Direct Proton Research Articles

Deep-red fluorescent poly(acrylic acid) hydrogel: Proton transfer to the water soluble dibasic luminescent dye followed by ion-pair formation

We developed a simple and versatile strategy to fabricate a highly luminescent and deep-red emitting supramolecular hydrogel (λem,max = 651 nm, ΦF = 0.17). The strategy is based on using water-soluble and highly luminescent bis-pyridine molecule, V-EO7PyDCS (1), which makes a direct acid-base proton transfer and subsequent ion-pair formation with commercial poly(acrylic acid) (PAA) in water to form the luminescent supramolecular hydrogel in-situ. It was shown that the ionic interaction between the pyridinium cation in the protonated form of 1 and carboxylate anion in that of PAA was responsible for the effective gelation as to make the transparent hydrogel of ~98% water content. Concurrently, the protonated form of 1 showed a highly efficient deep-red fluorescence in this supramolecular hydrogel according to its excellent dynamic ion-pair formation and photophysical behaviors. It is noteworthy that these hydrogels are homogeneous and transparent due to the excellent water solubility of di-basic crosslinker 1.

Direct proton range verification using oxygen-18 enriched water as a contrast agent

We propose the use of 18O-enriched water as a suitable contrast agent for potential in-vivo range verification in proton therapy. The low energy production threshold of 18F (2.6 MeV, proton range in water of 115 μm) leads to tissue activation in very close proximity to the maximum dose deposition, facilitating accurate range verification with off-line PET imaging.This idea has been explored in a phantom experiment. A 3D-printed phantom containing inserts with 18O-enriched water was irradiated with a 100-MeV, 8 × 8 cm2 proton beam, and the induced activity was measured with a small-animal PET-CT 30 min after irradiation. The images obtained were compared against Monte Carlo simulation using TOPAS.Good agreement was observed between reconstructed and simulated activity profiles (within 40% for specific 18F activity), with excellent spatial match to the simulated dose deposition. Because of the long half-life of 18F, the specific activity of the contrast agent could be separated and was clearly observed for more than 2 h after irradiation. Activity distribution maps were used to determine the position of the Bragg peak within 2 mm for three different regions of interest. These results show the potential of 18O-enriched water as a contrast agent in proton therapy.

Ordered Clusters of the Complete Oxidative Phosphorylation System in Cardiac Mitochondria.

The existence of a complete oxidative phosphorylation system (OXPHOS) supercomplex including both electron transport system and ATP synthases has long been assumed based on functional evidence. However, no structural confirmation of the docking between ATP synthase and proton pumps has been obtained. In this study, cryo-electron tomography was used to reveal the supramolecular architecture of the rat heart mitochondria cristae during ATP synthesis. Respirasome and ATP synthase structure in situ were determined using subtomogram averaging. The obtained reconstructions of the inner mitochondrial membrane demonstrated that rows of respiratory chain supercomplexes can dock with rows of ATP synthases forming oligomeric ordered clusters. These ordered clusters indicate a new type of OXPHOS structural organization. It should ensure the quickness, efficiency, and damage resistance of OXPHOS, providing a direct proton transfer from pumps to ATP synthase along the lateral pH gradient without energy dissipation.

Water as a Direct Proton Source for Asymmetric Hydroarylation Catalyzed by a Rh(I)–Diene: Access to Nonproteinogenic β2/γ2/δ2-Amino Acid Derivatives

A highly enantioselective rhodium-catalyzed intermolecular hydroarylation of α-aminoalkyl acrylates using water as a direct proton source has been realized by employing a chiral bicyclo[3.3.0] diene ligand, allowing efficient access to a broad range of α-aryl-methyl-substituted β2-, γ2-, and δ2-amino esters with excellent enantioselectivities (up to 98% ee) under exceptionally mild conditions. By utilizing this method, a series of structurally interesting benzo-fused heterocyclic molecules and the corresponding β2-, γ2-, and δ2-amino acids are facilely constructed.

Enantioselective Synthesis of Chiral Indane Derivatives by Rhodium-Catalyzed Addition of Arylboron Reagents to Substituted Indenes.

Rhodium-catalyzed asymmetric addition of arylboron reagents to indene derivatives proceeded to give 2-arylindanes in good yields with high enantioselectivity. Deuterium-labeling experiments indicated that the present reaction involved a 1,4-Rh shift from an initially formed benzylrhodium to an arylrhodium intermediate before protonation leading to the corresponding addition product. The asymmetric addition was also successful for acenaphthylene, which has a similar skeleton to indene, where it was found that the benzylrhodium intermediate underwent direct protonation without the 1,4-Rh shift.

Approaching the Nernst Detection Limit in an Electrolyte-Gated Metal Oxide Transistor

In this letter, we demonstrate direct high-sensitivity proton detection by novel electrolyte-gated thin-film transistors. Integrating a sol-gel derived oxide channel and liquid electrolytes, a current switching by a factor of 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7</sup> was achieved within a 0.5 V gate window. Manipulation of the ionic strength in the gating solution led to an impressively large electrostatic shift (48 mV/pH), outperforming reported devices and ultimately approaching the Nernst limit. By means of impedance spectroscopy and transient measurements, we identified spatial compression of ionic charges at the electrical double layers as the origin of sensitivity, with the response time being dominated by the ion-transport resistance.

Is there a direct solar proton impact on lower-stratospheric ozone?

Abstract. We investigate Arctic polar atmospheric ozone responses to solar proton events (SPEs) using MLS (Microwave Limb Sounder) satellite measurements (2004–now) and WACCM-D (Whole Atmosphere Community Climate Model) simulations (1989–2012). Special focus is on lower-stratospheric (10–30 km) ozone depletion that has been proposed earlier based on superposed epoch analysis (SEA) of ozonesonde anomalies (up to 10 % ozone decrease at ∼ 20 km). SEA of the satellite dataset provides no solid evidence of any average SPE impact on the lower-stratospheric ozone, although at the mesospheric altitudes a statistically significant ozone depletion is present. In the individual case studies, we find only one potential case (January 2005) in which the lower-stratospheric ozone level was significantly decreased after the SPE onset (in both model simulation and MLS observation data). However, similar decreases could not be identified in other SPEs of similar or larger magnitude. Due to the input proton energy threshold of &gt; 300 MeV, the WACCM-D model can only detect direct proton effects above 25 km, and simulation results before the Aura MLS era indicate no significant effect on the lower-stratospheric ozone. However, we find a very good overall consistency between WACCM-D simulations and MLS observations of SPE-driven ozone anomalies both on average and for the individual cases including January 2005.

Possible neutron and proton halo structure in the isobaric analog states of A=12 nuclei

The differential cross sections of the $^{11}\mathrm{B}(^{3}\mathrm{He},d)^{12}\mathrm{C}$ reaction leading to formation of the ${0}^{+}$ ground state and the 15.11-MeV 1 ${}^{+}$, 16.57-MeV ${2}^{\ensuremath{-}}$, and 17.23-MeV ${1}^{\ensuremath{-}}$ excited states of $^{12}\mathrm{C}$ are measured at ${E}_{\text{lab}}=25$ MeV. The analysis of the data is carried out within the coupled-reaction-channels method for the direct proton transfer to the bound and unbound states. The rms radii of the last proton in all states studied are determined. A comparison of the rms radii of the $^{12}\mathrm{B}, ^{12}\mathrm{C}$, and $^{12}\mathrm{N}$ nuclei in the isobaric analog states (IASs) with isospin $T=1$ determined by different methods allows us to arrive at a conclusion that these nuclei in the ${1}^{\ensuremath{-}}$ excited states at ${E}_{x}=2.62, 17.23,$ and $1.80$ MeV, respectively, possess one-nucleon (neutron or proton) halo structure. The enlarged radii and a large probability of the last neutron to be outside of the range of the interaction potential are also found for the ${2}^{\ensuremath{-}}$ states of $^{12}\mathrm{B}, ^{12}\mathrm{C}$, and $^{12}\mathrm{N}$ at ${E}_{x}=1.67, 16.57,$ and $1.19$ MeV, respectively. These IASs also can be regarded as candidates for states with one-nucleon (neutron or proton) halo.

An electroactive montmorillonite/polyaniline nanocomposite film: Superfast ion transport and ultra-affinity ion recognition for rapid and selective separation of Pb2+ ions

Although a variety of functional materials have been developed for the separation target ions, most of them suffer from sluggish uptake of ions and deficient selectivity. Herein, a nanocomposite electroactive film with a sandwich-like structure was facilely prepared by intercalating conductive polyaniline (PANI) into the interlayer of montmorillonite (MMT) with layered structure for rapid and selective separation of Pb2+ ions. This MMT/PANI nanocomposite film exhibited an extreme Pb2+ ion uptake rate (1422.67 μg∙(g∙s)−1), which exceeded those of conventional adsorbents by 2 to 4 orders of magnitude. Meanwhile, trace Pb2+ ions at ppb level in the wastewater were quantitatively detected by employing the MMT/PANI nanocomposite electroactive film based on its strong affinity towards Pb2+ ions. It was confirmed that the rapid and selective Pb2+ ion uptake/release by the MMT/PANI composite film was achieved via the directional proton migration powered by the electrochemical redox of the intercalated PANI, the superfast ion transport in atomically interlamellar ion transport path and the ultra-affinity ion recognition of ion capture sites on MMT layer. It is expected that such an MMT/PANI composite film could be a promising alternative of conventional materials for separating and detecting of Pb2+ ions in wastewater.

Hydrogen Bonding Enhances the Electrochemical Hydrogenation of Benzaldehyde in the Aqueous Phase

AbstractThe hydrogenation of benzaldehyde to benzyl alcohol on carbon‐supported metals in water, enabled by an external potential, is markedly promoted by polarization of the functional groups. The presence of polar co‐adsorbates, such as substituted phenols, enhances the hydrogenation rate of the aldehyde by two effects, that is, polarizing the carbonyl group and increasing the probability of forming a transition state for H addition. These two effects enable a hydrogenation route, in which phenol acts as a conduit for proton addition, with a higher rate than the direct proton transfer from hydronium ions. The fast hydrogenation enabled by the presence of phenol and applied potential overcompensates for the decrease in coverage of benzaldehyde caused by competitive adsorption. A higher acid strength of the co‐adsorbate increases the intensity of interactions and the rates of selective carbonyl reduction.

Hydrogen Bonding Enhances the Electrochemical Hydrogenation of Benzaldehyde in the Aqueous Phase.

The hydrogenation of benzaldehyde to benzyl alcohol on carbon‐supported metals in water, enabled by an external potential, is markedly promoted by polarization of the functional groups. The presence of polar co‐adsorbates, such as substituted phenols, enhances the hydrogenation rate of the aldehyde by two effects, that is, polarizing the carbonyl group and increasing the probability of forming a transition state for H addition. These two effects enable a hydrogenation route, in which phenol acts as a conduit for proton addition, with a higher rate than the direct proton transfer from hydronium ions. The fast hydrogenation enabled by the presence of phenol and applied potential overcompensates for the decrease in coverage of benzaldehyde caused by competitive adsorption. A higher acid strength of the co‐adsorbate increases the intensity of interactions and the rates of selective carbonyl reduction.

Metabolomics Profiling of Critically Ill Coronavirus Disease 2019 Patients: Identification of Diagnostic and Prognostic Biomarkers.

Objectives:Coronavirus disease 2019 continues to spread rapidly with high mortality. We performed metabolomics profiling of critically ill coronavirus disease 2019 patients to understand better the underlying pathologic processes and pathways, and to identify potential diagnostic/prognostic biomarkers.Design:Blood was collected at predetermined ICU days to measure the plasma concentrations of 162 metabolites using both direct injection-liquid chromatography-tandem mass spectrometry and proton nuclear magnetic resonance.Setting:Tertiary-care ICU and academic laboratory.Subjects:Patients admitted to the ICU suspected of being infected with severe acute respiratory syndrome coronavirus 2, using standardized hospital screening methodologies, had blood samples collected until either testing was confirmed negative on ICU day 3 (coronavirus disease 2019 negative) or until ICU day 10 if the patient tested positive (coronavirus disease 2019 positive).Interventions:None.Measurements and Main Results:Age- and sex-matched healthy controls and ICU patients that were either coronavirus disease 2019 positive or coronavirus disease 2019 negative were enrolled. Cohorts were well balanced with the exception that coronavirus disease 2019 positive patients suffered bilateral pneumonia more frequently than coronavirus disease 2019 negative patients. Mortality rate for coronavirus disease 2019 positive ICU patients was 40%. Feature selection identified the top-performing metabolites for identifying coronavirus disease 2019 positive patients from healthy control subjects and was dominated by increased kynurenine and decreased arginine, sarcosine, and lysophosphatidylcholines. Arginine/kynurenine ratio alone provided 100% classification accuracy between coronavirus disease 2019 positive patients and healthy control subjects (p = 0.0002). When comparing the metabolomes between coronavirus disease 2019 positive and coronavirus disease 2019 negative patients, kynurenine was the dominant metabolite and the arginine/kynurenine ratio provided 98% classification accuracy (p = 0.005). Feature selection identified creatinine as the top metabolite for predicting coronavirus disease 2019-associated mortality on both ICU days 1 and 3, and both creatinine and creatinine/arginine ratio accurately predicted coronavirus disease 2019-associated death with 100% accuracy (p = 0.01).Conclusions:Metabolomics profiling with feature classification easily distinguished both healthy control subjects and coronavirus disease 2019 negative patients from coronavirus disease 2019 positive patients. Arginine/kynurenine ratio accurately identified coronavirus disease 2019 status, whereas creatinine/arginine ratio accurately predicted coronavirus disease 2019-associated death. Administration of tryptophan (kynurenine precursor), arginine, sarcosine, and/or lysophosphatidylcholines may be considered as potential adjunctive therapies.

Innovative application of biopolymer composite as proton exchange membrane in microbial fuel cell utilizing real wastewater for electricity generation

Biopolymer composite for application as proton exchange membrane in microbial fuel cell (MFC) is investigated. Different amounts of PHB ranging from 5 to 15% (w/w) are composited within medium-chain-length polyhydroxyalkanoates (mcl-PHA) matrix to produce a scl/mcl-PHA membrane. The composite is compared to Nafion membrane for improved directional proton conduction in MFC. Composites with 10 and 15% (w/w) of PHB records two-fold maximum voltage potential compared to Nafion. A power density of 601 mW/m2 is recorded for PHB15% membrane, which is higher than that of Nafion (520 mW/m2). The MFC setup with composite membrane also shows higher maximum voltage potential, water uptake, power and current densities, chemical oxygen demand (COD) removal, ammoniacal nitrogen (NH3–N) removal as well as coulombic efficiency (CE) recovery. Composite membrane exhibits stronger resistivity to oxygen diffusion from cathode compartment to anode chamber, subsequently improving the overall MFC performance with real wastewater as substrate.

Changes of Exhaled Volatile Organic Compounds in Postoperative Patients Undergoing Analgesic Treatment: A Prospective Observational Study

Assessment and treatment of postoperative pain can be challenging as objective examination techniques to detect and quantify pain are lacking. We aimed to investigate changes of exhaled volatile organic compounds (VOCs) in patients with postoperative pain before and after treatment with opioid analgesics. In an observational study in 20 postoperative patients, we monitored for postoperative pain, hemodynamic parameters, and catecholamines before and during treatment. VOCs in the patients were determined by direct real-time proton transfer reaction time-of-flight mass spectrometry prior (0 min) and after piritramide application (15 min as well as 30 min). Cardiovascular variables changed and norepinephrine levels decreased during treatment. The VOCs acetonitrile (<0.001), acetaldehyde (p = 0.002), benzopyran (p = 0.004), benzene (p < 0.001), hexenal (p = < 0.001), 1-butanethiol (p = 0.004), methanethiol (p < 0.001), ethanol (p = 0.003), and propanol (p = < 0.001) changed significantly over time. Patients with Numeric Rating Scale (NRS) < 4 showed a significantly lower concentration of hexenal compared to patients with NRS > 4 at the time points 15 min (45.0 vs. 385.3 ncps, p = 0.047) and 30 min (38.3 vs. 334.6 ncps, p = 0.039). Breath analysis can provide additional information for noninvasive monitoring for analgesic treatment in postoperative patients.

From electricity to fuels: Descriptors for C1 selectivity in electrochemical CO2 reduction

Electrochemical reduction of carbon dioxide (CO2RR) over transition metals follows a complex reaction network. In this study, we combine observations from experimental literature with a theoretical analysis of energetics to rationalize that not all intermediates in the reduction of CO2 are formed through direct protonation steps. We derive a selectivity map for two-electron products (carbon monoxide (CO) and formate) on pure metal surfaces using only the CO and OH binding energies as descriptors. For the pure metals that are selective towards CO formation, the variation of the CO binding energy is sufficient to further subdivide the map into domains that predominantly form H2, CO, and more reduced products. Our analysis rationalizes experimentally observed product distributions in CO2RR across pure metal systems. Overall, we highlight the need for additional material screening descriptors for CO2R and the importance of considering competition from the elementary steps of the hydrogen evolution reaction.

Conditions for Chromospheric Plasma Acceleration or Trigger of Chromospheric Mass Ejections by Magnetic-field-aligned Electric Fields

Abstract Backward-propagating or reverse fluctuations in Alfvénic turbulence were recently found to produce magnetic-field-aligned (MFA) electric fields that can easily transfer their energy to the plasma, either in the form of heat (or electron beams that quickly dissipate their energy as heat) if electrons absorb most of the MFA energy, or in the form of translational motion of the plasma if the ions absorb most of the MFA energy. Conditions for the direct proton acceleration (jet formation) in the quiet chromosphere included a temperature ≤104 K and a magnetic field between about 10 and 100 G, conditions very similar to those under which chromospheric plasma jets or dynamic jet-like spicules are observed with the Interface Region Imaging Spectrograph. Here the conditions for direct ion acceleration by MFA electric fields are determined for a much broader range of electron densities and plasma temperatures, to include both quiet and flaring conditions of the chromospheric plasma. For the higher chromospheric electron densities of solar flaring conditions, direct ion and therefore plasma acceleration by MFA electric fields is found to be possible in the much stronger (kG) magnetic fields of active regions, provided the plasma temperature remains less than about 105 K. Under flaring conditions, the MFA electric fields may cause the acceleration or at least trigger the upward motion of dense (&gt;1012–1013 cm−3) chromospheric plasma. It is also suggested that chromospheric nonresonant MFA acceleration, by producing local electron beams, may eliminate the need for electron beams to propagate from the flaring corona down to the denser chromosphere.

A host\u2013guest approach to combining enzymatic and artificial catalysis for catalyzing biomimetic monooxygenation

Direct transfer of protons and electrons between two tandem reactions is still a great challenge, because overall reaction kinetics is seriously affected by diffusion rate of the proton and electron carriers. We herein report a host–guest supramolecular strategy based on the incorporation of NADH mimics onto the surface of a metal-organic capsule to encapsulate flavin analogues for catalytic biomimetic monooxygenations in conjunction with enzymes. Coupling an artificial catalysis and a natural enzymatic catalysis in the pocket of an enzyme, this host–guest catalyst–enzyme system allows direct proton and electron transport between two catalytic processes via NADH mimics for the monooxygenation of both cyclobutanones and thioethers. This host–guest approach, which involves the direct coupling of abiotic and biotic catalysts via a NADH-containing host, is quite promising compared to normal catalyst–enzyme systems, as it offers the key advantages of supramolecular catalysis in integrated chemical and biological synthetic sequences.

One-Pot Preparation of 9,10-Dihydrophenanthrenes Initiated by Rhodium(III)-Catalyzed C-H Activation and Relay Diels-Alder Reaction.

An efficient one-pot synthesis of multisubstituted 9,10-dihydrophenanthrenes from easily available 2-arylazaarenes and cyclohexadienone-tethered terminal alkynes (1,6-enynes) has been successfully achieved. This domino reaction proceeded smoothly through Cp*Rh(III)-catalyzed C-H activation, direct protonation of alkenyl-Rh intermediates, intramolecular Diels-Alder reaction, alkene isomerization, subsequent ring-opening aromatization, and acetylation. This strategy was pot-economical and tolerated a wide range of functional groups. Moreover, the potent anticancer activities against HepG2 cells were observed for these artificial 9,10-dihydrophenanthrene derivatives.

Structural insights into the role of the acid-alcohol pair of residues required for dioxygen activation in cytochrome P450 enzymes.

The cytochrome P450 heme monooxygenases commonly use an acid-alcohol pair of residues, within the I-helix, to activate iron-bound dioxygen. This work aims to clarify conflicting reports on the importance of the alcohol functionality in this process. Mutants of the P450, CYP199A4 (CYP199A4D251N and CYP199A4T252A), were prepared, characterised and their crystal structures were solved. The acid residue of CYP199A4 is not part of a salt bridge network, a key feature of paradigmatic model system P450cam. Instead, there is a direct proton delivery network, via a chain of water molecules, extending to the surface. Nevertheless, CYP199A4D251N dramatically reduced the activity of the enzyme consistent with a role in proton delivery. CYP199A4T252A decreased the coupling efficiency of the enzyme with a concomitant increase in the hydrogen peroxide uncoupling pathway. However, the effect of this mutation was much less pronounced than reported with P450cam. Its crystal structures revealed fewer changes at the I-helix, compared to the P450cam system. The structural changes observed within the I-helix of P450cam during oxygen activation do not seem to be required in this P450. These differences are due to the presence of a second threonine residue at position 253, which is absent in P450cam. This threonine forms part of the hydrogen bonding network, resulting in subtle structural changes and is also present across the majority of the P450 superfamily. Overall, the results suggest that while the acid-alcohol pair is important for dioxygen activation this process and the method of proton delivery can differ across P450s.Graphic abstract.

Kohn-Sham Density Functional Calculations Reveal Proton Wires in the Enolization and Carboxylase Reactions Catalyzed by Rubisco.

Ribulose 1,5-bisphosphate (RuBP) carboxylase-oxygenase (Rubisco) plays a fundamental role in the carbon cycle by fixing the atmospheric CO2 used in photosynthesis. Rubisco is all the more remarkable because it must catalyze some difficult multistep reaction chemistry involving proton transfers within the one active site. In the present study, we have used Kohn-Sham density functional theory at the B3LYP/6-31G* level with basis set superposition error and dispersion corrections (B3LYP-gCP-D3) to examine the possibility that the proton transfers can take place through molecular wires (including active-site water molecules) via the classical Grotthuss proton-shuttle mechanism. The results support an essential role for water molecules found in the crystal structures of Rubisco complexes as facilitators of proton transport in all the rate-limiting (catalytic) reaction steps through a network of short proton wires within the Rubisco active site. We suggest that completion of the initial product turnover (cycle) requires two excess protons produced in the initial carbamylation that is required for Rubisco activation. By use of proton wires, a large number of reaction steps may be accommodated within a single active site without necessitating the input of excessive conformational strain energy arising from the movement of residue side chains into positions where direct protonation of substrates can occur. The involvement of the identified types of proton wires in the kinetic mechanism is capable of providing a unique explanation for various experimental observations, including deuterium isotope effects and the results of site-directed mutagenesis experiments, and may thus provide a realistic solution to the problem of Rubisco's challenging chemistry.