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ESEEM modulation

ENDOR, the ESEEM modulation depth will increase for nuclei with smaller... [Pg.1579]

Fig. 5 Polarity and proticity analysis, (a) W-band rigid limit spectra of BR (PDB IMOL) spin labeled in the proton channel. The changes in g and are highlighted by vertical lines. Right panel, plots of g and vs nitroxide position showing the hydrophobic barrier in the channel. Adapted from [45]. (b) Structure of LHCIIb (PDB 2BHW) with two lAP spin labels attached with MMM at positions 52 and 196. Right panel, ESEEM traces detected on a water soluble standard (gray) and on the two spin labeled positions. Bottom, ESEEM modulation depths correlated with the water accessibility. Adapted from [47]... Fig. 5 Polarity and proticity analysis, (a) W-band rigid limit spectra of BR (PDB IMOL) spin labeled in the proton channel. The changes in g and are highlighted by vertical lines. Right panel, plots of g and vs nitroxide position showing the hydrophobic barrier in the channel. Adapted from [45]. (b) Structure of LHCIIb (PDB 2BHW) with two lAP spin labels attached with MMM at positions 52 and 196. Right panel, ESEEM traces detected on a water soluble standard (gray) and on the two spin labeled positions. Bottom, ESEEM modulation depths correlated with the water accessibility. Adapted from [47]...
The most basic use of ESEEM is the detection of proximity of nuclei of certain elements to an electron spin (local elemental analysis). This technique is based on the r dependence of the ESEEM modulation depth k for weakly coupled nuclei ... [Pg.47]

The electron-spm echo envelope modulation (ESEEM) phenomenon [37, 38] is of primary interest in pulsed EPR of solids, where anisotropic hyperfme and nuclear quadnipole interactions persist. The effect can be observed as modulations of the echo intensity in two-pulse and three-pulse experiments in which x or J is varied. In liquids the modulations are averaged to zero by rapid molecular tumbling. The physical origin of ESEEM can be understood in tenns of the four-level spin energy diagram for the S = I = model system... [Pg.1578]

More sophisticated pulse sequences have been developed to detect nuclear modulation effects. With a five-pulse sequence it is theoretically possible to obtain modulation amplitudes up to eight times greater than in a tlnee-pulse experunent, while at the same time the umnodulated component of the echo is kept close to zero. A four-pulse ESEEM experiment has been devised to greatly improve the resolution of sum-peak spectra. [Pg.1579]

Advanced EPR techniques such as CW and pulsed ENDOR, electron spin-echo envelope modulation (ESEEM), and two-dimensional (2D)-hyperfine sublevel correlation spectroscopy (HYSCORE) have been successfully used to examine complexation and electron transfer between carotenoids and the surrounding media in which the carotenoid is located. [Pg.168]

Resolvable modulation is detected on a three-pulse echo decay spectrum of predeuterated 3-carotene radical (Gao et al. 2005) as a function of delay time, T. The resulting modulation is known as ESEEM. Resolvable modulation will not be detected for nondeuterated P-carotene radical since the proton frequency is six times larger. The modulation signal intensity is proportional to the square root of phase sensitive detection and interfering two-pulse echoes and suppressed by phase-cycling technique (Gao et al. 2005). Analysis of the ESEEM spectrum yields the distance from the radical to the D nucleus, a the deuterium coupling constant, and the number of equivalent interacting nuclei (D). The details related to the analysis of the ESEEM spectrum are presented in Gao et al. 2005. [Pg.168]

Three-pulse ESEEM spectrum of perdeuterated P-carotene imbedded in Cu-MCM-41 exhibits an echo decay with an echo modulation due to deuterons. The three-pulse ESEEM is plotted as a function of time, and curves are drawn through the maximum and minima. From ratio analysis of these curves, a best nonlinear least-squares lit determines the number of interacting deuterons, the distance (3.3 0.2A), and the isotopic coupling (0.06 0.2MHz). This analysis made it possible to explain the observed reversible forward and backward electron transfer between the carotenoid and Cu2+ as the temperature was cycled (77-300 K). [Pg.169]

Y. Deligiannakis, M. Louloudi and N. Hadjiliadis, Electron spin echo envelope modulation (ESEEM) spectroscopy as a tool to investigate the coordination environment of metal centers, Coord. Chem. Rev., 2000, 204, 1. [Pg.164]

Double-resonance spectroscopy involves the use of two different sources of radiation. In the context of EPR, these usually are a microwave and a radiowave or (less common) a microwave and another microwave. The two combinations were originally called ENDOR (electron nuclear double resonance) and ELDOR (electron electron double resonance), but the development of many variations on this theme has led to a wide spectrum of derived techniques and associated acronyms, such as ESEEM (electron spin echo envelope modulation), which is a pulsed variant of ENDOR, or DEER (double electron electron spin resonance), which is a pulsed variant of ELDOR. The basic principle involves the saturation (partially or wholly) of an EPR absorption and the subsequent transfer of spin energy to a different absorption by means of the second radiation, leading to the detection of the difference signal. The requirement of saturability implies operation at close to liquid helium, or even lower, temperatures, which, combined with long experimentation times, produces a... [Pg.226]

Since the phenoxyls possess an S = ground state, they have been carefully studied by electron paramagnetic spectroscopy (EPR) and related techniques such as electron nuclear double resonance (ENDOR), and electron spin-echo envelope modulation (ESEEM). These powerful and very sensitive techniques are ideally suited to study the occurrence of tyrosyl radicals in a protein matrix (1, 27-30). Careful analysis of the experimental data (hyperfine coupling constants) provides experimental spin densities at a high level of precision and, in addition, the positions of these tyrosyls relative to other neighboring groups in the protein matrix. [Pg.155]

ESEEM Electron spin-echo envelope modulation... [Pg.205]

We do not know exactly where the hydrogen binds at the active site. We would not expect it to be detectable by X-ray diffraction, even at 0.1 nm resolution. EPR (Van der Zwaan et al. 1985), ENDOR (Fan et al. 1991b) and electron spin-echo envelope modulation (ESEEM) (Chapman et al. 1988) spectroscopy have detected hyperfine interactions with exchangeable hydrous in the NiC state of the [NiFe] hydrogenase, but have not so far located the hydron. It could bind to one or both metal ions, either as a hydride or H2 complex. Transition-metal chemistry provides many examples of hydrides and H2 complexes (see, for example. Bender et al. 1997). These are mostly with higher-mass elements such as osmium or ruthenium, but iron can form them too. In order to stabilize the compounds, carbonyl and phosphine ligands are commonly used (Section 6). [Pg.178]

ESEEM See electron spin echo envelope modulation. e,sem or e es e e em eserine See physostigmine. es-3,ren ... [Pg.140]

Electron Nuclear Double Resonance (ENDOR) and Electron Spin-Echo Envelope Modulation (ESEEM)... [Pg.129]

Electron nuclear double resonance (ENDOR) and electron spin-echo envelope modulation (ESEEM) are two of a variety of pulsed EPR techniques that are used to study paramagnetic metal centers in metalloenzymes. The techniques are discussed in Chapter 4 of reference la and will not be discussed in any detail here. The techniques can define electron-nuclear hyperfine interactions too small to be resolved within the natural width of the EPR line. For instance, as a paramagnetic transition metal center in a metalloprotein interacts with magnetic nuclei such as H, H, P, or these... [Pg.129]

ESEEM is a pulsed EPR technique which is complementary to both conventional EPR and ENDOR spectroscopy(74.75). In the ESEEM experiment, one selects a field (effective g value) in the EPR spectrum and through a sequence of microwave pulses generates a spin echo whose intensity is monitored as a function of the delay time between the pulses. This resulting echo envelope decay pattern is amplitude modulated due to the magnetic interaction of nuclear spins that are coupled to the electron spin. Cosine Fourier transformation of this envelope yields an ENDOR-like spectrum from which nuclear hyperfine and quadrupole splittings can be determined. [Pg.385]


See other pages where ESEEM modulation is mentioned: [Pg.6498]    [Pg.1579]    [Pg.6497]    [Pg.582]    [Pg.140]    [Pg.132]    [Pg.108]    [Pg.112]    [Pg.770]    [Pg.175]    [Pg.108]    [Pg.6498]    [Pg.1579]    [Pg.6497]    [Pg.582]    [Pg.140]    [Pg.132]    [Pg.108]    [Pg.112]    [Pg.770]    [Pg.175]    [Pg.108]    [Pg.1584]    [Pg.151]    [Pg.430]    [Pg.63]    [Pg.163]    [Pg.19]    [Pg.93]    [Pg.109]    [Pg.24]    [Pg.133]    [Pg.243]    [Pg.289]   


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