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At least 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1991

Template-directed synthesis of oligonucleotides under eutectic conditions

One of the most important sets of model prebiotic experiments consists of reactions that synthesize complementary oligonucleotides from preformed templates under nonenzymatic conditions. Most of these experiments are conducted at 4 degrees C using 0.01-0.1 M concentrations of activated nucleotide monomer and template (monomer equivalent). In an attempt to extend the conditions under which this type of reaction can occur, we have concentrated the reactants by freezing at -18 degrees C, which is close to the NaCl-H2O eutectic at -21 degrees C. The results from this set of experiments suggest that successful syntheses can occur with poly(C) concentrations as low at 5 x 10(-4) M and 2MeImpG concentrations at 10(-3) M. It was also anticipated that this mechanism might allow the previously unsuccessful poly(A)-directed synthesis of oligo(U)s to occur. However, no template effect was seen with the poly(A) and ImpU system. The failure of these conditions to allow template-directed synthesis of oligo(U)s supports the previously proposed idea that pyrimidines may not have been part of the earliest genetic material. Because of the low concentrations of monomer and template that would be expected from prebiotic syntheses, this lower temperature could be considered a more plausible geologic setting for template-directed synthesis than the standard reaction conditions.

NASA Discipline Number 52-20↗
NASA NTRS2000

A comparison of RNA with DNA in template-directed synthesis

Nonenzymatic template-directed copying of RNA sequences rich in cytidylic acid using nucleoside 5'-(2-methylimidazol-1-yl phosphates) as substrates is substantially more efficient than the copying of corresponding DNA sequences. However, many sequences cannot be copied, and the prospect of replication in this system is remote, even for RNA. Surprisingly, wobble-pairing leads to much more efficient incorporation of G opposite U on RNA templates than of G opposite T on DNA templates.

Non-NASA Center↗
DOE OSTI2024

Direct Synthesis of Layer-Tunable and Transfer-Free Graphene on Device-Compatible Substrates Using Ion Implantation Toward Versatile Applications

Direct synthesis of layer-tunable and transfer-free graphene on technologically important substrates is highly valued for various electronics and device applications. State of the art in the field is currently a two-step process: a high-quality graphene layer synthesis on metal substrate through chemical vapor deposition (CVD) followed by delicate layer transfer onto device-relevant substrates. Here, we report a novel synthesis approach combining ion implantation for a precise graphene layer control and dual-metal smart Janus substrate for a diffusion-limiting graphene formation to directly synthesize large area, high quality, and layer-tunable graphene films on arbitrary substrates without the post-synthesis layer transfer process. Carbon (C) ion implantation was performed on Cu–Ni film deposited on a variety of device-relevant substrates. A well-controlled number of layers of graphene, primarily monolayer and bilayer, is precisely controlled by the equivalent fluence of the implanted C-atoms (1 monolayer ~4 × 10 15 C-atoms/cm 2 ). Upon thermal annealing to promote Cu-Ni alloying, the pre-implanted C-atoms in the Ni layer are pushed toward the Ni/substrate interface by the top Cu layer due to the poor C-solubility in Cu. As a result, the expelled C-atoms precipitate into a graphene structure at the interface facilitated by the Cu-like alloy catalysis. After removing the alloyed Cu-like surface layer, the layer-tunable graphene on the desired substrate is directly realized. The layer-selectivity, high quality, and uniformity of the graphene films are not only confirmed with detailed characterizations using a suite of surface analysis techniques but more importantly are successfully demonstrated by the excellent properties and performance of several devices directly fabricated from these graphene films. Molecular dynamics (MD) simulations using the reactive force field (ReaxFF) were performed to elucidate the graphene formation mechanisms in this novel synthesis approach. With the wide use of ion implantation technology in the microelectronics industry, this novel graphene synthesis approach with precise layer-tunability and transfer-free processing has the promise to advance efficient graphene-device manufacturing and expedite their versatile applications in many fields.

36 MATERIALS SCIENCE↗
NASA NTRS1992

Nonenzymatic template-directed synthesis on oligodeoxycytidylate sequences in hairpin oligonucleotides

We have developed a novel method for studying template-directed synthesis in hairpin oligonucleotides. An unpaired segment at the 5'-terminus of the hairpin acts as an intramolecular template for the extension of the paired 3'-terminus. Products are analyzed by denaturing gel electrophoresis of [32P]-labeled hairpins. Using this system, we have studied the synthesis of oligoguanylates on an oligodeoxycytidylate template. We find that guanosine 5'-phosphoro(2-methyl)imidazolide adds efficiently to a terminal riboguanylate residue at temperatures in the range 0-37 degrees C but not at 50 degrees C. At 0 degree C, the half-time for addition of the first G residue is about 3 h, and the reaction rate is independent of pH in the range 6.5-8.0. The first addition reaction results in the formation of a predominantly 3'-5'-internucleotide bond. When the 3'-terminal riboguanylate residue is placed by a deoxyguanylate residue, the half-time for the first addition increases from about 3 to about 30 h.

NASA Discipline Exobiology↗
NASA NTRS1992

Nonenzymatic template-directed synthesis on hairpin oligonucleotides. 3. Incorporation of adenosine and uridine residues

We have used [32P]-labeled hairpin oligonucleotides to study template-directed synthesis on templates containing one or more A or T residues within a run of C residues. When nucleoside-5'-phosphoro(2-methyl)imidazolides are used as substrates, isolated A and T residues function efficiently in facilitating the incorporation of U and A, respectively. The reactions are regiospecific, producing mainly 3'-5'-phosphodiester bonds. Pairs of consecutive non-C residues are copied much less efficiently. Limited synthesis of CA and AC sequences on templates containing TG and GT sequences was observed along with some synthesis of the AA sequences on templates containing TT sequences. The other dimer sequences investigated, AA, AG, GA, TA, and AT, could not be copied. If A is absent from the reaction mixture, misincorporation of G residues is a significant reaction on templates containing an isolated T residue or two consecutive T residues. However, if both A and G are present, A is incorporated to a much greater extent than G. We believe that wobble-pairing between T and G is responsible for misincorporation when only G is present.

NASA Discipline Number 52-20↗
NASA NTRS1980

Template-directed synthesis and selective adsorption of oligoadenylates in hydroxyapatite

Polyuridylic acid is adsorbed completely from aqueous solution by hydroxyapatite under conditions that permit template-directed synthesis of oligoadenylates in free solution. The yield of oligoadenylates is enhanced to almost the same extent by poly(U) in the presence or the absence of hydroxyapatite. Under very similar conditions small quantities of hydroxyapatite adsorb higher-molecular-weight oligoadenylates selectively from a mixture of oligomers. On the basis of these results a mechanism for prebiotic oligonucleotide formation is proposed in which selective adsorption on hydroxyapatite or some other immobilized anion-exchanging material plays a major role. Monomers are released from the surface for reactivation, while oligomers are retained in a protected environment by adsorption to the apatite surface.

Gibbs, D.↗
DOE OSTI2022

Direct Synthesis of Highly Siliceous ZnO-FAU Zeolite with Enhanced Performance in Hydrocarbon Cracking Reactions

The hydrothermal stability and catalytic activity of zeolite Y (faujasite, FAU) is highly dependent on its composition. High silicon content is often desirable for catalytic applications; however, direct synthesis of faujasite with high silicon content (Si/Al > 2.5) is nontrivial. Here, we present an organic-free synthesis of FAU-type zeolite with Si/Al = 3.4 using zinc oxide as a modifier. A combination of spectroscopy and microscopy confirm that ZnO is well-distributed within zeolite pores as extra-framework species, and the nature of these species differs from bulk ZnO and framework zinc in Zn-FAU crystals. We demonstrate that the increased Si/Al ratio leads to improved hydrothermal stability, while catalytic cracking of 1-hexene and cumene show that ZnO-FAU exhibits significantly longer lifetime compared to in-house and commercial zeolite Y. Collectively, this study presents a facile and efficient method to prepare more siliceous FAU with enhanced catalytic performance.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS1997

Template-directed synthesis using the heterogeneous templates produced by montmorillonite catalysis. A possible bridge between the prebiotic and RNA worlds

The synthesis of oligoguanylates [oligo(G)s] is catalyzed by a template of oligocytidylates [oligo(C)s] containing 2',5'- and 3',5'-linked phosphodiester bonds with and without incorporated C5'ppC groupings. An oligo(C) template containing exclusively 2',5'-phosphodiester bonds also serves as a template for the synthesis of complementary oligo(G)s. The oligo(C) template was prepared by the condensation of the 5'-phosphorimidazolide of cytidine on montmorillonite clay. These studies establish that RNA oligomers prepared by mineral catalysis, or other routes on the primitive earth, did not have to be exclusively 3',5'-linked to catalyze template-directed synthesis, since oligo(C)s containing a variety of linkage isomers serve as templates for the formation of complementary oligo(G)s. These findings support the postulate that origin of the RNA world was initiated by the RNA oligomers produced by polymerization of activated monomers formed by prebiotic processes.

NASA Discipline Exobiology↗
DOE OSTI2025

Direct Synthesis of Polyester from Biomass Derived 1,6-hexanediol using a Copper-Ceria Catalyst

Biomass derived polyesters are gaining attention due to their increased mechanical and thermal properties, and also because of their biodegradability. These polyesters are typically synthesized from polycondensation reactions between diols with dicarboxylic acids using catalysts. Other methods such as alcoholysis and acidolysis of low molecular weight esters and alcoholysis of acyl chlorides are also well known. Direct conversion of diol to ester without using dicarboxylic acid is not well known, and to our knowledge has not been reported over a solid catalyst. In this study, we report a direct synthesis of polyester from 1,6-hexanediol using a copper-ceria catalyst without using a dicarboxylic acid monomer. The copper-ceria catalysts were synthesized by incipient wetness impregnation method and characterized using X-ray photoelectron spectroscopy (XPS), X-ray diffraction analysis (XRD), Brunauer-Emmett-Teller (BET), and infrared spectroscopy (IR). Our initial studies show that 1,6-hexanediol can be converted to corresponding polyester at higher temperatures under atmospheric pressures of CO2 or N2. The reaction products were analyzed using nuclear magnetic resonance spectroscopy (NMR), gel permeation chromatography (GPC), high performance liquid chromatography (HPLC), and IR spectroscopy.

Biomass derived diols↗
DOE OSTI2023

Direct synthesis and chemical vapor deposition of 2D carbide and nitride MXenes

Two-dimensional transition-metal carbides and nitrides (MXenes) are a large family of materials actively studied for various applications, especially in the field of energy storage. MXenes are commonly synthesized by etching the layered ternary compounds, called MAX phases. We demonstrate a direct synthetic route for scalable and atom-economic synthesis of MXenes, including compounds that have not been synthesized from MAX phases, by the reactions of metals and metal halides with graphite, methane, or nitrogen. The direct synthesis enables chemical vapor deposition growth of MXene carpets and complex spherulite-like morphologies that form through buckling and release of MXene carpet to expose fresh surface for further reaction. The directly synthesized MXenes showed excellent energy storage capacity for lithium-ion intercalation.

Wang, Di↗
NASA NTRS1992

Nonenzymatic template-directed synthesis on hairpin oligonucleotides. III - Incorporation of adenosine and uridine residues

Nonenzymatic template-directed incorporation of adenosine and uridine residues into template sequences was obtained using nucleoside-5-prime phosphoro (2-methyl)imidazolides as substrates and hairpin oligonucleotides as templates. The reactions are regiospecific, producing mainly 3-prime-5-prime phosphodiester bonds. Limited synthesis of CA and AC sequences was observed along with some synthesis of the AA sequences on templates containing TG and GT sequences, along wilth some synthesis of the AA sequences on templates containing TT sequences.

Wu, Taifeng↗
NASA NTRS1984

Chiral selection in poly(C)-directed synthesis of oligo(G)

An experimental study is reported which shows that poly(C)-directed oligomerization of activated guanosine mononucleotides proceeds readily if the monomers are of the same optical handedness as the template, and is far less efficient if the monomers are of the opposite handedness. However, in template-directed reactions with a racemic mixture, monomers of the opposite handedness to the template are incorporated as chain terminators at the 2'(3') end of the products. This inhibition raises an important problem for many theories of the origin of life.

Joyce, G. F.↗
NASA NTRS1979

Template-directed synthesis of oligoadenylates catalyzed by Pb/2+/ ions

The Pb(2+) ion is an effective catalyst for the template-directed condensation of ImpA on poly(U). This reaction generates up to 35% of oligomers 5 or more units long. Furthermore, the product is predominantly 3'-5'-linked (75%) unlike that from the uncatalyzed reaction which is more than 90% 2'-5'-linked. The significance of metal-ion catalysis for prebiotic polynucleotide formation is discussed.

Sleeper, H. L.↗
DOE OSTI2023

Direct Synthesis of Ammonia from Nitrate on Amorphous Graphene with Near 100% Efficiency

Abstract Ammonia is an indispensable commodity in the agricultural and pharmaceutical industries. Direct nitrate‐to‐ammonia electroreduction is a decentralized route yet challenged by competing side reactions. Most catalysts are metal‐based, and metal‐free catalysts with high nitrate‐to‐ammonia conversion activity are rarely reported. Herein, it is shown that amorphous graphene synthesized by laser induction and comprising strained and disordered pentagons, hexagons, and heptagons can electrocatalyze the eight‐electron reduction of NO 3 − to NH 3 with a Faradaic efficiency of ≈100% and an ammonia production rate of 2859 µg cm −2 h −1 at −0.93 V versus reversible hydrogen electrode. X‐ray pair‐distribution function analysis and electron microscopy reveal the unique molecular features of amorphous graphene that facilitate NO 3 − reduction. In situ Fourier transform infrared spectroscopy and theoretical calculations establish the critical role of these features in stabilizing the reaction intermediates via structural relaxation. The enhanced catalytic activity enables the implementation of flow electrolysis for the on‐demand synthesis and release of ammonia with >70% selectivity, resulting in significantly increased yields and survival rates when applied to plant cultivation. The results of this study show significant promise for remediating nitrate‐polluted water and completing the NO x cycle.

Huang, Libei↗
NASA NTRS1981

Template-directed synthesis of oligoguanylic acids - Metal ion catalysis

The effects of Zn(2+), Pb(2+) and other metal ions on the efficiency and stereo-selectivity of the template-directed oligomerization of guanosine 5'-phosphorimidazolide are investigated. Reactions were run in the presence of a polyC template in a 2,6-lutidine buffer, and products analyzed by high-performance liquid chromatography on an RPC-5 column. The presence of the Pb(2+) ion is found to lead to the formation of 2'-5' linked oligomers up to the 40-mer, while Zn(2+) favors the formation of predominantly 3'-5' linked oligomers up to the 35-mer. When amounts of uracil, cytidine or adenosine 5'-phosphorimidazole equal to those of the guanosine derivative are included in the reaction mixture, the incorrect base is incorporated into the oligomer about 10% of the time with a Pb(2+) catalyst, but less than 0.5% of the time with Zn(2+). The Sn(2+), Sb(3+) and Bi(3+) ions are also found to promote the formation of 2'-5' oligomers, although not as effectively as Pb(2+), while no metal ions other than Zn(2+) promote the formation of the 3'-5' oligomers. The results may be important for the understanding of the evolution of nucleic acid replication in the absence of enzymes.

Bridson, P. K.↗
NASA NTRS1984

Non-enzymatic template-directed synthesis on RNA random copolymers - Poly(C, U) templates

Random copolymer templates containing cytosine and uracil in ratios of 3:1 and 1:1 are used to explore the optimum conditions for efficient synthesis of guanine and adenine-containing oligonucleotides. The experimental procedure is described, including the preparation of mononucleoside 5'-phospho-2-methylimidazolides and random copolymers, the template-directed oligomerization, the removal and reintroduction of mononucleotides in interrupted reactions, the determination of oligomerization efficiency, the alkaline and enzymatic hydrolysis of reaction products, and the column chromatography. Results are presented and discussed for the dependence of adenine incorporation on the formation of short oligo(G)s, optimization of incorporation efficiencies by adjusting monomer concentrations, the characterization of oligomeric product distribution, and the regiospecificity of adenine incorporation. The prebiotic significance of the results is assessed.

Joyce, G. F.↗