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Results for “substrate selection”

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 433 records · Page 24
All sourcesNASA NTRSDOE OSTI
DOE OSTI2019

Photo-generated reactive oxygen species assisted tandem amine homocoupling and amine-alcohol cross-coupling reaction on mesoporous spinel cobalt oxide

Mesoporous spinel cobalt oxide (Co 3 O 4 ) with fine-tuned pore size distributions (9.6–17.6 nm) and different surface areas (33–85 m 2 /g) were synthesized using a series of nonionic surfactants. A direct influence of the chemical composition of the surfactants and calcination temperature on crystallite size, morphology, pore size/volume, surface area, valance band edge, and Co 2+ /Co 3+ ratio was recognized. Correlation between the aforementioned factors, transition metal ion incorporation and benzylamine homocoupling reaction was discussed. Shape-specific binding of amine on the cobalt oxide active sites was proposed based on substrate scope study. Tandem synthesis strategy to selectively synthesize amine (aliphatic/aromatic) homo-coupled imines and amine-alcohol cross-coupled imines was introduced. Low-intensity light-induced singlet oxygen and hydroxyl radical-mediated reaction mechanism was proposed based on the EPR, XPS, photoreactor, and reactive oxygen species scavenger tests. Selective and switchable synthesis of homo-coupled (yield 85%) and cross-coupled (yield 87%) products was achieved with sodium azide and mannitol additives.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2025

Predicting receptor-ligand pairing preferences in plant-microbe interfaces via molecular dynamics and machine learning

Microbiome assembly, structure, and dynamics significantly influence plant health. Secreted microbial signaling molecules initiate and mediate symbiosis by binding to structurally compatible plant receptors. For example, lipo-chitooligosaccharides (LCOs), produced by nitrogen-fixing rhizobial bacteria and various fungi, are recognized by plant lysin motif receptor-like kinases (LysM-RLKs), which activate the common symbiotic pathway. Accurately predicting these molecular interactions could reveal complementary signatures underlying the initial stages of endosymbiosis. Despite the breakthrough in protein-ligand structure prediction with deep learning-based tools, such as AlphaFold3, the large size and highly flexible nature of signaling compounds like LCOs present major challenges for detailed structural characterization and binding-affinity prediction. Typical structure-/physics-based methods of ligand virtual screening are designed for small, drug-like molecules, often rely on high-resolution, experimentally determined structures of the protein receptors, and rarely achieve sufficient sampling to obtain converged thermodynamic quantities with large ligands. In this study, we developed a hybrid molecular dynamics/machine learning (MD/ML) approach capable of predicting binding affinity rankings with high accuracy in systems involving large, flexible ligands, despite limited experimental structural information. Using coarse initial structural models, the predictions using the MD/ML workflow achieved strong alignment with experimental trends, particularly in the top-affinity tier for four legume LysM-RLKs (LYR3) binding to LCOs and a chitooligosaccharide. Furthermore, the MD-based conformation selection protocol provided critical structural insights into substrate specificity and binding mechanisms. This study demonstrates a powerful method to screen for challenging cognate ligand-receptors and advance our understanding of the molecular basis of microbial colonization in plants.

Lipo-chitooligosaccharides↗
DOE OSTI2022

Markovnikov alcohols via epoxide hydroboration by molecular alkali metal catalysts

Synthesis of branched “Markovnikov” alcohols is crucial to various chemical industries. The catalytic reduction of substituted epoxides under mild conditions is a highly attractive method for preparing such alcohols. Classical methods based on heterogeneous or homogeneous transition metal-catalyzed hydrogenation, hydroboration, or hydrosilylation usually suffer from poor selectivity, reverse regioselectivity, limited functional group compatibility, high cost, and/or low availability of the catalysts. Here we report the discovery of highly regioselective hydroboration of nonsymmetrical epoxides catalyzed by ligated archetypal reductants in organic chemistry – alkali metal triethylborohydrides. The chemoselectivity and turnover efficiencies of the present catalytic approach are excellent. Thus, terminal and internal epoxides with ene, yne, aryl, and halo groups were selectively and quantitatively reduced under a substrate-to-catalyst ratio (S/C) of up to 1000. Mechanistic investigations point to a mechanism reminiscent of frustrated Lewis pair action on substrates in which a nucleophile and Lewis acid act cooperatively on the substrate.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Structural evolution of a DNA repair self-resistance mechanism targeting genotoxic secondary metabolites

Abstract Microbes produce a broad spectrum of antibiotic natural products, including many DNA-damaging genotoxins. Among the most potent of these are DNA alkylating agents in the spirocyclopropylcyclohexadienone (SCPCHD) family, which includes the duocarmycins, CC-1065, gilvusmycin, and yatakemycin. The yatakemycin biosynthesis cluster in Streptomyces sp. TP-A0356 contains an AlkD-related DNA glycosylase, YtkR2, that serves as a self-resistance mechanism against yatakemycin toxicity. We previously reported that AlkD, which is not present in an SCPCHD producer, provides only limited resistance against yatakemycin. We now show that YtkR2 and C10R5, a previously uncharacterized homolog found in the CC-1065 biosynthetic gene cluster of Streptomyces zelensis , confer far greater resistance against their respective SCPCHD natural products. We identify a structural basis for substrate specificity across gene clusters and show a correlation between in vivo resistance and in vitro enzymatic activity indicating that reduced product affinity—not enhanced substrate recognition—is the evolutionary outcome of selective pressure to provide self-resistance against yatakemycin and CC-1065.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2021

Tunable, Bacterio-Instructive Scaffolds Made from Functional Graphenic Materials

The balance of bacterial populations in the human body is critical for human health. Researchers have aimed to control bacterial populations using antibiotic substrates. However, antibiotic materials that non-selectively kill bacteria can compromise health by eliminating beneficial bacteria, which leaves the body vulnerable to colonization by harmful pathogens. Due to their chemical tunablity and unique surface properties, graphene oxide (GO)-based materials – termed “functional graphenic materials” (FGMs) – have been previously designed to be antibacterial but have the capacity to actively adhere and instruct probiotics to maintain human health. Numerous studies have demonstrated that negatively and positively charged surfaces influence bacterial adhesion through electrostatic interactions with the negatively charged bacterial surface. We found that tuning the surface charge of FGMs provides an avenue to control bacterial attachment without compromising vitality. Using E. coli as a model organism for gram-negative bacteria, we demonstrate that negatively charged Claisen graphene (CG), a reduced and carboxylated FGM, is bacterio-repellent through electrostatic repulsion with the bacterial surface. Though positively charged poly-L-lysine (PLL) is antibacterial when free in solution by inserting into the bacterial cell wall, here, we found that covalent conjugation of PLL to CG (giving PLLn-G) masks the antimicrobial activity of PLL by restricting polypeptide mobility. This allows the immobilized positive charge of the PLLn-Gs to be leveraged for E. coli adhesion through electrostatic attraction. We identified the magnitude of positive charge of the PLLn-G conjugates, which is modulated by the length of the PLL peptide, as an important parameter to tune the balance between the opposing forces of bacterial adhesion and proliferation. We also tested adhesion of gram-positive B. subtilis to these FGMs and found that the effect of FGM charge is less pronounced. B. subtilis adheres nondiscriminatory to all FGMs, regardless of charge, but adhesion is scarce and localized. Overall, this work demonstrates that FGMs can be tuned to selectively control bacterial response, paving the way for future development of FGM-based biomaterials as bacterio-instructive scaffolds through careful design of FGM surface chemistry.

Eckhart, Karoline E.↗
DOE OSTI2022

A portable fiber optic sensor for the luminescent sensing of cobalt ions using carbon dots

Cobalt is critical to energy-relevant technologies, and demand for cobalt will increase significantly with growing global adoption of renewables. However, supply chain stability is threatened by economic and geopolitical factors, incentivizing domestic cobalt production from alternative resources such as coal, coal utilization byproducts (e.g., ash, acid mine drainage) and electronic waste. Rapid, inexpensive, and portable characterization techniques are needed to reduce production costs associated with cobalt prospecting and process monitoring. Here, in this research, we develop a compact, portable fiber optic luminescent probe for cobalt using phosphorus and nitrogen co-doped carbon dots as the sensing material. The carbon dot emission overlaps well with the cobalt absorption band at ~510 nm, leading to a selective decrease in emission as a function of cobalt concentration. The system responds nearly instantly to the presence of cobalt, with detection limits of 0.7 and 3.5 ppm in water and pH 1.68 buffer, respectively, providing comparable performance to a commercial spectrometer at a significantly lower cost. Moreover, the sensor is selective for cobalt in the presence of 13 of the most common metal ions encountered in coal utilization byproducts and is responsive to cobalt when spiked into an acid mine drainage leachate sample, highlighting the sensor's potential for real-world deployment in challenging matrices. In addition, integrating the carbon dots with a filter paper substrate produced ‘test strip’ sensors that exhibited a selective and sensitive visual response to cobalt using a handheld UV lamp. Taken together, the sensing system represents a significant step forward in the development of low-cost practical sensors for high-value metals in complex streams.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Structured sequences emerge from random pool when replicated by templated ligation

The central question in the origin of life is to understand how structure can emerge from randomness. The Eigen theory of replication states, for sequences that are copied one base at a time, that the replication fidelity has to surpass an error threshold to avoid that replicated specific sequences become random because of the incorporated replication errors [M. Eigen, Naturwissenschaften 58 (10), 465–523 (1971)]. Here, we showed that linking short oligomers from a random sequence pool in a templated ligation reaction reduced the sequence space of product strands. We started from 12-mer oligonucleotides with two bases in all possible combinations and triggered enzymatic ligation under temperature cycles. Surprisingly, we found the robust creation of long, highly structured sequences with low entropy. At the ligation site, complementary and alternating sequence patterns developed. However, between the ligation sites, we found either an A-rich or a T-rich sequence within a single oligonucleotide. Our modeling suggests that avoidance of hairpins was the likely cause for these two complementary sequence pools. What emerged was a network of complementary sequences that acted both as templates and substrates of the reaction. This self-selecting ligation reaction could be restarted by only a few majority sequences. The findings showed that replication by random templated ligation from a random sequence input will lead to a highly structured, long, and nonrandom sequence pool. This is a favorable starting point for a subsequent Darwinian evolution searching for higher catalytic functions in an RNA world scenario.

60 APPLIED LIFE SCIENCES↗
NASA NTRS1977

Processing on high efficiency solar collector coatings

Wavelength selective coatings for solar collectors are considered. Substrates with good infrared reflectivity were examined along with their susceptibility to physical and environmental damage. Improvements of reflective surfaces were accomplished through buffing, chemical polishing and other surface processing methods.

Roberts, M.↗
NASA NTRS1987

Guided-wave approaches to spectrally selective energy absorption

Results of experiments designed to demonstrate spectrally selective absorption in dielectric waveguides on semiconductor substrates are reported. These experiments were conducted with three waveguides formed by sputtering films of PSK2 glass onto silicon-oxide layers grown on silicon substrates. The three waveguide samples were studied at 633 and 532 nm. The samples differed only in the thickness of the silicon-oxide layer, specifically 256 nm, 506 nm, and 740 nm. Agreement between theoretical predictions and measurements of propagation constants (mode angles) of the six or seven modes supported by these samples was excellent. However, the loss measurements were inconclusive because of high scattering losses in the structures fabricated (in excess of 10 dB/cm). Theoretical calculations indicated that the power distribution among all the modes supported by these structures will reach its steady state value after a propagation length of only 1 mm. Accordingly, the measured loss rates were found to be almost independent of which mode was initially excited. The excellent agreement between theory and experiment leads to the conclusion that low loss waveguides confirm the predicted loss rates.

Stegeman, G. I.↗
NASA NTRS1988

High resolution video monitoring of coating thickness during plasma spraying

A new approach to monitoring the thickness of plasma sprayed coatings during application is described. The method employs a high resolution video camera and width analyzer to accurately measure the dimensions of samples having simple geometries. This approach is best suited for cylindrical or flat substrates but it may also work for selected locations on more complex geometries. Measurement accuracy is a function of specimen dimensions and extent of magnification. Tolerances of plus or minus 0.5 mil (0.13 mm) on final coating thickness can be achieved. Additionally, the plot of cumulative coating thickess versus the number of passes has proven to be a useful diagnostic tool. While the ideal plot is linear, strong deviations from linearity - indicating the need for corrective action - may be observed.

Miller, Robert A.↗
NASA NTRS2021

Landsat Derived Bathymetry of Lakes on the Arctic Coastal Plan of Northern Alaska

The Pleistocene sand sea on the Arctic Coastal Plain (ACP) of northern Alaska is underlain by anancient sand dune field, a geological feature that affects regional lake characteristics. Many of these lakes, whichcover approximately 20 % of the Pleistocene sand sea, are relatively deep (up to 25 m). In addition to the nat-ural importance of ACP sand sea lakes for water storage, energy balance, and ecological habitat, the need forwinter water for industrial development and exploration activities makes lakes in this region a valuable resource.However, ACP sand sea lakes have received little prior study. Here, we collect in situ bathymetric data to test12 model variants for predicting sand sea lake depth based on analysis of Landsat-8 Operational Land Imager(OLI) images. Lake depth gradients were measured at 17 lakes in midsummer 2017 using a Humminbird 798ciHD SI Combo automatic sonar system. The field-measured data points were compared to red–green–blue (RGB)bands of a Landsat-8 OLI image acquired on 8 August 2016 to select and calibrate the most accurate spectral-depth model for each study lake and map bathymetry. Exponential functions using a simple band ratio (withbands selected based on lake turbidity and bed substrate) yielded the most successful model variants. For eachlake, the most accurate model explained 81.8 % of the variation in depth, on average. Modeled lake bathymetrieswere integrated with remotely sensed lake surface area to quantify lake water storage volumes, which rangedfrom 1.056×10−3to 57.416×10−3km3. Due to variations in depth maxima, substrate, and turbidity betweenlakes, a regional model is currently infeasible, rendering necessary the acquisition of additional in situ datawith which to develop a regional model solution. Estimating lake water volumes using remote sensing will fa-cilitate better management of expanding development activities and serve as a baseline by which to evaluatefuture responses to ongoing and rapid climate change in the Arctic. All sonar depth data and modeled lakebathymetry rasters can be freely accessed at https://doi.org/10.18739/A2SN01440 (Simpson and Arp, 2018) andhttps://doi.org/10.18739/A2HT2GC6G (Simpson, 2019), respectively.

Claire E Simpson↗
DOE OSTI2018

Selective CO Production by Photoelectrochemical Methane Oxidation on TiO 2

The inertness of the C–H bond in CH 4 poses significant challenges to selective CH 4 oxidation, which often proceeds all the way to CO 2 once activated. Selective oxidation of CH 4 to high-value industrial chemicals such as CO or CH 3 OH remains a challenge. Presently, the main methods to activate CH 4 oxidation include thermochemical, electrochemical, and photocatalytic reactions. Of them, photocatalytic reactions hold great promise for practical applications but have been poorly studied. Existing demonstrations of photocatalytic CH 4 oxidation exhibit limited control over the product selectivity, with CO 2 as the most common product. The yield of CO or other hydrocarbons is too low to be of any practical value. In this work, we show that highly selective production of CO by CH4 oxidation can be achieved by a photoelectrochemical (PEC) approach. Under our experimental conditions, the highest yield for CO production was 81.9%. The substrate we used was TiO 2 grown by atomic layer deposition (ALD), which features high concentrations of Ti 3+ species. The selectivity toward CO was found to be highly sensitive to the substrate types, with significantly lower yield on P25 or commercial anatase TiO 2 substrates. Moreover, our results revealed that the selectivity toward CO also depends on the applied potentials. Based on the experimental results, we proposed a reaction mechanism that involves synergistic effects by adjacent Ti sites on TiO 2 . Spectroscopic characterization and computational studies provide critical evidence to support the mechanism. Furthermore, the synergistic effect was found to parallel heterogeneous CO 2 reduction mechanisms. Our results not only present a new route to selective CH 4 oxidation, but also highlight the importance of mechanistic understandings in advancing heterogeneous catalysis.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Plastic recognition and electrogenic uniport translocation of 1 st -, 2 nd -, and 3 rd -row transition and post-transition metals by primary-active transmembrane P 1B-2 -type ATPase pumps

Transmembrane P 1B -type ATPase pumps catalyze the extrusion of transition metal ions across cellular lipid membranes to maintain essential cellular metal homeostasis and detoxify toxic metals. Zn(II)-pumps of the P 1B-2 -type subclass, in addition to Zn 2+ , select diverse metals (Pb 2+ , Cd 2+ and Hg 2+ ) at their transmembrane binding site and feature promiscuous metal-dependent ATP hydrolysis in the presence of these metals. Yet, a comprehensive understanding of the transport of these metals, their relative translocation rates, and transport mechanism remain elusive. We developed a platform for the characterization of primary-active Zn(II)-pumps in proteoliposomes to study metal selectivity, translocation events and transport mechanism in real-time, employing a “multi-probe” approach with fluorescent sensors responsive to diverse stimuli (metals, pH and membrane potential). Together with atomic-resolution investigation of cargo selection by X-ray absorption spectroscopy (XAS), we demonstrate that Zn(II)-pumps are electrogenic uniporters that preserve the transport mechanism with 1 st -, 2 nd - and 3 rd -row transition metal substrates. Promiscuous coordination plasticity, guarantees diverse, yet defined, cargo selectivity coupled to their translocation.

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

Microlens-Enhanced Substrate Patterning and MBE Growth of GaP Nanowires

In this paper we demonstrate the results on selective area growth of GaP nanowires via self-catalyzed growth method using molecular beam epitaxy (MBE) technique on patterned Si(111) substrates. The pattern fabrication method on a base of the photolithography process over an array of microspherical lenses has been studied theoretically and then optimized in order to obtain the nanostructures with controlled morphology. It was found that the positive resist thickness corresponding to the best achievable resolution in the subwavelength region is 250 nm in case of 1.5 μm silica spheres and excitation with 365 nm LED. The silica growth mask for selective epitaxy was fabricated. The ordered array of GaP nanowires was synthesized with MBE. Large scale ordering and selectivity of the growth technique is demonstrated.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2020

Conversion of Polyolefin Waste to Liquid Alkanes with Ru-Based Catalysts under Mild Conditions

Chemical upcycling of waste polyolefins via hydrogenolysis offers unique opportunities for selective depolymerization compared to high temperature thermal deconstruction. Here, we demonstrate the hydrogenolysis of polyethylene into liquid alkanes under mild conditions using ruthenium nanoparticles supported on carbon (Ru/C). Reactivity studies on a model noctadecane substrate showed that Ru/C catalysts are highly active and selective for the hydrogenolysis of C(sp 3 )–C(sp 3 ) bonds at temperatures ranging from 200 to 250 °C. Under optimal conditions of 200 °C in 20 bar H 2 , polyethylene (average M w ~ 4000 Da) was converted into liquid n-alkanes with yields of up to 45% by mass after 16 h using a 5 wt % Ru/C catalyst with the remaining products comprising light alkane gases (C 1 –C 6 ). At 250 °C, nearly stoichiometric yields of CH 4 were obtained from polyethylene over the catalyst. The hydrogenolysis of long chain, low-density polyethylene (LDPE) and a postconsumer LDPE plastic bottle to produce C 7 –C 45 alkanes was also achieved over Ru/C, demonstrating the feasibility of this reaction for the valorization of realistic postconsumer plastic waste. By identifying Ru-based catalysts as a class of active materials for the hydrogenolysis of polyethylene, this study elucidates promising avenues for the valorization of plastic waste under mild conditions.

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

Activity profiling and crystal structures of inhibitor-bound SARS-CoV-2 papain-like protease: A framework for anti–COVID-19 drug design

Viral papain-like cysteine protease (PLpro, NSP3) is essential for SARS-CoV-2 replication and represents a promising target for the development of antiviral drugs. Here, we used a combinatorial substrate library and performed comprehensive activity profiling of SARS-CoV-2 PLpro. On the scaffold of the best hits from positional scanning, we designed optimal fluorogenic substrates and irreversible inhibitors with a high degree of selectivity for SARS PLpro. We determined crystal structures of two of these inhibitors in complex with SARS-CoV-2 PLpro that reveals their inhibitory mechanisms and provides a molecular basis for the observed substrate specificity profiles. Last, we demonstrate that SARS-CoV-2 PLpro harbors deISGylating activity similar to SARSCoV-1 PLpro but its ability to hydrolyze K48-linked Ub chains is diminished, which our sequence and structure analysis provides a basis for. Together, this work has revealed the molecular rules governing PLpro substrate specificity and provides a framework for development of inhibitors with potential therapeutic value or drug repurposing.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2017

Angle-Selective Reflective Filters for Exclusion of Background Thermal Emission

Selective filtering of spectral and angular optical transmission has recently attracted a great deal of interest. While optical passband and stop-band spectral filters are already widely used, angle-selective transmission and reflection filtering represents a less than fully explored alternative. Nonetheless, this approach can be promising for several applications, including stray radiation minimization and background emission exclusion. In this work, a concept for angle-selective reflection filtering using guided-mode resonance coupling is proposed. Although guided-mode resonance structures are already used for spectral filtering, in this work, a variation of angle-selective reflection filtering using guided-mode resonance coupling is proposed. We investigate angle-dependent properties of such structures for potential use as angle-selective reflective filters. Furthermore, we utilize interference between diffraction modes to provide tunable selectivity with a sufficient angular width. Combining these structures with thermal emitters can exclude selected emission angles for spatially selective thermal emissivity reduction toward sensitive targets, as well as directionally selective emissivity exclusion for suppression of solar heating. We show a very large selective reduction of heat exchange by 99.77% between an engineered emitter and a distant receiver using just a single-groove grating and an emitting substrate in the emitter’s side. Also, we show a selective reduction of heat exchange by approximately 77% between an emitter covered by engineered sets of angle-selective reflective filters and a nearby sensitive target. The suggested angle-selective structure may have applications in excluding background thermal radiation, in particular, thermal emission reduction for daytime radiative cooling, sensitive IR telescope detectors, and high-fidelity thermoluminescent spectroscopy.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2018

Enabling Low-Cost III-V/Si Integration Through Nucleation of GaP on v-Grooved Si Substrates

Growth of III-V materials on Si could enable dramatic cost reduction for III-V PV by eliminating the need for expensive III-V substrates and enabling high-efficiency tandem solar cells. The direct heteroepitaxy of III-V materials on Si for high-efficiency photovoltaics has progressed greatly in recent years, but most studies have focused on off-cut wafers polished using an expensive chemical-mechanical planarization process (which is not used for commercial solar cells). Alternative growth approaches are needed that can enable the integration of high material quality III-Vs with PV-grade Si materials. Here we demonstrate the use of cost-effective patterning and etching approaches to create templates for selective area epitaxy on PV-grade Si substrates. We investigate the nucleation of III-V materials on these substrates.

14 SOLAR ENERGY↗