Vibrational Stark Effect Spectroscopy

Chattopadhyay, Arun; Boxer, Steven G.

doi:10.1021/ja00109a038

Cited by 136 publications

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“…Stark spectroscopy of electronic transitions in proteins is now a standard method; 18,19 however, this technique is rarely applied to molecular vibrations. 20,21 In the present communication we report the first measurement of the Stark effect for a vibrational transition in a protein. Since molecular vibrations are ubiquitous, this may prove to be a generally useful method for mapping electric fields in proteins.…”

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confidence: 86%

Vibrational Stark Spectroscopy in Proteins: A Probe and Calibration for Electrostatic Fields

et al. 1999

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We report the first measurement of the vibrational Stark effect in a protein, providing quantitative information on the sensitivity of a vibrational transition to an applied electric field. This can be used to interpret changes in the vibrational frequency that are often observed when amino acids are changed or when a protein undergoes a structural change in terms of the change in the internal or matrix electric field associated with the perturbation. The vibrational Stark effect has been measured for the vibration of CO bound to the heme iron in myoglobin. The vibrational Stark effect is surprisingly large, giving a Stark tuning rate of (2.4/f) cm -1 /(MV/cm), where f is the local field correction; this is nearly 4 times larger than for free CO. It is also found that the change in dipole moment is parallel to the transition moment; that is, the change in dipole moment is in the direction perpendicular to the heme plane. Vibrational Stark effect data are also reported as a function of pH, for various mutants, for a modified picket fence porphyrin, and for cytochrome c. The Stark tuning rate is found to be very similar in all cases, indicating that the CO stretch frequency for CO bound to the heme iron is a sensitive and anisotropic local detector of changes in the electrostatic field. This information is used to evaluate electrostatics calculations for heme proteins.Electrostatic interactions are central to understanding the properties of molecules in the condensed phase and are especially important in complex organized systems such as proteins. A large body of theoretical work is directed at understanding the role played by electrostatics in folding, assembly, and catalysis. 1-8 Electrostatic interactions can be probed by measuring pK a shifts for titratable residues, 9-11 shifts in redox potential, 12,13 NMR chemical shifts, 14 and electrochromic band shifts (sometimes called internal Stark shifts). 15,16 Electrochromic band shifts in a protein result from the interaction between a probe chromophore and the electric field due to the surrounding organized environment of the protein matrix and associated prosthetic groups and solvent. This field is collectively called the matrix electric field F matrix , and the observed electrochromic band shift is ∆E ) hc∆ν j ) -∆µ‚F matrix , where ∆µ is the change in dipole moment associated with a spectroscopic transition.To interpret or calculate the electrochromic band shift in terms of the matrix electric field due to the protein or any other ordered environment, it is necessary to know ∆µ as this gives the intrinsic sensitivity of the transition to an electric field. 17 The magnitude and direction of ∆µ can be obtained by Stark spectroscopy which quantifies the effect of an externally applied electric field, F ext , on the transition. Stark spectroscopy of electronic transitions in proteins is now a standard method; 18,19 however, this technique is rarely applied to molecular vibrations. 20,21 In the present communication we report the first measurement of the Stark...

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confidence: 86%

Vibrational Stark Spectroscopy in Proteins: A Probe and Calibration for Electrostatic Fields

et al. 1999

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“…the shifting and splitting of spectral lines of atoms and molecules in the presence of an external static electric field. Understanding the Stark effect is important for the analysis of atomic and molecular rotational spectra (Chattopadhyay and Boxer 1995;Pierce and Boxer 1995). Thus, apart from the intrinsic interest of its own, the Stark problem can play the role of a model problem, from which one can obtain information about the properties of atoms when strong electric fields are present.…”

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Complete closed-form solutions of the Stark problem

Lantoine

Russell

2011

Celest Mech Dyn Astr

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Perturbed two-body problems play a special role in Celestial Mechanics as they capture the dominant dynamics for a broad range of natural and artificial satellites. In this paper, we investigate the classic Stark problem, corresponding to motion in a Newtonian gravitational field subjected to an additional uniform force of constant magnitude and direction. For both the two-dimensional and three-dimensional cases, the integrals of motion are determined, and the resulting quadratures are analytically integrated. A complete list of exact, closed-form solutions is deduced in terms of elliptic functions. It is found that all expressions rely on only seven fundamental solution forms. Particular attention is given to ensure that the expressions are well-behaved for very small perturbations. A comprehensive study of the phase space is also made using a boundary diagram to describe the domains of the general types of possible motion. Numerical examples are presented to validate the solutions.

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“…S1 and SI Text). To quantify the electric field sensitivity of a specific vibrational probe, a known external electric field is applied and the effect of the field on the IR absorption spectrum is measured (25)(26)(27), a method known as vibrational Stark effect (VSE) spectroscopy. The electric field sensitivity of a vibrational probe directly calibrated in this fashion is called the linear Stark tuning rate, jΔ~μ probe j [in units of cm −1 ∕ðMV∕cmÞ].…”

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Quantitative, directional measurement of electric field heterogeneity in the active site of ketosteroid isomerase

Fafarman¹,

Sigala²,

Schwans³

et al. 2012

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

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Understanding the electrostatic forces and features within highly heterogeneous, anisotropic, and chemically complex enzyme active sites and their connection to biological catalysis remains a longstanding challenge, in part due to the paucity of incisive experimental probes of electrostatic properties within proteins. To quantitatively assess the landscape of electrostatic fields at discrete locations and orientations within an enzyme active site, we have incorporated site-specific thiocyanate vibrational probes into multiple positions within bacterial ketosteroid isomerase. A battery of X-ray crystallographic, vibrational Stark spectroscopy, and NMR studies revealed electrostatic field heterogeneity of 8 MV∕cm between active site probe locations and widely differing sensitivities of discrete probes to common electrostatic perturbations from mutation, ligand binding, and pH changes. Electrostatic calculations based on active site ionization states assigned by literature precedent and computational pK a prediction were unable to quantitatively account for the observed vibrational band shifts. However, electrostatic models of the D40N mutant gave qualitative agreement with the observed vibrational effects when an unusual ionization of an active site tyrosine with a pK a near 7 was included. UV-absorbance and 13 C NMR experiments confirmed the presence of a tyrosinate in the active site, in agreement with electrostatic models. This work provides the most direct measure of the heterogeneous and anisotropic nature of the electrostatic environment within an enzyme active site, and these measurements provide incisive benchmarks for further developing accurate computational models and a foundation for future tests of electrostatics in enzymatic catalysis. E xtensive structural studies of enzymes have revealed that biological catalysis occurs within sequestered active site crevices that solvate reacting substrates with an anisotropic and chemically complex constellation of charged, polar, and hydrophobic groups. But beyond visualization of the chemical composition and architecture of active sites permitted by the rich library of available protein structures, our understanding of the electrostatic nature and properties of this highly heterogeneous environment and its role in molecular recognition and catalysis is largely based on simulations. Computations using three-dimensional structures routinely provide electrostatic potentials, as in Fig. 1A. These potentials have been used to identify and characterize protein-protein and protein-ligand binding sites, and interaction energies derived from these calculations have suggested key contributions from the electrostatic environment to enzymatic rate enhancement and specificity (1-5). However, even the most sophisticated computational methods have multiple approximations and limitations (6-8) and, most importantly, have not been rigorously evaluated through cycles of nontrivial computational predictions and experimental tests. Incisive and quantitative experimental measures o...

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Vibrational Stark Effect Spectroscopy

Cited by 136 publications

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Vibrational Stark Spectroscopy in Proteins: A Probe and Calibration for Electrostatic Fields

Vibrational Stark Spectroscopy in Proteins: A Probe and Calibration for Electrostatic Fields

Complete closed-form solutions of the Stark problem

Quantitative, directional measurement of electric field heterogeneity in the active site of ketosteroid isomerase

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