Remote electron transfer in the quenching of porphyrin fluorescence by oxidants

Kapinus, E. I.; Dilung, I. I.

doi:10.1016/0009-2614(90)85329-b

Cited by 10 publications

(8 citation statements)

References 15 publications

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“…Experimentally obtained molecular volumes provide means for estimation of effective radii, assuming spherical shape of the solute species. For example, molecular volumes, obtained from mass density, sound velocity, or refractivity measurements, allow for estimation of “average” effective radii. − Diffusivity characteristics of molecules and their ions yield values for their effective Stokes radii, − which represent their mass-transport properties . Alternatively, from X-ray or NMR structural data, the radius of a spherical solvation cavity can be ascribed to the distance from the center of mass of the solvated molecule to its most distal van der Waals boundary. − For moieties with highly irregular shapes, however, this approach provides dimensions that are an overestimation of the effective radii, reflecting their redox and charge-transfer behavior observed experimentally.…”

Section: Introductionmentioning

confidence: 99%

Electrochemical Reduction of Quinones: Interfacing Experiment and Theory for Defining Effective Radii of Redox Moieties

et al. 2010

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Using cyclic voltammetry, we examined the dependence of the reduction potentials of six quinones on the concentration of the supporting electrolyte. An increase in the electrolyte concentration, resulting in an increase in the solution polarity, caused positive shifts of the reduction potentials. We ascribed the observed changes in the potentials to the dependence of the solvation energy of the quinones and their anions on the media polarity. Analysis of the reduction potentials, using the Born solvation energy equation, yielded unfeasibly small values for the effective radii of the quinone species, that is, the experimentally obtained effective radii were up to 4-fold smaller than the radii of the solvation cavities that we calculated for the quinones. The nonspherical shapes of the quinones, along with the uneven charge density distribution in their anions, encompassed the underlying reasons for the discrepancies between the obtained experimental and theoretical values for the radii of these redox species. The generalized Born approach, which does not treat the solvated species as single spheres, provided means for addressing this discrepancy and yielded effective radii that were relatively close to the measured values.

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Section: Introductionmentioning

confidence: 99%

Electrochemical Reduction of Quinones: Interfacing Experiment and Theory for Defining Effective Radii of Redox Moieties

et al. 2010

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“…The value of W 0 calculated in this way is 3.6 × 10 10 s −1 and is comparable with the magnitude of this parameter reported for other electrontransfer reactions. 4,17,23 Substitution of the values for W 0 , R, and L obtained for the TPP*/NQ system into eq 7 yields a value for k act of 3.2 × 10 10 M −1 s −1 , which is around an order of magnitude smaller than the lower-limit of k act estimated for TPP*/BQ reflecting the much closer proximity achieved by the latter reaction pair.…”

Section: The Journal Of Physical Chemistry Amentioning

confidence: 85%

“…The functional form of the distance-dependent intrinsic reaction rate, w ( r ), depends on the type of reaction between F* and Q. A functional form for w ( r ) that has been used for reactions involving the transfer or exchange of an electron via tunnelling is shown in eq . ,,,,,,, w ( r ) = W 0 .25em exp [ − 2 L false( r − R false) ] …”

Section: Methodsmentioning

confidence: 99%

“…Understanding the intrinsic parameters associated with an electron-transfer reaction between two molecular entities is of fundamental scientific interest and has practical importance in the field of organic electronics. , Fluorescence quenching measurements of dilute solutions containing a mixture of the two reactants is the most straightforward method for extracting information about electron-transfer reaction parameters when at least one of the reactants is luminescent, and this approach has been widely utilized, such as for the study of the biologically relevant quenching of porphyrin fluorescence by quinones. − However, in many reaction systems of interest the electron-transfer rate is so fast that, even in low-viscosity fluid solutions, the overall rate of the reaction is influenced by the rate of approach of the reactants, ,− and this can complicate the recovery of the intrinsic electron-transfer reaction parameters.…”

Section: Introductionmentioning

confidence: 99%

“…A functional form for w(r) that has been used for reactions involving the transfer or exchange of an electron via tunnelling is shown in eq 2. 4,10,13,16,17,25,44,45…”

Section: ■ Introductionmentioning

confidence: 99%

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Diffusion-Facilitated Direct Determination of Intrinsic Parameters for Rapid Photoinduced Bimolecular Electron-Transfer Reactions in Nonpolar Solvents

et al. 2015

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Bimolecular fluorescence-quenching reactions involving electron-transfer between electronically excited 5,10,15,20-tetraphenyl-21H,23H-porphine (TPP*) and 1,4-benzoquinone (BQ) or 1,4-naphthoquinone (NQ) were investigated using a set of alkane solvents that enabled the rapid reaction kinetics to be probed over a wide viscosity range, while minimizing changes in other relevant solvent parameters. Relative diffusion coefficients and reaction distances were recovered directly from analysis of fluorescence decay curves measured on a nanosecond time scale. The electron transfer from TPP* to BQ requires reactant contact, consistent with tightly associated exciplex formation in these nonpolar solvents. In contrast, electron transfer from TPP* to NQ displays a clear distance dependence, indicative of reaction via a much looser noncontact exciplex. This difference is attributed to the greater steric hindrance associated with contact between the TPP*/NQ pair. The diffusion coefficients recovered from fluorescence decay curve analysis are markedly smaller than the corresponding measured bulk relative diffusion coefficients. Classical hydrodynamics theory was found to provide a satisfactory resolution of this apparent discrepancy. The calculated hydrodynamic radii of TPP and NQ correlate very well with the van der Waals values. The hydrodynamic radius obtained for BQ is a factor of 6 times smaller than the van der Waals value, indicative of a possible tight cofacial geometry in the (TPP(+)/BQ(-))* exciplex. The present work demonstrates the utility of a straightforward methodology, based on widely available instrumentation and data analysis, that is broadly applicable for direct determination of kinetic parameter values for a wide variety of rapid bimolecular fluorescence quenching reactions in fluid solution.

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The Analysis of the Electron Transfer Rate from Steady-State Fluorescence Spectroscopy

Nakaema

Leite

Sanches

1997

Archives of Biochemistry and Biophysics

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Remote electron transfer in the quenching of porphyrin fluorescence by oxidants

Cited by 10 publications

References 15 publications

Electrochemical Reduction of Quinones: Interfacing Experiment and Theory for Defining Effective Radii of Redox Moieties

Electrochemical Reduction of Quinones: Interfacing Experiment and Theory for Defining Effective Radii of Redox Moieties

Diffusion-Facilitated Direct Determination of Intrinsic Parameters for Rapid Photoinduced Bimolecular Electron-Transfer Reactions in Nonpolar Solvents

The Analysis of the Electron Transfer Rate from Steady-State Fluorescence Spectroscopy

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