Charge transfer transition, characteristics

The complexity of the low temperature MCD spectra of the oxidized and reduced trinuclear cluster shows the multiplicity of the predominantly S — Fe charge transfer transitions that contribute to the absorption envelope. While MCD spectroscopy provides a method of resolving the electronic transitions, assignment cannot be attempted without detailed knowledge of the electronic structure. However, the complexity of the low temperature MCD spectra is useful in that it furnishes a discriminating method for determining the type and redox state of protein bound iron-sulfur clusters. Each well characterized type of iron-sulfur cluster, i.e. [2Fe-2S], [3Fe-4S], and [4Fe-4S], has been shown to have a characteristic low temperature MCD spectrum in each paramagnetic redox state (1)... 

These tru 5-dioxoruthenium(VI) complexes have characteristic UV-vis absorption spectra. The fj-saturated nature of the macrocyclic tertiary amine ligands enables the high-energy metal-localized transition to be observed. " The weak vibronic structured band at 370-400nm has been assigned to (0 ) —> Ru charge transfer transition that is vibronically coupled to the... 

The most obvious characteristic of the spectra of low-spin five-coordinate complexes is the high intensity of the bands in the visible and near ultraviolet. For a long time this feature of the spectra raised doubts as to whether these low frequency bands should be considered as d—d transitions or charge-transfer transitions. 

Mattson, S. M. Rossman, G. R. (1987a) Identifying characteristics of charge transfer transitions in minerals. Phys. Chem. Minerals, 14, 94-9. 

To experimentally probe the electronic and thermal consequences of flash photolysis, a femtosecond time-resolved near-IR study of photoexcited Mb was undertaken (22). This study probed the spectral evolution of band III, a weak ( max 100 M-1 cm-1) near-IR charge transfer transition (14) centered near 13, 110 cm-1 that is characteristic of five-coordinate ferrous hemes in their ground electronic state (S = 2). Because band III is absent when the heme is electronically excited, the dynamics of its reappearance provides an incisive probe of relaxation back to the ground electronic state. Moreover, because the spectral characteristics of band III (integrated area center frequency line width) correlate strongly with temperature (23-26), the spectral evolution of band III also probes its thermal relaxation. 

An important physical property of 66 and its simple 1-alkyl homologs is the capacity to form dimeric complexes in solution as the temperature is lowered. No covalent bond is formed the complexes are believed to be 7t-complexes, and their formation is accompanied spectroscopically by the appearance of characteristic intermolecular charge-transfer transitions.245... 

A charge transfer transition is found at 425 nm in both met and oxy (vide infra) and is characteristic of the coupled binuclear copper site. Elimination of sulfur ligation leaves the most reasonable assignment of this feature as a phenolate-to-copper(II) CT transition (see Table 4). This indicates that tyrosine is bound to the binuclear cupric site and the most likely candidate for the endogenous bridge. 

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