J couplings

J couplings are not the only means in NMR for showing that two atoms lie close togetlier. Pairs of atoms,... 

One of the most attractive features of the CIDNP multiplet effect is that it allows detennination of the sign of the J coupling, which is often difficult to do by other methods. 

At this point the nomenclature used in XPS and AES should be explained. In XPS the spectroscopic notation is used, and in AES the X-ray notation. The two are equivalent, the different usage having arisen for historical reasons, but the differentiation is a convenient one. They are both based on the so-called j-j coupling scheme describing the orbital motion of an electron around an atomic nucleus, in which the... 

In order to explain qualitatively how CIDNP arises, the simple case of a radical pair in which only one component contains a nucleus (spin J) coupled to an electron (spin through a hyperfine coupling constant will be considered. 

First obtain a number of 2D NMR spectra (NOE, as well as J-coupling)... 

Exoerimsntal HMR Data NOEs/RDEs, (J-Couplings), (RDCs)... 

Figure 7. Potential energy diagram for HI, showing the two lowest ionization states (2n3//2 and 2 IT j, ) coupled to a neutral dissociative continuum (3Ao) at the three-photon (3

Kuboniwa H, Grezesiek S, Delaglio F, Bax A. Measurement of Hn-H J couplings in calcium-free calmodulin using new 2D and 3D water-flip-back methods. J Biomol NMR 1994 4 871-878. 

Grzesiek S, Kuboniwa H, Hinck AP, Bax A. Mutiple-quantum line narrowing for measurement of Ha-Hp J couplings in isotopically enriched proteins. J Am Chem Soc 1995 117 5312-5315. 

The previous experiment (COSY) demonstrated the interactions (J coupling) between protons via the bonding electrons. The NOE effect which we described in Section 1.1.6 functions because of the through-space interactions between protons, and we used the NOE difference and selective NOE experiments to demonstrate it. 

The number of NMR parameters available for measurement is rather small, consisting of the chemical shift, relaxation rates (/1 and lo), scalar (J) couplings, dipolar (D) couplings, cross-relaxation rates (the NOE), and hydrogen exchange rates. All of these have been quantified for many of the amide protons of A131 A, and most of the data suggest the presence of little persistent structure. 

Fundamental constants (Cx), spatial tensors in the principal axis frame ((fi3 m,)F), and spin tensors (Tjm) for chemical shielding (a), J coupling (J), dipole-dipole (IS), and quadrupolar coupling (Q) nuclear spin interactions (for more detailed definition of symbols refer to [50])... 

Homonuclear Dipolar Recoupling and J-Coupling Based Techniques... 

The idea of frequency selectivity is certainly not restricted to J-coupling mediated polarization transfer. Furthermore, frequency selective polarization transfer can also be realized by DQ recoupling techniques. For the technique of shift-evolution-assisted selective homonuclear recoupling (SEASHORE), which employs POST-C7 to construct an effective DQ coupling [82, 83], frequency selective polarization can be achieved when the transmitter offset is set to the... 

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