Rhenium abundance

Rhenium abundance in most rocks is measured in parts per billion or less and minerals in which it is a major constituent are rare. It is similar geochemically to molybdenum, which it commonly accompanies through magmatic and related hydrothermal stages, and is concentrated in molybdenite associated with various types of granite-related deposits. Molybdenites with some of the highest concentrations of rhenium are associated with porphyry Cu and Cu-Au deposits, which are the primary industrial source of rhenium. Rhenium can also be concentrated by low-temperature... 

The Re- Os method was first applied to extraterrestrial samples in the early 1960s when Hirt et al. (1963) reported a whole-rock isochron for 14 iron meteorites that gave an age of 4 Ga. Further development of this system was hindered by several technical difficulties. Rhenium and osmium each exist in multiple oxidation states and can form a variety of chemical species, so complete digestion of the samples, which is required to chemically separate rhenium and osmium for mass spectrometry, is difficult. In addition, accurate determination of rhenium abundance and osmium isotopic composition requires spiking the samples with isotopically labeled rhenium and osmium, and equilibration of spikes and samples is challenging. A third problem is that osmium and, particularly, rhenium are very difficult to ionize as positive ions for mass spectrometry. These problems were only gradually overcome. 

Hauri E. H. and Hart S. R. (1997) Rhenium abundances and systematics in oceanic basalts. Chem. Geol. 139, 185-205. 

Rhenium is a highly soluble element that is easily leached during weathering, so the rhenium abundances of loess cannot be used directly to infer its upper crustal abundance. Following Esser and Turekian (1993), Peucker-Ehrenbrink and... 

Since detailed chemical structure information is not usually required from isotope ratio measurements, it is possible to vaporize samples by simply pyrolyzing them. For this purpose, the sample can be placed on a tungsten, rhenium, or platinum wire and heated strongly in vacuum by passing an electric current through the wire. This is thermal or surface ionization (TI). Alternatively, a small electric furnace can be used when removal of solvent from a dilute solution is desirable before vaporization of residual solute. Again, a wide variety of mass analyzers can be used to measure m/z values of atomic ions and their relative abundances. 

Rhenium, atomic wt 186.2, occurs in nature as two nucHdes Re [14391-28-7] mass 184.9530, in 37.500% abundance and Re [14391-29-8], mass 186.9560, in 62.500% abundance. The latter isotope is radioactive, emitting very low energy radiation and having a half-life estimated at 4.3 ( 0.5) X 10 ° yr. The radioactive decay of this isotope has been used to date accurately the time of Earth s formation. 

Occurrence and Recovery. Rhenium is one of the least abundant of the naturally occurring elements. Various estimates of its abundance in Earth s cmst have been made. The most widely quoted figure is 0.027 atoms pet 10 atoms of silicon (0.05 ppm by wt) (3). However, this number, based on analyses for the most common rocks, ie, granites and basalts, has a high uncertainty. The abundance of rhenium in stony meteorites has been found to be approximately the same value. An average abundance in siderites is 0.5 ppm. In lunar materials, Re, when compared to Re, appears to be enriched by 1.4% to as much as 29%, relative to the terrestrial abundance. This may result from a nuclear reaction sequence beginning with neutron capture by tungsten-186, followed by p-decay of of a half-hfe of 24 h (4) (see Extraterrestrial materials). 

Technetium then became available in a weighable quantity because of uranium nuclear fission leading to the production of "Tc in nuclear reactors. The total amount of "Tc in the world at the end of 1993 is estimated to be 78 tons, more abundant than rhenium on the earth. 

For Mn2(CO)10, the ions corresponding to Mn2(CO)+ ( =8 or 9) were either not seen (247) or were of very low abundance (49,164), and Mn2(CO)7 was only apparent with less than the normal 70-V ionizing potential. All other Mn(CO)+ ( =0-5) and Mn2(CO)J (w=0-10) ions were observed, but no doubly charged ions were seen. The carbide ions MnC(CO)J (n=0-2) were observed in low abundance. Similar ions were found in the spectrum of Re2(CO)10, as also was the series Re2(CO) C+ ( = 0-5), and the doubly charged ions Re2(CO)2+ and Re2(CO) C2+ ( =0-6). Major differences in intensities in the two spectra can be attributed to the greater strength of the rhenium-rhenium bond. About 60% of the ions produced... 

Rhenium is an element known for its abundance of metal hydride complexes spanning a variety of oxidation states, for example, from Re(I), Re(CO)sH to Re(VII), ReH92 . However, despite the recent interest in light-driven H2 formation from different substrates (such as water) there are few recent photochemical studies of Re hydride complexes. 

The reason for it is not obvious since gold is not a very rare element on earth, and other metals, for example, platinum, rhodium, osmium, and rhenium, are less abundant and more expensive. Its yellow color cannot be the reason either, since other metals, such as copper, and its alloys as bronze or brass, have different colors from the bright silver of most of the metals. Probably, the reason resides in its noble character. In fact, gold does not tarnish with time, and coins and jewelry remain indefinitely unalterable even after long exposure to extremely aggressive conditions. 

After Niels Bohr s proposal of the atomic model and the reinterpretation of the periodic system by Moseley s rule, the search for the missing elements received a new impetus and numerous were the attempts to fill the last gaps in the periodic table. Several rare earths were isolated and, by 1924, only five elements were still to be discovered numbers 43, 61, 75, 85, and 87. Four of those elements are the natural radio-elements 43, 61, 85, and 87 and, for this reason, they escaped the searches led by chemists who were missing the right tool to isolate or even produce them in observable quantities. This was not the case with rhenium (element 75), the last stable element to be discovered and also one of the less abundant in the earth s crust. 

Cat B is an abundant and ubiquitously expressed cysteine peptidase of the papain family and makes up a major fraction of lysosomal enzymes that is capable of degrading components of the extracellular matrix in various diseases [30-32]. Cat B is also a prognostic marker for several types of cancer [33], and increased expression and secretion of cat B has been shown to be involved in the migration and invasion of various tumours [34—36], The precise role of cat B in solid tumours is not fully understood, but it has been proposed to participate, along with other cysteine cathepsins, in metastasis, angiogenesis, and tumour progression [37], Indeed, cat B inhibitors reduce both tumour cell motility and invasiveness in vitro [38], Recently, metal complexes based on rhenium, gold and palladium were shown to be effective inhibitors of cat B [39-44],... 

Table II shows quite reasonable results for natural abundance isotope ratios it must be noted that Cr Fe and Mg are frequently observed as interferences Heating a clean but unloaded filament gives rise to Cr and Fe ions implying that these two elements are contaminants of the rhenium filament ribbon Heating a filament loaded with silica gel and phosphoric acid gives rise to Mg ions as well as those from Cr and Fe while only Cr and Fe ions are seen when silica gel alone is on the filament This implies a Mg contamination of the acid Finally inhibition of one metal s emmission by another has been seen previously (5) The previously reported inhibition of iron by zinc and of cadmium by iron is seen in this work when the metals of Table II are contaminated with the appropriate ions ...

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