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All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Nuclear Data Sheets for A=59☆

-- Abstract: Evaluated spectroscopic data and level schemes from radioactive decay and nuclear reaction studies are presented for {sup 59}Sc, {sup 59}Ti, {sup 59}V, {sup 59}Cr, {sup 59}Mn, {sup 59}Fe, {sup 59}Co, {sup 59}Ni, {sup 59}Cu, {sup 59}Zn, {sup 59}Ga, and {sup 59}Ge. This evaluation for A=59 supersedes the earlier one by C. M. Baglin (2002Ba42) and updates for some nuclides in the ENSDF database. Highlights: of this evaluation are the following: In {sup 59}Fe, a new level at 568.45 keV (3/2{sup −}) has been added. This resolves a doublet at 570 keV, which was reflected in earlier evaluations (1983An22, 1993Ba85, 2002Ba42) and literature as well. Conflicting spin assignments for 2153.62 keV level of {sup 59}Co [9/2,13/2 in (α,pγ); (13/2) in ({sup 15}N,4nγ); 15/2 in (p,p′γ), (7/2{sup −}) in (n,n′γ)] exist in the literature and additional experimental work is needed to resolve the issue.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2015

Percutaneous Bone Biopsies: Comparison between Flat-Panel Cone-Beam CT and CT-Scan Guidance

PurposeThis study was designed to compare the accuracy of targeting and the radiation dose of bone biopsies performed either under fluoroscopic guidance using a cone-beam CT with real-time 3D image fusion software (FP-CBCT-guidance) or under conventional computed tomography guidance (CT-guidance).MethodsSixty-eight consecutive patients with a bone lesion were prospectively included. The bone biopsies were scheduled under FP-CBCT-guidance or under CT-guidance according to operating room availability. Thirty-four patients underwent a bone biopsy under FP-CBCT and 34 under CT-guidance. We prospectively compared the two guidance modalities for their technical success, accuracy, puncture time, and pathological success rate. Patient and physician radiation doses also were compared.ResultsAll biopsies were technically successful, with both guidance modalities. Accuracy was significantly better using FP-CBCT-guidance (3 and 5 mm respectively: p = 0.003). There was no significant difference in puncture time (32 and 31 min respectively, p = 0.51) nor in pathological results (88 and 88 % of pathological success respectively, p = 1). Patient radiation doses were significantly lower with FP-CBCT (45 vs. 136 mSv, p < 0.0001). The percentage of operators who received a dose higher than 0.001 mSv (dosimeter detection dose threshold) was lower with FP-CBCT than CT-guidance (27 vs. 59 %, p = 0.01).ConclusionsFP-CBCT-guidance for bone biopsy is accurate and reduces patient and operator radiation doses compared with CT-guidance.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2017

Imaging of Vanadium in Microfossils: A New Potential Biosignature

Being able to distinguish unambiguously the biogenicity of microfossil-like structures in the ancient rock record is a fundamental predicament facing Archean paleobiologists and astrobiologists. Therefore, novel methods for discriminating biological from non-biological chemistries of microfossil-like structures are of the utmost importance in the search for evidence of early life on Earth. This too, is important for the search for life on Mars; either by in situ analyses via rovers, or sample return missions for future analysis here on Earth. Here, we report the application of synchrotron X-ray fluorescence imaging of vanadium, within thermally altered organic-walled microfossils of bona fide biological origin. From our data, we demonstrate that vanadium is present within microfossils of undisputable biological origin. It is well known in the organic geochemistry literature, that elements such as vanadium are enriched and contained within crude oils, asphalts, and black shales that have been formed by diagensis of biological organic material. It has been demonstrated that the origin of vanadium is due to the diagenetic alteration of precursor chlorophyll and heme porphyrin pigment compounds from living organisms. Here, we propose that taken together, microfossil-like morphology, carbonaceous composition, and the presence of vanadium could be used in tandem as a biosignature to ascertain the biogenecity of putative microfossil-like structures.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2018

Characterization of an M-Cluster-Substituted Nitrogenase VFe Protein

ABSTRACT The Mo- and V-nitrogenases are two homologous members of the nitrogenase family that are distinguished mainly by the presence of different heterometals (Mo or V) at their respective cofactor sites (M- or V-cluster). However, the V-nitrogenase is ~600-fold more active than its Mo counterpart in reducing CO to hydrocarbons at ambient conditions. Here, we expressed an M-cluster-containing, hybrid V-nitrogenase in Azotobacter vinelandii and compared it to its native, V-cluster-containing counterpart in order to assess the impact of protein scaffold and cofactor species on the differential reactivities of Mo- and V-nitrogenases toward CO. Housed in the VFe protein component of V-nitrogenase, the M-cluster displayed electron paramagnetic resonance (EPR) features similar to those of the V-cluster and demonstrated an ~100-fold increase in hydrocarbon formation activity from CO reduction, suggesting a significant impact of protein environment on the overall CO-reducing activity of nitrogenase. On the other hand, the M-cluster was still ~6-fold less active than the V-cluster in the same protein scaffold, and it retained its inability to form detectable amounts of methane from CO reduction, illustrating a fine-tuning effect of the cofactor properties on this nitrogenase-catalyzed reaction. Together, these results provided important insights into the two major determinants for the enzymatic activity of CO reduction while establishing a useful framework for further elucidation of the essential catalytic elements for the CO reactivity of nitrogenase. IMPORTANCE This is the first report on the in vivo generation and in vitro characterization of an M-cluster-containing V-nitrogenase hybrid. The “normalization” of the protein scaffold to that of the V-nitrogenase permits a direct comparison between the cofactor species of the Mo- and V-nitrogenases (M- and V-clusters) in CO reduction, whereas the discrepancy between the protein scaffolds of the Mo- and V-nitrogenases (MoFe and VFe proteins) housing the same cofactor (M-cluster) allows for an effective assessment of the impact of the protein environment on the CO reactivity of nitrogenase. The results of this study provide a first look into the “weighted” contributions of protein environment and cofactor properties to the overall activity of CO reduction; more importantly, they establish a useful platform for further investigation of the structural elements attributing to the CO-reducing activity of nitrogenase.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2024

Manganese and Vanadium Co-Exposure Induces Severe Neurotoxicity in the Olfactory System: Relevance to Metal-Induced Parkinsonism

Chronic environmental exposure to toxic heavy metals, which often occurs as a mixture through occupational and industrial sources, has been implicated in various neurological disorders, including Parkinsonism. Vanadium pentoxide (V 2 O 5 ) typically presents along with manganese (Mn), especially in welding rods and high-capacity batteries, including electric vehicle batteries; however, the neurotoxic effects of vanadium (V) and Mn co-exposure are largely unknown. In this study, we investigated the neurotoxic impact of MnCl 2 , V 2 O 5 , and MnCl 2 -V 2 O 5 co-exposure in an animal model. C57BL/6 mice were intranasally administered either de-ionized water (vehicle), MnCl 2 (252 µg) alone, V 2 O 5 (182 µg) alone, or a mixture of MnCl 2 (252 µg) and V 2 O 5 (182 µg) three times a week for up to one month. Following exposure, we performed behavioral, neurochemical, and histological studies. Our results revealed dramatic decreases in olfactory bulb (OB) weight and levels of tyrosine hydroxylase, dopamine, and 3,4-dihydroxyphenylacetic acid in the treatment groups compared to the control group, with the Mn/V co-treatment group producing the most significant changes. Interestingly, increased levels of α-synuclein expression were observed in the substantia nigra (SN) of treated animals. Additionally, treatment groups exhibited locomotor deficits and olfactory dysfunction, with the co-treatment group producing the most severe deficits. The treatment groups exhibited increased levels of the oxidative stress marker 4-hydroxynonenal in the striatum and SN, as well as the upregulation of the pro-apoptotic protein PKCδ and accumulation of glomerular astroglia in the OB. The co-exposure of animals to Mn/V resulted in higher levels of these metals compared to other treatment groups. Taken together, our results suggest that co-exposure to Mn/V can adversely affect the olfactory and nigral systems. These results highlight the possible role of environmental metal mixtures in the etiology of Parkinsonism.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2018

Respirable Uranyl-Vanadate-Containing Particulate Matter Derived From a Legacy Uranium Mine Site Exhibits Potentiated Cardiopulmonary Toxicity

Exposure to windblown particulate matter (PM) arising from legacy uranium (U) mine sites in the Navajo Nation may pose a human health hazard due to their potentially high metal content, including U and vanadium (V). To assess the toxic impact of PM derived from Claim 28 (a priority U mine) compared with background PM, and consider the putative role of metal species U and V. Two representative sediment samples from Navajo Nation sites (Background PM and Claim 28 PM) were obtained, characterized in terms of chemistry and morphology, and fractioned to the respirable (≤ 10 μm) fraction. Mice were dosed with either PM sample, uranyl acetate, or vanadyl sulfate via aspiration (100 µg), with assessments of pulmonary and vascular toxicity 24 h later. Particulate matter samples were also examined for in vitro effects on cytotoxicity, oxidative stress, phagocytosis, and inflammasome induction. Claim 28 PM 10 was highly enriched with U and V and exhibited a unique nanoparticle ultrastructure compared with background PM 10 . Claim 28 PM10 exhibited enhanced pulmonary and vascular toxicity relative to background PM 10 . Both U and V exhibited complementary pulmonary inflammatory potential, with U driving a classical inflammatory cytokine profile (elevated interleukin [IL]-1β, tumor necrosis factor-α, and keratinocyte chemoattractant/human growth-regulated oncogene) while V preferentially induced a different cytokine pattern (elevated IL-5, IL-6, and IL-10). Claim 28 PM 10 was more potent than background PM 10 in terms of in vitro cytotoxicity, impairment of phagocytosis, and oxidative stress responses. Resuspended PM 10 derived from U mine waste exhibit greater cardiopulmonary toxicity than background dusts. Finally, rigorous exposure assessment is needed to gauge the regional health risks imparted by these unremediated sites.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2020

Direct Measurement of Crossover and Interfacial Resistance of Ion-Exchange Membranes in All-Vanadium Redox Flow Batteries

Among various components commonly used in redox flow batteries (RFBs), the separator plays a significant role, influencing resistance to current as well as capacity decay via unintended crossover. It is well-established that the ohmic overpotential is dominated by the membrane and interfacial resistance in most aqueous RFBs. The ultimate goal of engineering membranes is to improve the ionic conductivity while keeping crossover at a minimum. One of the major issues yet to be addressed is the contribution of interfacial phenomena in the influence of ionic and water transport through the membrane. In this work, we have utilized a novel experimental system capable of measuring the ionic crossover in real-time to quantify the permeability of ionic species. Specifically, we have focused on quantifying the contributions from the interfacial resistance to ionic crossover. The trade-off between the mass and ionic transport impedance caused by the interface of the membranes has been addressed. The MacMullin number has been quantified for a series of electrolyte configurations and a correlation between the ionic conductivity of the contacting electrolyte and the Nafion® membrane has been established. The performance of individual ion-exchange membranes along with a stack of various separators have been explored. We have found that utilizing a stack of membranes is significantly beneficial in reducing the electroactive species crossover in redox flow batteries compared to a single membrane of the same fold thickness. For example, we have demonstrated that the utilization of five layers of Nafion ® 211 membrane reduces the crossover by 37% while only increasing the area-specific resistance (ASR) by 15% compared to a single layer Nafion ® 115 membrane. Therefore, the influence of interfacial impedance in reducing the vanadium ion crossover is substantially higher compared to a corresponding increase in ASR, indicating that mass and ohmic interfacial resistances are dissimilar. We have expanded our analysis to a combination of commercially available ion-exchange membranes and provided a design chart for membrane selection based on the application of interest (short duration/high-performance vs. long-term durability). The results of this study provide a deeper insight into the optimization of all-vanadium redox flow batteries (VRFBs).

UV/Vis spectroscopy↗
DOE OSTI2017

Molybdenum-Based Diazotrophy in a Sphagnum Peatland in Northern Minnesota

We present that Microbial N 2 fixation (diazotrophy) represents an important nitrogen source to oligotrophic peatland ecosystems, which are important sinks for atmospheric CO 2 and are susceptible to the changing climate. The objectives of this study were (i) to determine the active microbial group and type of nitrogenase mediating diazotrophy in an ombrotrophic Sphagnum-dominated peat bog (the S1 peat bog, Marcell Experimental Forest, Minnesota, USA); and (ii) to determine the effect of environmental parameters (light, O 2 , CO 2 , and CH 4 ) on potential rates of diazotrophy measured by acetylene (C 2 H 2 ) reduction and 15 N 2 incorporation. A molecular analysis of metabolically active microbial communities suggested that diazotrophy in surface peat was primarily mediated by Alphaproteobacteria ( 15 N 2 was suppressed 90% by O 2 and 55% by C 2 H 2 and was unaffected by CH 4 and CO 2 amendments. These results suggest that peatland diazotrophy is mediated by a combination of C 2 H 2 -sensitive and C 2 H 2 -insensitive microbes that are more active at low concentrations of O 2 and show similar activity at high and low concentrations of CH 4 . Importance: Previous studies indicate that diazotrophy provides an important nitrogen source and is linked to methanotrophy in Sphagnum-dominated peatlands. However, the environmental controls and enzymatic pathways of peatland diazotrophy, as well as the metabolically active microbial populations that catalyze this process, remain in question. In conclusion, our findings indicate that oxygen levels and photosynthetic activity override low nutrient availability in limiting diazotrophy and that members of the Alphaproteobacteria (Rhizobiales) catalyze this process at the bog surface using the molybdenum-based form of the nitrogenase enzyme.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

Temperature Dependence of Uranium and Vanadium Adsorption on Amidoxime-Based Adsorbents in Natural Seawater

Recent advances in the development of amidoxime-based adsorbents have made it highly promising for seawater uranium extraction. However, there is a great need to understand the influence of temperature on the uranium sequestration performance of the adsorbents in natural seawater. Here in this work, the apparent enthalpy and entropy of the sorption of uranium (VI) and vanadium (V) with amidoxime-based adsorbents were determined in natural seawater tests at 8, 20, and 31 °C that cover a broad range of ambient seawater temperature. The sorption of U was highly endothermic, producing apparent enthalpies of 57 ± 6.0 and 59 ± 11 kJ mol -1 and apparent entropies of 314 ± 21 and 320 ± 36 J K-1 mol -1 , respectively, for two adsorbent formulations. In contrast, the sorption of V showed a much smaller temperature sensitivity, producing apparent enthalpies of 6.1 ± 5.9 and -11 ± 5.7 kJ mol -1 and apparent entropies of 164 ± 20 and 103 ± 19 J K -1 mol -1 , respectively. This new thermodynamic information suggests that amidoxime-based adsorbents will deliver significantly increased U adsorption capacities and improved selectivity in warmer waters. A separate field study of seawater uranium adsorption conducted in a warm seawater site (Miami, FL, USA) confirm the observed strong temperature effect on seawater uranium mining. Lastly, this strong temperature dependence demonstrates that the warmer the seawater where the amidoxime-based adsorbents are deployed the greater the yield for seawater uranium extraction.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

Materials Data on DyCrTeO6 by Materials Project

DyCrTeO6 is beta Vanadium nitride-derived structured and crystallizes in the trigonal P-31c space group. The structure is three-dimensional. Dy3+ is bonded to six equivalent O2- atoms to form DyO6 octahedra that share corners with six equivalent CrO6 octahedra and edges with three equivalent TeO6 octahedra. The corner-sharing octahedral tilt angles are 59°. All Dy–O bond lengths are 2.26 Å. Cr5+ is bonded to six equivalent O2- atoms to form CrO6 octahedra that share corners with six equivalent DyO6 octahedra and corners with six equivalent TeO6 octahedra. The corner-sharing octahedra tilt angles range from 42–59°. All Cr–O bond lengths are 2.10 Å. Te4+ is bonded to six equivalent O2- atoms to form TeO6 octahedra that share corners with six equivalent CrO6 octahedra and edges with three equivalent DyO6 octahedra. The corner-sharing octahedral tilt angles are 42°. All Te–O bond lengths are 1.96 Å. O2- is bonded in a distorted trigonal planar geometry to one Dy3+, one Cr5+, and one Te4+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Materials Data on HoCrTeO6 by Materials Project

HoCrTeO6 is beta Vanadium nitride-derived structured and crystallizes in the trigonal P-31c space group. The structure is three-dimensional. Ho3+ is bonded to six equivalent O2- atoms to form HoO6 octahedra that share corners with six equivalent CrO6 octahedra and edges with three equivalent TeO6 octahedra. The corner-sharing octahedral tilt angles are 59°. All Ho–O bond lengths are 2.25 Å. Cr5+ is bonded to six equivalent O2- atoms to form CrO6 octahedra that share corners with six equivalent HoO6 octahedra and corners with six equivalent TeO6 octahedra. The corner-sharing octahedra tilt angles range from 42–59°. All Cr–O bond lengths are 2.10 Å. Te4+ is bonded to six equivalent O2- atoms to form TeO6 octahedra that share corners with six equivalent CrO6 octahedra and edges with three equivalent HoO6 octahedra. The corner-sharing octahedral tilt angles are 42°. All Te–O bond lengths are 1.97 Å. O2- is bonded in a distorted trigonal planar geometry to one Ho3+, one Cr5+, and one Te4+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on LiTiFeF6 by Materials Project

LiTiFeF6 is beta Vanadium nitride-derived structured and crystallizes in the trigonal P321 space group. The structure is three-dimensional. Li1+ is bonded to six F1- atoms to form LiF6 octahedra that share corners with two equivalent FeF6 octahedra, corners with six equivalent TiF6 octahedra, and edges with two equivalent FeF6 octahedra. The corner-sharing octahedra tilt angles range from 44–59°. There are a spread of Li–F bond distances ranging from 2.01–2.18 Å. Ti2+ is bonded to six F1- atoms to form TiF6 octahedra that share corners with four equivalent FeF6 octahedra, corners with six equivalent LiF6 octahedra, and an edgeedge with one FeF6 octahedra. The corner-sharing octahedra tilt angles range from 44–53°. There are a spread of Ti–F bond distances ranging from 1.96–2.04 Å. There are two inequivalent Fe3+ sites. In the first Fe3+ site, Fe3+ is bonded to six equivalent F1- atoms to form FeF6 octahedra that share corners with six equivalent LiF6 octahedra and edges with three equivalent TiF6 octahedra. The corner-sharing octahedral tilt angles are 59°. All Fe–F bond lengths are 2.10 Å. In the second Fe3+ site, Fe3+ is bonded to six F1- atoms to form FeF6 octahedra that share corners with six equivalent TiF6 octahedra and edges with three equivalent LiF6 octahedra. The corner-sharing octahedra tilt angles range from 47–53°. There are three shorter (2.08 Å) and three longer (2.11 Å) Fe–F bond lengths. There are three inequivalent F1- sites. In the first F1- site, F1- is bonded in a distorted trigonal planar geometry to one Li1+, one Ti2+, and one Fe3+ atom. In the second F1- site, F1- is bonded in a distorted trigonal planar geometry to one Li1+, one Ti2+, and one Fe3+ atom. In the third F1- site, F1- is bonded in a 3-coordinate geometry to one Li1+, one Ti2+, and one Fe3+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on LiTiCoF6 by Materials Project

LiTiCoF6 is beta Vanadium nitride-derived structured and crystallizes in the trigonal P321 space group. The structure is three-dimensional. Li1+ is bonded to six F1- atoms to form LiF6 octahedra that share corners with two equivalent CoF6 octahedra, corners with six equivalent TiF6 octahedra, and edges with two equivalent CoF6 octahedra. The corner-sharing octahedra tilt angles range from 40–59°. There are a spread of Li–F bond distances ranging from 1.99–2.17 Å. Ti4+ is bonded to six F1- atoms to form TiF6 octahedra that share corners with four equivalent CoF6 octahedra, corners with six equivalent LiF6 octahedra, and an edgeedge with one CoF6 octahedra. The corner-sharing octahedra tilt angles range from 40–50°. There is four shorter (1.93 Å) and two longer (1.97 Å) Ti–F bond length. There are two inequivalent Co1+ sites. In the first Co1+ site, Co1+ is bonded to six equivalent F1- atoms to form CoF6 octahedra that share corners with six equivalent LiF6 octahedra and edges with three equivalent TiF6 octahedra. The corner-sharing octahedral tilt angles are 59°. All Co–F bond lengths are 2.15 Å. In the second Co1+ site, Co1+ is bonded to six F1- atoms to form CoF6 octahedra that share corners with six equivalent TiF6 octahedra and edges with three equivalent LiF6 octahedra. The corner-sharing octahedra tilt angles range from 46–50°. All Co–F bond lengths are 2.12 Å. There are three inequivalent F1- sites. In the first F1- site, F1- is bonded in a 3-coordinate geometry to one Li1+, one Ti4+, and one Co1+ atom. In the second F1- site, F1- is bonded in a distorted trigonal planar geometry to one Li1+, one Ti4+, and one Co1+ atom. In the third F1- site, F1- is bonded in a 3-coordinate geometry to one Li1+, one Ti4+, and one Co1+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Fe10O9F11 by Materials Project

Fe10O9F11 is beta Vanadium nitride-derived structured and crystallizes in the monoclinic Pm space group. The structure is three-dimensional. there are six inequivalent Fe+2.90+ sites. In the first Fe+2.90+ site, Fe+2.90+ is bonded to two O2- and four F1- atoms to form FeO2F4 octahedra that share corners with eight FeO4F2 octahedra and edges with two FeO2F4 octahedra. The corner-sharing octahedra tilt angles range from 43–59°. There is one shorter (1.97 Å) and one longer (1.98 Å) Fe–O bond length. There are two shorter (2.06 Å) and two longer (2.15 Å) Fe–F bond lengths. In the second Fe+2.90+ site, Fe+2.90+ is bonded to two O2- and four F1- atoms to form FeO2F4 octahedra that share corners with eight FeO3F3 octahedra and edges with two FeO2F4 octahedra. The corner-sharing octahedra tilt angles range from 40–54°. There is one shorter (1.89 Å) and one longer (1.94 Å) Fe–O bond length. There are a spread of Fe–F bond distances ranging from 2.02–2.12 Å. In the third Fe+2.90+ site, Fe+2.90+ is bonded to three O2- and three F1- atoms to form FeO3F3 octahedra that share corners with eight equivalent FeO3F3 octahedra and edges with two equivalent FeO2F4 octahedra. The corner-sharing octahedra tilt angles range from 45–54°. There is one shorter (1.91 Å) and two longer (1.95 Å) Fe–O bond length. All Fe–F bond lengths are 2.14 Å. In the fourth Fe+2.90+ site, Fe+2.90+ is bonded to four O2- and two F1- atoms to form FeO4F2 octahedra that share corners with eight equivalent FeO2F4 octahedra and edges with two equivalent FeO3F3 octahedra. The corner-sharing octahedra tilt angles range from 46–52°. All Fe–O bond lengths are 2.02 Å. There are one shorter (2.06 Å) and one longer (2.07 Å) Fe–F bond lengths. In the fifth Fe+2.90+ site, Fe+2.90+ is bonded to three O2- and three F1- atoms to form FeO3F3 octahedra that share corners with eight FeO2F4 octahedra and edges with two FeO3F3 octahedra. The corner-sharing octahedra tilt angles range from 45–54°. There are a spread of Fe–O bond distances ranging from 1.94–1.96 Å. There are a spread of Fe–F bond distances ranging from 2.05–2.37 Å. In the sixth Fe+2.90+ site, Fe+2.90+ is bonded to three O2- and three F1- atoms to form FeO3F3 octahedra that share corners with eight FeO2F4 octahedra and edges with two FeO4F2 octahedra. The corner-sharing octahedra tilt angles range from 40–59°. There are a spread of Fe–O bond distances ranging from 1.89–2.02 Å. There are a spread of Fe–F bond distances ranging from 2.14–2.23 Å. There are five inequivalent O2- sites. In the first O2- site, O2- is bonded in a distorted trigonal planar geometry to three Fe+2.90+ atoms. In the second O2- site, O2- is bonded in a 3-coordinate geometry to three Fe+2.90+ atoms. In the third O2- site, O2- is bonded in a trigonal planar geometry to three Fe+2.90+ atoms. In the fourth O2- site, O2- is bonded in a distorted trigonal planar geometry to three Fe+2.90+ atoms. In the fifth O2- site, O2- is bonded in a trigonal planar geometry to three Fe+2.90+ atoms. There are seven inequivalent F1- sites. In the first F1- site, F1- is bonded in a distorted T-shaped geometry to three Fe+2.90+ atoms. In the second F1- site, F1- is bonded in a distorted trigonal planar geometry to three Fe+2.90+ atoms. In the third F1- site, F1- is bonded in a 3-coordinate geometry to three Fe+2.90+ atoms. In the fourth F1- site, F1- is bonded in a 3-coordinate geometry to three Fe+2.90+ atoms. In the fifth F1- site, F1- is bonded in a 3-coordinate geometry to three Fe+2.90+ atoms. In the sixth F1- site, F1- is bonded in a 3-coordinate geometry to three Fe+2.90+ atoms. In the seventh F1- site, F1- is bonded in a distorted trigonal planar geometry to three Fe+2.90+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Electrochemical Characterization of Isolated Nitrogenase Cofactors from Azotobacter vinelandii

The nitrogenase cofactors are structurally and functionally unique in biological chemistry. Despite a substantial amount of spectroscopic characterization of protein-bound and isolated nitrogenase cofactors, electrochemical characterization of these cofactors and their related species is far from complete. Herein we present voltammetric studies of three isolated nitrogenase cofactor species: the iron–molybdenum cofactor (M-cluster), iron–vanadium cofactor (V-cluster), and a homologue to the iron–iron cofactor (L-cluster). We observe two reductive events in the redox profiles of all three cofactors. Of the three, the V-cluster is the most reducing. The reduction potentials of the isolated cofactors are significantly more negative than previously measured values within the molybdenum–iron and vanadium–iron proteins. Finally, the outcome of this study provides insight into the importance of the heterometal identity, the overall ligation of the cluster, and the impact of the protein scaffolds on the overall electronic structures of the cofactors.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2016

Micro-differential scanning calorimeter for liquid biological samples

Here, we developed an ultrasensitive micro-DSC (differential scanning calorimeter) for liquid protein sample characterization. Our design integrated vanadium oxide thermistors and flexible polymer substrates with microfluidics chambers to achieve a high sensitivity (6 V/W), low thermal conductivity (0.7 mW/K), high power resolutions (40 nW), and well-defined liquid volume (1 μl) calorimeter sensor in a compact and cost-effective way. Furthermore, we demonstrated the performance of the sensor with lysozyme unfolding. The measured transition temperature and enthalpy change were in accordance with the previous literature data. This micro-DSC could potentially raise the prospect of high-throughput biochemical measurement by parallel operation with miniaturized sample consumption.

42 ENGINEERING↗
DOE OSTI2016

The in vivo hydrocarbon formation by vanadium nitrogenase follows a secondary metabolic pathway

The vanadium (V)-nitrogenase of Azotobacter vinelandii catalyses the in vitro conversion of carbon monoxide (CO) to hydrocarbons. Here we show that an A. vinelandii strain expressing the V-nitrogenase is capable of in vivo reduction of CO to ethylene (C 2 H 4 ), ethane (C 2 H 6 ) and propane (C 3 H 8 ). Moreover, we demonstrate that CO is not used as a carbon source for cell growth, being instead reduced to hydrocarbons in a secondary metabolic pathway. These findings suggest a possible role of the ancient nitrogenase as an evolutionary link between the carbon and nitrogen cycles on Earth and establish a solid foundation for biotechnological adaptation of a whole-cell approach to recycling carbon wastes into hydrocarbon products. Furthermore, this study has several repercussions for evolution-, environment- and energy-related areas.

59 BASIC BIOLOGICAL SCIENCES↗