Nuclear magnetic resonance contact shifts

It may be noted that the nuclear magnetic resonance contact shifts of some paramagnetic metallocenes and l,l -dimethyl derivatives may not be understood by analogy with those in substituted benzene anions [85c]. Perhaps the mechanism of delocalization of unpaired spin density to the ring substituents of metallocenes involves some direct metal-substituent interaction. 

Nuclear magnetic resonance (NMR) S Chemical shift, coupling constants, and spectroscopy nuclear Overhauser effect allows calculation of contact points, distances, and conformation... 

The paramagnetic properties of Co(II) have been utilized in some biochemical applications of nuclear magnetic resonance. Cobalt(II)-induced contact shifts were observed in lysozyme (26). A preferential binding of Co2+ to a single site presumably involving two carboxyl groups was deduced. This technique might become very informative in studies of metal ion-dependent enzyme systems. 

Another contribution to variations of intrinsic activity is the different number of defects and amount of disorder in the metallic Cu phase. This disorder can manifest itself in the form of lattice strain detectable, for example, by line profile analysis of X-ray diffraction (XRD) peaks [73], 63Cu nuclear magnetic resonance lines [74], or as an increased disorder parameter (Debye-Waller factor) derived from extended X-ray absorption fine structure spectroscopy [75], Strained copper has been shown theoretically [76] and experimentally [77] to have different adsorptive properties compared to unstrained surfaces. Strain (i.e. local variation in the lattice parameter) is known to shift the center of the d-band and alter the interactions of metal surface and absorbate [78]. The origin of strain and defects in Cu/ZnO is probably related to the crystallization of kinetically trapped nonideal Cu in close interfacial contact to the oxide during catalyst activation at mild conditions. A correlation of the concentration of planar defects in the Cu particles with the catalytic activity in methanol synthesis was observed in a series of industrial Cu/Zn0/Al203 catalysts by Kasatkin et al. [57]. Planar defects like stacking faults and twin boundaries can also be observed by HRTEM and are marked with arrows in Figure 5.3.8C [58],... 

Nuclear magnetic resonance (NMR) Chemical shift, nuclear coupling constants, relaxation times For paramagnetic proteins enhanced chemical shift resolution, contact and dipolar shifts, spin delocalisation, magnetic coupling from temperature dependence of shifts. 

The so-called heavy-atom chemical shift of light nuclei in nuclear magnetic resonance (NMR) had been identified as a spin-orbit effect early on by Nomura etal. (1969). The theory had been formulated by Pyykktt (1983) and Pyper (1983), and was previously treated in the framework of semi-empirical MO studies (PyykktJ et al. 1987). The basis for the interpretation of these spin-orbit effects in analogy to the Fermi contact mechanism of spin-spin coupling has been discussed by Kaupp et al. (1998b). 

Nuclear magnetic resonance spectra of these compounds are highly informative in this regard. The lineshapes of the Sn and resonances are dominated by the coupling of the nuclei with the unpaired electron spins. This interaction results in large resonance shifts arising from both the Fermi contact and the pseudo-contact (dipolar) interaction. 

Nuclear magnetic resonance (NMR) spectroscopy Reduced coupling constant, NMR spectroscopy Paramagnetic complexes, NMR spectroscopy Contact shifts Dipolar shifts Isotropic shifts... 

The bound fraction p represents the ratio of the number of segments in close contact with the surface (i.e. in trains) to the total number of segments in the polymer chain. The polymer bound fraction, p, can be directly determined using spectroscopic methods such as infrared (IR), electron spin resonance (ESR) and nuclear magnetic resonance (NMR). The IR method depends on measuring the shift in some absorption peak for a polymer and/or surface group [62-64]. The ESR and NMR methods depend on the reduction in the mobility of the segments that are in close contact with the... 

The coupling of the unpaired electrons with the nucleus being observed generally results in a shift in resonance frequency that is referred to as a hyperfine isotropic or simply isotropic shift. This shift is usually dissected into two principal components. One, the hyperfine contact, Fermi contact or contact shift derives from a transfer of spin density from the unpaired electrons to the nucleus being observed. The other, the dipolar or pseudocontact shift, derives from a classical dipole-dipole interaction between the electron magnetic moment and the nuclear magnetic moment and is geometry dependent. 

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