Many years before its discovery in 1937, technetium (Tc) was theorized by Dimitri Mendeleev during the formulation of the periodic table in 1869. It was finally discovered after decades of false identifications by being synthesized in the laboratory.1 As the famous scientific comic writer puts it, “The dose from a 1-liter cube of [technetium] wouldn’t be enough to be lethal in our experiment, but it’s still substantial. If you spent all day wearing it as a hat – or breathed it in as dust – it could definitely kill you.”2 One of the defining characteristics of technetium is that it is the lightest element with no stable isotopes. This property makes Technetium especially interesting and useful. Physicists study this to look at the nuclear stability of This makes it a very interesting element to both chemists and physicists as well as physicians.
Being unstable technetium has many uses in the medical world. It is very useful due to the length of its half-life. The excited form of technetium (formed by the irradiation of Molybdenum-99 or from fission of Urainium-235 or Plutonium-239) has a half-life of about 6 hours, which give doctors enough time to use it as a chemical tag, but it stays in the patient’s system short enough that the emissions from the radioactive decay are still detectible at low concentrations of technetium. Tagging is where the chemical tag binds to the thing in question and is observed using radiation. This makes technetium very useful for this purpose. It is also soluble in blood at body temperature which is helpful for getting the technetium around the body.1 Many of the other tagging compounds either have half-lives out of a useful range or are not as soluble in blood at body temperature which makes them less desirable chemical tags. Due to its relatively short half-life when in its excited form and its solubility in human bodily conditions, technetium is works well as a chemical tag.
One of the diseases that makes use of technetium compounds as chemical tags is Alzheimer’s disease. Amyloid-β plaques in the brain have been linked with Alzheimer’s, so being able to detect the presence of these plaques is imperative to early diagnosis. As researchers have found, certain technetium complexes are very useful in this area while others are not. Using tridentate ligands, the researchers found that fac-[99mTc(CO)3L2] is taken into the brain and binds to these plaques.3 This molecule has an excited isotope of technetium with a molecular mass of 99 and two tridentate ligands. Once the binding has occurred, the researchers were able to find the plaques from the radioactive decay of the technetium centers.
Technetium has many properties that other elements do not have due to its nuclear stability. Being the lightest element with no stable isotope already makes it an interesting element to study, especially since it is the only element in its period that is unstable. The uses of these complexes have been found to be good for tagging in biological systems. Complexes with two tridentate ligands work well at binding and tagging amyloid-β plaques that are linked to Alzheimer’s disease. This kind of research as well as research into removing these plaques greatly progresses the research into Alzheimer’s treatment. While technetium complexes are very useful in identification in medical purposes, it is still radioactive and is not a hat.
References
1. Aspden, H. Hadronic Journal 1987, 10.
2. Munroe, R. What If?: Serious Scientific Answers to Absurd Hypothetical Questions; Houghton Mifflin Harcourt: United States, 2014; p 39.
33. Hayne, D. J.; North, A. J.; Fodero-Tavoletti, M.; White, J. M.; Hung, L. W.; Rigopoulos, A.; McLean, C. A.; Adlard, P. A.; Ackermann, U.; Tochon-Danguy, H.; Villemagne, V. L.; Barnham, K. J.; Donnelly, P. S.Dalton Trans. 2015, 44 (11), 4933–4944.