57Fe chemical shifts

Fe chemical shift (from 0.32 to 0.41 mm/s), consistent with substantial localization of the extra negative charge on the core Fe atoms. 

Finally, we should note that a particularly important area of application where density functional techniques, in spite of the deficiencies noted above, are virtually without competition is provided by biochemically relevant molecules, such as enzymes or nucleic acids. The techniques discussed in this section are virtually the only quantum chemical methods which can be applied in this context due to their outstanding price/performance ratio. For example, the 13C and 15N chemical shifts in bacteriochlorophyll A have been studied by Facelli, 1998, and in another investigation the 57Fe, 13C and 170 shifts in iron porphyrin derivatives gave important clues as to the structural details of these species, as shown by McMahon et al 1998. 

Figure 10. Graph showing the correlation between experimental 57Fe NMR chemical shifts (points at top left are organometallics,from Biihl, Ref. 20, at bottom right, they are for metalloporphyrins, see Ref 19) and theoretical G94/B3LYP results. The solid circles represent shieldings computed directly from protein crystal structures containing tilted/bent Fe-C-0 subunits, and are inconsistent with experiment. See Refs. 19,23 for more details.

Mink, L.M., Christensen, KA. and Walker, F.A. (1992) Rapid detection of 57Fe NMR chemical shifts of model hemes an approximate correlation between 57Fe and 31P chemical shifts of Fe(II) porphyrins bound to phosphine axial ligands./. Am. Chem. Soc., 114, 6930-6931. 

Some less frequently encountered nuclides, such as 57Fe and 59Co, have chemical shift ranges of more than 10,000 ppm, hence encompass a very large frequency range in spite of smaller magnetogyric ratios. The chemical shift of monatomic 129Xe gas is very sensitive to its environment, and hyperpolarized xenon (Section 2.5) can be used to probe adsorption sites in solids. 

Fig. 1. 62.8 MHz 2°7Pb NMR spectrum of (Cp)Fe(CO)2-PbMe3 (25 °C =5% in C6D6), recorded by using the refocused INEPT pulse sequence with CPD H decoupling (200 transients with a repetition time of 8 s and an acquisition time of 4 s).94 The line width h, /2 = 2 Hz is rather small for 207Pb NMR signals and makes it possible to observe 57Fe satellites and also 13C satellites in order to measure accurately the isotope-induced chemical shifts...

Abstract. We report the results of experimental and theoretical studies of 13C and 15N shifts in proteins and model systems, together with 57Fe shifts and Mossbauer quadrupole splittings (electric field gradients) in metalloporphyrins and metalloproteins. The ability to relate these spectroscopic observables to structure by using quantum chemical methods opens up new opportunities for predicting and refining protein structure. 

The Mossbauer effect is sensitive to the oxidation and spin state of iron and the environment around the iron nucleus therefore different chemical species yield different Mossbauer spectra. Furthermore all spin states and oxidation states of iron are accessible to the technique. There are three main components of a Mossbauer spectrum. The isomer shift arises from the electron density at the 57Fe nucleus the quadrupole splitting results from the electric field gradient produced by electrons and ions around the 57Fe nucleus, and the nuclear Zeeman splitting is sensitive to the spin state and magnetic coupling of the iron. 

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