Doubly selective

Doubly selective ID-TOCSY experiments have been proposed to specifically transfer in-phase magnetization from two designated spins [57, 58]. This transfer will only take place if the two spins are connected by a scalar coupling. This method is achieved by using a double-selective spin-lock after the selective excitation of transverse magnetization of a desired spin. The doubly selective spin-lock can be obtained by using cosine-modulated... 

Sjj 1/2) are also characteristic for many selective homonuclear Hartmann-Hahn experiments based on doubly selective rf irradiation (see Section X.C). 

For highly selective Hartmann-Hahn transfer between two spins i and j with offsets p, and Vj, Konrat et al. (1991) introduced an attractive alternative to CW irradiation. Their method, named doubly selective HOHAHA, is based on the use of two separate CW rf fields with identical amplitudes pf, which are irradiated at the resonance frequencies p, and Vj of the spins, between which polarization transfer is desired. In the limit I / I I. Vjl this experiment is the exact homonuclear analog of het-eronuclear Hartmann-Hahn transfer (Hartmann and Hahn, 1962), where matched rf fields are irradiated at the resonance frequencies of two different nuclear species (see Section XI). If the necessary hardware for pulse shaping is available, doubly selective homonuclear irradiation can be... 

Jij/2, in complete analogy to the heteronuclear case (Chingas et al., 1981 Ernst et al., 1991). The concomitant increase of the transfer time by a factor of 2 is characteristic for heteronuclear and doubly selective homonuclear Hartmann-Hahn transfer. During doubly selective irradiation, mismatched spins m are effectively decoupled if c vf and Jim and the three spins i, j, and m approach an effective POO... 

Polarization can be transferred simultaneously within several spin pairs without cross-talk if different rf amplitudes are used for each pair of spins in the multiply selective irradiation scheme. This principle has been used in Hartmann-Hahn Hadamard spectroscopy (HAHAHA), where a phaseencoding scheme is used to separate simultaneously acquired spectra that represent individual doubly selective Hartmann-Hahn transfer experiments (Kupce and Freeman, 1993e). 

In the CABBY-2 sequence the numbers in parentheses indicate the amplitude of the individual rf pulses in units of kilohertz, scaled for applications at 600 MHz. With an rf amplitude of 1.6 kHz, the CABBY-4 sequence effects selective transfer between the 3, 4, 5, and 5" protons in the deoxyribose moiety of DNA at 600 MHz. Additional highly selective and band-selective sequences based on doubly selective irradiation schemes are discussed in Section X.C. 

In the homonuclear case, the synchronous and matched irradiation at two frequencies and Vj can be implemented by placing the transmitter midway between the selected frequency ranges Rj and Rj and by modulating a band-selective multiple-pulse sequence with cos r(i, — Vj)/2]. This method can be regarded as an extension of the doubly selective HOHAHA experiment (Konrat et al., 1991), where a weak square pulse, rather than a multiple-pulse sequence, is amplitude-modulated. Implementations based on the principle of interleaved DANTE sequences (Morris and Freeman, 1978 Patt, 1992 Kupce and Freeman, 1992c) are also feasible. 

Sjj < cos (Shaka et al., 1988 Bax et al., 1990b) Hence, doubly selective Hartmann-Hahn transfer with s, = 1/2 is, in general, advantageous if vj - > 2 I. Shirakawa et al. (1995) used doubly selective WALTZ-16... 

If the coupling constants are known in advance, the total mixing time can be reduced in multiple-step selective coherence-transfer experiments by using the selective homonuclear analog of the optimized heteronuclear two-step Hartmann-Hahn transfer technique proposed by Majumdar and Zuiderweg (1995). In this technique [concatenated cross-polarization (CCP)] a doubly selective transfer step (DCP) is concatenated with a triple selective mking step (TCP). For the case of a linear three-spin system with effective planar coupling tensors, a CCP experiment yields complete polarization transfer between the first and the third spin and the total transfer... 

The two-dimensional PICSY experiment (pure-in-phase correlation spectroscopy Vincent et al., 1992, 1993) can also be regarded as a highly selective E.TACSY experiment. In these experiments, coherence transfer is accomplished by doubly selective rf irradiation with relatively low rf amplitudes, which are on the order of 50 Hz for each sideband. Hence, the polarization state of a passive spin remains essentially undisturbed if mir where is the smallest frequency difference between... 

Broadband Hartmann-Hahn transfer can also be of assistance in alternative approaches to determine coupling constants that do not rely on E.COSY-type multiplets that are separated by large one-bond couplings. The homonuclear two-dimensional PICSY (pure in-phase correlation spectroscopy) experiment (Vincent et al., 1992, 1993), which is based on selective Hartmann-Hahn transfer using doubly selective irradiation, can... 

Mismatch-optimized IS transfer Nuclear Overhauser enhancement Nuclear Overhauser effect spectroscopy Numerically optimized isotropic-mbdng sequence Preservation of equivalent pathways Pure in-phase correlation spectroscopy Planar doubly selective homonuclear TACSY Relayed correlation spectroscopy Radiofrequency... 

The selection of protons coupled to is followed by the standard Si- H correlated experiment. As a result isotopomers containing both and Si isotopes are selected and the Si- C coupling can be measured in the indirectly detected dimension (see Figure 15). In a closely related experiment [91] the first 90° X pulse is also substituted by a doubly selective pulse in order to improve suppression of unwanted peaks. Not only is the Si- C coupling... 

Figure 14 The BIS HMQC pulse sequence. The first 90° proton pulse in the standard HMQC experiment is substituted by a doubly selective 90° pulse. Dec. = decoupling, bisel = doubly selective pulse...

Harman. Yamaguchi and co-workers next reported an extensive heteronuclear long-range correlation study of the pyridoindole alkaloid harman (15) involving both and The authors employed and compared several pulse sequences in their study including /-HMBC, selective /-HMBC, and doubly selective /-HMBC experiments. Their study is also atypical in that they report the measurements of the various "/nh coupling constants observed for harman. 

Figure 8.45. A general scheme for implementing the doubly selective ID TOCSY-NOESY experiment for observing NOEs originating from hidden resonances. The selectivity of the 180° pulses may be optimised independently for the two target resonances 1 and 2.

Figure 8.46. The application of a doubly selective IDTOCSY-NOESY experiment to reveal NOEs from the buried resonance of 8.14. Trace (b) shows the ID-TOCSY from the resolved used in preparation to reveal the shift of 114 (r = 80 ms) and trace (c) shows the full TOCSY-NOESY combination selecting the target resonances (labelled in red) of Hl and H4 respectively (t = 80 ms TOCSY, 4(X) ms NOESY). Each transfer step included zero-quantum filtration as described above.

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