A study of conformation about the aryl C-N bonds in N-aryl imides by dynamic N.M.R. spectroscopy

1976 ◽  
Vol 29 (2) ◽  
pp. 295 ◽  
Author(s):  
SM Verma ◽  
NB Singh
Keyword(s):  
Energy Barrier ◽  
Phenyl Group ◽  
Spectral Studies ◽  
Free Rotation ◽  
Conformational Study ◽  
Temperature Dependent ◽  
Restricted Rotation ◽  
Planar Conformation

A series of α, β-(9,10-dihydroanthracene-9,10-diyl)-N-arylsuccinimide derivatives has been prepared and their N.M.R. spectral studies are reported. The effect of the substituents at the N-phenyl group on the conformational process about the aryl C-N bond has been investigated.The asymmetric cage moiety present in this system was employed for the conformational study.� The N.M.R. spectra provided evidence for the non-planar conformation and restricted rotation about the aryl C-N bond in the case of ortho-substituted derivatives. Electronegative substituents were found to have a preferred conformation (anti to the cage moiety). The energy barrier (ΔGt) of the order of 86 kJ/mol has been determined by their temperature-dependent spectra. Free rotation about the aryl C-N bond was observed for the meta- and para-substituted derivatives. No buttressing effect by meta substituents has been noticed.

Rotationsbarriere der Endgruppen bei Poly- methinoxonolen verschiedener Kettenlänge / Rotation Barrier of the End Groups of Polymethine Oxonols with Different Chain Lengths

1976 ◽  
Vol 31 (8) ◽  
pp. 1017-1018 ◽  
Author(s):  
H. Oehling ◽  
F. Baer
Keyword(s):  
Nmr Spectra ◽  
Rotation Barrier ◽  
Free Enthalpy ◽  
Temperature Dependent ◽  
Restricted Rotation ◽  
H Nmr ◽  
Enthalpy Of Activation ◽  
End Groups ◽  
Electron Contribution ◽  
Chain Lengths

Abstract Polymethine oxonols show temperature dependent 1H-NMR-spectra because of restricted rotation of the end groups. The dependence of the value of the corresponding free enthalpy of activation AGt on the length of the poly-methine chain can be explained by the change of the π-electron contribution to ⊿G≠.

scholarly journals Experimental and computational evaluation of the barrier to torsional rotation in a butadiyne-linked porphyrin dimer

2016 ◽  
Vol 18 (7) ◽  
pp. 5264-5274 ◽  
Author(s):  
Martin D. Peeks ◽  
Patrik Neuhaus ◽  
Harry L. Anderson
Keyword(s):  
Absorption Spectrum ◽  
Energy Barrier ◽  
Temperature Dependent ◽  
Computational Evaluation ◽  
Nir Absorption ◽  
Torsional Rotation ◽  
Porphyrin Dimer

Temperature-dependent changes in the UV-vis-NIR absorption spectrum of a butadiyne linked porphyrin dimer have been used to determine the height of the energy barrier to torsional rotation.

Complexes of uranyl β-diketonates with sulphoxides

1973 ◽  
Vol 26 (1) ◽  
pp. 85 ◽  
Author(s):  
MS Subramanian ◽  
SA Pai ◽  
VK Manchanda
Keyword(s):  
Magnetic Resonance ◽  
Steric Hindrance ◽  
Proton Magnetic Resonance ◽  
Free Rotation ◽  
Sulphur Atom ◽  
Neutral Donor ◽  
Restricted Rotation ◽  
Metal Bond ◽  
Methylene Group ◽  
Magnetic Resonance Spectra

The proton magnetic resonance spectra of the synergistic complexes of uranyl β-diketonates with dihexyl sulphoxide as the neutral donor give a multiplet consisting of eight lines for the terminal methylene group protons adjacent to the sulphur atom of the sulphoxide and a triplet for the β-methylene protons. This conforms to an ABX2 pattern arising as a result of nonequivalence of the two protons of the terminal methylene group as a result of steric hindrance to free rotation about the C-S bond. The presence of such restricted rotation has been adduced as evidence for a direct donor-metal bond.

scholarly journals A model-free temperature-dependent conformational study ofn-pentane in nematic liquid crystals

2015 ◽  
Vol 142 (2) ◽  
pp. 024904 ◽  
Author(s):  
E. Elliott Burnell ◽  
Adrian C. J. Weber ◽  
Ronald Y. Dong ◽  
W. Leo Meerts ◽  
Cornelis A. de Lange
Keyword(s):  
Liquid Crystals ◽  
Nematic Liquid Crystals ◽  
Conformational Study ◽  
Temperature Dependent ◽  
Model Free

The Barrier to Rotation in 9,10-Bis(2,3-dimethylphenyl)phenanthrene: Conformational Interconversion Observed at High Temperatures by Means of Gas Chromatography

1985 ◽  
Vol 38 (2) ◽  
pp. 307 ◽  
Author(s):  
Y Lai ◽  
PJ Marriott ◽  
B Tan
Keyword(s):  
Gas Chromatography ◽  
High Temperatures ◽  
Thermodynamic Data ◽  
Energy Barrier ◽  
Variable Temperature ◽  
High Energy ◽  
Free Rotation ◽  
Temperature Range ◽  
Conformational Interconversion ◽  
High Energy Barrier

A mixture of the syn and anti conformers of 9,10-bis(2,3- dimethylphenyl ) phenanthrene was prepared. The unexpectedly high energy barrier for the free rotation of the two aryl rings is described. Variable temperature 1H n.m.r . studies failed to provide thermodynamic data for the conformational inter-conversion due to limitations in practicably measurable temperature range. The energies of activation for both interconversion processes were, however, determined by gas chromatographic studies in the temperature range of 225-300°C.

Conformational analysis about the N-N bond by P.M.R. spectroscopy: N'-derivatives of N-amino-1,2,3,4-tetrahydro-9-oxo-1,4-ethanonaphthalene-endo-2,3-dicarboximide

1973 ◽  
Vol 26 (9) ◽  
pp. 1963 ◽  
Author(s):  
SM Verma ◽  
O Subba Rao
Keyword(s):  
Maleic Anhydride ◽  
Conformational Analysis ◽  
Conformational Changes ◽  
Major Product ◽  
Diels Alder ◽  
Conformational Study ◽  
Temperature Dependent ◽  
Spectral Changes ◽  
Derivatives Of

A series of N?-derivatives of N-amino-1,2,3,4-tetrahydro-9-oxo-1,4- ethanonaphthalene-endo-2,3-dicarboximide have been prepared and their p.m.r. spectra studied. The non-planar ?cage-moiety? structure has been used in the conformational study. Temperature dependent spectral changes have been related to conformational changes about the N-N bond. ��� The endo configuration of the major product obtained in Diels-Alder addition of maleic anhydride on β-naphthol has been strongly evidenced.

Phenyl group as a probe in the 1H nuclear magnetic resonance study of the conformations of quaternary heteroaromatic carbapenem antibiotics. Identification of the site of quaternization in -SCH2- substituted nitrogen-containing heteroaromatic derivatives

1988 ◽  
Vol 66 (7) ◽  
pp. 1546-1551 ◽  
Author(s):  
Vanga S. Rao ◽  
Jean-Paul Daris ◽  
Marcel Menard
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Phenyl Group ◽  
Nuclear Magnetic Resonance Study ◽  
Conformational Study ◽  
Magnetic Resonance Study ◽  
Heteroaromatic Compounds ◽  
1H Nuclear Magnetic Resonance ◽  
Nuclear Magnetic

The phenyl group is shown as a useful probe in sensing the environment in the 1H nuclear magnetic resonance conformational study of a variety of quaternary heteroaromatic carbapenem derivatives. The influence of the -SCH2- substituent in determining the site of quaternization in nitrogen-containing heteroaromatic compounds is demonstrated through the acidity measurements of these methylene protons.

scholarly journals Enhancing the Inhomogeneonus Photodynamics of Canonical Bacteriophytochrome

2021 ◽  
Author(s):  
Jakub Rydzewski ◽  
Katarzyna Walczewska-Szewc ◽  
Sylwia Czach ◽  
Marco Caricato ◽  
Sijin Ren ◽  
...  
Keyword(s):  
Energy Barrier ◽  
Deinococcus Radiodurans ◽  
Metastable States ◽  
Signal Transduction Pathways ◽  
Nanometer Scale ◽  
Thermal Transition ◽  
Enhanced Sampling ◽  
Temperature Dependent ◽  
Dark Reversion ◽  
First Time

The ability of phytochromes to act as photoswitches in plants and microorganisms depends on interactions between a bilin-like chromophore and a protein. The interconversion occurs between the spectrally distinct red (Pr) and far-red (Pfr) conformers. This conformational change is triggered by the photoisomerization of the chromophore D-ring pyrrole. In this study, as a representative example of a phytochrome-bilin system, we take biliverdin IXα (BV) bound to bacteriophytochrome (BphP) from Deinococcus radiodurans. In the absence of light, we use an enhanced sampling molecular dynamics (MD) method to overcome the photoisomerization energy barrier. We find that the calculated free energy (FE) barriers between essential metastable states agree with spectroscopic results. We show that the enhanced dynamics of the BV chromophore in BphP triggers nanometer-scale conformational movements that propagate by two experimentally determined signal transduction pathways. Most importantly, we describe how the metastable states enable a thermal transition known as the dark reversion between Pfr and Pr, through a previously unknown intermediate state of Pfr. Here, for the first time, the heterogeneity of temperature-dependent Pfr states is presented at the atomistic level. This work paves a way toward understanding the complete mechanism of the photoisomerization of a bilin-like chromophore in phytochromes.

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