Metal shift

Metal shift refers to the phenomenon in which certain metals shift from one organ to another as a result of the presence of a pollutant. This is among the earliest biological indicators of toxic response. For example, rats fed vanadium (V) at concentrations up to 150 ppm were shown to cause iron to move into the liver and spleen. When vanadium concentrations were at 250 ppm or above, however, iron moved out of the liver and spleen. As a result, the iron level in the spleen was decreased to one half to one third of the normal content, while that in the liver was decreased to one third of the normal content (Furst 1960). These results indicate that treatment with vanadium will lead to depletion of iron in these tissues. 

The phenomenon of metal shift in rats exposed to fluoride has been reported (Yoshida et al. 1991). Administration of fluoride to rats increased serum Zn levels whereas the levels of Se and Al in the whiskers were decreased. 

A similar phenomenon has been observed with rats exposed to ozone. When the rats were exposed to this pulmonary irritant for 4 h, the animals showed increased levels of copper, molybdenum, and zinc in the lungs, while these metals were decreased in the liver. This would indicate an altered hemodynamics and changes in cellular permeability in a secondary affected organ. 

---

Simple diastereoselection in the reactions of 2-butenylboron compounds and aldehydes is critically dependent on the configurational stability of the reagentslb. As a general rule, most 2-bulenylorganometallics arc sensitive to sequential 1,3-metal shifts (1,3-metallotropic rearrangements) that result in E- to Z-olefin isomerization via the l-methyl-2-propenylmetal isomer. 

Dixon, J. R., W. D. Wagner, T. D. Martin, R. G. Keenan, and H. E. Stokinger. Metal shifts as early indicators of response from low-grade pulmonary irritation. Toxicol. Appl. Pharmacol. 9 225-233, 1966. 

Even though the outlined approach allowed the successful rationalisation of many experimentally observed shift/structure and shift/reactivity correlations, Leitner et al. have pointed out that such relations cannot be expected to be universally valid and require that structural variations are modest and avoid large simultaneous changes in parameters that may have opposite effects on metal chemical shifts.61 To overcome these drawbacks and establish a more rational interpretation of chemical shift trends, they used a combination of experimental and computational efforts to assess the importance of different electronic and structural factors on the metal chemical shifts of a series of rhodium complexes with bidentate chelating bisphosphine ligands. The basis of their approach is first the validation of experimentally observed metal shifts by... 

Fluorine-to-metal shift, in metal—fluoride bond a-activation, 1, 735... 

The Early Transition Metals shifted v(V=0) bands, indicating a cis-trans equilibrium relative intensities suggest that the trans-isomer predominates for dik = acac and the cis for dik = bzac and dbm, and that the latter is the exclusive isomer for dik = dpm, tta, and tfa. A polymeric structure was suggested for the solid tta and tfa complexes. 

Recently a comparative study of the asymmetric Diels-Alder reactions of both (5)-benzyl 2-p-tolylsulfinylacrylate (167) and (S)-benzyl methyl 2-p-tolylsulfinyl maleate (168) was carried out.104 Consequently, improved mechanistic models were developed in order to explain the behavior of such sulfinyl maleate and acrylate dienophiles in asymmetric Diels-Alder reactions.104 It was postulated that conformational equilibrium around the C-S bond must be completely shifted toward the rotamer with the sulfinyl oxygen in an s-cis arrangement (the most stable from an electrostatic point of view), making favored approach of the diene from the less hindered upper face supporting the lone electron pair (Fig. 7). The chelation of the sulfinyl and carbonyl oxygens with metals shifts the conformational equilibria... 

Fig. 13 shows the recovery of neutron-irradiated W as deduced from resistivity measurements. Irradiations with fast neutrons are within certain limits comparable to ion bombardments. One observes clearly the different stages I to III which one finds for most other metals shifted to either lower or higher temperatures. 

Carter, G.C., Bennett, L.H. Kahan, D.J. (1977) Metallic Shifts in NMR Parts 1-3, Oxford, Pergamon. 

Yoshida, Y., K. Kono, M. Watanabe, and H. Watanabe. 1991. Metal shift in rats exposed to fluoride. Environ. Sci. 1 1-9. 

Rhodium ( Rh) (/ = 112). The calculated Rh NMR chemical shifts (GIAO-B3LYP/II level) for a range of bis(r -alkene)(2,4-pentanedionato)rho-dium(I) complexes agree well with solution NMR data. The empirical correlation between transition-metal shifts and stability constants could be confirmed for simple alkenes, since the computed relative Rh-alkene binding energies were found to correlate with 5( Rh). 

---