Carr/Purcell/Meiboom/Gill spin

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). 

When a spectrum has severely broadened resonances in the presence of less broadened resonances, it is possible to use a Carr-Purcell-Meiboom-Gill spin-echo sequence to remove the broadened resonances, facilitating the interpretation of the remaining signals. By setting certain parameters of the sequence, it is possible to progressively remove peaks with less and less broadening. ... 

Another way to detect slow motions is by deuteron transverse spin relaxation experiments using a modified Carr-Purcell-Meiboom-Gill spin echo pulse sequence [42-44]. Information about the dynamics of liquid crystals can be retrieved from the frequency dispersion (see Fig. 2) and the anisotropy of relaxation rates. 

Carr-Purcell-Meiboom-Gill spin echo pulse sequence 599... 

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. ... 

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]. 

R. Lefort, J. W. Wiench, M. Pruski and J.-P. Amoureux, Optimization of data acquisition and processing in Carr-Purcell-Meiboom-Gill multiple quantum magic angle spinning nuclear magnetic resonance. /. Chem. Phys., 2002,116, 2493-2501. 

Carr-Purcell-Meiboom-Gill nuclear quadrupolar coupling constant receptivity relative to aH electric field gradient nuclear spin quantum number magic-angle spinning... 

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). 

Static imaging experiments conducted on fluid-saturated samples are used to determine porosity distributions. Carr-Purcell-Meiboom-Gill (CPMG) imaging is used to evaluate the spin density. The local relaxation is modeled in order to estimate the intrinsic magnetization intensity, which is proportional to the amount of saturating fluid. 

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... 

When NMR was performed the media hydrated with 1 1 H20 D20 were packed in 10 mm NMR tubes to reach a sample height of 8 to 10 mm. A 90° pulse WALTZ sequence was used with acquisition parameters 7.45 to 780 /AS pulse width, 1500 to 20,000 Hz pulse width, 0.012 to 0.166 sec acquisition time and recycle delay > 5Ti. Spin-spin relaxation time (T2) was determined with a Carr-Purcell-Meiboom-Gill (CPMG) pulse sequence with interpulsed spacing (t) ranging from 5 to 500 ms. At least eight different T values were used for each T2 determination. 

CPMG Carr-Purcell-Meiboom-Gill T2-dependent spin-echo sequence 2.4.4... 

As two phases in quadrature will allow Carr-Purcell Meiboom-Gill, T, and or other spin-locking experiments, we recommend this as a minimum. However, providing different rf phases for the transmitter pulses is not difficult and this capability should not increase the cost of the spectrometer very much so you might as well go for four orthogonal phases. As discussed elsewhere, the phase shifts can be performed in the IF stage rather than at the carrier frequency so that one phase shifting network can suffice for all carrier frequencies. 

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