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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.

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At least 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2016

A new family of metal borohydride guanidinate complexes: Synthesis, structures and hydrogen-storage properties

We report on a new class of complex hydrides: borohydride guanidinate complexes (MBH{sub 4}·nCN{sub 3}H{sub 5}, M=Li, Mg, and Ca). They can be prepared via facile solid-state synthesis routes. Their crystal structures were successfully determined using a combination of X-ray diffraction, first-principles calculations and neutron vibrational spectroscopy. Among these compounds, Mg(BH{sub 4}){sub 2}·6CN{sub 3}H{sub 5} is composed of large complex Mg[CN{sub 3}H{sub 5}]{sub 6}{sup 2+} cations and surrounding BH{sub 4}{sup -} ions, while Ca(BH{sub 4}){sub 2}·2CN{sub 3}H{sub 5} possesses layers of corner-sharing Ca[BH{sub 4}]{sub 4}(CN{sub 3}H{sub 5}){sub 2} octahedra. Our dehydrogenation results show that ≈10 wt% hydrogen can be released from MBH{sub 4}·nCN{sub 3}H{sub 5} (M=Li, Mg, and Ca) at moderate temperatures with minimal ammonia and diborane contamination thanks to the synergistic effect of C-N bonds from guanidine and hydridic H from borohydrides leading to a weakening of the N-H bonds, thus impeding ammonia gas liberation. Further tuning the dehydrogenation with different cation species indicates that Mg(BH{sub 4}){sub 2}·nCN{sub 3}H{sub 5} can exhibit the optimum properties with nearly thermally neutral dehydrogenation and very high purity hydrogen release. - Graphical abstract: A new family of complex hydrides: borohydride guanidinates, was developed with diverse crystal structures and remarkable hydrogen storage properties. - Highlights: • A new family of complex hydrides, borohydride guanidinate complexes, are synthesized. • Their diverse crystal structures are determined using combined characterizations. • These compounds can release ~10 wt% pure H{sub 2} at moderate temperatures. • Dehydrogenation thermodynamics and H{sub 2} purity can be tuned by varying cation species.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2014

A comparative study on the aggregating effects of guanidine thiocyanate, guanidine hydrochloride and urea on lysozyme aggregation

Highlights: • Lysozyme aggregated in guanidine thiocyanate (1.0 and 2.0 M). • Lysozyme aggregated in guanidine hydrochloride (4 and 5 M). • Lysozyme did not aggregated at any concentration (0.5–5 M) of urea. • Unfolding pathway is more important than unfolding per se in aggregation. - Abstract: Protein aggregation and its subsequent deposition in different tissues culminate in a diverse range of diseases collectively known as amyloidoses. Aggregation of hen or human lysozyme depends on certain conditions, namely acidic pH or the presence of additives. In the present study, the effects on the aggregation of hen egg-white lysozyme via incubation in concentrated solutions of three different chaotropic agents namely guanidine thiocyanate, guanidine hydrochloride and urea were investigated. Here we used three different methods for the detection of the aggregates, thioflavin T fluorescence, circular dichroism spectroscopy and atomic force microscopy. Our results showed that upon incubation with different concentrations (0.5, 1.0, 2.0, 3.0, 4.0, 5.0 M) of the chemical denaturants, lysozyme was aggregated at low concentrations of guanidine thiocyanate (1.0 and 2.0 M) and at high concentrations of guanidine hydrochloride (4 and 5 M), although no fibril formation was detected. In the case of urea, no aggregation was observed at any concentration.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2014

Guanidine and guanidinium cation in the excited state—theoretical investigation

Diverse ab initio and density-functional-theory methods were used to investigate geometries, energies, and electronic absorption spectra of guanidine and its protonated form, as well as their photo-deactivation processes. It was shown that the guanidine is a weakly absorbing species with the excitation spectrum consisting mostly of transitions to the Rydberg excited states and one valence n-π{sub 4} state. The lowest energy band has a maximum at ca. 6.9 eV (∼180 nm). The protonation of guanidine affects its excitation spectrum substantially. A major shift of the Rydberg states to higher energies is clearly visible and strongly absorbing transitions from the ground state to the π{sub 3}-π{sub 4} and π{sub 2}-π{sub 4} states appears at 7.8 eV (∼160 nm). Three low-lying conical intersections (two for guanidine and one for protonated guanidine) between the ground state and the first excited singlet state were located. They are accessible from the Franck–Condon region through amino N–H stretching and out-of-plane deformations in guanidine and protonated guanidine, respectively. The relaxation of the π{sub 3}-3s Rydberg state via amino N–H bond stretching was hindered by a barrier. The nondissociated conical intersection in protonated guanidine mediates the radiationless deactivation of the compound after excitation into the π{sub 3}-π{sub 4} state. This fact is detrimental for the photostability of guanidine, since its conjugate acid is stable in aqueous solution over a wide pH range and in protein environment, where guanidinium moiety in arginine is expected to be in a protonated form.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2017

Structural basis for ligand binding to the guanidine-II riboswitch

The guanidine-II riboswitch, also known as mini-ykkC, is a conserved mRNA element with more than 800 examples in bacteria. It consists of two stem–loops capped by identical, conserved tetraloops that are separated by a linker region of variable length and sequence. Like the guanidine-I riboswitch, it controls the expression of guanidine carboxylases and SugE-like genes. The guanidine-II riboswitch specifically binds free guanidinium cations and functions as a translationally controlled on-switch. Here we report the structure of a P2 stem–loop from the Pseudomonas aeruginosa guanidine-II riboswitch aptamer bound to guanidine at 1.57 Å resolution. The hairpins dimerize via the conserved tetraloop, which also contains the binding pocket. Two guanidinium molecules bind near the dimerization interface, one in each tetraloop. The guanidinium cation is engaged in extensive hydrogen bonding to the RNA. Contacts include the Hoogsteen face of a guanine base and three nonbridging phosphate oxygens. Cation–π interactions and ionic interactions also stabilize ligand binding. Finally, the guanidine-II riboswitch utilizes the same recognition strategies as the guanidine-I riboswitch while adopting an entirely different and much smaller RNA fold.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2013

Recommended Guanidine Suppressor for the Next-Generation Caustic-Side Solvent Extraction Process

The guanidine recommended for the Next-Generation Caustic-Side is N,N',N'-tris(3,7-dimethyloctyl)guanidine (TiDG). Systematic testing has shown that it is significantly more lipophilic than the previously recommended guanidine DCiTG, the active extractant in the commercial guanidine product LIX -79, while not otherwise changing the solvent performance. Previous testing indicated that the extent of partitioning of the DCiTG suppressor to the aqueous strip solution is significantly greater than expected, potentially leading to rapid depletion of the suppressor from the solvent and unwanted organic concentrations in process effluents. Five candidate guanidines were tested as potential replacements for DCiTG. The tests included batch extraction with simulated waste and flowsheet solutions, third-phase formation, emulsion formation, and partition ratios of the guanidine between the solvent and aqueous strip solution. Preliminary results of a thermal stability test of the TiDG solvent at one month duration indicated performance approximately equivalent to DCiTG. Two of the guanidines proved adequate in all respects, and the choice of TiDG was deemed slightly preferable vs the next best guanidine BiTABG.

cesium↗
DOE OSTI2026

Cyanobacterial Biofertilizer Production by Guanidine-Producing Enzymes

Cyanobacterial production of a biofertilizer shows promise as an environmentally benign alternative to conventional nitrogen fertilizers, reducing environmental and energy burdens through light-driven nitrogen and carbon fixation. One route to realizing the potential for a nitrogen-rich, slow-releasing biofertilizer involves the genetic engineering of cyanobacteria to produce guanidine. Recent advances have demonstrated enzymatic guanidine production in cyanobacteria, but an understanding of cyanobacterial guanidine metabolism is still limited. This Perspective highlights strategies and opportunities for cyanobacterial guanidine production in a Design−Build−Test−Learn cycle. Exploring new guanidine-producing enzymes via phylogenetics could expand candidate enzymes, while understanding the metabolism of substrates can identify constraints and opportunities in substrate utilization. Additionally, guanidine sensing and export are crucial areas of study to enable continuous fertilizer production and stable nitrogen flux. These strategies will guide the development of advanced nitrogen biofertilizer strategies for the agricultural sector.

09 BIOMASS FUELS↗
DOE OSTI2021

A Guanidine-Degrading Enzyme Controls Genomic Stability of Ethylene-Producing Cyanobacteria

Recent studies have revealed the prevalence and biological significance of guanidine metabolism in nature. However, the metabolic pathways used by microbes to degrade guanidine or mitigate its toxicity have not been widely studied. Here, via comparative proteomics and subsequent experimental validation, we demonstrate that Sll1077, previously annotated as an agmatinase enzyme in the model cyanobacterium Synechocystis sp. PCC 6803, is more likely a guanidinase as it can break down guanidine rather than agmatine into urea and ammonium. The model cyanobacterium Synechococcus elongatus PCC 7942 strain engineered to express the bacterial ethylene-forming enzyme (EFE) exhibits unstable ethylene production due to toxicity and genomic instability induced by accumulation of the EFE-byproduct guanidine. Co-expression of EFE and Sll1077 significantly enhances genomic stability and enables the resulting strain to achieve sustained high-level ethylene production. These findings expand our knowledge of natural guanidine degradation pathways and demonstrate their biotechnological application to support ethylene bioproduction.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2017

Structural basis for guanidine sensing by the ykkC family of riboswitches

Regulation of gene expression by cis-encoded riboswitches is a prevalent theme in bacteria. Of the hundreds of riboswitch families identified, the majority of them remain as orphans, without a clear ligand assignment. The ykkC orphan family was recently characterized as guanidine-sensing riboswitches. In this work, we present a 2.3 Å crystal structure of the guanidine-bound ykkC riboswitch from Dickeya dadantii. The riboswitch folds into a boot-shaped structure, with a coaxially stacked P1/P2 stem forming the boot, and a 3'-P3 stem–loop forming the heel. Sophisticated base-pairing and cross-helix tertiary contacts give rise to the ligand-binding pocket between the boot and the heel. The guanidine is recognized in its positively charged guanidinium form, in its sp 2 hybridization state, through a network of coplanar hydrogen bonds and by a cation–π stacking contact on top of a conserved guanosine residue. Disruption of these contacts resulted in severe guanidinium-binding defects. These results provide the structural basis for specific guanidine sensing by ykkC riboswitches and pave the way for a deeper understanding of guanidine detoxification—a previously unappreciated aspect of bacterial physiology.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2021

A Process Intensification Approach for CO 2 Absorption Using Amino Acid Solutions and a Guanidine Compound

Environmentally friendly amino-acid salt solutions are used for the absorption of carbon dioxide from concentrated flue-gas streams via chemical absorption. Process intensification reduces operating and capital costs by combining chemical reactions and separation operations. Here, we present a new process-intensification approach that combines the CO 2 capture and the amino-acid regeneration steps into a single process carried out in a slurry three-phase reactor. The absorbed CO 2 precipitates as a solid carbonated guanidine compound. The cycle is completed by separation of the solid precipitate to strip the CO 2 and regenerate the guanidine compound, while the liquid solution is recycled to the slurry reactor. The process was studied by modifying a model developed by the authors for a gas-liquid bubble column without the presence of the guanidine compound. The guanidine precipitation reaction was accounted for using kinetic parameters calculated by the authors in another study. The proposed model was implemented by modifying an existing computer code used for the simulation of gas-liquid bubble columns. The calculated results showed that the proposed cycle can significantly reduce energy, equipment, and operating costs and can make an important contribution to developing a competitive cost-effective large-scale process for CO 2 capture.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Impacts of Guanidine Degradation Products on Next Generation Solvent (NGS) Caustic Side Solvent Extraction (CSSX) Processing

Savannah River National Laboratory researchers have been requested to perform testing to assess the potential for build-up of guanidine degradation compounds in the Next Generation Solvent Caustic Side Solvent Extraction process. Testing was also requested to determine the impact of guanidine degradation compounds [3,7-dimethyloctylamine (iDA) and Bis-N,N’-(3,7-dimethyloctyl)urea (DiDU)] on cesium behavior in the flowsheet. Twelve partitioning experiments were performed to quantify the partitioning coefficient of identified guanidine degradation compounds in various organic-aqueous mixtures. Six Extraction, Scrub, and Strip (ESS) experiments were performed to quantify the impact of degradation products on cesium behavior.

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

Guanidine Riboswitch-Regulated Efflux Transporters Protect Bacteria against Ionic Liquid Toxicity

Plant cell walls contain a renewable, nearly limitless supply of sugar that could be used to support microbial production of commodity chemicals and biofuels. Imidazolium ionic liquid (IIL) solvents are among the best reagents for gaining access to the sugars in this otherwise recalcitrant biomass. However, the sugars from IIL-treated biomass are inevitably contaminated with residual IILs that inhibit growth in bacteria and yeast, blocking biochemical production by these organisms. IIL toxicity is, therefore, a critical roadblock in many industrial biosynthetic pathways. Although several IIL-tolerant (IIL T ) bacterial and yeast isolates have been identified in nature, few genetic mechanisms have been identified. In this study, we identified two IIL T Bacillus isolates as well as a spontaneous IIL T Escherichia coli lab strain that are tolerant to high levels of two widely used IILs. We demonstrate that all three IIL T strains contain one or more pumps of the small multidrug resistance (SMR) family, and two of these strains contain mutations that affect an adjacent regulatory guanidine riboswitch. Furthermore, we show that the regulation of E. coli sugE by the guanidine II riboswitch can be exploited to promote IIL tolerance by the simple addition of guanidine to the medium. Our results demonstrate the critical role that transporter genes play in IIL tolerance in their native bacterial hosts. The study presented here is another step in engineering IIL tolerance into industrial strains toward overcoming this key gap in biofuels and industrial biochemical production processes.

09 BIOMASS FUELS↗
DOE OSTI2016

CO 2 Capture from Ambient Air by Crystallization with a Guanidine Sorbent

Carbon capture and storage is an important strategy for stabilizing the increasing concentration of atmospheric CO 2 and the global temperature. A possible approach toward reversing this trend and decreasing the atmospheric CO 2 concentration is to remove the CO 2 directly from air (direct air capture). In this paper, we report a simple aqueous guanidine sorbent that captures CO 2 from ambient air and binds it as a crystalline carbonate salt by guanidinium hydrogen bonding. The resulting solid has very low aqueous solubility (K sp =1.0(4)×10 -8 ), which facilitates its separation from solution by filtration. The bound CO 2 can be released by relatively mild heating of the crystals at 80–120 °C, which regenerates the guanidine sorbent quantitatively. Finally and thus, this crystallization-based approach to CO 2 separation from air requires minimal energy and chemical input, and offers the prospect for low-cost direct air capture technologies.

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

Thermal stability study of a new guanidine suppressor for the next-generation caustic-side solvent extraction process

Cesium stripping performance of thermally stressed solvent degrades slowly over time in batch tests of the Next Generation Caustic-Side Solvent Extraction (NGS) process. NGS is currently used at pilot scale at the Savannah River Site for the selective removal of cesium from high-level salt waste. Recently a new guanidine, N,N',N" -tris(3,7-dimethyloctyl)guanidine (TiDG), was chosen for use as the suppressor, a lipophilic organic base needed for stripping, and the present study was undertaken to address the question of its stability. The NGS process solvent was evaluated for a period of three months under a variety of temperature and storage conditions. The performance of the solvent was tested at 30-day increments using a standard extraction, scrub, strip, and extraction (ES 2 S 3 E) sequence. Lastly, the results provide insight on the effects of storage and process conditions, the stripping behavior of TiDG, and the stability of the new solvent composition.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2013

Assessment of the Impact of a New Guanidine Suppressor In NGS on F/H Laboratory Analyses For DWPF and Saltstone MCU Transfers

Implementation of the Next Generation Solvent (NGS) in the Modular Caustic-Side Solvent Extraction Unit (MCU) will now proceed with a new suppressor compound, 1,2,3-tris(3,7-dimethyloctyl)guanidine (TiDG), replacing the originally planned suppressor for NGS, 1,3-dicyclohexyl-2-(11-methyldodecyl) guanidine (DCiTG). The Savannah River National Laboratory (SRNL) was tasked with evaluating the potential impact to F/H Laboratory analyses supporting the Defense Waste Processing Facility (DWPF) Waste Acceptance Criteria (WAC) used to qualify transfers of MCU Strip Effluent (SE) into the facility and the Saltstone WAC used to qualify transfers of Tank 50 containing Decontaminated Salt Solution (DSS) from MCU into Saltstone. This assigned scope is covered by a Task Technical and Quality Assurance Plan (TTQAP). Previous impact evaluations were conducted when the DCiTG suppressor was planned for NGS and concluded that there was no impact to either the determination of MCU SE pH nor the analysis of Isopar ® L carryover in the MCU SE and DSS streams. SRNL reported on this series of cross-check studies between the SRNL and F/H Laboratories. The change in suppressor from DCiTG to TiDG in the NGS should not impact the measurement of Isopar ® L or pH in SE or DSS necessary to satisfy DWPF and Saltstone WAC (Tank 50) criteria, respectively. A statistical study of the low bias observed in Isopar ® L measurements in both SRNL and F/H Laboratories may be necessary now that the final NGS composition is fixed in order to quantify the low bias so that a proper correction can be applied to measurements critical to the DWPF and Saltstone WACs. Depending upon the final DWPF WAC requirement put in place for SE pH, it could become necessary to implement an alternative ICP-AES measurement of boron. The current blended solvent system testing in SRNL should address any impacts to Isopar ® L carryover into either the DSS or the SE. It is recommended that SRNL monitor the current blended solvent work underway with simulants in SRNL as well as any DWPF CPC testing done with the new SE stream to ascertain whether any need develops that could result in modification of any currently planned F/H Laboratory testing protocols.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2019

Carbon Capture via Crystallization with a Guanidine Ligand

Carbon capture and storage (CCS) is an important strategy aimed at stabilizing the atmospheric CO2 concentration and thereby the global temperature. In conventional fossil fuel-fired power plants, the resulting flue gas is released into the air without any carbon dioxide scrubbing, which gradually increases the atmospheric CO 2 concentration (currently at approximately 409 ppm). Implementation of post-combustion capture (PCC) of carbon dioxide, whereby the CO 2 emitted by power plants is captured and stored into geological repositories, would enable us to continue to use relatively cheap fossil fuels such as coal, natural gas, and oil, but with significantly reduced CO 2 emissions. A recent report by the International Energy Agency indicated that by 2050 CCS could reduce the annual CO 2 emissions by almost 6 gigatones, which represents about 14% of the total carbon emission reduction necessary to limit the global temperature increase by 2 ºC by the end of the 21st century (International Energy Agency, 2016). This goal will be accomplished by developing inexpensive materials that can be used to effectively capture CO 2 and be regenerated with minimal energy penalty. This project helped address this need by introducing new materials and mechanisms for CO 2 capture. The goal of this project was to demonstrate a bench-scale CO 2 capture process based on a novel guanidinium (bi)carbonate crystallization approach, and ultimately develop an energy-efficient and cost-effective technology for CO 2 capture from flue gas. The project built on our recent discovery of a new class of aqueous guanidine sorbents that react with carbon dioxide and crystallize as carbonate or bicarbonate salts of very low aqueous solubility (Brethomé, 2018; Williams, 2019). The resulting guanidinium (bi)carbonate crystals release the CO 2 upon mild heating at 80-120 ºC, which regenerates the guanidine ligands quantitatively (Figure 1). The potential advantage of this crystallization-based approach over traditional amine scrubbing methods (i.e., using aqueous MEA) is that it allows sorbent regeneration by heating the solid crystals alone, without the bulk solution, making this process more energy-efficient.

20 FOSSIL-FUELED POWER PLANTS↗
DOE OSTI2018

Antimicrobial Activity of Polyhexamethylene Guanidine Derivatives Introduced into Polycaprolactone

The research was aimed at determining the abundance of biofilm formation by Escherichia coli and Staphylococcus aureus on the surface of polycaprolactone (PCL) with polyhexamethylene guanidine (PHMG) derivatives and effect of the derivatives on extracellular hydrolytic enzymes and intracellular dehydrogenases. Biofilm abundance was determined by spectrophotometry, using crystal violet staining. Hydrolytic enzymes after contact with the film were determined with the use of non-specific substrate—fluorscein diacetate. The effect of PHMG derivatives on dehydrogenases activity was assessed using the test, where triphenyltetrazolium chloride (TTC) is reduced to triphenylformazan (TF). The PCL containing PHMG granular polyethylene wax and salt of sulfanilic acid (0.6–1% wt.) strongest inhibited biofilm formation. PHMG derivatives introduced into PCL were found to slightly affect hydrolases activity in both E. coli and S. aureus at a concentration of 0.2 and 0.6%. It was also found that dehydrogenases activity was inhibited by PCL films containing PHMG derivatives. PCL containing 1% of PHMG sulfanilate strongest inhibited hydrolases activity, whereas PCL modified with 1% of PHMG granular polyethylene wax showed the highest inhibitory effect on the activity of both enzymes. W-PCL and A-PCL composites (at concentration of 0.6%) have optimal combination of antibiofilm activity and biodegradability.

60 APPLIED LIFE SCIENCES↗