Dispersed Optical Heterodyne Detected Birefringence and Dichroism of Transparent Liquids

Constantine, S.; Zhou, Yuxiang; Morais, J.; Ziegler, L. D.

doi:10.1021/jp971227s

Cited by 40 publications

(54 citation statements)

References 37 publications

(181 reference statements)

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“…The most distinguishing feature of the results in Figures 5-7, compared to the nonreactive samples, is the presence of a second mode at ∼80 cm -1 (and sometimes higher harmonics at ∼120 cm -1 and ∼160 cm -1 ), in addition to the low-frequency mode near 40 cm -1 . The mode near 80 cm -1 is significantly enhanced relative to ν 40 when detuned detection conditions are employed, 32,42,49 and as a result, ν 80 was emphasized in earlier studies 6 conducted under such conditions.…”

Section: Resultsmentioning

confidence: 96%

Investigations of Anharmonic Low-Frequency Oscillations in Heme Proteins

et al. 2001

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The technique of femtosecond coherence spectroscopy is applied to a variety of photostable and photochemically active heme protein samples. With the exception of cobalt-substituted myoglobin, strong oscillations are detected near 40 cm -1 in all of the samples studied. Additional modes near 80, 120, and 160 cm -1 are observed in the photochemically active samples. The amplitude and phase behavior of the low-frequency modes are studied by tuning the pump/probe carrier wavelength across the Soret absorption spectrum. A simple harmonic model is not able to account for the observed relative intensities of these modes or the carrier wavelength dependence of their frequency and phase. As a result, we develop an anharmonic model where the oscillatory signal is damped as the result of heterogeneity in the potential surface. The underlying source of the heterogeneity in the anharmonic potential surface is found to be correlated with the inhomogeneous broadening of the Soret band. The presence of the higher harmonics in the photochemically active samples demonstrates that the anharmonic mode is strongly coupled to the ligand photodissociation reaction (i.e., upon photolysis it is displaced far from equilibrium). Moreover, the observation of the ∼40 cm -1 oscillations in all of the ironbased heme protein samples, including porphine and protoporphyrin IX model compounds, suggests that this mode is associated with nuclear motion of the core of the porphyrin macrocycle. Since normal mode calculations and prior kinetic models predict the frequency of the heme "doming mode" to be near 50 cm -1 , we suggest that the reaction coupled oscillations at ∼40 and ∼80 cm -1 are a direct reflection of anharmonic heme doming dynamics. Evidence for coupling between the heme doming dynamics and the Fe-His stretching mode is also presented.

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Section: Resultsmentioning

confidence: 96%

Investigations of Anharmonic Low-Frequency Oscillations in Heme Proteins

et al. 2001

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“…The main points to note here are that the 40 cm -1 mode is clearly a property of the sample and that the frequency content of the FCS signals can be selected using the dispersed detection scheme. 25,45,46 In Figures 2 and 3, the probe pulse was dispersed through a monochromator, which was detuned from the carrier frequency, prior to detection by the PMT. When a detuning of several nm is employed, the FCS signals are filtered so that only the highfrequency vibrational components of the polarizability are observed.…”

Section: Resultsmentioning

confidence: 99%

“…25,45,46 The low-frequency modes that are revealed using the dispersed detection scheme are significant in that they likely represent important heme/protein motions that are intimately associated with the reaction coordinate for diatomic ligand binding. One motion that is believed to be important to the ligand binding and dissociation processes involves the "doming" of the heme group and the concomitant displacement of the iron atom from an in-plane position to roughly 0.4 Å out of the heme plane.…”

Section: Introductionmentioning

confidence: 99%

Investigations of Coherent Vibrational Oscillations in Myoglobin

et al. 2000

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The technique of femtosecond coherence spectroscopy (FCS) is applied to the heme protein myoglobin. Photostable samples of deoxy myoglobin (Mb) and photochemically active samples of the nitric oxide adduct (MbNO) are investigated. The pump-induced change in the probe transmittance for both samples displays coherent oscillations that, when transformed into the frequency domain, are in agreement with the resonance Raman spectrum of deoxy Mb. This indicates that the coherences associated with the photoreactive sample (MbNO) arise from the rapidly changing forces appearing in the crossing region(s) between the reactant and product state potential energy surfaces. The relative phase and amplitude of the Fe-His vibration, associated with the sole covalent linkage between the heme and the protein, are analyzed as a function of sample state and pump/probe carrier frequency. The dependence of the phase on carrier frequency is found to be significantly different for the "field driven" coherence in Mb and the "reaction driven" coherence in MbNO. In MbNO we observe a dip in amplitude and a phase flip near 439 nm for the Fe-His mode, whereas in deoxy Mb we observe a nearly constant phase and amplitude for this mode across the Soret absorption band. These observations are shown to be in good agreement with a simple theoretical model of the pump-probe experiment. Finally, we present recent observations of strong low-frequency oscillations, occurring near 40 cm -1 in both species and near 80 cm -1 for MbNO.

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“…16 As they have shown, there is no net energy exchange between the applied field and the sample. As a result the solvent signal is expected to disappear when the pump-probe response is integrated over all detection frequencies.…”

Section: Methodsmentioning

confidence: 98%

Two-Dimensional Electronic Spectroscopy of Chlorophyll a: Solvent Dependent Spectral Evolution

2015

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The interaction of the monomeric chlorophyll Q band electronic transition with solvents of differing physical-chemical properties is investigated through two-dimensional electronic spectroscopy (2DES). Chlorophyll constitutes the key chromophore molecule in light harvesting complexes. It is well known that the surrounding protein in the light harvesting complex fine tunes chlorophyll electronic transitions to optimize energy transfer. Therefore an understanding of the influence of the environment on the monomeric chlorophyll electronic transitions is important. The Q band 2DES are inhomogeneous at early times, particularly in hydrogen bonding polar solvents, but also in nonpolar solvents like cyclohexane. Interestingly this inhomogeneity persists for long times, even up to the nanosecond timescale in some solvents. The reshaping of the 2DES occurs over multiple timescales and was assigned mainly to spectral diffusion. At early times the reshaping is Gaussianlike, hinting at a strong solvent reorganization effect. The temporal evolution of the 2DES response was analysed in terms of a Brownian oscillator model. The spectral densities underpinning the Brownian oscillator fitting were recovered for the different solvents. The absorption spectra and Stokes shift were also properly described by this model. The extent and nature of inhomogeneous broadening was a strong function of solvent, being larger in H-bonding and viscous media and smaller in nonpolar solvents. The fastest spectral reshaping components were assigned to solvent dynamics, modified by interactions with the solute.

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Dispersed Optical Heterodyne Detected Birefringence and Dichroism of Transparent Liquids

Cited by 40 publications

References 37 publications

Investigations of Anharmonic Low-Frequency Oscillations in Heme Proteins

Investigations of Anharmonic Low-Frequency Oscillations in Heme Proteins

Investigations of Coherent Vibrational Oscillations in Myoglobin

Two-Dimensional Electronic Spectroscopy of Chlorophyll a: Solvent Dependent Spectral Evolution

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