PROJECT SUMMARY/ABSTRACT The goal of this project is to prepare tritium labeled compounds using the compound [Mn(CO)3(µ3-OH)]4 (1) enriched with 3H atoms. Research in the Lacy group using 1 resulted in the discovery that d4-1 facilitates hydrogen isotope exchange (HIE) with toluene under ambient conditions. This work continues this discovery toward applications with tritium. The innovation in using 3H enriched 1 for labeling is that 1 is thermodynamically stable and kinetically inert, except toward HIE, which is the desirable property for a labeling compound/catalyst. Additionally, it is composed of only Mn iron and carbon monoxide and hydroxide ligands, it does not contain an organic ligand. Purification of 1 from 3H-labeled material is very simple, which essentially takes advantage of the low solubility of 1 or facile decomposition under UVA irradiation without solvent degradation. The irradiated decomposition products are only manganese oxides, CO gas, and H2, all of which can be easily separated from 3H-labeled material. Aim 1 will demonstrate that this is possible. Aim 2 will explore and expand the substrate scope. Namely, the original discovery by the Lacy group was with toluene. The proposed work will expand the substrates to those including, but not limited to, substituted benzenes (e.g., chlorobenzene, bromobenzene, iodobenzene, nitrobenzene, phenol, anisole, aniline, xylenes, mesitylene, hexamethylbenzene, pyridines, furans, thiophenes, imidazoles, benzimidazoles, pyrrole, pyridines, pyrazoles, pyrazines, conjugated dienes) and amino acids (e.g., phenylalanine, tryptophan, histidine). Additionally, pharmaceutical targets including, but not limited to, Ibuprofen, Cimetidine, Pyrantel, Nitrofurantoin. A unique aspect 1 is that it can be used with neat substrate. Aim 3 will explore fundamental chemical aspects of the labeling chemistry including the thermochemistry, mechanism, and synthetic modifications that might be required to facilitate Aim 1 and/or Aim 2. The long-term goals are to (i) develop large scale preparation of 1 enriched with 3H, (ii) to do so using 3H2 gas instead of tritium oxide, and to (iii) develop the technology with 1 for field use in pharmacology. The advantage of using 3H2 gas is that it is much easier and safe to store and handle than tritium oxide. Pure tritium oxide is corrosive and undergoes self-radiolysis, which is why it is usually manipulated in very low concentrations. Thus, technologies that use 3H2 are more desirable than those that use tritium oxide, and efforts toward 1 leverage and expand the advantages afforded from 3H2. The relevance to human health is that 3H-labeled compounds are commonly used in pharmacology and the development of 1 in this area reduces the need for toxic and expensive metal-based labeling strategies.