Multiple quantum NMR ,

FIGURE 9.11. Proton multiple-quantum NMR spectrum of 5CB-dn at 26 C. Only one-half of the symmetric zero- to eight-quantum regions is shown. The full width shown is 500 kHz (after Ref. [9.37]). 

Very recently, advanced multiple quantum (MQ) NMR approaches have been developed which provide highly 

In MQ-NMR motional dynamics are parameterized by one or, more commonly, a distribution of residual dipolar coupling values, which represent the time- and ensemble-averaged interaction strength between two protons along the chain length. It is important to note that while the majority of the alternative techniques outlined above also rely on this phenomenon, the data resulting from the MQ-NMR experiments pioneered by Saalwachter and coworkers [63] can be analyzed in a model-free way with no assumptions about various motional limits, functional forms of dynamical correlation functions, etc. 

The residual dipolar coupling magnitude, can be expressed generally through the simple relation [101], 

The MQ-NMR experiment consists of three main parts. First magnetization is converted (or excited) into a state governed by a dipolar double-quantum (DQ) Hamiltonian. This spin state reflects correlated, two-spin interactions that can 

This observation illustrates an interesting possibility of probing torsion angles by a controlled evolution of the intramolecular MQ signals, just as discussed by Levitt and co-workers [61]. 

---

The spectrometer supports phase cycling, asynchronous sequence implementation, and parameter-array experiments. Thus, most standard solid-state NMR experiments are feasible, including CPMAS, multiple-pulse H decoupling such as TPPM, 2D experiments, multiple-quantum NMR, and so on. In addition, the focus of development is on its extension of, or modification to, the hardware and/or the software, in the spirit of enabling the users to put their own new ideas into practice. In this paper, several examples of such have been described. They include the compact NMR and MRI systems, active compensation of RF pulse transients, implementation of a network analyzer, dynamic receiver-gain increment,31 and so on. 

It is interesting to note that several of the concepts for improving NMR technology, as listed by Levy and Craik, in 1988, already have been partially or fully achieved (1) two-dimensional Fourier transform (FT NMR) (2) high-resolution NMR in solids (3) new types of pulse sequences (4) chemically induced dynamic nuclear polarization (5) multiple quantum NMR and (6) NMR imaging (MRI). 

Great progress was made by Marzilli143 on using -detected multiple-quantum NMR, in the structure determination of d(TGGT). 

X-ray diffraction, and solid-state heteronuclear multiple-quantum NMR investigations. Angewandte Chemie (International Ed. in English), 38, 3039-42. 

Selective Residual Dipolar Couplings by 1H Multiple-Quantum NMR Spectroscopy... 

A. Bax and M. F. Summer, and C assignments from sensitivity-enhanced detection of heteronuclear multiple-bond connectivity by 2D multiple quantum NMR,/Am. Chem. Soc. 108 (1986),2093-2094. 

Probing Degradation in Complex Engineering Silicones by Multiple Quantum NMR... 

Figure 1. Multiple Quantum NMR pulse. Growth curves are obtained by incrementing either the interpulse delays or the number of multiple pulse excitation trains in the conversion and reconversion sequences. (Reproduced from reference 13. Copyright 2005 American Chemical Society.)...

Multiple Quantum NMR methods have been used to characterize the results of multiple degradation mechanisms on complex silicone polymer composites. 

Multiple Quantum NMR Experiments of Non-Integer 161 Spin Quadrupolar Nuclei... 

Multiple quantum NMR experiments of non-integer spin quadrupolar nuclei... 

Cho G, Yesinowski JP (1993) Multiple-quantum NMR dynamics in the quasi-one-di-mensional distribution of protons in hydroxyapatite. Chem Phys Lett 205 1-5... 

---