Raman studies clusters

Fig. 21. Cluster conversions involving [Fe3S4]+ clusters. The cluster conversion in (c) has been proposed on the basis of EPR, VTMCD, and resonance Raman studies, but has yet to be confirmed by Mossbauer or more direct structural techniques.

Resonance Raman studies on the putative prismane protein would provide other important information. In the frequency region of 200-430 cm the putative prismane protein showed bands that at first sight seemed to be typical for Fe-S clusters, but at a closer look appeared to be broader than those observed in basic Fe-S proteins. Also, the resonance frequencies were slightly different from known Fe-S clusters, and it was contended that A prismane-type [6Fe-6S] core is clearly an excellent candidate in light of the available analytical and biophysical data [28]. 

Resonance Raman studies of the recombinant proteins showed vibrational bands at the 200-430 cm region characteristic of iron-sulfur clusters (124). Most interestingly, on Fe and O isotope sensitive band was detected at 801 cm which could be attributed to either a Fe(IV)=0 species or a monobridged Fe-O-Fe structure. This observation, together with Mossbauer analysis, which indicated a mixed N, 0, and S ligand environment for cluster 2, suggests a Fe-O-Fe or Fe=0 unit as part of the structure for cluster 2. 

R M. Felker, P. M. Maxton, and M. W. Schaeffer, Nonlinear Raman studies of weakly bound complexes and clusters in molecular beams. Chem. Rev. 94, 1787 1805 (1994). 

Resonance Raman studies of Fe- and Cu-contalnlng proteins have led to the Identification of tyrosine, histidine, cysteine, and hydroxide ligands as well as Fe-0 and Fe-S clusters. For the Fe-0 clusters, the frequency and oxygen Isotope dependence of the Fe-O-Fe symmetric stretch relates to Fe-O-Fe bond angle, while the peak Intensity relates to the disposition of the other ligands In the cluster. 

Furthennore, resonance Raman studies of aconitase by Johnson et al. (53) demonstrated homologous spectra for both inactive and active aconitase. This suggests similar vibrational modes and thus similar core structures for the two forms. Finally, a cubane structure for the [3Fe-4S] cluster is supported by recent protein crystallographic studies of inactive aconitase by Robbins and Stout (54). (Recent results from Jensen s group (55) on the redetermination of the crystal structure of the Azotobacter ferredoxin I clearly show that the 3Fe cluster does not have a [3Fe-3S] ring structure, as originally determined (37), but has a [3Fe-4S] cubane structure.)... 

High Nuclearity Metal Carbonyl Clusters, 14, 285 Infrared Intensities of Metal Carbonyl Stretching Vibrations, 10, 199 Infrared and Raman Studies of -Complexes, 1, 239 Insertion Reactions of Compounds of Metals and Metalloids, 5, 225 Insertion Reactions of Transition Metal-Carbon Bonded Compounds I. Carbon Monoxide Insertion, 11, 87... 

TR3 spectra were used to obtain data on the ligand modes of both high- and low-spin isomers of [Fe(L)]2+, where L = /V,/V,/V, /V -tetrakis(2-pyridylmethyl)-6,6,-bis(aminomethyl)-2,2 -bipyridine or V,V -bis(benzyl)-7V,7V -bis(2-pyridyl-methyl)-6,6,-bis(aminomethyl)-2,2 -bipyridine.193 Resonance Raman and TR3 data were used to obtain detailed ligand mode information for Ru(bi-py)2(dpp)2+ and (bipy)2Ru(dpp)Ru(bipy)24+, where dpp = 2,3-bis(2-pyridyl)-pyazine, and their bipy-d8 analogues.194 A resonance Raman study has been carried out on electronic communication and delocalisation in complexes involving two Ru3 clusters linked by a pyrazine ligand.195... 

Quicksall and Spiro S34) have assigned bands at 208, 164, and 105 cm in the Raman spectrum of Ir4(CO)x2 to i, <2, and e iridium-iridium modes. This assignment is based on an idealized Td symmetry of the cluster and would suggest that the solid state structure 377) persists in solution. An infrared and Raman study by Abel el al. (5) has confirmed this assignment. 

The combined use of spectroscopy and protein engineering techniques provides a unique approach for the study of the mechanism of ferrochelatase and in the elucidation of the role of its intriguing [2Fe-2S] cluster. Mossbauer studies of kinetic intermediates and fluorimetric and resonance Raman studies of both mammalian and yeast (i.e. devoid of the [2Fe-2S] cluster) ferrochelatases, reacted with porphyrin or porphyrin analogs, should be undertaken. Determination of the three-dimensional structures of the complexes of ferrochelatase with substrate or inhibitors will also be of crucial importance. 

Clusters are generally considered to be aggregates of one or two elements, so that methods for determining structural information about molecules are obvious candidates for the study of clusters. A long established and one of the most accurate methods - X-ray diffraction - can sometimes be used, and we shall give examples below. Structural information can often be found from the rotations and vibrations of molecules, and infrared and Raman spectroscopy have also been used for this purpose. The improvement in mass separation techniques in recent years has provided new possibilities for studying clusters and their ions. Cluster cations with many thousands of atoms can be detected, and high-resolution spectroscopy can be performed on cluster anions. The analysis of... 

Raman Studies of Weakly Bound Complexes and Clusters in Molecular Beams. 

Because of the high technological potential of tellurite glasses, their basic structures have been studied by X-ray [5,6,17], electron energy loss spectroscopy [18], neutron diffraction [8, 17, 19, 20], nuclear magnetic resonance [NMR] [17, 21-27], Raman studies [2, 22-24, 26-29], and ab initio cluster calculation [8, 23, 28-35]. 

Vibrational spectroscopic studies have been reported on clusters containing a ( M3-H) ligand and approximate metal-metal force constant calculations have been carried out on some small carbonyl clusters. A simple quantitative treatment of relative CO i.r. band intensities for [M3(CO)i2] (M=Ru and Os) has been presented together with a comparative i.r. and Raman study of the v(CO) region in [MaM 3 a (CO)i2] (M = Ru, M =Os, x=0, 1, 2, 3). It has been noted that the A 2 vibrational mode of the axial CO s in [Ru3(CO)i2] is identical to the collective CO stretching mode of CO adsorbed on Ru(001) and an inelastic electron-tunneling study of [Ru3(CO)i2] on aluminium oxide has been reported. ... 

Plenary 9. J W Nibler et al, e-mail address niblerj chem.orst.edu (CARS and SRS). High resolution studies of high lymg vibration-rotational transitions in molecules excited in electrical discharges and low density monomers and clusters in free jet expansions. Ionization detected (REMPI) SRS or IDSRS. Detect Raman... 

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