Core formation

A strategy to solve this problem is to separate the core formation process from the reduction of metal ions in the cores as shown in Scheme 1, and use solvent (EG) and simple ions (OH , etc.) as the stabilizers [11]. In the first step of this process, metal salts hydrolyzed in the alkaline solution of EG to give rise to metal hydroxide or oxide colloids, which were then reduced by EG at elevated temperature to produce colloidal metal nanoclusters in the... 

The alkaline EG S5mthesis method is a very effective technology for the chemical preparation of unprotected metal and alloy nanoclusters stabilized by EG and simple ions. This method is characterized by two steps involving the formation of metal hydroxide or oxide colloidal particles and the reduction of them by EG in a basic condition. The strategy of separating the core formation from reduction processes provides a valid route to overcome the obstacle in producing stable unprotected metal nanoclusters in colloidal solutions with high metal concentrations. Noble metal and alloy nanoclusters such as Pt, Rh, Ru, Os, Pt/Rh and Pt/Ru nanoclusters with small particle... 

Gas emission before core formation contact with metallic iron leads to a strongly reducing atmosphere containing only H2, H2O, CH4 and CO. 

Gas emission after core formation the redox state in the iron-containing minerals of the Earth s crust is determined by the ratio of Fe2+ to Fe3+. 

Mishustin, I.N., Hanauske, M., Bhattacharyya, A., Satarov, L.M., Stoecker, H., Greiner, W. (2003). Catastrophic rearrangement of a compact star due to the quark core formation. Phys.Lett., B552 1-8. 

Figure 19.5 Representation of the crystal growth mechanism for ferritin core formation. (From Lewin et al., 2005. Copyright with permission from The Royal Society of Chemistry, 2005.)...

While core formation during hydrolysis of Fe(III) produces electrically neutral ferri-hydrite, it also produces protons two per Fe(II) oxidized and hydrolysed, whether due to iron oxidation and hydrolysis at the ferroxidase centre, followed by further hydrolysis and migration to the core nucleation sites or by direct Fe(II) oxidation and hydrolysis on the mineral surface of the growing core. These protons must either be evacuated from the cavity or else their charges must be neutralized by incoming anions, and it... 

Kleine T, Munker C, Mezger K, Palme H (2002) Rapid accretion and early core formation. Nature 418 952-955... 

Lee DC, Halliday AN (1995) Hafnium-tungsten chronometry and the timing of terrestrial core formation. Nature 378 771-774... 

Gulotta, M. Gilmanshin, R. Buscher, T.C. Callender, R.H. Dyer, R.B. Core formation in apomyoglobin probing the upper reaches of the folding... 

Fe(III) Clusters on Ferritin Protein Coats and Other Aspects of Iron Core Formation... 

Variations in ferritin protein coats coincide with variations in iron metabolism and gene expression, suggesting an Interdependence. Iron core formation from protein coats requires Fe(Il), at least experimentally, which follows a complex path of oxidation and hydrolytic polymerization the roles of the protein and the electron acceptor are only partly understood. It is known that mononuclear and small polynuclear Fe clusters bind to the protein early in core formation. However, variability in the stoichiometry of Fe/oxidant and the apparent sequestration and stabilization of Fe(II) in the protein for long periods of time indicate a complex microenvironment maintained by the protein coats. Full understanding of the relation of the protein to core formation, particularly at intermediate stages, requires a systematic analysis using defined or engineered protein coats. 

The Iron/Proteln Interface. Interactions of Iron with the protein coat of ferritin are most easily characterized In the early stages of core formation when most. If not all, of the Iron present Is In contact with the protein coat. In the complete core, bulk Iron Is Inorganic. To date, the protein coat has been little examined early In Iron core formation except In terms of effects on the Iron environment. Studies of the Iron early In core formation will be discussed later. 

The function of all ferritin molecules is to store iron. However, the mechanisms by which iron enters the core or is released from the core 1ji vivo is poorly understood. Experimentally, Fe(II), but not Fe(III), mixed with ferritin protein coats forms normal iron cores. Moreover, reductants such as thloglycollate or reduced flavins can reverse the process of core formation and release Fe(II) from the core. Since such reductants occur in vivo, reduction of ferritin cores may also occur vivo. 

Low Fe/Proteln (Fe <10-12/Molecule). Ferritin protein coats have multiple (8-12) binding sites for a variety of metals. Including Fe(II), Fe(IIl), V(IV), Mn(II), Tb(III), Cd(II), Zn(II), and Cu(II) (e.g., 5,34-36, and reviewed In Ref. 37). At least some of the metals bind at the three-fold channels. The location of the nucleatlon sites Is presently unknown. However, If the three-fold channels are the nucleatlon sites for core formation, core growth could block the channels, thus Inhibiting further accretion INSIDE the protein coat and could lead to the addition of Fe OUTSIDE the protein coat. Such an effect would obviate the sequestering function of the protein. Three forms of Fe have been observed bound to ferritin protein coats (apoferrltln) mononuclear, dlnuclear, and multlnuclear clusters. 

In vitro. Fe(ll) is required to initiate core formation. The steps Include binding to the protein coat, oxidation and migration to form an Fe(III) cluster on the protein (or migration and oxidation on a cluster already formed on the protein), followed by the addition and oxidation of hundreds to thousands of Fe atoms a... 

Morula cell, 35 101 Mosaic spread, 47 471 [Mo,S4([9]aneN3),], structure, 37 154 Mo—S bridge, 38 55 M04S4 clusters, preparation, 38 26-27 [Mo,84] core, formation, 38 59 M04S4 cores... 

Figure 5-8 A Pb-Pb isochron that determined the age of the Earth to be about 4.55 Ga. Stony and iron meteorites as well as a sediment of the Earth are plotted on a Pb-Pb isochron. The sediment, as a "bulk sample of the silicate Earth in terms of Pb isotopes, plots on the same line as the meteorites, suggesting that the Earth and meteorites formed at the same time and are the same age. Erom Patterson (1956). Later studies reveal a more detailed evolution history of the Earth, including core formation (about 4.53 Ga), atmospheric formation (about 4.45 Ga), and crustal evolution.

Another example is provided by the chemical fractionation of tungsten into planetary cores. Tungsten has a short-lived radioactive isotope, W, which decays into Hf. Tungsten is siderophile and hafnium is lithophile. Consequently, the daughter isotope, 182Hf, will be found either in the core or the mantle depending on how quickly metal fractionation (core formation) occurred relative to the rate of decay. The Hf- W system is used to date core formation on planetary bodies. We will discuss the details of using radioactive isotopes as chronometers in Chapters 8 and 9. 

Rushmer, T., Minarik, W. G. and Taylor, G. J. (2000) Physical processes of core formation. In Origin ofthe Earth and Moon, eds. Canup, R. M. and Righter, K. Tucson University of Arizona Press, pp. 227-243. 

Taylor, G. J. (1992) Core formation in asteroids. Journal of Geophysical Research, 97, 14717-14726. 

Burkhardt, C., Kleine, T., Bourdon, B. et al. (2008) Hf-W mineral isochron for Ca, Al-rich inclusions age of the solar system and the timing of core formation in planetesimals. Geochimica et Cosmochimica Acta, 72, 6177—6197. 

Harper, C. L. and Jacobsen, S. B. (1996) Evidence for 182Hf in the early solar system and constraints on the timescale of terrestrial core formation. Geochimica et Cosmochimica Acta, 60, 1131-1153. 

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