Coupling constant residual

Because of the availability of n.m.r. spectrometers with heteronuclear lock capabilities, the applied decoupling frequency is no longer restricted to decouple only at the solvent proton frequency in off-resonance decoupling experiments. The improved instrumentation should simplify the determination of residual coupling constants. 

NMR spectrum (Pachler, 1972). A plot of the residual coupling constants /r against different Av values allows the correlation of specific carbon resonances with the known proton chemical shifts (Pachler et aL, 1976b). 

Figure 1 The principal sources of structural data are the NOEs, which give information on the spatial proximity d of protons coupling constants, which give information on dihedral angles < i and residual dipolar couplings, which give information on the relative orientation 0 of a bond vector with respect to the molecule (to the magnetic anisotropy tensor or an alignment tensor). Protons are shown as spheres. The dashed line indicates a coordinate system rigidly attached to the molecule.

Furrer, J., John, M., Kessler, H., Luy, B. /-Spectroscopy in the presence of residual dipolar couplings determination of one-bond coupling constants and scalable resolution. 

Kramer, F., Deshmukh, M. V., Kessler, H., Glaser, S. J. Residual dipolar coupling constants an elementary derivation of key equations. Cone. Magn. Reson. A... 

Instrumentation. H and NMR spectra were recorded on a Bruker AV 400 spectrometer (400.2 MHz for proton and 100.6 MHz for carbon) at 310 K. Chemical shifts (< are expressed in ppm coupling constants (J) in Hz. Deuterated DMSO and/or water were used as solvent chemical shift values are reported relative to residual signals (DMSO 5 = 2.50 for H and 5 = 39.5 for C). ESl-MS data were obtained on a VG Trio-2000 Fisons Instruments Mass Spectrometer with VG MassLynx software. Vers. 2.00 in CH3CN/H2O at 60°C. Isothermal titration calorimetry (ITC) experiments were conducted on a VP isothermal titration calorimeter from Microcal at 30°C. 

The conformation of nonsulfated L-idosyluronic acid residues is a controversial issue, especially on account of a possible role of the 2-O-sulfo substituent in determining the relative orientation of biologically relevant groups. However, the interproton coupling-constants observed for (nonsulfated) methyl a-D-idopyranosiduronic acid131 and dermatan sulfate350 are essentially the same as those of the sulfated L-iduronate resi-... 

Fig. 9. — (a) H-N.m.r. Spectrum (270 MHz, Resolution-enhanced) of Beef-lung Heparin in D20 (40%, w/v) at 90° (b) Computer-simulated Spectrum, with Calculated, Interproton Coupling-Constants (/, at 35°) for the Amino Sugar (A) and L-Iduronic acid (I) Residues.84... 

Figure 35 shows the proton spectra which we obtain you can see that they are of much better quality than those we got from the on-flow experiment. The signals for acetonitrile and residual HDO have been cleanly removed using the WET sequence referred to above, and resolution and signal-noise are much better, so we can obtain coupling constants exactly. 

A third useful example is provided by aromatic residues, where the coupling constant between ortho protons is large (xx-xx Hz), while that between meta protons is much smaller (1-3 Hz). The coupling between para protons is often of the same magnitude as the Hnewidth. 

Fig. 9. The 3/Hn coupling constants versus temperature for different alanine residues in XAO peptide. The reversibility of 3/hn coupling constant versus temperature was checked by measurements with temperature increasing from 2° to 56°C (labeled as heating) or decreasing from 56° to 6°C (labeled as cooling). The errors are the same in heating and cooling measurements the error bars are shown only for heating measurements for clarity. The conditions were temperature from 2° to 56°C, concentration ca. 4 mM, in 30 mM sodium acetate buffer (pH = 4.6, 10% D20 ). From Shi et al. (2002). Proc. Natl. Acad. Sd. USA 99, 9190-9195, 2002 National Academy of Sciences, USA.

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