Resonance Raman detection

Selective Resonance Raman Detection of Carotenes and Lycopene in Human Skin.104... 

SELECTIVE RESONANCE RAMAN DETECTION OF CAROTENES AND LYCOPENE IN HUMAN SKIN... 

Ermakov IV, Ermakova MR, McClane RW, and Gellermann W (2001a), Resonance Raman detection of carotenoid antioxidants in living human skin, Opt. Lett. 26 1179-1181. 

Ermakov IV, McClane RW, Gellermann W, and Bernstein PS (2001b), Resonant Raman detection of macular pigment levels in the living human retina, Opt. Lett. 26 202-204. 

Champion, P.M., Stallard, B.R., Wagner, G.G., and Gunsalus, I.C. (1982) Resonance Raman detection of a Fe-S bond, in Cytochrome P-450 Structure andFunction, National Symposium, Minsk, p. 7. 

Photodissociation of a N-methylimidazole ligand from [OEPFe(N-MeIm)2]+ has been studied using resonance Raman detection. " The rate constants for ligand dissociation and association are k =5.3 x 10 s (as compared to 950 s for the non-photoactivated dissociation " ) and k+ = 3.7 X 10 s, respectively. " ... 

Bangcharoenpaurpong, O., A.K. Rizos, P.M. Champion, D. Jollie, and S.G. Sligar (1986). Resonance Raman detection of bound dioxygen in cytochrome P-450cam. J. Biol. Chem. 261, 8089-8092. 

Mak PJ, Denisov IG, Victoria D, Makris TM, Deng T, Sligar SG, Kincaid JR (2007) Resonance Raman detection of the hydroperoxo intermediate in the cytochrome P450 enzymatic cycle. J Am Chem Soc 129 6382-6383... 

Other work using picosecond laser spectroscopy has shown that these reactions proceed via a solvent intermediate, M(CO)5(solvent), which forms in a few picoseconds after the laser pulse and then decays to products. Lee and Harris have observed formation of the solvated species Cr(CO)5(C5H,2) with t = 17 ps and the decay of the vibrationally excited Cr(CO)j with t 21 ps (apparently at ambient temperature). These observations are at variance with those of Spears and co-woikers, who claim that the bare Cr(CO)j persists on the 100-ps time scale at 22°C. Hopkins and co-workers have used resonance Raman detection to show that the 100-ps process is due to thermal relaxation of the excited vibrational state, probably of Cr(CO)5(CgH,2). 

Figure 10.15 Resonance Raman detection of populations in electronically excited states and following creation of state molecules by laser excitation at frequency Probing molecules at frequency will generate intense resonance Raman emission at if the - transition is El -allowed, because is in near-resonance with the energy separation between vibration less and some vibronic level of S2. Probing at frequency tu will generate similarly intense emission only if appreciable population has accumulated in by intersystem crossing from S, since a is in resonance with the T — T, energy gap. This excited-state selectivity of resonance Raman scattering has rendered it a useful tool for monitoring time-resolved excited state dynamics.

Ionic polysulfides dissolve in DMF, DMSO, and HMPA to give air-sensitive colored solutions. Chivers and Drummond [88] were the first to identify the blue 83 radical anion as the species responsible for the characteristic absorption at 620 nm of solutions of alkali polysulfides in HMPA and similar systems while numerous previous authors had proposed other anions or even neutral sulfur molecules (for a survey of these publications, see [88]). The blue radical anion is evidently formed by reactions according to Eqs. (5)-(8) since the composition of the dissolved sodium polysulfide could be varied between Na2S3 and NaaS with little impact on the visible absorption spectrum. On cooling the color of these solutions changes via green to yellow due to dimerization of the radicals which have been detected by magnetic measurements, ESR, UV-Vis, infrared and resonance Raman spectra [84, 86, 88, 89] see later. 

The yellow disulfide radical anion and the briUiant blue trisulfide radical anion often occur together for what reason some authors of the older Hterature (prior to 1975) got mixed up with their identification. Today, both species are well known by their E8R, infrared, resonance Raman, UV-Vis, and photoelectron spectra, some of which have been recorded both in solutions and in solid matrices. In solution these radical species are formed by the ho-molytic dissociation of polysulfide dianions according to Eqs. (7) and (8). 8ince these dissociation reactions are of course endothermic the radical formation is promoted by heating as well as by dilution. Furthermore, solvents of lower polarity than that of water also favor the homolytic dissociation. However, in solutions at 20 °C the equilibria at Eqs. (7) and (8) are usually on the left side (excepting extremely dilute systems) and only the very high sensitivity of E8R, UV-Vis and resonance Raman spectroscopy made it possible to detect the radical anions in liquid and solid solutions see above. 

Heating of certain alkali halides with elemental sulfur also produces colored materials containing the anions 82 or 83 which replace the corresponding halide ions. For example, NaCl and KI crystals when heated in the presence of sulfur vapor incorporate di- and trisulfide monoanions [116-119] which can be detected, inter alia, by resonance Raman spectroscopy [120, 121] ... 

In certain pink and red colored ultramarine varieties an additional red colored species absorbing at /lniax=520 nm has been detected but its identity has been disputed it may be the radical anion 84 or the neutral molecule 84 [86, 124-126]. In fact, the cfs-planar isomer of the latter absorbs at /lmax=520 nm in the gas phase and one of its fundamental vibrations (678 cm" ) [127] matches exactly a resonance Raman line of the red chro-... 

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. 

Since there are a large number of different experimental laser and detection systems that can be used for time-resolved resonance Raman experiments, we shall only focus our attention here on two common types of methods that are typically used to investigate chemical reactions. We shall first describe typical nanosecond TR spectroscopy instrumentation that can obtain spectra of intermediates from several nanoseconds to millisecond time scales by employing electronic control of the pnmp and probe laser systems to vary the time-delay between the pnmp and probe pnlses. We then describe typical ultrafast TR spectroscopy instrumentation that can be used to examine intermediates from the picosecond to several nanosecond time scales by controlling the optical path length difference between the pump and probe laser pulses. In some reaction systems, it is useful to utilize both types of laser systems to study the chemical reaction and intermediates of interest from the picosecond to the microsecond or millisecond time-scales. 

Raman spectroscopy has enjoyed a dramatic improvement during the last few years the interference by fluorescence of impurities is virtually eliminated. Up-to-date near-infrared Raman spectrometers now meet most demands for a modern analytical instrument concerning applicability, analytical information and convenience. In spite of its potential abilities, Raman spectroscopy has until recently not been extensively used for real-life polymer/additive-related problem solving, but does hold promise. Resonance Raman spectroscopy exhibits very high selectivity. Further improvements in spectropho-tometric measurement detection limits are also closely related to advances in laser technology. Apart from Raman spectroscopy, areas in which the laser is proving indispensable include molecular and fluorescence spectroscopy. The major use of lasers in analytical atomic... 

Application of Resonance Raman Spectroscopy to the Detection of Carotenoids In Vivo... 

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