Resonance Raman spectroscopy determination

Excited Electronic States, Electronic and Resonance Raman Spectroscopy Determination of Molecular Distortions in (Zink and Shin). 

Determining the Geometries of Molecules and Ions in Excited States by Using Resonance Raman Spectroscopy... 

A variety of physical methods has been used to ascertain whether or not surface ruthenation alters the structure of a protein. UV-vis, CD, EPR, and resonance Raman spectroscopies have demonstrated that myoglobin [14, 18], cytochrome c [5, 16, 19, 21], and azurin [13] are not perturbed structurally by the attachment of a ruthenium complex to a surface histidine. The reduction potential of the metal redox center of a protein and its temperature dependence are indicators of protein structure as well. Cyclic voltammetry [5, 13], differential pulse polarography [14,21], and spectroelectrochemistry [12,14,22] are commonly used for the determination of the ruthenium and protein redox center potentials in modified proteins. 

Resonance Raman Spectroscopy. A review of the interpretation of resonance Raman spectra of biological molecules includes a consideration of carotenoids and retinal derivatives. Another review of resonance Raman studies of visual pigments deals extensively with retinals. Excitation profiles of the coherent anti-Stokes resonance Raman spectrum of j8-carotene have been presented. Resonance Raman spectroscopic methods have been used for the detection of very low concentrations of carotenoids in blood plasma and for the determination of carotenoid concentrations in marine phytoplankton, either in situ or in acetone extracts. ... 

Resonance Raman Spectroscopy. If the excitation wavelength is chosen to correspond to an absorption maximum of the species being studied, a 102—104 enhancement of the Raman scatter of the chromophore is observed. This effect is called resonance enhancement or resonance Raman (RR) spectroscopy. There are several mechanisms to explain this phenomenon, the most common of which is Franck-Condon enhancement. In this case, a band intensity is enhanced if some component of the vibrational motion is along one of the directions in which the molecule expands in the electronic excited state. The intensity is roughly proportional to the distortion of the molecule along this axis. RR spectroscopy has been an important biochemical tool, and it may have industrial uses in some areas of pigment chemistry. Two biological applications include the determination of helix transitions of deoxyribonucleic acid (DNA) (18), and the elucidation of several peptide structures (19). A review of topics in this area has been published (20). 

Zink JI, Kim Shin K-S (1991) Molecular distortions in excited electronic states determined from electronic and resonance Raman spectroscopy, In Volman DH, Hammond GS, Neckers DC (eds) Advances in Photochemistry, vol. 16. John Wiley Sons, New York and reference therein... 

The geometry changes which transition metal complexes undergo when excited electronic states are populated are determined by using a combination of electronic emission and absorption spectroscopy, pre-resonance Raman spectroscopy, excited state Raman spectroscopy, and time-dependent theory of molecular spectroscopy. 

This expression for the complete overlap is Fourier transformed to give the electronic emission spectrum. In order to carry out the calculation it is necessary to know the frequencies and the displacements for all of the displaced normal modes. In addition, the energy difference between the minima of the two potential surfaces E0 and the damping r must be known. As will be discussed below, the frequencies and displacements can be experimentally determined from pre-resonance Raman spectroscopy, and the energy difference between the ground and excited states and the damping can be obtained from the electronic absorption spectrum and/or emission spectrum. 

Figure 7 shows a plot of spin equilibria calculated from the data in Figure 6. The two sloping lines correspond to the temperature range where a thermal spin equilibrium exists. From the difference in height between them, the free energy difference between the equilibria in the R and T structures is calculated as 0.9-1.2 kcal/mol Fe, in agreement with the value derived from the IR measurements mentioned above, and with a recently published determination of the spin equilibrium by resonance Raman spectroscopy (46).

A critical pre-requisite to using Raman and resonance Raman spectroscopy to examine the excited-state structural dynamics of nucleic acids and their components, is the determination of the normal modes of vibration for the molecule of interest. The most definitive method for determining the normal modes is exhaustive isotopic substitution, subsequent measurement of the IR and Raman spectra, and computational analysis with the FG method of Wilson, Decius, and Cross [77], Such an analysis is rarely performed presently because of the improvements in accuracy of ab initio and semi-empirical calculations. Ab initio computations have been applied to most of the nucleobases, which will be described in more detail below, resulting in relatively consistent descriptions of the normal modes for the nucleobases. 

Previous reviews of UV resonance Raman spectroscopy applied to nucleic acids and their components were done in 1987 [94] and 2005 [95], This review will focus exclusively on the application of UV resonance Raman spectroscopy in determining excited-state structure and dynamics of nucleic acids and their components. This review will cover the nucleic acid components first and gradually build up to nucleic acids. 

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