Double-quantum coherence spectroscopy

Until now the double-quantum coherence spectroscopy has not often been used for silicon frameworks. In double-quanmm coherence spectroscopy the silicon nucleus is almost ten times as sensitive as the C nucleus because of the higher natural abundance of Si (4.7% compared with 1.1% C). Disadvantages of the Si nucleus are the long relaxation times T i) and the negative nuclear Overhauser effect (NOE). In practice, this means that a very long recording time is necessary unless a relaxation reagent such as Cr(acac)3 is used. 

R.P. Mason, G. Cha, G.H. Gorrie, E.E. Babcock, P.P. Antich, Glutathione in whole blood A novel determination using double quantum coherence transfer proton NMR spectroscopy, FEBS Lett. 318 (1993) 30-34. 

By allowing multiple-quantum coherence to process during the evolution period of a two-dimensional experiment, Drobny et al. were able to detect its effects indirectly. This idea subsequently blossomed into the new technique of filtration through double-quantum coherence. Multiple-quantum coherence of order n possesses an n-fold sensitivity to radiofrequency phase shifts, which permits separation from the normal single-quantum coherence. This concept inspired the popular new techniques of double-quantum filtered correlation spectroscopy (DQ-COSY) and the carbon-carbon backbone experiment (INADEQUATE), both designed to extract useful connectivity information from undesirable interfering signals. 

Applying the idea of using multiple quantum coherence to correlate protons has also been explored. Mated and Freeman [60] reported the first experimental demonstration of proton double quantum correlated spectroscopy. The Fi axis in these experiments is used to present H chemical shift in the usual fashion. In contrast, the Fj axis is used for the double quantum frequency axis. Protons correlated to one another via double quantum coherence will exhibit a response in Fj at the algebraic sum of the offsets of the coupled resonances relative to the transmitter frequency. A scant few apphcations have been reported including an exploratory study of strychnine (2) [61] and the structural characterization of the marine natural product plumericin [62],... 

A suit of 2D-NMR techniques that include chemical-shift correlation spectroscopy (COSY), double-quantum filtered correlation spectroscopy (DQF-COSY), total correlation spectroscopy (TOCSY), and heteronuclear multiple-quantum coherence spectroscopy (HMQC) have been used for... 

A modified COSY (two-dimensional correlated spectroscopy) revamped with an asymmetric Z-gradient echo detection (CRAZED) sequence was designed to obtain a better CEST contrast image based on the inter-molecular double quantum coherence method." Experiments were performed on an agar-glucose phantom, and the results demonstrate the feasibility of this method. 

A series of complex cage polysilanes has been synthesized starting from t-BuCl2SiSiCl2Bu-t by Masamune and coworkers . When t-BuCl2SiSiCl2Bu-t is treated with lithium naphthalenide in DME, reductive oligomerization takes place and, somewhat surprisingly, tricyclo[2.2.0.0 ]hexasilane and tetracyclo[3.3.0.0 . 0 ]octasilane derivatives are obtained (Scheme 25). The unexpected structures of the products were established by double quantum coherence Si-NMR spectroscopy and X-ray crystallography. 

To conclude this section on 2D NMR of liquid crystals, some studies of more exotic liquid crystalline systems are pointed out. Polymer dispersed nematic liquid crystals have attracted much attention because of their applications as optical display panels. Deuteron 2D quadrupole echo experiments have been reported [9.28] in the isotropic and nematic phases of / -deuterated 5CB dispersed in polymers. A similar technique was used [9.29] to study two model bilayer membranes. Both studies allow determination of the lineshape F(u ) due to quadrupolar interactions and the homogeneous linewidth L(u ) of the individual lines [9.28]. The 2D quadrupole echo experiment has also been used [9.30] to separate chemical shift and quadrupolar splitting information of a perdeuterated solute dissolved in a lyotropic liquid crystal. The method was compared with the multiple-quantum spectroscopy that is based on the observation of double-quantum coherence whose evolution depends on the chemical shift but not on the quadrupolar splitting. The multiple-quantum method was found to give a substantial chemical shift resolution. The pulse sequences for these methods and their treatment using density matrix formalism were summarized [9.30] for a spin 1=1 system with non-zero chemical shift. Finally, 2D deuteron exchange NMR was used [9.31] to study ring inversion of solutes in liquid crystalline solvents. 

P— P correlations in aluminophosphates, and Si— oi correlations in sodium borosihcate glass and silicate-1. Interestingly, they demonstrated covariance processing in double-quantum correlation experiments employing POST-C7 [71], BABA [72], and INADEQUATE [73]. In double-quantum 2D spectroscopy, time evolution along the indirect dimension is characterized by the frequencies given by the sum of the chemical shifts between the correlated spins so that horizontal pairs of correlation peaks appear as shown in Fig. 3. There, 125 data sets were acquired with a step of 12.5 ps. Thus, the coherence profile during the evolution time was truncated at 1.6 ms. 

Freeman, D., Hurd, R. Metabolic Specific Methods Using Double Quantum Coherence Transfer Spectroscopy. Vol. 27, pp. 199-222 Freeman, R., Robert, J.B. A Brief History of High Resolution NMR. Vol. 25, pp. 1-16 Freude, D., Haase, J. Quadrupole Effects in Solid-State Nuclear Magnetic Resonance. 

Two-Dimensional Double-Quantum Coherence Echo Correlated Spectroscopy (DECSY)... 

Two-dimensional double-quantum coherence NMR spectroscopy has been found useful for analyzing connectivity in spectra as well as Jhh connectivity in spectra. Double-quantum or multiple-quantum filter has also been used for unraveling complex, overlapping H-NMR spectra. A new... 

M. Ikura and K. Hikichi, Two dimensional double quantum coherence echo correlated spectroscopy (DECSY), J. Am. Chem. Soc., 106 4275 (1984) and references therein. 

Figure 1.45 Coherence transfer pathways in 2D NMR experiments. (A) Pathways in homonuclear 2D correlation spectroscopy. The first 90° pulse excites singlequantum coherence of order p= . The second mixing pulse of angle /3 converts the coherence into detectable magnetization (p= —1). (Bra) Coherence transfer pathways in NOESY/2D exchange spectroscopy (B b) relayed COSY (B c) doublequantum spectroscopy (B d) 2D COSY with double-quantum filter (t = 0). The pathways shown in (B a,b, and d) involve a fixed mixing interval (t ). (Reprinted from G. Bodenhausen et al, J. Magn. Resonance, 58, 370, copyright 1984, Rights and Permission Department, Academic Press Inc., 6277 Sea Harbor Drive, Orlando, Florida 32887.)...

In several kinds of correlation spectroscopy it is customary to also exploit the evolution of either zero quantum (ZQ) or double quantum (DQ) coherences. As shown in Fig. 7.1, they correspond to the transition — + + — and... 

A complex, multiply bridged 1,2,3,4-adduct of C60 (168) (Scheme 1.11) including a noninherently chiral addition pattern as well as a multitude of stereogenic centers in the addend moiety was obtained in a tandem reaction between the alkaloid scandine and Ceo-324 The sequence included a photoin-duced addition of the tertiary amine subunit of the alkaloid and a [2 + 2] cycloaddition of its vinyl group to the adjacent intrahexagonal formal double bond of the fullerene. The structural elucidation included 1H-1 H COSY-, HMQC- (heteronuclear multiple quantum coherence), HMBC-, and ROESY-(rotating frame Overhauser enhancement spectroscopy) NMR experiments and... 

Double-Quantum. (DQ) Proton Spectroscopy. Multiple-quantum (MQ) coherences are routinely used in high-resolution solution-state NMR spectroscopy. The MQ coherences cannot be observed directly and the application of two-dimensional methodology is required. The Double-Quantum (DQ) methodology is particularly useful to derive the information on the spatial proximity of different spins on the basis of the homonuclear dipolar couplings. ... 

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