Resonance Raman spectroscopy excitation profile

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 has been used to directly probe the origin of CT transitions through the construction of RR excitation profiles, which have been collected for (L-A(j)MoO(bdt) and (L-Af5)MoO(tdt) in the solid state at 140 K using laser excitation at wavelengths between 457.9 and 528.7 nm (23). This wavelength range encompasses the absorption envelopes of bands 4 and 5. As can be observed in Fig. 10, the three vibrational bands for (L-A( )MoO(bdt)... 

Peticolas was the first to measure the UV resonance Raman spectrum and excitation profile (resonance Raman intensity as a function of excitation wavelength) of adenine monophosphate (AMP) [147, 148], The goal of this work, besides demonstrating the utility of UV resonance Raman spectroscopy, was to elucidate the excited electronic states responsible for enhancement of the various Raman vibrations. In this way, a preliminary determination of the excited-state structures and nature of each excited electronic state can be obtained. Although the excited-state structural dynamics could have been determined from this data, that analysis was not performed directly. 

This initial report was followed closely by the UV resonance Raman spectra of uridine (UMP), cytidine (CMP) and guanidine (GMP) monophosphates by Nishimura, et al. [149] and the application of UV resonance Raman spectroscopy to nucleic acids and their components started in earnest. In the years that followed, Peticolas and Spiro provided much of the research effort in this area. For nucleosides and nucleotides, Peticolas studied guanosine [150], UMP [151-154], GMP [152, 155], AMP [144, 152, 156] and CMP [153], Spiro was the only one to measure the UV resonance Raman spectra of TMP, in addition to those of all the other naturally occurring nucleotides [157, 158], For all of these nucleotides, UV resonance Raman excitation profiles have been determined. 

What is remarkable is that all of these early measurements of the UV resonance Raman spectra of nucleic acid components involved computational and theoretical support to their experimental findings. For example, Spiro used CINDO calculations to determine the nature of the excited electronic states of the nucleotides [157], In the early and mid 1970 s, many researchers were also attempting to understand resonance Raman spectroscopy, the types of information it could provide, and a unifying theoretical framework to the intensities [147, 159-172], UV resonance Raman spectra provided some of the first experimental evidence to test the various theoretical models. Peticolas attempted to fit the observed experimental excitation profiles of AMP [156], UMP [151, 154] and CMP [152, 153] to the sum-over-states model for the resonance Raman cross-sections. From these simulations, they were able to obtain preliminary excited-state structural dynamics of the nucleobase chromophores of the nucleotides for UMP [151, 153, 158] and CMP [153], For AMP, the experimental excitation profiles were simulated with an A-term expression, but the excited-state structural changes were not obtained. Rather, the goal of that work was to identify the electronic transitions within the lowest-energy absorption band of adenine [156],... 

The final two examples of the determination of excited state distortions are large bimetallic compounds whose electronic absorption spectra are broad and featureless. We must turn entirely to resonance Raman spectroscopy to measure the distortions because all of the information in the electronic spectrum is buried under the envelope. Fortunately, the resonance Raman profiles contain a great deal of information. These molecules were chosen as illustrative examples precisely because the resonance Raman spectra are so rich. The spectrum contains long overtone progressions and combination bands. Excitation profiles of not only the fundamentals but also of overtones and combination bands will be used to determine the distortions. The power of time-dependent theory from Section III.F and experimental examples of the effects of A on fundamentals, overtones, and combination bands are shown. The calculated distortions provide new insight about the orbitals involved in the electronic transition. 

Raman and Infrared Spectroscopy. Two reviews deal with resonance Raman spectroscopy of carotenoid-containing biomolecules and micro-organisms152 and of carotenoids and chlorophylls in photosynthetic bacteria.153 The resonance Raman excitation profile of lycopene in acetone has been determined.154 Calculations previously used for (3-carotene do not explain the lycopene data. Several papers report detailed studies of the time-resolved resonance Raman spectra of... 

Resonance Raman Spectroscopy. This technique is finding increasing application in the carotenoid field. Details of the resonance Raman spectra of jS-caro-tene," y-carotene carotene (166)], and torulene [3, 4 -didehydro-/3, /f-carotene (167)]" have been given. Details of the Raman excitation profiles of... 

B2y, and >42 vibrations are expected to be polarized (p), depolarized (dp), and inversely polarized (tp ), respectively. These polarization properties, together with their vibrational frequencies, were used by Spiro and his coworkers to make complete assignments of vibrational spectra of the Fe-porphin skeletons of a series of heme proteins. They showed that the resonance Raman spectrum may be used to predict the oxidation and spin states of the Fe atom in heme proteins. For example, the Fe atom in oxyhemoglobin has been shown to be low-spin Fc(IIl). It should be noted that the A2y mode, which is normally Raman inactive, is observed under the resonance condition. Although the modes are rather weak in Fig. I-19, these vibrations are enhanced markedly and exclusively by the excitation near the B band since the A-term resonance is predominant under such condition. The majority of compounds studied thus far exhibit the A-term rather than the l -term resonance. A more complete study of resonance Raman spectra involves the observation of excitation profiles (Raman intensity plotted as a function of the exciting frequency for each mode), and the simulation of observed excitation proliles based on various theories of resonance Raman spectroscopy. ... 

Infrared and Raman Spectroscopy. Resonance Raman spectra of aW-trans- and 15-CW-/3-carotene have been compared.The ps resonance Raman spectrum of /8-carotene has been described,and solvent effects on the excitation profile of the line of jS-carotene have been studied. Model calculations have been used to interpret observed jS-carotene Raman spectra and excitation profiles. Raman scattering spectra of j8-carotene-l2 complexes have been determined. Resonance Raman spectra of carotenoids have been used as an intrinsic probe for membrane potential, e.g. neurosporene [7,8-dihydro-(/r,(/r-carotene (183)] in chromatophores of Rhodopseudomonas sphaeroides. ° Resonance Raman spectroscopy and i.r. spectroscopy have been used in studies of the chromophore of visual pigments and visual cycle intermediates and of bacteriorhodopsin and its photocycle intermediates. ... 

In principle, resonance Raman spectroscopy allows the direct determination of the S value of each vibrational mode in practice the analysis is difficult because reliable excitation profiles and, preferably, absolute intensity measurements are required. Whether the P Raman data permit this kind of modeling remains to be seen. 

In each carotenoid, the 2A (0-0) energy for the absorptive transition determined by resonance-Raman excitation profile in the crystalline state is in complete agreement with that for the emissive transition determined by fluorescence spectroscopy in n-hexane solution, a fact which strongly suggests that neither the Stokes shift nor the dependence on the polarizabiliry of the environment (in -hexane solution vs. in crystal) is present in this particular electronic state. 

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