Fluorescence detected magnetic resonance

Huber MM, Staubli AB, Kustedjo K, Gray MHB, Shih J, Fraser SE, Jacobs RE, Meade TJ (1998) Fluorescently detectable magnetic resonance imaging agents. Bioconjug Chem 9 242-249... 

Time-resolved laser flash ESR spectroscopy generates radicals with nonequilibrium spin populations and causes spectra with unusual signal directions and intensities. The signals may show absorption, emission, or both and be enhanced as much as 100-fold. Deviations from Boltzmann intensities, first noted in 1963, are known as chemically induced dynamic electron polarization (CIDEP). Because the splitting pattern of the intermediate remains unaffected, the CIDEP enhancement facilitates the detection of short-lived radicals. A related technique, fluorescence detected magnetic resonance (FDMR) offers improved time resolution and its sensitivity exceeds that of ESR. The FDMR experiment probes short-lived radical ion pairs, which form reaction products in electronically excited states that decay radiatively. ... 

Similarly, fluorescence detected magnetic resonance effects observed during the pulse radiolysis of anthracene-dio in the presence of 2,3-dimethyl-l-butene support the presence of 8 equivalent methyl groups. Because the splitting, Odi = 0.82 mT, was approximately one-half that of the monomer splitting, Omon =1.71 mT, the sandwich dimer 91 + was invoked. ... 

The allenes bearing four tert-butyl or four trimethylsilyl groups at the terminal carbons react in methylene chloride with antimony pentachloride. The cation radicals formed contain an unpaired electron delocalized along the neighbouring -rr-bonds. The conclusion is based on the analysis of 1H, 13C, and 29Si ESR spectra (Bolze et al. 1982) as well as on photoelectron spectra (Elsevier et al. 1985 Kamphius et al. 1986). These data have found corroboration in a recent study (Werst Trifunac 1991). The tetramethylallene cation radical spectrum was observed by fluorescent-detected magnetic resonance. The well-resolved multiplet due to this cation radical consists of a binomial 13-line pattern owing to 12 equivalent methyl protons. This is in full accord with Scheme 3-60. 

A related technique, fluorescence detected magnetic resonance (FDMR), is suitable for the observation of short-lived radical ion pairs with lifetime in the range of... 

Fluorescence detected magnetic resonance effects observed during the pulse radiolysis of anthracene-d10 in the presence of tetramethylethene portray an additional facet of the cyclobutane radical cation system [345, 346]. The spectra [eight ( ) equivalent methyl groups, ad = 8.2 G approximately one half of the monomer splitting, am = 17.1 G] are compatible with a dimer cation. In analogy to the benzene dimer radical cation [347, 348] they were interpreted as evidence for a sandwich , one molecule above the other [346],... 

Detection using fluorescence-detected magnetic resonance (FDMR)... 

Hence, the radical cation derived directly from the parent [1.1.1.1 Jpagodane has to have rather a short lifetime. Fortunately, the application of a time-resolved technique, fluorescence-detected magnetic resonance revealed a radical cation possessing 8 equivalent protons with a H hfc of 0.96 mT being substantially smaller than... 

Two different types of pulsed EPR experiments are possible a spectrum can be measured at a fixed time after the pulse by variation of the field strength B (Eq. 72), or the time profile of a particular spectral line can be measured at constant B to give kinetic information. One vziriation of this kinetic method is to detect the recombination of singlet-state radical ion pairs in liquid hydrocarbons by the fluorescence of the product excited state [142]. This technique is known as fluorescence-detected magnetic resonance (FDMR) and provides information on the spin dynamics of the radical ion pair as well as the chemical kinetics. 

Many studies used radiation chemistry to produce the radical and radical cations and anions of various dienes in order to measure their properties. Extensive work was devoted to the radical cation of norbomadiene in order to solve the question whether it is identical with the cation radical of quadricyclane . Desrosiers and Trifunac produced radical cations of 1,4-cyclohexadiene by pulse radiolysis in several solvents and measured by time-resolved fluorescence-detected magnetic resonance the ESR spectra of the cation radical. The cation radical of 1,4-cyclohexadiene was produced by charge transfer from saturated hydrocarbon cations formed by radiolysis of the solvent. In a similar system, the radical cations of 1,3- and 1,4-cyclohexadiene were studied in a zeolite matrix and their isomerization reactions were studied. Dienyl radicals similar to many other kinds of radicals were formed by radiolysis inside an admantane matrix. Korth and coworkers used this method to create cyclooctatrienyl radicals by radiolysis of bicyclo[5.1.0]octa-2,5-diene in admantane-Di6 matrix, or of bromocyclooctatriene in the same matrix. Williams and coworkers irradiated 1,5-hexadiene in CFCI3 matrix to obtain the radical cation which was found to undergo cyclization to the cyclohexene radical cation through the intermediate cyclohexane-1,4-diyl radical cation. 

Psencik J, Searle GFW, Hala J and Schaafsma TJ (1994) Fluorescence-detected magnetic resonance (FDMR) of green sulfurphotosynthetic bacteria Chlorobium sp. Photosynth Res 40 1-10... 

Schmittel and Burghart have produced an excellent review, Understanding Reactivity Patterns of Radical Cations . The detection and observation of radical cations are highly desirable, but also have often been difficult, owing to their short lifetimes. West and Trifunac have developed a technique known as time-resolved fluorescence-detected magnetic resonance (FDMR) that gives the maximum possible time resolution for EPR and thus a window into fast radical cation reactions in solution. They have also linked this work with matrix isolation of radical cations using microporous zeolite reactors. 

Electron Spin Resonance Electron spin resonance measures the effect of micro-waves on a molecule with spin (usually a free radical or triplet) in a magnetic field. The detection can be either through the absorption of microwave energy (conventional ESR) or the effect of a microwave frequency on the emission of light (Fluorescence Detected Magnetic Resonance FDMR). Because the transition energy of the electron in a molecule depends on the interaction of that electron with much of the molecule, spectra have many lines and contain substantial information about the structure of the species being studied. 

Fig.4. Fluorescence detected magnetic resonance spectra of Chi a/b-protein 2 and of Chi a in vitro. For native protein (a) D =...

Searle, G.F.W., Koehorst, R.B.M., Schaafsma, T.J., Miller, B.L., and von Wettstein, D. (1981). Fluorescence detected magnetic resonance (FDMR) spectroscopy of chlorophyll-proteins from barley, Carlsberg Res. Comm. 46, 183-194. 

This emission is assigned to fluorescence from the antenna-Bchl-b Sj-state. The fluorescence detected magnetic resonance (FDMR) spectrum given in fig. 2 was obtained in this emission band. (For a recent review on FDMR of bacterial photosynthesis see Hoff. 1982). From this spectrum d was calculated to be (160 + 2) x 10 cm , and e = (38 + 1) x 10 cm This is in good agreement with previously published results obtained with EPR-spectroscopy (Prince et al., 1976). 

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