Stokes Shift as a Tool for Probing the Solvent Reorganization Energy

Mertz, Edward L.; Tikhomirov, V. A.; Krishtalik, L. I.

doi:10.1021/jp963042b

Cited by 58 publications

(48 citation statements)

References 39 publications

(117 reference statements)

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“…This geometry reduced the uncertainties and resulted in p Ϸ 2 compared with p Ϸ 4 obtained in ref. 24. The value of i Ϸ 455 cm Ϫ1 remained unchanged.…”

Section: Methodsmentioning

confidence: 93%

“…The intramolecular reorganization energy for proflavine, has been previously determined by comparing the measured s ϩ i with calculated s for a series of solvents with well characterized dielectric properties (24). The medium reorganization energy, denoted here as scal , was calculated in ref.…”

Section: Methodsmentioning

confidence: 99%

“…The medium reorganization energy, denoted here as scal , was calculated in ref. 24 within the framework of the dielectric continuum model as follows. The cavity formed by proflavine in the surrounding solvent was approximated by an oblate spheroid.…”

Section: Methodsmentioning

confidence: 99%

“…Intrinsic uncertainties in the shape of the cavity and in the electron density redistribution were accounted for by a scaling parameter p, assuming that the true value of s is related to scal as s ϭ p scal . The values of i and p were extracted simultaneously by linear regression analysis of the dependence of measured s ϩ i on calculated scal for a series of reference solvents (24).…”

Section: Methodsmentioning

confidence: 99%

“…24, using the van der Waals surface of proflavine rather than an oblate spheroid as the solvent-inaccessible cavity, and solving the Poisson equation numerically with the help of the DELPHI program (25). This geometry reduced the uncertainties and resulted in p Ϸ 2 compared with p Ϸ 4 obtained in ref.…”

Section: Methodsmentioning

confidence: 99%

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Low dielectric response in enzyme active site

Mertz

Krishtalik

2000

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

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125

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The kinetics of charge transfer depend crucially on the dielectric reorganization of the medium. In enzymatic reactions that involve charge transfer, atomic dielectric response of the active site and of its surroundings determines the efficiency of the protein as a catalyst. We report direct spectroscopic measurements of the reorganization energy associated with the dielectric response in the active site of ␣-chymotrypsin. A chromophoric inhibitor of the enzyme is used as a spectroscopic probe. We find that water strongly affects the dielectric reorganization in the active site of the enzyme in solution. The reorganization energy of the protein matrix in the vicinity of the active site is similar to that of low-polarity solvents. Surprisingly, water exhibits an anomalously high dielectric response that cannot be described in terms of the dielectric continuum theory. As a result, sequestering the active site from the aqueous environment inside low-dielectric enzyme body dramatically reduces the dielectric reorganization. This reduction is particularly important for controlling the rate of enzymatic reactions. Many enzymatic reactions are charge transfer processes. Their activation free energy is affected by the dielectric properties of the milieu of the reacting groups (1). It has been suggested that small dielectric response at the active site could be a physical reason for high catalytic activity (2-4).Direct measurements of local dielectric properties at enzyme active sites have never been made. Most of the current knowledge is based on circumstantial evidence. Different existing data can be used to support opposing points of view. For instance, the average static dielectric constant of proteins s Ϸ 4 was estimated from measurements on dry powders (5-9). However, x-ray data indicate that the mobility of atoms near enzymes active sites is higher than average (10, 11) and, thus, the dielectric response should be enhanced. Furthermore, active sites are typically situated within several angstroms of the protein surface. A wide range of dielectric response was predicted from molecular simulations for various proteins: A gradual increase from Ϸ 3 in the center of globule to about Ϸ 10 at its periphery was found in refs. 12-19. Even higher values of 25-35 were calculated by taking into account fluctuations of ionizable surface groups (18,19). Finally, highly polarizable aqueous surroundings may contribute to the dielectric response, to increase the uncertainty even further.Thus, local dielectric properties at enzyme active sites have remained unclear. In the present paper, we attempt to resolve this issue by direct measurement. A spectroscopic technique proposed in refs. 20 and 21 and further developed in refs. 22-24 is used. The reorganization energy is determined from absorption and emission spectra of proflavine noncovalently bound in the active site of ␣-chymotrypsin. We evaluate the contributions to the dielectric reorganization of the protein interior and of the surrounding solvent by comparing the spectra of t...

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“…This geometry reduced the uncertainties and resulted in p Ϸ 2 compared with p Ϸ 4 obtained in ref. 24. The value of i Ϸ 455 cm Ϫ1 remained unchanged.…”

Section: Methodsmentioning

confidence: 93%

Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

See 3 more Smart Citations

Low dielectric response in enzyme active site

Mertz

Krishtalik

2000

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

Self Cite

125

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Fluorescence Lifetime Measurements, Applications of

Bright

Pandey

Baker

2000

Encyclopedia of Analytical Chemistry

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Over the years, the emissive characteristics (spectral, temporal, and polarization) of fluorophores have been widely used to probe the local environments of fluorescent centers. Fluorescence lifetime and rotational reorientation time measurements, in particular, offer a means to elucidate subtle features when examining, for example, complex systems involving environmental heterogeneity, energy transfer, quenching pathways, or excited state reactions. Further, because fluorescence occurs on the nanosecond (10 −9 s) timescale, competing or perturbing kinetic processes like collisional quenching, solvent relaxation, energy transfer, and rotational reorientation can affect the fluorescence. Thus, a carefully chosen fluorophore can serve as an internal nanosecond or faster stopwatch of environmental fluctuations. This article is divided into a brief introduction, a short discussion on instrumentation, and several sections on various applications of excited state fluorescence measurements.

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A Genetic Algorithm Approach to Design Principles for Organic Photovoltaic Materials

Sousa

Filho

Silva

et al. 2020

Advcd Theory and Sims

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Stokes Shift as a Tool for Probing the Solvent Reorganization Energy

Cited by 58 publications

References 39 publications

Low dielectric response in enzyme active site

Low dielectric response in enzyme active site

Fluorescence Lifetime Measurements, Applications of

A Genetic Algorithm Approach to Design Principles for Organic Photovoltaic Materials

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