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At least 163 records · Page 9
All sourcesNASA NTRSDOE OSTI
NASA NTRS1994

Kinetic and mechanistic analysis of dinucleotide and oligonucleotide formation from the 5'-phosphorimidazolide of adenosine on Na(+)-montmorillonite

The rate constants for the condensation reaction of the 5'-phosphorimidazolide of adenosine (ImpA) to form dinucleotides and oligonucleotides have been measured in the presence of Na(+)-volclay (a Na(+)-montmorillonite) in pH 8 aqueous solution at 25 degrees C. The rates of the reaction of ImpA with an excess of adenosine 5'-monophosphoramidate (NH2pA), P1,P2-diadenosine 5',5'-pyrophosphate (A5'ppA), or adenosine 5'-monophosphate (5'-AMP or pA) in the presence of the montmorillonite to form NH2pA3'pA, A5'ppA3'pA, and pA3'pA, respectively, were measured. Only 3',5'-linked products were observed. The magnitude of the rate constants decrease in the order NH2pA3'pA > A5'-ppA3'pA > pA3'pA. The binding of ImpA to montmorillonite was measured, and the adsorption isotherm was determined. The binding of ImpA to montmorillonite and the formation of higher oligonucleotides is not observed in the absence of salts. Mg2+ enhances binding and oligonucleotide formation more than Ca2+ and Na+. The rate constants for the oligonucleotide formation were determined from the reaction products formed from 10 to 40 mM ImpA in the presence of Na(+)-montmorillonite using the computer program SIMFIT. The magnitudes of the rate constants for the formation of oligonucleotides increased in the order 2-mer < 3-mer < 4-mer ... 7-mer. The rate constants for dinucleotide and trinucleotide formation are more than 1000 times larger than those measured in the absence of montmorillonite. The rate constants for the formation of dinucleotide, trinucleotide, and tetranucleotide are 41,2.6, and 3.7 times larger than those for the formation of oligo(G)s with a poly(C) template. The hydrolysis of ImpA was accelerated 35 times in the presence of the montmorillonite. The catalytic ability of montmorillonite to form dinucleotides and oligonucleotides is quantitatively evaluated and possible pathways for oligo(A) formation are proposed.

NASA Discipline Exobiology↗
NASA NTRS1985

In vivo inhibition of polyamine biosynthesis and growth in tobacco ovary tissues

Post fertilization growth of tobacco ovary tissues treated with inhibitors of polyamine (PA) biosynthesis was examined in relation to endogenous PA titers and the activities of arginine decarboxylase (ADC, EC 4.1.1.19) and ornithine decarboxylase (ODC, EC 4.1.1.17). DL-alpha-Difluoromethylornithine (DFMO) and DL-alpha-difluoromethylarginine (DFMA), specific, irreversible ("suicide") inhibitors of ODC and ADC in vitro, were used to modulate PA biosynthesis in excised flowers. ODC represented >99% of the total decarboxylase activity in tobacco ovaries. In vivo inhibition of ODC with DFMO resulted in a significant decrease in PA titers, ovary fresh weight and protein content. Simultaneous inhibition of both decarboxylases by DFMO and DFMA produced only a marginally greater depression in growth and PA titers, indicating that ODC activity is rate-limiting for PA biosynthesis in these tissues. Paradoxically, DFMA alone inhibited PA biosynthesis, not as a result of a specific inhibition of ADC, but primarily through the inactivation of ODC. In vivo inhibition of ODC by DFMA appears to result from arginase-mediated hydrolysis of this inhibitor to urea and DFMO, the suicide substrate for ODC. Putrescine conjugates in tobacco appear to function as a storage form of this amine which, upon hydrolysis, may contribute to Put homeostasis during growth.

NASA Program Space Biology↗
NASA NTRS2007

Effects of Hind Limb Unloading on Pharmacokinetics of Procainamide in Mice

The pharmacokinetics (PK) of medications administered to astronauts could be altered by the conditions in space. It is prudent to expect that low gravity and free floating (and associated hemodynamic changes) could affect the absorption, distribution, metabolism and excretion of the drugs. Knowledge of these alterations is essential for adjusting the dosage and the regimen of drug administration. Among the medications of special interest are the cardiovascular drugs, especially the antiarrhythmic agents. In this study we used hind limb unloaded (HLU) mice as a model to investigate possible changes in the PK of a common antiarrhythmic drug procainamide (PA). Prior to drug administration the experimental animals were tail suspended for 24 hours and the control animals were kept free. PA (150-250 mg per kg) was given orally by a gavage procedure. After that the experimental mice were kept suspended for additional 1, 2, 3 and 6 hours. At these time points the serum concentration of PA and N-acetyl-procainamide (NAPA), an active metabolite which is formed by N-acetyltransferase in the liver, were measured by the fluorescence polarization immunoassay (FPIA) on the AxSYM autoanalyzer (Abbott Laboratories, Abbott Park, IL). The serum level of PA in HLU mice at 1 hour after administration was almost 40% lower than in controls. At 2-3 hours the difference still maintained, however, it was not statistically significant; at 6 hours no difference was detected. The level of NAPA in HLU mice was slightly lower at 1 and 2 hours but the difference did not reach statistical significance. The estimated PA half-life time in HLU mice was almost 55% longer than in control animals. These results confirm that hind limb unloading and related hemodynamic changes significantly alter the PK of PA. The effects are most likely primarily associated with a decrease in the drug absorption, especially within the first two hours after administration. At the same time prolongation of the PA half-life time in the HLU mice points towards slower drug elimination from the circulation.

Risin, Semyon A.↗
NASA NTRS2016

Temporal Characteristics and Energy Deposition of Pulsating Auroral Patches

We present a careful statistical analysis of pulsating aurora (PA) using all-sky green line (557.7 nm) images obtained at 3.3 Hz. Six well-defined individual PA patches are identified and extracted using a contouring technique. Quantitative parameters such as the patch duration (on-time and off-time), peak intensity, and integrated intensity are determined for each patch and each pulsation. The resulting characteristics serve as strict observational constraints that any of the many competing theories attempting to explain PA must predict. The purpose of this paper is to determine the characteristics of PA patches in order to provide better observational constraints on the suggested mechanisms. All aspects of the temporal behavior of the individual patches appear to be erratic. Historically, PA has been defined very loosely and we argue that the use of the term pulsating is inappropriate since our findings and other published results are not regularly periodic and thus a more appropriate term may be fluctuating aurora. Further, we find that the observational constraints do not fit well with the flow cyclotron maser theory, which in particular is suggested to create PA patches. There is no clear candidate of the suggested mechanisms and drivers to explain the observational constraints set by the PA patches in a satisfactory manner.

Humberset, B. K.↗
DOE OSTI2022

Molecular insights into the structure-property relationships of 3D printed polyamide reverse-osmosis membrane for desalination

3D-printing is an emerging method for manufacturing polyamide (PA) reserve osmosis (RO) membranes for water treatment and desalination, which can precisely control membrane structural properties, such as thickness, roughness, and resolution. However, the synthesis-structure (i.e., degree of cross-linking (DC), m-phenylenediamine/trimesoyl chloride (MPD/TMC) ratio, and membrane thickness) to property (permeability and water-salt selectivity) relationships for these membranes has not been well understood. At the same time, a microscopic understanding of the physical mechanism of water and salt transport is needed to guide the design of high-performance 3D-printed membranes and improve the printing efficiency. Furthermore, the atomic-scale transport features and energetics of water and salt ions are studied at high pressure for the 3D-printed PA RO membranes with the different DCs and MPD/TMC ratios through non-equilibrium molecular dynamics (NEMD) simulations. Factoring in membrane structure properties, rejection ratio of salt ions and pressure-dependent water flux, 3D-printed PA membranes having an MPD/TMC ratio of 3.0:2.0 and a DC between 80%~90% attains ideal performance: high water flux, high rejection of salt ions, and excellent structural integrity. Mechanistically, water permeability for highly cross-linked PA RO membranes depends on the temporary on-and-off channels that allow water molecules to jump from one cavity to another at high pressure. In addition, higher pressures cause rapid compaction of PA membranes’ free volume and membrane thickness. Membrane failure at high pressure is determined by the DC and MPD/TMC ratios-dependent compressive yield strength. In short, these findings provide physical insights for optimizing existing PA membranes and designing next-generation desalination membranes at the molecular level.

3D-printed PA RO membrane↗
DOE OSTI2020

Materials Data on PaCl2O by Materials Project

PaOCl2 crystallizes in the orthorhombic Pbam space group. The structure is three-dimensional. there are three inequivalent Pa4+ sites. In the first Pa4+ site, Pa4+ is bonded in a 7-coordinate geometry to three O2- and four Cl1- atoms. There are two shorter (2.23 Å) and one longer (2.26 Å) Pa–O bond lengths. There are two shorter (2.79 Å) and two longer (2.81 Å) Pa–Cl bond lengths. In the second Pa4+ site, Pa4+ is bonded in a 9-coordinate geometry to four O2- and five Cl1- atoms. There are a spread of Pa–O bond distances ranging from 2.29–2.41 Å. There are a spread of Pa–Cl bond distances ranging from 2.84–3.06 Å. In the third Pa4+ site, Pa4+ is bonded in a 8-coordinate geometry to three O2- and five Cl1- atoms. There are two shorter (2.16 Å) and one longer (2.34 Å) Pa–O bond lengths. There are a spread of Pa–Cl bond distances ranging from 2.78–3.08 Å. There are three inequivalent O2- sites. In the first O2- site, O2- is bonded to four Pa4+ atoms to form distorted corner-sharing OPa4 tetrahedra. In the second O2- site, O2- is bonded in a distorted trigonal non-coplanar geometry to three Pa4+ atoms. In the third O2- site, O2- is bonded in a distorted trigonal planar geometry to three Pa4+ atoms. There are six inequivalent Cl1- sites. In the first Cl1- site, Cl1- is bonded in a distorted L-shaped geometry to two Pa4+ atoms. In the second Cl1- site, Cl1- is bonded in a distorted L-shaped geometry to two equivalent Pa4+ atoms. In the third Cl1- site, Cl1- is bonded in a 3-coordinate geometry to three Pa4+ atoms. In the fourth Cl1- site, Cl1- is bonded in a distorted L-shaped geometry to two equivalent Pa4+ atoms. In the fifth Cl1- site, Cl1- is bonded in a 2-coordinate geometry to three Pa4+ atoms. In the sixth Cl1- site, Cl1- is bonded in a bent 150 degrees geometry to two Pa4+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Pa3Si by Materials Project

Pa3Si is Uranium Silicide structured and crystallizes in the cubic Pm-3m space group. The structure is three-dimensional. Pa is bonded to eight equivalent Pa and four equivalent Si atoms to form distorted PaPa8Si4 cuboctahedra that share corners with twelve equivalent PaPa8Si4 cuboctahedra, edges with eight equivalent SiPa12 cuboctahedra, edges with sixteen equivalent PaPa8Si4 cuboctahedra, faces with four equivalent SiPa12 cuboctahedra, and faces with fourteen equivalent PaPa8Si4 cuboctahedra. All Pa–Pa bond lengths are 3.14 Å. All Pa–Si bond lengths are 3.14 Å. Si is bonded to twelve equivalent Pa atoms to form SiPa12 cuboctahedra that share corners with twelve equivalent SiPa12 cuboctahedra, edges with twenty-four equivalent PaPa8Si4 cuboctahedra, faces with six equivalent SiPa12 cuboctahedra, and faces with twelve equivalent PaPa8Si4 cuboctahedra.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Pa3Sb by Materials Project

Pa3Sb is Uranium Silicide structured and crystallizes in the cubic Pm-3m space group. The structure is three-dimensional. Pa is bonded to eight equivalent Pa and four equivalent Sb atoms to form distorted PaPa8Sb4 cuboctahedra that share corners with twelve equivalent PaPa8Sb4 cuboctahedra, edges with eight equivalent SbPa12 cuboctahedra, edges with sixteen equivalent PaPa8Sb4 cuboctahedra, faces with four equivalent SbPa12 cuboctahedra, and faces with fourteen equivalent PaPa8Sb4 cuboctahedra. All Pa–Pa bond lengths are 3.25 Å. All Pa–Sb bond lengths are 3.25 Å. Sb is bonded to twelve equivalent Pa atoms to form SbPa12 cuboctahedra that share corners with twelve equivalent SbPa12 cuboctahedra, edges with twenty-four equivalent PaPa8Sb4 cuboctahedra, faces with six equivalent SbPa12 cuboctahedra, and faces with twelve equivalent PaPa8Sb4 cuboctahedra.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Pa3Te by Materials Project

Pa3Te is Uranium Silicide structured and crystallizes in the cubic Pm-3m space group. The structure is three-dimensional. Pa is bonded to eight equivalent Pa and four equivalent Te atoms to form distorted PaPa8Te4 cuboctahedra that share corners with twelve equivalent PaPa8Te4 cuboctahedra, edges with eight equivalent TePa12 cuboctahedra, edges with sixteen equivalent PaPa8Te4 cuboctahedra, faces with four equivalent TePa12 cuboctahedra, and faces with fourteen equivalent PaPa8Te4 cuboctahedra. All Pa–Pa bond lengths are 3.24 Å. All Pa–Te bond lengths are 3.24 Å. Te is bonded to twelve equivalent Pa atoms to form TePa12 cuboctahedra that share corners with twelve equivalent TePa12 cuboctahedra, edges with twenty-four equivalent PaPa8Te4 cuboctahedra, faces with six equivalent TePa12 cuboctahedra, and faces with twelve equivalent PaPa8Te4 cuboctahedra.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Pa3Ge by Materials Project

Pa3Ge is Uranium Silicide structured and crystallizes in the cubic Pm-3m space group. The structure is three-dimensional. Pa is bonded to eight equivalent Pa and four equivalent Ge atoms to form distorted PaPa8Ge4 cuboctahedra that share corners with twelve equivalent PaPa8Ge4 cuboctahedra, edges with eight equivalent GePa12 cuboctahedra, edges with sixteen equivalent PaPa8Ge4 cuboctahedra, faces with four equivalent GePa12 cuboctahedra, and faces with fourteen equivalent PaPa8Ge4 cuboctahedra. All Pa–Pa bond lengths are 3.17 Å. All Pa–Ge bond lengths are 3.17 Å. Ge is bonded to twelve equivalent Pa atoms to form GePa12 cuboctahedra that share corners with twelve equivalent GePa12 cuboctahedra, edges with twenty-four equivalent PaPa8Ge4 cuboctahedra, faces with six equivalent GePa12 cuboctahedra, and faces with twelve equivalent PaPa8Ge4 cuboctahedra.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Pa3Re by Materials Project

Pa3Re is beta Cu3Ti-like structured and crystallizes in the hexagonal P6_3/mmc space group. The structure is three-dimensional. Pa is bonded to eight equivalent Pa and four equivalent Re atoms to form distorted PaPa8Re4 cuboctahedra that share corners with four equivalent RePa12 cuboctahedra, corners with fourteen equivalent PaPa8Re4 cuboctahedra, edges with six equivalent RePa12 cuboctahedra, edges with twelve equivalent PaPa8Re4 cuboctahedra, faces with four equivalent RePa12 cuboctahedra, and faces with sixteen equivalent PaPa8Re4 cuboctahedra. There are a spread of Pa–Pa bond distances ranging from 2.92–3.30 Å. There are two shorter (3.10 Å) and two longer (3.18 Å) Pa–Re bond lengths. Re is bonded to twelve equivalent Pa atoms to form RePa12 cuboctahedra that share corners with six equivalent RePa12 cuboctahedra, corners with twelve equivalent PaPa8Re4 cuboctahedra, edges with eighteen equivalent PaPa8Re4 cuboctahedra, faces with eight equivalent RePa12 cuboctahedra, and faces with twelve equivalent PaPa8Re4 cuboctahedra.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on NdPa3 by Materials Project

Pa3Nd is Uranium Silicide structured and crystallizes in the cubic Pm-3m space group. The structure is three-dimensional. Pa is bonded to eight equivalent Pa and four equivalent Nd atoms to form PaNd4Pa8 cuboctahedra that share corners with twelve equivalent PaNd4Pa8 cuboctahedra, edges with eight equivalent NdPa12 cuboctahedra, edges with sixteen equivalent PaNd4Pa8 cuboctahedra, faces with four equivalent NdPa12 cuboctahedra, and faces with fourteen equivalent PaNd4Pa8 cuboctahedra. All Pa–Pa bond lengths are 3.36 Å. All Pa–Nd bond lengths are 3.36 Å. Nd is bonded to twelve equivalent Pa atoms to form NdPa12 cuboctahedra that share corners with twelve equivalent NdPa12 cuboctahedra, edges with twenty-four equivalent PaNd4Pa8 cuboctahedra, faces with six equivalent NdPa12 cuboctahedra, and faces with twelve equivalent PaNd4Pa8 cuboctahedra.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on NpPa3 by Materials Project

NpPa3 crystallizes in the hexagonal P6_3/mmc space group. The structure is three-dimensional. Np is bonded to twelve equivalent Pa atoms to form NpPa12 cuboctahedra that share corners with six equivalent NpPa12 cuboctahedra, corners with twelve equivalent PaNp4Pa8 cuboctahedra, edges with eighteen equivalent PaNp4Pa8 cuboctahedra, faces with eight equivalent NpPa12 cuboctahedra, and faces with twelve equivalent PaNp4Pa8 cuboctahedra. There are six shorter (3.09 Å) and six longer (3.32 Å) Np–Pa bond lengths. Pa is bonded to four equivalent Np and eight equivalent Pa atoms to form distorted PaNp4Pa8 cuboctahedra that share corners with four equivalent NpPa12 cuboctahedra, corners with fourteen equivalent PaNp4Pa8 cuboctahedra, edges with six equivalent NpPa12 cuboctahedra, edges with twelve equivalent PaNp4Pa8 cuboctahedra, faces with four equivalent NpPa12 cuboctahedra, and faces with sixteen equivalent PaNp4Pa8 cuboctahedra. There are a spread of Pa–Pa bond distances ranging from 3.07–3.33 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on SmPa3 by Materials Project

Pa3Sm is Uranium Silicide structured and crystallizes in the cubic Pm-3m space group. The structure is three-dimensional. Pa is bonded to eight equivalent Pa and four equivalent Sm atoms to form PaSm4Pa8 cuboctahedra that share corners with twelve equivalent PaSm4Pa8 cuboctahedra, edges with eight equivalent SmPa12 cuboctahedra, edges with sixteen equivalent PaSm4Pa8 cuboctahedra, faces with four equivalent SmPa12 cuboctahedra, and faces with fourteen equivalent PaSm4Pa8 cuboctahedra. All Pa–Pa bond lengths are 3.34 Å. All Pa–Sm bond lengths are 3.34 Å. Sm is bonded to twelve equivalent Pa atoms to form SmPa12 cuboctahedra that share corners with twelve equivalent SmPa12 cuboctahedra, edges with twenty-four equivalent PaSm4Pa8 cuboctahedra, faces with six equivalent SmPa12 cuboctahedra, and faces with twelve equivalent PaSm4Pa8 cuboctahedra.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on TmPa3 by Materials Project

Pa3Tm is Uranium Silicide structured and crystallizes in the cubic Pm-3m space group. The structure is three-dimensional. Pa is bonded to eight equivalent Pa and four equivalent Tm atoms to form PaTm4Pa8 cuboctahedra that share corners with twelve equivalent PaTm4Pa8 cuboctahedra, edges with eight equivalent TmPa12 cuboctahedra, edges with sixteen equivalent PaTm4Pa8 cuboctahedra, faces with four equivalent TmPa12 cuboctahedra, and faces with fourteen equivalent PaTm4Pa8 cuboctahedra. All Pa–Pa bond lengths are 3.33 Å. All Pa–Tm bond lengths are 3.33 Å. Tm is bonded to twelve equivalent Pa atoms to form TmPa12 cuboctahedra that share corners with twelve equivalent TmPa12 cuboctahedra, edges with twenty-four equivalent PaTm4Pa8 cuboctahedra, faces with six equivalent TmPa12 cuboctahedra, and faces with twelve equivalent PaTm4Pa8 cuboctahedra.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Pa3Zn by Materials Project

Pa3Zn is Uranium Silicide structured and crystallizes in the cubic Pm-3m space group. The structure is three-dimensional. Pa is bonded to eight equivalent Pa and four equivalent Zn atoms to form PaPa8Zn4 cuboctahedra that share corners with twelve equivalent PaPa8Zn4 cuboctahedra, edges with eight equivalent ZnPa12 cuboctahedra, edges with sixteen equivalent PaPa8Zn4 cuboctahedra, faces with four equivalent ZnPa12 cuboctahedra, and faces with fourteen equivalent PaPa8Zn4 cuboctahedra. All Pa–Pa bond lengths are 3.19 Å. All Pa–Zn bond lengths are 3.19 Å. Zn is bonded to twelve equivalent Pa atoms to form ZnPa12 cuboctahedra that share corners with twelve equivalent ZnPa12 cuboctahedra, edges with twenty-four equivalent PaPa8Zn4 cuboctahedra, faces with six equivalent ZnPa12 cuboctahedra, and faces with twelve equivalent PaPa8Zn4 cuboctahedra.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Pa3Nb by Materials Project

Pa3Nb is beta-derived structured and crystallizes in the hexagonal P6_3/mmc space group. The structure is three-dimensional. Pa is bonded to eight equivalent Pa and four equivalent Nb atoms to form distorted PaPa8Nb4 cuboctahedra that share corners with four equivalent NbPa12 cuboctahedra, corners with fourteen equivalent PaPa8Nb4 cuboctahedra, edges with six equivalent NbPa12 cuboctahedra, edges with twelve equivalent PaPa8Nb4 cuboctahedra, faces with four equivalent NbPa12 cuboctahedra, and faces with sixteen equivalent PaPa8Nb4 cuboctahedra. There are a spread of Pa–Pa bond distances ranging from 3.00–3.37 Å. There are two shorter (3.12 Å) and two longer (3.30 Å) Pa–Nb bond lengths. Nb is bonded to twelve equivalent Pa atoms to form NbPa12 cuboctahedra that share corners with six equivalent NbPa12 cuboctahedra, corners with twelve equivalent PaPa8Nb4 cuboctahedra, edges with eighteen equivalent PaPa8Nb4 cuboctahedra, faces with eight equivalent NbPa12 cuboctahedra, and faces with twelve equivalent PaPa8Nb4 cuboctahedra.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Pa3Mo by Materials Project

Pa3Mo is beta Cu3Ti-like structured and crystallizes in the hexagonal P6_3/mmc space group. The structure is three-dimensional. Pa is bonded in a 12-coordinate geometry to eight equivalent Pa and four equivalent Mo atoms. There are a spread of Pa–Pa bond distances ranging from 2.94–3.34 Å. There are two shorter (3.08 Å) and two longer (3.26 Å) Pa–Mo bond lengths. Mo is bonded to twelve equivalent Pa atoms to form a mixture of corner and face-sharing MoPa12 cuboctahedra.

36 MATERIALS SCIENCE↗