Linebroadening effects

What, then, is the end-group pattern that emerges from sequential addition of reactive components We calculated the expected line-broadening effects for randomly functionalized dendrimers and compared them to the experimentally observed linebroadening effects. Figure 13.18 compares the experimental results from the stackplot in Figure 13.16 to the calculated results. Because a wide body of hterature now indicates that dendrimer end groups can backfold into the interior of the dendrimer (Ballauff and Likos 2004), we included a volume shell in our calculations. 

Figure 8.2.4 Effect on the resonant frequencies of samples A to D of applying a z-gradient during data acquisition. The gradient strengths are in the order G3 > G2 > G > 0. The linebroadening effects on individual resonances are not shown for clarity...

Determined from ESR spectrum sign from asymmetric linebroadening effect. 

E. Coli deoxyribonucleic acid (DNA) polymerase I. Zn was found to have a linebroadening effect which was partially eliminated on addition of stoichiometric amounts of a DNA analog. 

The other downfield peaks show no significant line broadening nor changes in intensity within experimental error. Peak A especially remains narrow, which contrasts with its linewidth behavior because of added Mn (Gorenstein et al, 1981), where A shows a rapid linear increase in linewidth at low Mn2+/tRNA ratios. This result gives us confidence that the linebroadening effects are not due to paramagnetic metal-ion impurities in the Et solution. 

NMR analysis of a paramagnetic biomolecule may require modifications to the standard experiments. In some cases, this is to compensate for deleterious line broadening caused by unpaired electrons, which interferes with detection of resonances and NOEs. In other cases, modifications are made to take advantage of the effects of unpaired electrons to selectively observe nuclei in the vicinity of the paramagnetic metal. The effects of the metal on the NMR spectrum depend largely on the Xs value, which determines amount of linebroadening (equations 16 and 17). For systems with relatively short tg, few, if any, modifications need to be made, whereas study of systems with long tg require specially tailored experiments to obtain any information on nuclei in the vicinity of the metal site. ... 

This function signal improves S/N as it cuts down the high frequency noise contribution. It causes Lorentzian linebroadening, LB being the broadening (in Hz) produced by the function, and it reduces effects caused by truncation of the FID. 

This can be used to improve the S/N by using Gaussian linebroadening. If the constant is set to a negative value, S/N will be degraded but the line is narrower (i.e. resolution enhancement). Such a process is often used in solution since it requires good S/N to be effective. 

Fig. 5.—The Effect of Gd + on the C Resonances of the Proton-decoupled, Natural-abundance, K -N.m.r. Spectrum of 6. [The concentration of compound 6 was 168 toM in HjO, pH 7. The vertical gam of the spectra of solutions containing large proportions of paramagnetic, relaxation reagent was increased slightly, so that broadening effects could be clearly observed. (A) Sample contained no Gd , and requited 27,000 accumulations. A linebroadening factor of 2.3 Hz was used during the data processing. (B) Sample contained...

It is well known, however, that the width of a spectral line, at least in principle, yields information on the dephasing dynamics of the optical transition. Spectral lineshapes of purely electronic transitions in solids unfortunately are seldom determined by dynamic interactions, but, at least at low temperature, quite often by the effects of strain. The observed, named inhomogeneous linewidth is therefore of little interest. In case of vibronic transitions, however, the effect of vibrational relaxation on the lineshape may exceed the inhomogeneous linebroadening. Even so, classical spectroscopy quite often fails to elucidate the nature and strength of the perturbing forces on the optical (homogeneous) lineshape. 

The linebroadening of chloride, bromide and iodide NMR signals effected by substituted ammonium ions was described in the preceding subsection. In addition to this phenomenon, which could be ascribed to an altered halide ion quadrupole relaxation rate close to nonpolar groups, another type of halide ion relaxation enhancement is obtained in the presence of monoalkylammonium ions with long alkyl chains. 

The dramatic effect of small hydrophobic cations on halide ion quadrupole relaxation is well documented (see Section 5.1.5) but not very much is known about the halogen shielding in these solutions [306 336], One reason for this is that the considerable linebroadening makes precise measurements quite difficult. A few observations for aqueous tetraalkylammonium halide solutions are given in the work of... 

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