Chemically induced dynamic nuclear polarization III (anomalous multiplets of radical coupling and disproportionation products)

Kaptein, Robert; Oosterhoff, L.J.

doi:10.1016/0009-2614(69)80105-3

Cited by 190 publications

(45 citation statements)

References 4 publications

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“…Similar spectra were observed 48,74,79,87,[91][92][93] and analyzed earlier. 92,93 The spectrum is polarized in net absorption due to the triplet mechanism 45,[94][95][96][97][98] and shows a doublet of singlets due to the diphenylphosphinoyl radical 1a. The observed phosphorus hyperfine coupling constant of a(P R ) ) 36.2 ( 0.1 mT agrees with literature values.…”

Section: S(τ)mentioning

confidence: 99%

A Novel Approach for Measuring Absolute Rate Constants by Pulsed Electron Spin Resonance: Addition of Phosphinoyl and 2-Hydroxy-2-propyl Radicals to Several Alkenes^,

Weber

Turro

2003

J. Phys. Chem. A

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A time-resolved Fourier transform electron spin resonance (TR FT ESR) method for determining absolute rate constants of reactive, free radical reactions is described. The phase memory times T M of a family of reacting radicals were measured precisely by electron spin-echo (ESE) detection. In all cases the ESE signal decays show a simple pseudo-first-order behavior. Rate constants of the reactions were extracted from the linear relationship between the reciprocal of the T M values and the alkene concentrations. The validity of the method is demonstrated for the measurement of the rate constant for addition of different phosphinoyl and 2-hydroxy-2-propyl radicals to several acrylates, methyl methacrylate, and vinyl pivalate in organic solvents at room temperature. The results are in excellent agreement with those obtained by other kinetic investigations employing time-resolved steady-state electron spin resonance (TR CW ESR) and optical absorption spectroscopy. The technique is shown to be applicable to systems with rate constants between 10 4 and 10 8 M -1 s -1 , a range covered by the alkenes examined.

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Section: S(τ)mentioning

confidence: 99%

A Novel Approach for Measuring Absolute Rate Constants by Pulsed Electron Spin Resonance: Addition of Phosphinoyl and 2-Hydroxy-2-propyl Radicals to Several Alkenes^,

Weber

Turro

2003

J. Phys. Chem. A

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“…The relative yields of pR and ground state P depend strongly on the electron spin dynamics of the radical pair state (31)(32)(33), pF which in turn is influenced by any applied magnetic field EXPERIMENTAL Reaction centers were purified from Rhodopseudomonas sphaeroides R-26 chromatophores by the method of Stein and Wraight (unpublished) by extraction with 0.45% lauryldimethylamine oxide (LDAO) in 0.1 M NaCl, fractionation in solution with 30% and 50% saturated (NH4)2SO4, and DEAE-cellulose column chromatography. Quinone-free samples were prepared according to Okamura et al (27); all solutions used in the extraction were kept anaerobic.…”

mentioning

confidence: 99%

Magnetic resonance spectroscopy of the primary state, P ^F , of bacterial photosynthesis

Bowman

Budil

Closs

et al. 1981

Proc. Natl. Acad. Sci. U.S.A.

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We have obtained the magnetic resonance spectrum of the radical pair state pF by using reaction yield detected magnetic resonance spectroscopy. The magnetic resonance spectrum is quite sensitive to the local environment of pF. The data place limits on the lifetime of triplet pF and the distance of charge separation.(24). Optical measurements of the pR yield upon recombination show large magnetic field effects and have become one method of studying the radical pair state. In addition, we have found by optical measurements that the pR yield also is influenced by resonant microwaves applied to the radical pair. This is a convenient method to record the EPR spectrum of pF. Most of the transient states involved in the primary events of photosynthesis are paramagnetic, making magnetic resonance and magnetic field effects two convenient methods of studying the photosynthetic apparatus. Magnetic resonance spectros-'copy has been used extensively to help identify the radical intermediates and products of photosynthesis. In addition, the magnetic resonance spectrum and its electron spin polarization and the magnetic field dependence ofvarious reaction products have yielded some information about electron-electron dipolar interactions between radicals and about the exchange interactions that are so important for electron transfer. As attempts are made to see increasingly earlier intermediates, experimental difficulties arise due to the steadily decreasing lifetimes ofthese states. For example, in bacterial photosynthetic reaction centers, one of the earliest states is a radical pair consisting of the cation of the primary donor, P+, and the anion of a bacteriopheophytin intermediate acceptor, I-(1, 2). From the EPR spectrum of this radical pair, both the electron exchange interaction, J, and the electron-electron dipolar interaction (and hence distance of separation) can in principle be determined. However, the short lifetime of this radical pair state, pF (3) (which even in blocked reaction centers is only 10 nsec) has prevented its direct observation by conventional EPR techniques, and interactions within pF have been studied only indirectly by optical spectroscopy (3-10) or through magnetic field effects (11-16). We report here the observation ofthe magnetic resonance spectrum of this radical pair state pF at physiological temperatures by using reaction yield detected magnetic resonance (RYDMAR) spectroscopy (17-21).This radical pair state forms within about 5 psec (3, 4, 10) and decays within 200 psec or about 10 nsec (7, 8), depending on whether or not further electron transfer is blocked.When the transfer of an electron from I-to the iron-ubiquinone acceptor (22, 23), Fe-Q, is prevented by removal or chemical reduction of the quinone, charge recombination of a triplet radical pair produces the lowest excited triplet state of p, pR (7,8,(24)(25)(26)(27)(28)(29)(30), while recombination ofa singlet radical pair produces both P and I in their singlet ground states (15, 24). The relative yields of pR and ground ...

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“…Radical pair mechanism (RPM) CIDEP is produced by the singlet (S)-triplet (T) spin state evolution of this transient species (see Fig. 1, inset) [12,13,28,31,39]. RPM spin polarization can be due to mixing of the S and T O RP states (ST 0 RPM) or, in the case that the exchange interaction J between the unpaired electrons is less than 0, S and T 1 states (ST_ 1 RPM).…”

Section: Radical Pair Mechanismmentioning

confidence: 99%

“…The magnitude of the polarization Pi depends on the radical pair lifetime so that it is expected to increase with increasing solvent viscosity. In media in which radical pair dissociation is inhibited, i.e., high-viscosity solvents, or in systems for which the ST 0 mixing terms are large, ST 0 RPM spin polarization can be generated as well without the separation-reencounter scenario [39]. The cont¡ of this direct process is represented by the last term in Eq.…”

Section: Radical Pair Mechanismmentioning

confidence: 99%

A closer look at photochemical reactions of transition-metal compounds by time-resolved EPR

et al. 2004

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Abstraet.A review is given of applications of time-resolved electron paramagnetic resonance (TREPR) in the field of photochemistry of transition-metal compounds. The two main TREPR techniques used in these studies are described. A brief overview is given of chemically induced dynamic electron polarization mechanisms that can affect TREPR spectra and that can gire insights into the mechanism of photochemical reactions. Following these background sections, experimental results are presented. The discussion focuses in particular on the Fourier-transform EPR studies of photoinduced metal-alkyl bond homolysis reactions of a series of transition-metal (Co, Ru, Re, Pt) complexes carried out by the authors.

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Chemically induced dynamic nuclear polarization III (anomalous multiplets of radical coupling and disproportionation products)

Cited by 190 publications

References 4 publications

A Novel Approach for Measuring Absolute Rate Constants by Pulsed Electron Spin Resonance: Addition of Phosphinoyl and 2-Hydroxy-2-propyl Radicals to Several Alkenes^,

A Novel Approach for Measuring Absolute Rate Constants by Pulsed Electron Spin Resonance: Addition of Phosphinoyl and 2-Hydroxy-2-propyl Radicals to Several Alkenes^,

Magnetic resonance spectroscopy of the primary state, P ^F , of bacterial photosynthesis

A closer look at photochemical reactions of transition-metal compounds by time-resolved EPR

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Chemically induced dynamic nuclear polarization III (anomalous multiplets of radical coupling and disproportionation products)

Cited by 190 publications

References 4 publications

A Novel Approach for Measuring Absolute Rate Constants by Pulsed Electron Spin Resonance: Addition of Phosphinoyl and 2-Hydroxy-2-propyl Radicals to Several Alkenes,

A Novel Approach for Measuring Absolute Rate Constants by Pulsed Electron Spin Resonance: Addition of Phosphinoyl and 2-Hydroxy-2-propyl Radicals to Several Alkenes,

Magnetic resonance spectroscopy of the primary state, P F , of bacterial photosynthesis

A closer look at photochemical reactions of transition-metal compounds by time-resolved EPR

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A Novel Approach for Measuring Absolute Rate Constants by Pulsed Electron Spin Resonance: Addition of Phosphinoyl and 2-Hydroxy-2-propyl Radicals to Several Alkenes^,

A Novel Approach for Measuring Absolute Rate Constants by Pulsed Electron Spin Resonance: Addition of Phosphinoyl and 2-Hydroxy-2-propyl Radicals to Several Alkenes^,

Magnetic resonance spectroscopy of the primary state, P ^F , of bacterial photosynthesis