Calculation of Coherence-Transfer Behavior under Planar versus Isotropic Mixing Hamiltonians and Application to HeteronuclearJCross-Polarization Experiments in Solution-State NMR Spectroscopy

✍ Scribed by V.V. Krishnan; Mark Rance

• Publisher: Elsevier Science
• Year: 1997
• Tongue: English
• Weight: 133 KB
• Volume: 124
• Category: Article
• ISSN: 1090-7807
• DOI: 10.1006/jmre.1996.1037

✦ Synopsis

The heteronuclear J cross-polarization technique has been only appropriate for a two-spin system, while calculations involving three or more spins require the use of the proper demonstrated by a number of groups to be an effective means for achieving coherence transfer in solution-state NMR spec-Hamiltonian; use of the ZTOCSY program with its isotropic mixing Hamiltonian is invalid in the application described troscopy (1). While the majority of modern experiments rely on the approach of ''spin-order transfer by RF pulses'' (1), by Kellogg and Schweitzer. None of the qualitative conclusions in the Kellogg and Schweitzer study are affected by the such as the INEPT (2) or DEPT (3) techniques, for effecting the desired transfer of spin order among nuclear spins of computational error, but the quantitative results are modified somewhat. Some aspects of the distinct nature of coherence different species, the general approach of ''spin-order transfer under an average Hamiltonian'' (1) has some advantages transfer under isotropic mixing and J cross polarization have been explicitly described by Chandrakumar and co-workers in a number of specific situations (1,(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14). Of relevance for the present paper is the work of 16), and implicitly by a number of groups.

In the discussions below, we will use the following, some-(9-11), which demonstrated very well the advantages of the heteronuclear cross-polarization technique in transferring what loose, nomenclature. The acronym TOCSY (total correlation spectroscopy) will be used, as it was originally de-spin order between 31 P and 1 H nuclei in nucleic acids. As Kellogg and co-workers, as well as others (12), have pointed fined (18), to refer to coherence transfer in a homonuclear spin system under the influence of an isotropic mixing Ham-out, the cross-polarization techniques can have a sensitivity advantage over INEPT methods when both heteronuclear iltonian (vide infra). The acronym CP (cross polarization)

will refer to coherence transfer between spins of different and homonuclear coherence-transfer steps are desirable, since both processes occur simultaneously under the influ-nuclear species under the influence of a planar coupling Hamiltonian (19) of the general form H Å pJ(I y S y / I z S z ). ence of the cross-polarization Hamiltonian.

The purpose of the present Note is to address a specific In the original applications of CP experiments, on-resonance CW RF fields were applied to the two nuclear species, with aspect of the theoretical calculations presented by Kellogg and Schweitzer (11) for the coherence-transfer behavior in the relative amplitudes fulfilling the Hartmann-Hahn matching condition (4, 20, 21). However, in current applications the heteronuclear ( 1 H, 31 P) spin system present in dinucleotide fragments. These calculations employed a computer pro-in solution-state studies, phase-modulated RF schemes are normally employed to increase the spectral bandwidth over gram (ZTOCSY) which was written specifically to simulate coherence-transfer behavior in homonuclear spin systems which efficient, heteronuclear coherence transfer can be achieved (1). The CP sequences typically employed, such under the influence of an isotropic mixing Hamiltonian (17). Kellogg and Schweitzer indicated that the program was used as DIPSI-2 (22) applied to each nuclear species, are generally quite effective at promoting homonuclear coherence transfer in their study without modification, and that the presence of heteronuclear spins was taken into account by scaling down as well; thus, we shall use the term CP-TOCSY to refer to the case where heteronuclear coherence transfer via an the heteronuclear coupling constants by 50%, to reflect the reduced rate of coherence transfer between two spins of effective, planar Hamiltonian and homonuclear transfer via an isotropic mixing Hamiltonian occur simultaneously. We different nuclear species compared to that between two spins of the same species. However, as we shall demonstrate be-avoid the use of the term hetero-TOCSY, as this should perhaps be reserved for the situation in which an ''isotropic'' low, merely scaling the heteronuclear coupling constant is 205