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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Journal of chemical ecology 19 (1993), S. 237-247 
    ISSN: 1573-1561
    Keywords: Salicylic acid ; allelopathy ; plant-water status ; water stress ; 13C ; carbon isotopes ; soybean ; Glycine max
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract Soybean seedlings [Glycine max (L.) Merr.] were used as the test species to study the allelopathic influence of salicylic acid (SA) on short- and long-term plant water status. Plants were grown in greenhouse conditions in nutrient culture medium amended with SA. Treatments were initiated 10 days after germination and continued for either 14 or 28 days. The threshold for inhibition of seedling growth over a 28-day treatment was 0.15 mM SA. Seedlings grown with 0.3 mM SA consistently had higher leaf diffusive resistance and lower transpiration and water potentials than control plants. The stable carbon isotope ratio (13C:12C) in tissue from both the 0.15 and 0.30 mM SA-treated plants was significantly higher than control seedlings, indicating SA caused a chronic water stress during the 28-day treatment. These data show that an interference with plant-water relationships is one mechanism whereby this allelochemical inhibits plant growth.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: An evaluation of the CHARMm force field for small molecules is described. Using different force field conditions and computational techniques, a wide variety of compounds are analyzed. rms deviations of Cartesian coordinates for 49 diverse organic molecules taken from the Cambridge Crystallographic Data Base and internal coordinate geometries for 28 other molecules are reported. Results are described with different dielectrics, dihedral constraints, and crystal packing to allow analysis of deviations from experimental data and give precise statements of the reliability of the parameters used in the force field. Torsional barriers (rms = 0.4) and conformational energy differences (rms = 0.4) are examined and comparisons made to other force fields such as MM2, Tripos, and DREIDING. The results confirm that CHARMm is an internally consistent all purpose force field with energy terms for bonds, angles, dihedrals, and out-of-plane motions, as well as nonbonded electrostatic and van der Waals interactions. Reported CHARMm results (rms = 0.006 Å for bonds, rms = 1.37° for angles, and rms = 3.2° for dihedrals) are in excellent agreement with high quality electron diffraction data. © 1992 by John Wiley & Sons, Inc.
    Additional Material: 5 Tab.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 11 (1990), S. 654-662 
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: Previous 4-21G ab initio geometry optimizations of various conformations of the model dipeptides (N-acetyl N'methyl amides) of glycine (GLY) and the alanine (ALA) have been used to help refine the empirical force constants and equilibrium geometry in the CHARMM force field for peptides. Conformationally dependent geometry trends from ab initio calculations and positions of energy minima on the ab initio energy surfaces have been used as guides in the parameter refinement, leading to modifications in the bond stretch, angle bending, and some torsional parameters. Preliminary results obtained with these refined empirical parameters are presented for the protein Crambin. Results for the cyclic (Ala-Pro-DPhe)2 are compared with those from other calculations. It seems that the dihedral angle fit achieved by the new parameters is significantly improved compared with results from force fields whose derivation does not include ab initio geometry trends.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
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