Conformational Preferences of ortho-Substituted Benzophenones. Correlations Between Carbon-13 Nuclear Magnetic Resonance Shieldings and Calculated Torsional Angles

1973 ◽  
Vol 51 (7) ◽  
pp. 1053-1059 ◽  
Author(s):  
Gerald Wallace Buchanan ◽  
Giorgio Montaudo ◽  
Paulo Finocchiaro
Keyword(s):  
Minimum Energy ◽  
Conformational Energy ◽  
Conformational Preference ◽  
Contour Maps ◽  
Linear Relationships ◽  
Conformational Energy Calculations ◽  
Conformational Preferences ◽  
Conformational Properties ◽  
Torsional Angles ◽  
Semi Empirical

The results of an investigation of the conformational properties of some benzophenones are reported. Carbon-13 n.m.r. spectra provide a generally applicable method to study the conformational preference of these compounds through the C=O shifts. Semi-empirical conformational energy calculations have been used to build contour maps of relative conformational energy as a function of the two internal rotation angles of these molecules. Conformations of minimum energy, as detected from the contour maps, have been assumed as the most stable. The phenyl torsional angles corresponding to these conformations, plotted against the C=O shifts, furnish linear relationships.

scholarly journals Ab Initioand DFT Studies of Conformational Properties of Heteroatom Containing Ketene Analogues and Their Comparison with the Related Cyclic Analogues

2012 ◽  
Vol 9 (1) ◽  
pp. 193-202 ◽  
Author(s):  
S. Zahra Sayyed-Alangi ◽  
Mohammad T. Baei
Keyword(s):  
Transition State ◽  
Minimum Energy ◽  
Basis Set ◽  
Global Minima ◽  
Stable Conformer ◽  
Trans Conformation ◽  
Conformational Interconversion ◽  
Conformational Properties ◽  
Torsional Angles ◽  
Single Bonds

Minimum-energy and transition state geometries of 3-thioxoprop-2-enethial, 3-thioxoacrylaldehyde, 3-oxoprop-2-enethial, 3-selenoxoprop-2-enethial, 3-thioxoprop-2-eneselenal, 3-selenoxoprop-2-eneselenal, 3-oxoacrylaldehyde, 3-selenoxoacrylaldehyde and 3-oxoprop-2-eneselenal were calculated using HF, B3LYP and MP2 levels of theory and 6-31+G*basis set by rotation around the related -C-C- single bonds. In all of the above mentioned molecules, the s-trans conformation was obtained as the most stable conformer with the 180°dihedral angle, apart from 3-oxoprop-2-enethial and 3-thioxoprop-2-eneselenal which theirs-cisconformers were appeared more stability than related tos-transforms. Their perpendicular geometries, with torsional angles approximately 90°, were as transition state for conformational interconversion between the two global minima forms. Cyclic structures all of the above mentioned molecules were unstable than their linear forms.

Conformational Energy Calculations on the Eosinophil Chemotactic Peptide Analog Val-Gly-Ala-Glu: Comparison of Theory and Experiment

1988 ◽  
Vol 41 (12) ◽  
pp. 1841
Author(s):  
J Bremer ◽  
GL Mendz
Keyword(s):  
Theoretical Calculations ◽  
Chemical Shifts ◽  
Minimum Energy ◽  
Conformational Energy ◽  
Coupling Constants ◽  
Amide Proton ◽  
Energy Calculations ◽  
Peptide Analog ◽  
Conformational Energy Calculations ◽  
Nuclear Overhauser

Conformational energy calculations have been employed to obtain minimum energy conformations of the peptide Val- Gly-Ala-Glu , an analogue of eosinophil chemotactic tetrapeptides. The calculated conformations of the peptide can be described as an ensemble of structures in which the C-terminal and N-terminal regions of the molecule are in close proximity. The charge state of the peptide showed a marked effect on the calculated conformation, and the results were also sensitive to the electrostatic environment. The calculations performed on the dianionic form of the molecule showed good agreement with experimental n.m.r . Data on coupling constants, amide-proton resonance chemical shifts and temperature coefficients, nuclear Overhauser effects, side-chain rotamer populations, and binding of paramagnetic ions, obtained in dimethyl sulfoxide solutions. The calculations demonstrate some of the inherent problems facing theoretical calculations of peptide structure.

Comparison of Theoretical and Experimental Determinations of cis/trans Proline Isomer Ratios: Effect of Molecular Charge State

1989 ◽  
Vol 42 (7) ◽  
pp. 1011 ◽  
Author(s):  
J Bremer ◽  
GL Mendz
Keyword(s):  
Minimum Energy ◽  
Direction Cosine ◽  
Statistical Weight ◽  
Dielectric Constants ◽  
Conformational Energy ◽  
Conformational Energy Calculations ◽  
End Groups ◽  
Molecular Charge ◽  
Theoretical Predictions ◽  
Atomic Coordinates

The resonances of the 1H and 13C n.m.r. spectra of the peptide Pro-Pro-Pro in aqueous solutions have been assigned to specific nuclei by employing one- and two-dimensional techniques and pH titrations. Minimum energy conformations of the tripeptide in different ionization states were estimated by conformational energy calculations with two effective dielectric constants. The cis/trans isomer ratios of the lowest energy conformers obtained for each set of conditions were compared to the isomer ratios measured from the 13C n.m.r. spectra of the peptide in the cationic, zwitterionic and anionic forms. The theoretical predictions did not agree with the experimental data. The conformations and geometry of triprolyl sequences in the uncharged pentapeptide Ac- Gly-Pro-Pro-Pro-Gly-NHMe were investigated for different isomer configurations of the proline residues. The structure of the molecule was characterized by its conformational energy and by two other parameters estimated from the atomic coordinates of each conformation: the distance between atoms located at the end groups, and the direction cosine between vectors defined at the N- and C-terminal ends of the molecule. About 90% of the statistical weight of the lowest energy conformers corresponded to extended geometries of the triprolyl sequence.

scholarly journals Conformational energy calculations for dinucleotide molecules. A study of the component mononucleotide adenosine 3'-monophosphate

1975 ◽  
Vol 149 (3) ◽  
pp. 585-596 ◽  
Author(s):  
J M Thornton ◽  
P M Bayley
Keyword(s):  
Population Distribution ◽  
Conformational Energy ◽  
Conformational States ◽  
Energy Calculations ◽  
Strong Electrostatic Interaction ◽  
Crystalline Environment ◽  
Conformational Energy Calculations ◽  
Semi Empirical ◽  
Intramolecular Forces ◽  
Positively Charged

Semi-empirical conformational energy calculations were performed for the mononucleotides 5'-AMP, NMN+ and 3'-AMP. Only intramolecular forces are considered. Essentially all conformational states were explored to investigate the population distribution likely to be found in a non-crystalline environment. The calculations suggest that 5'-AMP and 3'-AMP are relatively flexible and a mixture of conformational states is expected. In contrast, the results for NMN+ suggest that a strong electrostatic interaction between the positively charged nicotinamide nitrogen atom and negatively charged phosphate oxygen is possible, stabilizing a few specific states. This interaction will be most significant in a solvent-free situation or an apolar environment.

Conformational energy calculations on the glycan chain of peptidoglycan

1986 ◽  
Vol 14 (3) ◽  
pp. 629-630 ◽  
Author(s):  
ALAN MARSDEN ◽  
BARRY ROBSON ◽  
J. STUART THOMPSON
Keyword(s):  
Conformational Energy ◽  
Energy Calculations ◽  
Glycan Chain ◽  
Conformational Energy Calculations
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