Pulse electron double resonance PELDOR

Weber et al. have developed pulsed electron double resonance (PELDOR) at S-band, and used it to probe the dipolar and exchange interactions in the bis-nitroxides 13 - 16, where in the ester-bridged compounds the exchange interactions are diminished relative to the acetylene-bridged compounds, whilst maintaining a similar separation.10 They also demonstrate distance measurements by this technique. 

Milov, A. D., Maryasov, A. G., and Tsvetkov, Y. D. (1998). Pulsed electron double resonance (PELDOR) and its applications in ffee-radicals research. Appl. Magn. Reson. 15, 107—143. 

The understanding of structure-dynamics-function relationships in oligonucleotides or oligonucleotide/protein complexes calls for biophysical methods that can resolve the structure and dynamics of such systems on the critical nanometer length scale. A modern electron paramagnetic resonance (EPR) method called pulsed electron-electron double resonance (PELDOR or DEER) has been shown to reliably and precisely provide distances and distance distributions in the range of 1.5-8 nm. In addition, recent experiments proved that a PELDOR experiment also contains information on the orientation of labels,... 

Several pulse methods were developed for estimation distances between two slowly-relaxing spins. In a pulse electron-electron double resonance (PELDOR) technique a spin echo is created by a two-pulse sequence at one microwave frequency. The timing of a pulse at a second microwave frequency is varied (Milov et al., 1998). This method is suitable for analysis of weak dipolar interactions. 3-pulse PELDOR with all three pulses at the same microwave frequency ( 2 + 1 sequence) was proposed by Raitsimling and his co-workers (2000). A specific feature of the 2 + 1 technique is suppression of dipolar interaction of randomly distributed spins, which allows the selection of a dipolar interaction between radicals. Using a 4- pulse experiments it was possible to eliminate an inherent dead experimental deadtime that limits the magnitude of the dipolar interaction in 2 + 1 sequence and in 3-pulse ELDOR experiments (Pannier et al., 2000). 

Pulsed methods [82] increase the range of distance sensitivity. They can be used to separate the dipole-dipole interaction from other contributions of the spin Hamiltonian. At very large available microwave power, distances can be measured well by double quantum coherence (DQC) that uses a single frequency. With the power available on commercial spectrometers, double electron electron resonance [DEER, an acronym which is synonymously used with PELDOR (Pulsed Electron Double Resonance)] is the more sensitive technique and is thus most widely applied in the... 

At high peptide concentration (peptide/lipid ratio 1 20 mol mol ), the ESEEM amplitudes were found to change substantially the peak amplitude for the spin-label position near the N-terminus is markedly reduced. Thus, by increasing the concentration of peptide its N-terminus becomes immersed deeper in the membrane - the peptide orientation becomes closer to transmembrane. Data from pulse electron-electron double resonance (PELDOR) showed that the peptide aggregates in the form of dimers, in a head to head configuration. " Transmembrane dimers are long enough and apparently can lead to the formation of channels in the membrane. 

Two traditions have evolved concerning the naming of pulsed electron-electron double resonance, calling these experiments either DEER (double electron-electron resonance) or PELDOR (pulsed electron-electron double resonance). In the ensuing discussion we use each author s preferred designation for their experiments. The absence of a dead-time in the four-pulse DEER experiment is an advantage relative to the three-pulse DEER experiment. When all of the pulses of the three-pulse DEER experiment are at the same frequency, it becomes the 2 +1 pulse sequence.13,14... 

With the basic pulsed ELDOR (PELDOR) sequence shown in Fig. 3a, such a measurement at t = 0 corresponds to overlapping pump and observer pulses. This leads to signal distortions unless the two frequencies are applied to two well-isolated modes of a bimodal resonator. Furthermore, pulses at the two frequencies have to be amplified in two separate high-power amplifiers. The requirement for such specialized hardware and the restriction to a fixed frequency difference imposed by the bimodal resonator is overcome by using the four-pulse double electron-electron resonance (DEER) experiment (Fig. 4b). 

Another class of methods measures inter-spin dipolar interactions using pulses that selectively manipulate different spin populations. The representative of this class, which is widely used in SDSL, is double electron-electron resonance (DEER, also known as PELDOR, Fig. 6). In the dead-time free DEER scheme, a three-pulse sequence is applied to the observer spin (spin A) to generate a refocused echo at a specific... 

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