Hartmann-Hahn transfer frame

Various authors have used different names for Hartmann-Hahn-type experiments that emphasize distinct experimental or theoretical aspects. For example, heteronuclear Hartmann-Hahn transfer in liquids has been called coherence transfer in the rotating frame (Muller and Ernst, 1979), J cross-polarization (JCP Chingas et al., 1981), heteronuclear crosspolarization (Ernst et al., 1991), HEHAHA (heteronuclear Hartmann-Hahn transfer Morris and Gibbs, 1991), and hetero TOCSY (total correlation spectroscopy Brown and Sanctuary, 1991). Homonuclear Hartmann-Hahn transfer has been referred to as TOCSY (Braunschweiler... 

More generally, C = 0 if the effective coupling term 2irI,J J Iy is a zero-quantum operator in the effective field frame that is defined by and Bf (see Section II) and if the effective fields are matched (ly B l = lyyBj 1). Because these conditions are identical with the conditions for efficient Hartmann-Hahn transfer, the approximation... 

Homonuclear Hartmann-Hahn transfer functions for off-resonant CW irradiation have been derived for two coupled spins 1 /2 (Bazzo and Boyd, 1987 Bothner-By and Shukla, 1988 Elbayed and Canet, 1990) and for the AX 2 spin system (Chandrakumar et al., 1990). In the multitilted frame, Hartmann-Hahn transfer functions under mismatched effective fields are related to polarization- and coherence-transfer functions in strongly coupled spin systems (Kay and McClung, 1988 McClung and Nakashima, 1988 Nakai and McDowell, 1993). Numerical simulations of homonuclear... 

In a system consisting of two coupled spins 1/2, Hartmann-Hahn transfer can be conveniently analyzed based on the one-to-one correspondence between the evolution of the density operator in the zero-quantum space that is spanned by the operators (ZQ),, (ZQ)y, and (ZQ) [Eq. (14)] and the magnetization trajectory of a single, uncoupled spin in the usual rotating frame (Muller and Ernst, 1979 Chingas et al., 1981 Kadkhokaei et al., 1991 see Fig. 2). This equivalence can be used for the construction of zero-quantum analogs of well-known composite pulses. Effective phase shifts of the zero-quantum field can be implemented by short periods of precession about the z axis of the zero-quantum frame... 

Based on the correspondence between rf pulses in the usual rotating frame and Hartmann-Hahn transfer in the zero-quantum frame (see Sections II and VIII.C), Mohebbi and Shaka (1991b) introduced an alternative approach for the construction of (band-) selective Hartmann-Hahn transfer. In direct analogy to DANTE sequences (Bodenhausen et al., 1976 Morris and Freeman, 1978) and binomial solvent suppression... 

The first heteronuclear Hartmann-Hahn transfer in the liquid state preceded the homonuclear analogs of the experiment by about two decades. In their seminal paper on nuclear double resonance in the rotating frame, Hartmann and Hahn (1962) focused on heteronuclear polarization transfer in the solid state with the help of two matched CW rf fields with However, in the same paper, Hartmann and Hahn also discussed the coherent heteronuclear transfer of polarization for pairs of /-coupled heteronuclear spins in liquids and reported polarization-transfer experiments between H and P in hypophosphorous acid. Heteronuclear Hartmann-Hahn transfer in liquids with CW irradiation was applied by several groups (Maudsley et al., 1977 Muller and Ernst, 1979 Bertrand et al., 1978a, b Murphy et al., 1979 Chingas et al., 1979a, b, 1981). A detailed analysis of the experiment was presented by Muller and Ernst (1979) and by Chingas et al. (1981). Matched CW irradiation at the... 

The combination of HOHAHA transfer with cross-relaxation in the rotating frame leads to TOCSY-ROESY (TORO) or ROESY-TOCSY (ROTO) experiments (Kessler et al., 1988a Williamson et al., 1992). Two-dimensional hetero-TOCSY-NOESY experiments (Kellogg et al., 1992 Kellogg and Schweitzer, 1993), which combine heteronuclear Hartmann-Hahn transfer with a homonuclear NOESY mixing step, have been used for a P-driven assignment strategy of RNA and DNA spectra. 

The Hartmann-Hahn MQ-CP transfer can be achieved when the rf frequency of spin I in the rotating frame is sufficiently close to one of the SQ or MQ nutation frequencies of spin S, co/ut = oJlf. In the case O/ > co/f, the nutation frequency for a symmetric MQ coherence of order p is given by [222, 229]... 

I must admit that I was only remotely familiar with this work when my associate, Donald Davis, accidentally discovered some persistent artifacts in an experiment now known as rotating frame Overhauser spectroscopy. These artifacts showed magnetization transfer between J-coupled spins and to me the explanation for this transfer looked very similar to the so-called Hartmann-Hahn magnetization transfer, used in sohd state NMR to enhance sensitivity. Once the analogy was clear, it was quite straightforward to improve the magnetization transfer process and to make it work really well. 

The standard cross-polarization scheme due to Hartmann and Hahn requires the simultaneous application of spin-lock fields to both nuclear species, e. g. H and C. For optimum polarization transfer, the amplitudes Beff of the fields effective in the rotating frames of each nucleus have to match the Hartmann-Hahn condition (cf. Section 3.3.1)... 

One approach to improve the electron-nuclear polarization transfer rate in ONP experiments is to adapt time-tested Hartmann-Hahn-type approaches. Groups at Heidelberg and Leiden separately developed similar approaches (respectively dubbed Hartmann-Hahn ONP (HHONP) and nuclear orientation via electron spin locking (NOVEL) ) whereby a spin-lock mw pulse sequence is applied to the electrons such that their frequency in the rotating frame matches the Larmor frequency of the H nuclei in the lab frame. Thus, the formerly forbidden electron/nuclear flip-flop transitions effectively become thermodynamically allowed , improving the efficiency of the polarization transfer compared to MIONP experiments performed outside this Hartmann-Hahn condition. The polarization transfer typically occurs on the ps time scale, generally faster than both the electronic T and the triplet lifetime. ... 

HHCP is a fundamental technique widely used in ssNMR spectroscopy. With this mechanism, the polarization of one nucleus can be transferred to another nucleus [26, 27]. This transfer requires the rotating frame Hartmann-Hahn matching condition to be satisfied ... 

Hartmann and Hahn [39] showed that CP can be achieved when two rf fields Bin and B c = 4Bih are simultaneously applied. Jn/jc = 4, so, when B c = 4Bm energy is transferred between them, or they are cross-polarized, because Tc ic = Th ih (which is called the Hartmann-Hahn match of heteronuclear rotating-frame frequencies). In the CP experiment C nuclei obtain their spin polarization from H nuclei, so, not only do the shorter proton spin-lattice relaxation times determine the repetition rate of... 

The most commonly used 2D nmr technique applied to through-bond interactions is termed (7 ) correlated spectroscopy (COSY), others are total correlation spectroscopy (TOCSY), which allows somewhat longer-range through-bond connectivities to be observed than with COSY, spin echo coherence transfer spectroscopy (SECSY), relayed coherence transfer spectroscopy (RELAY), double quantum spectroscopy (DQNMR) and homonuclear Hartmann-Hahn spectroscopy (HOHAHA). The most commonly used 2D nmr technique applied to through-space interactions is termed nuclear Overhauser effect spectroscopy (NOESY) also used is the closely related rotating-frame NOESY (ROE-SY). 

The technique applied most frequently for heteronuclear dipolar recoupling is cross polarization. Heteronuclear dipolar interactions can facilitate polarization transfer between spins in the doubly rotating frame if two rf spinlock fields with appropriate field strengths are applied simultaneously on both channels. The ratio between the rf field amplitudes and on the proton and the heteronuclear rf channel under MAS at a spinning frequency Vrai has to match the Hartmann-Hahn condition ... 

Although H and nuclei have Larmor frequencies different by a factor of four, Hartmann and Hahn [12] showed that energy may be transferred between them in the rotating reference frame when... 

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