116 results on '"Nikita N. Lukzen"'
Search Results
2. Marcus Cross-Relationship Probed by Time-Resolved CIDNP
- Author
-
Maksim P. Geniman, Olga B. Morozova, Nikita N. Lukzen, Günter Grampp, and Alexandra V. Yurkovskaya
- Subjects
chemically induced nuclear polarization (CIDNP) ,guanosine monophosphate ,tyrosine anion ,short-lived radicals ,degenerate electronic exchange ,Marcus theory ,Biology (General) ,QH301-705.5 ,Chemistry ,QD1-999 - Abstract
The time-resolved CIDNP method can provide information about degenerate exchange reactions (DEEs) involving short-lived radicals. In the temperature range from 8 to 65 °C, the DEE reactions of the guanosine-5′-monophosphate anion GMP(-H)− with the neutral radical GMP(-H)•, of the N-acetyl tyrosine anion N-AcTyrO− with a neutral radical N-AcTyrO•, and of the tyrosine anion TyrO− with a neutral radical TyrO• were studied. In all the studied cases, the radicals were formed in the reaction of quenching triplet 2,2′-dipyridyl. The reorganization energies were obtained from Arrhenius plots. The rate constant of the reductive electron transfer reaction in the pair GMP(-H)•/TyrO− was determined at T = 25 °C. Rate constants of the GMP(-H)• radical reduction reactions with TyrO− and N-AcTyrO− anions calculated by the Marcus cross-relation differ from the experimental ones by two orders of magnitude. The rate constants of several other electron transfer reactions involving GMP(-H)−/GMP(-H)•, N-AcTyrO−/N-AcTyrO•, and TyrO−/TyrO• pairs calculated by cross-relation agree well with the experimental values. The rate of nuclear paramagnetic relaxation was found for the 3,5 and β-protons of TyrO• and N-AcTyrO•, the 8-proton of GMP(-H)•, and the 3,4-protons of DPH• at each temperature. In all cases, the dependences of the rate of nuclear paramagnetic relaxation on temperature are described by the Arrhenius dependence.
- Published
- 2023
- Full Text
- View/download PDF
3. Magnetic Field Effect in Bimolecular Rate Constant of Radical Recombination
- Author
-
Alexander B. Doktorov and Nikita N. Lukzen
- Subjects
radicals ,spin-selective radical recombination ,magnetic and spin effects in chemical reactions ,diffusion-influenced reactions ,spin chemistry ,Biology (General) ,QH301-705.5 ,Chemistry ,QD1-999 - Abstract
The influence of magnetic fields on chemical reactions, including biological ones, has been and still is a topical subject in the field of scientific research. Experimentally discovered and theoretically substantiated magnetic and spin effects in chemical radical reactions form the basis of research in the field of spin chemistry. In the present work, the effect of a magnetic field on the rate constant of the bimolecular spin-selective recombination of radicals in the bulk of a solution is considered theoretically for the first time, taking into account the hyperfine interaction of radical spins with their magnetic nuclei. In addition, the paramagnetic relaxation of unpaired spins of the radicals and the non-equality of their g-factors that also influence the recombination process are taken into account. It is found that the reaction rate constant can vary in magnetic field from a few to half a dozen percent, depending on the relative diffusion coefficient of radicals, which is determined by the solution viscosity. It is shown that the consideration of hyperfine interactions gives rise to the presence of resonances in the dependence of the rate constant on the magnetic field. The magnitudes of the magnetic fields of these resonances are determined by the hyperfine coupling constants and difference in the g-factors of the recombining radicals. Analytical expressions for the reaction rate constant of the bulk recombination for magnetic fields larger than hfi (hyperfine interaction) constants are obtained. In general, it is shown for the first time that accounting for hyperfine interactions of radical spins with magnetic nuclei significantly affects the dependence of the reaction rate constant of the bulk radical recombination on the magnetic field.
- Published
- 2023
- Full Text
- View/download PDF
4. Exchange coupling transformations in Cu (II) heterospin complexes of 'breathing crystals' under structural phase transitions
- Author
-
Vitaly A. Morozov, Marina V. Petrova, and Nikita N. Lukzen
- Subjects
Physics ,QC1-999 - Abstract
Family of “breathing crystals” is the polymer-chain complexes of Cu(hfac)2 with nitroxides. The polymer chains consist of one-, two- or three-spin clusters. The “breathing crystals” experience simultaneous magnetic and Jahn-Teller type structural phase transitions with change of total cluster spin and drastic change of bond lengths (ca. 10-12%). For the first time the intra-cluster magnetic couplings in ”breathing crystals” have been calculated both by band structure methods GGA + U and hybrid DFT (B3LYP and PBE0) for the isolated exchange clusters. The temperature dependence of the magnetic coupling constant was calculated for two polymer-chain compounds of the “breathing crystal” family - C21H19CuF12N4O6 with the chains containing two-spin clusters and C22H21CuF12N4O6 with the chains of alternating three-spin clusters and one-spin sites. It was found that adding a Hubbard-like parameter not only to the copper 3d electrons but also to the oxygen 2p electrons (GGA + Ud + Up approach) results in an improved description of exchange coupling in the “breathing crystal” compounds. At the same time treatment of the isolated clusters by a large basis hybrid DFT with high computational cost provides a similar quality fit of the experimental magneto-chemical data as that for the GGA + Ud + Up band structure calculation scheme. Our calculations also showed that in spite of the abrupt transformation of the magnetic coupling constant under the phase transition, the band gap in the “breathing crystals” remains about the same value with temperature decrease.
- Published
- 2015
- Full Text
- View/download PDF
5. Readout of spin quantum beats in a charge-separated radical pair by pump-push spectroscopy
- Author
-
David Mims, Jonathan Herpich, Nikita N. Lukzen, Ulrich E. Steiner, and Christoph Lambert
- Subjects
Multidisciplinary - Abstract
Quantum oscillations in radical pairs The spin dynamics of photoinduced radical pairs, involving an interconversion between singlet and triplet spin states, plays an important role in nature, for example, in avian magnetoreception. The spin interconversion is a truly quantum process with characteristic coherent oscillations (quantum beats) that should be reflected in the reaction kinetics. However, their experimental observation has remained challenging. Mims et al . developed an optical readout technique that can directly monitor the singlet-triplet interconversion quantum beats, as demonstrated for a photoinduced, charge-separated state of an electron donor–acceptor dyad (see the Perspective by Hore). The present work opens a new way to monitor the spin evolution in radical pairs, which will be important not only in biological physics but also in organic solar cells and other practical applications. —YS
- Published
- 2021
6. Analytical solution for the inverting pulses with constant adiabaticity
- Author
-
Konstantin L. Ivanov, Alexander V. Snadin, Alexei S. Kiryutin, and Nikita N. Lukzen
- Subjects
Nuclear and High Energy Physics ,Biophysics ,Condensed Matter Physics ,Biochemistry - Abstract
The exact solution was found for inverting pulses with constant adiabaticity for spin ½. The analytical relationship between the time-varying frequency of the microwave resonant field (or RF field in the case of NMR) and its amplitude time dependence such that the adiabaticity parameter remains constant for the single isochromat throughout the pulse is found. Comparison with EPR (hyperbolic tangent)-(hyperbolic secant) pulse method was carried out. On the basis of the analytical solution the pulses with different dependences of the microwave field amplitude conserving the constant adiabaticity have been constructed. The pulses exhibit rather sharp inversion selectivity that can be used in the field of EPR, NMR and MRI.
- Published
- 2022
7. Exchange interaction in short-lived flavine adenine dinucleotide biradical in aqueous solution revisited by CIDNP (chemically induced dynamic nuclear polarization) and nuclear magnetic relaxation dispersion
- Author
-
Hans-Martin Vieth, Konstantin L. Ivanov, Olga B. Morozova, Ivan V. Zhukov, Renad Z. Sagdeev, Natalya N. Fishman, Alexey S. Kiryutin, Alexandra V. Yurkovskaya, Mikhail S. Panov, and Nikita N. Lukzen
- Subjects
0301 basic medicine ,Flavin adenine dinucleotide ,QC501-766 ,biology ,CIDNP ,Relaxation (NMR) ,Flavin group ,Chromophore ,010402 general chemistry ,Photochemistry ,01 natural sciences ,Cofactor ,0104 chemical sciences ,Electricity and magnetism ,03 medical and health sciences ,Electron transfer ,chemistry.chemical_compound ,030104 developmental biology ,chemistry ,Excited state ,biology.protein - Abstract
Flavin adenine dinucleotide (FAD) is an important cofactor in many light-sensitive enzymes. The role of the adenine moiety of FAD in light-induced electron transfer was obscured, because it involves an adenine radical, which is short-lived with a weak chromophore. However, an intramolecular electron transfer from adenine to flavin was revealed several years ago by Robert Kaptein by using chemically induced dynamic nuclear polarization (CIDNP). The question of whether one or two types of biradicals of FAD in aqueous solution are formed stays unresolved so far. In the present work, we revisited the CIDNP study of FAD using a robust mechanical sample shuttling setup covering a wide magnetic field range with sample illumination by a light-emitting diode. Also, a cost efficient fast field cycling apparatus with high spectral resolution detection up to 16.4 T for nuclear magnetic relaxation dispersion studies was built based on a 700 MHz NMR spectrometer. Site-specific proton relaxation dispersion data for FAD show a strong restriction of the relative motion of its isoalloxazine and adenine rings with coincident correlation times for adenine, flavin, and their ribityl phosphate linker. This finding is consistent with the assumption that the molecular structure of FAD is rigid and compact. The structure with close proximity of the isoalloxazine and purine moieties is favorable for reversible light-induced intramolecular electron transfer from adenine to triplet excited flavin with formation of a transient spin-correlated triplet biradical F⚫−-A⚫+. Spin-selective recombination of the biradical leads to the formation of CIDNP with a common emissive maximum at 4.0 mT detected for adenine and flavin protons. Careful correction of the CIDNP data for relaxation losses during sample shuttling shows that only a single maximum of CIDNP is formed in the magnetic field range from 0.1 mT to 9 T; thus, only one type of FAD biradical is detectable. Modeling of the CIDNP field dependence provides good agreement with the experimental data for a normal distance distribution between the two radical centers around 0.89 nm and an effective electron exchange interaction of −2.0 mT.
- Published
- 2021
8. KONSTANTIN L'VOVICH IVANOV
- Author
-
Nikita N. Lukzen
- Subjects
2019-20 coronavirus outbreak ,Coronavirus disease 2019 (COVID-19) ,Chemistry ,Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) ,General Materials Science ,General Chemistry ,Virology - Published
- 2021
9. Author response for 'KONSTANTIN L'VOVICH IVANOV'
- Author
-
Nikita N. Lukzen
- Published
- 2021
10. Multiplet-to-net CIDEP conversion by MW-pulses with adiabatically ramped amplitude
- Author
-
Konstantin L. Ivanov and Nikita N. Lukzen
- Subjects
Physics ,010304 chemical physics ,Spin states ,Biophysics ,Order (ring theory) ,010402 general chemistry ,Condensed Matter Physics ,Net (mathematics) ,01 natural sciences ,0104 chemical sciences ,Amplitude ,0103 physical sciences ,Condensed Matter::Strongly Correlated Electrons ,Singlet state ,Physical and Theoretical Chemistry ,Atomic physics ,Molecular Biology ,Multiplet - Abstract
A method is proposed to manipulate electron spin order of spin-correlated radical pairs. As radical pairs are often born in a well-defined spin state, e.g. in the singlet state, they acquire Chemic...
- Published
- 2019
11. Exchange interaction in short lived flavin adenine dinucleotide biradical in aqueous solution revisited by CIDNP and nuclear magnetic relaxation dispersion
- Author
-
Renad Z. Sagdeev, Mikhail S. Panov, Alexey S. Kiryutin, Alexandra V. Yurkovskaya, Konstantin L. Ivanov, Ivan V. Zhukov, Natalya N. Fishman, Olga B. Morozova, Nikita N. Lukzen, and Hans-Martin Vieth
- Subjects
Flavin adenine dinucleotide ,chemistry.chemical_compound ,Electron transfer ,chemistry ,biology ,CIDNP ,Excited state ,Relaxation (NMR) ,biology.protein ,Flavin group ,Chromophore ,Photochemistry ,Cofactor - Abstract
Flavin adenine dinucleotide (FAD) is an important cofactor in many light-sensitive enzymes. The role of the adenine moiety of FAD in light induced electron transfer was obscured because it involves an adenine radical, short-lived with a weak chromophore. However, an intramolecular electron transfer from adenine to flavin was revealed several years ago by R. Kaptein by using chemically induced dynamic nuclear polarization (CIDNP). The question whether one or two types of biradicals of FAD in aqueous solution are formed stays unresolved so far. In the present work, we revisited the CIDNP study of FAD using a robust mechanical sample shuttling setup covering a wide magnetic field range with sample illumination by a light emitting diode. Also, a cost efficient fast field cycling apparatus with high spectral resolution detection up to 16.4 T for nuclear magnetic relaxation dispersion studies was built based on a 700 MHz NMR spectrometer. Site-specific proton relaxation dispersion data for FAD show a strong restriction of the relative motion of its isoalloxazine and adenine rings with coincident correlation times for adenine, flavin and their ribityl-phosphate linker. This finding is consistent with the assumption that the molecular structure of FAD is rigid and compact. The structure with close proximity of the isoalloxazine and purine moieties is favorable for reversible light induced intramolecular electron transfer from adenine to triplet excited flavin with formation of a transient spin-correlated triplet biradical F•−-A•+. Spin selective recombination of the biradical leads to the formation of CIDNP with a common emissive maximum at 4.0 mT detected for adenine and flavin protons. Careful correction of the CIDNP data for relaxation losses during sample shuttling shows that only a single maximum of CIDNP is formed in the magnetic field range from 0.1 mT to 9 T; thus, only one type of FAD biradical is detectable. Modeling of the CIDNP field dependence provides good agreement with the experimental data for a normal distance distribution between the two radical centers around 0.89 nm and an effective electron exchange interaction of −2.0 mT.
- Published
- 2021
12. Giant magnetic field effects in donor-acceptor triads: On the charge separation and recombination dynamics in triarylamine-naphthalenediimide triads with bis-diyprrinato-palladium(II), porphodimethenato-palladium(II), and palladium(II)-porphyrin photosensitizers
- Author
-
Jessica S Brand, Christoph Lambert, Marco Holzapfel, Nikita N. Lukzen, Ulrich Steiner, David Mims, and Stefan Riese
- Subjects
education.field_of_study ,Materials science ,010304 chemical physics ,Population ,General Physics and Astronomy ,010402 general chemistry ,Photochemistry ,01 natural sciences ,Photoinduced electron transfer ,0104 chemical sciences ,Intersystem crossing ,Excited state ,0103 physical sciences ,Photosensitizer ,Singlet state ,Physical and Theoretical Chemistry ,Triplet state ,education ,Ground state - Abstract
A series of triads consisting of a triarylamine donor, a naphthalenediimide acceptor, and a palladium photosensitizer bridge was investigated for the photoinduced electron transfer processes and the spin chemistry involved. In this series, the ligand in the palladium photosensitizer was varied from bis-dipyrrinato to porphodimethenato and to a porphyrin. With the porphyrin photosensitizer, no charge separated state could be reached. This is caused by the direct relaxation of the excited photosensitizer to the ground state by intersystem crossing. The bis-dipyrrinato-palladium photosensitizer gave only a little yield (7%) of the charge separated state, which is due to the population of a metal centered triplet state and a concomitant geometrical rearrangement to a disphenoidal coordination sphere. This state relaxes rapidly to the ground state. In contrast, in the porphodimethenato-palladium triads, a long lived (μs to ms) charge separated state could be generated in high quantum yields (66%-74%) because, here, the population of a triplet metal centered state is inhibited by geometrical constraints. The magnetic field dependent transient absorption measurement of one of the porphodimethenato triads revealed a giant magnetic field effect by a factor of 26 on the signal amplitude of the charge separated state. This is the consequence of a magnetic field dependent triplet-singlet interconversion that inhibits the fast decay of the charge separated triplet state through the singlet recombination channel. A systematic comparative analysis of the spin-dependent kinetics in terms of three classical and one fully quantum theoretical methods is provided, shedding light on the pros and cons of each of them.
- Published
- 2020
13. Multifrequency Nuclear Magnetic Resonance as an Efficient Tool To Investigate Heterospin Complexes in Solutions
- Author
-
Mariya V. Edeleva, Konstantin L. Ivanov, Victor I. Ovcharenko, Sergey V. Fokin, Nikita N. Lukzen, Natalya N. Fishman, and Galina V. Romanenko
- Subjects
010304 chemical physics ,Chemistry ,Nuclear magnetic resonance spectroscopy ,010402 general chemistry ,Kinetic energy ,01 natural sciences ,0104 chemical sciences ,Magnetic field ,Paramagnetism ,Laser linewidth ,0103 physical sciences ,Physical chemistry ,Diamagnetism ,Physical and Theoretical Chemistry ,Chemical equilibrium ,Line (formation) - Abstract
We report a multifrequency NMR study of heterospin complexes [Eu(SQ)3Ln], where SQ is 3,6-di(tert-butyl)-1,2-semiquinone, L is THF, Py or Dipy and n is the number of diamagnetic ligands. Multifrequency NMR experiments allowed us to determine the effective paramagnetic shifts of the ligands (L = THF or Py) and the chemical equilibrium constant for [Eu(SQ)3(THF)2]. In addition, we have found a strong magnetic field effect on the NMR line broadening, giving rise to very broad NMR lines at high magnetic field. We attribute this effect to broadening under fast exchange conditions when the NMR spectrum represents a homogeneously broadened line with a width proportional to the square of NMR frequency difference of the free and bound forms of L. Consequently, the linewidth strongly increases with the magnetic field. This broadening effect allows one to determine relevant kinetic parameters, i.e., the effective exchange time. The strong broadening effect allows one to exploit the [Eu(SQ)3(THF)2] complex as an effi...
- Published
- 2020
14. Chapter 9. Manipulating Singlet Order with Adiabatic Pulses
- Author
-
Konstantin L. Ivanov, Hans-Martin Vieth, Nikita N. Lukzen, Alexandra V. Yurkovskaya, Alexey S. Kiryutin, and Bogdan A. Rodin
- Subjects
Physics ,Amplitude ,Spins ,Pulse-amplitude modulation ,Relaxation (NMR) ,Condensed Matter::Strongly Correlated Electrons ,Singlet state ,Atomic physics ,Adiabatic process ,Pulse (physics) ,Spin-½ - Abstract
A family of methods is introduced for creating, manipulating and observing nuclear singlet spin order. The basic element is conversion between longitudinal magnetisation and singlet spin order, M2S and S2M. It is based on near-resonance radio-frequency pulses of adiabatically varying amplitude that guide the spins through regions of avoided level-crossings of the system. After discussing the theoretical concepts, we illustrate the practical application of such Adiabatic Passage Spin Order Conversion (APSOC) by analysing the relaxation decay of singlet order independent of the coupling strength of the spin pair. By combining several such pulse sequences and varying their carrier frequency, a filter is designed for Singlet Order Selection (SOS) and suppression of all other spectral components. It enables background-free detection of selected spin pairs. To ease the constraint of slow amplitude variation while staying within the limits of adiabaticity the pulse amplitude profile is shaped so that only near level-crossings speed is reduced, but increased elsewhere; optimum control methods are used to find the ideal pulse shape. In this way adverse relaxation effects during pulses are minimised. Conversion factors close to the theoretical maximum are thus achievable. With such a toolbox not only highly efficient conversion is possible, but also other manipulations of spin order, e.g. polarisation transfer between different spin species or anti-phase to in-phase transformation of spectral components.
- Published
- 2020
15. Nanoviscosity effect on the spin chemistry of an electron donor/Pt-complex /electron acceptor triad - classical and quantum kinetics interpretation
- Author
-
Alexander Schmiedel, Marco Holzapfel, Stefan Riese, Nikita N. Lukzen, Christoph Lambert, Lena Mungenast, and Ulrich Steiner
- Subjects
chemistry.chemical_classification ,Materials science ,010304 chemical physics ,Kinetics ,Biophysics ,Triad (anatomy) ,Charge (physics) ,Electron donor ,Electron acceptor ,010402 general chemistry ,Condensed Matter Physics ,Photochemistry ,01 natural sciences ,Photoinduced electron transfer ,0104 chemical sciences ,chemistry.chemical_compound ,medicine.anatomical_structure ,Spin chemistry ,chemistry ,0103 physical sciences ,medicine ,Flash photolysis ,Physical and Theoretical Chemistry ,Molecular Biology - Abstract
The magnetic-field dependent charge recombination kinetics upon ns-laser flash photolysis of a novel triarylamine/cyclometalated platinum complex/napthalenediimide triad (DPtA) have been measured i...
- Published
- 2018
16. J-Resonance Line Shape of Magnetic Field-Affected Reaction Yield Spectrum from Charge Recombination in a Linked Donor–Acceptor Dyad
- Author
-
Julian Schäfer, Ulrich Steiner, Christoph Lambert, and Nikita N. Lukzen
- Subjects
Physics ,Zeeman effect ,Exchange interaction ,Relaxation (NMR) ,Resonance ,02 engineering and technology ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,Molecular physics ,0104 chemical sciences ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials ,symbols.namesake ,General Energy ,Spin chemistry ,symbols ,Singlet state ,Physical and Theoretical Chemistry ,0210 nano-technology ,Hyperfine structure ,Spin-½ - Abstract
Magnetic field effects (MFEs) allow detailed insight into spin conversion processes of radical pairs that are formed, for example, in all charge separation processes, and are supposed to play the key role in avian navigation. In this work, the MFE of charge recombination in the charge-separated state of a rigid donor–bridge–acceptor dyad was analyzed by a classical and a quantum theoretical model and represents a paradigm case of understanding spin chemistry with unprecedented detail. The MFE is represented by magnetic field-affected reaction yield (MARY) spectra that exhibit a sharp resonance, resulting from S/T level crossing as the Zeeman splitting equals twice the exchange interaction. Although in the classical kinetic model, the spin conversion processes between the four singlet and triplet substates are shown for the first time to obey an identical generalized energy dependence, quantum theory proves that the MARY resonance line is composed of relaxation, coherent hyperfine induced spin mixing, and ...
- Published
- 2018
17. Mapping 13C hyperfine couplings and exchange interactions in short-lived charge separated states of rigid donor–bridge–acceptor dyads
- Author
-
Christoph Lambert, Julian Schäfer, Alexey S. Kiryutin, Ulrich Steiner, Nikita N. Lukzen, Ivan V. Zhukov, Natalya N. Fishman, Hans-Martin Vieth, and Alexandra V. Yurkovskaya
- Subjects
Coupling constant ,Materials science ,CIDNP ,Intramolecular force ,Polar effect ,General Physics and Astronomy ,Molecule ,Charge (physics) ,Physical and Theoretical Chemistry ,Acceptor ,Hyperfine structure ,Molecular physics - Abstract
A detailed experimental study on reversible photo-induced intramolecular charge separation is presented based on NMR detection of Chemically Induced Dynamic Nuclear Polarization (CIDNP). From variation of such polarization with the external magnetic field the coupling constants of isotropic and anisotropic hyperfine interaction at individual 13C sites are measured in the short-lived charge separated state of dyad molecules composed of donor-bridge-acceptor parts. The objects of study were rigid donor-bridge- acceptor dyads, consisting of triarylamine as a donor, naphthalene diimide (NDI) as an acceptor, and a meta-conjugated diethynyl benzene fragment as a bridge. By systematic variation of side groups in the bridging moiety their influence on the electron withdrawing strength is traced. In combination with similar data for the 1H positions obtained previously for the same compounds (I. Zhukov, et al J. Chem. Phys 2020, 152, 014203) our results provide a reliable basis for determination of the spin density distribution in the charge separated state of such dyads.
- Published
- 2021
18. Non-Markovian Kinetics of Reactions in Solutions
- Author
-
Konstantin L. Ivanov, A.B. Doktorov, and Nikita N. Lukzen
- Subjects
symbols.namesake ,Chemistry ,Kinetics ,symbols ,Markov process ,Statistical physics - Published
- 2019
19. Integral Encounter Theory: A Universal Method for Kinetic Description of Multistage Reactions in Solutions
- Author
-
Nikita N. Lukzen and Konstantin L. Ivanov
- Subjects
Physics ,Statistical physics ,Kinetic energy - Published
- 2019
20. Magnetic field and orientation dependence of solid-state CIDNP
- Author
-
Jörg Matysik, Hans-Martin Vieth, Pavlo Bielytskyi, Nikita N. Lukzen, Daniel Gräsing, Gunnar Jeschke, Denis V. Sosnovsky, and Konstantin L. Ivanov
- Subjects
Spin dynamics ,General Physics and Astronomy ,Field dependence ,010402 general chemistry ,01 natural sciences ,Nuclear magnetic resonance ,symbols.namesake ,0103 physical sciences ,Physical and Theoretical Chemistry ,Anisotropy ,Hyperfine structure ,Physics ,Zeeman effect ,010304 chemical physics ,Condensed matter physics ,CIDNP ,Polarization (waves) ,0104 chemical sciences ,Magnetic field ,Photosynthetic reaction center ,Anisotropic interactions ,Magnetic fields ,symbols - Abstract
The magnetic field dependence of Chemically Induced Dynamic Nuclear Polarization (CIDNP) in solid-state systems is analyzed theoretically with the aim to explain the puzzling sign change of polarization found at low fields [D. Grasing et al., Sci. Rep. 7, 12111 (2017)]. We exploit the analysis of polarization in terms of level crossings and level anti-crossings trying to identify the positions of features in the CIDNP field dependence with specific crossings between spin energy levels of the radical pair. Theoretical treatment of solid-state CIDNP reveals a strong orientation dependence of polarization due to the spin dynamics conditioned by anisotropic spin interactions. Specifically, different anisotropic CIDNP mechanisms become active at different magnetic fields and different molecular orientations. Consequently, the field dependence and orientation dependence of polarization need to be analyzed together in order to rationalize experimental observations. By considering both magnetic field and orientation dependence of CIDNP, we are able to explain the previously measured CIDNP field dependence in photosynthetic reaction centers and to obtain a good qualitative agreement between the experimental observations and theoretical results.
- Published
- 2019
21. The Quantum Dynamical Basis of a Classical Kinetic Scheme Describing Coherent and Incoherent Regimes of Radical Pair Recombination
- Author
-
Johannes H. Klein, Ulrich Steiner, Christoph Lambert, and Nikita N. Lukzen
- Subjects
Physics ,010304 chemical physics ,Basis (linear algebra) ,Quantum mechanics ,0103 physical sciences ,Kinetic scheme ,Statistical physics ,Physical and Theoretical Chemistry ,010402 general chemistry ,01 natural sciences ,Quantum ,Recombination ,0104 chemical sciences - Abstract
In recent work from this group (J. H. Klein et al. J. Am. Chem. Soc. 2015, 137, 11011), the magnetic field dependent charge recombination kinetics in donor/Ir-complex/acceptor triads has been determined with outstanding accuracy and reproducibility. The field-dependent kinetics has been analyzed in terms of a classical reaction scheme including the field-independent rate parameters of singlet recombination (rate constant k S) and S/T0 mixing (rate constant k ST0) and the field-dependent rate constant k±(B) connecting central and outer Zeeman levels. In the present work, the extraction of k± from the experimental data is more precisely defined and the appearance of a “coherent” and “incoherent” regime of spin motion in a double log plot of k± vs. B is confirmed. The experimental decay curves have been reproduced by a full quantum dynamical model based on the stochastic Liouville equation, which was solved numerically, taking into account isotropic hyperfine coupling with five nuclear spins (1 N on donor radical, 4 H on acceptor radical) and anisotropic hyperfine coupling with the nitrogen nucleus at the donor radical. The results of the quantum calculations serve as a rigorous basis of interpreting the classical parameter k±. Furthermore, it is demonstrated that the incoherent part of spin motion is essential for a full understanding of the charge recombination kinetics even in the “coherent” regime.
- Published
- 2016
22. A Copper–Nitroxide Adduct Exhibiting Separate Single Crystal-to-Single Crystal Polymerization–Depolymerization and Spin Crossover Transitions
- Author
-
Elvina Chubakova, Marina V. Petrova, Victor I. Ovcharenko, Artem S. Bogomyakov, Sergey V. Fokin, Nikita N. Lukzen, Galina V. Romanenko, Maria M. Petrova, Galina G. Levkovskaya, Zhanna V. Dobrokhotova, Ekaterina M. Zueva, V.A. Morozov, Elena V. Rudyakova, Igor B. Rozentsveig, and Renad Z. Sagdeev
- Subjects
Nitroxide mediated radical polymerization ,Magnetic moment ,010405 organic chemistry ,Depolymerization ,Stereochemistry ,Spin transition ,chemistry.chemical_element ,010402 general chemistry ,01 natural sciences ,Copper ,0104 chemical sciences ,Inorganic Chemistry ,Crystallography ,chemistry ,Polymerization ,Spin crossover ,Physical and Theoretical Chemistry ,Single crystal - Abstract
A complex cascade of solid-state processes initiated by variation of temperature was found for the heterospin complex [Cu(hfac)2L(Me/Et)] formed in the reaction of copper(II) hexafluoroacetylacetonate [Cu(hfac)2] with stable nitronyl nitroxide 2-(1-methyl-3-ethyl-1H-pyrazol-4-yl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazole-3-oxide-1-oxyl (L(Me/Et)). The cooling of the compound below 260 K initiated a solid-state chemical reaction, which led to a depolymerization of chains and formation of a pair heterospin complex [Cu(hfac)2L(Me/Et)2][[Cu(hfac)2]3L(Me/Et)2]. Further decrease in temperature below 144 K led to a spin transition accompanied by a drastic decrease in the effective magnetic moment from 2.52 to 2.24 μB. When the compound was heated, the order of effects was reversed: at first, the magnetic moment abruptly increased, and then the molecular fragments of the pair cluster united into polymer chains. Two hysteresis loops correspond to this cascade of temperature-induced structural transformations on the experimental dependence μeff(T): one at high (T↑ = 283 K and T↓ = 260 K) and the other at low (T↑ = 161 K, T↓ = 144 K) temperature. The spin transitions were also recorded for the [[Cu(hfac)2]3L(Bu/Et)2] and [[Cu(hfac)2]5L(Bu/Et)4] molecular complexes, which are models of the trinuclear fragment of the {[Cu(hfac)2]3L(Me/Et)2} pair cluster.
- Published
- 2016
23. Magnetic field effect on recombination of radicals diffusing on a two-dimensional plane
- Author
-
Nikita N. Lukzen, Vladimir M. Sadovsky, Konstantin L. Ivanov, and Renad Z. Sagdeev
- Subjects
Physics ,010304 chemical physics ,Spin states ,Spins ,Radical ,General Physics and Astronomy ,Electron ,010402 general chemistry ,01 natural sciences ,Molecular physics ,0104 chemical sciences ,Magnetic field ,0103 physical sciences ,Physical and Theoretical Chemistry ,Diffusion (business) ,Hyperfine structure ,Recombination - Abstract
Magnetic Field Effects (MFEs) on the recombination of radicals, which diffuse on an infinite plane, are studied theoretically. The case of spin-selective diffusion-controlled recombination of Radical Pairs (RPs) starting from a random spin state is considered assuming uniform initial distribution of the radicals. In this situation, reaction kinetics is described by a time-dependent rate coefficient K(t), which tends to zero at long times. Strong MFEs on K(t) are predicted that originate from the Δg and hyperfine driven singlet-triplet mixing in the RP. The effects of spin relaxation on the magnetic field are studied, as well as the influence of the dipole-dipole interaction between the electron spins of the RP. In the two-dimensional case, this interaction is not averaged out by diffusion and it strongly affects the MFE. The results of this work are of importance for interpreting MFEs on lipid peroxidation, a magnetosensitive process occurring on two-dimensional surfaces of cell membranes.
- Published
- 2020
24. Positive electronic exchange interaction and predominance of minor triplet channel in CIDNP formation in short lived charge separated states of D-X-A dyads
- Author
-
Christoph Lambert, Natalya N. Fishman, Julian Schäfer, Ivan V. Zhukov, Mikhail S. Panov, Hans-Martin Vieth, Alexandra V. Yurkovskaya, Ulrich Steiner, Alexey S. Kiryutin, and Nikita N. Lukzen
- Subjects
chemistry.chemical_classification ,Physics ,education.field_of_study ,010304 chemical physics ,CIDNP ,Population ,General Physics and Astronomy ,Electron donor ,Electron acceptor ,010402 general chemistry ,01 natural sciences ,Acceptor ,Molecular physics ,0104 chemical sciences ,chemistry.chemical_compound ,chemistry ,0103 physical sciences ,Ultrafast laser spectroscopy ,Physical and Theoretical Chemistry ,Triplet state ,education ,Hyperfine structure - Abstract
Previous transient absorption measurements using the magnetically affected reaction yield (MARY) technique for a series of rigidly linked electron donor/electron acceptor dyads (D-X-A) consisting of a triarylamine donor, a naphthalene diimide acceptor, and a meta-conjugated diethynylbenzene unit as a bridge had revealed the presence of electronic exchange interaction, J, in the photoexcited charge separated (CS) state. Here, we present results obtained by photochemically induced dynamic nuclear polarization (photo-CIDNP) that allows for determining the sign of J. By variation of the magnetic field from 1 mT to 9.4 T, pronounced absorptive maxima of CIDNP were detected for more than 20 1H nuclei disregarding the sign of their hyperfine coupling constants in the transient charge separated state, with positions of maxima close to those found by the MARY technique. Quantitative comparison of the observed CIDNP signals for various D-X-A dyads reveals an increase in the CIDNP enhancement factor with increasing population of the triplet state determined by MARY spectroscopy at zero magnetic field. For CIDNP of the methyl groups of the TAA donor dyads, we found in all studies a good linear dependence between the CIDNP signal amplitude and the initial population of the CS triplet state. The linear relationship together with the absorptive CIDNP allows us to conclude that (i) the sign of the electronic exchange interaction Jex is positive, (ii) CIDNP is formed predominantly in the vicinity of level anticrossing between the T+ and S electronic levels, and (iii) coherent triplet-singlet transitions are induced by hyperfine interaction and accompanied by simultaneous electron and nuclear spin flip, T+β→Sα.
- Published
- 2020
25. Magnetic field effects in rigidly linked D-A dyads: Extreme on-resonance quantum coherence effect on charge recombination
- Author
-
Alexander Schmiedel, David Mims, Christoph Lambert, Ulrich Steiner, Nikita N. Lukzen, and Marco Holzapfel
- Subjects
Physics ,education.field_of_study ,010304 chemical physics ,Field (physics) ,Population ,General Physics and Astronomy ,Resonance ,010402 general chemistry ,01 natural sciences ,Molecular physics ,0104 chemical sciences ,Excited state ,0103 physical sciences ,Singlet state ,Physical and Theoretical Chemistry ,Triplet state ,Spin (physics) ,education ,Hyperfine structure - Abstract
Charge recombination in the photoinduced charge separated (CS) state of a rigidly linked donor/bridge/acceptor triad with a triarylamine (TAA) donor, a 1,3-diethynyl-2,5-dimethoxy benzene bridge (OMe), and a perylenediimide (PDI) unit as an acceptor, represents a spin chemical paradigm case of a rigid radical ion pair formed with singlet spin and recombining almost exclusively to the locally excited PDI triplet state (3PDI). The magnetic field dependence of the CS state decay and 3PDI formation kinetics are investigated from 0 to 1800 mT by nanosecond laser flash spectroscopy. The time-resolved magnetic field affected reaction yields spectra of the CS state population and 3PDI population exhibit a sharp and deep resonance at 18.9 mT, indicating level crossing of the S and T+ levels separated by an exchange interaction of J = 18.9/2 mT at zero field. The kinetics are biexponential around the resonance field and monoexponential outside that range. The monoexponential behavior can be simulated by a classical kinetic model assuming a single field dependent double Lorentzian function for the energy gap dependence of all spin conversion processes. The full field dependence of the kinetics has been simulated quantum theoretically. It has been shown that incoherent and coherent hyperfine coupling contribute to S/T+ spin conversion at all fields and that the biexponentiality of the kinetics at resonance is due to a partitioning of the overall kinetics into 2/3 of the singlet hyperfine states exhibiting strong isotropic coupling to T+ and 1/3 of the singlet hyperfine states that do not or only weakly couple isotropically to T+.
- Published
- 2019
26. Kinetics of target searching by means of two diffusion-like motions
- Author
-
Nikita N. Lukzen and Konstantin L. Ivanov
- Subjects
Classical mechanics ,Chemistry ,Kinetics ,General Physics and Astronomy ,Repair enzyme ,Motion (geometry) ,A-DNA ,Statistical physics ,Physical and Theoretical Chemistry ,Special case ,Small target ,Diffusion (business) ,General expression - Abstract
A theoretical approach to stochastic searching of a small target is developed, which can be applied, for instance, to searching for a damaged site on the DNA molecule by a DNA repair enzyme. It is assumed that the searching molecule moves along a chain of sites by means of stochastic jumps to the adjacent positions (one-dimensional ‘sliding’); the second motion models diffusion in three dimensions. A general expression is obtained for the flux to the damaged site. A special case is analyzed where the second motion is treated as effective 1D diffusion; the effective searching time is estimated. It is shown that the faster second motion shortens the searching time. A more realistic case where the second kind of motion leads to jumps not only to the adjacent site is also treated: it is shown that the diffusional search is facilitated even further.
- Published
- 2014
27. Analysis of Nutation Patterns in Fourier-Transform NMR of Non-Thermally Polarized Multispin Systems
- Author
-
Alexandra V. Yurkovskaya, Hans-Martin Vieth, Andrey N. Pravdivtsev, Nikita N. Lukzen, Konstantin L. Ivanov, and Egor A. Nasibulov
- Subjects
Physics ,education.field_of_study ,Spin states ,Nutation ,Population ,Product operator formalism ,Spin isomers of hydrogen ,Superposition principle ,symbols.namesake ,Fourier transform ,symbols ,Hyperpolarization (physics) ,Physical and Theoretical Chemistry ,Atomic physics ,education - Abstract
The complex spin order of hyperpolarized multispin systems giving rise to anomalous NMR spectral patterns that vary with the RF excitation angle is analyzed by decomposing its nutation behavior in a superposition of Fourier harmonics. The product operator formalism is applied to calculating the spectral contributions of the various mutual alignments of scalar coupled spins. Two cases are treated, namely systems exhibiting only differences in population of their spin states and systems showing in addition zero-quantum coherences between states, a situation often seen at hyperpolarization. After deriving the general solution a number of representative examples are discussed in detail. The theoretical treatment is applied to analyzing the spin order observed in a hyperpolarized two-spin system that is prepared in the singlet state by para-hydrogen induced polarization.
- Published
- 2013
28. Magnetic field and spin effects on the recombination of radicals on two-dimensional surfaces
- Author
-
Konstantin L. Ivanov, Vladimir M. Sadovsky, Robert Kaptein, Nikita N. Lukzen, and Renad Z. Sagdeev
- Subjects
Physics ,Nuclear magnetic resonance ,Condensed matter physics ,Spin polarization ,Radical ,Physical and Theoretical Chemistry ,Spin (physics) ,Recombination ,Magnetic field - Published
- 2013
29. Exploiting adiabatically switched RF-field for manipulating spin hyperpolarization induced by parahydrogen
- Author
-
Alexandra V. Yurkovskaya, Konstantin L. Ivanov, Hans-Martin Vieth, Nikita N. Lukzen, and Alexey S. Kiryutin
- Subjects
Spin states ,Spins ,Chemistry ,General Physics and Astronomy ,Spin isomers of hydrogen ,Polarization (waves) ,Induced polarization ,Nuclear magnetic resonance ,Condensed Matter::Strongly Correlated Electrons ,Hyperpolarization (physics) ,Physical and Theoretical Chemistry ,Atomic physics ,Spin (physics) ,Multiplet - Abstract
A method for precise manipulation of non-thermal nuclear spin polarization by switching a RF-field is presented. The method harnesses adiabatic correlation of spin states in the rotating frame. A detailed theory behind the technique is outlined; examples of two-spin and three-spin systems prepared in a non-equilibrium state by Para-Hydrogen Induced Polarization (PHIP) are considered. We demonstrate that the method is suitable for converting the initial multiplet polarization of spins into net polarization: compensation of positive and negative lines in nuclear magnetic resonance spectra, which is detrimental when the spectral resolution is low, is avoided. Such a conversion is performed for real two-spin and three-spin systems polarized by means of PHIP. Potential applications of the presented technique are discussed for manipulating PHIP and its recent modification termed signal amplification by reversible exchange as well as for preparing and observing long-lived spin states.
- Published
- 2015
30. Kinetic analysis of the search for damaged DNA bases by repair enzymes: theoretical investigation of diffusion-controlled steps
- Author
-
Konstantin L. Ivanov, Nikita N. Lukzen, and Vladimir V. Koval
- Subjects
Quantitative Biology::Biomolecules ,Repair enzymes ,DNA repair ,DNA damage ,Kinetics ,General Chemistry ,Nucleobase ,chemistry.chemical_compound ,Crystallography ,chemistry ,Diffusion (business) ,Biological system ,Dispersion (chemistry) ,DNA - Abstract
The kinetics of the search for damaged DNA bases by repair enzymes was theoretically studied. In particular, the characteristic features of the diffusive motion of the enzyme were investigated. Compact analytical expressions for the average search time and its dispersion were obtained for two models of the one-dimensional motion of the enzyme along the DNA fragment: continuous diffusion and stochastic jumps. It was shown that the kinetics of the search is essentially non-exponential due to characteristic features of the diffusive motion.
- Published
- 2011
31. CPMG echo amplitudes with arbitrary refocusing angle: Explicit expressions, asymptotic behavior, approximations
- Author
-
Nikita N. Lukzen, A.B. Doktorov, and M.V. Petrova
- Subjects
Electromagnetic field ,Physics ,Nuclear and High Energy Physics ,Offset (computer science) ,business.industry ,Mathematical analysis ,Biophysics ,Generating function ,Pulse sequence ,Condensed Matter Physics ,Magnetic Resonance Imaging ,Biochemistry ,Expression (mathematics) ,Electromagnetic Fields ,Amplitude ,Optics ,Spin echo ,business ,Algorithms ,Excitation - Abstract
Exact explicit analytical expression for echoes in the Carr-Purcell-Meiboom-Gill sequence with arbitrary excitation and refocusing angles and resonance offset of RF pulses was obtained, employing the generating functions formalism developed earlier by authors. Asymptotic form and analytical approximation for echoes were derived in an elegant way and analyzed in details. In particular, it was shown that depending on T(1), T(2) and parameters of the pulse sequence, oscillatory behavior of echoes can take place. Accuracy of asymptotic forms and approximations were tested by comparison with exactly calculated echo amplitudes. Besides, it was shown, that the generating function approach can be applied to the consideration of terminated pulse sequences, when after-pulses echoes are registered.
- Published
- 2011
32. Quantitative Approach to CIDNP in Proteins with Several Polarizable Residues on the Surface
- Author
-
Olga B. Morozova, Alexandra V. Yurkovskaya, Nikita N. Lukzen, Kenneth Hun Mok, and Konstantin L. Ivanov
- Subjects
Steric effects ,Quantitative Biology::Biomolecules ,CIDNP ,Chemistry ,Polarizability ,Chemical physics ,Kinetics ,Native state ,Analytical chemistry ,Kinetic energy ,Polarization (electrochemistry) ,Chemical reaction ,Atomic and Molecular Physics, and Optics - Abstract
A quantitative theoretical approach to protein chemically induced dynamic nuclear polarization (CIDNP) is formulated in the present work, which is based on the theory of sterically specific chemical reactions in liquids. Kinetic equations for polarization of all CIDNP-active accessible amino acid residues are presented. Relations between the kinetic parameters and the total side-chain accessibility (TSA) values are established. Numerical calculations of the CIDNP kinetics are also shown to demonstrate how the time behavior of polarization depends on TSA. The present theoretical approach was applied to model time-resolved protein CIDNP data obtained for Tyr59 and His68 of ubiquitin in the native state. Comparison of theoretical predictions with the experimental data confirms the accuracy of the approach.
- Published
- 2011
33. A Theoretical and Experimental Study of NMR Contrasting Properties of Nanocomposites Based on Ferric Oxides Stabilized by Arabinogalactan Matrix
- Author
-
A. V. Yurkovskaya, Boris G. Sukhov, Boris A. Trofimov, Hans-Martin Vieth, Galina P. Aleksandrova, Andrey A. Savelov, M. V. Petrova, V. I. Ovcharenko, Artem S. Bogomyakov, Nikita N. Lukzen, and Alexey S. Kiryutin
- Subjects
Materials science ,Nanocomposite ,Relaxation (NMR) ,Mineralogy ,Nanoparticle ,Maghemite ,engineering.material ,Homogeneous distribution ,Atomic and Molecular Physics, and Optics ,Condensed Matter::Materials Science ,chemistry.chemical_compound ,chemistry ,Chemical engineering ,Ferromagnetism ,Arabinogalactan ,engineering ,Magnetite - Abstract
Nuclear magnetic resonance relaxation properties of aqueous solution containing nanocomposites based on magnetite and maghemite nanoparticles stabilized by arabinogalactan obtained from Baikal larch (Larix sibirica) wood matrix were investigated. The relaxation properties of the solutions, namely, viscosity dependences of T 1 and T 2 and magnetic field dependence of T 1, were studied experimentally. Two models of the nanocomposite granular structure corresponding to two limiting cases of ferromagnetic material distribution over the arabinogalactan matrix were considered. The first one assumes a homogeneous distribution of magnetite and maghemite nanoparticles over the spherical arabinogalactan matrix, while the second one considers a single hard ferromagnetic core at the center of the spherical arabinogalactan matrix. Theoretical fitting of the experimental results within these models was performed.
- Published
- 2011
34. Consistent Treatment of Spin-Selective Recombination of a Radical Pair Confirms the Haberkorn Approach
- Author
-
Kiminori Maeda, Marina V. Petrova, Konstantin L. Ivanov, and Nikita N. Lukzen
- Subjects
Work (thermodynamics) ,Kinetic equations ,Chemistry ,Quantum mechanics ,Dephasing ,Electron ,Physics::Chemical Physics ,Physical and Theoretical Chemistry ,Atomic physics ,Quantum ,Recombination ,Spin-½ ,Quantum Zeno effect - Abstract
In the present work, we have shown that consistent derivation of the kinetic equations describing the electron spin-selective recombination of radical pairs confirms the conventional Haberkorn approach. The derivation has been based on considering the interaction of the reactive system (radical pair and product state) with the thermal bath. The consistency of this approach has also been substantiated by numerical simulations performed for the purely quantum mechanical model of the recombining radical pair. Finally, we have shown that the quantum Zeno effect on radical pair recombination is not an exclusive feature of the approach recently proposed by Kominis, as it should be present at any rate of the singlet-triplet dephasing in the radical pair, which always accompanies the recombination process.
- Published
- 2010
35. The effect of dipolar interaction on the magnetic isotope effect
- Author
-
Nikita N. Lukzen, Matin Mojaza, and J. Boiden Pedersen
- Subjects
Chemistry ,Exchange interaction ,General Physics and Astronomy ,Molecular physics ,Magnetic field ,Dipole ,Computational chemistry ,Kinetic isotope effect ,Physics::Atomic Physics ,Physical and Theoretical Chemistry ,Magnetic isotope effect ,Hyperfine structure ,Isotopes of magnesium ,Magnetic dipole–dipole interaction - Abstract
A multi-channel kinetic description is used to study the magnetic isotope effect (MIE) in zero magnetic field. The maximal isotope effect is equal to the number of channels, two for the hyperfine interaction but four for the electron spin dipole–dipole interaction of the intermediate radical pair. Quantum mechanical calculations agree with these conclusion and show that large MIE may be obtained even in the presence of a strong exchange interaction. The observed magnesium isotope effect on the rate of enzymatic synthesis of adenosine triphosphate (ATP) is approximately 3 implying that the dipolar interaction is responsible for the effect. Our calculations provide support for the proposed mechanism.
- Published
- 2010
36. Viscosity dependence of rubrene fluorescence quenching by organic radicals via energy transfer
- Author
-
Martin Justinek, Nikita N. Lukzen, Gonzalo Angulo, Günter Grampp, and Stephan Landgraf
- Subjects
chemistry.chemical_compound ,Viscosity ,Reaction rate constant ,Quenching (fluorescence) ,Galvinoxyl ,chemistry ,Radical ,Kinetics ,Analytical chemistry ,Physical chemistry ,Physical and Theoretical Chemistry ,Rubrene ,Fluorescence - Abstract
The kinetics of rubrene (5,6,11,12-tetraphenylnaphthacene) fluorescence quenching by energy transfer to the radicals of N,N,N',N'-tetramethyl-para-phenylenediamine (TMPD+*), tetracyanoquinonedimethane (TCNQ-*) and galvinoxyl (2,6-di-tert-butyl-alpha-(3,5-di-tert-butyl-4-oxo-2,5-cyclohexadien-1-ylidene)-p-tolyloxy; GAL*), have been measured in solvents of different viscosities. At room temperature the observed quenching rate constants vary between 0.12 and 7.8 x 10(10) M(-1) s(-1), always exceeding the diffusion rate constants given by the simplest version of Smoluchowski theory combined with the rate constants for dipole-dipole energy transfer. This discrepancy is explained by accounting for the non-stationary stage in the Förster kinetics, even though the experimental fluorescence decays are apparently mono-exponential.
- Published
- 2009
37. Separation of integral and multiplet nuclear polarization by means of spin echo magnetization phase analysis
- Author
-
Renad Z. Sagdeev, M. V. Petrova, Konstantin L. Ivanov, and Nikita N. Lukzen
- Subjects
Physics ,Magnetization ,Nuclear magnetic resonance ,Condensed matter physics ,Spin polarization ,Pulsed EPR ,Spin echo ,Magnetization transfer ,Physical and Theoretical Chemistry ,Insensitive nuclei enhanced by polarization transfer ,Multiplet ,Neutron spin echo - Published
- 2009
38. The generating functions formalism for the analysis of spin response to the periodic trains of RF pulses. Echo sequences with arbitrary refocusing angles and resonance offsets
- Author
-
Igor V. Koptyug, Nikita N. Lukzen, Andrey A. Savelov, M. V. Petrova, and Renad Z. Sagdeev
- Subjects
Nuclear and High Energy Physics ,Offset (computer science) ,Analytical expressions ,Radio Waves ,Chemistry ,Biophysics ,Generating function ,Signal Processing, Computer-Assisted ,Models, Theoretical ,Image Enhancement ,Condensed Matter Physics ,Magnetic Resonance Imaging ,Biochemistry ,Computational physics ,Kinetics ,Formalism (philosophy of mathematics) ,Magnetization ,Amplitude ,Nuclear magnetic resonance ,Flip angle ,Image Processing, Computer-Assisted ,Spin echo ,Spin Labels ,Algorithms ,Tomography, Optical Coherence - Abstract
The generating functions (GF) formalism was applied for calculation of spin density matrix evolution under the influence of periodic trains of RF pulses. It was shown that in a general case, closed expression for the generating function can be found that allows in many cases to derive analytical expressions for the generating function of spin density matrix (magnetization, coherences). This approach was shown to be particularly efficient for the analysis of multi-echo sequences, where one has to average over various frequency isochromats. The explicit analytical expressions for the generating function for echo amplitudes in a Carr–Purcell–Meiboom–Gill (CPMG) echo sequence, a multiecho sequence with incremental phase of refocusing pulse, a gradient echo sequence including transient period were obtained for an arbitrary flip angle and an arbitrary resonance offset. Comparison of the theory and the spin-echo experiments was done, demonstrating a good agreement.
- Published
- 2009
39. Searching for the Exchange Shift: a Set of Test Systems
- Author
-
Alexey Potapov, E. Yu. Fursova, Galina V. Romanenko, Yu. N. Molin, V. I. Ovcharenko, Nikita N. Lukzen, and D. V. Stass
- Subjects
Electron nuclear double resonance ,Spins ,Pulsed EPR ,Chemistry ,Analytical chemistry ,Electron ,Atomic and Molecular Physics, and Optics ,Spectral line ,Ion ,law.invention ,Paramagnetism ,law ,Atomic physics ,Electron paramagnetic resonance - Abstract
We suggest that intramolecular exchange coupling J in solutions can possibly be measured with just a ruler using an analogue of the nuclear magnetic resonance paramagnetic shift. If one of the two coupled electron spins is rapidly relaxing, the resulting electron paramagnetic resonance (EPR) spectrum of the system is the resolved spectrum for the second spin with a shifted g-factor. The amount and the sense of the shift are both linear in J, which thus can be obtained from the measured shift by simple algebra. We prepared a set of complexes of rare-earth ions with nitroxides to probe this idea, but the sought effect was not yet found indicating J < 0.1 cm−1 for these systems. Either the radical centers should be brought closer to the central lanthanide ion, or the ion itself should be substituted for a rapidly relaxing transition-metal ion, e.g., Cr2+ or Co2+. Furthermore we report evolving EPR spectra that reflect the inner life of the complexes in solution.
- Published
- 2008
40. A theory of spin-Peierls transitions in chains of exchange clusters
- Author
-
V. I. Ovcharenko, V. A. Morozov, and Nikita N. Lukzen
- Subjects
Quantum phase transition ,Phase transition ,Spin polarization ,Chain (algebraic topology) ,Condensed matter physics ,Spin crossover ,Chemistry ,General Chemistry ,Spin (physics) ,Electron magnetic dipole moment ,Spin magnetic moment - Abstract
A theoretical approach to analysis of magnetic structural phase transitions of chain polymer heterospin complexes is proposed. The approach is based on the model for spin-Peierls phase transition of chain exchange clusters. The type of the phase transition depends on the elastic constant of the chain.
- Published
- 2008
41. Theory of Spin-Peierls Transitions in Chains of Exchange Clusters
- Author
-
Nikita N. Lukzen, V. A. Morozov, and Victor I. Ovcharenko
- Subjects
Phase transition ,Condensed matter physics ,Chemistry ,Materials Chemistry ,Physical and Theoretical Chemistry ,Elasticity (economics) ,Surfaces, Coatings and Films - Abstract
A theoretical approach to the analysis of magnetostructural phase transitions of chain polymeric heterospin complexes is suggested. The approach is based on a model of the spin-Peierls transition in chains of exchange clusters. The chain elasticity parameter is found to be a main factor determining the order of phase transition.
- Published
- 2008
42. Analytical derivation of multiple spin echo amplitudes with arbitrary refocusing angle
- Author
-
Nikita N. Lukzen and Andrey A. Savelov
- Subjects
Physics ,Nuclear and High Energy Physics ,Condensed matter physics ,Echo-Planar Imaging ,Biophysics ,Reproducibility of Results ,Physics::Optics ,Image Enhancement ,Condensed Matter Physics ,Models, Biological ,Sensitivity and Specificity ,Biochemistry ,Amplitude ,Models, Chemical ,Flip angle ,Quantum electrodynamics ,Image Interpretation, Computer-Assisted ,Spin echo ,Computer Simulation ,Spin Labels ,Algorithms - Abstract
Explicit non-recursive expressions for spin echo amplitudes have been derived for CPMG sequences with arbitrary refocusing flip angle.
- Published
- 2007
43. On the magnetic field and isotope effects in enzymatic phosphorylation
- Author
-
J. Boiden Pedersen, Nikita N. Lukzen, and Anatoly L. Buchachenko
- Subjects
chemistry.chemical_classification ,Physics::Biological Physics ,Quantitative Biology::Biomolecules ,Reaction mechanism ,Magnesium ,Inorganic chemistry ,General Physics and Astronomy ,chemistry.chemical_element ,equipment and supplies ,Magnetic field ,Quantitative Biology::Subcellular Processes ,chemistry.chemical_compound ,Enzyme ,chemistry ,Kinetic isotope effect ,Phosphorylation ,Physical and Theoretical Chemistry ,human activities ,Isotopes of magnesium ,Adenosine triphosphate - Abstract
A huge magnesium isotope effect on the rate of enzymatic synthesis of adenosine triphosphate (ATP) has recently been reported. This indicates that the reaction involves an intermediate ion-radical pairs and should be sensitive to external magnetic fields. We have calculated the rate of ATP production based on a previously proposed molecular reaction mechanism. The calculated maximum isotope effect is in agreement with experiment. Magnetic field is predicted to increase the rate of ATP formation by 60% for samples enriched by magnetic magnesium ( 25 Mg) while decreasing the rate by 9% for naturally occurring samples.
- Published
- 2007
44. Highly Efficient Polarization of Spin-1/2 Insensitive NMR Nuclei by Adiabatic Passage through Level Anticrossings
- Author
-
Alexandra V. Yurkovskaya, Konstantin L. Ivanov, Nikita N. Lukzen, Hans-Martin Vieth, and Andrey N. Pravdivtsev
- Subjects
Physics ,Nuclear magnetic resonance ,Substrate molecule ,Molecule ,General Materials Science ,Singlet state ,Physical and Theoretical Chemistry ,Atomic physics ,Adiabatic process ,Rotating reference frame ,Polarization (waves) ,Spin (physics) ,Rf excitation - Abstract
A method is proposed to transfer spin order from para-hydrogen, that is, the H2 molecule in its singlet state, to spin-1/2 heteronuclei of a substrate molecule. The method is based on adiabatic passage through nuclear spin level anticrossings (LACs) in the doubly rotating frame of reference; the LAC conditions are fulfilled by applying resonant RF excitation at the NMR frequencies of protons and the heteronuclei. Efficient conversion of the para-hydrogen-induced polarization into net polarization of the heteronuclei is demonstrated; the achieved signal enhancements are about 6400 for (13)C nuclei at natural abundance. The theory behind the technique is described; advantages of the method are discussed in detail.
- Published
- 2015
45. Calculation of transient CIDEP spectra of spin-correlated radical pairs in nanotubes
- Author
-
Günter Grampp, V.A. Morozov, Konstantin L. Ivanov, Nikita N. Lukzen, and Daniel R. Kattnig
- Subjects
Nanotube ,Spins ,Condensed matter physics ,Chemistry ,Radical ,General Physics and Astronomy ,Electron ,Molecular physics ,Spectral line ,law.invention ,Magnetic field ,law ,Physical and Theoretical Chemistry ,Electron paramagnetic resonance ,Polarization (electrochemistry) - Abstract
The chemically induced dynamic electron polarization (CIDEP) formed by spin-correlated radical pairs in nanotubes is studied theoretically. Numerical solutions of the stochastic Liouville equation of the density operator are obtained by finite-difference methods. The nanotube is modelled as a one-dimensional nanoreactor with the relative motion of the radicals assumed to be free diffusion. The effect of the non-averaged dipole–dipole interaction of the electron spins on the CIDEP formation is studied in detail. Furthermore, the influence of the radical mobility and the nanotube orientation with respect to the external magnetic field are elucidated.
- Published
- 2006
46. Chemical polarization of electrons of spin-correlated radical ion pairs in nanotubes
- Author
-
Konstantin L. Ivanov, Günter Grampp, V. A. Morozov, Daniel R. Kattnig, Renad Z. Sagdeev, and Nikita N. Lukzen
- Subjects
Materials science ,Radical ion ,Electron ,Physical and Theoretical Chemistry ,Atomic physics ,Spin (physics) ,Polarization (electrochemistry) - Published
- 2006
47. Theoretical study of the CIDNP kinetics of the reaction of a photo-excited dye with a reactive spot on the surface of a sphere: application to CIDNP of proteins
- Author
-
Konstantin L. Ivanov, P. J. Hore, Nikita N. Lukzen, and A. V. Yurkovskaya
- Subjects
Steric effects ,Chemistry ,CIDNP ,Kinetics ,Biophysics ,Condensed Matter Physics ,Photochemistry ,Reaction rate constant ,Excited state ,Steric factor ,Molecule ,Physical and Theoretical Chemistry ,Polarization (electrochemistry) ,Molecular Biology - Abstract
Time-resolved chemically induced dynamic nuclear polarization (CIDNP) in sterically specific photoreactions of proteins with excited dye molecules is studied theoretically by means of the integral encounter theory. The protein is modeled as a chemically inert sphere with one small reactive spot, with steric factor f modeling a single accessible CIDNP-active amino acid residue on its surface. Kinetic equations describing the dye-quenching kinetics and the CIDNP time evolution are obtained, and the non-trivial f dependence of the rate constant of dye quenching, the geminate CIDNP intensity, the radical recombination rate constant and the nuclear T 1 relaxation time are studied. Protein CIDNP kinetics are compared with those of free amino acids.
- Published
- 2006
48. Singlet and Triplet Products of the Geminate Recombination of a Radical Pair with a Single Magnetic Nucleus (I = 1/2)
- Author
-
A.I. Burshtein, Jørgen Boiden Pedersen, and Nikita N. Lukzen
- Subjects
Chemistry ,Diradical ,Radical ,Singlet fission ,Exchange interaction ,Singlet state ,Physical and Theoretical Chemistry ,Triplet state ,Atomic physics ,Magnetic field ,Spin-½ - Abstract
The double-channel recombination and separation of the photochemically created singlet radical pair is investigated, taking into account the spin conversion in a zero magnetic field and the arbitrary initial distance between the radicals. The quantum yields of the singlet and triplet products and the free radicals production are found analytically, assuming that the recombination of the diffusing radicals occurs at contact. All the yields are related to the singlet and triplet populations of the recombining radical pair, subjected to spin conversion and contact exchange interaction. The general analytical expressions for the quantum yields are specified for the particular limits of the weak and strong exchange. They are greatly simplified in the case of polar solvents, especially at the contact start. A close similarity is obtained with the results of a previously developed incoherent model of spin conversion, provided that the conversion rate is appropriately related to the hyperfine coupling constant.
- Published
- 2005
49. The effect of signs of hyperfine coupling constant on MARY spectra affected by degenerate electron exchange
- Author
-
Daniel R. Kattnig, Nikita N. Lukzen, and Günter Grampp
- Subjects
Condensed matter physics ,Chemistry ,Electron exchange ,Degenerate energy levels ,General Physics and Astronomy ,Spectral line ,chemistry.chemical_compound ,Amplitude ,Ab initio quantum chemistry methods ,Pyrene ,Physical and Theoretical Chemistry ,Atomic physics ,Constant (mathematics) ,Sign (mathematics) - Abstract
It is demonstrated that the shape of MAgnetic field effect on Reaction Yield (MARY) spectra depends substantially on the relative signs of the hyperfine coupling constants (HFC) of the constituents of the transient radical pair. The effect is exemplified in terms of the pyrene/benzene-1,4-dicarbonitrile system, the spin dynamics of which are calculated with rigorous account of all HFCs and the peculiarities caused by a degenerate electron exchange reaction. It is shown that MARY spectra calculated using the same sign for all HFCs and those obtained using the signs as predicted from ab initio calculations differ significantly with respect to the amplitude of the low magnetic field feature.
- Published
- 2005
50. Indications for unequal rates of ion-molecular charge transfer reaction for biphenyl radical anion and cation from MARY and OD ESR spectra
- Author
-
Yu. N. Molin, V.N. Verkhovlyuk, Nikita N. Lukzen, and D.V. Stass
- Subjects
Hexane ,Biphenyl ,Esr spectra ,chemistry.chemical_compound ,Radical ion ,Chemistry ,organic chemicals ,Molecular charge ,General Physics and Astronomy ,Molecule ,Physical and Theoretical Chemistry ,Photochemistry ,Ion - Abstract
MARY and Optically Detected ESR techniques were used to infer that radical cation and radical anion of biphenyl in concentrated hexane solutions have substantially different second moments of their ESR spectra. This observation is interpreted in terms of different types of processes between the two radical ions and the neutral parent molecule. It is suggested that dimerization is prevalent for biphenyl radical cation, while biphenyl radical anion is rather involved in fast ion-molecular charge transfer reaction.
- Published
- 2005
Catalog
Discovery Service for Jio Institute Digital Library
For full access to our library's resources, please sign in.