Search NASA⌕ Search

SEARCH · Search NASA

Results for “Ferric Compounds”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

9 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

A requirement for an active proton delivery network supports a compound I-mediated C–C bond cleavage in CYP51 catalysis

CYP51 enzymes (sterol 14α-demethylases) are cytochromes P450 that catalyze multistep reactions. The CYP51 reaction occurs in all biological kingdoms and is essential in sterol biosynthesis. It removes the 14α-methyl group from cyclized sterol precursors by first forming an alcohol, then an aldehyde, and finally eliminating formic acid with the introduction of a Δ14–15 double bond in the sterol core. The first two steps are typical hydroxylations, mediated by an electrophilic compound I mechanism. The third step, C–C bond cleavage, has been proposed to involve either compound I (i.e. FeO 3+ ) or, alternatively, a proton transfer-independent nucleophilic ferric peroxo anion (compound 0, i.e. Fe 3+ O 2 – ). In this work, using comparative crystallographic and biochemical analyses of WT human CYP51 (CYP51A1) and its D231A/H314A mutant, whose proton delivery network is destroyed (as evidenced in a 1.98-Å X-ray structure in complex with lanosterol), we demonstrate that deformylation of the 14α-carboxaldehyde intermediate requires an active proton relay network to drive the catalysis. These results indicate a unified, compound I-based mechanism for all three steps of the CYP51 reaction, as previously established for CYP11A1 and CYP19A1. We anticipate that our approach can be applied to mechanistic studies of other P450s that catalyze multistep reactions, such as C–C bond cleavage.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Linking the Spin Transition of Ferric Iron in δ‐(Al,Fe)OOH to Water Storage in the Lower Mantle

As the most massive geochemical reservoir, the lower mantle affects the Earth's budget of volatile elements, including hydrogen or H 2 O. The properties of minerals in the lower mantle are further affected by changes in the electronic configurations of iron cations, that is, by spin transitions. The feedback between spin transitions and potential storage of H 2 O in solid hydrous phases in the lower mantle, however, remains unexplored. By combining high‐pressure nuclear resonant inelastic X‐ray scattering and high‐pressure high‐temperature X‐ray diffraction experiments, we constrained the thermal equation of state of δ‐(Al,Fe)OOH, a member of the phase H solid solution. Based on the derived thermal equation of state of δ‐(Al,Fe)OOH and the underlying thermodynamic model, we calculate the excess Gibbs free energy that arises from the spin transition of ferric iron in this compound and evaluate the effect on phase equilibria. The results of our analysis show that the spin transition of ferric iron in phase H may significantly reduce the thermodynamic activity and hence the concentration of H 2 O in a coexisting hydrous melt. As a consequence, nominally anhydrous minerals of the lower mantle may become dehydrated in the presence of phase H. Our analysis further suggests that, under certain conditions, the spin transition may expand the thermal stability of Fe 3+ ‐bearing phase H and create a geochemical link between the storage of H 2 O in phase H and ferric iron in the lower mantle.

Buchen, Johannes [Univ. of Bayreuth (Germany); Cal↗
DOE OSTI2021

Iron-activated persulfate oxidation degrades aqueous Perfluorooctanoic acid (PFOA) at ambient temperature

Perfluorooctanoic acid (PFOA, C 8 HF 15 O 2 ) is an industrial surfactant that is highly resistant to natural breakdown processes such as those mediated by heat, hydrolysis, photolysis, and biodegradation. Many efforts have been developed to breakdown PFOA to less harmful species due to its widespread human exposure and potential toxicity. However, these methods require high temperature or specialized equipment with serious disadvantages of high energy cost for long-term use. For this paper, we investigated the effectiveness of PFOA degradation by ferrous iron-activated persulfate oxidation (IAPO) under various aqueous geochemical conditions. Approximately 64% of PFOA (initial concentration = 1.64 μmol L –1 ) was degraded after 4 h under illuminated anoxic conditions at ambient temperature. This degradation rate and magnitude support the potential use of IAPO as a novel inexpensive and environmentally friendly method to remediate PFOA in soil and groundwater.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Chemical-Biological Cyclic Process for Hexavalent Chromium Reduction to Trivalent Chromium in Aqueous Medium - 20224

Conventional treatment of chromium contamination focuses on immobilization of the highly toxic and water-soluble form Cr(VI), by reducing it to the relatively less toxic and less mobile trivalent form, Cr(III), using reducing compounds like ferrous sulfate or ferrous iron, Fe(II). The Cr(VI) also respond to biodegradation and subsequent reduction. During the reduction reaction, Fe(II) is oxidized to ferric, Fe(III), which, being at the highest oxidation state, has no ability to reduce Cr(VI), and therefore remediation process terminates. The good news is that metal-reducing bacteria, S. oneidensis MR-1, can regenerate Fe(II) from Fe(III) with the help of an organic electron donor in an appropriate bacterial media. Thus, in the Cr(VI) chemical remediation process, Fe(II) to Fe(III) conversion is reversed by the biological process, regenerating Fe(II) and the Cr(VI) chemical reduction process continues in a cyclic fashion. This study presents the results of regeneration of Fe(II) from fresh Fe(III) as well as from the reaction products of Cr(VI) and Fe(II). Both fresh Fe(III) and reaction product Fe(III) exhibited the same reduction behavior. Fe(II) production increased with the increase of initial concentration of Fe(III), resulting in 87.5% Fe(II) regeneration. The extent of Fe(III) reduction (Fe(II)t/Fe(III)0.hour) was 21 times higher than the extent of Cr(VI) reduction (Cr(VI)t/Cr(VI)0.hour) by S. oneidensis MR-1. In a cyclic process of sequential Cr(VI) addition, the amount of Fe(II) regeneration decreased with the increase in cycle number, a fixed quantity of starting S. oneidensis MR-1 could regenerate Fe(II) at least five times in a ten-hour period. More importantly, regenerated Fe(II) instantly reduced Cr(VI) to Cr(III). So, Fe(II) regeneration with metal-reducing bacteria has a good potential for application in groundwater and wastewater remediation in reducing Cr(VI) to Cr(III). As a comparison of chemical to biological transformation, chemical transformation of Cr(VI) by Fe(II) was almost 600 times greater than that of biological transformation. Therefore a chemical-biological cyclic process offers potential applications for remediation of groundwater and hexavalent chromium contaminated waste sites. (authors)

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2026

Can ferric-oxyl excited states explain elongated iron-oxygen bonds in heme peroxidase catalytic intermediates?

The use of X-ray structures to determine and interpret the ferryl iron-oxygen bond order in molecular oxygen-activating heme enzymes has, in the past, been controversial. This has mainly stemmed from the susceptibility of ferryl species to X-ray-induced electronic state changes. In this work we establishe using time-resolved serial femtosecond X-ray crystallography (tr-SFX) on a dye-decolourising peroxidase that the ferryl intermediate species (Compounds I and II) captured following in situ mixing of microcrystals with H 2 O 2 have single, rather than the double bond character expected. X-ray emission validated tr-SFX data with quantum refinement, time-dependent-DFT calculations and QM/MM geometry optimizations together support the concept that the single iron-oxygen bond character is not an indication of ferryl reduction or a protonated form (Fe IV -OH) but is instead attributed to the existence of accessible excited states possessing ferric-oxyl (Fe III –O •– ) character. Such states offer insight into the nature of ferryl heme.

Williams, Lewis J. [University of Essex, Colcheste↗
DOE OSTI2023

In Situ Structural Observation of a Substrate- and Peroxide-Bound High-Spin Ferric-Hydroperoxo Intermediate in the P450 Enzyme CYP121

The P450 enzyme CYP121 from Mycobacterium tuberculosis catalyzes a carbon–carbon (C–C) bond coupling cyclization of the dityrosine substrate containing a diketopiperazine ring, cyclo(l-tyrosine-l-tyrosine) (cYY). An unusual high-spin (S = 5/2) ferric intermediate maximizes its population in less than 5 ms in the rapid freeze-quenching study of CYP121 during the shunt reaction with peracetic acid or hydrogen peroxide in acetic acid solution. Here, we show that this intermediate can also be observed in the crystalline state by EPR spectroscopy. By developing an on-demand-rapid-mixing method for time-resolved serial femtosecond crystallography with X-ray free-electron laser (tr-SFX-XFEL) technology covering the millisecond time domain and without freezing, we structurally monitored the reaction in situ at room temperature. After a 200 ms peracetic acid reaction with the cocrystallized enzyme–substrate microcrystal slurry, a ferric-hydroperoxo intermediate is observed, and its structure is determined at 1.85 Å resolution. The structure shows a hydroperoxyl ligand between the heme and the native substrate, cYY. The oxygen atoms of the hydroperoxo are 2.5 and 3.2 Å from the iron ion. The end-on binding ligand adopts a near-side-on geometry and is weakly associated with the iron ion, causing the unusual high-spin state. This compound 0 intermediate, spectroscopically and structurally observed during the catalytic shunt pathway, reveals a unique binding mode that deviates from the end-on compound 0 intermediates in other heme enzymes. The hydroperoxyl ligand is only 2.9 Å from the bound cYY, suggesting an active oxidant role of the intermediate for direct substrate oxidation in the nonhydroxylation C–C bond coupling chemistry.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Formation of Zerovalent Iron in Iron-Reducing Cultures of Methanosarcina barkeri

Methanogenic archaea have been shown to reduce iron from ferric [Fe(III)] to ferrous [Fe(II)] state, but minerals that form during iron reduction by different methanogens remain to be characterized. Here, we show that zerovalent iron (ZVI) minerals, ferrite [α-Fe(0)] and austenite [γ-Fe(0)], appear in the X-ray diffraction spectra minutes after the addition of ferrihydrite to the cultures of a methanogenic archaeon, Methanosarcina barkeri (M. barkeri). M. barkeri cells and redox-active, nonenzymatic soluble organic compounds in organic-rich spent culture supernatants can promote the formation of ZVI; the latter compounds also likely stabilize ZVI. Methanogenic microbes that inhabit organic- and Fe(III)-rich anaerobic environments may similarly reduce Fe(III) to Fe(II) and ZVI, with implications for the preservation of paleomagnetic signals during sediment diagenesis and potential applications in the protection of iron metals against corrosion and in the green synthesis of ZVI.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2023

Lactiplantibacillus plantarum uses ecologically relevant, exogenous quinones for extracellular electron transfer

Extracellular electron transfer (EET) is a metabolic process that frequently uses quinones to couple intracellular redox reactions with extracellular electron acceptors. The physiological relevance of this metabolism for microorganisms capable of EET but unable to synthesize their own quinones remains to be determined. To address this question, we investigated quinone utilization by Lactiplantibacillus plantarum, a microorganism required for food fermentations, that performs EET and is also a quinone auxotroph. L. plantarum selectively used 1,4-dihydroxy-2-naphthoic acid (DHNA) and more hydrophilic naphthoquinones for EET reduction of insoluble iron (ferrihydrite). However, quinones used for EET also inhibited L. plantarum growth in non-aerated conditions. Transcriptomic analysis showed that DHNA-induced oxidative stress in L. plantarum, but this was alleviated when the electron acceptor, ferric ammonium citrate (FeAC), was included in the growth medium. Although DHNA and FeAC induced L. plantarum EET, this metabolism was still dependent on direct access to environmental electron shuttles. To determine whether quinone-producing food fermentation bacteria could be sources of those electron shuttles, L. plantarum EET was measured after incubation with Lactococcus lactis and Leuconostoc mesenteroides. Quinone-producing L. lactis, but not a quinone-deficient L. lactis ΔmenC mutant, increased L. plantarum ferrihydrite reduction and medium acidification through an EET-dependent mechanism. L. plantarum EET was also stimulated by L. mesenteroides, resulting in greater environmental acidification and transient increases in L. plantarum cell numbers. Our findings show that L. plantarum overcomes the toxic effects of exogenous quinones to use those compounds for EET-conferred, ecological advantages during the early stages of food fermentations.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2026

The oleaginous yeast Cutaneotrichosporon oleaginosum modifies corn stover alkali lignin

The current paradigm in synthetic biology for lignin bioconversion platforms includes primarily bacteria and filamentous fungi. Yeast are notoriously understudied for their role in lignin degradation and utilization, despite their ubiquity in saprophytic microbial communities. A few publications report lignin-modifying yeasts, but investigations to date have relied on model aromatic compounds or lignin-containing substrates replete with other carbon sources. In this work, we use a suite of analytical tools to evaluate interactions between corn stover-extracted lignin and the oleaginous yeast Cutaneotrichosporon oleaginosum. Notably, 2D-NMR analysis showed a significant decrease in the H-lignin component as well as resinol (β-β) and phenylcoumaran (β-5) linkages. Using super-resolution fluorescence microscopy, we demonstrated that this yeast may uptake polymeric lignin and/or undertakes interactions at the cellular envelope. To explore mechanisms of lignin modification, transport, and aromatics catabolism, extensive secretomics and proteomics analyses were conducted. Compared to carbon-limited glucose and “No Carbon” controls, several putative laccases, quinone reductases, superoxide dismutases, and glyoxal/oxalate oxidases were upregulated in the lignin condition. Excitingly, two ferric reductases and an oxalate exchanger were only observed in the lignin condition. These results indicate that C. oleaginosum may perform extracellular quinone redox cycling to generate lignin-modifying reactive oxygen species. These findings enhance our understanding of yeast-lignin interactions and provide valuable insights for validation studies and metabolic engineering.

09 BIOMASS FUELS↗