Thermodynamics on the first hydrolysis reaction of dysprosium and holmium in aqueous solutions: potentiometry and calorimetry

Qingye Zhou; Hu Song; Shufeng Zhao; Xiang Li; Yuyu Liang; Chenchen Yuan; Zeng Huang; Jun Tu; Xingliang Li

doi:10.1515/ract-2025-0078

Article

Thermodynamics on the first hydrolysis reaction of dysprosium and holmium in aqueous solutions: potentiometry and calorimetry

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Published/Copyright: November 10, 2025

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From the journal Radiochimica Acta Volume 114 Issue 1

Abstract

The potential release of Dy³⁺ and Ho³⁺ ions from ¹⁶⁶Dy/¹⁶⁶Ho or ¹⁶⁶Ho microspheres during radionuclide therapy poses a radiotoxicological risk, as their biochemical behavior is governed by hydrolysis. This study presents a comprehensive thermodynamic investigation of the first hydrolysis step of Dy³⁺ and Ho³⁺ in aqueous solutions, employing potentiometry and isothermal titration calorimetry (ITC). We report, for the first time, the direct calorimetric determination of the hydrolysis enthalpies for these lanthanides. Our results identify two viable models for the first hydrolysis step – monomeric [Ln (OH)]²⁺ and dimeric [Ln₂(OH)₂]⁴⁺ species – with thermodynamic parameters quantified for both. The hydrolysis reactions are endothermic and predominantly electrostatic. Under simulated physiological conditions (pH 7–8), 15–20 % of Dy³⁺ and 22–27 % of Ho³⁺ are hydrolyzed. A key practical implication is that hydrolysis is thermodynamically disfavored at low temperatures, suggesting that refrigerated storage of microspheres can minimize ion release. These findings provide critical thermodynamic benchmarks for predicting lanthanide speciation and recommend storing therapeutic microspheres at low temperatures to suppress hydrolysis.

Keywords: holmium; dysprosium; hydrolysis; potentiometry; calorimetry

Corresponding authors: Jun Tu and Xingliang Li, CAEA Center of Excellence on Nuclear Technology Application for Radioisotope and Radiopharmaceutical, Nuclear Medicine and Theragnostic Key Laboratory of Sichuan Province, Targeted Radiopharmaceuticals Creation Key Laboratory of Sichuan Province, Institute of Nuclear Physics and Chemistry, China Academy of Engineering Physics, Mianyang, Sichuan, 621999, China, E-mail:tujun@caep.cn (J Tu), xingliang@caep.cn (X Li)

Funding source: Central Government Guiding Fund for Local Science and Technology Development, Sichuan Province

Acknowledgement

This work is supported by the Central Government Guiding Fund for Local Science and Technology Development, Sichuan Province.

Research ethics: Not applicable.
Informed consent: Not applicable.
Author contributions: All authors have accepted responsibility for the entire content of this manuscript and approved its submission.
Use of Large Language Models, AI and Machine Learning Tools: None declared.
Conflict of interest: The authors state no conflict of interest.
Research funding: Central Government Guiding Fund for Local Science and Technology Development, Sichuan Province.
Data availability: The authors confirm that the data supporting the findings of this study are available within the article.

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Received: 2025-08-17

Accepted: 2025-10-24

Published Online: 2025-11-10

Published in Print: 2026-01-23

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https://doi.org/10.1515/ract-2025-0078

Keywords for this article

holmium; dysprosium; hydrolysis; potentiometry; calorimetry