Kiminori Maeda | Saitama University , Japan (original) (raw)
Papers by Kiminori Maeda
Chemical communications (Cambridge, England), Jan 13, 2015
We show that the effects of applied magnetic fields on radical pair reactions can be sensitively ... more We show that the effects of applied magnetic fields on radical pair reactions can be sensitively measured from sample volumes as low as ∼100 femtolitres using total internal reflection fluorescence microscopy. Development of a fluorescence-based microscope method is likely to be a key step in further miniaturisation that will allow detection of magnetic field effects on single molecules.
International Journal of Molecular Sciences
Radical pair kinetics is determined by the coherent and incoherent spin dynamics of spin pair and... more Radical pair kinetics is determined by the coherent and incoherent spin dynamics of spin pair and spin-selective chemical reactions. In a previous paper, reaction control and nuclear spin state selection by designed radiofrequency (RF) magnetic resonance was proposed. Here, we present two novel types of reaction control calculated by the local optimization method. One is anisotropic reaction control and the other is coherent path control. In both cases, the weighting parameters for the target states play an important role in the optimizing of the RF field. In the anisotropic control of radical pairs, the weighting parameters play an important role in the selection of the sub-ensemble. In coherent control, one can set the parameters for the intermediate states, and it is possible to specify the path to reach a final state by adjusting the weighting parameters. The global optimization of the weighting parameters for coherent control has been studied. These manifest calculations show t...
The time resolved feature of the MARY (Magnetic field effect on Reaction Yield) spectra is studie... more The time resolved feature of the MARY (Magnetic field effect on Reaction Yield) spectra is studied in the system of Diphenyl(2,4,6-trimethyl-benzoyl)phosphineoxide (TMDPO) in micelle. Two kinds of magnetic field effects (MFE) can be distinguished in the different time scales. First one is generated in the time scale less than 50 ns and negative (decrease the transient absorption in comparison with that at zero magnetic field) at less than 100mT and positive at larger than 100mT. Second one has only positive effect and more apparent at larger than 100mT. The rapid component is rationalized as the hyperfine induced mechanisms, and slow rise component is assigned to the relaxation mechanisms. By the theoretical model calculation, it is indicated that the primary diffusion process of the radical pair plays an important role on the MARY time profile especially in the system with large hyperfine coupling constant like the system of TMDPO.
Chemical Physics Letters, 2021
Abstract Low Magnetic field effects on a photoinduced electron transfer reaction between benzophe... more Abstract Low Magnetic field effects on a photoinduced electron transfer reaction between benzophenone and 1,4-diazabicyclo [2.2.2] octane (DABCO) in an ionic liquid of N,N,N-trimethyl-N-propylammonium bis(trifluoromethanesulfonyl) were studied with nanosecond transient absorption measurements. At a magnetic field (∼2 mT) comparable with the hyperfine coupling in DABCO cation, so-called low field effects (LFEs), whose effect is opposite to the magnetic field effects caused by the hyperfine coupling mechanism, were observed on the yield of the benzophenone anion radical. The magnitude of the LFE is linearly increased with the increase of the lifetime of the radical ion pair. The present study provides basic data to clarify the mechanism of LFEs in biological systems.
The Journal of Chemical Physics, 2020
Recently, AWG (arbitrary waveform generator) based pulse electron paramagnetic resonance and nucl... more Recently, AWG (arbitrary waveform generator) based pulse electron paramagnetic resonance and nuclear magnetic resonance have been developed in a high field regime for the improvement of sensitivity and selectivity and quantum information processing. Here, we propose the application of AWG based reaction control of radical pairs in a rather low magnetic field regime. We calculated the locally optimized radio frequency (RF) field with the control theory by Sugawara [J. Chem. Phys. 118(15), 6784–6800 (2003)]. The calculation results manifest the applicability of AWG-RF fields to reaction control (reaction yield detected magnetic resonance), stimulated nuclear polarization, magnetic isotope selection, and coherent control of the spin dynamics.
Molecular Physics, 2019
The dynamics of the radical pairs generated from the electron transfer reaction from indole deriv... more The dynamics of the radical pairs generated from the electron transfer reaction from indole derivatives to flavin derivatives are studied by three techniques, time resolved magnetic field effect (TR-MARY) and pulse absorption detected magnetic resonance (ADMR), and absorption detected switching of external magnetic field techniques (AD-SEMF). The three techniques complementarily work for the precise analysis of the radical pair kinetics. The results by all three techniques reflect the difference of the hydrophobic nature of the radicals in the lifetime of RP in a micelle. Overcoming the difficulty of the determination of the short RP lifetime under the nearly quasi steady state due to slow and inhomogeneous decay kinetics of the precursor triplet excited state, AD-SEMF analysis enabled us to determine the kinetic parameters, which is consistent with the qualitatively observed by the other techniques.
The Journal of Physical Chemistry B, 2018
For realization of low-cost organic photon energy conversion, the supramolecular approach has bee... more For realization of low-cost organic photon energy conversion, the supramolecular approach has been a focus of attention as a counter approach to precise synthesis of covalentlylinked donor (D) − acceptor (A) molecules. Here we report photogeneration of a long-lived (~ 3
The Journal of Physical Chemistry, 1993
ABSTRACT
Res Chem Intermediates, 2003
The Journal of Physical Chemistry, 1993
CIDNP and CIDNP-detected ESR spectra are observed in the photolysis of benzoquinone and its methy... more CIDNP and CIDNP-detected ESR spectra are observed in the photolysis of benzoquinone and its methyl derivatives. In low concentrations of solutions, the sign of the CIDNP of the ring and methyl protons of benzoquinones is in accord with the prediction from the Kaptein rule; however, at high concentrations, the sign is reversed. From the sign of the dynamic nuclear polarization that is observed as a component of the CIDNPdetected ESR spectrum, the mechanism of the cross-relaxation in free radicals is determined. From the correlation between the sign of the dynamic nuclear polarization and the sign of the CIDNP, the anomalous sign of the CIDNP observed at high concentrations is ascribed to generation of an electron spin polarization by the anisotropy in the intersystem crossing (triplet mechanism) and subsequent transfer of this polarization to the nuclei by the cross-relaxation in free radicals. Thus, the triplet mechanism of CIDNP is well substantiated.
The Journal of Physical Chemistry, 1993
Photoinduced electron transfer from the zinc tetraphenylporphyrin moiety to the viologen unit in ... more Photoinduced electron transfer from the zinc tetraphenylporphyrin moiety to the viologen unit in linked compounds in reversed micelles generated radical pairs, which afforded chemically induced dynamic electron polarization (CIDEP) spectra at room temperature. The CIDEP spectra varied with the number of methylene groups (n) in the alkyl spacer of the linked compounds. In the case of longer spacers (n =
The Journal of Physical Chemistry, 1993
The magnetic field dependence of the low-field chemically induced dynamic nuclear polarization (C... more The magnetic field dependence of the low-field chemically induced dynamic nuclear polarization (CIDNP) on the photocleavage of cyclodecanone and cyclododecanone was measured at various temperatures. The magnetic field effect at which CIDNP intensity is maximum is shifted to larger magnetic field as temperature increases. This is interpreted as due to the increase of the effective exchange integral of the intermediate biradicals at higher temperatures. The observed magnetic field dependence is simulated with a theoretical model based on the stochastic Liouville equation. The observed temperature dependence of the effective exchange integral is interpreted as due to the shrinking of the effective alkyl chain at higher temperature.
Physical Chemistry Chemical Physics, 2015
Prompt fluorescence measurements on flavin-based photoreactions are shown to provide a step-chang... more Prompt fluorescence measurements on flavin-based photoreactions are shown to provide a step-change in sensitivity for the detection of magnetic field effects in these biologically relevant systems.
Physical Chemistry Chemical Physics, 2009
Zeitschrift für Physikalische Chemie, 1992
ABSTRACT
Chemical Physics Letters, 2011
Chemical Physics Letters, 2011
Spin-selective reactions of radical pairs have traditionally been modelled theoretically by addin... more Spin-selective reactions of radical pairs have traditionally been modelled theoretically by adding phenomenological rate equations to the quantum mechanical equation of motion of the radical pair spin density matrix. More recently an alternative set of rate expressions, based on a quantum measurement approach, has been suggested. Here we show how these two reaction operators can be seen as limiting cases of a more general reaction scheme.
Chemical Physics Letters, 1997
ABSTRACT
Chemical Physics, 1998
ABSTRACT
Chemical communications (Cambridge, England), Jan 13, 2015
We show that the effects of applied magnetic fields on radical pair reactions can be sensitively ... more We show that the effects of applied magnetic fields on radical pair reactions can be sensitively measured from sample volumes as low as ∼100 femtolitres using total internal reflection fluorescence microscopy. Development of a fluorescence-based microscope method is likely to be a key step in further miniaturisation that will allow detection of magnetic field effects on single molecules.
International Journal of Molecular Sciences
Radical pair kinetics is determined by the coherent and incoherent spin dynamics of spin pair and... more Radical pair kinetics is determined by the coherent and incoherent spin dynamics of spin pair and spin-selective chemical reactions. In a previous paper, reaction control and nuclear spin state selection by designed radiofrequency (RF) magnetic resonance was proposed. Here, we present two novel types of reaction control calculated by the local optimization method. One is anisotropic reaction control and the other is coherent path control. In both cases, the weighting parameters for the target states play an important role in the optimizing of the RF field. In the anisotropic control of radical pairs, the weighting parameters play an important role in the selection of the sub-ensemble. In coherent control, one can set the parameters for the intermediate states, and it is possible to specify the path to reach a final state by adjusting the weighting parameters. The global optimization of the weighting parameters for coherent control has been studied. These manifest calculations show t...
The time resolved feature of the MARY (Magnetic field effect on Reaction Yield) spectra is studie... more The time resolved feature of the MARY (Magnetic field effect on Reaction Yield) spectra is studied in the system of Diphenyl(2,4,6-trimethyl-benzoyl)phosphineoxide (TMDPO) in micelle. Two kinds of magnetic field effects (MFE) can be distinguished in the different time scales. First one is generated in the time scale less than 50 ns and negative (decrease the transient absorption in comparison with that at zero magnetic field) at less than 100mT and positive at larger than 100mT. Second one has only positive effect and more apparent at larger than 100mT. The rapid component is rationalized as the hyperfine induced mechanisms, and slow rise component is assigned to the relaxation mechanisms. By the theoretical model calculation, it is indicated that the primary diffusion process of the radical pair plays an important role on the MARY time profile especially in the system with large hyperfine coupling constant like the system of TMDPO.
Chemical Physics Letters, 2021
Abstract Low Magnetic field effects on a photoinduced electron transfer reaction between benzophe... more Abstract Low Magnetic field effects on a photoinduced electron transfer reaction between benzophenone and 1,4-diazabicyclo [2.2.2] octane (DABCO) in an ionic liquid of N,N,N-trimethyl-N-propylammonium bis(trifluoromethanesulfonyl) were studied with nanosecond transient absorption measurements. At a magnetic field (∼2 mT) comparable with the hyperfine coupling in DABCO cation, so-called low field effects (LFEs), whose effect is opposite to the magnetic field effects caused by the hyperfine coupling mechanism, were observed on the yield of the benzophenone anion radical. The magnitude of the LFE is linearly increased with the increase of the lifetime of the radical ion pair. The present study provides basic data to clarify the mechanism of LFEs in biological systems.
The Journal of Chemical Physics, 2020
Recently, AWG (arbitrary waveform generator) based pulse electron paramagnetic resonance and nucl... more Recently, AWG (arbitrary waveform generator) based pulse electron paramagnetic resonance and nuclear magnetic resonance have been developed in a high field regime for the improvement of sensitivity and selectivity and quantum information processing. Here, we propose the application of AWG based reaction control of radical pairs in a rather low magnetic field regime. We calculated the locally optimized radio frequency (RF) field with the control theory by Sugawara [J. Chem. Phys. 118(15), 6784–6800 (2003)]. The calculation results manifest the applicability of AWG-RF fields to reaction control (reaction yield detected magnetic resonance), stimulated nuclear polarization, magnetic isotope selection, and coherent control of the spin dynamics.
Molecular Physics, 2019
The dynamics of the radical pairs generated from the electron transfer reaction from indole deriv... more The dynamics of the radical pairs generated from the electron transfer reaction from indole derivatives to flavin derivatives are studied by three techniques, time resolved magnetic field effect (TR-MARY) and pulse absorption detected magnetic resonance (ADMR), and absorption detected switching of external magnetic field techniques (AD-SEMF). The three techniques complementarily work for the precise analysis of the radical pair kinetics. The results by all three techniques reflect the difference of the hydrophobic nature of the radicals in the lifetime of RP in a micelle. Overcoming the difficulty of the determination of the short RP lifetime under the nearly quasi steady state due to slow and inhomogeneous decay kinetics of the precursor triplet excited state, AD-SEMF analysis enabled us to determine the kinetic parameters, which is consistent with the qualitatively observed by the other techniques.
The Journal of Physical Chemistry B, 2018
For realization of low-cost organic photon energy conversion, the supramolecular approach has bee... more For realization of low-cost organic photon energy conversion, the supramolecular approach has been a focus of attention as a counter approach to precise synthesis of covalentlylinked donor (D) − acceptor (A) molecules. Here we report photogeneration of a long-lived (~ 3
The Journal of Physical Chemistry, 1993
ABSTRACT
Res Chem Intermediates, 2003
The Journal of Physical Chemistry, 1993
CIDNP and CIDNP-detected ESR spectra are observed in the photolysis of benzoquinone and its methy... more CIDNP and CIDNP-detected ESR spectra are observed in the photolysis of benzoquinone and its methyl derivatives. In low concentrations of solutions, the sign of the CIDNP of the ring and methyl protons of benzoquinones is in accord with the prediction from the Kaptein rule; however, at high concentrations, the sign is reversed. From the sign of the dynamic nuclear polarization that is observed as a component of the CIDNPdetected ESR spectrum, the mechanism of the cross-relaxation in free radicals is determined. From the correlation between the sign of the dynamic nuclear polarization and the sign of the CIDNP, the anomalous sign of the CIDNP observed at high concentrations is ascribed to generation of an electron spin polarization by the anisotropy in the intersystem crossing (triplet mechanism) and subsequent transfer of this polarization to the nuclei by the cross-relaxation in free radicals. Thus, the triplet mechanism of CIDNP is well substantiated.
The Journal of Physical Chemistry, 1993
Photoinduced electron transfer from the zinc tetraphenylporphyrin moiety to the viologen unit in ... more Photoinduced electron transfer from the zinc tetraphenylporphyrin moiety to the viologen unit in linked compounds in reversed micelles generated radical pairs, which afforded chemically induced dynamic electron polarization (CIDEP) spectra at room temperature. The CIDEP spectra varied with the number of methylene groups (n) in the alkyl spacer of the linked compounds. In the case of longer spacers (n =
The Journal of Physical Chemistry, 1993
The magnetic field dependence of the low-field chemically induced dynamic nuclear polarization (C... more The magnetic field dependence of the low-field chemically induced dynamic nuclear polarization (CIDNP) on the photocleavage of cyclodecanone and cyclododecanone was measured at various temperatures. The magnetic field effect at which CIDNP intensity is maximum is shifted to larger magnetic field as temperature increases. This is interpreted as due to the increase of the effective exchange integral of the intermediate biradicals at higher temperatures. The observed magnetic field dependence is simulated with a theoretical model based on the stochastic Liouville equation. The observed temperature dependence of the effective exchange integral is interpreted as due to the shrinking of the effective alkyl chain at higher temperature.
Physical Chemistry Chemical Physics, 2015
Prompt fluorescence measurements on flavin-based photoreactions are shown to provide a step-chang... more Prompt fluorescence measurements on flavin-based photoreactions are shown to provide a step-change in sensitivity for the detection of magnetic field effects in these biologically relevant systems.
Physical Chemistry Chemical Physics, 2009
Zeitschrift für Physikalische Chemie, 1992
ABSTRACT
Chemical Physics Letters, 2011
Chemical Physics Letters, 2011
Spin-selective reactions of radical pairs have traditionally been modelled theoretically by addin... more Spin-selective reactions of radical pairs have traditionally been modelled theoretically by adding phenomenological rate equations to the quantum mechanical equation of motion of the radical pair spin density matrix. More recently an alternative set of rate expressions, based on a quantum measurement approach, has been suggested. Here we show how these two reaction operators can be seen as limiting cases of a more general reaction scheme.
Chemical Physics Letters, 1997
ABSTRACT
Chemical Physics, 1998
ABSTRACT