Modeling DOTA Decarboxylation in the Context of α-Radiolysis Using DFT Calculations.

Area of Science:

• Radiochemistry
• Computational Chemistry
• Materials Science

Background:

• Aminopolycarboxylic acids, such as 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA), are crucial chelating agents in nuclear energy.
• Radiolytic degradation of DOTA is a concern during its use and disposal, necessitating mechanistic understanding.

Purpose of the Study:

• To investigate the decarboxylation mechanism of DOTA in aqueous solutions using computational methods.
• To elucidate the pathways and energetic barriers involved in DOTA's radiolytic degradation.

Main Methods:

• Density Functional Theory (DFT) calculations were employed to model the decarboxylation reaction of DOTA.
• Two distinct reaction pathways were proposed and analyzed: direct cleavage and radical formation.

Main Results:

• Direct cleavage involves sequential barriers, with a high activation energy of 73.3 kcal mol⁻¹ for decarboxylation.
• Radical formation at a deprotonated carboxyl group, initiated by OH• radicals, significantly reduces the decarboxylation barrier to 18.3 kcal mol⁻¹.
• Radical-mediated degradation is identified as a more energetically favorable pathway for DOTA decomposition.

Conclusions:

• The study highlights that radical attack is a key factor in promoting DOTA degradation under radiolysis.
• Understanding these degradation pathways is crucial for managing DOTA in nuclear applications and waste disposal.