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  • 1
    Electronic Resource
    Electronic Resource
    Diastereoselective Synthesis of Cyclododeca-1,6-diallenes ( = cyclododeca-l,2,6,7-tetraenes) (1997)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 80 (1997), S. 414-420 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The synthesis of substituted cyclododeca-1,6-diallenes.( = cyclododeca-1,2,6,7-tetraenes) from cyclododeca-5,11-diyne-1,4-diols is described (Schemes 1 and 3). The ca. 1:1 mixtures of the stereoisomers of the cyclododeca-1,6-diallenes were formed in high yields from the ca. 1:1 diastereoisomer mixtures of the 1,4-disubstituted cyclododeca-5,11-diynes by reactions with Me2CuLi or t-BuMgCl/CuII. In mechanistically relevant experiments with the pure diastereoisomers of 1,4-dimethylcyclododeca-5,11-diyne-1,4-diol, it is demonstrated that the configuration is conserved in these reactions. The first synthesis of a 1-substituted cyclododeca-2,8-diyne bearing only one propargylic leaving group gives access to a mixed 12-membered allen-yne (Scheme 5).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19970800207
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  • 2
    Electronic Resource
    Electronic Resource
    Synthesis and Structure of Functionalized Cyclododecadiynes and -dienes (1996)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 79 (1996), S. 2164-2175 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The cyclododecadiynes 3b-d, 8b-d, and 10b-c with functionalities in two propargylic positions, as well as the monofunctionalized diyne 13b have been prepared from simple open-chain building blocks. In the DMPU ( = N,N'-dimethylpropyleneurea)-assisted ring-closing alkylation of 1,7-diynes, the twelve-membered ring compounds have been prepared in yields of 16-55%. The preparation of the diene-diyne 15 and the cyclododeca-5,11-diyne-1,4-dione 18 are described.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19960790811
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  • 3
    Electronic Resource
    Electronic Resource
    Stereoselective inhibition of thromboxane-induced coronary vasoconstriction by 1,4-dihydropyridine calcium channel antagonists (1990)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 2 (1990), S. 233-240 
    Details
    ISSN: 0899-0042
    Keywords: 1,4-dihydropypyridine enantiomers ; stereoselectivity ; thromboxane A2 (TxA2) ; coronary vasoconstriction ; calcium channel binding ; blood pressure ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The biological activity of the (+)-S- and (-)-R-enantiomers of niguldipine, of the (-)-S- and (+)-R-enantiomers of felodipine and nitrendipine, and of rac-nisoldipine and rac-nimodipine was investigated in vitro and in vivo. Inhibition of coronary vasoconstriction due to the thromboxane A2 (TxA2)-mimetic U-46619 in guinea pig Langendorff hearts, displacement of (+)-[3H]isradipine from calcium channel binding sites of guinea pig skeletal muscle T-tubule membranes, and blood pressure reduction in spontaneously hypertensive rats were determined. The enantiomers were obtained by stereoselective synthesis. Cross-contamination was 〈0.5% for both S- and R-enantiomers of niguldipine and nitrendipine and 〈1% for those of felodipine. From the doses necessary for a 50% inhibition of coronary vasoconstriction, stereoselectivity ratios for (+)-(S)-/(-)-(R)-niguldipine, (-)-(S)-/(+)-(R)-felodipine, and (-)-(S)-/(+)-(R)-nitrendipine of 28, 13, and 7, respectively, were calculated. The potency ratio racnisoldipine/rac-nimodipine was 3.5. Ratios obtained from binding experiments and antihypertensive activity were (+)-(S)-/(-)-(R)-niguldipine = 45 and 35, (-)-(S)-/(+)-(R)-felodipine = 12 and 13, (-)-(S)-/(+)-(R)-nitrendipine = 8 and 8, and rac-nisoldipine/rac-nimodipine = 8 and 7, respectively. Highly significant correlations were found between the in vitro potency of the substances to prevent U-46619-induced coronary vasoconstriction and their affinity for calcium channel binding sites as well as their antihypertensive activity. The mechanism of TxA2-induced coronary vasoconstriction in guinea pig Langendorff hearts can be readily explained by a transmembrane influx of extracellular Ca2+ susceptible to stereoselective blockade by 1,4-dihydropyridine calcium channel antagonists.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chir.530020408
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  • 4
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    On the Fragmentation of Rotating Interstellar Clouds (1981)
    In:  CASI
    Details
    Publication Date: 2005-11-09
    Description: Simple physical arguments are used to estimate the time scale for fragmentation of a collapsing, rotating, isothermal, interstellar cloud. This time scale is compared with a similarly estimated time scale for the collapse upon itself of a transitory ring structure. It is shown to be plausible for a cloud with a given ratio of rotational to gravitational energy (beta) that as the ratio of thermal to gravitational energy (alpha) is varied, there is an intermediate range of alpha where a ring forms and collapses on itself, prior to fragmentation. For higher or lower alpha however, the cloud fragments prior to ring self-collapse. The analysis is compared with the results of numerical multidimensional, gravitational, hydrodynamical collapse and shown to be in good agreement with them.
    Keywords: Astrophysics
    Type: Astrophysical Journal; Volume 244; 40-44
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  • 5
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    A Heuristic Criterion for Instability to Fragmentation in Rotating, Interstellar Clouds (1982)
    In:  Other Sources
    Details
    Publication Date: 2011-08-23
    Description: A heuristic criterion, based on linear perturbation analysis, is applied to the initial growth of density perturbations in isothermal or adiabatic gas clouds, with initially uniform density and uniform rotation. The heuristic criterion is shown to be consistent with the available results from numerical calculations of cloud collapse. The criterion predicts that perturbations varying as cos (m(phi)) will be most likely to grow when )pi is small, unless the cloud is nearly pressureless.
    Keywords: Astrophysics
    Type: Astrophysical Journal (ISSN 0004-637X); Volume 259; 159-165
    Format: text
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  • 6
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    Emerging Science of Comparative Solar System Formation - An Exoplanet Exploration Perspective (2015)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: No abstract available
    Keywords: Astrophysics
    Type: AIAA SPACE Conference and Exhibition; Aug 31, 2015 - Sep 02, 2015; Pasadena, CA; United States
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  • 7
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    The Gemini Planet-Finding Campaign: The Frequency of Giant Planets Around Debris Disk Stars (2013)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: We have completed a high-contrast direct imaging survey for giant planets around 57 debris disk stars as part of the Gemini NICI Planet-Finding Campaign. We achieved median H-band contrasts of 12.4 mag at 0farcs5 and 14.1 mag at 1'' separation. Follow-up observations of the 66 candidates with projected separation 〈500 AU show that all of them are background objects. To establish statistical constraints on the underlying giant planet population based on our imaging data, we have developed a new Bayesian formalism that incorporates (1) non-detections, (2) single-epoch candidates, (3) astrometric and (4) photometric information, and (5) the possibility of multiple planets per star to constrain the planet population. Our formalism allows us to include in our analysis the previously known Pictoris and the HR 8799 planets. Our results show at 95% confidence that 〈13% of debris disk stars have a 5 M Jup planet beyond 80 AU, and 〈21% of debris disk stars have a 3 M Jup planet outside of 40 AU, based on hot-start evolutionary models. We model the population of directly imaged planets as d(sq.)N/dMda m(sub ) a(sup ), where m is planet mass and a is orbital semi-major axis (with a maximum value of a(sub max)). We find that 〈 -0.8 and/or 〉 1.7. Likewise, we find that 〈 -0.8 and/or a(sub max) 〈 200 AU. For the case where the planet frequency rises sharply with mass ( 〉 1.7), this occurs because all the planets detected to date have masses above 5 M(sub Jup), but planets of lower mass could easily have been detected by our search. If we ignore the Pic and HR 8799 planets (should they belong to a rare and distinct group), we find that 〈20% of debris disk stars have a 3 M(sub Jup) planet beyond 10 AU, and 〈 -0.8 and/or 〈 -1.5. Likewise, 〈 -0.8 and/or a(sub max) 〈 125 AU. Our Bayesian constraints are not strong enough to reveal any dependence of the planet frequency on stellar host mass. Studies of transition disks have suggested that about 20% of stars are undergoing planet formation; our non-detections at large separations show that planets with orbital separation 〉40 AU and planet masses 〉3 M(sub Jup) do not carve the central holes in these disks.
    Keywords: Astrophysics
    Type: GSFC-E-DAA-TN11868 , The Astrophysical Journal (ISSN 0004-637X) (e-ISSN 1538-4357); 773; 2; 179
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  • 8
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    Mixing and Transport in the Solar Nebula (2003)
    In:  CASI
    Details
    Publication Date: 2019-07-10
    Description: Boss & Vanhala (2000, 2001) prepared reviews of triggered collapse and injection models, using Prudence Foster's finite differences code at very high spatial resolution (440 x 1440 cells) to demonstrate the convergence of the R-T fingers in triggered injection models. A two dimensional hydrodynamical calculation with unprecedentedly high spatial resolution (960 x 2880 zones, or almost 3 million grid points) demonstrated that it suitable shock front can both trigger the collapse of an otherwise stable presolar cloud, and inject shock front particles into the collapsing cloud through the formation of what become Rayleigh-Taylor fingers of compressed fluid layers falling into the gravitational potential well of the growing protostar. These calculations suggest that heterogeneity derived from these R-T fingers will persist down to the scale of their injection onto the surface of the solar nebula. Haghighipour developed a numerical code capable of calculating the orbital evolution of dust grains of varied sizes in a gaseous nebula, subject to Epstein and Stokes drag as well as the self-gravity of the disk. In collaboration with the PI and George W. Wetherill, Haghighipour has been involved in development of a new idea on the possibility of rapid formation of ice giant planets via the disk instability mechanism. Haghighipour studied the stability of a five-body system consisting of the Sun and four protoplanets by numerically integrating their equations of motions. Using Levison and Duncan s SWIFT integrator, Haghighipour showed that, depending on the orbital parameters of the bodies, such a system can be stable for 0.1-10 Myr. Time periods of 1 Myr or more are long enough to be consistent with the time scale proposed for the formation of giant planets by the disk instability mechanism and the photoevaporation of the gaseous envelopes of the outermost protoplanets by a nearby OB star, resulting in the formation of ice giant planets. The PI has used his three dimensional models of marginally gravitationally unstable disks to study the preservation of isotopic heterogeneity in evolving protoplanetary disks. Such heterogeneity might arise from the infall onto the disk s surface of solids processed in the X-wind region of the disk, or derived from stellar nucleosynthesis and injected by R-T fingers. The technique used consists of solving a color equation, identical to the gas continuity equation, which follows the time evolution in three space dimensions of an arbitrarily placed initial color field, i.e., a dye inserted the disk. The models show that significant concentrations of color could persist for time periods of about a thousand years or more, even in the most dynamically active region of such a disk. Such a time period might be long enough for solids to coagulate and grow to significant sizes while retaining the isotopic signature of their birth region in the nebula.
    Keywords: Astrophysics
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  • 9
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    Star Formation and the Solar System (1988)
    In:  CASI
    Details
    Publication Date: 2019-08-15
    Description: We have seen that studies of nearby star-forming regions are beginning to reveal the first signs of protoplanetary disks. Studies of interstellar and interplanetary grains are starting to provide clues about the processing and incorporation of matter into the Solar System. Studies of meteorites have yielded isotopic anomalies which indicate that some of the grains and inclusions in these bodies are very primitive. Although we have not yet detected a true interstellar grain, some of these materials have not been extensively modified since their removal from the ISM. We are indeed close to seeing our interstellar heritage. The overlap between astronomical and Solar System studies is in its infancy. What future experiments, observations, and missions can be performed in the near future that will greatly enhance our understanding of star formation and the formation of the Solar System?
    Keywords: Astrophysics
    Type: NASA-TM-112436 , NAS 1.15:112436 , Galactic and Extragalactic Star Formation; 232; 311-327|Jun 24, 1987; Whistler; Canada
    Format: application/pdf
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