Resonance Raman contribution

Fig. 4.4. Influence of carotenoid pre-resonant Raman contributions on cluster analysis result. The dendrogram was obtained using the same parameters as in the one displayed in Fig. 4.3. However, the spectra of the used data set were obtained without decomposing carotenoid before the Raman experiments. The species sallow, horse-chestnut and large-leaved linden form a distinct cluster due to the intense carotenoid contribution. The corresponding spectra are shown in Fig. 4.5 traces a, c and e. Reprinted with permission from [52]...

The elimination of sample luminescence using a diode laser was demonstrated by measuring SER spectra of tris(2,2 -bipyridine)ruthenium(II), [RB,], in bulk solution. RBj is a highly luminescent compound that has lecdved considerable interest because of its unique excited state properties (24-26). However, because of its intense visible luminescence, it is difficult to obtain luminescence-free Raman spectra even with SER enhancement. Further, visible-wavelength Raman spectra of this compound are usually complicated by resonance Raman contributions to the spectrum. 

Figure 1. (Bottom) Fourier transform Raman spectrum of the RC from Rb. sphaeroides 2.4.1 in the presence of ascorbate (reduced RC) this spectrum is dominated by the preresonance contributions of the primary donor in its reduced state, P. (Top) Fourier transform resonance Raman spectrum of the RC in the presence of ferricyanide this spectrum contains resonance Raman contributions of the primary donor in its oxidized state, P" "- and includes the bands at 1600, 1643, and 1717 cm". Conditions room temperature, 200 mW of 1064 nm excitation, coaddition of 1000 interferograms, 4 cm resolution.

First, it is possible to excite a chromophore corresponding to the active site, and detennine which modes interact with it. Second, by using UV excitation, the amino acids with phenyl rings (tryptophan and tyrosine, and a small contribution from phenylalanine) can be selectively excited [4], The frequency shifts in the resonance Raman spectrum associated with them provide infomiation on their enviromnent. 

It turns out that the CSP approximation dominates the full wavefunction, and is therefore almost exact till t 80 fs. This timescale is already very useful The first Rs 20 fs are sufficient to determine the photoadsorption lineshape and, as turns out, the first 80 fs are sufficient to determine the Resonance Raman spectrum of the system. Simple CSP is almost exact for these properties. As Fig. 3 shows, for later times the accuracy of the CSP decays quickly for t 500 fs in this system, the contribution of the CSP approximation to the full Cl wavefunction is almost negligible. In addition, this wavefunction is dominated not by a few specific terms of the Cl expansion, but by a whole host of configurations. The decay of the CSP approximation was found to be due to hard collisions between the iodine atoms and the surrounding wall of argons. Already the first hard collision brings a major deterioration of the CSP approximation, but also the role of the second collision can be clearly identified. As was mentioned, for t < 80 fs, the CSP... 

NIS of synchrotron radiation yields details of the dynamics of Mossbauer nuclei, while conventional MS yields only limited information in this respect (comprised in the Lamb-Mossbauer factor /). NIS shows some similarity with Resonance Raman- and IR-spectroscopy. The major difference is that, instead of an electronic resonance (Raman and IR), a nuclear resonance is employed (NIS). NIS is site-selective, i.e., only those molecular vibrations that contribute to the overall... 

Conventional MS in the energy domain has contributed a lot to the understanding of the electronic ground state of iron centers in proteins and biomimetic models ([55], and references therein). However, the vibrational properties of these centers, which are thought to be related to their biological function, are much less studied. This is partly due to the fact that the vibrational states of the iron centers are masked by the vibrational states of the protein backbone and thus techniques such as Resonance Raman- or IR-spectroscopy do not provide a clear picture of the vibrational properties of these centers. A special feature of NIS is that it directly reveals the fraction of kinetic energy due to the Fe motion in a particular vibrational mode. 

In summary, NIS provides an excellent tool for the study of the vibrational properties of iron centers in proteins. In spectroscopies like Resonance Raman and IR, the vibrational states of the iron centers are masked by those of the protein backbone. A specific feature of NIS is that it is an isotope-selective technique (e.g., for Fe). Its focus is on the metal-ligand bond stretching and bending vibrations which exhibit the most prominent contributions to the mean square displacement of the metal atom. 

Another explanation for their resonance Raman results could be a change in the zwitterionic nature of the merocyanine isomers in the different solvents which may result in changes in the Raman transition probabilities, or the spectral changes could be due to solvent shifts of the absorption spectrum, resulting in a change in the relative contribution of the different vibrational modes to each resonance Raman spectrum. We note that in the same article, the authors report the transient absorption spectra of the merocyanine forms, which clearly show that the BIPS spectrum in cyclohexane has more discrete vibrational modes than are observed in the polar solvents, which show more spectral broadening. Al-... 

Aramaki and Atkinson were also active in work on the spiro-oxazines [65]. They noted that for NOSH in many polar and nonpolar solvents the picosecond time-resolved resonance Raman spectra simply built up over 50 psec with no shape evolution. The same finding was concluded from transient absorption measurements over the same time scale. The spectra/absorbances were then constant for 1.5 nsec. These authors suggest that only two isomers can be expected to contribute to the merocyanine spectra because those trans about the y-methene bridge bond attached to the naphthalene ring are sterically crowded due to short interproton distances. There was no evidence for the X transient in their study however, the 50-psec convoluted pulse profile may be expected to mask this sortlifetime species even if it were present. 

Figure 9. Resonance Raman spectrum of the 2Fe-2S-4Cys cluster In oxidized spinach ferredoxln. Protein ( 2 mM) maintained at 15 K In a helium Dlsplex and probed with 488.0 nm excitation. Spectral contribution of Ice In 220-320 cm" 1 region has been subtracted. (Data from Ref. 21). Starred features Indicate peaks Identified as totally symmetric Aig vibrations (23,24).

UV resonance Raman study of betanova, while consistent with a (3-sheet secondary structure, provides no evidence for a cooperative thermal transition 223 The CD spectra reported by Boyden and Asher 223 showed no indication of (3-sheet features, even at 0 °C, and were indicative of an unordered conformation. It has been suggested 115,223 that the CD in the 220 nm region is dominated by aromatic side-chain contributions, yet the resonance Raman data suggest a molten globule-like structure, which appears inconsistent with substantial CD contributions from aromatic side chains 224 ... 

It is not necessary here to give details of other spectroscopic methods. However, Table V summarizes the information that some of these methods can give about proteins. Valuable contributions have been made by electronic (UV) spectroscopy in determining the site symmetry and spin state of transition metal ions, often isomorphous substitutions for naturally occurring ions such as Zn2+. However, epr, fluorescence, resonance, Raman, and so on, have also been used extensively, as Table V shows. All in all it is these methods that have revealed the most about the electronic states of atoms and groups in proteins. 

Figure 23-5 Resonance Raman spectra. (A) Of the retinaldehyde-containing bacteriorhodopsin bR568 (see Fig. 23-45) and its 12,14-2H and 14-13C isotopic derivatives. (B) Of bRS68 labeled with the dominant internal coordinates that contribute to the normal modes. From Lugtenburg et al 7...

There may be a relatively large charge separation, e.g. in MoSj- and almost equal net charges on the metal and sulfur atoms, e.g. in [Mo2S(CN),2]6-. 78a MO calculations on the latter ion show that there are k MOs delocalized over three centers. Resonance Raman studies further indicate that the delocalization extends over the whole linear N—C—Mo—S—Mo—C—N system. The tt(S) -> t/(Mo) donation induces a decrease of electron density on the sulfur and is, therefore, responsible for an unusual charge transfer transition Mo-+S (band at 27100cm-1), quite the reverse assignment to that in examples with terminal sulfide where a considerable p contribution also has to be anticipated (see Table l).3,4... 

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