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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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4 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS2018

Discreditation of Bobdownsite and the Establishment of Criteria for the Identification of Minerals with Essential Monofluorophosphate (PO3F2-)

Bobdownsite, IMA number 2008-037, was approved as a new mineral by the Commission on New Minerals, Nomenclature and Classification (CNMNC) as the fluorine endmember of the mineral whitlockite. The type locality of bobdownsite is in Big Fish River, Yukon Canada, and bobdownsite was reported to be the first naturally occurring mineral with essential monofluorophosphate (PO3F2-). The type specimen of bobdownsite has been reinvestigated by electron probe microanalysis (EPMA), and our data indicate that fluorine abundances are below detection in the mineral. In addition, we conducted detailed analysis of bobdownsite from the type locality by gas chromatography isotope ratio mass spectrometry, Raman spectroscopy, EPMA, and NMR spectroscopy. These data were compared with previously published data on synthetic monofluorophosphate salts. Collectively, these data indicate that bobdownsite is indistinguishable from whitlockite with a composition along the whitlockite-merrillite solid solution. Bobdownsite is therefore discredited as a valid mineral species. An additional mineral, krásnoite, has been purported to have monofluorophosphate components in its structure, but reexamination of those data indicate that F- in krásnoite forms bonds with Al, similar to OH- bonded to Al in perhamite. Consequently, krásnoite also lacks monofluorophosphate groups, and there are currently no valid mineral species with monofluorophosphate in their structure. We recommend that any future reports of new minerals that contain essential monofluorophosphate anions be vetted by abundance measurements of fluorine, vibrational spectroscopy (both Raman and FTIR), and where paramagnetic components are permissibly low, NMR spectroscopy. Furthermore, we emphasize the importance of using synthetic compounds containing monofluorophosphate anions as a point of comparison in the identification of minerals with essential monofluorophosphate. Structural data that yield satisfactory P-F bond lengths determined by X-ray crystallography, coupled with direct chemical analyses of fluorine in a material do not constitute sufficient evidence alone to identify a new mineral with essential monofluorophosphate anions.

McCubbin, Francis M.↗
NASA NTRS1992

Lower temperature curing thermoset polyimides utilizing a substituted norbornene endcap

Methoxycarbonyl bridgehead substituted nadic diacid monomethyl ester, when used as an endcapping monomer, lowered the cure temperature of thermoset PMR polyimides without seriously affecting other desirable properties, such as glass transition temperature and thermal oxidative stability. The C-13 CP/MAS NMR of model compounds was used to follow the cure of resin systems using both the unmodified nadic endcap and the methoxycarbonyl-substituted endcap. Rheological analysis and differential scanning calorimetry DSC also provided evidence for the lower curing nature of the substituted endcap. Two regioisomers of the bridgehead-substituted endcap were isolated, and their chemical structures were elucidated by X-ray crystallography. The model compound and molecular modeling studies conducted ruled out the possibility of regioisomeric imide formation in the substituted endcaps.

Waters, John F.↗
NASA NTRS1994

Crystal structure of a four-stranded intercalated DNA: d(C4)

The crystal structure of d(C4) solved at 2.3-A resolution reveals a four-stranded molecule composed of two interdigitated or intercalated duplexes. The duplexes are held together by hemiprotonated cytosine-cytosine base pairs and are parallel stranded, but the two duplexes point in opposite directions. The molecule has a slow right-handed twist of 12.4 degrees between covalently linked cytosine base pairs, and the base stacking distance is 3.1 A. This is in general agreement with the NMR studies. A biological role for DNA in this conformation is suggested.

Non-NASA Center↗
NASA NTRS2003

Crystallization and preliminary X-ray analysis of Der f 2, a potent allergen derived from the house dust mite (Dermatophagoides farinae)

Although a number of allergens have been identified and isolated, the underlying molecular basis for the potent immune response is poorly understood. House dust mites (Dermatophagoides sp.) are ubiquitous contributors to atopy in developed countries. The rhinitis, dermatitis and asthma associated with allergic reactions to these arthropods are frequently caused by relatively small (125-129 amino acids) mite proteins of unknown biological function. Der f 2, a major allergen from the mite D. farinae, has been recombinantly expressed, characterized and crystallized. The crystals belong to the tetragonal space group I4(1)22, with unit-cell parameters a = b = 95.2, c = 103.3 A. An essentially complete (97.2%) data set has been collected to 2.4 A at a synchrotron source. Attempts to solve the crystal structure of Der f 2 by molecular replacement using the NMR coordinates for either Der f 2 or Der p 2 (the homologous protein from D. pteronyssinus) failed, but preliminary searches using the crystalline Der p 2 atomic coordinates appear to be promising.

Pyroglyphidae/chemistry/immunology↗