Xenon Xe-129 (13965-99-6) Physical and Chemical Properties
Xenon Xe-129
Stable xenon isotope commonly supplied as isotopically enriched gas for hyperpolarization and specialized imaging and research applications, handled under pressurized-gas supply protocols.
| CAS Number | 13965-99-6 |
| Family | Noble gas (inert gas) |
| Typical Form | Colorless gas (compressed or cryogenic supply) |
| Common Grades | EP |
Xenon Xe-129 is an isotopically defined, monoatomic noble gas belonging to the xenon element class. Structurally it is a closed-shell, monoatomic species with electronic configuration [Kr]4d10 5s2 5p6 in the neutral ground state; as an isotope of xenon it shares the same chemical identity (Xe, oxidation state zero) while differing in nuclear mass and spin properties. The isotope Xe-129 has a monoisotopic/exact mass of \(128.90478086\) and is one of the naturally occurring stable isotopes of xenon; its nuclear spin is \(1/2\), which enables nuclear magnetic resonance (NMR) observability and makes it suitable for hyperpolarization techniques.
Chemically Xe-129 behaves like other noble gases: extremely low polarity, negligible chemical reactivity under ambient conditions, and essentially no acid–base behavior as conventionally defined for molecular species. Lipophilicity is greater than that of small permanent gases due to xenon’s higher polarizability, producing modest solubility in nonpolar and fatty tissues relative to aqueous media. Xenon shows no hydrolysis or oxidization in water or air at ambient conditions, although it can form stable compounds (xenon oxides, fluorides, and complex cationic or anionic species) only under strong oxidizing and highly controlled laboratory conditions.
The capacity of Xe-129 for nuclear hyperpolarization (enhancement of nuclear spin polarization by several orders of magnitude) underlies its principal contemporary industrial and clinical relevance as a contrast agent for pulmonary magnetic resonance imaging (MRI) and as a research tool in NMR spectroscopy and imaging. Regulatory authorization for clinical use of hyperpolarized Xe-129 as an inhaled MRI contrast agent for the evaluation of lung ventilation has been obtained. Common commercial grades reported for this substance include: EP.
Basic Physical Properties (Density, Melting Point, Boiling Point)
Atomic Weight
The isotopic mass reported for Xe-129 is \(128.90478086\) (monoisotopic/exact mass as provided). Natural-abundance information indicates Xe-129 occurs at approximately \(26.4\%\) atom fraction in natural xenon.
Appearance and Physical State
Xenon is a clear, colorless, monoatomic gas under standard laboratory conditions. As a noble gas it exists as single atoms with very weak van der Waals interactions; condensed phases (liquid, solid) require cryogenic temperatures and/or high pressures.
Density
No experimentally established value for this property is available in the current data context.
Melting Point
Melting point: \(161.7\ \mathrm{K}\).
Boiling Point
Boiling point: \(166.6\ \mathrm{K}\).
Chemical Properties (Reactivity and Oxidation States)
Oxidation States
Under normal conditions xenon is present in oxidation state 0 (xenon(0)); this is the chemically inert, monoatomic form relevant to Xe-129 gas and to hyperpolarized gas applications. Chemically significant positive oxidation states (e.g., +2, +4, +6, +8) occur only in laboratory synthesis under strongly oxidizing conditions and are not relevant to typical handling of the elemental gas.
Reactivity with Air and Water
Xe-129 (as neutral xenon gas) is effectively inert toward atmospheric components and water at ambient temperature and pressure; it does not hydrolyze or react with oxygen, nitrogen, or water in normal service conditions. Reactions to form xenon compounds require specialized reagents (strong oxidizers, fluorination agents) and low-temperature/high-pressure or plasma conditions.
Reactivity with Acids and Bases
No conventional acid–base reactivity is exhibited by neutral xenon gas; it does not undergo protonation or deprotonation and is not susceptible to attack by common Brønsted acids or bases under ambient conditions.
Isotopic Composition
Stable Isotopes
Xe-129 is a naturally occurring stable isotope of xenon with reported natural abundance of approximately \(26.4\%\) (atom percent). Its nuclear spin of \(1/2\) makes it NMR-active and suitable for hyperpolarization methods used in imaging and spectroscopy.
Radioisotopes
Metastable and radioactive xenon isotopes exist (notations such as 129mXe appear in technical lists), but the neutral ground-state isotope Xe-129 discussed here is stable. Specific data for decay schemes, half-lives, or radiological parameters for metastable isotopes are not provided in the current data context.
Thermodynamic Parameters
Heat Capacity and Related Data
No experimentally established value for this property is available in the current data context.
Enthalpy and Gibbs Energy
No experimentally established value for this property is available in the current data context.
Identifiers and Synonyms
Registry Numbers and Codes
- CAS number: 13965-99-6
- UNII: 9C7571UDT5; 726Q6M95ZA
- ChEBI: CHEBI:52453
- ChEMBL: CHEMBL4594411
- DrugBank: DB17386
- DSSTox Substance ID: DTXSID401028031
- KEGG: D12496
- NCI Thesaurus Code: C128034
- RXCUI: 2626219; 2626220
- InChI: InChI=1S/Xe/i1-2
- InChIKey: FHNFHKCVQCLJFQ-YPZZEJLDSA-N
- SMILES: [129Xe]
- Molecular formula: Xe
- Molecular weight: \(128.90478086\)
- Exact mass: \(128.90478086\)
- Monoisotopic mass: \(128.90478086\)
Synonyms and Common Names
Available depositor-supplied synonyms and alternate names include: Xenon Xe-129; XENOVIEW; Xenon, isotope of mass 129; 129Xe; Xe 129; 9C7571UDT5; Xenon xe-129 hyperpolarized; Xenon xe-129m; Xenon, xe-129m; RefChem:902350; xenon-129; 13965-99-6; UNII-9C7571UDT5; 726Q6M95ZA; Hp 129xe; UNII-726Q6M95ZA; Xenon xe-129, hyperpolarized; Xenon-129 isotope; 129mXe isotope; Xenoview (TN); 129Xe isotope; Isotope:129mXe; xenon-129 atom; Isotope:129Xe; 129Xe radioisotope; 129mXe (isotope); 129Xe (isotope); Isotope:Xenon-129; Xenon-129m isotope; Isotope:Xenon-129m; Xenon-129m; Xenon Xe 129 hyperpolarized; (129)Xe; (129)54Xe. (This list is derived from available supplier/depositor synonyms.)
Industrial and Commercial Applications
Major Use Sectors
- Medical imaging: hyperpolarized Xe-129 is used as an inhaled contrast agent for MRI-based assessment of lung ventilation and gas distribution.
- Biomedical research: NMR and MRI research exploiting hyperpolarized noble-gas physics and xenon–host interactions.
- Diagnostic imaging adjuncts: applications in functional lung imaging and research into pulmonary disease mechanisms.
- Ancillary uses in imaging research include use as an inhaled tracer for gas exchange and, historically, as an inhaled anesthetic at high concentrations.
Typical Application Examples
- Administration of hyperpolarized Xe-129 gas by inhalation for MRI visualization of ventilated regions in the lung; hyperpolarization increases nuclear polarization by several orders of magnitude, producing detectable NMR signal from the gaseous phase.
- Experimental assessment of gas exchange and solubility distribution between airspaces and pulmonary tissue due to xenon’s soluble fraction and affinity for fatty tissues.
- Use in cerebral blood flow measurements in specialized imaging modalities (e.g., as an inhaled tracer for CT-based perfusion techniques).
- At concentrations above approximately \(50\%\) (inhaled), xenon exhibits anesthetic properties; such anesthetic use has been documented in controlled clinical settings but is separate from hyperpolarized contrast applications.
Safety and Handling Overview
Storage and Handling Considerations
Xenon is supplied and stored as a compressed liquefied gas in cylinders or specialized cryogenic containers. As a pressurized gas, containers must be secured, protected from heat, and handled with standard gas-cylinder safety procedures. Condensed/liquid xenon requires cryogenic handling precautions. Because xenon is an inert gas it presents an asphyxiation hazard in oxygen-displacing scenarios; ensure adequate ventilation and oxygen monitoring in confined spaces. For clinical hyperpolarized gas systems, follow equipment-specific guidance for polarization apparatus, transfer lines, and patient delivery systems.
For transportation, packaging, and classification details consult product-specific shipping documentation and applicable regulations; do not assume transport classifications without verifying current regulatory guidance.
Occupational Exposure and Protective Measures
Occupational controls should prioritize prevention of oxygen displacement and inhalation of pressurized gas releases. Use engineering controls (ventilation, oxygen monitors) in enclosed or poorly ventilated areas. Standard PPE for gas cylinder handling (safety footwear, eye protection, gloves) and cryogenic protection where applicable is recommended. Be aware of xenon’s anesthetic effects at high concentrations—avoid prolonged exposure to elevated xenon atmospheres and monitor clinical/procedural settings for occupational exposure. For detailed hazard, transport and regulatory information, users should refer to the product-specific Safety Data Sheet (SDS) and local legislation.
