Micellized Radical Pairs Research Articles

Time-Resolved Detection of Magnetic Field Effects on Radical Pairs in Micelles: Two-Step Two-Laser Fluorescence Spectroscopy of Transient Radicals

A two-step two-laser fluorescence spectroscopy method was employed to enable time-resolved detection of magnetic field effects (MFEs) on radical pairs (RPs). In the photoinduced hydrogen abstraction reaction of benzophenone (BP) in sodium dodecyl sulfate (SDS) micellar solution, fluorescence from the BP ketyl radical (BPH•) was observed under various magnetic fields; BPH• forms RPs with hydrogen-abstracted SDS radicals (•SDS) in the micelles. Kinetic parameters of the RP dynamics such as the spin relaxation rate, the generation rate, and the escape rate were determined from the simple analysis. The MFEs on BPH• observed from the fluorescence measurements were explained by the spin relaxation mechanism proposed by Hayashi and Nagakura. In this study, we demonstrate that two-step two-laser fluorescence spectroscopy in combination with a magnetic field provides valuable information about photochemical reactions in which RPs play important roles.

Influence of nitroxides on CIDNP of micellised radical pairs and short-lived biradicals

The effects of stable nitroxide radicals on stimulated nuclear polarization (SNP) and chemically induced dynamic nuclear polarization (CIDNP) in short-lived consecutive biradicals and radical pairs in homogeneous solutions as well as spin-correlated radical pairs in micelles were studied in high and low magnetic fields. It is shown that experimentally observed effects of nitroxide additions on CIDNP and SNP can be well simulated taking into account only the increase in the rates of relaxation in the paramagnetic species constituting radical pairs or biradicals. Effects of coherent spin evolution in three-spin systems under study seem to be of negligible importance.

CIDEP of Micellized Radical Pairs in Low Magnetic Fields

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.

Investigation of Radical Pairs in Micelles Using Spin Polarization Techniques

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Interplay of Molecular and Spin Dynamics in Formation and Decay Kinetics of Linked and Micellized Radical Pairs: Effects of Organizing Factors and Magnetic Field

ChemInformVolume 33, Issue 42 p. 290-290 Reviews Interplay of Molecular and Spin Dynamics in Formation and Decay Kinetics of Linked and Micellized Radical Pairs: Effects of Organizing Factors and Magnetic Field Peter P. Levin, Peter P. Levin Inst. Biochem. Physiol. Microorg., Russ. Acad. Sci., Pushchino, Moscow 142292, RussiaSearch for more papers by this authorVladimir Ya. Shafirovich, Vladimir Ya. Shafirovich Inst. Biochem. Physiol. Microorg., Russ. Acad. Sci., Pushchino, Moscow 142292, RussiaSearch for more papers by this author Peter P. Levin, Peter P. Levin Inst. Biochem. Physiol. Microorg., Russ. Acad. Sci., Pushchino, Moscow 142292, RussiaSearch for more papers by this authorVladimir Ya. Shafirovich, Vladimir Ya. Shafirovich Inst. Biochem. Physiol. Microorg., Russ. Acad. Sci., Pushchino, Moscow 142292, RussiaSearch for more papers by this author First published: 19 May 2010 https://doi.org/10.1002/chin.200242290AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article. Volume33, Issue42October 22, 2002Pages 290-290 RelatedInformation

A Manifestation of two-quantum transitions in the ODEPR spectra of the spin-correlated radical pairs in micelles

Optically detected electron paramagnetic resonance spectra of the spin-correlated radical pairs diffusing inside a spherical region are numerically simulated taking into account an exchange interaction between partners of the pairs. It is shown that these spectra contain the lines induced by the two-quantum transitions. The shape and the width of this two-quantum transition line are analyzed as depending on magnetic resonance parameters, on molecular kinetic parameters and chemical reactivity of radicals.

Microwave-Induced Quantum Beats in Micellized Radical Pairs under Spin-Locking Conditions

The effect of short microwave pulse irradiation on the spin correlated radical pairs generated by the hydrogen abstraction reaction of triplet excited xanthone with tert-butyl-substituted phenols in a micellar sodium dodecyl sulfate solution is investigated by a time-resolved transient optical absorption technique. An increase in the microwave pulse duration under the electron spin resonant conditions leads to the alternation of the radical pair concentration. It is explained by the periodical change of the radical pair spin state population with an angular frequency of ω1 = γeB1 due to the pumping with resonant microwave field B1. The double frequency (2ω1) quantum beats are observed under spin-locking conditions. The behavior of quantum beats in this case is rationalized by the effect of microwave pulse on the electron spins of both radicals in the radical pair and reflects the spin dynamics in the triplet manifold of radical pairs that is isolated from that of the singlet during the microwave pulse by ...

Temperature and Salt Addition Effect on the Micellized Radical Pairs Recombination Studied by Stimulated Nuclear Polarization

It was found that the shape of the 13C stimulated nuclear polarization (SNP) spectra, detected in the photolysis of dibenzyl ketone (DBK) and α-methyldeoxybenzoine (MDB), exhibits a noticeable temperature dependence. For the relatively large sodium dodecylsulfate (SDS) micelles, the temperature increase leads to the increase in the line width of SNP spectra, while in the smaller sodium octylsulfate (SOS) micelles the splitting in the SNP spectra decreases. From the comparison of the experimental data with the model calculations based on the numerical solution of the Liouville equation, the influence of the temperature and salt additions on the collision rate of radicals in micelle interior was evaluated. The obtained activation energy of the translational diffusion of small radicals is Ea = 6.7 ± 0.25 kcal/mol and Ea = 5.6 ± 0.2 kcal/mol for SDS and SOS micelles, respectively. Additionally, the influence of temperature and salt additions on the lifetime of the micellized radical pairs (RPs) formed in the ...

Theoretical and experimental studies of chemically induced dynamic nuclear polarization kinetics in recombination of radical pairs by the method of switched external magnetic field. II. C13 CIDNP of micellized radical pairs

The method of C13 chemically induced dynamic nuclear polarization in a switched external magnetic field (SEMF CIDNP) has been applied for the first time in an experimental investigation of micellized radical pairs (RP). Using the examples of three photochemical reactions it has been shown, that SEMF CIDNP allows the investigation of the kinetics of short-lived micellized RPs with high time-resolution in low and intermediate magnetic fields. The experimental kinetics have been analyzed and simulated on the basis of a previously developed theory [Parnachev et al., J. Chem. Phys. 107, 9942 (1997)]. It has been demonstrated that such an analysis provides information on the rates of radical escape from the micelle, on electron relaxation and on the rate of S–T− transitions. The analysis of the estimated rates of S–T− transitions showed that the exchange interaction is essentially anisotropic in the RPs studied.

Magnetic Field Effects on the Dynamics of Radical Pairs in Micelles: A New Approach to Understanding the “Cage Effect”

ABSTRACTThe effect of temperature on the photolysis of dibenzyl ketone and 4‐methyldibenzyl ketone in sodium dodecyl sulfate micelles was studied by laser flash photolysis and product distributions derived from steady‐state photolysis. At high temperatures, the product distribution and radical decay kinetics are primarily due to random encounters of radicals, and the “cage effect” cannot be rationalized by geminate recombination reactions that occur before the radicals escape from the micelles. A mechanism is proposed in which the enhancement of the crosstermination product derived from random encounters is due to the different partitioning of each radical species between the micelles and the aqueous phase, thereby leading to different rates for the self‐termination reactions.

Magnetic Field Effects on the Dynamics of Radical Pairs in Micelles: A New Approach to Understanding the “Cage Effect”

Magnetic Field Effects on the Dynamics of Radical Pairs in Micelles: A New Approach to Understanding the “Cage Effect”

Spin-correlated radical pairs in micellar systems: mechanism of CIDEP and the micelle size dependence

Abstract A new model of time-resolved EPR in micellized radical pairs is introduced. The model is based on numerical integration of the master Liouville equation for spin-correlated (micellized) pairs and free (escaped) radicals. The diffusion of radicals is considered in terms of a supercage model. This approach is used to analyze data on laser flash photolysis of 13 C-carbonyl labelled ketone α-deoxybenzoin in aqueous sodium alkyl (10–12) sulphate solutions. EPR lines of 13 C-benzoyl radicals exhibit antiphase structure (APS) typical of spin-correlated pairs. Due to very large APS splitting, 0.8–1.5 mT, the ST 0 polarized lines from free benzoyl radicals can be isolated spectrally. The observed line shape of the APS cannot be accounted for in the standard model of effective exchange potential. The shape of the APS is shown to be controlled by spin exchange relaxation in micellized pairs.

Unusual Dynamics of Micellized Radical Pairs Generated from Photochemically Active Amphiphiles

Unusual Dynamics of Micellized Radical Pairs Generated from Photochemically Active Amphiphiles

Laser Flash Spectroscopic Investigation of Micellized Radical Pairs. Direct Measurement of the Exit Rates of Micellized Radicals

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTLaser Flash Spectroscopic Investigation of Micellized Radical Pairs. Direct Measurement of the Exit Rates of Micellized RadicalsNicholas J. Turro and Chung-Hsi WuCite this: J. Am. Chem. Soc. 1995, 117, 44, 11031–11032Publication Date (Print):November 1, 1995Publication History Published online1 May 2002Published inissue 1 November 1995https://doi.org/10.1021/ja00149a036RIGHTS & PERMISSIONSArticle Views64Altmetric-Citations13LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (289 KB) Get e-Alerts Get e-Alerts

An exactly solvable model of the dipole-dipole relaxation of the electron spins of micellized radical pairs

An exact analytical calculation of the dipole-dipole relaxation rate of electron spins in a micelle is proposed for a spherically symmetrical model of radical diffusion. The results obtained are close to the Monte Carlo numerical calculations of the dipole-dipole relaxation. The results for the dipole-dipole relaxation in homogeneous solutions, adapted to micellized radical pairs, approximate well our calculations for intermediate and large micelles at all magnetic fields.

Investigation of chemical and spin dynamics in micellized radical pairs by time-resolved stimulated nuclear polarization. Theory and experiment

A numerical solution of the stochastic Liouville equation for a microreactor model is applied to the theoretical treatment of time-resolved stimulated nuclear polarization data, obtained during the investigation of micellized radical pairs, conducted in two different modes. Escape rate constants and relaxation parameters of radical pairs formed in the photolysis of methyldeoxybenzoin and benzoin in alkyl sulfate micelles of different sizes have been obtained. The conditions of the S−T 0 quantum oscillations in SNP kinetics have been determined.

Magnetic field effects on the dynamics of nitroxide-based singlet radical pairs in micelles

Magnetic field effects on the dynamics of nitroxide-based singlet radical pairs in micelles

Magnetic field and magnetic isotope effects on the recombination kinetics of covalently-linked ketyl-phenoxyl triplet radical pairs

The recombination kinetics of three photogenerated covalently-linked ketyl-phenoxyl triplet radical pairs,3[PhC.(OD)C6H4O(CH2) n OC6H4C6H4O.] (n=3, 6, and 10), and of the corresponding deuterated derivatives were examined by the laser flash technique under an external magnetic field (up to 0.2 T) in a CDCl3/CD3OD (2∶1) mixture. In zero magnetic field, radical pairs (RPs) with small exchange interactions (n=6 and 10) are characterized by high values of the magnetic isotope effect (MIE), which reach 3 for pairs withn=10. Under strong magnetic fields (up to 0.2 T), the values of MIE decrease to 1.2 to 1.1. The photochemical behavior of covalently-linked RPs is compared with that of similar unlinked RPs in micelles.

Time-resolved ESR examination of a simple supramolecular guest-host system. Electron spin exchange interaction in micellized spin-correlated radical pairs

The electron spin exchange interaction between micellized spin-correlated radical pairs (SCRP) is investigated by time-resolved electron spin resonance (TRESR) spectroscopy. On the basis of the SCRP model proposed independently by Closs and McLauchlan, an effective exchange interaction (Jeff) can be extracted either from a direct reading of the observed TRESR spectra or through spectral simulation. The results for a series of micellized radical pairs (of similar electronic and magnetic structure) show that the Jvalues are a function of the effective micelle size experienced by a given micellized radical pair and also a function of the radical pair molecular structure for a given micelle size. The values of Jeff can be systematically manipulated by varying the size of the micelles and/or the structure of the radical pairs. The results are shown to be consistent with a simple model of the structure of the micelle which includes the relationship between the magnitude of the exchange interaction between the fragments of the micellized radical pair and the micellar parameters such as the frequency of geminate pair reencounters, the relative diffusion coefficient of the fragments in the micelles, and the effective volume of the micelle explored by the pair during the time of observation. It is shown that a micellized radical pair, because of interactive spin and molecular dynamics, constitutes a simple and useful model of a guest-host supramolecular structure so that variations of the micelle size and the radical

Exchange Interaction in Micellized Radical Pairs*

Exchange Interaction in Micellized Radical Pairs*