Selective homonuclear

The idea of frequency selectivity is certainly not restricted to J-coupling mediated polarization transfer. Furthermore, frequency selective polarization transfer can also be realized by DQ recoupling techniques. For the technique of shift-evolution-assisted selective homonuclear recoupling (SEASHORE), which employs POST-C7 to construct an effective DQ coupling [82, 83], frequency selective polarization can be achieved when the transmitter offset is set to the... 

Similar selective homonuclear polarization-transfer schemes have been used for the subsequent homonuclear directed transfer of polarization along the polypeptide chain. 

Suchard, S. N., and Melzer, J. E., in Spectroscopic Constants for Selected Homonuclear Diatomic Molecules, Vol. II. Report SAMSO-TR-76-31,1976. 

Fig. 3.4 One pulse experiment with selective homonuclear decoupling...

Although in general, only one multiple-pulse sequence is applied to homonuclear spin systems, it can be useful to apply different multiple-pulse sequences to several nuclear species at the same time by using separate rf channels. In heteronuclear Hartmann-Hahn experiments, the same multiple-pulse sequence is usually applied simultaneously to two or more nuclear species. However, some selective homonuclear Hartmann-Hahn experiments are also based on the simultaneous irradiation of a multiple-pulse sequence at two or more different frequencies (see Section X). If only a single homonuclear rf channel is used, this can be achieved experimentally by adding an amplitude or phase modulation to the sequence, in order to create appropriate irradiation sidebands (Konrat... 

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

Mohebbi and Shaka (1991b) also developed selective homonuclear Hartmann-Hahn experiments based on zero-quantum analogs of DANTE sequences (Bodenhausen et al., 1976 Morris and Freeman, 1978) and binomial solvent suppression methods (Plateau and Gueron, 1982 Sklenaf and Starcuk, 1982 Hore, 1983) (see Section X.C). 

Highly Selective Homonuclear Hartmann-Hahn Experiments... 

Fig. 28. Offset dependence of selective homonuclear Flartmann-Hahn experiments. (A) for CW irradiation along the x axis with vf = 10 kHz. (B) Transfer efficiency for z magnetization during the zero-quantum analog of a 1-2-1 sequence based on FLOPSY-8 with A = 200 /Lis and v/ = 10 kFIz (Mohebbi and Shaka, 1991b).

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... 

Band-Selective Homonuclear Hartmann-Hahn Transfer... 

Selective Homonuclear Hartmann-Hahn Mixing Sequences "... 

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... 

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... 

Figure 5 Band-selective homonuclear H- H WURST decoupling of Si(CH2)CH3 resonances in compound 1 recorded at 400 MHz ( H) frequency on a Varian Unity Plus spectrometer, (a) The ordinary spectrum (b) expansion of the Si-H region of (a) (c) the same as (b) in a band-selectively H- H decoupled spectrum with decoupling band centred on SiCH2 and SiCHj peaks between -0.6 and +0.6 ppm...

Table 2 shows the enthalpies of dissociation of selected homonuclear gaseous species observed during the investigations listed in Table 3. The ion intensities determined are shown in Table 4 for some spedes as an example. Obviously, they decrease strongly if the size of the moleeules increases.

In a homonuclear decoupling experiment a particular multiplet is irradiated suppressing the coupling interaction between the irradiated nucleus and its coupling partners. A comparison of the standard coupled ID spectrum and the selectively homonuclear decoupled spectrum reveals which nuclei are coupled. Whether a homonuclear decoupling experiment or a 2D homonuclear COSY experiment would be the best solution for multiplet analysis in a one-dimensional spectrum depends very much on the nature of the problem under investigation. If a large number of multiplets need to be irradiated then a two-dimension approach may be preferable. 

In recent publications, the 1H and 13C NMR spectra of lovastatin were fuily assigned by the use of selective homonuclear and heteronuclear decoupling and two dimensional techniques (14,15). 

Fig. 7.5 Solution-state H NMR spectrum of is the simple, coupled H NMR spectrum 1-chloroethene and 1-fluoroethene. The results (or the double negative F undecoupled") of of selective homonuclear decoupling are shown 1-fluoroethene, which has twice as many H in (b) and (c). The results of heteronuclear de- transitions as shown in (d) and (e) (each line is coupling are shown in (d) and (e). Not shown then a doublet from /( H— F), n = 2, 3).

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