Optical detected ESR

Metalloporphyrins Optically detected ESR, 87, 88 microwave induced delayed phosphorescence, 87, 89 Zeeman spectroscopy, 94 MCD, 95 resonance Raman spectra, 97, 100, 101 ESR, 88,96 photolysis 142 ... 

The observed magnetic field dependence of the rate constants ( o and k ) of radical pair decays shown in Fig. 12-9 can be explained quantitatively by the following procedures (1) We can see from by Eq. (12-24) that ks is represented by the sum of k and k + k. (2) The magnetic field independent kg. values for the reactions in micellar solutions can well be determined with an optical-detected ESR technique, which will be explained in Chapter 14. 

Optical detected ESR spectra of the ion-radical pair (naphthalene)7 (naphthalene) " for 1.15xlO" M naphthalene solution in squalane at room temperature at various microwave fields (Hi). (Reproduced from Ref. [13b] by permission from The American Chemical Society)... 

The sublevel properties of triple excited states of organic molecules have been studied extensively also by ESR spectroscopy. In addition to the ordinary steady-state ESR spectroscopy, time-resolved ESR and optical-detection ESR spectroscopy have also been applied. 

Various optical detection methods have been used to measure pH in vivo. Fluorescence ratio imaging microscopy using an inverted microscope was used to determine intracellular pH in tumor cells [5], NMR spectroscopy was used to continuously monitor temperature-induced pH changes in fish to study the role of intracellular pH in the maintenance of protein function [27], Additionally, NMR spectroscopy was used to map in-vivo extracellular pH in rat brain gliomas [3], Electron spin resonance (ESR), which is operated at a lower resonance, has been adapted for in-vivo pH measurements because it provides a sufficient RF penetration for deep body organs [28], The non-destructive determination of tissue pH using near-infrared diffuse reflectance spectroscopy (NIRS) has been employed for pH measurements in the muscle during... 

Because electrochemistry provides a unique controlled means of adding or subtracting electrons to or from a compound, it can be used to produce transiently stable species for study by other physical methods such as optical and ESR spectroscopy and mass spectroscopy. Conversely, electrochemistry is an especially sensitive means for the detection of reaction products from photolysis and pyrolysis reactions. 

The charged quasiparticles can be probed by electrical dc conductivity measurements (for polarons), magnetic susceptibility (for polarons and bipolarons), electron-spin resonance (ESR) (for polarons) and optical measurements (for polarons and bipolarons). As ESR is well suited for studying spin-carrying polarons, optical modification of the ESR (optically detected magnetic resonance ODMR) can be applied to link the emissive or absorbing properties of the polymer with its spin state. 

Methods of determination of used ESR Laser flash photolysis (LFP) with IR or optical detection. 

FIGURE 11. Optical detection of ESR of the triplet state of benzophenone showing the fine and superfine structure of aNL = 1 transitions. 

PMDR distinguishes this field from the general field of optical microwave double resonance (OMDR) by being confined to the studies of the magnetic, radiative, nonradiative, and structural properties of the lowest triplet state of molecules that exhibit phosphorescence radiation. Titles such as optical detection of ESR transitions are not correct since the interest in this field goes beyond the magnetic properties of the triplet state. 

As has been observed in ESR, transfer hyperfine interaction resulting from the transfer of a small but finite electron spin-density from the excited triplet state of a guest to the nucleus of the host has also been optically detected (60) in zf, as was observed in ESR (61,62). 

The main advantages of the optical detection of zf transitions are (a) the need of using single crystals and magnets is eliminated (b) zf transitions for very shortlived triplet states may be detected as long as the short lifetime is a result of an allowed radiative process and (c) the cost of the experimental set-up is not as high as the ESR equipment. The disadvantages are (a) a liquid helium set-up is required, at least at the present time,... 

Multiple Types of Copper in One Enzyme. When the blue copper oxidases were first investigated, attention naturally centered on the copper responsible for the intense blue color and the highly unusual ESR signal. Since both the unique optical and ESR parameters of the Cu(II) disappeared when the proteins were denatured, any more normal Cu(II) detected by ESR in these proteins was most often attributed to denatured enzyme (60). However, as more extensive studies on homogeneous samples of the blue copper oxidases were carried out, it became clear that... 

Pulse radiolysis studies using optical detection suggested the main species in equilibrium to be the ot-aminoalkyl radical (31) and the A -protonated ot-aminoalkyl radical (32) whereas results from ESR studies were indicative of protonation at the a-carbon site to form the iV-centered radical cation (30). A subsequent study showed that these results could be attributed to kinetic and thermodynamic factors [84]. Thus iV-protonation resulting in the formation of 32 is kinetically favored and is hence observed in the short time-scales involved in pulse-radiolysis systems. In the longer times involved in ESR measurements the thermodynamically more stable N-centered radical cation will be observed. The pA a of 30 and 32 were estimated as 8.0 and 3.6 by use of pulse radiolysis [84]. Using the equation for similar keto enol tautomerism of barbituric acid [97], the ratio of 30/32 was estimated to be 10 /10 = 10", indicating the N-centered radical (30) to be the predominant protonated species. 

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