J-coupling measurement

In a recent work,138 we have attempted to parameterize the Karplus dependence of 3 7c,oi i couplings taking advantage of the redundant set of J couplings measured for the two anomeric forms of a simple monosaccharide, 4,6-O-benzylidene-l-metoxy-D-glucose (Figure 1). 

Some new developments and applications of the solid state NMR published between October 2001 and October 2003 have been reviewed briefly by Dybowski et al Reviews section of this publication highlights important new articles published in the recent years. A selection of new NMR techniques and chemical shift and J-coupling measurements has been reviewed. In addition, applications of solid state NMR techniques to study porous materials, semiconductors and ionic conductors, glasses, polymers and biological materials have been described. 

The DJiEt, x) values obtained from the J-coupling measurements are plotted as a function ofx in Figure 10. It can be seen there that (here is a clear oscillation in DJiEj) across the speetrum. This represents the first experimental observation of a spatially-resolved oscillatory variation in caused by the presence of a metal surface. 

To date NMR protein structures have usually been calculated on the basis of interproton distances and dihedral angles derived from NOE and J coupling measurements, respectively. Each structure determination necessitates a large number of sophisticated experiments, so that data acquisition and subsequent analysis may take several months. The value of the solution structure lies in the fact that it provides a starting point for the study of protein/substrate interactions, a knowledge of which may then aid drug design. 

J A measure of the coupling constant in nuclear magnetic resonance. 

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 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. 

Vilardaga, J. P., Bunemann, M., Krasel, C., Castro, M. and Lohse, M. J. (2003). Measurement of the millisecond activation switch of G protein-coupled receptors in living cells. Nat. Biotechnol. 21, 807-12. 

Scalar (J) interactions between nuclei are transmitted indirectly through the electrons of the bonds. In the solid state, the effects of J couplings are usually obscured by the dipolar, chemical shift, and quadrupolar contributions to the linewidth. Nevertheless, the measurement and utilization of J couplings are possible even if... 

One of the NMR experiments most commonly used to measure the CaHa dipolar coupling is a J-modulated pseudo-three-dimensional version of the constant time 13C-HSQC [48, 49]. The J coupling values are extracted by using time-domain fitting in the third dimension. Since spectral overlap is very common in 13C-HSQC of proteins, sometimes only a few... 

The NMR experiment most commonly used to measure dipolar couplings of atoms that belong to side chains [49], provides the sum of the J couplings of both C-Hj and C-H2 in the case of methylenes, so that the sum of both dipolar couplings is obtained. In order to use the data in the structure calculation the energy function that is minimized has the form ... 

That the second term indeed can be neglected is illustrated in the following example. The CCR rates were measured in a small peptide weakly bound to STAT-6, a 100 kDa protein. The signals that are split by the heteronuclear j coupling are of equal intensity for the free peptide. After addition of protein, the signal intensities of the individual... 

Multiplicity is brought about due to the splitting of the signal of one set of equivalent nuclei by the magnetic fields of adjacent sets of nuclei i.e., spin-spin interactions. The distance between the peaks of a regular multiplet is termed as the coupling constant, designated as J, and measured in Hz. 

All other factors are constants. The angle 9 is the projection angle between bond vectors and is the sole unknown in Eq. 1, and can be readily and precisely determined by measurement of the cross-correlated dipolar relaxation rate. It should be emphasized that 9 is measured directly, without the need of experimental calibration as in the Karplus curve for J-coupling constants for example. 

The inclusion of the number of protons at each chemical shift proved to be key the number of false positives increased 5-7 fold (depending on how diverse the set of test compounds were) if this parameter was excluded. Various refinements were tested, but the most successful was the J Filter which disallowed a combination in which the number of couplings measured at a given chemical shift in the experimental spectrum was greater than in the predicted. This proved to be particularly valuable in the differentiation of isomers, where changes in the overall table of chemical shifts alone, could be quite subtle. The inconsistent appearance of labile protons in the experimental spectrum reduced the accuracy and it was asserted that where possible, they should be removed from both the experimental spectrum and the predicted spectrum. The mismatch level not only encoded the divergence of the experimental spectrum and the postulated structure, but also encoded... 

An important first step in interpreting the C-13 spectra is to distinguish a-carbons from 3-carbons, i.e. methine from methylene. Observation of multiplicity when the proton decoupler is off is one way, but this is not always easy if the lines are broadened by chemical shift multiplicity. Measurement of has been used for this purpose since the 3-carbon with two bonded protons relaxes about twice as fast as the a-carbon with only one. A very positive way is by deuterium labelling. In Fig. 3 is shown the main-chain 25 MHz carbon spectrum of two styrene-S02 copolymers containing 58 mol% styrene, or a ratio of styrene to SO2 of 1.38 (7 ). In the bottom one, 3,3-d2-styrene has been used, cind all the 3-carbon resonances are distinguishable from the a-carbon resonances since the presence of deuterium has eliminated their nuclear Overhauser effect because of this eind the deuterium J coupling ( 20 Hz), they are markedly smaller eind broader than the a-carbon resonances. 

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