Spectral width Spin echo

During the acquisition, it is possible to reduce the baseline rolling by using suitable pulse sequences. The most commonly used are the RIDE (ring-down elimination) sequence, first proposed by Ellis7 14 (slightly different from a sequence introduced by Canet et al.15), the ACOUSTIC sequence, proposed by Patt,16 and a series of extended spin-echo sequences.14 However, all these sequences result in inefficient excitation over a wide range of frequencies, and therefore they can be applied only to restricted spectral widths. 

The measurement of one-bond coupling constants from the distance between the multiplet components in HSQC spectrum becomes unreliable for large proteins due to the differential relaxation that can severely broaden one of the components, and even make it undetectable. Luy and Marino proposed to overcome this problem by introduction of J-modulation to the sharp TROSY component. The JE-TROSY experiment starts with a spin-echo J-evolution period, which is followed by a traditional TROSY detection sequence. As the result the resonances are independently modulated by the single-bond coupling, which leads to the displacement of the cross-peak in the independent spectral dimension after the 3D Fourier transformation. This displacement is measured either relative to zero frequency if real FT is used in the J-dimension, or as the splitting between the pseudo multiplet components if the complex FT is applied. The spectral width in the J-dimension is normally set to twice the value of the... 

When the spectral width of the CT is too large to apply spinning-based techniques, the Hahn-echo or quadrupolar-echo sequence can be used to acquire the static spectrum to minimize the distortion of the line-shape owing to the probe ringing. The stationary spectra also contain information about the CSA. If the quadrupolar and the CS interactions both contribute to the line-shape, both the EFG and the CS tensors may be determined. 

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