Quadrupole coupling constants chlorides

The above model has been used by Bull et al. (102) to analyse the chloride NMR relaxation data for several proteins. The overall correlation time(s) was estimated from the Debye-Stokes-Einstein equation or, when available, was taken from dielectric relaxation measurements. In order to perform the calculations, also the "true" value of the chloride quadrupole coupling constant in the site is needed. This is, however, not known and therefore Bull et al. estimated a value for Cl bound to a NH3 group of 3.6 MHz based on the electrostatic model of Cohen and Reif (103). In this way it was possible to calculate the values shown in Table 6. Obviously the model used is an oversimplification however, it is noteworthy that all internal correlation times come out with a reasonable value of about 1 ns. 

TABLE 8. 35C1 quadrupole coupling constants and asymmetry parameters of carbonyl chlorides... 

A. C. Legon, P. D. Aldrich, and W. H. Flygare,/. Am. Chem. Soc., 104, 1486 (1982). The Rotational Spectrum, Chlorine Nuclear Quadrupole Coupling Constants, and Molecular Geometry of a Hydrogen-Bonded Dimer of Cyclopropane and Hydrogen Chloride. 

Halogenomethanes. Several theoretical studies of the electronic structures of the halogenomethanes have been undertaken. SCF-MO calculations of the electric dipole moments and nuclear quadrupole coupling constants of a series of isoelectronic molecules including methyl chloride (FCl, HOCl, NH2CI, CH3CI) have been made and compared with the experimentally determined values. 

In absence of experimental data on the relaxation rate in sites (c) and (d) in Cl, these were calculated from estimated electric quadrupole coupling constants and rotational correlation times. The excess line width of the chloride NMR signal was experimentally observed to be directly proportional to the total concentration... 

Further information on Cl binding to LADH is provided by Bull et al. [442] who, from Cl T and T measurements, obtained (see Section 8.1) the correlation time of bound Cl to be 23 ns at 6°C and ca. 9 ns at 25°C. Assuming Pt(CN) excludes two chloride ions per enzyme molecule, the quadrupole coupling constant,, is obtained... 

In Table 8.4 we have collected values of Cl quadrupole coupling constants and correlation times for a number of protein-chloride complexes. In a few cases, has been obtained experimentally from a comparison of T and T2 or from the frequency dependence of relaxation. In order to make possible a comparison between different proteins we have also calculated from experimental line width data using correlation times estimated by means of the Debye-Stokes-Einstein relation for spherical molecules. We then proceeded similarly as described in Ref. [4Z1],... 

Table 8.4. Quadrupole Coupling Constants of Various Protein-Chloride Complexes (cf. Ref.. 431 )... 

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