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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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NASA NTRS1995

A possible prebiotic synthesis of pantetheine, a precursor to coenzyme A

The involvement of coenzyme A in many enzyme reactions suggests that it acted in this capacity very early in the development of life on Earth. Particularly relevant in this regard is its role in the activation of amino acids and hydroxy acids in the biosynthesis of some peptide antibiotics--a mechanism of peptide synthesis that forms the basis for the proposal that a thioester world could have preceded the RNA world. The components of coenzyme A have been shown to be probable prebiotic compounds: beta-alanine, pantoyl lactone and cysteamine and possibly adenosine. We show here that the pantetheine moiety of coenzyme A (which also occurs in a number of enzymes) can be synthesized in yields of several per cent by heating pantoyl lactone, beta-alanine and cysteamine at temperatures as low as 40 degrees C. These components are extremely soluble and so would have been preferentially concentrated in evaporating bodies of water, for example on beaches and at lagoon margins. Our results show that amide bonds can be formed at temperatures as low as 40 degrees C, and provide circumstantial support for the suggestion that pantetheine and coenzyme A were important in the earliest metabolic systems.

NASA Discipline Number 52-20↗

NASA NTRS1972

CMB-13 research on carbon and graphite

The effects of grinding on Santa Maria coke are considered, as well as the production of resin-bonded graphite from the coke. Kynol fibers, properties and purities of coal tar pitches, carbonization of resin components, synthesis of gamma BL (4-furfuryl 2-pentenoic acid gamma lactone), and a glass-like carbon powder for use as a filler are also discussed. The hydrogen contents of commercial cokes and graphites are tabulated, and a quantimet image-analyzing computer and its operation are described.

Smith, M. C.↗

NASA NTRS1974

Pyrolysis of amino acids - Mechanistic considerations

Pyrolysis of several structurally different amino acids in a column at 500 C showed differences in the mechanisms and final products. The aliphatic protein amino acids decompose mainly by simple decarboxylation and condensation reactions, while the beta amino acids undergo deamination to unsaturated acids. Alpha amino acids with alpha alkyl substituents undergo an unusual intramolecular SN1 reaction with the formation of an intermediate alpha lactone which decomposes to yield a ketone. The alpha alkyl substituents appear to stabilize the developing negative charge formed by partial heterolytic cleavage of the alpha carbon - NH3 bond. The gamma and delta amino acids give 2-pyrrolidinone and 2-piperidone respectively, while the epsilon acids yield mixed products.

Ratcliff, M. A., Jr.↗

NASA NTRS1990

Template-directed oligomerization of 5-prime-deoxy 5-nucleosideacetic acid derivatives

5-prime-deoxy 5-nucleosideacetic acids H-II are isostructural analogs of nucleotides with a carboxylate group in the place of the 5-prime-phosphate group. In this work, their oligomerization in aqueous solution was studied using a water-soluble carbodiimide as the condensing agent in the presence or absence of an appropriate polynucleotide template. Condensation of adenylic acid analogs IIa, IIIa, and Va in the presence of polyuridylic acid were found to be the most efficient reactions. Cyclization of the activated monomers to lactones and the insolubility of the oligomers in aqueous solution were found to be obstacles to the efficient formation of long oligomers.

Harada, Kazuo↗

NASA NTRS1990

Synthesis of 5'-deoxy-5'-nucleosideacetic acid derivatives

Several new 5'-deoxy-5'-nucleosideacetic acid derivatives have been synthesized by the reactions of alkoxycarbonylmethylene triphenylphosphoranes with nucleoside 5'-aldehydes. The oligomerization of adenine derivatives IIa, IIIa, IV, V and guanine derivatives IIc and IIIc in aqueous solution was studied using a water-soluble carbodiimide as a condensing agent. It is found that the saturated acid (IV) tends to cyclize to the lactone, while IIa and unsaturated acids (IIIa and V) oligomerized efficiently, especially in the presence of poly (U) as a template.

Harada, Kazuo↗

NASA NTRS1996

Potentially Prebiotic Syntheses of Condensed Phosphates

In view of the importance of a prebiotic source of high energy phosphates, we have investigated a number of potentially prebiotic processes to produce condensed phosphates from orthophosphate and cyclic trimetaphosphate from tripolyphosphate. The reagents investigated include polymerizing nitriles, acid anhydrides, lactones, hexamethylene tetramine and carbon suboxide. A number of these processes give substantial yields of pyrophosphate from orthophosphate and trimetaphosphate from tripolyphosphate. Although these reactions may have been applicable in local areas, they are not sufficiently robust to have been of importance in the prebiotic open ocean.

Keefe, Anthony D.↗

NASA NTRS1998

Development of High Conductivity Lithium-Ion Electrolytes for Low Temperature Cell Applications

NASA has continued interest in developing power sources which are capable of operating at low temperatures (-20 C and below) to enable future missions, such as the Mars Rover and Lander. Thus, under a program sponsored by the Mars Exploration Program, we have been involved in developing Li-ion batteries with improved low temperature performance. To accomplish this task, the focus of the research has been upon the development of advanced electrolyte systems with improved low temperature properties. This had led to the identification of a carbonate-based electrolyte, consisting of 1.0 M LiPF6 in EC + DEC + DMC (33:33:34), which has been shown to have excellent performance at -20 C in Li-ion AA-size prototype cells. Other groups are also actively engaged in developing electrolytes which can result in improved low temperature performance of Li-ion cells, including Polystor, Yardney, and Covalent. In addition to developing cells capable of operation at -20 C, there is continued interest in systems which can successfully operate at even lower temperatures (less than -30 C) and at high discharge rates (greater than C/2). Thus, we are currently focusing upon developing advanced electrolytes which are highly conductive at low temperatures and will result in cells capable of operation at -40 C. One approach to improve the low temperature conductivity of ethylene carbonate-based electrolytes involves adding co-solvents which will decrease the viscosity and extend the liquid range. Candidate solvent additives include formates, acetates, cyclic and aliphatic ethers, lactones, as well as other carbonates. Using this approach, we have prepared a number of electrolytes which contain methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), ethyl proprionate (EP), and 1,2-dimethoxyethane (DME), some of which have been characterized and reported. Other groups have also reported electrolytes based on mixtures of carbonates and acetates. In the present study, electrolytes which have been identified to have good low temperature conductivity and stability were incorporated into lithium-graphite cells for evaluation. Using various electrochemical methods, including ac impedence and DC micropolarization techniques, the film formation characteristics of graphite electrodes in contact with various lectrolyte formulations was investigated.

Smart, M. C.↗

NASA NTRS1993

Prebiotic syntheses of vitamin coenzymes: II. Pantoic acid, pantothenic acid, and the composition of coenzyme A

Pantoic acid can by synthesized in good prebiotic yield from isobutyraldehyde or alpha-ketoisovaleric acid + H2CO + HCN. Isobutyraldehyde is the Strecker precursor to valine and alpha-ketoisovaleric acid is the valine transamination product. Mg2+ and Ca2+ as well as several transition metals are catalysts for the alpha-ketoisovaleric acid reaction. Pantothenic acid is produced from pantoyl lactone (easily formed from pantoic acid) and the relatively high concentrations of beta-alanine that would be formed on drying prebiotic amino acid mixtures. There is no selectivity for this reaction over glycine, alanine, or gamma-amino butyric acid. The components of coenzyme A are discussed in terms of ease of prebiotic formation and stability and are shown to be plausible choices, but many other compounds are possible. The gamma-OH of pantoic acid needs to be capped to prevent decomposition of pantothenic acid. These results suggest that coenzyme A function was important in the earliest metabolic pathways and that the coenzyme A precursor contained most of the components of the present coenzyme.

NASA Discipline Number 52-20↗

NASA NTRS2006

Biomimetic/Optical Sensors for Detecting Bacterial Species

Biomimetic/optical sensors have been proposed as means of real-time detection of bacteria in liquid samples through real-time detection of compounds secreted by the bacteria. Bacterial species of interest would be identified through detection of signaling compounds unique to those species. The best-characterized examples of quorum-signaling compounds are acyl-homoserine lactones and peptides. Each compound, secreted by each bacterium of an affected species, serves as a signal to other bacteria of the same species to engage in a collective behavior when the population density of that species reaches a threshold level analogous to a quorum. A sensor according to the proposal would include a specially formulated biomimetic film, made of a molecularly imprinted polymer (MIP), that would respond optically to the signaling compound of interest. The MIP film would be integrated directly onto an opticalwaveguide- based ring resonator for optical readout. Optically, the sensor would resemble the one described in Chemical Sensors Based on Optical Ring Resonators (NPO-40601), NASA Tech Briefs, Vol. 29, No. 10 (October 2005), page 32. MIPs have been used before as molecular- recognition compounds, though not in the manner of the present proposal. Molecular imprinting is an approach to making molecularly selective cavities in a polymer matrix. These cavities function much as enzyme receptor sites: the chemical functionality and shape of a cavity in the polymer matrix cause the cavity to bind to specific molecules. An MIP matrix is made by polymerizing monomers in the presence of the compound of interest (template molecule). The polymer forms around the template. After the polymer solidifies, the template molecules are removed from the polymer matrix by decomplexing them from their binding sites and then dissolving them, leaving cavities that are matched to the template molecules in size, shape, and chemical functionality. The cavities thus become molecular-recognition sites that bind only to molecules matched to the sites; other molecules are excluded. In a sensor according to the proposal, the MIP would feature molecular recognition sites that would bind the specific signaling molecules selectively according to their size, shape, and chemical functionality (see figure). As the film took up the signaling molecules in the molecular recognition sites, the index of refraction and thickness of the film would change, causing a wavelength shift of the peak of the resonance spectrum. It has been estimated that by measuring this wavelength shift, it should be possible to detect as little as 10 picomoles of a peptide signaling compound.

Homer, Margie↗