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  • Lunar and Planetary Science and Exploration  (65)
  • General Chemistry  (61)
  • 2000-2004  (82)
  • 1975-1979  (44)
  • 1
    Publikationsdatum: 2019-08-15
    Beschreibung: The Mars Climate Orbiter failed to achieve Mars orbit on September 23, 1999. On December 3, 1999, Mars Polar Lander and two Deep Space 2 microprobes failed. As a result, the NASA Administrator established the Mars Program Independent Assessment Team (MPIAT) with the following charter: 1) Review and analyze successes and failures of recent Mars and Deep Space Missions which include: a) Mars Global Surveyor, b) Mars Climate Orbiter, c) Pathfinder, d) Mars Polar Lander, e) Deep Space 1, and f) Deep Space 2; 2) Examine the relationship between and among, NASA Jet Propulsion Laboratory (JPL), California Institute of Technology (Caltech), NASA Headquarters, and industry partners; 3) Assess effectiveness of involvement of scientists; 4) Identify lessons learned from successes and failures; 5) Review revised Mars Surveyor Program to assure lessons learned are utilized; 6) Oversee Mars Polar Lander and Deep Space 2 failure reviews; and 7) Complete by March 15, 2000. In-depth reviews were conducted at NASA Headquarters, JPL, and Lockheed Martin Astronautics (LMA). Structured reviews, informal sessions with numerous Mars Program participants, and extensive debate and discussion within the MPIAT establish the basis for this report. The review process began on January 7, 2000, and concluded with a briefing to the NASA Administrator on March 14, 2000. This report represents the integrated views of the members of the MPIAT who are identified in the appendix. In total, three related reports have been produced: a summary report, this report entitled "Mars Program Independent Assessment Team Report," and the "Report on the Loss of the Mars Polar Lander and Deep Space 2 Missions".
    Schlagwort(e): Lunar and Planetary Science and Exploration
    Format: application/pdf
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  • 2
    ISSN: 1434-193X
    Schlagwort(e): Tetrakis(dimethylamino)naphthalenes ; Basicity ; Hydrogen bonds ; Cyclicvoltammetry ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: ---For comparison to the recently described 2,3,6,7-tetrakis(dimethylamino)naphthalene (1) the three isomers 2,3, and 4 were synthesized. The basicities of this group of isomers are strongly dependent upon the different mutual orientations of the pairs of dimethylamino substituents: only the isomers 3 and, partially, 4, both with dimethylamino groups in adjacent peri-positions of the naphthalene, are strong “proton sponges”. For the isomers 1 and 2 with the same number and kind of twofold dimethylamino substituents in neighbouring ortho-positions, however, no significant basicity increase is observed. To explain this difference between the two groups of isomers it is suggested that in the ortho-pairs of 1 and 2 the C-N bonds diverge considerably, leading to an increased N···N distance and consequently to less stable [N···H···N]+ hydrogen bonds in contrast to the parallel C-N bonds in the peri-substituted isomers 3 and 4. X-ray crystal structure analyses of the bases and of some of the salts derived therefrom were solved and are discussed. Cyclic voltammetry indicates that 1 to 4 are strong electron donors, reacting easily to radical cations or dications which with suitable acids have been obtained as salts.
    Zusätzliches Material: 3 Ill.
    Materialart: Digitale Medien
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  • 3
    Digitale Medien
    Digitale Medien
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 1727-1734 
    ISSN: 1434-193X
    Schlagwort(e): Self-assembly ; Vapor-pressure osmometry ; Resorcin[4]arenes ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: ---Resorcin[4]arene tetracarboxylic acids 5,6 (A) and resorcin[4]arene tetrapyridines 2,3 (P) self-assemble in chloroform solution to form stable heterotopic AP dimers. Data from NMR titration and dilution experiments, as well as from vapor-pressure osmometry (VPO), indicate that the AP dimer is formed with an association constant greater than 107 M-1. Solid-solution extraction experiments are indicative of the formation of a 2:1 trimer (A2P), while self-associated homotopic species (A2 and A3) can be detected by NMR and VPO. Analysis of the heterotopic noncovalent assembly process over a range of compositions shows that these other species are much less stable than the AP heterodimer, which is the exclusive species at an A/P concentration ratio of 1:1 (〉 99.7% of the total at 10 mM).
    Zusätzliches Material: 6 Ill.
    Materialart: Digitale Medien
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  • 4
    Digitale Medien
    Digitale Medien
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 527-538 
    ISSN: 1434-193X
    Schlagwort(e): Furans ; Pyrans ; Dihydropyran-2-ylidenes ; Ring closure ; Addition reaction ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: ---On treatment with base the pentynones 8a-f undergo anionic addition reactions of the resulting enolate species to the alkyne moiety and afford the 2,5-disubstituted furans 10a-f in yields ranging from 10-91%. The proposed mechanism involves the 2-methylene-dihydrofurans 11 as intermediates which tautomerize to yield the observed products. In the case of the α-picolyl derivative 8g both possible enolates 12 and 13 are formed which are subsequently transformed to the products 10g and 14g, respectively. Starting with the hexynones 9a-e an analogous reaction takes place with the formation of the pyran derivatives 15 and 16 in comparable yields. Under the same reaction conditions the n-butyl ketone 9f gives rise to two isomeric compounds, namely the 4H-pyran 16f and the cyclohexenone 17. This result is explained by assuming initial formation of two isomeric enolates which react either by O- or C-attack on the carbon-carbon triple bond.
    Zusätzliches Material: 5 Tab.
    Materialart: Digitale Medien
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  • 5
    Digitale Medien
    Digitale Medien
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 633-638 
    ISSN: 1434-193X
    Schlagwort(e): Amide linkage ; Phosphodiester ; Hammerhead ribozyme ; Oligonucleotides ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: ---A nucleoside dimer in which the natural phosphodiester bond is replaced by an isosteric amide linkage has been prepared. This dimer analogue was subsequently incorporated chemically at the cleavage position of a hammerhead ribozyme substrate. Although the resulting substrate analogue exhibited a high affinity for the ribozyme as shown by gel retardation assays, the amide bond proved to be fully resistant to cleavage under standard conditions of ribozyme cleavage activity.
    Zusätzliches Material: 3 Ill.
    Materialart: Digitale Medien
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  • 6
    ISSN: 1434-193X
    Schlagwort(e): Biotin ; Fullerenes ; Membranes ; Nanostructures ; Reflectometric interference spectroscopy ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: -As a prototype for a new class of lipid membrane components, the lipophilic fullerene derivative (so-called lipofullerene) 1 was synthesized and characterized. This mixed [1:5]-hexakisadduct consists of ten long alkyl chains within five didodecyl malonate addends and a linker malonate carrying a (+)-biotin unit as part of an amphiphilic spacer. The malonates are attached to the fullerene core in an octahedral addition pattern, which was achieved by two successive cyclopropanation sequences with the functional precursor malonate 8 and dodecyl malonate 10. The final step of the synthesis of 1 was the attachment of activated biotin 5 with the deprotected precursor 11. Binding experiments followed by reflectometric interference spectroscopy [RIfS] proved the capability of 1 to bind specifically the protein streptavidin (SA) through the biotin unit. The amphiphilic behavior of 1 was demonstrated by Langmuir Blodgett (LB) film investigations.
    Zusätzliches Material: 3 Ill.
    Materialart: Digitale Medien
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  • 7
    ISSN: 1434-193X
    Schlagwort(e): Fullerenes ; Cycloadditions ; Donor-acceptor systems ; Cyclic voltammetry ; Photoinduced electron transfer ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: ---The new C60 and C70 adducts 1b, 1d-1k, 1m, 6d, 7d, and 8d have been synthesized by [2+3] cycloadditions of the appropriate nitrile oxides. Variations in the distance and geometry of the donor and acceptor substituents are seen to have an influence on the redox behavior of the fullerene adducts in cyclic voltammetry experiments. The isoxazolo-fullerenes 1c, 1d, and 1i show shifts of about 30 mV or 40 mV to more negative values compared with the reference compound 1a. On the other hand, strong acceptor properties are detected in the case of compound 1e, which shows a positive shift of 30 mV relative to 1a. Moreover, time-resolved fluorescence spectroscopy has shown that upon excitation of the fullerene moiety in the polar solvent benzonitrile, an electron is transferred from the donor substituent to the first excited singlet state of the fullerene, thereby reducing the excited-state lifetime. Our data demonstrate that the electron-transfer rate in donor-substituted fullerenes can be controlled by the electron-donating property of the substituent as well as the electronic structure and/or length of the spacer used. The C70 regioisomers 6d, 7d, and 8d exhibit differences in their spectroscopic characteristics.
    Zusätzliches Material: 3 Ill.
    Materialart: Digitale Medien
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  • 8
    Digitale Medien
    Digitale Medien
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 701-705 
    ISSN: 1434-193X
    Schlagwort(e): Asymmetric catalysis ; Catalysis ; Addition reactions ; N ligands ; Nickel ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: ---Quaternary stereocenters were constructed with an enantioselectivity of up to 91% ee under aerobic conditions and at ambient temperature in the Michael reaction of β-dicarbonyl compounds and methyl vinyl ketone with Ni(OAc)2·4H2O and optically active trans-1,2-diaminocyclohexane as a chiral catalyst.
    Zusätzliches Material: 1 Tab.
    Materialart: Digitale Medien
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  • 9
    Digitale Medien
    Digitale Medien
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 181-186 
    ISSN: 1434-193X
    Schlagwort(e): Carbohydrates ; Oligosaccharides ; Glycosylations ; Organic synthetic methods ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: ---The tetrasaccharide 5-aminopentyl glycoside β-D-Manp-(1→4)-β-D-Glcp-(1→4)-α-L-Rhap-(1→3)-β-D-Glcp-1-O-(CH2)5NH2(22) related to the exopolysaccharide of Arthrobacter sp. CE-17 was synthesized by coupling of the properly protected disaccharide blocks β-D-Manp-(1→4)-β-D-Glcp-1-S-Ph (11) and α-L-Rhap-(1→3)-β-D-Glcp-1-O-(CH2)5NHZ (20). Building block 11 was obtained by intramolecular β-mannosylation of a malonyl-tethered disaccharide glycoside which was prepared from phenyl 4,6-O-benzylidene-1-thio-β-D-glucopyranoside (1) and ethyl 2,3,4-tri-O-benzyl-1-thio-α-D-mannopyranoside (5) in 5 steps. Building block 20 was obtained by coupling N-Z-protected 5-aminopentyl 2-O-benzyl-4,6-O-benzylidene-β-D-glucopyranoside (14) obtained from the non-benzylated counterpart 12 with ethyl 2,3-di-O-benzoyl-4-O-chloroacetyl-1-thio-α-L-rhamnopyranoside (18) obtained in 3 steps from ethyl 2,3-O-isopropylidene-1-thio-α-L-rhamnopyranoside (15).
    Zusätzliches Material: 1 Ill.
    Materialart: Digitale Medien
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  • 10
    ISSN: 1434-193X
    Schlagwort(e): Asymmetric synthesis ; Phosphazene base ; Pyridyl epoxide ; Furyl epoxide ; Pyridyl alcohol ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: ---trans-1-(2-Pyridyl)-, trans-1-(3-pyridyl)-, trans-1(2-furyl)-, and trans-1(3-furyl)-2-phenyl epoxides with enantiomeric purities ranging from 96.8 to 99.8% [in favor of the (+, EtOH)-isomer] are obtained in two steps from pure (R,R,R)-oxathiane which is recovered (85-90%) and reused. The chiral bidentate ligand 2-phenyl-(S)-1-(2-pyridyl)ethanol with 99.6% ee was obtained in three steps and 67% overall isolated yield.
    Zusätzliches Material: 1 Ill.
    Materialart: Digitale Medien
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