Matvey Fedin - Academia.edu (original) (raw)
Papers by Matvey Fedin
The journal of physical chemistry. B, Jan 4, 2015
Triarylmethyl radicals (trityls, TAMs) represent a relatively new class of spin labels. The long ... more Triarylmethyl radicals (trityls, TAMs) represent a relatively new class of spin labels. The long relaxation of trityls at room temperature in liquid solutions makes them a promising alternative for traditional nitroxides. In this work we have synthesized a series of TAMs including perdeuterated Finland trityl (D36 form), mono-, di-, and triester derivatives of Finland-D36 trityl, the deuterated form of OX63, the dodeca-n-butyl homologue of Finland trityl, and triamide derivatives of Finland trityl with primary and secondary amines attached. We have studied room-temperature relaxation properties of these TAMs in liquids using pulsed electron paramagnetic resonance (EPR) at two microwave frequency bands. We have found the clear dependence of phase memory time (Tm ∼ T2) on the magnetic field: room-temperature Tm values are ∼1.5-2.5 times smaller at the Q-band (34 GHz, 1.2 T) than at the X-band (9 GHz, 0.3 T). This trend is ascribed to the contribution from g-anisotropy that is negligib...
The journal of physical chemistry. B, Jan 4, 2015
Triarylmethyl (trityl, TAM) based spin labels represent a promising alternative to nitroxides for... more Triarylmethyl (trityl, TAM) based spin labels represent a promising alternative to nitroxides for EPR distance measurements in biomolecules. Herewith, we report synthesis and comparative study of series of model DNA duplexes, 5'-spin-labeled with TAMs and nitroxides. We have found that the accuracy (width) of distance distributions obtained by double electron-electron resonance (DEER/PELDOR) strongly depends on the type of radical. Replacement of both nitroxides by TAMs in the same spin-labeled duplex allows narrowing of the distance distributions by a factor of 3. Replacement of one nitroxide by TAM (orthogonal labeling) leads to a less pronounced narrowing but at the same time gains sensitivity in DEER experiment due to efficient pumping on the narrow EPR line of TAM. Distance distributions in nitroxide/nitroxide pairs are influenced by the structure of the linker: the use of a short amine-based linker improves the accuracy by a factor of 2. At the same time, a negligible depe...
Inorganic chemistry, Jan 11, 2015
Breathing crystals" based on copper(II) hexafluoroacetylacetonates and pyrazolyl-substituted nitr... more Breathing crystals" based on copper(II) hexafluoroacetylacetonates and pyrazolyl-substituted nitronyl nitroxides comprise the exchange-coupled clusters within the polymeric chains. Owing to an interplay of exchange interaction between copper(II) and nitroxide spins and Jahn−Teller nature of copper(II) complex, the breathing crystals demonstrate thermally and light-induced magnetostructural transitions in many aspects similar to the classical spin crossover. Herewith, we report the first application of variable temperature (VT) far/mid Fourier transform infrared (FTIR) spectroscopy and mid FTIR microscopy to breathing crystals. This VT-FTIR study was aimed toward clarification of the transitions mechanism previously debated on the basis of superconducting quantum interference device, X-ray diffraction, and electron paramagnetic resonance data. VT-FTIR showed the onset of new vibrational bands during phase transitions occurring at the expense of several existing ones, whose intensity was significantly reduced. The most pronounced spectral changes were assigned to corresponding vibrational modes using quantum chemical calculations. A clear-cut correlation was found between temperature-dependent effective magnetic moment of studied compounds and the observed VT-FTIR spectra. Importantly, VT-FTIR confirmed coexistence of two types of copper(II)−nitroxide clusters during gradual magnetostructural transition. Such clusters correspond to weakly coupled and strongly coupled spin states, whose relative contribution depends on temperature. The pronounced difference in the VT-FTIR spectra of two states in breathing crystals is a fingerprint of magnetostructural transition, and understanding of these characteristics achieved by us will be useful for future studies of breathing crystals as well as their diamagnetic analogues.
Inorganica Chimica Acta, 2008
Chain complex of copper(II) hexafluoroacetylacetonate with pyrazole-substituted nitronyl nitroxid... more Chain complex of copper(II) hexafluoroacetylacetonate with pyrazole-substituted nitronyl nitroxide containing exchange-coupled copper(II)–nitroxide clusters has been studied using electron paramagnetic resonance (EPR) spectroscopy. The structural rearrangements at low temperatures induce spin transitions in one half of the copper(II)–nitroxide clusters and effectively lead to reversible diamagnetic dilution. This results in significant changes of EPR spectra and allows us to obtain the value
Journal of The American Chemical Society, 2008
... K. Yu.; Fokin, SV; Tretyakov, EV; Romanenko, GV; Ikorskii, VN Russ. Chem. Bull. Int. Ed.2004,... more ... K. Yu.; Fokin, SV; Tretyakov, EV; Romanenko, GV; Ikorskii, VN Russ. Chem. Bull. Int. Ed.2004, 53, 2406−2427. ... Victor I. Ovcharenko, Galina V. Romanenko, Ksenia Yu. Maryunina, Artem S. Bogomyakov and Elena V. Gorelik. Inorganic Chemistry 2008 47 (20), 9537-9552. ...
![Research paper thumbnail of Erratum to "Copper(II) complexes with pyrazolyl-substituted nitronyl and imino nitroxides" [Polyhedron 27 (2008) 739-740] (DOI:10.1016/j.poly.2007.11.003)](https://attachments.academia-assets.com/43258903/thumbnails/1.jpg)
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Lecture Notes in Physics, 2006
An overview of the various multiple-photon processes in electron paramagnetic resonance (EPR) spe... more An overview of the various multiple-photon processes in electron paramagnetic resonance (EPR) spectroscopy is given. First, we describe different types of multiple-photon transitions that can be observed with monochromatic and bichromatic microwave fields in spin systems with unequally spaced energy levels and in two-level systems. Then we discuss multiple-photon processes that are based on a bichromatic radiation field consisting of
The Journal of Physical Chemistry A, 2007
The complexes of Cu2+ hexafluoroacetylacetonate with two pyrazol-substituted nitronyl nitroxides ... more The complexes of Cu2+ hexafluoroacetylacetonate with two pyrazol-substituted nitronyl nitroxides are the choice systems to study the spin dynamics of strongly exchange-coupled spin triads. The large values of exchange coupling (ca. 100 cm-1) and high-resolution electron paramagnetic resonance (EPR) at Q- and W-bands (35 and 94 GHz) allowed us to observe and interpret specific characteristics of these systems. An electron spin exchange process has been found between different multiplets of the spin triad, which manifests itself as a significant shift of the EPR line position with temperature. We propose that the spin exchange process is caused by the modulation of exchange interaction between copper and nitroxides by lattice vibrations. The estimations of the rate of exchange process and model calculations essentially support the observed phenomena. The studied characteristics of strongly coupled spin triads explain previously obtained results, agree with literature, and should be accounted for in future investigations of similar spin systems.
The Journal of Physical Chemistry A, 2006
The complex of Cu(2+) hexafluoroacetylacetonate with two pyrazol-substituted nitronyl nitroxides ... more The complex of Cu(2+) hexafluoroacetylacetonate with two pyrazol-substituted nitronyl nitroxides represents an unusual exchange-coupled three-spin system. The antiferromagnetic exchange coupling, which already atT < 150 K is larger than the thermal energy kT, induces the transition from a total spin state S = (3)/(2) to a state S = (1)/(2) and produces static spin polarization. Anomalous electron paramagnetic resonance (EPR) spectra of an S = (1)/(2) state were detected experimentally and described theoretically. The effective g factor of the three-spin system is smaller than 2, despite the fact that all the individual components have g > 2. The observed signals with g < 2 are highly informative and can be employed for determination of the sign and value of the exchange interaction in three-spin nitroxide-copper-nitroxide clusters.
The Journal of Physical Chemistry A, 2005
We report the first experimental study of chemically induced electron spin polarization (CIDEP) p... more We report the first experimental study of chemically induced electron spin polarization (CIDEP) processes in low magnetic fields for spin-correlated radical pairs (SCRPs) in micellar environments. Photoexcitation of (2,4,6-trimethylbenzoyl) diphenylphosphine oxide (TMBDPO) leads to the radical pair comprised of acyl radical 1 and phosphonyl radical 2. The spin polarization, which is very strong in free solution even at zero field, was detected using L-band time-resolved electron paramagnetic resonance (TREPR) spectroscopy with specially modified resonators. The mechanism of formation and decay of low field CIDEP in SCRPs is presented and discussed. The prominent difference between low and high field spectra in micelles is the absence of anti-phase structure for radical 2 with HFI a > B0. This feature is consistent with the proposed polarization mechanism and theoretical predictions.
Russian Chemical Bulletin, 2006
The review summarizes the results of studies on specific features of spin relaxation of radicals ... more The review summarizes the results of studies on specific features of spin relaxation of radicals in liquids in weak magnetic fields.
Russian Chemical Bulletin, 2010
The reaction of copper nitrate Cu(NO3)2·3H2O with potassium salt of 1,1-cyclohexanediacetic acid ... more The reaction of copper nitrate Cu(NO3)2·3H2O with potassium salt of 1,1-cyclohexanediacetic acid (H2CHDAA) in an EtOH-toluene mixture affords the polymeric complex {[(EtOH)2Cu2(CHDAA)2]·EtOH n (1). The addition of pyridine to the Cu(NO3)2·3H2O-K2CHDAA reaction system in an EtOH-MeCN mixture results in the isolation of the unusual octadecanuclear heterometallic cluster [K2(η1-H2O)6(η1-py)8Cu16-(η1-OH)2(μ4-CHDAA)16]·EtOH·MeCN·3H2O (2). In complex 2, the hexadecanuclear metal carboxylate dianion (η1-H2O)6(η1-py)8Cu16(η1-OH)2(μ4-CHDAA)16 acts as
Physical Chemistry Chemical Physics, 2003
ABSTRACT
Physical Chemistry Chemical Physics, 2009
Spin triads of copper(ii) with two nitroxides are responsible for the magnetic anomalies in a new... more Spin triads of copper(ii) with two nitroxides are responsible for the magnetic anomalies in a new family of molecular-magnetic compounds called "breathing crystals". We have shown previously that electron paramagnetic resonance (EPR) spectroscopy allows one to investigate the peculiarities of these systems and obtain valuable information on exchange interactions governing the magnetic anomalies. One of the key processes revealed is the dynamic mixing between different spin multiplets that leads to a coalescence of individual EPR lines at high temperatures. The rates of the mixing were found to be fast at EPR frequencies between 9 and 94 GHz. In the present work, we expose the spin triads to higher microwave frequencies of up to 244 GHz in order to reach the conditions of intermediate or slow mixing rates. Three representatives of the family of breathing crystals have been studied. Based on the simulations of EPR data at 34, 122 and 244 GHz, the rates of the mixing processes have been estimated and conclusions on their character and temperature dependence have been drawn. The insights from high-field EPR clarify previously obtained results and aid in the further development of EPR approaches for studying these and similar systems. It is suggested that the static and dynamic Jahn-Teller effects may play an important role in the mechanisms governing the observed spin exchange effects.
Physical Chemistry Chemical Physics, 2009
Multifrequency continuous wave (cw) and echo-detected (ED) electron paramagnetic resonance (EPR) ... more Multifrequency continuous wave (cw) and echo-detected (ED) electron paramagnetic resonance (EPR) was employed to study the mobility of nitroxides confined in nanocapsules. The complexes p-hexanoyl calix[4]arene with 4-methoxy-2,2,6,6-tetramethylpiperidine-N-oxyl (MT) and N-(2-methylpropyl)-N-(1-diethylphosphono-2,2-dimethylpropyl)-aminoxyl (DEPN) were studied by X-, W-band and 360 GHz cw EPR at temperatures between 90 and 370 K. Thereby we were able to extract the canonical values of the hyperfine and g-tensors of the encapsulated radicals as well as information on restricted orientational dynamics of the caged spin probes. Comparing cw and ED-EPR data obtained on MT@C6OH we found that between 90 and 200 K the caged nitroxide undergoes isotropic small-angle fluctuations (librations), whereas at higher temperatures restricted rotations of the radical with correlation times of 0.75 Â 10 À10 s and 1.2 Â 10 À10 s dominate at 325 and 300 K, respectively. The activation energy of the rotational motion of encapsulated MT radicals was evaluated as E a = 1.0 kcal mol À1 , which is comparable to the magnitude of van der Waals interactions. Compared to MT, the reorientational motion of DEPN was found to be slower and more isotropic.
Molecular Physics, 2002
Chemically induced electron±nuclear polarization at low magnetic ®elds is considered theoreticall... more Chemically induced electron±nuclear polarization at low magnetic ®elds is considered theoretically for a radical with one magnetic nucleus. It is shown that large non-equilibrium populations of the radical spin levels are expected to exist under low magnetic ®elds. This large electron±nuclear polarization has been observed experimentally during the photolysis of two phosphine oxides using a modi®ed L-band TREPR setup. The TREPR spectra and kinetics of dimethoxyphosphonyl and diphenylphosphonyl radicals have been measured and analysed in low magnetic ®elds, and excellent agreement between experiment and theory has been achieved.
Journal of Magnetic Resonance, 2006
A sensitivity of recently developed method of amplitude-modulated continuous wave EPR (AM-CW-EPR)... more A sensitivity of recently developed method of amplitude-modulated continuous wave EPR (AM-CW-EPR) is studied depending on the parameters of the modulation field. The case of the significant saturation and high modulation frequency is addressed. It is found, that the rapid resonance passage effect is essential for AM-CW-EPR. However, its manifestation is different comparing to the conventional CW-EPR experiment. Both experimental data and numerical simulations support the enhancement of the AM-CW-EPR sensitivity under the rapid passage conditions for the modulating magnetic field, which is important for practical use of the method.
The journal of physical chemistry. B, Jan 4, 2015
Triarylmethyl radicals (trityls, TAMs) represent a relatively new class of spin labels. The long ... more Triarylmethyl radicals (trityls, TAMs) represent a relatively new class of spin labels. The long relaxation of trityls at room temperature in liquid solutions makes them a promising alternative for traditional nitroxides. In this work we have synthesized a series of TAMs including perdeuterated Finland trityl (D36 form), mono-, di-, and triester derivatives of Finland-D36 trityl, the deuterated form of OX63, the dodeca-n-butyl homologue of Finland trityl, and triamide derivatives of Finland trityl with primary and secondary amines attached. We have studied room-temperature relaxation properties of these TAMs in liquids using pulsed electron paramagnetic resonance (EPR) at two microwave frequency bands. We have found the clear dependence of phase memory time (Tm ∼ T2) on the magnetic field: room-temperature Tm values are ∼1.5-2.5 times smaller at the Q-band (34 GHz, 1.2 T) than at the X-band (9 GHz, 0.3 T). This trend is ascribed to the contribution from g-anisotropy that is negligib...
The journal of physical chemistry. B, Jan 4, 2015
Triarylmethyl (trityl, TAM) based spin labels represent a promising alternative to nitroxides for... more Triarylmethyl (trityl, TAM) based spin labels represent a promising alternative to nitroxides for EPR distance measurements in biomolecules. Herewith, we report synthesis and comparative study of series of model DNA duplexes, 5'-spin-labeled with TAMs and nitroxides. We have found that the accuracy (width) of distance distributions obtained by double electron-electron resonance (DEER/PELDOR) strongly depends on the type of radical. Replacement of both nitroxides by TAMs in the same spin-labeled duplex allows narrowing of the distance distributions by a factor of 3. Replacement of one nitroxide by TAM (orthogonal labeling) leads to a less pronounced narrowing but at the same time gains sensitivity in DEER experiment due to efficient pumping on the narrow EPR line of TAM. Distance distributions in nitroxide/nitroxide pairs are influenced by the structure of the linker: the use of a short amine-based linker improves the accuracy by a factor of 2. At the same time, a negligible depe...
Inorganic chemistry, Jan 11, 2015
Breathing crystals" based on copper(II) hexafluoroacetylacetonates and pyrazolyl-substituted nitr... more Breathing crystals" based on copper(II) hexafluoroacetylacetonates and pyrazolyl-substituted nitronyl nitroxides comprise the exchange-coupled clusters within the polymeric chains. Owing to an interplay of exchange interaction between copper(II) and nitroxide spins and Jahn−Teller nature of copper(II) complex, the breathing crystals demonstrate thermally and light-induced magnetostructural transitions in many aspects similar to the classical spin crossover. Herewith, we report the first application of variable temperature (VT) far/mid Fourier transform infrared (FTIR) spectroscopy and mid FTIR microscopy to breathing crystals. This VT-FTIR study was aimed toward clarification of the transitions mechanism previously debated on the basis of superconducting quantum interference device, X-ray diffraction, and electron paramagnetic resonance data. VT-FTIR showed the onset of new vibrational bands during phase transitions occurring at the expense of several existing ones, whose intensity was significantly reduced. The most pronounced spectral changes were assigned to corresponding vibrational modes using quantum chemical calculations. A clear-cut correlation was found between temperature-dependent effective magnetic moment of studied compounds and the observed VT-FTIR spectra. Importantly, VT-FTIR confirmed coexistence of two types of copper(II)−nitroxide clusters during gradual magnetostructural transition. Such clusters correspond to weakly coupled and strongly coupled spin states, whose relative contribution depends on temperature. The pronounced difference in the VT-FTIR spectra of two states in breathing crystals is a fingerprint of magnetostructural transition, and understanding of these characteristics achieved by us will be useful for future studies of breathing crystals as well as their diamagnetic analogues.
Inorganica Chimica Acta, 2008
Chain complex of copper(II) hexafluoroacetylacetonate with pyrazole-substituted nitronyl nitroxid... more Chain complex of copper(II) hexafluoroacetylacetonate with pyrazole-substituted nitronyl nitroxide containing exchange-coupled copper(II)–nitroxide clusters has been studied using electron paramagnetic resonance (EPR) spectroscopy. The structural rearrangements at low temperatures induce spin transitions in one half of the copper(II)–nitroxide clusters and effectively lead to reversible diamagnetic dilution. This results in significant changes of EPR spectra and allows us to obtain the value
Journal of The American Chemical Society, 2008
... K. Yu.; Fokin, SV; Tretyakov, EV; Romanenko, GV; Ikorskii, VN Russ. Chem. Bull. Int. Ed.2004,... more ... K. Yu.; Fokin, SV; Tretyakov, EV; Romanenko, GV; Ikorskii, VN Russ. Chem. Bull. Int. Ed.2004, 53, 2406−2427. ... Victor I. Ovcharenko, Galina V. Romanenko, Ksenia Yu. Maryunina, Artem S. Bogomyakov and Elena V. Gorelik. Inorganic Chemistry 2008 47 (20), 9537-9552. ...
Lecture Notes in Physics, 2006
An overview of the various multiple-photon processes in electron paramagnetic resonance (EPR) spe... more An overview of the various multiple-photon processes in electron paramagnetic resonance (EPR) spectroscopy is given. First, we describe different types of multiple-photon transitions that can be observed with monochromatic and bichromatic microwave fields in spin systems with unequally spaced energy levels and in two-level systems. Then we discuss multiple-photon processes that are based on a bichromatic radiation field consisting of
The Journal of Physical Chemistry A, 2007
The complexes of Cu2+ hexafluoroacetylacetonate with two pyrazol-substituted nitronyl nitroxides ... more The complexes of Cu2+ hexafluoroacetylacetonate with two pyrazol-substituted nitronyl nitroxides are the choice systems to study the spin dynamics of strongly exchange-coupled spin triads. The large values of exchange coupling (ca. 100 cm-1) and high-resolution electron paramagnetic resonance (EPR) at Q- and W-bands (35 and 94 GHz) allowed us to observe and interpret specific characteristics of these systems. An electron spin exchange process has been found between different multiplets of the spin triad, which manifests itself as a significant shift of the EPR line position with temperature. We propose that the spin exchange process is caused by the modulation of exchange interaction between copper and nitroxides by lattice vibrations. The estimations of the rate of exchange process and model calculations essentially support the observed phenomena. The studied characteristics of strongly coupled spin triads explain previously obtained results, agree with literature, and should be accounted for in future investigations of similar spin systems.
The Journal of Physical Chemistry A, 2006
The complex of Cu(2+) hexafluoroacetylacetonate with two pyrazol-substituted nitronyl nitroxides ... more The complex of Cu(2+) hexafluoroacetylacetonate with two pyrazol-substituted nitronyl nitroxides represents an unusual exchange-coupled three-spin system. The antiferromagnetic exchange coupling, which already atT < 150 K is larger than the thermal energy kT, induces the transition from a total spin state S = (3)/(2) to a state S = (1)/(2) and produces static spin polarization. Anomalous electron paramagnetic resonance (EPR) spectra of an S = (1)/(2) state were detected experimentally and described theoretically. The effective g factor of the three-spin system is smaller than 2, despite the fact that all the individual components have g > 2. The observed signals with g < 2 are highly informative and can be employed for determination of the sign and value of the exchange interaction in three-spin nitroxide-copper-nitroxide clusters.
The Journal of Physical Chemistry A, 2005
We report the first experimental study of chemically induced electron spin polarization (CIDEP) p... more We report the first experimental study of chemically induced electron spin polarization (CIDEP) processes in low magnetic fields for spin-correlated radical pairs (SCRPs) in micellar environments. Photoexcitation of (2,4,6-trimethylbenzoyl) diphenylphosphine oxide (TMBDPO) leads to the radical pair comprised of acyl radical 1 and phosphonyl radical 2. The spin polarization, which is very strong in free solution even at zero field, was detected using L-band time-resolved electron paramagnetic resonance (TREPR) spectroscopy with specially modified resonators. The mechanism of formation and decay of low field CIDEP in SCRPs is presented and discussed. The prominent difference between low and high field spectra in micelles is the absence of anti-phase structure for radical 2 with HFI a > B0. This feature is consistent with the proposed polarization mechanism and theoretical predictions.
Russian Chemical Bulletin, 2006
The review summarizes the results of studies on specific features of spin relaxation of radicals ... more The review summarizes the results of studies on specific features of spin relaxation of radicals in liquids in weak magnetic fields.
Russian Chemical Bulletin, 2010
The reaction of copper nitrate Cu(NO3)2·3H2O with potassium salt of 1,1-cyclohexanediacetic acid ... more The reaction of copper nitrate Cu(NO3)2·3H2O with potassium salt of 1,1-cyclohexanediacetic acid (H2CHDAA) in an EtOH-toluene mixture affords the polymeric complex {[(EtOH)2Cu2(CHDAA)2]·EtOH n (1). The addition of pyridine to the Cu(NO3)2·3H2O-K2CHDAA reaction system in an EtOH-MeCN mixture results in the isolation of the unusual octadecanuclear heterometallic cluster [K2(η1-H2O)6(η1-py)8Cu16-(η1-OH)2(μ4-CHDAA)16]·EtOH·MeCN·3H2O (2). In complex 2, the hexadecanuclear metal carboxylate dianion (η1-H2O)6(η1-py)8Cu16(η1-OH)2(μ4-CHDAA)16 acts as
Physical Chemistry Chemical Physics, 2003
ABSTRACT
Physical Chemistry Chemical Physics, 2009
Spin triads of copper(ii) with two nitroxides are responsible for the magnetic anomalies in a new... more Spin triads of copper(ii) with two nitroxides are responsible for the magnetic anomalies in a new family of molecular-magnetic compounds called "breathing crystals". We have shown previously that electron paramagnetic resonance (EPR) spectroscopy allows one to investigate the peculiarities of these systems and obtain valuable information on exchange interactions governing the magnetic anomalies. One of the key processes revealed is the dynamic mixing between different spin multiplets that leads to a coalescence of individual EPR lines at high temperatures. The rates of the mixing were found to be fast at EPR frequencies between 9 and 94 GHz. In the present work, we expose the spin triads to higher microwave frequencies of up to 244 GHz in order to reach the conditions of intermediate or slow mixing rates. Three representatives of the family of breathing crystals have been studied. Based on the simulations of EPR data at 34, 122 and 244 GHz, the rates of the mixing processes have been estimated and conclusions on their character and temperature dependence have been drawn. The insights from high-field EPR clarify previously obtained results and aid in the further development of EPR approaches for studying these and similar systems. It is suggested that the static and dynamic Jahn-Teller effects may play an important role in the mechanisms governing the observed spin exchange effects.
Physical Chemistry Chemical Physics, 2009
Multifrequency continuous wave (cw) and echo-detected (ED) electron paramagnetic resonance (EPR) ... more Multifrequency continuous wave (cw) and echo-detected (ED) electron paramagnetic resonance (EPR) was employed to study the mobility of nitroxides confined in nanocapsules. The complexes p-hexanoyl calix[4]arene with 4-methoxy-2,2,6,6-tetramethylpiperidine-N-oxyl (MT) and N-(2-methylpropyl)-N-(1-diethylphosphono-2,2-dimethylpropyl)-aminoxyl (DEPN) were studied by X-, W-band and 360 GHz cw EPR at temperatures between 90 and 370 K. Thereby we were able to extract the canonical values of the hyperfine and g-tensors of the encapsulated radicals as well as information on restricted orientational dynamics of the caged spin probes. Comparing cw and ED-EPR data obtained on MT@C6OH we found that between 90 and 200 K the caged nitroxide undergoes isotropic small-angle fluctuations (librations), whereas at higher temperatures restricted rotations of the radical with correlation times of 0.75 Â 10 À10 s and 1.2 Â 10 À10 s dominate at 325 and 300 K, respectively. The activation energy of the rotational motion of encapsulated MT radicals was evaluated as E a = 1.0 kcal mol À1 , which is comparable to the magnitude of van der Waals interactions. Compared to MT, the reorientational motion of DEPN was found to be slower and more isotropic.
Molecular Physics, 2002
Chemically induced electron±nuclear polarization at low magnetic ®elds is considered theoreticall... more Chemically induced electron±nuclear polarization at low magnetic ®elds is considered theoretically for a radical with one magnetic nucleus. It is shown that large non-equilibrium populations of the radical spin levels are expected to exist under low magnetic ®elds. This large electron±nuclear polarization has been observed experimentally during the photolysis of two phosphine oxides using a modi®ed L-band TREPR setup. The TREPR spectra and kinetics of dimethoxyphosphonyl and diphenylphosphonyl radicals have been measured and analysed in low magnetic ®elds, and excellent agreement between experiment and theory has been achieved.
Journal of Magnetic Resonance, 2006
A sensitivity of recently developed method of amplitude-modulated continuous wave EPR (AM-CW-EPR)... more A sensitivity of recently developed method of amplitude-modulated continuous wave EPR (AM-CW-EPR) is studied depending on the parameters of the modulation field. The case of the significant saturation and high modulation frequency is addressed. It is found, that the rapid resonance passage effect is essential for AM-CW-EPR. However, its manifestation is different comparing to the conventional CW-EPR experiment. Both experimental data and numerical simulations support the enhancement of the AM-CW-EPR sensitivity under the rapid passage conditions for the modulating magnetic field, which is important for practical use of the method.