Chemical shift paramagnetic species

The aims of this study were to observe isotropically shifted signals for metal ions like copper(II), which usually give signals broadened beyond detection, and to relate the observed shifts and relaxation times to those of the uncoupled ions in order to understand the phenomena in theoretical terms. This approach allows the power of the NMR technique to fully exploit paramagnetic species and obtain information on spin delocalization, chemical bonding and so on. It is likely that the theory also applies to coupled metal ion-H adical systems like those proposed for derivatives of peroxidases (compound I), which contain iron(IV) and a heme radical (44). 

Under certain conditions, chemical shifts and nuclear spin-spin splittings may be observed in paramagnetic species. See p. 280. 

The transverse relaxation rate enhancement / 2P could be treated in the same way if it were not for the difference in chemical shift A com between the paramagnetic and the diamagnetic species. As has already been shown, the difference in chemical shift causes a line broadening — an increasing in R2M — even when the... 

The large paramagnetic contribution to the chemical shifts for the meso-aryl protons is consistent with the presence of a porphyrin 7r-radical species (45). The shift pattern for these signals (o-H upfield, m-H and p-CH3 downfield) is similar to that observed for (TPP )Fein(Cl04)2 (o-H, p-H upfield, m-H downfield), which exhibits ferromagnetic coupling between the porphyrin 7r-radical spin and the metal spin (45). The small... 

The goal of many biomolecular NMR studies is characterization of global molecular structure. In metallo-biomolecules, and in particular, for paramagnetic species, it is sometimes preferable to use NMR to perform a more focused study of the metal ion coordination enviroiunent and the metal electronic structure. Metal sites show great variation in the effects on chemical shifts and line widths and thus often call for tailored approaches. In this section, characteristics of some of the metalloproteins metal sites most frequently studied by NMR are summarized. Examples have been selected to illustrate approaches described in this chapter such as metal substitution, use of pseudocontact shifts, RDCs, relaxation enhancement, and detection of nuclei other than H. 

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