A Look Inside the World of Chemistry: Developments and Applications of Yttrium

A Look Inside the World of Chemistry: Developments and Applications of Yttrium

By Alex Morgan

The realm of chemical inquiry is a vast, beautifully strange world, whose scope is seemingly limitless; with fields of study in all disciplines of chemistry expanding- and new ones emerging- there is a place for all curious and inquisitive minds in the realm of chemical research. This perpetual need for people interested in pursuing this scientific research is magnified further by the fact that all of these fields examine questions so deeply complex that one can spend a lifetime looking into the mysteries in but a small niche of a particular area. To simultaneously demonstrate this fact, as well as the importance, beauty and utility inherent to scientific work, I will explore the research done surrounding but a single element of the periodic table: Yttrium. First, I will elucidate the history and the basic elemental facts surrounding the element, then describe some of the important and recent work done in fields ranging from medicine to engineering. In doing so, I hope to convince you of the real possibility that exists for pursing such work, and of the value and satisfaction that one can find for oneself in doing so.

        Yttrium was first discovered by Johan Gadolin, a chemist from Finland, in 17941. He was the first to recognize the new element present in a sample of ore discovered in Swedish mine near the town of Ytterby. Carl Arrhenius, a lieutenant in the Swedish army and part-time chemist, is recognized for discovering the dark mineral near the Ytterby mine and sending samples to several chemical colleagues for analysis, including Gadolin (he suspected it contained the newly-discovered element tungsten). Arrhenius named the sample Ytterbite, after the town near the mine; similarly, with the discovery of the new element within the ore, Gadolin and his colleague Ekeberg, who confirmed his results, named the element after the town as well: hence, Yttrium. Interestingly, several other rare elements were discovered later from samples taken from the Ytterby mine, namely ytterbium, terbium and erbium, as well as holmium, thulium and gadolinium2. [pic 1][pic 2]

        Yttrium is the 39th element in the periodic table, the first element in the second row of the d-block transition metals, in the fifth period of the table itself. As a pure sample, it appears to be light-gray, lustrous and relatively soft for a metal. Yttrium is the 28th most-abundant element in the earth’s crust, having greater abundance than elements such as gold, silver, lead and tin3. Yttrium has the electron configuration [Kr]4s25d1, thus having only 3 valence electrons. It is generally found in nature to be in the third oxidation state (having all 3 valence electrons removed), in forms such as Y2O3 or Y2(CO3)3. Yttrium is known to have 25 different isotopes, ranging from 79Y to 103Y1. Only one of these isotopes, however, is stable and found to be naturally occurring: Yttrium-89; all others are synthetic by-products of nuclear reactions, are radioactive and have known half-lives.

        While Yttrium is the 28th most abundant element on Earth, an interesting puzzle exists: the Moon has a far higher level of Yttrium found in the soil and rock samples taken during the Apollo moon landing1. Earth, on average has a concentration of 33 ppm of Yttrium in its crust, while the moon samples have been measured to range between 54 to 213 ppm. This has called into question some theories of how the moon was formed- from this evidence, it’s makeup is not entirely from materials of just the Earth; possible explanations include the composition of a meteor impacting the earth contributing to the high levels of rare-earth metals such as Yttrium, or that the Moon is an entirely foreign object from Earth that was simply “captured” at some point by Earth’s gravity.[pic 3]

Yttrium has applications in medicine, particularly in the area of cancer radiation treatments. Yttrium-90, 90Y, is a radioactive isotope of yttrium which is a by-product of the decay of strontium-90 4, which is formed in nuclear reactors through the fission of uranium. The 90Y is formed from the β-decay of strontium-90:[pic 4]

90Sr → 90Y + β

Where the Greek letter β represents the emission of an electron from the nucleus, resulting in the conversion of a neutron into a proton, thus increasing the number of protons in the nucleus by one which alters the elemental nature of the nucleus. The 90Y itself also undergoes β-decay into zirconium-90, a decay which has a half-life of 64 hours. It is this radioactive decay which is useful in radiotherapy of certain forms of cancer, notably cancer of the liver and neuroendocrine system5,6. The isotope is employed by two different mechanisms, each one used to treat one of the aforementioned cancers: selective internal radiation therapy is used to treat cancer of the liver, while peptide receptor radionuclide therapy is used to effectively treat cancer of the neuroendocrine system. Selective internal radiation therapy involves the use of “microspheres” of the radioactive isotope, approximately 30 microns in diameter, which are directly inserted to the artery supplying blood to the tumours via a catheter.  The isotope is then carried to the cancerous area, where it settles and emits cell-killing radiation to the afflicted area. This treatment is far more selective than external or orally-taken radiative treatments, as it is sent directly to the area of need, thus minimizing the negative effects of radiation on other parts of the patient’s body and improving the overall quality of life during treatments, and can be done on an outpatient basis (ie. the patient is not required to stay at the hospital throughout the treatment process)5. The peptide receptor radionuclide therapy is similarly effective, but a touch more ingenious in its selectivity: The radioactive isotope is bound to a particular hormone in order to target the cancerous area. As a result, the only areas targeted are areas with receptor sites for that particular hormone. Once the isotopically-labelled hormone is in place the beta-decay results in radiation killing only the cancerous cells and those nearby6. Any excess of the radioisotope is excreted through the urine. The development of these techniques marks several advances: first and foremost, it serves as a creative application of a small portion of nuclear waste from uranium fission; second, both techniques improve radiative treatment of cancer for the patient, as the treatments minimize the side-effects of radiation on healthy cells and organs in the body, and thus seriously improve the quality of life of cancer patients during treatment.