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NASA NTRS2002

Laboratory Measurements of Solar-Wind/Comet X-Ray Emission and Charge Exchange Cross Sections

The detection of X-rays from comets such as Hyakutake, Hale-Bopp, d Arrest, and Linear as they approach the Sun has been unexpected and exciting. This phenomenon, moreover, should be quite general, occurring wherever a fast solar or stellar wind interacts with neutrals in a comet, a planetary atmosphere, or a circumstellar cloud. The process is, O(+8) + H2O --> O(+7*) + H2O(+), where the excited O(+7*) ions are the source of the X-ray emissions. Detailed modeling has been carried out of X-ray emissions in charge-transfer collisions of heavy solar-wind Highly Charged Ions (HCIs) and interstellar/interplanetary neutral clouds. In the interplanetary medium the solar wind ions, including protons, can charge exchange with interstellar H and He. This can give rise to a soft X-ray background that could be correlated with the long-term enhancements seen in the low-energy X-ray spectrum of ROSAT. Approximately 40% of the soft X-ray background detected by Exosat, ROSAT, Chandra, etc. is due to Charge Exchange (CXE): our whole heliosphere is glowing in the soft X-ray due to CXE.

Chutjian, A.↗

DOE OSTI2022

Medium-independent hydrogen atom binding isotherms of nickel oxide electrodes

Adsorption and transfer of hydrogen atoms at solid/solution interfaces are fundamental to heterogeneous catalysis for chemical energy transformations and other processes. Reported here are electrochemical and spectroelectrochemical measurements of the thermodynamics of H-atom binding to nickel oxide electrodes, both the average and the distribution of NiO–H bond dissociation free energies (BDFEs). These are perhaps the first measurements of binding isotherms at non-metal electrodes. Remarkably, both the BDFEs and the non-Langmuirian isotherms are the same in water, acetonitrile, and dimethylformamide, and with different buffers and proton activities. Such medium independence of the BDFEs and isotherms has not been previously reported for any binary material. The medium independence supports the common use of computed hydrogen binding energies as intrinsic descriptors of surface reactivity, while the broadened isotherms add a level of complexity to such analyses. Furthermore, this work demonstrates the capability to derive key thermodynamic parameters at chemically reactive solid-liquid interfaces.

13 HYDRO ENERGY↗

DOE OSTI2022

MEASUREMENT OF THE GENERALIZED POLARIZABILITIES OF THE PROTON IN VIRTUAL COMPTON SCATTERING

Understanding how the visible matter in the universe arises from its elementary quark and gluon constituents is a central question for science. The visible world is founded on the proton, the only composite building block of matter that is stable in nature. Consequently, understanding the formation of matter relies on explaining the dynamics and the properties of the proton?s bound state. A fundamental property of the proton involves the system?s response to an external electromagnetic (EM) field. It is characterized by the EM polarizabilities that describe how easily the charge and magnetization distributions inside the system are distorted by the EM field. When the polarizabilities are generalized to finite momentum transfer, their Fourier transform can map out the spatial distribution of the polarization densities in a proton subject to an EM field. This thesis focuses on the measurement of the proton generalized polarizabilities (GPs) at low four-momentum transfer in experimental Hall C at the Thomas Jefferson National Accelerator Facility (TJNAF). Among the six independent GPs, we will focus on the electric (aE1) and the magnetic (bM1) scalar GPs. The GPs can be accessed through measurements of the Virtual Compton Scattering reaction, by replacing the incoming real photon of the Compton scattering process with a space-like virtual photon. The outgoing real photon provides the EM perturbation to the system. In addition, the Dispersion Relation Formalism is used for generalized polarizability extraction. In this work, the two scalar GPs measured with unprecedented precision, and the measurements help explore a momentum transfer region where an anomalous enhancement of the electric GP that contradicts the predictions of nuclear theory has been observed.

Li, Ruonan↗

DOE OSTI2025

Heterobimetallic multi-site concerted proton electron transfer (MS-CPET) promotes coordination-induced O–H bond weakening

Coordination-induced bond weakening of X–H bonds (X = O, N, C) has been observed in a number of low-valent transition metal compounds. However, the impact of an appended electron reservoir on the bond dissociation free energy of the O–H bond (BDFE O–H ) of a substrate bound to a d 0 metal is poorly understood. To gain insight into the ability of separated deprotonation and oxidation sites to decrease the BDFE O–H during proton-coupled electron transfer (PCET) reactions, a bimetallic system in which the sites of proton and electron loss are two distinct metal sites is described. Herein, the interconversion of tris(phosphinoamide) Zr/Co complexes HO–Zr(MesNP i Pr 2 ) 3 CoCN t Bu and O$≡$Zr(MesNP i Pr 2 ) 3 CoCN t Bu via hydrogen atom addition/abstraction was studied. Since the Zr center remains in the d 0 Zr IV state throughout these transformations, the electron transfer process is mediated by the appended redox-active Co 0/I center. A series of open-circuit potential (OCP) measurements on the HO–Zr(MesNP i Pr 2 ) 3 CoCN t Bu and O$≡$Zr(MesNP i Pr 2 ) 3 CoCN t Bu complexes was performed, from which the BDFE O–H was found to be 64 ± 1 kcal mol −1 . The BDFE O–H value was further verified through a series of stoichiometric H atom transfer reactions, stoichiometric protonation/deprotonation reactions, and computational studies.

Chemistry↗

DOE OSTI2023

Chemical Recycling of Thiol Epoxy Thermosets via Light-Driven C–C Bond Cleavage

Epoxy thermosets are high-volume materials that play a central role in a wide range of engineering applications; however, technologies to recycle these polymers remain rare. Here, we present a catalytic, light-driven method that enables chemical recycling of industrially relevant thiol epoxy thermosets to their original monomer at ambient temperature. This strategy relies on the proton-coupled electron transfer (PCET) activation of hydroxy groups within the polymer network to generate key alkoxy radicals that promote the fragmentation of the polymer through C–C bond β-scission. The method fully depolymerizes insoluble thiol epoxy thermosets into well-defined mixtures of small-molecule products, which can collectively be converted into the original monomer via a one-step dealkylation process. Notably, this process is selective and efficient even in the presence of other commodity plastics and additives commonly found in commercial applications. Finally, these results constitute an important step toward making epoxy thermosets recyclable and more generally exemplify the potential of PCET to offer a more sustainable end-of-life for a diverse array of commercial plastics.

36 MATERIALS SCIENCE↗

NASA NTRS2002

Passive dosimetry aboard the Mir Orbital Station: external measurements

This paper reports results from the first measurements made on the exterior of a LEO spacecraft of mean dose equivalent rate and average quality factor as functions of shielding depth for shielding less than 1 g/cm2 Al equivalent. Two sets of measurements were made on the outside of the Mir Orbital Station; one near solar maximum in June 1991 and one near solar minimum in 1997. Absorbed dose was measured using stacks of TLDs. LET spectrum from charged particles of LET infinity H2O > o r= 5keV/micrometers was measured using stacks of CR-39 PNTDs. Results from the TLD and PNTD measurements at a given shielding depth were combined to yield mean total dose rate, mean dose equivalent rate, and average quality factor. Measurements made near solar maximum tend to be greater than those made during solar minimum. Both mean dose rate and mean dose equivalent rate decrease by nearly four orders of magnitude within the first g/cm2 shielding illustrating the attenuation of both trapped electrons and low-energy trapped protons. In order to overcome problems with detector saturation after standard chemical processing, measurement of LET spectrum in the least shielded CR-39 PNTD layer (0.005 g/cm2 Al) was carried out using an atomic force microscope. c2002 Elsevier Science Ltd. All rights reserved.

manned↗

DOE OSTI2026

Understanding Adsorption and Reactions at Aqueous Oxide Interfaces with Neural Network Potential Molecular Dynamics

Chemical processes at metal oxide−water interfaces are of central importance in geochemistry, biology, and energy technologies. A better understanding of these processes would allow us to make a significant step toward optimizing and controlling them, which could in turn lead to broader impacts. Computational modeling is indispensable to accomplishing this task because complexity and disorder often make it difficult to extract atomistic information from experiments. Balancing computational cost and accuracy, simulation schemes based on efficient machine learning representations of the potential energy surface (PES) predicted by ab initio calculations have become increasingly popular over the past decade. In particular, several studies have demonstrated the ability of machine learning models to accurately reproduce the complex ab initio PESs of aqueous oxide interfaces, allowing simulations of systems and processes that are not accessible with ab initio methods. In this Account, we review our recent efforts to understand adsorption processes and reactions at aqueous oxide interfaces using deep potential molecular dynamics (DPMD), a simulation scheme employing deep neural networks (DNNs), which has proven to be quite successful in accurately describing many different systems in the condensed phase. After summarizing the DPMD methodology, we first review our work on the acid−base chemistry of oxide surfaces in contact with water, a fundamental characteristic that controls proton transfer and surface charge at the interface. We focus on the aqueous interface of rutile IrO 2 , an oxide material thus far considered the best catalyst for the oxygen evolution reaction (OER). We show that this interface is characterized by a large fraction of dissociated water and a strong Brønsted acidity of the surface sites, in good agreement with the experimentally measured value of the point of zero proton charge. In our second example, we investigate how the adsorption of organic species from ambient air or water affects the structure and wettability of the aqueous interfaces of TiO 2 , a prototypical photocatalytic material. This is a question that is relevant to understanding the UV-induced hydrophilicity of TiO 2 surfaces, a property at the basis of self-cleaning windows and related applications. Specifically focusing on formic and acetic acids, the two most common atmospheric organic acids, our simulations reveal that these acids control the wettability of TiO 2 largely through acid−base chemistry at the interface rather than chemisorption on the oxide surface, a finding that could help improve the design of self-cleaning surfaces and photocatalytic devices. Finally, we review our recent study of methanol at TiO 2 −water interfaces, a system whose interest is largely motivated by the role of methanol in enhancing photocatalytic hydrogen evolution on TiO 2 . Our simulations provide mechanistic insights into the coupled roles of the organic adsorbate and water at the TiO 2 interface, with implications for how methanol enhances the activity of H 2 evolution.

adsorption↗

DOE OSTI2025

Structural Insights into the Dynamics of Water in SOD1 Catalysis and Drug Interactions

Superoxide dismutase 1 (SOD1) is a crucial enzyme that protects cells from oxidative damage by converting superoxide radicals into H 2 O 2 and O 2 . This detoxification process, essential for cellular homeostasis, relies on a precisely orchestrated catalytic mechanism involving the copper cation, while the zinc cation contributes to the structural integrity of the enzyme. This study presents the 2.3 Å crystal structure of human SOD1 (PDB ID: 9IYK), revealing an assembly of six homodimers and twelve distinct active sites. The water molecules form a complex hydrogen-bonding network that drives proton transfer and sustains active site dynamics. Our structure also uncovers subtle conformational changes that highlight the intrinsic flexibility of SOD1, which is essential for its function. Additionally, we observe how these dynamic structural features may be linked to pathological mutations associated with amyotrophic lateral sclerosis (ALS). By advancing our understanding of hSOD1’s mechanistic intricacies and the influence of water coordination, this study offers valuable insights for developing therapeutic strategies targeting ALS. Our structure’s unique conformations and active site interactions illuminate new facets of hSOD1 function, underscoring the critical role of structural dynamics in enzyme catalysis. Moreover, we conducted a molecular docking analysis using SOD1 for potential radical scavengers and Abelson non-receptor tyrosine kinase (c-Abl, Abl1) inhibitors targeting misfolded SOD1 aggregation along with oxidative stress and apoptosis, respectively. The results showed that CHEMBL1075867, a free radical scavenger derivative, showed the most promising docking results and interactions at the binding site of hSOD1, highlighting its promising role for further studies against SOD1-mediated ALS.

60 APPLIED LIFE SCIENCES↗

NASA NTRS1991

Ionosphere-exosphere coupling through charge exchange and momentum transfer in hydrogen-proton collisions

The implications of a traditional assumption of exospheric physics, that collisions of hydrogen atoms and protons preferentially result in charge exchange with negligible momentum transfer are examined. Initially adopted as a necessary convenience to accommodate limited computer resources in exosphere model calculations, this approximation results in a direct transformation of the proton velocity distribution into a hot component of neutral hydrogen. With expanding computational facilities, the need for the approximation has passed. As the first step toward its replacement with a realistic, quantum mechanical model of the H - H(+) collision process, differential and cumulative cross sections were calculated for quantum elastic scattering of indistinguishable nuclei for a fine grid of encounter energies and scattering angles. These data are used to study the nature of ionosphere-exosphere coupling through H - H(+) collisions, and to demonstrate that the distribution of velocities of scattered H produced in the traditional exospheric charge exchange approximation, as well as that arising from an alternative, fluid dynamic approach, leads to unacceptable abundances of coronal atoms in long-term, highly elliptic trajectories.

Hodges, R. R., Jr.↗

NASA NTRS2023

Prospects of Detecting Nonthermal Protons in Solar Flares via Lyman Line Spectroscopy: Revisiting the Orrall-Zirker Effect

Solar flares are efficient particle accelerators, with a substantial fraction of the energy released manifesting as nonthermal particles. While the role that nonthermal electrons play in transporting flare energy is well studied, the properties and importance of nonthermal protons are rather less well understood. This is in large part due to the paucity of diagnostics, particularly at the lower-energy (deka-keV) range of nonthermal proton distributions in flares. One means to identify the presence of deka-keV protons is by an effect originally described by Orrall & Zirker. In the Orrall–Zirker effect, nonthermal protons interact with ambient neutral hydrogen, and via charge exchange produce a population of energetic neutral atoms (ENAs) in the chromosphere. These ENAs subsequently produce an extremely redshifted photon in the red wings of hydrogen spectral lines. We revisit predictions of the strength of this effect using modern interaction cross sections, and numerical models capable of self-consistently simulating the flaring nonequilibrium ionization stratification, and the nonthermal proton distribution (and, crucially, their feedback on each other). We synthesize both the thermal and nonthermal emission from Ly α and Ly β, the most promising lines that may exhibit a detectable signal. These new predictions are weaker and more transient than prior estimates, but the effects should be detectable in fortuitous circumstances. We degrade the Ly β emission to the resolution of the Spectral Imaging of the Coronal Environment (SPICE) instrument on board Solar Orbiter, demonstrating that though likely difficult, it should be possible to detect the presence of nonthermal protons in flares observed by SPICE.

Solar flares↗

DOE OSTI2024

EPCAPE-PT-LANL Measurements: Proton Transfer Reaction Mass Spectrometer

Coastal cities offer a unique environment for studying aerosol-cloud interactions and the effects of urban emissions on cloud properties. As part of the Eastern Pacific Cloud Aerosol Precipitation Experiment (EPCAPE), the Partitioning Thrust by Los Alamos National Laboratory (EPCAPE-PT-LANL) was conducted. Our campaign focused on measuring the optical and chemical properties of aerosols and their interactions within marine stratocumulus clouds in La Jolla, California. EPCAPE-PT-LANL enhances the primary goals of EPCAPE through innovative observations of vapor-phase transitions between aerosols and cloud droplets, the impact of black carbon on aerosol-cloud dynamics, and the effects of cloud processing on aerosol optical properties. Instrument: IONICON High-Resolution PTR-TOF-MS - Trace VOC Analyzer. Concentrations were calculated based on theoretical reaction rates of each species with H3O+. Details of the calculation are found in the PTR-MS Ionicon Manual. Data Notes: It is a high-resolution PTR-TOF-MS we have sub-selected relevant species. Contact us if you want additional data products from this instrument. Header: - CalculatedAcetonitrile[ppbv]: The concentration of acetonitrile expressed in parts per billion by volume (ppbv). - CalculatedAcetaldehyde[ppbv]: The concentration of acetaldehyde expressed in parts per billion by volume (ppbv). - CalculatedAcetone[ppbv]: The concentration of acetone expressed in parts per billion by volume (ppbv). - CalculatedAceticAcid[ppbv]: The concentration of acetic acid expressed in parts per billion by volume (ppbv). - CalculatedIsoprene[ppbv]: The concentration of isoprene expressed in parts per billion by volume (ppbv). - CalculatedMVK[ppbv]: The concentration of methyl vinyl ketone (MVK) and methacrolein (MACR) expressed in parts per billion by volume (ppbv). - CalculatedMEK[ppbv]: The concentration of methyl ethyl ketone (MEK) expressed in parts per billion by volume (ppbv). - CalculatedBenzene[ppbv]: The concentration of benzene expressed in parts per billion by volume (ppbv). - CalculatedToluene[ppbv]: The concentration of toluene expressed in parts per billion by volume (ppbv).

54 ENVIRONMENTAL SCIENCES↗

NASA NTRS2006

NASA Radiation Track Image GUI for Assessing Space Radiation Biological Effects

The high-charge high-energy (HZE) ion components of the galactic cosmic rays when compared to terrestrial forms of radiations present unique challenges to biological systems. In this paper we present a deoxyribonucleic acid (DNA) breakage model to visualize and analyze the impact of chromatin domains and DNA loops on clustering of DNA damage from X rays, protons, and HZE ions. Our model of DNA breakage is based on a stochastic process of DNA double-strand break (DSB) formulation that includes the amorphous model of the radiation track and a polymer model of DNA packed in the cell nucleus. Our model is a Monte-Carlo simulation based on a randomly located DSB cluster formulation that accomodates both high- and low-linear energy transfer radiations. We demonstrate that HZE ions have a strong impact on DSB clustering, both along the chromosome length and in the nucleus volume. The effects of chromosomal domains and DNA loops on the DSB fragment-size distribution and the spatial distribution of DSB in the nucleus were studied. We compare our model predictions with the spatial distribution of DSB obtained from experiments. The implications of our model predictions for radiation protection are discussed.

Ponomarev, Artem L.↗

DOE OSTI2021

R -parity violation axiogenesis

We show that the rotation of the QCD axion field, aided by B–L violation from supersymmetric R-parity violating couplings, can yield the observed baryon abundance. Strong sphaleron processes transfer the angular momentum of the axion field into a quark chiral asymmetry, which R-parity violating couplings convert to the baryon asymmetry of the Universe. We focus on the case of dimensionless R-parity violating couplings with textures motivated by grand unified theories and comment on more general scenarios. The axion decay constant and mass spectrum of supersymmetric particles are constrained by Big Bang nucleosynthesis, proton decay from the R-parity violation, and successful thermalization of the Peccei-Quinn symmetry breaking field. Axion dark matter may be produced by the axion rotation via the kinetic misalignment mechanism for axion decay constants below 10 10 GeV, or by the conventional misalignment mechanism for 10 11-12 GeV. The viable parameter region can be probed by proton decay and axion searches. This scenario may also have connections with collider experiments, including searches for long-lived particles, and observations of gravitational waves.

Beyond Standard Model↗

DOE OSTI2020

Proton Transfer Dynamics in the Aprotic Proton Accepting Solvent 1-Methylimidazole

The dynamics of proton transfer to the aprotic solvent 1-methylimidazole (MeIm, proton acceptor) from the photoacid 8-hydroxypyrene-1,3,6-trisulfonic acid trisodium salt (HPTS) were investigated using fast fluorescence measurements. The closely related molecule, 8- methoxypyrene-1,3,6-trisulfonic acid trisodium salt (MPTS), which is not a photoacid, was also studied for comparison. Following optical excitation, the wavelength-dependent population dynamics of HPTS in MeIm resulting from the deprotonation process were collected over the entire fluorescence emission window. Analysis of the time-dependent fluorescence spectra revealed four distinct fluorescence bands that appear and decay on different time scales. We label these four states as: protonated (P), associated I (A I ), associated II (A II ), and deprotonated (D). We find that the simple kinetic scheme of P → A I → A II → D is not consistent with the data. Instead, the kinetic scheme that describes the data has P decaying into A I , which mainly goes on to deprotonation (D), but AI can also feed into A II . A II can return to A I or decay to the ground state, but does not deprotonate within experimental error. Finally, quantum chemistry and excitedstate QM/MM Born-Oppenheimer molecular dynamics simulations indicate that A I and A II are two H-bonding conformations of MeIm to the HPTS hydroxyl, axial and equatorial, respectively.

14 SOLAR ENERGY↗

DOE OSTI2020

Prompt-delayed γ-ray spectroscopy of neutron-rich 119.121 In isotopes

The Z = 50 shell closure, near N = 82, is unique in the sense that it is the only shell closure with the spin-orbit partner orbitals, π g 9 / 2 and π g 7 / 2 , enclosing the magic gap. The interaction of the proton hole/particle in the above-mentioned orbitals with neutrons in the νh 11/2 orbital is an important prerequisite to the understanding of the nuclear structure near N = 82 and the νπ interaction. To explore the structural similarity between the high-spin isomeric states in In ( Z = 49), Sn ( Z = 50), and Sb ( Z = 51) isotopes from a microscopic point of view. In addition, to understand the role of a proton hole or particle in the spin-orbit partner orbitals, π g 9 / 2 and π g 7 / 2 , respectively, with neutron holes in the ν h 11 / 2 orbital on these aforementioned isomers. The fusion and transfer induced fission reaction Be 9 ( U 238 , f ) with 6.2 MeV/u beam energy, using a unique setup consisting of AGATA, VAMOS++, and EXOGAM detectors, was used to populate through the fission process and study the neutron-rich In 119 , 121 isotopes. This setup enabled the prompt-delayed γ -ray spectroscopy of isotopes in the time range of 100 ns – 200 μ s . In the odd- A In 119 , 121 isotopes, indications of a short half-life 19/2 - isomeric state, in addition to the previously known 25/2 + isomeric state, were observed from the present data. Further, new prompt transitions above the 25/2 + isomer in In 121 were identified along with reevaluation of its half-life. The experimental data were compared with the theoretical results obtained in the framework of large-scale shell-model calculations in a restricted model space. Furthermore, the ( π g 9 / 2 ν h 11 / 2 ; I | H ^ | π g 9 / 2 ν h 11 / 2 ; I ) two-body matrix elements of residual interaction were modified to explain the excitation energies and the B ( E 2) transition probabilities in the neutron-rich In isotopes. The (i) decreasing trend of E (29/2 + ) - E (25/2 + ) in odd-In (with dominant configuration π g 9 / 2 - 1 ν h 11 / 2 - 2 and maximum aligned spin of 29/2 + ) and (ii) increasing trend of E (27/2 + ) - E (23/2 + ) in odd-Sb (with dominant configuration π g 7 / 2 + 1 ν h 11 / 2 - 2 and maximum aligned spin of 27/2 + ) with increasing neutron number could be understood as a consequence of hole-hole and particle-hole interactions, respectively.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗

DOE OSTI2020

A High Precision Measurement of the Proton Charge Radius at JLab

The elastic electron-proton (e-p) scattering and the spectroscopy of hydrogen atoms are the two traditional methods to determine the proton charge radius (r p ). In 2010, a new method using muonic hydrogen (µH) 1 spectroscopy reported a r p result that was nearly ten times more precise but significantly smaller than the values from the compilation of all previous r p measurements. This discrepancy is often referred to as the "proton charge radius puzzle". In order to investigate the puzzle, the PRad experiment (E12-11-106) was first proposed in 2011 and performed in 2016 in Hall B at the Thomas Jefferson National Accelerator Facility, with both 1.1 and 2.2 GeV electron beams. The experiment measured the e-p elastic scattering cross sections in an unprecedented low values of momentum transfer squared region (Q 2 = 2.1× 10 -4 -0.06 (GeV/c) 2 ), with a sub-percent precision. The PRad experiment utilized a calorimetric method that was magnetic-spectrometer-free. Its detector setup included a large acceptance and high resolution calorimeter (HyCal), and two large-area, high spatial-resolution Gas Electron Multiplier (GEM) detectors. To have a better control over the systematic uncertainties, the absolute e-p elastic scattering cross section was normalized to that of the well-known Møller scattering process, which was measured simultaneously during the experiment. For each beam energy, all data with different Q 2 were collected simultaneously with the same detector setup, therefore sharing the same integrated luminosity. The windowless H 2 gas-flow target utilized in the experiment largely removed a typical background source, the target cell windows. The proton charge radius was determined as r p = 0.831±0.007 stat. ±0.012 p fm, which is smaller than the average r p from previous e-p elastic scattering experiments, but in agreement with the µH spectroscopic results within the experimental uncertainties.

Source record↗

DOE OSTI2022

Preface: special issues on photosystem II

Here, the appearance of oxygenic photosynthesis 3–4 billion years ago is arguably one of the most important evolutionary developments which radically transformed both the biotic and abiotic landscapes of Earth. The presence of molecular oxygen enabled the evolution of complex lifeforms requiring large amounts of chemical energy which could only be produced by aerobic respiration. Additionally, molecular oxygen remodeled the geochemistry of the planet during its transition from a reducing to an oxidizing atmosphere during the Great Oxidation Event. Central to these processes is Photosystem II (PS II), the light energy-driven, water-plastoquinone oxidoreductase which initially evolved in cyanobacteria and subsequently was incorporated, along with Photosystem I (PS I), the cytochrome b 6 f complex and the Ndh complex, into all algae and higher plants by the process of endosymbiosis. This membrane protein complex releases molecular oxygen and protons as the byproducts of water splitting and produces plastoquinol, which provides reducing equivalents that are used sequentially by the cytochrome b 6 /f complex, PS I, and ultimately, as NADPH + H + , by the Calvin–Benson–Bassham cycle. Additionally, the protons released by PS II (and those pumped by the cytochrome b 6 /f complex and the NDH complex (during cyclic electron transfer)) form the proton motive force that drives ATP synthesis via the ATP Synthase, thus providing the chemical energy source for carbon fixation.

59 BASIC BIOLOGICAL SCIENCES↗

NASA NTRS2010

Electrochemical Hydrogen Peroxide Generator

Two-electron reduction of oxygen to produce hydrogen peroxide is a much researched topic. Most of the work has been done in the production of hydrogen peroxide in basic media, in order to address the needs of the pulp and paper industry. However, peroxides under alkaline conditions show poor stabilities and are not useful in disinfection applications. There is a need to design electrocatalysts that are stable and provide good current and energy efficiencies to produce hydrogen peroxide under acidic conditions. The innovation focuses on the in situ generation of hydrogen peroxide using an electrochemical cell having a gas diffusion electrode as the cathode (electrode connected to the negative pole of the power supply) and a platinized titanium anode. The cathode and anode compartments are separated by a readily available cation-exchange membrane (Nafion 117). The anode compartment is fed with deionized water. Generation of oxygen is the anode reaction. Protons from the anode compartment are transferred across the cation-exchange membrane to the cathode compartment by electrostatic attraction towards the negatively charged electrode. The cathode compartment is fed with oxygen. Here, hydrogen peroxide is generated by the reduction of oxygen. Water may also be generated in the cathode. A small amount of water is also transported across the membrane along with hydrated protons transported across the membrane. Generally, each proton is hydrated with 3-5 molecules. The process is unique because hydrogen peroxide is formed as a high-purity aqueous solution. Since there are no hazardous chemicals or liquids used in the process, the disinfection product can be applied directly to water, before entering a water filtration unit to disinfect the incoming water and to prevent the build up of heterotrophic bacteria, for example, in carbon based filters. The competitive advantages of this process are: 1. No consumable chemicals are needed in the process. The only raw materials needed are water and oxygen or air. 2. The product is pure and can therefore be used in disinfection applications directly or after proper dilution with water. 3. Oxygen generated in the anode compartment is used in the electrochemical reduction process; in addition, external oxygen is used to establish a high flow rate in the cathode compartment to remove the desired product efficiently. Exiting oxygen can be recycled after separation of liquid hydrogen peroxide product, if so desired. 4. The process can be designed for peroxide generation under microgravity conditions. 5. High concentrations of the order of 6-7 wt% can be generated by this method. This method at the time of this reporting is superior to what other researchers have reported. 6. The cell design allows for stacking of cells to increase the hydrogen peroxide production. 7. The catalyst mix containing a diquaternary ammonium compound enabled not only higher concentration of hydrogen peroxide but also higher current efficiency, improved energy efficiency, and catalyst stability. 8. The activity of the catalyst is maintained even after repeated periods of system shutdown. 9. The catalyst system can be extended for fuel-cell cathodes with suitable modifications.

Tennakoon, Charles L. K.↗