โ Scribed by K.J. Jung; J.S. Tauskela; J. Katz
No coin nor oath required. For personal study only.
New double-quantum filtering (DQF) schemes are theoretically phase in the pulse sequence, has been maintained ( 1developed by reformulating the equations describing the double-3, 14 -16 ) , except for improvement of phase-cycling quantum (DQ) signal. The equations describing the second-and schemes to eliminate some unwanted signals or to select third-rank DQ signals are simplified by restricting the RF phases as the specific coherent pathway ( 17 -19 ) .
required for DQF. The equations are then factorized into two terms However, the conventional DQF scheme has some underepresenting the separate contribution to the DQ signal from the RF sirable properties. One undesirable property is that the thirdpulses involved in the preparation and evolution times. This allows rank DQ signal is extremely sensitive to the flip angles (u) analysis of the DQ signal of a particular DQF scheme separately for of the creation and readout RF pulses. As u deviates from each of these times in a concise manner. By use of the reformulated 90ะ to 54.7ะ or 125.3ะ, the third-rank DQ signal declines equations, the conventional DQF scheme is shown to be only one of rapidly to null. This property may decrease the attainable four possible DQF schemes. The three new DQF schemes offer some desirable properties over the conventional DQF scheme. In the con-DQ signal due to the inhomogeneous RF field over the samventional DQF scheme, the third-rank DQ signal declines rapidly ple volume such as in the case of excitation with a surface to null as the flip angles of the creation and readout RF pulses RF coil (7). In addition, since the functional form of this deviate from 90ะ to 54.7ะ or 125.3ะ. In addition, the second-and sensitivity to u is different from those for the second-rank third-rank DQ signals in the conventional DQF scheme are opposite DQ signal and the triple-quantum signal, the comparison of in their polarities, resulting in attenuation of the total DQ signal the third-rank DQ signal with other multiple-quantum sigdue to destructive interference between them. In one of three new nals can be inaccurate for an inhomogeneous RF field or DQF schemes, the DQ signal does not vanish at 54.7ะ and 125.3ะ, an inaccurate RF flip angle (13, 20). Another undesirable but varies smoothly with the same functional dependence on the property is that the second-and third-rank DQ signals are RF flip angles as the second-rank DQ and triple-quantum signals.
opposite in their polarities, resulting in attenuation of the Furthermore, in two of the three new DQF schemes, the secondand third-rank DQ signals have the same polarity so that the total total DQ signal through destructive interference between DQ signal may be enhanced through constructive interference bethem (9-13).
tween them. These features of new DQF schemes have been con-In the conventional derivation of the equations for the firmed experimentally.
๐ SIMILAR VOLUMES
The homonuclear dipolar coupling of a directly bonded 13 C-13 C pair has been used to create a dipolar double-quantum filter (D-DQF) to remove the natural-abundance 13 C background in 13 Cf 2 Hg rotationalecho double-resonance (REDOR) experiments. The most efficient version of this experiment has th
Methodology for the assignment of 13 C CPMAS spectra is still in its infancy. Previous methods of CPMAS spectral editing have utilized differences in the strength of the 13 C-1 H dipolar interaction or the rate and spin thermodynamics of crosspolarization from protons to carbon, to differentiate bet