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  • Computational Chemistry and Molecular Modeling  (23)
  • Conformations  (1)
  • 11
    Electronic Resource
    Electronic Resource
    An ab initio study of the relative stabilities of the isomers of CH2N2 and SiH2N2 (1983)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 4 (1983), S. 1-8 
    Details
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: Ab initio SCF calculations of the equilibrium geometries have been carried out on nine possible isomers of MH2N2, where M = C or Si, and compared with the results of MNDO calculations. The results for the carbon compounds are in good agreement with available experimental data, but in the case of the silicon compounds, the molecules are predicted to be unstable with respect to decomposition to SiH2 and N2. The inclusion of electron correlation at the MP3 level does not alter the order of the relative stabilities, although the importance of the correlation contribution varies substantially between the different isomers.
    Additional Material: 3 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcc.540040102
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  • 12
    Electronic Resource
    Electronic Resource
    Theoretical studies of some new Anti-Malarial drugs (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 40 (1991), S. 231-245 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Qinghaosu (Artemisinin), is a sequiterpene lactone containing a peroxide group, which has been used from ancient times as an anti-malarial agent in Chinese medicine [1]. Unlike chloroquine and related compounds used as anti-malarial agents, resistant strains of malaria have not developed so far to qinghaosu. In this article; we present the results of a theoretical study of the structure of this and related molecules, using both semi-empirical and ab-initio quantum chemical methods, and an investigation of the known structure/activity (S/A) relationships of Qinghaosu and related molecules as anti-malarials using Molecular Electrostatic Potential (MEP) maps. The unusual 1,2,4-trioxane ring system, and other ring systems containing the peroxide linkage occurring in qinghaosu have also been studied in some detail. We speculate that the reactivity of this system in this context is related to a rather dramatic region of negative potential that surrounds the molecule and that includes the —O—O— linkage as well as the ring oxygen atom.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560400723
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  • 13
    Electronic Resource
    Electronic Resource
    Computational studies of the structures and properties of potential antimalarial compounds based on the 1,2,4-trioxane ring structure. I. Artemisinin-like molecules (1994)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 52 (1994), S. 117-131 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Artemisinin and related molecules are potential antimalarials that contain the 1,2,4-trioxane ring system. Several new derivatives have been synthesized and tested in Geneva, and this article presents the results of a systematic study of the structure of these molecules, both by the semiempirical PM3 method and using ab initio SCF methods. The results highlight the feasibility of full optimizations with 3-21G and 6-31G* basis sets for these large molecules. Molecular electrostatic potential (MEP) maps are evaluated and used in an attempt to identify the key features of the molecules that are necessary for their activity. There is good agreement between the PM3 and ab initio maps as to the qualitative predictions. © 1994 John Wiley & Sons, Inc.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560520710
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  • 14
    Electronic Resource
    Electronic Resource
    Hydrogen-bonding effects, electrostatic potential, and the antitumor activity of flavone acetic acid and related compounds. II. Ab initio studies on the second stable conformations (1996)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 60 (1996), S. 897-909 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: We previously studied the first stable conformations of flavone acetic acid and related compounds. In this article, a similar investigation was carried out on the second stable conformation of the same compounds. Emphasis is on the conformation dependence of the hydrogen-bonding effects, the molecular electrostatic potential (MEP), and the antitumor activity shown by these compounds. The results show that the second conformation is about 7.0 kcal mol-1 higher in energy and possibly is an inactive conformation as no correlation has been found between the antitumor activity and the MEP features. In addition, a detailed comparison with the first conformation, which is probably the active conformation, has been made of the geometry, the total energy, the Mulliken charges on some important atoms, hydrogen-bonding effects, and the MEP minima and isosurfaces. The role of the hydrogen-bonding effects, which was unclear in our previous work, is clarified in this work. The possible molecular basis of the antitumor activity is suggested. © 1996 John Wiley & Sons, Inc.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
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  • 15
    Electronic Resource
    Electronic Resource
    Hydrogen-bonding effects, electrostatic potential, and the antitumor activity of flavone acetic acid and related compounds. III. Ab initio studies on the conformation space (1997)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 62 (1997), S. 97-113 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Restricted geometry optimizations at the ab initio SCF level with the 3-21G basis set were employed to investigate the conformation space of flavone acetic acid (FAA) and its related compounds. All the conformations are produced from a conformation which is, according to our previous work, probably the active conformation in terms of antitumor activity shown by these compounds. Detailed studies on FAA were carried out while only brief discussions are made on the analogs. The main results obtained are that (1) FAA is a very flexible molecule, e.g., with the energy barrier up to about 3 kcal mol-1 from the reference conformation, the important torsional angle τ1 can change from 27.0° to 117.0°, τ2 from -168.0° to 2.0°, and τ3 from -50.0° to 30.0°; (2) the hydrogen-bonding effect plays an important role in determining lower-energy conformations; (3) among all the FAA conformations considered, some are active and some are inactive; (4) it seems that the analogs will have similar behavior to FAA when the torsional angle τ3 is restricted to the values which are around the equilibrium values; and (5) the hypothesis put forward previously has been further developed in this work. Now, we postulate that efficient charge transfers will lower the energy and that proper charge transfers will activate the molecule. There are mainly two different types of charge transfer corresponding to two different types of conformation, which are specified in this article. © 1997 John Wiley & Sons, Inc.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
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  • 16
    Electronic Resource
    Electronic Resource
    Hydrogen-bonding effects, electrostatic potential, and the antitumor activity of flavone acetic acid and related compounds. I. Ab initio studies on the first stable conformations (1995)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 54 (1995), S. 313-324 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Ab initio investigations have been carried out to account for the antitumor activity of flavone acetic acid (FAA) and related compounds. The hydrogen-bonding conformation was chosen for all the compounds and obtained through a restricted geometry optimization with the 3-21G basis set. Three key regions in the molecular electrostatic potential isosurfaces [V(r) ∼ -0.015 au] are found to be involved in the activity. Region 1 is the most important. Its existence implies the activity and its size determines the strength of the activity. Region 2 is another factor which can change the strength of the activity. Region 3 corresponds to the hydrogen-bonding effects which have been analyzed in detail, but its role is still not clear. Finally, basis-set effects on the molecular electrostatic potential have been briefly discussed. © 1995 John Wiley & Sons, Inc.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560540507
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  • 17
    Electronic Resource
    Electronic Resource
    Quantum chemical investigations of charge transfer interactions in relation to the electronic theory of cancer. IV. The interaction of formamide and the enol tautomers of several glyoxals (1980)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 1 (1980), S. 400-406 
    Details
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: The results of ab initio “supermolecule” calculations of the charge transfer between formamide and the enol forms of methylglyoxal, ethylglyoxal, dimethylglyoxal, and propenylglyoxal are compared for several different conformations of the constituent molecules. The enols were found to be poorer electron acceptors than their respective keto isomers.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcc.540010411
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  • 18
    Electronic Resource
    Electronic Resource
    Koopmans' theorem ionization potentials of methyl and silyl halides, chalcogenides, amines, and phosphines: An ab InitioSCF study (1983)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 4 (1983), S. 9-14 
    Details
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: Koopmans' theorem ionization potentials have been calculated for a series of hydrides, methyls, and silyls HnX, (CH3)nX, and (SiH3)nX (X = F, Cl, n = 1; X = O, S, n = 2; X = N, P, n = 3), together with some mixed species (MH3)nXH3-n (X = N, P; M = C, Si) using ab initio SCF methods. The calculated values give excellent agreement with experimental values without the inclusion of d functions. For the chlorides, HCl, CH3Cl, and SiH3Cl, the values vary rather little over a wide range of basis sets, and are unaffected by the inclusion of d functions.
    Additional Material: 5 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcc.540040103
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  • 19
    Electronic Resource
    Electronic Resource
    Ab initio calculations on the effect of different basis sets and electron correlation on the transition state for the reactions HNC ⇌ HCN and BCN ⇌ BNC (1984)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 5 (1984), S. 1-10 
    Details
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: The geometry of the ground states of the isomers and transition state for the systems HCN ⇌ HNC and BCN ⇌ BNC have been investigated using a wide variety of basis sets, both at the self-consistent-field (SCF) level and including correlation at the second-, and third-order Møller-Plesset (MP2 and MP3) levels. The barrier to isomerization and the isomerization energy were shown to be strongly dependent on the basis set and method, particularly for the BCN system.
    Additional Material: 5 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcc.540050102
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  • 20
    Electronic Resource
    Electronic Resource
    A theoretical study of the rotational isomers of nitrosomethanol by semiempirical (AM1) and ab initio methods (1988)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 9 (1988), S. 212-221 
    Details
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: The conformational potential energy surface as a function of the two internal torsion angles in C-nitrosomethanol has been obtained using the semiempirical AM1 method. Optimized geometries are reported for the local minima on this surface and also for the corresponding points on the HF/6-31G, 6-31G*, and 6-31G** surfaces. All methods predict cis and trans minima which occur in degenerate pairs, each pair being connected by a transition state of Cs symmetry. The AM1 structures are found to compare well with the corresponding ab initio structures. Ab initio HF/6-31G and HF/6-31G* harmonic vibrational frequencies are reported for the cis and trans forms of nitrosomethanol. When scaled appropriately the calculated frequencies are found to compare well with experimental frequencies. The ab initio calculations predict the energy barrier for cis → trans isomerization to be between 5.8 and 6.5 kcal/mol with the trans → cis isomerization barrier lying between 2.3 and 6.5 kcal/mol. The corresponding AM1 energy barriers are around 1 kcal/mol lower in energy. The ab initio calculations predict the barrier to conversion between the two cis rotamers to be very small with the AM1 value being around 1 kcal/mol. Both AM1 and ab initio calculations predict interconversion between trans rotamers to require between 1.2 and 1.4 kcal/mol.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcc.540090305
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