Through-space spin coupling

In addition to sample rotation, a particular solid state NMR experiment is further characterized by the pulse sequence used. As in solution NMR, a multitude of such sequences exist for solids many exploit through-space dipolar couplings for either signal enhancement, spectral assignment, interauclear distance determination or full correlation of the spectra of different nuclei. The most commonly applied solid state NMR experiments are concerned with the measurement of spectra in which intensities relate to the numbers of spins in different environments and the resonance frequencies are dominated by isotropic chemical shifts, much like NMR spectra of solutions. Even so, there is considerable room for useful elaboration the observed signal may be obtained by direct excitation, cross polarization from other nuclei or other means, and irradiation may be applied during observation or in echo periods prior to... 

These experiments provide identification of the through-bond spin coupling network as well as through-space proximity between spins. Examples of the application of these techniques have demonstrated the efficiency of these techniques in establishing the assignment, sequence and linkage site information for oligo- and poly-saccharides [59-60, 62-65], and for saponins [29]. 

The direct contribution (c3)dir arises from the through-space dipolar coupling of the nuclear magnetic moments and, as expected, it decreases as the internuclear distance increases with increasing v, because of its R l dependence. The second contribution (C3)ec is the axial component of the tensorial electron-coupled spin-spin interaction the scalar part of this interaction is given by the value of C4. In the v = 0 level the direct contribution is estimated by English and Zorn [51] to be 1.15 kHz, and the electron-coupled part is -0.23 kHz. 

Bridged or Through-space Magnetically Coupled Complexes of High-spin Iron(III) Porphyrins with Other Types of Metal Complexes Possible Models for Cytochrome Oxidase, Assimilatory Sulfite Reductases, and Sulfite Oxidase... 

The analysis of the composition of the active-space spin-coupling pattern, together with evidence coming from orbital overlaps, clearly indicates that the orbital pairs 2), ( 3, 4) and (1/ 5, are preserved all the way from the reactant, through the TS, to the product. 

The tlirough-space nuclear overhauser effect (NOE) can provide information on sites where metals interact even if the metals do not form stable bonds through which spin coupling can be transferred. For instance, metal-HS interactions can be studied by NOE spectroscopy (NOESY) by measuring interactions between the protons within the HS molecules before and after the addition of metals to understand the conformational changes that occur within the molecules (Kingery et al., 2001). An alternative approach is to measure the heteronuclear overhauser effect (HOE) directly between the metal ion and the HS proton in close proximity by HOE spectroscopy (HOES), as has been demonstrated for organo-Li complexes (Bauer, 1995). 

Bagno, A. Saielli, G. Scorrano, G. Through-space spin-spin coupling in van der Waals dimers and CH/n interacting systems. An ab initio and DFT study. Chem. 

A closely related 2D NMR technique, termed NOESY, permits the establishment of through-space coimectivities. This technique relies on the through-space dipolar coupling of nuclear spins and uses a 2D version of the nuclear... 

Other basic 2-D experiments include J spectroscopy, which displays scalar-coupled multiplets along the second dimension, and nuclear Overhauser effect spectroscopy (NOESY, pronounced nosy ), which exploits through-space dipolar couplings to provide conformational information. In the NOESY experiment, protons are selectively irradiated as data are acquired, and the effect of neighboring nuclei is monitored by their mutual enhancement. NOESY is one example of an exchange experiment, in which magnetization is transferred from spin to spin. 

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