species appear only after this step [5]. Together, these findings suggest that for Ba0.5Sr0.5Fe0.8Zn0.2O3- d and Ba0.5Sr0.5Co0.8Fe0.2O3- dthe oxygen reduction to water proceeds via intermediate uptake of O into surface oxygen vacancies. [1] R. Merkle, D. Poetzsch, J. Maier, ECS Transact. 66(2) (2015) 95 [2] D. Poetzsch, R. Merkle, J. Maier, Adv. Funct. Mater. 25 (2015) 1542 [3] D. Poetzsch, R. Merkle, J. Maier, Faraday Discussions 182 (2015) 129 [4] D. Poetzsch, R. Merkle, J. Maier, Phys. Chem. Chem. Phys. 16 (2014) 16446 [5] D. Poetzsch, R. Merkle, J. Maier, J. Electrochem. Soc. 162 (2015) F939 [6] R. Zohourian, R. Merkle, J. Maier, Solid State Ionics doi:10.1016/j.ssi.2016.09.012

Mechanism of formate-nitrite transporters by dielectric shift of substrate acidity.

Bacterial formate-nitrite transporters (FNTs) regulate the metabolic flow of small, weak mono-acids. Recently, the eukaryotic PfFNT was identified as the malaria parasite's lactate transporter and novel drug target. Despite crystal data, central mechanisms of FNT gating and transport remained unclear. Here, we show elucidation of the FNT transport mechanism by single-step substrate protonation involving an invariant lysine in the periplasmic vestibule. Opposing earlier gating hypotheses and electrophysiology reports, quantification of total uptake by radiolabeled substrate indicates a permanently open conformation of the bacterial formate transporter, FocA, irrespective of the pH Site-directed mutagenesis, heavy water effects, mathematical modeling, and simulations of solvation imply a general, proton motive force-driven FNT transport mechanism: Electrostatic attraction of the acid anion into a hydrophobic vestibule decreases substrate acidity and facilitates protonation by the bulk solvent. We define substrate neutralization by proton transfer for transport via a hydrophobic transport path as a general theme of the Amt/Mep/Rh ammonium and formate-nitrite transporters.