Definition/Introduction
Xenon is an element with the symbol Xe, has an atomic number 54, and belongs to group 18 of the periodic table. Xe is a monoatomic, inert gas, first discovered in 1898 by British chemists William Ramsay (1852-1916) and Morris Travers (1872-1961) in the residue left after partial evaporation of liquid air (with krypton as an impurity).[1] Xe is a colorless, odorless, non-pungent, nontoxic, nonexplosive, and environmentally friendly noble gas. Xe exists in trace amounts in the Earth's atmosphere, with a concentration of only 0.086 ppm, and is also found in gases emitted from certain mineral springs. The name Xe is derived from the Greek word for "stranger," which reflects its rarity. Of its 9 naturally occurring isotopes, Xe-132 is the most abundant.
Xe has several notable physical and chemical properties, including a boiling point of 166.6 K and a melting point of 161.7 K. The density of Xe is 5.851 g/dm2, and it exhibits a blue-green color spectrum. With an oil-gas partition coefficient of 1.9, Xe is one of the noble gases and is the most soluble gas in oil (lipids). Although Xe typically does not react with most elements, it can form specific compounds with substances such as water, hydroquinone, and phenol. This noble gas can be oxidized by highly electronegative groups, resulting in the formation of salts. For example, the compound Xe-hexafluoroplatinate was first synthesized in 1962 by chemist Neil Bartlett (1932–2008). This was the first noble gas chemical compound reported in the scientific literature. Other Xe fluorides are the Xe difluoride (XeF2), Xe tetrafluoride (XeF4), and Xe hexafluoride (XeF6).
Xe can be produced through the fractional distillation of liquefied air, but its high cost limits industrial use. One application is the Xe lamp—a type of arc lamp that uses Xe gas to produce an intense white light similar to sunlight. Xe lamps consist of a glass or quartz tube with 2 tungsten electrodes at the ends, filled with Xe gas after the air is evacuated. These lamps are used in street lighting, photo flashes, projectors, car headlights, and marine lighting. Xe is also used in lasers, x-ray tubes, the food industry for microorganism sterilization, and aerospace applications.
Xenon in Medicine
The primary medical use of Xe is as a radioactive diagnostic agent in clinical imaging and as an inhaled anesthetic for general anesthesia. Xe also has applications in organ protection, ophthalmology, and dermatology.
Clinical imaging: Xe is indicated for assessing cerebral blood flow via Xe-enhanced computed tomography (CT), pulmonary function evaluation, and lung imaging. Xe is also used in nuclear medicine through techniques such as CT, single-photon emission CT (SPECT), and magnetic resonance imaging (MRI). In summary, Xe can be used to measure cerebral blood flow, perform whole-brain scans, and conduct lung ventilation studies using MRI (¹³¹Xe), SPECT (¹³³Xe), and CT (¹²?Xe).
General anesthesia: The anesthetic proprieties of Xe were discovered in 1939, with initial applications in mice by JH Lawrence in 1940, and later tested on human volunteers by Cullen and Gross in 1951.[2] In addition, it is indicated in selected patients due to its cardiovascular stability, cerebral protection, and favorable pharmacokinetics, including low solubility and lack of metabolism. Moreover, the use of Xe is environmentally friendly, as it does not have a significant environmental impact.[3]
Organ protection: An important area of research is Xe-induced organ protection. For instance, Xe has been proposed as a means to prevent ischemia or reperfusion damage following Stanford type-A acute aortic dissection surgery.[4] Several preclinical investigations conducted on various models subjected to preconditioning, real-time conditioning, and postconditioning have demonstrated that Xe may provide significant neuroprotective and cardioprotective effects. These effects are dose-dependent and are thought to result from Xe's interference with glutamatergic transmission, as glutamate receptors are involved in both anesthesia and acute neurological injury through apoptotic processes, as well as its ability to inhibit the inflammatory cascade.[5][6]
The combination of Xe with hypothermia is a fascinating hypothesis. Xe appears to offer neuroprotective properties even at sub-anesthetic concentrations, suggesting these effects can occur independently of its anesthetic effect.[7] Regardless of the precise mechanism, the potential clinical applications of Xe for organ protection are significant. For example, Jia et al demonstrated that intermittent Xe exposure protects against gentamicin-induced nephrotoxicity.[8] This renal protection is crucial for kidney transplantation, as it helps prevent ischemia or reperfusion damage, delays rejection, and reduces the risk of chronic nephropathy.[9] Xe has also shown promise in treating neurobehavioral dysfunction from brain insults,[10] cardiac arrest-induced cerebral ischemia,[11] and neonatal hypoxia-ischemia.[12]
Other clinical uses: In addition to this research, Xe has been studied for its potential in treating various conditions, including dementia, epilepsy, Alzheimer disease, and obsessive-compulsive disorders.[13][14][15][16] Moreover, Xe is used in ophthalmology for laser therapy and dermatology for removing skin lesions. Despite these potential uses, the high cost remains a significant limitation, with the market price for anesthesia ranging from approximately £6 to £12 per liter.