Spin echo spectra

Fig. 4. Neutron spin echo spectra for the self-(above) and pair-(below) correlation functions obtained from PDMS melts at 100 °C. The data are scaled to the Rouse variable. The symbols refer to the same Q-values in both parts of the figure. The solid lines represent the results of a fit with the respective dynamic structure factors. (Reprinted with permission from [41]. Copyright 1989 The American Physical Society, Maryland)...

Fig. 3.29 Neutron-spin echo spectra from polyethylene melts of various molecular weights. The Q values correspond to squares Q=0.03 A circles Q=0.05 A triangles (up) Q=0.077 A diamonds Q=0.096 A triangles (down) Q=0.115 A crosses Q=0.15 k Filled symbols refer to a wavelength of the incoming neutrons A=8 A and open symbols refer to A=15 A. For lines, see explanation in text (Reprinted with permission from [71]. Copyright 2002 The American Physical Society)...

Extensive analysis of the EPR and redox behavior of this unusual copper protein led to the hypothesis that the protein might contain a Cu(A) site similar to that in cytochrome oxidase (Riester et ai, 1989) and that the unusual seven-line EPR is due to the Cu(A)-type site. An alternative interpretation of this EPR is based on electron spin-echo spectroscopy as well, and that is that the seven-line EPR is due to a half-met Cu—Cu pair and to unusual type I sites (Jin et ai, 1989). Three sets of spin-echo peaks can be attributed to nitrogens on imidazole ligands to a CuA-type site and to another imidazole on the half-met site. The electron spin-echo spectra of cytochrome oxidase are similar, although there is not enough copper in cytochrome oxidase for a half-met site. Conceivably, the property of delocalization of the paramagnetic electron could be effected by the proposed bridging between Cub and heme as (nomenclature summarized by Capaldi, 1990), which are proposed to be 3-4 A apart. 

Diffusion-ordered spectroscopy (DOSY)45 is a NMR spectroscopic technique that separates the NMR signals of different compounds according to their diffusion coefficient (D, their rate of diffusion in a particular medium). A series of spin echo spectra is measured with different pulsed field gradient strengths, and the signal decays are fitted to give diffusion coefficients for each compound present. In 2D DOSY this... 

Experimental three pulse electron spin echo spectra of Ag (A) in Lij2 A zeolite. The two large sharper peaks below 1 ps are due to two pulse interference. 

Cu isotopes both with nuclear spin I-3/2. The nucle r g-factors of these two isotopes are sufficiently close that no resolution of the two isotopes is typically seen in zeolite matrices. No Jahn-Teller effects have been observed for Cu2+ in zeolites. The spin-lattice relaxation time of cupric ion is sufficiently long that it can be easily observed by GSR at room temperature and below. Thus cupric ion exchanged zeolites have been extensively studied (5,17-26) by ESR, but ESR alone has not typically given unambiguous information about the water coordination of cupric ion or the specific location of cupric ion in the zeolite lattice. This situation can be substantially improved by using electron spin echo modulation spectrometry. The modulation analysis is carried out as described in the previous sections. The number of coordinated deuterated water molecules is determined from deuterium modulation in three pulse electron spin echo spectra. The location in the zeolite lattice is determined partly from aluminum modulation and more quantitatively from cesium modulation. The symmetry of the various copper species is determined from the water coordination number and the characteristics of the ESR spectra. 

Experimental three pulse electron spin echo spectra of two types of Chi in Na -A zeolite. Chi (( (D-CO-is the dominant copper species in site S2 in freshly prepared, hydrated Nai2 A and Cu +(0z)j(D20)2 in site S2 is the dominant species after partial dehydration under vacuum at room temperature. The different deuterium modulation depths characterize the different numbers of coordinated waters in these two Cu species. 

Figure 5.8 H spin-echo spectra of (a) y-Al203(without Al irradiation), (b) S03/y-Al203(without Al irradiation), (c) SOfy-Al203(with Al irradiation), (d) difference spectrum of (b) and (c). Asterisks denote spinning sidebands. Adapted from ref [49] reprinted with permission from the Royal Society of Chemistry.

Figure 8.35. A selection of " Zr NMR spectra. A. Stepped-frequency spin-echo spectra of 3 phases of Zr02, adapted from Bastow (1994). B. 14.1 T MAS NMR spectra of Ba and Sr zirconates. Asterisks denote spinning side bands. Note the broader lineshape with possible quadrupolar structure of the more distorted Zr site in SrZrO. From Dec et al. (1993), by permission of the American Chemical Society. C. Static stepped-frequency NMR spectrum of Na2ZrSi05. 1996. D. Stepped-frequency NMR spectrum of Zr metal (lower) with simulated spectrum (upper). 1992. D. Static Zr NMR spectrum of the central transition of A Zr. From Bastow et al. (1992, 1996, 1998b), by permission of the copyright owners.

Fig. 27a-c P A1 /-Resolved experiment on AIPO4 berlinite, acquired with Uj=13 kHz a pulse sequence hi, cl time and frequency domains of the Al spin-echo spectra (no P pulse) b2, c2 time and frequency domains of the P A1 /-Resolved spectra (symbols) with their modelling (continuous line). Reprinted with permission from [72], Massiot D et al. (2003) J Mag Reson 164 160-164. Copyright (2003) Elsevier Science... 

Figure 1.28 Experimental (solid lines) and simulated (dashed lines) spin-echo spectra of 6F-Trp41-M2TMD at 6.5 kHz MAS at pH 5.3 (a) and pH 8.0 (b). Side-chain conformations (bottom view) of Trp41 (blue) and His37 (green) in the TM channel structure of the homo-tetrameric M2 protein are shown to the right side of the spectra. At pH 8.0, the structural parameters implicate an inactivated state, while at pH 5.3 the tryptophan conformation represents the activated state. See color plate 1.28.

In biofluids with high protein or lipid contents, spin-echo spectra must normally be employed to eliminate broad resonances. 

In single pulse and spin-echo spectra of normal human and animal plasma, there are few resonances in the chemical shift range to high frequency of 85.3 when measured in the pH range 3 to 8.5. However, on acidification of the plasma to pH <2.5, resonances from histidine and phenylalanine become detectable. In plasma from patients with Wilson s disease (liver degeneration secondary to an inborn error of caeruloplasin/copper metabolism), weak signals from histidine and tyrosine are seen in spin-echo spectra at pH 7.6, but... 

Fig. 19. Calculated intensities of C U1 multiplets of fluxional (RLi) aggregates in Li /-modulated spin-echo spectra as a function of evolution time for = 2 (—), 3 (...), 4 (-------). Data from ret 26.

Fig. 14.7. ID static C NMR spectra for a biaxially drawn PET film with its machine direction (MD) parallel to the receiver coil axis. Spectra (a) and (b) were obtained after cross-polarization and a Hahn spin echo. Spectra (c) and (d) were obtained with single-pulse excitation using a 1-s recycle delay, which selects for the most highly mobile segments. Little orientation dependence is observed for the mobile components.

The investigator thus has the option of searching for quaternaries which might be masked by protonated carbons by setting X = 1/2J or, it might be more desirable to sort by CH/CH3 and CH2/C. It is also possible to combine normal spin-echo and modulated spin-echo spectra to arrive at edited subspectra containing only carbons of one type (6,14-17). 

The SPEMAS technique has the advantage to be quantitative if the recycle delay is well calibrated as a function of the spin-lattice relaxation times (TO previously measured on each signal. However, CP experiment is not much applied for quantitative aspects because the signal intensities are not only dependant of the total nuclei concentrations but also of their dynamics. In order to get quantitative reliable data fi om CPMAS data, a series of spectra have been recorded in order to exactly determine the match of optimum cross polarization, the proton decoupling power, the pulse width and the delay times. These parameter calibrations are essential before further analyses even if they take a long time. Concerning the spin-echo experiment, the low intensity of signals for few transients excluded precise parameter calibration. Anjnvay, measurements of spin-spin relaxations times (T2) is necessary for reliable quantification of spin-echo spectra. 

The 31p spin echo spectra were recorded under static conditions, using a 90°x-t-180°y-t- (acquire sequence). The 90° pulse was 4.2 ms and t was 20 ps. For each sample, the irradiation frequency was varied in increments of 100 kHz above and below the 3ip resonance of H3PO4. The number of spectra thus recorded was dictated by the frequency limits beyond which no spectral intensity was visible. The 3lp NMR Spin Echo Mapping information was then obtained by superposition of all spectra. 

Fig. 36. Dealuminated mordenite. H spin-echo spectra [98D1]. The samples were calcinated at 823 K for 2 h (a) without Al irradiation and (b) with Al irradiation (on resonance). The difference spectrum of (a) and (b) is shown in (c). (d) H/ Al TRAPDOR fractions (1 - ///q) for dealuminated mordenite as function of the Al irradiation frequency offset [98D1].

Figure 24. Part of the 7-modulaled "C NMR spin-echo spectra of camphor. Note the distinction between the C-3 methylene and the C-4 methine carbons with a shift difference of only 0.3 ppm.

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