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  • Biochemistry  (2)
  • Theoretical, Physical and Computational Chemistry  (2)
  • 1
    ISSN: 0020-7608
    Keywords: hydrogen bonding ; DNA ; base analogs ; stacking interaction ; reaction field ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In a recent experimental study, it was reported that replacement of thymine in the adenine-thymine base pair of DNA by its molecular analogs which cannot form proper hydrogen bonds with adenine (A) does not cause disruption of DNA structure and synthesis. AM1 and ab initio molecular orbital calculations and electric field mapping were carried out in order to examine the possibility of pairing of A with each one of two analogs of thymine in the gas phase. Self-consistent reaction field calculations were also carried out on the individual molecules and their pairs using the polarized continuum model in order to examine their stability in aqueous media. Our results are broadly in agreement with the conclusions drawn in the above-mentioned experimental work.   © 1998 John Wiley & Sons, Inc. Int J Quant Chem 68: 351-355, 1998
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 0020-7608
    Keywords: hybridization displacement charge ; transferability of properties ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Molecular electrostatic potential (MEP) maps and MEP-derived charges for certain molecules were studied by the ab initio approach using the 6-31G basis set. These results were used to obtain the parameters (K and ζ) for fluorine, sulfur, and chlorine required for the hybridization displacement charge (HDC) calculations employing the MNDO and AMI methods. The HDC combined with Löwdin charges, distributed continuously in three-dimension spherically and symmetrically, were shown to reproduce ab initio MEP features of molecules fairly well. This method of computing the MEP was applied to two molecules of pharmacological importance, namely, dimaprit and mustard gas. It is shown by studying the cis and trans forms of two amino acids that transferability of the MEP is appreciably less acceptable than that of charges in going from one conformation to the other.   © 1998 John Wiley & Sons, Inc. Int J Quant Chem 66: 149-156, 1998
    Additional Material: 2 Ill.
    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 5 (1984), S. 225-229 
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: Changes of electronic charge distribution following the lowest singlet n-π* transitions of benzaldehyde, benzamide, benzoic acid, the phthalaldehydes, pyridine, and the diazines have been examined using the CNDO-S/CI method. A Singlet n-π* transition is found as a general rule to direct electronic charges to the para position of the atom in the ring that carries the lone pair or to which the substituent carrying the lone pair is attached.
    Additional Material: 2 Tab.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: VE-PPP, CNDO/2, and CNDO/s-CI methods have been used to investigate the electronic spectrum and structure of benzaldehyde. Electronic charge distributions and bond orders in the ground and lowest excited singlet π* ← π and π* ← n states of the molecule have been studied. The molecule has been shown to be nonplanar in the lowest π* ← n excited singlet state, in agreement with the conclusions drawn from the study of vibrational spectra. Dipole moments in both excited states have been shown to be larger than the ground-state value. Thus, the ambiguity in the experimental result for the π* ← π n excited singlet state dipole moment has been resolved. It has been shown that the n orbital is mainly localized on the CHO group. Furthermore, charge distributions, dipole moments, and molecular geometries are shown to be very different in the excited singlet π* ← π and π* ← n states.
    Additional Material: 4 Tab.
    Type of Medium: Electronic Resource
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