Extraction of Noble and Rare‐Earth Metals from Aqueous Solutions by DNA Cross‐Linked Hydrogels

Abstract

Technologies for the accumulation of noble and rare-earth elements have attracted significant attention in the past decade owing to their increasing industrial demand. Chitosan, as well as other compounds with relatively high amine functional group content, have already been shown to be efficient, inexpensive, and environmentally friendly adsorbents of these valuable metals. [1] Complexation of DNA with many metal ions is also well known [2] and the high affinity of DNA phosphates for various rare-metal ions was demonstrated in recent reports by Takahashi et al. [3] Although originally only the biological aspect of DNA was intensively investigated, many studies focused on the application of DNA as a functional material. [4] For example, we [5] and others [6] have successfully demonstrated the application of DNA for the extraction of hazardous metal ions and organic contaminants from aqueous solutions. Similarly, the application of DNA for the extraction of noble and rare-metal ions can be considered. However, owing to the high colloidal stability of DNA in aqueous solution, either deposition of DNA on a suitable solid substrate (e.g., inorganic micro-beads used in columns [6b] ) or post-treatment of DNA complexes with condensation chemicals to induce DNA phase separation from the aqueous phase, [5a] are required.Herein, we propose a single-step extraction of noble-metal (Au, Pd) and rare-earth (Yb) ions from aqueous solutions by using a DNA hydrogel, which possesses intrinsic DNA affinity to the metal ions. The DNA hydrogel was prepared according to a modified procedure reported by Tanaka and Amiya, [7] who studied DNA hydrogels in relation to phase transition in lowpolar solvents. DNA is a suitable natural polymer for the collection of metal ions because the amine and phosphate groups of DNA can act as chelating sites for metal ions.Typically, the sodium salt of DNA from salmon milt (0.1 g) was mixed with MilliQ water (400 mL) and a 1 m aqueous solution of NaOH (320 mL, final solution pH 13-14), and crosslinked by the addition of ethylene glycol diglycidyl ether (EGDE; 50 mL) at room temperature during 2 hours of incubation. Cross-linking occurs through the reaction between amino groups of the DNA nitrous bases and epoxy groups of EDGE, as shown in Scheme 1. [8] The resulting hydrogel was transferred into MilliQ water (200 mL) and incubated for 24 hours to remove unreacted EGDE, NaOH, and non-cross-linked DNA. The hydrogel was then equilibrated against MilliQ water (300 mL) twice in 24 hours. The resulting hydrogel contained 1.5 mm DNA (DNA phosphates per hydrogel volume), as determined by UV spectroscopy measurements of the DNA hydrogel after ultrasonic homogenization for 5 minutes.In all extraction experiments, the same amount of DNA was used, that is, 2.5 g of DNA hydrogel with a DNA concentration Scheme 1. Cross-linking reaction between two DNA nucleotides and EDGE.

DNA-Assisted Solubilization of Carbon Nanotubes and Construction of DNA-MWCNT Cross-Linked Hybrid Hydrogels

“…DNA hydrogel is a relatively new type of DNA-based material promising as rare metal adsorbent [ 11 ], reactor for synthesis of metal nanomaterials [ 12 ], supercapacitor [ 13 ], vehicle for drug/gene delivery [ 14 ], and in other applications. Further functionalization of DNA hydrogels opens up new opportunities to use such hybrids for various materials science and biological applications.…”

Size control of gold nanoparticles synthesized in a DNA hydrogel

“…DNA forms strong complexes with Au 3+ , and thus can efficiently concentrate Au 3+ in aqueous solution, as we described in a previous report . Au 3+ is absorbed by the DNA hydrogel when the hydrogel film is soaked in a 5 mL solution of HAuCl 4 taken in a large excess (4 mmol L −1 ) to the available DNA binding sites.…”

“…DNA is well known for its high affinity for noble and transition metals due to efficient coordination of purine and pyrimidine bases with metal ions, and it was recently demonstrated that this affinity can be utilized for the enrichment of transition metals in a DNA hydrogel matrix . Because the previously reported hybrid hydrogels containing metal nanoparticles were based on polymeric materials with low affinity for metal precursors, DNA hydrogels might be advantageous for providing very efficient concentrating of metal ions inside the hydrogels as well as for control nanoparticle growth.…”

DNA Hydrogel Assemblies: Bridging Synthesis Principles to Biomedical Applications

“…Concentrating of transition metal ions by DNA stems from the presence of purine and pyrimidine bases as well as phosphate groups in the backbone of DNA, which can act as efficient chelation sites. This is the main logic behind the extraction of transition metals from aqueous solutions by DNA hydrogel as an absorbent . This finding has prompted scientists to use DNA hydrogels for controllable synthesis of metal nanoparticles.…”