Impacts of molecular architecture on the radiation-induced degradation and reaction kinetics of hydrophobic diglycolamides with the solvated electron and the dodecane radical cation

Given their proposed use as trivalent actinide-lanthanide separation ligands, the role of molecular architecture on the radiation robustness of diglycolamide (DGA) molecules has been investigated. This study examined three prototypical molecules with differences in their aliphatic chain architecture: <i>N</i>,<i>N</i>,<i>N</i>',<i>N</i>'-tetra(<i>n</i>-octyl)diglycolamide (TODGA), <i>N</i>,<i>N</i>,<i>N</i>',<i>N</i>'-tetra(2-ethylhexyl)diglycolamide (T2EHDGA), and <i>N</i>,<i>N</i>'-dimethyl-<i>N</i>,<i>N</i>'-dioctyldiglycolamide (DMDODGA). Rate coefficients and activation parameters are reported for the reactivity of each DGA with the solvated electron (e_solv^-) and the corresponding dodecane radical cation (RH˙⁺) over the temperature range of 10.0 to 44.1 °C. These measurements indicate that DMDODGA is the most chemically reactive with both transient radicals, which may be attributed to this molecule's more accessible backbone. Complementary gamma dose accumulation studies (≤450 kGy) under envisioned process conditions-50 mM DGA in <i>n</i>-dodecane solvent-afforded dose constants for the loss of DGA of <i>d</i> = (4.52 ± 0.30) × 10^-3, (5.59 ± 0.13) × 10^-3, and (6.21 ± 0.12) × 10^-3 kGy^-1 for T2EHDGA, DMDODGA, and TODGA, respectively. These dose constants indicate that varying DGA architecture affords subtle differences in chemical reactivity, leading to varying rates of radiolytic degradation under envisioned actinide-lanthanide separation conditions. However, more ambitious DGA frameworks, such as modifying the backbone, branching of the aliphatic chains, and/or changing the size of the chain may be required for larger gains in radiolytic longevity while optimizing actinide-lanthanide selectivity.