Temperature and pH driven association in uranyl aqueous solutions

TL;DR

This study uses molecular dynamics simulations to investigate how temperature and pH influence uranyl ion association in aqueous solutions, revealing that higher temperature reduces association while pH adjustments can promote or inhibit it.

Contribution

It provides new insights into the effects of temperature and pH on uranyl ion association dynamics through detailed simulation and structural analysis.

Findings

Higher temperature decreases uranyl association.

Hydroxide ions promote uranyl dimer and trimer formation.

Protons inhibit uranyl association.

Abstract

An association behavior of uranyl ions in aqueous solutions is explored. For this purpose a set of all-atom molecular dynamics simulations is performed. During the simulation, the fractions of uranyl ions involved in dimer and trimer formations were monitored. To accompany the fraction statistics one also collected distributions characterizing average times of the dimer and trimer associates. Two factors effecting the uranyl association were considered: temperature and pH. As one can expect, an increase of the temperature decreases an uranyl capability of forming the associates, thus lowering bound fractions/times and vice versa. The effect of pH was modeled by adding H^+ or OH^- ions to a "neutral" solution. The addition of hydroxide ions OH^- favors the formation of the associates, thus increasing bound times and fractions. The extra H^+ ions in a solution produce an opposite effect, thus lowering the uranyl association capability. We also made a structural analysis for all the observed associates to reveal the mutual orientation of the uranyl ions.