Technetium

Technetium.—Technetium(vi) has been shown to be a viable chemical species in alkaline aqueous solution. It is generated by reduction of [ Tc04] with eaq in 0.1 M-NaOH solution (A = 2.5 x 10 s ) and exhibits a broad 

The technetium complex TcCl(CO)3(PPh3)2 in combination with EtAlCl2 is moderately active for metathesis of pent-2-ene (Lorenz 1982). 

ORIGIN OF NAME Technetium s name was derived from the Greek word technetos, meaning artificial.  

ISOTOPES There are 47 isotopes. None are stable and all are radioactive. Most are produced artificially in cyclotrons (particle accelerators) and nuclear reactors. The atomic mass of its isotopes ranges from Tc-85 to Tc-118. Most of technetium s radioactive isotopes have very short half-lives. The two natural radioisotopes with the longest half-lives—Tc-98 = 4.2x10+ years and Tc-99 = 2.111 xl0+ years—are used to establish technetium s atomic weight. 

As the central member of the triad of metals in group 7, technetium (period 5) has similar physical and chemical properties as its partners manganese (period 4) above it and rhenium (period 6) below it. The sizes of their atomic radii do not vary greatly Mn = 127, Tc = 136, and Re = 137. Neither does their level of electronegativity vary significantly Mn = 1.5, Tc = 

Technetium metal is grayish-silver and looks much like platinum. As with most transition elements, technetium in pure form is a noncorrosive metal. It requires only 55 ppm of technetium added to iron to transform the iron into a noncorroding alloy. Because of technetiums radioactivity, its use as an alloy metal for iron is limited so as to not expose humans to unnecessary radiation. 

Technetiums melting point is 2,172°C, its boiling point is 4,877°C, and its density is 

The continual availability of technetium-99m in the department greatly simplifies the logistics of supply of this short half-life radioisotope and the economy of scale associated with its use reduces its cost by an order of magnitude compared with 1-123 and In-111. Because technetium-99m is so widely available, it is 

Antibody labelling methods are normally described either as direct in which the technetium is complexed directly by the atoms present in the protein chain 

Reduction-mediated technetium-99m labelling of antibodies with 2-mercaptoethanol 

Purge 100 ml of phosphate-buffered saline (PBS) with nitrogen on ice for 30 min. 

Calculate the volume of 2-mercaptoethanol that must be added to the antibody to give a molar ratio of 2000 1 (2-ME Ab) This translates to 0.47 p-1 of mercaptoethanol/ mg of antibody. 

The continuing development of technetium complexes for radiopharmaceutical use is reflected in a large number of publications in this field. There are very few thorough investigations of kinetics and mechanisms of reactions of technetium compounds, but a number of investigations have yielded qualitative indications of reactivity or of mechanism. Many papers in the latter class are mentioned here it is to be hoped that their kinetic and mechanistic aspects will be properly developed in the near future. 

Technetium complexes with dtpa, dmsa, or mdp (methylene diphos-phonate) can be prepared by exchange reactions of the respective rhenium complexes with pertechnetate. Despite the complication that redox as well as substitution is involved here, rates correlate with metal-ligand bond strengths. A detailed kinetic study of these reactions would be welcome. Another type of ligand exchange reaction where kinetic studies are needed is the similar situation encountered in the preparation of technetium(III), (IV), or (V) complexes by reduction of pertechnetate with tin(II) complexes of the respective ligands. 

Photochemical aquation of hexachlorotechnetate(IV) has been reviewed.Chloride substitution by thiocyanate, to give [Tc(NCS)6], is 

The dinuclear anion [Tc2Cl8] undergoes substitution by acetate, as by pivalate, only slowly. Although [Tc2Cl8] is very 

Substitution Reactions—Nos. 6 and Above Other Inert Centers 

The expected kinetic inertness of the d center technetium(I) is demonstrated by the sluggishness reported for preparative substitution reactions of the newly 

In 1937 Perrier and Segre bombarded a molybdenum target with deuterons to produce technetium as the first man-made element [34]. This element has 31 known isotopes with mass numbers firom 86 to 117, and all are radioactive. The most readily available isotope is Tc = 2.1 X10 years), which can be isolated from spent nuclear fuel where it constitutes approximately 6% of the fission product yield of U. In the recovery process, the pertechnetate anion, [ TcO, ] , is extracted with pyridine firom aqueous solution and ultimately isolated as [NH j [TcO, ] with a purity of better than 99.9% [35]. The ammonium salt is readily available at a reasonable cost from Oak Ridge National Laboratory [36]. 

All other starting materials trace their origins to this commercial source of the element. Ammonium pertechentate from the supplier is black in color rather than the expected pure white. This is due to self-reduction to TcO over long periods of time. Fortunately, the TcOj coating represents only a small fraction of the total mass and is easily converted back to pertechnetate by the recrystallization of the salt from a warm basic aqueous peroxide solution. 

The orange Tc2(02CCH3) Br2 complex can be prepared, also in low yield, by refluxing (TBAljTCjBrj in an acetic acid/acetic anhydride mixture [49]. 

A green bis-acetate compound Tc2(02CCH3)2Cl4 can be prepared in essentially quantitative yield from the reaction of Tc2(02CCH3)4Cl2 with gaseous hydrochloric acid at 150 °C (Eq. (7.3)) [51]. In work described below, technetium trichloride (a-XcCl3) was obtained from the reaction of 

A geometry optimization of Tc2(02CCH3)2Cl4 was performed using the Tao, Perdew, Staroverov, and Scuseria hybrid functional (TPSSh) at the triple-zeta valence plus polarization (TZVPP) basis set [53]. The results show that the calculated Tc-Tc, Tc-Cl, and Tc-O bond distances are in good agreement with the experimental values (Table 7.5). The largest deviation is found for the Tc-Tc distance. 

Despite its limited crystal field stabilization, the d complex bis(4-chloroben-zenethiolato)bis(l,2-bis dimethylphosphino ethane)technetium(II), (20), undergoes relatively slow trans to cis isomerization, with a rate constant of 1.6 x s in dichloromethane at ambient temperature. The low-spin d complex [Tc(acac)3] shows a similar reactivity with respect to exchange with C-labeled acac to [Cr(acac)3]. Activation parameters for the technetium complex are AFT = 119 kJ mol and A5 = -27 J mol in acetylacetone.  

Half-lives for hydrolysis of Tc—Cl to Tc—OH have been determined for four so-called BATO complexes. These contain a semiencapsulating tris-dioxime ligand with a borate cap and the chloride ligand the technetium is seven-coordinate, (21), with Y = OH or Me and either R = Me or pairs of R comprise cyclohexyl rings. Rate constants lie in the range 19 to 1.2 x lO s for the four complexes examined, at 20 to 37 There is also some very qualitative kinetic information on base hydrolysis and ligand exchange (Cl for Br and vice versa) in this type of complex. These reactions have half-lives of minutes in media such as aqueous acetonitrile.  

Technetium(IV) is an oxidation state where high crystal field activation energies may be expected, and indeed substitution at [TcBrg] and at [TcF ] is very slow. Under forcing conditions the latter gives di-/i.-oxo-di-technetium species, indicating a complex mechanism. The much-studied and much-used 

8 Inert-Metal Complexes Other Inert Centers 

The nitrogen analogs of the well-known [TCOX4] anions mentioned above are technetium(VI) species [TcNX4] . The chlorides in [TcNC ] are labile, being easily and quickly replaced by bromide or by fluoride. There is some qualitative information on the conversion of [TcNCU] into [Tc04], whose mechanism involves both substitution and electron transfer.  

T0060 Argonne National Laboratory, Aqueous Biphasic Extraction System 

T0062 Argonne National Laboratory, Ceramicrete Stabilization Technology 

T0066 Argonne National Laboratory, Transuranium Extraction (TRUEX) Process 

T0151 Ceramic Immobilization of Radioactive Wastes—General 

T0709 Sevenson Environmental Services, Inc., MAECTITE Chemical Treatment Process 

Taste and smell are well-known chemical senses however, the specific genes and proteins involved in some tastes have not yet been fully identified. SEE ALSO Artificial Sweeteners Molecular Structure Neurotransmitters. 

Mark F. Connors, Barry W. and Paradiso, Michael A. (1996). Neuroscience Exploring the Brain. Baltimore Williams Wilkins. 

Kinnamon, Sue C. (2000). A Plethora of Taste Receptors Minireview. Neurm 25 507-510. Also available from http //hsc.virginia.edu/ . 

Zigmond, Michael J. Bloom, Floyd E. Landis, Story C. Roberts, James L. and Squire, Larry R., eds. (1999). Fundamental Neuroscience. San Diego Academic Press. 

Henahan, Sean. Molecular Basis of Good Taste and Tasteful Research. Access Excellence the National Health Museum. Available from http //www. accessexcellence.org/ . 

Ground state electron configuration Crystal structure  

Discovery The element was first produced by irradiation of molybdenum in an atomic reactor. The new metal was identified in 1937 by E. G. Segrd and C. Perrier in Palermo. The metal was given its name technetium, as it was the first element manufactured in a technical way. 

Most important mineral No Tc-minerals of importance are known. In 1988, however, minute Tc quantities were detected in a deep molybdenum mine in Colorado. 

Ranking in order of abundance in earth crust 89-92 Mean content in earth crust - 

Technetium is a radioactive, silvery gray metal that tarnishes slowly in moist air. The chemistry of technetium is related to that of rhenium. In medical practice different Tc compounds are used. One is sodium pertechnetate Na TcO,. The radioactive isotope is absorbed in tumors that can later be located by radioactive detection. 

There seems to be some disagreement as to the rapidity with which hexa-halogenotechnetates(IV) undergo hydrolysis. The aquation of [TcCl6] is very slow in strong acid, less slow or fairly fast in dilute acid, and rapid 

Substitution Reactions of Inert Metal Complexes—6 and Above 

Tarasov, Buslaev, and co-workers observed a nine-line pattern for polycrystalline K[Tc04], arising from first-order quadrupole perturbation. The NQCC, calculated for = 0 from the spacing between two symmetrically disposed satellites (217 kHz) is 5.2(2) and so exceeds the values for K[Mn04] (1.6) and Na3[V04] 

Three forms of mercury(II) oxide are known and solubility data are available for all three. The solubility data relate to reaction (2.13) (M = Hg, x = 1). 

The ionic radius of two-coordinate mercury(II) has been reported to be 0.69 A (Shannon, 1976). 

There has been a single study that has postulated data for the stability constants of the hydrolysis reactions of molybdenum(III) (Mit kina, Mel chakova and Peshkova, 1978). Three species were postulated including MoOH, MofOHlj and Mo(OH)g(aq). The experiments in the study were conducted at 20 C and in 1.0 mol 1 (Na,H)Cl, and the stability constants proposed for the three species were log = -2.0 0.1, log P2 = —4.6 0.1 and log = —7.3 0.1. Mit kina, 

Mel chakova and Peshkova (1978) assumed that the protolysis constant of water for the conditions used was log = -14.0. This value is somewhat different from that derived in the present review for the conditions studied, that is, log =-13.88. This difference indicates that the stability constants proposed should be more positive than indicated by 0.12 log units per OH molecule in each proposed species. This suggests that the stability of molybdenum(lll) hydrolysis species would be substantially more stable than those of chromium(lll). This is considered unlikely on the basis of the corresponding ionic radii of the two ions. Molybdenum(III) has a larger ionic radius than chromium(III) (Shannon, 1976) and, as such, would likely have hydrolysis species of lesser stability. Thus, the stability constants listed by Mit kina, Mel chakova and Peshkova (1978) are not retained (but see Chapter 16). 

M = TcO +,. = 0) of log /CjjQ = —32.3. The minimum solubility was found to be log Kgi2 = -8.24 0.41 that was independent of the chloride concentration used, although there was some scatter in the minimum solubility data of Meyer et al. Eriksen et al. (1992) also studied the solubility of technetium dioxide across the pH range of 6 -12.2. They found a minimum solubility of log = —8.17 0.05, 

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Gr. technetos, artificial) Element 43 was predicted on the basis of the periodic table, and was erroneously reported as having been discovered in 1925, at which time it was named masurium. The element was actually discovered by Perrier and Segre in Italy in 1937. It was found in a sample of molybdenum, which was bombarded by deuterons in the Berkeley cyclotron, and which E. Eawrence sent to these investigators. Technetium was the first element to be produced artificially. Since its discovery, searches for the element in terrestrial material have been made. Finally in 1962, technetium-99 was isolated and identified in African pitchblende (a uranium rich ore) in extremely minute quantities as a spontaneous fission product of uranium-238 by B.T. Kenna and P.K. Kuroda. If it does exist, the concentration must be very small. Technetium has been found in the spectrum of S-, M-, and N-type stars, and its presence in stellar matter is leading to new theories of the production of heavy elements in the stars. 

Until 1960, technetium was available only in small amounts and the price was as high as 2800/g. It is now commercially available to holders of O.R.N.L. permits at a price of 60/g. 

It is reported that mild carbon steels may be effectively protected by as little as 55 ppm of KTc04 in aerated distilled water at temperatures up to 250oC. This corrosion protection is limited to closed systems, since technetium is radioative and must be confined. 9sTc has a specific activity of 6.2 X lOs Bq/g. Activity of this level must not be allowed to spread. 99Tc is a contamination hazard and should be handled in a glove box. 

Physical Properties. Molybdenum has many unique properties, leading to its importance as a refractory metal (see Refractories). Molybdenum, atomic no. 42, is in Group 6 (VIB) of the Periodic Table between chromium and tungsten vertically and niobium and technetium horizontally. It has a silvery gray appearance. The most stable valence states are +6, +4, and 0 lower, less stable valence states are +5, +3, and +2. 

The isotope molybdenum-99 is produced in large quantity as the precursor to technetium-99y, a radionucleide used in numerous medical imaging procedures such as those of bone and the heart (see Medical imaging technology). The molybdenum-99 is either recovered from the fission of uranium or made from lighter Mo isotopes by neutron capture. Typically, a Mo-99 cow consists of MoO adsorbed on a lead-shielded alumina column. The TcO formed upon the decay of Mo-99 by P-decay, = 66 h, has less affinity for the column and is eluted or milked and either used directly or appropriately chemically derivatized for the particular diagnostic test (100). 

Each has been recovered and used in various quantities. Rhodium, palladium, and technetium have also been recovered for potential catalytic or precious metal appHcations (34,35). 

A. U. Blackham md J. Palmer, Technetium as a Catalyst in Organic Reactions, AT945-1-2017, Atimtic Richfield Hmford Co., Richlmd, Wash., July 1967. 

Many of the uranium fission fragments are radioactive. Of special interest are technetium-99 [14133-76-7] and iodine-129 [15046-84-1] having half-Hves of 2.13 X 10 yr and 1.7 x 10 yr, respectively. Data on all isotopes are found in Reference 6 (see also Radioisotopes). 

Several modes of waste management are available. The simplest is to dilute and disperse. This practice is adequate for the release of small amounts of radioactive material to the atmosphere or to a large body of water. Noble gases and slightly contaminated water from reactor operation are eligible for such treatment. A second technique is to hold the material for decay. This is appHcable to radionucHdes of short half-life such as the medical isotope technetium-9 9m = 6 h), the concentration of which becomes negligible in a week s holding period. The third and most common approach to waste... 

Plutonium was the first element to be synthesized in weighable amounts (6,7). Technetium, discovered in 1937, was not isolated until 1946 and not named until 1947 (8). Since the discovery of plutonium in 1940, production has increased from submicrogram to metric ton quantities. Because of its great importance, more is known about plutonium and its chemistry than is known about many of the more common elements. The metallurgy and chemistry are complex. MetaUic plutonium exhibits seven aUotropic modifications. Five different oxidation states are known to exist in compounds and in solution. 

Gmelin Handbuch derAnorganischen Chemie, Technetium, Spriager-Vedag, Berlin, 1982. 

Certain neutral technetium complexes can be used to image cerebral perfusion (Fig. 4). Those in Figure 4a and 4b have been approved for clinical use. Two other complexes (Fig. 4c and 4d) were tested in early clinical trials, but were not developed further. An effective cerebral perfusion agent must first cross the blood brain barrier and then be retained for the period necessary for image acquisition. Tc-bicisate is retained owing to a stereospecific hydrolysis in brain tissue of one of the ester groups to form the anionic complex TcO(ECD) , which does not cross the barrier. This mechanism of retention is termed metaboHc trapping. 

Several hydrophilic, anionic technetium complexes can be used to perform imaging studies of the kidneys. Tc-Mertiatide (Fig. 5a) is rapidly excreted by active tubular secretion, the rate of which is a measure of kidney function. Tc-succimer (Fig. 5b), on the other hand, accumulates in kidney tissue thus providing an image of kidney morphology. 

Many kits contain the indicated biologically active ingredient in a lyophilized form with stannous chloride. A Tc-labeled radiopharmaceutical, which can be used for six hours, is formed when mixed with Tc pertechnetate. Preparation of the agent is at room temperature, unless otherwise stated. Technetium-99m. Available Tc kits are Hsted below. 

Technetium-9 9m sestamibi is used in myocardial perfusion imaging for the evaluation of ischemic heart disease. It is prepared from a lyophilized kit containing tetrakis(2-methoxy isobutyl isonittile) copper(I) tetrafluoroborate stored under nitrogen. Upon reconstitution with up to 5.6 GBq (150 mCi) of 99mTc pertechnetate, the product is formed by boiling for 10 minutes. 

Technetium-99m oxidronate is a bone imaging agent used to demonstrate areas of altered osteogenesis. It is rapidly cleared from the blood and taken up in areas of bone that are undergoing osteogenesis. The kit is a vial containing a lyophilized powder where sodium oxidronate is the active... 

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