Conformational Properties of Nickel(II) Octaethylporphyrin in Solution. 2. A Low-Temperature Optical Absorption Spectroscopy Study

Cupane, Antonio; Leone, Maurizio; Cordone, Lorenzo; Gilch, Harald; Dreybrodt, Wolfgang; Unger, and Esko; Schweitzer‐Stenner, Reinhard

doi:10.1021/jp953304u

Cited by 21 publications

(35 citation statements)

References 33 publications

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“…* 7 transitions with in-plane vibrational modes of organic macrocycles (Schomacker and Champion, 1986). 3. In agreement with expectations of the literature (Schomacker and Champion, 1989;Cupane et al, 1996), no relevant temperature dependence of coupling constants is observed; in fact, eventual variations of S values are within +5%. For this reason, S values were taken to be constant in the fittings of the spectra at various temperatures.…”

Section: Spectral Analysissupporting

confidence: 92%

Local dynamics of DNA probed with optical absorption spectroscopy of bound ethidium bromide

Cupane

Bologna

Rizzo

et al. 1997

Biophysical Journal

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We have studied the local dynamics of calf thymus double-helical DNA by means of an "optical labeling" technique. The study has been performed by measuring the visible absorption band of the cationic dye ethidium bromide, both free in solution and bound to DNA, in the temperature interval 360-30 K and in two different solvent conditions. The temperature dependence of the absorption line shape has been analyzed within the framework of the vibronic coupling theory, to extract information on the dynamic properties of the system; comparison of the thermal behavior of the absorption band of free and DNA-bound ethidium bromide gave information on the local dynamics of the double helix in the proximity of the chromophore. For the dye free in solution, large spectral heterogeneity and coupling to a "bath" of low-frequency (soft) modes is observed; moreover, anharmonic motions become evident at suitably high temperatures. The average frequency of the soft modes and the amplitude of anharmonic motions depend upon solvent composition. For the DNA-bound dye, at low temperatures, heterogeneity is decreased, the average frequency of the soft modes is increased, and anharmonic motions are hindered. However, a new dynamic regime characterized by a large increase in anharmonic motions is observed at temperatures higher than approximately 280 K. The DNA double helix therefore appears to provide, at low temperatures, a rather rigid environment for the bound chromophore, in which conformational heterogeneity is reduced and low-frequency motions (both harmonic vibrations and anharmonic contributions) are hindered. The system becomes anharmonic at approximately 180 K; however, above approximately 280 K, anharmonicity starts to increase much more rapidly than for the dye free in solution; this can be attributed to the onset of wobbling of the dye in its intercalation site, which is likely connected with the onset of (functionally relevant) DNA motions, involving local opening/unwinding of the double helix. As shown by parallel measurements of the melting curves, these motions precede the melting of the double helix and depend upon solvent composition much more than does the melting itself.

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Section: Spectral Analysissupporting

confidence: 92%

Local dynamics of DNA probed with optical absorption spectroscopy of bound ethidium bromide

Cupane

Bologna

Rizzo

et al. 1997

Biophysical Journal

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“…1) listed in Table 7 were now used to estimate υQ Table 9. Apparently, 15 B 2u is substantially weaker coupled to the B-state transition than the investigated A 2u and B 1u modes. Its strong Raman intensity is due solely to the comparatively strong saddling distortion of the macrocycle.…”

Section: Evaluation Of Heme Deformationsmentioning

confidence: 68%

Non‐planar heme deformations and excited state displacements in horseradish peroxidase detected by Raman spectroscopy at Soret excitation

Huang

Schweitzer‐Stenner

2005

J Raman Spectroscopy

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We studied the out-of-plane modes of horseradish peroxidase (HRP) in different spin, oxidation and ligation states by measuring the respective resonance Raman spectra with (near) Soret excitation. The non-planar modes of the heme are Raman inactive for planar macrocycles, but become resonance Raman active in the presence of out-of-plane deformations. The thus induced Raman scattering results mostly from Franck-Condon type coupling. We observed bands from a variety of out-of-plane modes such as g 5 , g 6 , g 7 .A 2u / modes, g 21 and g 22 .E g /, g 15 .B 2u / and g 11 .B 1u /. The appearance of these bands is clearly indicative of non-planar deformations of the same symmetry. We determined the relative intensities of all sufficiently intense Raman modes of ferric pentacoordinated, quantum mixed and hexacoordinated low-spin as well as of ferrous pentacoordinated high-spin HRP C. The apparent vibronic coupling parameters were obtained from a self-consistent analysis of the Raman intensities and the respective optical absorption spectrum. They revealed significantly reduced displacements of the excited B-state for the ferrous, deoxy-like state compared with the resting ferric state. An analysis of the obtained coupling strengths of out-of-plane modes revealed that they are predominantly induced by static non-planar deformations along the normal coordinates of the lowest wavenumber modes of a given symmetry type. We used the deformations of the heme in resting HRP C to determine the vibronic coupling strength of the experimentally detectable out-of-plane modes and subsequently employed this information to obtain the non-planar deformations for the investigated ferric hexacoordinated low-spin state. This yielded a substantial reduction of the ruffling distortion, whereas the doming deformation remained mostly unaffected by the change of the iron's spin and ligation state.

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“…to compare them to the coupling constants S hj obtained from the fit of the lineshape of the Soret band (Cupane et al, 1996a). The frequency of the mode is denoted by hj .…”

Section: Resonance Raman Measurementsmentioning

confidence: 99%

Protein Dynamics in an Intermediate State of Myoglobin: Optical Absorption, Resonance Raman Spectroscopy, and X-Ray Structure Analysis

Engler

Ostermann

Gassmann

et al. 2000

Biophysical Journal

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A metastable state of myoglobin is produced by reduction of metmyoglobin at low temperatures. This is done either by irradiation with x-rays at 80 K or by electron transfer from photoexcited tris(2, 2'-bipyridine)-ruthenium(II) at 20 K. At temperatures above 150 K, the conformational transition toward the equilibrium deoxymyoglobin is observed. X-ray crystallography, Raman spectroscopy, and temperature-dependent optical absorption spectroscopy show that the metastable state has a six-ligated iron low-spin center. The x-ray structure at 115K proves the similarity of the metastable state with metmyoglobin. The Raman spectra yield the high-frequency vibronic modes and give additional information about the distortion of the heme. Analysis of the temperature dependence of the line shape of the Soret band reveals that a relaxation within the metastable state starts at approximately 120 K. Parameters representative of static properties of the intermediate state are close to those of CO-ligated myoglobin, while parameters representative of dynamics are close to deoxymyoglobin. Thus within the metastable state the relaxation to the equilibrium is initiated by changes in the dynamic properties of the active site.

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Conformational Properties of Nickel(II) Octaethylporphyrin in Solution. 2. A Low-Temperature Optical Absorption Spectroscopy Study

Cited by 21 publications

References 33 publications

Local dynamics of DNA probed with optical absorption spectroscopy of bound ethidium bromide

Local dynamics of DNA probed with optical absorption spectroscopy of bound ethidium bromide

Non‐planar heme deformations and excited state displacements in horseradish peroxidase detected by Raman spectroscopy at Soret excitation

Protein Dynamics in an Intermediate State of Myoglobin: Optical Absorption, Resonance Raman Spectroscopy, and X-Ray Structure Analysis

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