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  • Chemistry  (99)
  • Aircraft Stability and Control
  • GENERAL
  • Inorganic Chemistry
  • 2015-2019  (20)
  • 1955-1959  (81)
  • 1940-1944
  • 2018  (20)
  • 1957  (81)
  • 1
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    Quantifying hot carrier and thermal contributions in plasmonic photocatalysis (2018)
    American Association for the Advancement of Science (AAAS)
    In: Science
    Details
    Publication Date: 2018-10-05
    Description: Photocatalysis based on optically active, "plasmonic" metal nanoparticles has emerged as a promising approach to facilitate light-driven chemical conversions under far milder conditions than thermal catalysis. However, an understanding of the relation between thermal and electronic excitations has been lacking. We report the substantial light-induced reduction of the thermal activation barrier for ammonia decomposition on a plasmonic photocatalyst. We introduce the concept of a light-dependent activation barrier to account for the effect of light illumination on electronic and thermal excitations in a single unified picture. This framework provides insight into the specific role of hot carriers in plasmon-mediated photochemistry, which is critically important for designing energy-efficient plasmonic photocatalysts.
    Keywords: Chemistry
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Geosciences , Computer Science , Medicine , Natural Sciences in General , Physics
    Published by American Association for the Advancement of Science (AAAS)
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  • 2
    Electronic Resource
    Electronic Resource
    Ion exchange separation of gram quantities of americium from a kilogram of lanthanum (1957)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 3 (1957), S. 286-288 
    Details
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The separation of 4.5 g. of americium from approximately a kilogram of light rare earths (primarily lanthanum) was achieved on a pilot plant scale by chromatographic displacement of the mixture from Dowex-50 resin with 0.1% ammonium citrate at pH 8 into hydrogen-form Dowex-50. The americium collected into a narrow band and was eluted free from lanthanum but contained an equal weight of cerium. A 6- and a 2-in.-diam. column were used in tandem. Use of a final column with a much smaller diameter would have permitted a cleaner separation from cerium, but this was left for a laboratory-scale separation by a different process. Precipitation, which was observed in the columns during the first runs, was later avoided entriely by use of high flow rates both initially and during the transfer between columns. No adverse effects were noted from ∼15 curies of alpha activity.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/aic.690030228
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  • 3
    Electronic Resource
    Electronic Resource
    Vapor-liquid equilibria for hydrogen-light-hydrocarbon systems at low temperatures (1957)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 3 (1957), S. 33-36 
    Details
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Experimental equilibrium vapor and liquid compositions are reported for the hydrogen-methane system at -150°, -200°, and -250°F. and at pressures of 500 to 4,000 lb./sq. in. The ternary system hydrogen-methane-propane was studied at 0°, -100°, and -200°F. at 500 and 1,000 lb./sq. in. Phase compositions were determined for a limited number of similar conditions for the hydrogen-methane-propylene and hydrogen-methane-ethylene-ethane-propylene-propane systems.
    Additional Material: 12 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/aic.690030107
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  • 4
    Electronic Resource
    Electronic Resource
    Phase behavior of hydrogen-light-hydrocarbon systems (1957)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 3 (1957), S. 236-241 
    Details
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The decreasing solubility of hydrogen in hydrocarbons with decreasing temperature continues down to the freezing point of the hydrocarbons, around -300°F. This behavior is shown to be an enlargement of phenomena exhibited by normal hydrocarbon mixtures. Methods of predicting equilibrium-phase compositions are presented for hydrogen in ligh-hydrocarbon systems. The correlations are satisfactory for binary and certain ternary systems, but are not reliable for complex mixtures.
    Additional Material: 18 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/aic.690030219
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  • 5
    Electronic Resource
    Electronic Resource
    Le comportement diélectrique des polymères en solutions diluées (1957)
    Hoboken, NJ : Wiley-Blackwell
    Journal of Polymer Science 23 (1957), S. 233-240 
    Details
    ISSN: 0022-3832
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Dielectric properties and loss factors have been measured for dilute solutions of polyvinyl chloride in tetrahydrofuran and mixtures of this solvent with heptane, for solutions of polymethyl methacrylate in benzene and toluene, and for solutions of polyvinyl acetate in toluene. Concentrations varied from 0.5 to 8 g./100 ml. Frequencies ranged from 0.01 to 35 megacycles/sec., and temperatures from -35° to +25°C.Only one sample of polyvinyl chloride was used (DP = 1,750), but six fractions of methyl polymethacrylate (DP = 240 - 12,500) and four of polyvinyl acetate (DP = 2,550-23,250). Numerical values for the three polymers were rather similar. The root mean square dipole moments were proportional to the square root of DP. Relaxation times were practically independent of DP.
    Notes: Les propriétés diélectriques et les facteurs de perte ont été mesurés pour des solutions diluées de chlorure de polyvinyle dans le tétrahydrofurane et des mélanges de ce solvant avec l'heptane, pour des solutions de polyméthacrylate de méthyle dans le benzène et le toluène, et pour des solutions d'acétate de polyvinyle dans le toluène. Les concentrations variaient de 0.5 à 8 g./100 ml. Les fréquences allaient de 0.01 à 35 mégacycles/sec. et les température de -35° à +25°C. Un seul échantillon de chlorure de polyvinyle a été utilisé (DP = 1750); par contre quatre fractions de polyméthacrylate de méthyle (DP = 240-12.500) et quatre d'acétate de polyvinyle (DP = 2.550-23.250) ont été utilisées. Les valeurs numériques des trois polymères étaient plutǒt similaires. Les moments dipolaires moyens étaient proportionnels à la carrée du DP. Les temps de rélaxation étaient pratiquement indépendants du DP.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pol.1957.1202310322
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  • 6
    Electronic Resource
    Electronic Resource
    Stoffwechselprodukte von Actinomyceten. 9. Mitteilung. GranaticinHerrn Prof. Dr. T. Reichstein zum 60. Geburtstag gewidmet. (1957)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 40 (1957), S. 1262-1269 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Aus dem Kulturfiltrat eines Streptomyceten-Stammes, der vorläufig bei Streptomyces olivaceus (Waksman) Waksman & Henrici eingeordnet wurde, liess sich ein kristalliner, antibiotisch wirksamer Farbstoff mit lackmusähnlichen Eigenschaften - das Granaticin - isolieren. Wie aus dem auf röntgenographischem Wege bestimmten Molekulargewicht, den analytischen Daten und Absorptionsspektren des Farbstoffes und seines Tetra-O-acetyl-Derivates folgt, handelt es sich vermutlich um eine tricyclische Tetrahydroxy-chinon-dicarbonsäure C22H20O10.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19570400518
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  • 7
    Electronic Resource
    Electronic Resource
    Stoffwechselprodukte von Actinomyceten. 7. Mitteilung. Echinomycin (1957)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 40 (1957), S. 199-204 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Aus den Kulturbrühen von Streptomyces echinatus n. sp. wurde ein neues lipophiles, neutrales Antibioticum - das Echinomycin, C29H37O7N7S - isoliert und durch analytische Daten, UV.- und IR.- Absorptionsspektrum, sowie biologische Wirksamkeit charakterisiert.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19570400124
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  • 8
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    Teaching an old carbocation new tricks: Intermolecular C-H insertion reactions of vinyl cations (2018)
    American Association for the Advancement of Science (AAAS)
    In: Science
    Details
    Publication Date: 2018-07-27
    Description: Vinyl carbocations have been the subject of extensive experimental and theoretical studies over the past five decades. Despite this long history in chemistry, the utility of vinyl cations in chemical synthesis has been limited, with most reactivity studies focusing on solvolysis reactions or intramolecular processes. Here we report synthetic and mechanistic studies of vinyl cations generated through silylium–weakly coordinating anion catalysis. We find that these reactive intermediates undergo mild intermolecular carbon-carbon bond–forming reactions, including carbon-hydrogen (C–H) insertion into unactivated sp 3 C–H bonds and reductive Friedel-Crafts reactions with arenes. Moreover, we conducted computational studies of these alkane C–H functionalization reactions and discovered that they proceed through nonclassical, ambimodal transition structures. This reaction manifold provides a framework for the catalytic functionalization of hydrocarbons using simple ketone derivatives.
    Keywords: Chemistry
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Geosciences , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 9
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    Separation of enantiomers by their enantiospecific interaction with achiral magnetic substrates (2018)
    American Association for the Advancement of Science (AAAS)
    In: Science
    Details
    Publication Date: 2018-06-22
    Description: It is commonly assumed that recognition and discrimination of chirality, both in nature and in artificial systems, depend solely on spatial effects. However, recent studies have suggested that charge redistribution in chiral molecules manifests an enantiospecific preference in electron spin orientation. We therefore reasoned that the induced spin polarization may affect enantiorecognition through exchange interactions. Here we show experimentally that the interaction of chiral molecules with a perpendicularly magnetized substrate is enantiospecific. Thus, one enantiomer adsorbs preferentially when the magnetic dipole is pointing up, whereas the other adsorbs faster for the opposite alignment of the magnetization. The interaction is not controlled by the magnetic field per se, but rather by the electron spin orientations, and opens prospects for a distinct approach to enantiomeric separations.
    Keywords: Chemistry
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Geosciences , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 10
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    Real-time imaging of adatom-promoted graphene growth on nickel (2018)
    American Association for the Advancement of Science (AAAS)
    In: Science
    Details
    Publication Date: 2018-03-16
    Description: Single adatoms are expected to participate in many processes occurring at solid surfaces, such as the growth of graphene on metals. We demonstrate, both experimentally and theoretically, the catalytic role played by single metal adatoms during the technologically relevant process of graphene growth on nickel (Ni). The catalytic action of individual Ni atoms at the edges of a growing graphene flake was directly captured by scanning tunneling microscopy imaging at the millisecond time scale, while force field molecular dynamics and density functional theory calculations rationalize the experimental observations. Our results unveil the mechanism governing the activity of a single-atom catalyst at work.
    Keywords: Chemistry
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Geosciences , Computer Science , Medicine , Natural Sciences in General , Physics
    Published by American Association for the Advancement of Science (AAAS)
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