7-coupled spin network

The ID homonuclear Hartmann-Hahn (HOHAHA) experiment is an excellent way to determine complete coupled spin networks (18). The following pulse sequence is used ... 

An approach to the determination of the orientation of the carbonyl CSA tensor in a dipolar coupled spin network has been proposed. " The... 

The DQFCOSY spectrum of RpII in D O is shown in Figure 2. Each cross peak in this spectrum identifies a pair of coupled spins of the amino acid side chains. Since couplings are not propagated efficiently across amide bonds, all groups of coupled spins occur within individual amino acids. The chemical structure of an amino acid side chain is reflected in the characteristic coupling network and chemical shifts (13). Valine spin system (CH-CH-(CH3)2) explicitly shown in Figure 2 as an example. 

The HOHAHA spectrum (100 ms) of podophyllotoxin is presented. The HOHAHA, or TOCSY (total correlation spectroscopy), spectrum (100 ms) shows coupling interactions of all protons within a spin network, irrespective of whether they are directly coupled to one another or not. As in COSY spectra, peaks on the diagonal are ignored as they arise due to magnetization that is not modulated by coupling interactions. Podophyllotoxin has only one large spin system, extending from the C-1 proton to the C4 and 015 protons. Identify all homonuclear correlations of protons within this spin system based on the crosspeaks in the spectrum. 

One-dimensional double-resonance or homonuclear spin-spin decoupling experiments can be used to furnish information about the spin network. However, we have to irradiate each proton signal sequentially and to record a larger number of ID H-NMR spectra if we wish to determine all the coupling interactions. Selective irradiation (saturation) of an individual proton signal is often difficult if there are protons with close chemical shifts. Such information, however, is readily obtainable through a single COSY experiment. 

A 3D spectrum of a three-spin subsystem in which all the nuclei are coupled to one another, such as C(H/i)(Hb)-C(Hc), will lead to 27 peaks, comprising six cross-peaks, 12 cross-diagonal peaks (six at o) — o>2 and the other six at 0)2 = (O3), six back-transfer peaks, and three diagonal peaks. However, in the case of a linear three-spin network (e.g., CH -CHg-CHc), the number of peaks will depend on whether two equal (e.g., COSY-COSY or NOESY-NOESY) or unequal (e.g., COSY-NOESY) mixing processes are... 

Morello, A., Stamp, P.C.E. and Tupitsyn, I. (2006) Pairwise decoherence in coupled spin qubit networks. Phys. Rev. 

Mixed phase lineshapes, typical for the multistep RELAY spectra, sometimes make the identification of individual signals difficult. At the same time, for extensive networks of coupled spins, the TOCSY transfer proved... 

C This pulse sequence, the popular homonuclear 2D COSY (COrelation Speciro-scopY) experiment, was designed to determine the entire H/ H-coupling network of a molecule within a single experiment. The sequence consist of all four elements, i.e. a preparation, a evolution, a mixing and a detection period. The evolution period serves to introduce the second time (tl) domain of a 2D experiment and in the mixing period, which is actually a pulse, polarizations are exchanged among the coupled spins. 

However, in all the papers mentioned above the authors analyzed only three-dimensional (3D) systems, while a two-dimensional (2D) case is also experimentally observed surfaces of various absorbers, heterogeneous catalysts, photocatalysts, etc. In [137], Fel dman and Lacelle examined the quenched disorder average of nonequilibrium magnetization, i.e., a free induction decay G(t) and its relative fluctuations for dipolar coupled homonuclear spins in dilute substitutionally disordered lattices. The studies of NMR free induction decays and their relative fluctuations revealed that the functional form of the disorder average (G(t))c depends on the space-filling dimentionality D of the lattice. Explicit evaluations of these averages for dilute spin networks with D = 1, 2, 3 were presented in [137] ... 

If the effective coupling network contains closed loops, it is only possible to correct all zero-quantum phases if the loop sum of the zero-quantum phases is zero for all loops. For a loop of L coupled spins, where the spins are labeled from 1 to L, the loop sum of the zero-quantum phases is defined as... 

The most direct assessment of Hartmann-Hahn mixing sequences is based on the efficiency of polarization or coherence transfer. Fortunately, the transfer efficiency between two coupled spins is usually sufficient to characterize the transfer properties in extended coupling networks. Several offset-dependent quality factors have been proposed that are based on magnetization-transfer functions T r) (see Section VI) between two spins i and j with offsets v, and Vj. 

TOCSY (Total Correlation Spectroscopy) is another important homonuclear 2D correlation experiment where correlations arise due to the presence of homonuclear scalar coupling.In the standard COSY experiment, crosspeaks appear for spins in which the scalar coupling occurs over typically two to four bonds. In the TOCSY experiment crosspeaks can appear for spins separated by many more bonds as long as they are part of a contiguous network of coupled spins. The correlations are effected by the application of a series of low-power rf pulses termed the spin-lock. The duration of the spin-lock period determines the extent to which the correlations are propagated through the spin system. The TOCSY experiment is a useful complement to the COSY methods for the elucidation of complex structures. 

Hence the pattern produced by the coupling gives important information about the local spin network and has proved very useful in liquids for identifying the local fragments of molecules, especially in large molecules such as proteins. If a spin-I is coupled to several spins S then including the Zeeman interaction the Hamiltonian is... 

In MQNMR, individual spins become correlated with each other over time by interaction through their dipolar couplings. The rate at which MQ coherences develop is a complex function of the coupling constants present in the spin system. In solids, where the network of dipole-coupled spins is... 

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