Carr-Purcell-Meiboom-Gill pulse

In electron spin echo relaxation studies, the two-pulse echo amplitude, as a fiinction of tire pulse separation time T, gives a measure of the phase memory relaxation time from which can be extracted if Jj-effects are taken into consideration. Problems may arise from spectral diflfrision due to incomplete excitation of the EPR spectrum. In this case some of the transverse magnetization may leak into adjacent parts of the spectrum that have not been excited by the MW pulses. Spectral diflfrision effects can be suppressed by using the Carr-Purcell-Meiboom-Gill pulse sequence, which is also well known in NMR. The experiment involves using a sequence of n-pulses separated by 2r and can be denoted as [7i/2-(x-7i-T-echo) J. A series of echoes separated by lx is generated and the decay in their amplitudes is characterized by Ty. ... 

CPMG pulse sequence Carr-Purcell-Meiboom-Gill pulse sequence. A pulse sequence used for removing broad signals from a spectrum by multiple defocusing and refocusing pulses. 

D. G. Hughes and G. Lindblom, "Baseline drift in the Carr-Purcell-Meiboom-Gill pulsed NMR experiment," J. Magn. Resonance 26, 469-479 (1977). 

NMR studies of metals in sohd state non-metallic materials such as zeolites, inorganic complexes, glasses, coals, polymers, metalloproteins, and RNA have been reviewed. The role of solid state NMR spectroscopy in investigating the structural and functional aspects of these materials with no long range order is evaluated. This overview presents several developments of solid state NMR to the study of a variety of metal containing materials. In particular, the use of the quadrupolar Carr-Purcell-Meiboom-Gill pulse sequence for the acquisition of solid state NMR spectra of quadrupolar nuclei with low natural abundances and low NMR frequencies, and applications of solid state Cd NMR are covered in detail. 

Carr-Purcell-Meiboom-Gill pulse sequences. The spectra were dominated by the second-order quadrupolar interaction. 

CPMG (Carr-Purcell-Meiboom-Gill) pulse sequence to odd-half-integer quadrupolar spin systems. It was found that QCPMG (controlled CPMG) can be one order of magnitude more sensitive than quadrupolar echo MAS experiments. Assisted by numerical simulation, the QCPMG MAS experiments can be used to determine the quadrupolar as well as chemical shift tensors. ... 

Fig. 23a-c. Relative amplitude of the slowly decaying tail of the transverse relaxation curve measured in a linear polyethylene (PE), b polydimethylsiloxane (PDMS), and c polytetrahydrofuran (PTHF) as a function of the molecular mass [36], The data have been recorded with standard Hahn echo and Carr/Purcell/Meiboom/Gill pulse sequences. The values of the critical molecular weight are indicated on the abscissa axes. Extrapolating the data for M - Mc suggests q l as predicted by the whip model (Eq, 167)... 

Measurement of a true T2 can be obtained using a spin-echo pulse sequence, such as the Carr-Purcell-Meiboom-Gill (CPMG) sequence, which minimizes the loss of phase coherence caused by inhomogeneities (Kemp, 1986). 

T2 measurements usually employ either Carr-Purcell-Meiboom-Gill (CPMG) [7, 8] spin-echo pulse sequences or experiments that measure spin relaxation (Tlp) in the rotating frame. The time delay between successive 180° pulses in the CPMG pulse sequence is typically set to 1 ms or shorter to minimize the effects of evolution under the heteronuc-lear scalar coupling between 1H and 15N spins [3]. 

Figure 10.7 Carr-Purcell-Meiboom Gill (CPMC) sequence and NMR signal. (A) CPMC pulse sequence, (B) CPMC decay signal, and (C) Laplace inversion of the CPMC decay signal.

The trick introduced by Meiboom and Gill (14) is to dephase all n pulses in the Carr Purcell train by an angle of 90° with respect to the initial ti/2 pulse. It is easily shown that, without this phase change, imperfections of the 71 pulses are cumulative, whereas with the 90° phase change, a self-compensation occurs for all echoes of even number. The CPMG (Carr-Purcell-Meiboom-Gill) experiment can be handled in two ways ... 

Spin-spin relaxation times T2 are determined by the Carr-Purcell-Meiboom-Gill spin echo pulse sequence and provide information about slower molecular motions (66,67). 

Values of the spin-spin relaxation-time (Tz) for individual spectral lines may be measured by Fourier transformation of the echoes produced by a Carr-Purcell-Meiboom-Gill type of pulse sequence,174 but only in a simple manner, if there is no homonuclear spin-coupling present.175 Refocusing of the dispersing magnetization-vector by... 

Ti reports on fast dynamics on a timescale of ps-ns, whereas T2 relaxation depends on both fast and slower dynamics (ps-ns and xs-ms). The experimentally measured T2 relaxation times include an exchange contribution that can be measured by a Carr-Purcell-Meiboom-Gill (CPMG) pulse train (25, 26) or an effective spin-lock field (27-29). The combination of T2 and Tip measurements allows determination of the contribution of chemical exchange to the relaxation time. Eurthermore, relaxation dispersion experiments have been developed to measure slow time-scale xs-ms dynamic processes (30-35). 

ID, one-dimensional 2D, two-dimensional 3D, three-dimensional AMP, adenosine monophosphate CNDO, complete neglect of differential overlap COSY, correlation spectroscopy CPMG, Carr-Purcell-Meiboom-Gill NMR pulse sequence CT, constant time dAMP, deoxyadenosine monophosphate DFT, density functional... 

As a biologically relevant example of solid-state NMR on quadrupolar nuclei. Fig, 11 shows experimental and simulated Zn solid-state NMR spectra of zinc diimidazole diacetate which may be considered a model compound for Zn in metalloproteins. The experimental spectrum was obtained by sampling the FID in between the refocusing pulses in a quadrupolar version of the Carr-Purcell-Meiboom-Gill experiment (QCPMG), 5 In this manner, the hundred kHz wide second-order quadrupolar powder pattern is split into a manifold of spin-echo sidebands with the consequence of highly... 

The T2 of the mobile phase is determined by a Carr-Purcell-Meiboom-Gill (CPMG) pulse sequence in that work. Based on an easily accessible NMR parameter, i.e., T2, the above empirical correlation, which is claimed by the... 

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