Resonance Raman studies of Rieske-type proteins

Resonance Raman (RR) spectra are reported for the [2Fe-2S] Rieske protein from Thermus thermophilus (TRP) and phthalate dioxygenase from Pseudomonas cepacia (PDO) as a function of pH and excitation wavelength. Depolarization ratio measurements are presented for the RR spectra of spinach ferredoxin (SFD), TRP, and PDO at 74 K. By comparison with previously published RR spectra of SFD, we suggest reasonable assignments for the spectra of TRP and PDO. The spectra of PDO exhibit virtually no pH dependence, while significant changes are observed in TRP spectra upon raising the pH from 7.3 to 10.1. One band near 270 cm-1, which consists of components at 266 cm-1 and 274 cm-1, is attributed to Fe(III)-N(His) stretching motions. We suggest that these two components arise from conformers having a protonated-hydrogen-bonded imidazole (266 cm-1) and deprotonated-hydrogen-bonded imidazolate (274 cm-1) coordinated to the Fe/S cluster and that the relative populations of the two species are pH-dependent; a simple structural model is proposed to account for this behavior in the respiratory-type Rieske proteins. In addition, we have identified RR peaks associated with the bridging and terminal sulfur atoms of the Fe-S-N cluster. The RR excitation profiles of peaks associated with these atoms are indistinguishable from each other in TRP (pH 7.3) and PDO and differ greatly from those of [2Fe-2S] ferredoxins. The profiles are bimodal with maxima near 490 nm and > approx. 550 nm. By contrast, bands associated with the Fe-N stretch show a somewhat different enhancement profile. Upon reduction, RR peaks assigned to Fe-N vibrations are no longer observed, with the resulting spectrum being remarkably similar to that reported for reduced adrenodoxin. This indicates that only modes associated with Fe-S bonds are observed and supports the idea that the reducing electron resides on the iron atom coordinated to the two histidine residues. Taken as a whole, the data are consistent with an St2FeSb2Fe[N(His)]t2 structure for the Rieske-type cluster.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/29687/1/0000014.pd

Raman spectroscopy and principal factor multivariate curve resolution analysis of concentrated A1[sub 2]O[sub 3]-Na[sub 2]O-H[sub 2]O solutions

Principal factor multivariate curve resolution has been applied to a series of Raman spectra for samples representing, highly concentrated alkaline aluminate slurries. Factors are extracted that represent the behavior of the dominant chemical species present, including aluminate monomer, aluminate oligomers, water, and hydroxide. The analysis is particularly useful in unraveling the numerous contributions in the v(0H) region of the spectrum. These extracted factors were further examined by comparing their scores to measured physiochemical properties such as density, relative humidity, and molar concentrations of components, weight fractions, and water activity

Time-dependent Raman analysis of metal-to-ligand charge transfer excited states: Application to radiative and nonradiative decay

The photophysical properties of the emitting metal-to-ligand charge transfer (MLCT) excited states of the complexes, [Os(bpy)3]2+, [Os(bpy)2(py)2]2+, and [Os(bpy)(py)4]2+ (bpy = 4-4′-bipyridine, py = pyridine) have been characterized in aqueous solution at room temperature by absorption, emission, and Raman spectroscopies and by emission lifetimes and emission quantum yields. A spectroscopic model has been developed by using the time-dependent theory of Raman scattering, taking into account interference effects on resonance Raman profiles arising from interactions between the different ligands. A model based on the cylindrical model of Sension and Strauss provides a good fit to the data. The mode-specific vibrational parameters obtained from the spectroscopic analysis are used to calculate the vibrational contributions to the radiative and nonradiative decay rate constants for each of the complexes. These results and the experimental rate constants were used to calculate vibrationally induced electronic coupling matrix elements (Vk) for nonradiative decay and also transition moments, M, for radiative decay. For radiative decay, the average transition moment for the three complexes was 0.05Å, and for nonradiative decay, the average value of Vk was 910 cm-1. Within a reasonable margin of error, the Franck-Condon contributions are in agreement with values obtained in a previous study that used the single mode approximation and a Franck-Condon analysis of emission spectra

Synthesis of polypyridyl complexes of ruthenium(II) containing three different bidentate ligands

[Extract] A general synthetic method has been developed for the synthesis of heteroleptic tris(polypyridyl) complexes of ruthenium(II), [Ru(pp)(pp')(pp")]²⁺. This method opens new avenues for the preparation of molecular assemblies and for the systematic variation of excited-state properties. For example, the results of a study on the ground- and excited-state properties of a series of these complexes reveal a strategy for the preparation of black chromophores which will absorb light strongly throughout the visible region of the spectrum