Cellular metals

Sunda, W. G. and Huntsman, S. A. (1998). Processes regulating cellular metal accumulation and physiological effects phytoplankton as model systems, Sci. Total Environ., 219, 165-181. 

Among the trace metals, Hudson and Morel [7] postulated that Fe and Zn were closest to a diffusion-limited situation based upon measured cellular metal quotas and concentrations in marine systems (e.g. Zn would be diffusion limited for cells > 20 pm). Similarly, Hassler and Wilkinson [90] showed that for cells grown under conditions of Zn starvation, transport was diffusion limited for [Zn2+] < 10 12 mol dm. Fortin and Campbell [91] showed that, in the presence of chloride, the Ag transport flux to Chlamydomonas reinhardtii was close to a diffusion limitation at the lower Ag concentrations that were examined. Diffusion limitation of trace metals is most likely in systems where the concentrations are low and concentrations of competing metals are high, especially for essential metals that are taken up by passive diffusion across the membrane [8], The final point of essentiality could be especially important when transport systems are upregulated in response to lowmetal concentrations (see also Section 2.2 [90,92]). 

Minimum value of hmt required to maintain a cellular metal quota that is sufficient for the microorganism to grow at 90% of its maximum rate... 

Figure 18.16 Hypothetical model for the metallobiology of AP in Alzheimer s disease. (From Bush, 2003. Copyright 2003, with permission from Elsevier.) The proposed sequence of events (1) concentration of iron and copper increase in the cortex with aging. There is an overproduction of APP and AP in an attempt to suppress cellular metal-ion levels. (2) Hyper-metallation of AP occurs which may facilitate H202 production. (3) Hyper-metallated AP reacts with H202 to generate oxidized and cross-linked forms, which are liberated from the membrane. (4) Soluble AP is released from the membrane and is precipitated by zinc which is released from the synaptic vesicles. Oxidized AP is the major component of the plaque deposits. (5) Oxidized AP initiates microglia activation. (6) H202 crosses cellular membranes to react with Cu and Fe, and generate hydroxyl radicals which oxidize a variety of proteins and lipids.

Sousa A.I., I. Caqador, A.I. Lillebp, and M. Pardal. 2008. Heavy metal accumulation in Halimione portulacoides Intra- and extra-cellular metal binding sites. Chemosphere 70 850-857. 

Once the metal has been removed from the environment, it must be transported into the cell for use. In most cases, environmental metal levels are significantly lower than the cellular metal quota (Table 1). This dichotomy requires organisms to concentrate... 

Table 1 Known biochemical functions of selected trace elements that are known to account for a sizeable fraction of cellular metals in marine microorganisms.

T. Dillard, F. NGuyen, S. Forest, Y. Bienvenu, J. Bartout, L. Salvo, R. Dendievel, E. Maire, P. Cloetens, and C. Lantuejoul, in Cellular metals and metal foaming technology, 2003, pp. 1-6. Verlag MIT Publishing,. 

Figure 8. Initial rate of Cu(II) release from an organic complex CuL as a function of the Al-for-Cu metal-exchange rate constant calculated for [Al] = 6/rM, [CuL] = 0.06 piM, where d[Cu(II)]/(/l = /c[AI][CuL] (assuming negligible change in [Al] and [CuL] over some initial time). This ia compared with an estimated range for the metal uptake rate by phytoplankton calculated for 10 cellsL-1 and a cellular metal uptake rate of x 0.5-2.5 x 10" 16 mol cell-1 h 1 (Sunda and Huntsman, 1986 Harrison and Morel, 1986). Also shown are the estimated maximum rate constantl...

LIGHTWEIGHT CELLULAR METALS WITH HIGH STRUCTURAL EFFICIENCY... 

Key words cellular metals, metallic foam, open- and closed-cell foam, hollow-sphere foam, optimized truss structures, honeycomb. 

Cellular solids are a class of materials with low densities and novel physical, mechanical, thermal, electrical, and acoustic properties. Low-density cellular metals can feature a wide variety of topologies to include open-cell foam, closed-cell foam, hollow-sphere foam, periodic/optimized truss structures, and honeycomb. Metallic foams consist of air dispersed in a solid matrix, similar to polymer foams such as polystyrene or food foams such as whipped cream. Closed-cell foams feature solid faces such that each cell is independently sealed from its neighboring cells, whereas open-cell foams (also known as porous metals, metal sponges and truss-type materials) do not contain cell walls they only have cell edges. Hollow-sphere foams consist of an assembly of individual hollow spheres. 

Lightweight cellular metals with high structural efficiency... 

Additional topics relating to the theme of metallic materials with high structural efficiency included phase reactions and equilibria in relevant systems (Bulanova, Ukraine), fundamental mechanisms of dynamic recovery and recrystallization (Leffers, Denmark Montheillet, France), joining by friction stir welding (Jata, USA), production of cellular metals (Sanders, USA) and... 

C. Tekoglu, P. Onck (2003). A comparison of discrete and Cosserat continuum analyses for cellular materials. In Cellular Metals and Metal Foaming Technology (Eds. J. Banhart, M. Ashby, M. Fleck). MlTVerlag, Berlin. 

Sacrificial systems these absorb energy and prevent the load from transferring to the stmc-ture that is being protected. The use of cellular metals as cladding materials has been investigated [12,13] with possible application to the hull of a mine-resistant vehicle. However, such systems require a (heavy) protective faceplate and need a thick core in order to be effective. Hence, this type of system is impractical for blast protection on board aircraft, where weight and volume are critical. 

It is also known that cellular metal ion concentrations change with age. An illustration of such age changes in human lens nuclei is given in Table I (22). We hypothesize that these changing concentrations of metal ions that are essential to genetic information transfer, yet can alter it, can affect information transfer and therefore contribute to the changes that are associated with the aging process. 

Cellular metal ion transport is biologically important because our muscular and nervous systems are regulated by charged species. Cells use membrane channels to extract potassium ions selectively from environments containing both K+ and Na+. Because the K+ ion is /argerthan the Na+ ion, this process cannot be accomplished by simply restricting the channel diameter. Dr. Roderick MacKinnon showed that potassium selectivity arises from a preferential interaction between the potassium cation and the atoms of the protein amino acids composing the channel walls. 

Wang, M., and W.X. Wang. 2008. Cadmium toxicity in a marine diatom as predicted by the cellular metal sensitive fraction. Environ. Sci. Technol. 42 940-946. 

Tian, J., Lu, T.J., Hodson, H.P., Queheillalt, D.T. and Wadley, H.N.G. (2007). Cross-flow heat exchange of textile cellular metal core sandwich panels. International Journal of Heat and Mass Transfer, Vol. 50, pp. 2521-2536. 

---