Adsorption of nucleotides and nucleic acids on goethite nanoparticles: mode, sites and relationship with phosphate and non-phosphate structures†

The impact of iron (hydr)oxide adsorption on nucleotides and nucleic acids (NNAs) in the environment varies. However, there is a lack of quantitative reports on how iron (hydr)oxide adsorption changes with different NNA structures. Here we examined NNAs with varying numbers of P–O(H) groups (including P–OH and P–O⁻, ranging from 2 to 4200–36 000) and different nucleoside structures for their adsorption onto iron (hydr)oxide nanoparticles (i.e., goethite) at pH 7.0. The adsorption of NNA was driven by formation of Fe–O–P bonds, which could be hindered by the presence of phosphoric acid (PA) anions due to their overlapping adsorption sites on goethite. Analysis of OH⁻ release during adsorption indicated that 2 to 2110–29 600 P–O(H) groups in the NNA molecule were involved in Fe–O–P bonding, with the engagement increasing with the number of P–O(H) groups. The increase in P–O(H) groups in Fe–O–P bonding resulted in a two-step increase in adsorption strength (based on phosphorus atoms). Initially, the adsorption strength was weaker than that of PA (for nucleoside monophosphates). Then it became comparable to that of PA (for nucleoside diphosphates and triphosphates) and eventually exceeded that of PA (for nucleic acids). The weaker affinity of the nucleoside moiety to goethite (in the case of nucleotides) and the hindrance of P–O(H) in forming Fe–O–P bonds due to molecular assembly and aggregation (for nucleic acids) reduced the adsorption enhancement through Fe–O–P bonding. These findings highlight the importance of both phosphate and non-phosphate structures in NNA adsorption, which can contribute to the assessment of environmental impacts of NNAs in iron-rich soil and water systems, particularly in relation to the phosphorus cycle and the spread of antibiotic resistance genes.