First-Principles Study of Soliton Hyperfine Interactions in Polyacetylene

1990 ◽  
Vol 209 ◽  
Author(s):  
C. T. White ◽  
F. W. Kutzler ◽  
J. W. Mintmire ◽  
M. R. Cook
Keyword(s):  
Density Functional ◽  
Local Density ◽  
Hyperfine Interactions ◽  
Double Resonance ◽  
Broad Band ◽  
Coupling Constants ◽  
Electron Nuclear Double Resonance ◽  
Neutral Radical ◽  
Fermi Contact ◽  
Spin Densities

ABSTRACTAll-trans-polyacetylene is considered the prototypical broad band gap quasi onedimensional organic semiconductor. Intrinsicsoliton defects have long been known to be important to the understanding of the observed properties of this system at low doping levels. Magnetic resonance techniques provide powerful experimental probes into the nature and environment of these neutral-radical defects. In an earlier work we showed that firstprinciples spin-polarized local density functional (LDF) methods reliably predict proton Fermi-contact coupling constants for planar, neutral, organic π-radicals. We have also used these methods to calculate the Fermi-contact proton coupling constants associated with the soliton defect in polyacetylene.Herein we compare the results of these earlier soliton calculations to results from recent electron-nuclear double-resonance (ENDOR) experiments. Our predicted ratio of the negative to positive spin densities is in good agreement with these ENDORstudies. The negative spin densities arise from spin-polarization effects which are found to cause the soliton level at midgap to be split by several tenths of an eV.

Air-stable Curved π-Radical Based on Corannulene: Dynamic Electronic-spin Structure Induced by Temperature-dependent Conformational Changes

2010 ◽  
Vol 63 (12) ◽  
pp. 1627 ◽  
Author(s):  
Akira Ueda ◽  
Kanako Ogasawara ◽  
Shinsuke Nishida ◽  
Kozo Fukui ◽  
Kazunobu Sato ◽  
...  
Keyword(s):  
Conformational Changes ◽  
Density Functional ◽  
Variable Temperature ◽  
Double Resonance ◽  
Triple Resonance ◽  
Phase Variable ◽  
Temperature Dependent ◽  
Electron Nuclear Double Resonance ◽  
Neutral Radical ◽  
Electronic Spin

A new corannulene-based curved neutral π-radical bearing a tert-butylnitroxide moiety has been synthesized and isolated as an air-stable solid. Direct attachment of the spin centre to the corannulene skeleton gives rise to an extensive spin-delocalization onto the curved π-conjugated system from the nitroxide moiety. This salient electronic feature in the curved neutral radical system and its high stability have allowed us to find a dynamic electronic-spin behaviour induced by the temperature-dependent conformational change of the nitroxide moiety, as studied by liquid-phase variable-temperature electron spin resonance and 1H electron-nuclear double resonance and electron-nuclear-nuclear triple resonance spectroscopies with the help of density functional theory calculations.

scholarly journals Selective 13C labelling reveals the electronic structure of flavocoenzyme radicals

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Erik Schleicher ◽  
Stephan Rein ◽  
Boris Illarionov ◽  
Ariane Lehmann ◽  
Tarek Al Said ◽  
...  
Keyword(s):  
Electronic Structure ◽  
Blue Light ◽  
Density Functional ◽  
Double Resonance ◽  
Density Functional Theory Calculations ◽  
Microwave Frequency ◽  
Fine Tuning ◽  
Electron Nuclear Double Resonance ◽  
Intermediate Radical ◽  
Wide Range

AbstractFlavocoenzymes are nearly ubiquitous cofactors that are involved in the catalysis and regulation of a wide range of biological processes including some light-induced ones, such as the photolyase-mediated DNA repair, magnetoreception of migratory birds, and the blue-light driven phototropism in plants. One of the factors that enable versatile flavin-coenzyme biochemistry and biophysics is the fine-tuning of the cofactor’s frontier orbital by interactions with the protein environment. Probing the singly-occupied molecular orbital (SOMO) of the intermediate radical state of flavins is therefore a prerequisite for a thorough understanding of the diverse functions of the flavoprotein family. This may be ultimately achieved by unravelling the hyperfine structure of a flavin by electron paramagnetic resonance. In this contribution we present a rigorous approach to obtaining a hyperfine map of the flavin’s chromophoric 7,8-dimethyl isoalloxazine unit at an as yet unprecedented level of resolution and accuracy. We combine powerful high-microwave-frequency/high-magnetic-field electron–nuclear double resonance (ENDOR) with 13C isotopologue editing as well as spectral simulations and density functional theory calculations to measure and analyse 13C hyperfine couplings of the flavin cofactor in DNA photolyase. Our data will provide the basis for electronic structure considerations for a number of flavin radical intermediates occurring in blue-light photoreceptor proteins.

Solution Tetrahydrobiopterin Radical vs. the Enzyme-Bound Radical: A Paramagnetic Reconciliation

2021 ◽  
Vol 16 ◽  
Author(s):  
Yaser Nejaty Jahromy
Keyword(s):  
Nitric Oxide ◽  
Density Functional ◽  
Double Resonance ◽  
Nicotinamide Adenine Dinucleotide Phosphate ◽  
Cation Radical ◽  
Spectral Simulation ◽  
Electron Nuclear Double Resonance ◽  
Paramagnetic Resonance ◽  
Isotropic Hyperfine Coupling ◽  
The 1960S

Background: Nitric oxide synthase (NOS) catalyzes the formation of nitric oxide (NO) and citrulline from L-arginine, dioxygen (O2), and nicotinamide adenine dinucleotide phosphate (NADPH) in a two-step reaction, with the enzyme-bound intermediate Nω-hydroxy-L-arginine (NHA). Previous electron paramagnetic resonance (EPR) studies of NOS reaction have shown that (6R, 1'R, 2'S)-6-(l',2'-dihydroxypropyl)-5,6,7,8-tetrahydropterin (H4B) acts as a single electron donor in both steps of the reaction, resulting in the transient generation of a tetrahydropterin cation radical (H4B•+). Results: H4B•+ can also be chemically generated in strongly acidic solutions. EPR studies of chemically generated H4B•+ and similar pterin radicals date back to the 1960s. However, the reported paramagnetic parameters of H4B•+ in NOS do not seem to match the corresponding reported parameters for either H4B•+ or other pterin centered radicals chemically generated in solution. In particular, the rather isotropic hyperfine coupling of ca. 45 MHz for 1H6 of H4B•+ in NOS is at least 15 MHz larger than that of H4B•+ or any other previously studies pterin solution radical. In the work reported here, a combination of 9.5 - 9.8 GHz contentious wave (cw-) EPR, 34GHz 1H electron nuclear double resonance (ENDOR), spectral simulation and Density Functional Theory (DFT) calculations were used to investigate this seeming discrepancy. Conclusion: We demonstrated that the differences in the paramagnetic parameters of the chemically generated H4B radicals in solutions and those of the H4B radicals in NOS are consistent with the presence of two different conformers of the same cation radical in the two media.

Electron nuclear double resonance in solutions. Spin densities in triarylmethyl radicals

1968 ◽  
Vol 90 (16) ◽  
pp. 4225-4231 ◽  
Author(s):  
A. H. Maki ◽  
R. D. Allendoerfer ◽  
J. C. Danner ◽  
R. T. Keys
Keyword(s):  
Double Resonance ◽  
Electron Nuclear Double Resonance ◽  
Spin Densities ◽  
Triarylmethyl Radicals
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