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  • Organic Chemistry  (2,690)
  • Q
  • 1995-1999  (2,693)
  • 1
    Electronic Resource
    Electronic Resource
    Mt. Melbourne volcano, antarctica: Evidence of seismicity related to volcanic activity (1996)
    Springer
    Pure and applied geophysics 146 (1996), S. 305-318 
    Details
    ISSN: 1420-9136
    Keywords: Volcanic seismicity ; polarization analysis ; Q ; volcanic processes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Characterization of the microseismic activity (M L 〈2.0) has been performed at Mt. Melbourne since 1990. We recorded a group of low frequency events with common morphological characteristics, i.e., an emerging onset, an unclear second phase and a sharply dropping coda. Spectral analysis of events recorded at more than one station indicates that the seismogram characteristics and spectral content are largely due to source effects. A polarization filter applied to a set of three component data revealed a first phase made up ofP waves followed (after about 0.9–1.4 sec.) by a second phase probably composed ofSH-type waves. Particle motion analysis detected a seismic ray angle direction mainly between N70°E and N110°E and apparent angle of incidence between 35° and 48° for the first phase. The studied seismicity was localized in an area on the eastern slope of Mt. Melbourne Volcano which presents a surface temperature anomaly (Mazzarini andSalvini, 1994). We formulate two hypotheses for the type of earthquakes recorded: 1) long-period events involving active presence of magmatic fluids in the source processes; 2) or the result of fracturing processes (shear?) in a medium characterized by transition between brittle and plastic behaviors. In the latter hypothesis the superficial thermal anomaly may be a symptom of this behavior at depth and is confirmed by the lown values observed for the exponential fit in the codaQ analysis.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00876495
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  • 2
    Electronic Resource
    Electronic Resource
    Overbreak and underbreak in underground openings Part 2: causes and implications (1996)
    Springer
    Geotechnical and geological engineering 14 (1996), S. 325-340 
    Details
    ISSN: 1573-1529
    Keywords: overbreak ; underbreak ; digital image processing ; tunnelling ; blasting assessment ; tunnel profiling ; RMR ; Q ; powder factor ; perimeter powder factor
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Summary The newly developed light sectioning method has been used to investigate some of the causes and costs of overbreak and underbreak. Investigations at the Aquamilpa Hydroelectric Project in Mexico have shown decreased overbreak and increased underbreak as a result of increased rock quality and decreased explosive energy. A new measure of explosive energy, the ‘perimeter powder factor’ (PPF), has been defined and shown to be useful in the context of tunnel-wall rock damage. Tentative results indicate that explosive energy (PPF) may be a more important factor in producing underbreak, whereas rock quality may be a greater factor in producing overbreak. A site-specific equation is given for predicting overbreak or underbreak as a function of rock quality and explosive energy, with an evaluation of the cost of underbreak and overbreak.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00421947
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  • 3
    Electronic Resource
    Electronic Resource
    Formation and reactivity of acyl glucuronides: The influence of chirality (1995)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 7 (1995), S. 1-9 
    Details
    ISSN: 0899-0042
    Keywords: acyl glucuronide ; enantiomer ; epimer ; diastereomer ; nonsteroidal antiinflammatory drug ; 2-arylpropionic acid ; systemic cycling ; reactivity ; hydrolysis ; covalent binding ; drug-protein adduct ; regioisomer ; aglycone ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chir.530070102
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  • 4
    Electronic Resource
    Electronic Resource
    Retention model for the resolved enantiomers of felodipine on chiral-AGP using micellar mobile phases (1995)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 7 (1995), S. 23-27 
    Details
    ISSN: 0899-0042
    Keywords: felodipine ; retention model ; micellar mobile phases ; chiral resolution ; CHIRAL-AGP ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A retention model for the chiral separation of an uncharged solute, felodipine, on CHIRAL-AGP, using a micellar mobile phase is proposed. The model assumes the presence of two stereoselective sites and each enantiomer was found to interact with different sites. Addition of a chiral aliphatic alcohol, (+)-(S)-2-octanol, preferentially interacted with the binding site for (-)-(S)-felodipine. The monomeric form of the micellar agent (Tween® 20) competed with the enantiomers for the adsorption sites, and the formation of a 1:1 complex between the enantiomers and the micelles was assumed. The retention of the solutes was effectively controlled by adding small quantities (〈1.63 × 10-3 M) of the nonionic detergent Tween 20 to the mobile phase. Baseline separation was achieved by addition of 1.0 mM n-octylamine to the mobile phase; 8.14 × 10-4 M Tween 20 in phosphate buffer pH 7.0. The separation factor (α = 1.74) was unaffected by the detergent concentration in the presence of 1.0 mM n-octylamine. © 1995 Wiley-Liss, Inc.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chir.530070105
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  • 5
    Electronic Resource
    Electronic Resource
    Enantioselectivity suggests a cytosolic origin for a commercial pig liver esterase preparation (1995)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 7 (1995), S. 40-43 
    Details
    ISSN: 0899-0042
    Keywords: enantioselectivity ; pig liver esterase ; hydrolysis ; oxazepam ; chiral stationary phase HPLC ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A widely utilized pig liver esterase preparation has been found to be derived essentially exclusively from the cytosolic fraction of pig livers. Esterases in cytosol and microsomes prepared from a fresh pig liver hydrolyzed the S- and R-enantiomers of racemic oxazepam 3-acetate (rac-OXA) with specific activity ratios of approximately 2.3:1 and 1:62, respectively. Product formations were analyzed by chiral stationary phase high-performance liquid chromatography. The commercial pig liver esterase preparation showed greater activity toward S-OXA than did the esterases in the cytosolic fraction prepared from fresh pig liver. The results established that (i) esterases contained in microsomes and cytosol of pig liver have opposite enantioselectivity in the hydrolysis of rac-OXA and (ii) the commercial pig liver esterase preparation has a cytosolic origin. © 1995 Wiley-Liss, Inc.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chir.530070108
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  • 6
    Electronic Resource
    Electronic Resource
    Masthead (1995)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 7 (1995) 
    Details
    ISSN: 0899-0042
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chir.530070201
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  • 7
    Electronic Resource
    Electronic Resource
    Studies in chiral symmetry breaking crystallization I: The effects of stirring and evaporation rates (1995)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 7 (1995), S. 62-68 
    Details
    ISSN: 0899-0042
    Keywords: chiral symmetry breaking ; chiral autocatalysis ; asymmetric crystallization ; origin of optical activity ; secondary nucleation ; stirred crystallization ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Chiral symmetry breaking can be realized in stirred crystallization of Na-ClO3. We present experimental and theoretical studies of the random distribution of crystal enantiomeric excess (cee) for various stirring and solvent evaporation rates. For a fixed solvent evaporation rate, as the stirring RPM is increased, the probability distribution of cee initially broadens and subsequently develops a sharp peak close to cee = 1. On further increase of stirring rate, the probability distribution once again broadens. This broad probability distribution becomes narrow, with a sharp peak near cee = 1, if the solvent evaporation rate is decreased. Thus we show some ways in which the probability distribution of cee can be controlled in stirred crystallization. In particular, our study shows that the stirring rate and the solvent evaporation rate can be adjusted to maximize crystal enantiomeric excess. © 1995 Wiley-Liss, Inc.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chir.530070203
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  • 8
    Electronic Resource
    Electronic Resource
    Circular dichroism spectroscopy of 2-aminotetralins (1995)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 7 (1995), S. 82-89 
    Details
    ISSN: 0899-0042
    Keywords: CD ; conformational behaviour ; configuration ; helicity rules ; 2-aminotetralin ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The circular dichroism (CD) spectra of a series of oxygenated 2-(dipropylamino)tetralin derivatives are reported. On the basis of known absolute configurations and conformational preferences of the compounds, the validity of published correlations between the sign of the 1Lb Cotton effect and the three-dimensional structure was examined. Contrary to predictions, substitution in position 6 or 7 of the tetralin moiety did not change the sign of the 1Lb Cotton effect. An unexpected sign inversion was, however, observed in some of the compounds containing methyl substituents in the nonaromatic ring. The occurrence of this inversion was not correlated with a change in conformational behaviour and varied depending on the position and nature of the aromatic substituent. No correlations were obvious between the sign of the 1Lb Cotton effect and the absolute configuration and conformational preferences of the compounds. Therefore, at present, CD spectroscopy does not appear to be useful in assignments of the absolute configurations of 2-(dipropylamino)tetralin derivatives. © 1995 Wiley-Liss, Inc.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chir.530070206
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  • 9
    Electronic Resource
    Electronic Resource
    The influence of protective groups on diastereofacial selectivity of Diels-Alder cycloaddition reactions (1995)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 7 (1995), S. 96-102 
    Details
    ISSN: 0899-0042
    Keywords: conformational effect ; intramolecular ; allylic ; stereogenic ; steric ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The diastereofacial selectivity of both inter- and intramolecular Diels-Alder reactions with dienes having an allylic stereogenic center has been studied by varying the allylic oxygen protective group. Four different hydroxy protective groups were investigated including benzyl, t-butyldiphenylsilyl, triethylsilyl, and t-butyldimethylsilyl ethers. For intermolecular reactions, the benzyl ether derivative gave the highest sπ-facial selectivity through a transition state in which the allylic stereocenter favors the CH eclipsed conformation. For intramolecular cycloadditions, the t-butyldimethylsilyl group gave a slightly higher selectivity than the benzyl ether derivative through a transition state in which the allylic stereocenter favors the CO eclipsed conformation. The opposite diastereofacial selectivity observed for inter- and intramolecular reactions is explained by considering both steric and electronic effects. © 1995 Wiley-Liss, Inc.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chir.530070208
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  • 10
    Electronic Resource
    Electronic Resource
    Chiral enamines derived from 2-(2′-pyrido)acetophenone and 2-(2′-quinolino)acetophenone as ligands in copper(I) catalyzed enantioselective cyclopropanations (1995)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 7 (1995), S. 115-120 
    Details
    ISSN: 0899-0042
    Keywords: chiral 1,5-bisnitrogen ligands ; homogeneous asymmetric cyclopropanation ; copper(I) complexes ; enantioselectivity ; chiral gas chromatography ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Optically active enamines of 2-(2′-pyrido)acetophenone or 2-(2′-quinolino)acetophenone with (R)-1-phenylethylamine, (R)-1-(1-naphthyl)ethylamine, (R)-cyclohexylethylamine, and (R)-phenylglycinol were prepared and their copper(I) complexes used in the enantioselective cyclopropanation of styrene with ethyl- and menthyldiazoacetate. Enantioselectivities of up to 42% enantiomeric excess were obtained for cis/trans 2-phenylcyclopropan-1-carboxylic acid ethyl esters, as determined by gas-liquid chromatography (GLC) on chiral chromatographic columns. © 1995 Wiley-Liss, Inc.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chir.530070302
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