The effett of medium on cidnp kinetics in geminate recombination of biradicals. Experiment and calculation

Yurkovskaya, Alexandra V.; Tsentalovich, Yu. P.; Lukzen, Nikita N.; Sagdeev, R. Z.

doi:10.1163/156856792x00119

Cited by 19 publications

(35 citation statements)

References 23 publications

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“…19 The time-resolved CIDNP setup has been described in detail earlier. 20 A sample in a commercial Pyrex tube was irradiated inside the probehead of an MSL-300 Bruker NMR spectrometer by an excimer laser (308 nm, pulse energy up to 120 mJ). The probehead was specially designed for the TR CIDNP experiments.…”

Section: Methodsmentioning

confidence: 99%

“…In order to fit the calculations to the experimental kinetic data, we had to limit the biradical lifetime τ 0 by including the non-zero scavenging rate constant k sc into the calculations. 20 The best fit was obtained at k sc ) τ 0 -1 ) 10 6 s -1 . 20 The kinetics of CIDNP generation in different products could provide direct evidence for the presence of the consecutive biradicals.…”

Section: H Cidnp Kinetics At High Magnetic Fieldsmentioning

confidence: 96%

“…20 The best fit was obtained at k sc ) τ 0 -1 ) 10 6 s -1 . 20 The kinetics of CIDNP generation in different products could provide direct evidence for the presence of the consecutive biradicals. To detect the CIDNP kinetics, we used the rf pulses of the half-width 150 ns.…”

Section: H Cidnp Kinetics At High Magnetic Fieldsmentioning

confidence: 96%

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H and ¹³C Nuclear Polarization in Consecutive Biradicals during the Photolysis of 2,2,12,12-Tetramethylcyclododecanone

et al. 1997

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CIDNP effects arising in the geminate evolution of consecutive biradicals formed during the photolysis of 2,2,12,12-tetramethylcyclododecanone were investigated by the low-and high-field 1 H and 13 C CIDNP and time-resolved 1 H CIDNP methods. The 1 H field dependence of nuclear polarization induced in the recombination and disproportionation products of the consecutive biradicals as well as the 13 C CIDNP spectra at low and high magnetic fields was analyzed. It was confirmed that two types of biradicals (acyl-alkyl and bisalkyl) of different chain lengths contribute to the spin polarization. Model calculations of the geminate recombination kinetics were based on the numerical solution of the stochastic Liouville equation for the Fourier transform of the biradical spin density matrix. A detailed kinetic analysis of the CIDNP effects allowed us to reveal all chemical transformations of the alkyl-acyl and bisalkyl biradicals and to estimate the probability of the "hidden" recombination of the biradicals to the starting ketone, as well as to determine the product distribution.

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Section: Methodsmentioning

confidence: 99%

Section: H Cidnp Kinetics At High Magnetic Fieldsmentioning

confidence: 96%

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H and ¹³C Nuclear Polarization in Consecutive Biradicals during the Photolysis of 2,2,12,12-Tetramethylcyclododecanone

et al. 1997

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“…S4 ) is observed. In case of biradicals (zwitterion), formed due to an intramolecular electron transfer photo-CIDNP 1 H NMR kinetics are expected on ns timescale 35 , 36 , whereas in case of intermolecular electron transfer this is on μs timescale 37 . Therefore the electron transfer occurring in F10T is necessarily intramolecular.…”

Section: Resultsmentioning

confidence: 99%

Magnetic field effect in natural cryptochrome explored with model compound

Paul

Kiryutin

Guo

et al. 2017

Sci Rep

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Many animals sense the Earth’s magnetic-field and use it for navigation. It is proposed that a light-dependent quantum effect in cryptochrome proteins, residing in the retina, allows for such an iron-free spin-chemical compass. The photochemical processes, spin-dynamics and its magnetic field dependence in natural cryptochrome are not fully understood by the in vivo and in vitro studies. For a deeper insight into these biophysical mechanisms in cryptochrome, we had introduced a flavin-tryptophan dyad (F10T). Here we present the magnetic field dependence of 1H photo-CIDNP NMR on F10T and a theoretical model for low-field photo-CIDNP of F10T. This model provides mixing mechanism of energy-levels and spin-dynamics at low magnetic fields. Photo-CIDNP has been observed even at Earth’s magnetic field (~0.05 mT). These experiments prove F10T to be an excellent model compound establishing the key mechanism of avian-magnetoreception and provide insight into the optimal behaviour of cryptochrome at Earth’s magnetic field.

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“…The same energy barrier was obtained from the fitting of Δ B for the 1 H CIDNP field dependence in the low-temperature range by variation of D ‘. For the temperature dependence of τ c we used the expression τ c =τ c0 ( T 0 / T )(η/η 0 ) where η 0 = η(298 K) = 0.58 cP and τ c0 = τ c (298 K) = 8 × 10 -11 s. It was shown previously that the proportionality τ c ∝ η/ T gives a good description of the CIDNP biradical kinetics at variable temperature …”

Section: Discussionmentioning

confidence: 99%

Spin and Molecular Dynamics of Biradicals as Studied by Low Field Nuclear Polarization at Variable Temperature

et al. 1999

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1H and 13C chemically induced dynamic nuclear polarization (CIDNP) and time-resolved stimulated nuclear polarization (SNP) have been applied to the investigation of spin and molecular dynamics in biradicals, generated in the photolysis of 2,2,12,12-tetramethylcyclododecanone, at low magnetic field in the temperature range from 200 to 360 K. This reaction involves two consecutive biradical stages, the primary acyl−alkyl and the secondary bis-alkyl biradical, with different reaction products. Characteristic differences in the CIDNP field dependencies and SNP decay times for nuclei of different reaction products are seen at high temperatures. Upon cooling, the emission maximum position shifts to low field and the width of the 1H CIDNP field dependencies of the acyl−alkyl biradical products decreases. Below 243 K these effects reverse direction, furthermore, a significant slowing down of the SNP decay is observed. Calculations of the 1H and 13C CIDNP field dependencies and the SNP kinetics for the primary biradical have been performed based on the numerical solution of the stochastic Liouville equation for the biradical spin density matrix. They use a model of restricted diffusion for the description of the molecular dynamics and take into account the distance dependence of the exchange interaction. Good quantitative agreement between the calculations and experimental data is found for the whole temperature range when using the appropriate dependence of some of the parameters on temperature. In particular, it was necessary for the quantitative simulation in the low temperature range to introduce a temperature dependence of the biradical reactivity. The model calculations qualitatively confirm that the low-temperature broadening of the CIDNP field dependencies, and the increase of the SNP decay time are caused by the slowing down of the molecular mobility and the decreasing of reactivity. For the products of the secondary biradical, a qualitative interpretation is given showing that in comparison with the products of the primary biradical spin−orbit interaction is of less importance for the biradical spin dynamics, that the influence of the molecular mobility under the temperature variation is more pronounced, that the lifetime is longer, and that the nuclear polarization is more efficiently formed.

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The effett of medium on cidnp kinetics in geminate recombination of biradicals. Experiment and calculation

Cited by 19 publications

References 23 publications

H and ¹³C Nuclear Polarization in Consecutive Biradicals during the Photolysis of 2,2,12,12-Tetramethylcyclododecanone

H and ¹³C Nuclear Polarization in Consecutive Biradicals during the Photolysis of 2,2,12,12-Tetramethylcyclododecanone

Magnetic field effect in natural cryptochrome explored with model compound

Spin and Molecular Dynamics of Biradicals as Studied by Low Field Nuclear Polarization at Variable Temperature

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The effett of medium on cidnp kinetics in geminate recombination of biradicals. Experiment and calculation

Cited by 19 publications

References 23 publications

H and 13C Nuclear Polarization in Consecutive Biradicals during the Photolysis of 2,2,12,12-Tetramethylcyclododecanone

H and 13C Nuclear Polarization in Consecutive Biradicals during the Photolysis of 2,2,12,12-Tetramethylcyclododecanone

Magnetic field effect in natural cryptochrome explored with model compound

Spin and Molecular Dynamics of Biradicals as Studied by Low Field Nuclear Polarization at Variable Temperature

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Product

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H and ¹³C Nuclear Polarization in Consecutive Biradicals during the Photolysis of 2,2,12,12-Tetramethylcyclododecanone

H and ¹³C Nuclear Polarization in Consecutive Biradicals during the Photolysis of 2,2,12,12-Tetramethylcyclododecanone