Facile Process for Metallizing DNA in a Multitasking Deep Eutectic Solvent for Ecofriendly C–C Coupling Reaction and Nitrobenzene Reduction

Abstract

Metallized DNA is an exciting functional material having widespread utility toward multifunctional applications. However, conventional DNA metallization processes are time-consuming and multistep and, most importantly, the helicity of DNA is destroyed during the metallization process. Herein, an ecofriendly and rapid approach has been demonstrated to metallize salmon milt DNA with Pd and Fe3O4 in deep eutectic solvent (DES; ChoCl–EG 1:2 mol ratio) without disturbing the structural integrity of the biopolymer. Besides maintaining the stability of DNA at high temperature, DES played the dual role of (i) a solvent for DNA metallization and (ii) a reducing agent for reduction of Pd(II) to Pd(0) during the metallization process. Microscopic studies confirmed the stepwise formation of aggregated coil type morphology in metallized DNA (Pd–DNA–Fe3O4). Whereas, the interactions between Pd and Fe3O4 with DNA in Pd–DNA–Fe3O4 were probed by different analytical tools, which suggested that Pd interacted with phosphate groups and Fe3O4 interacted with the base pairs of DNA. Circular dichroism spectroscopy analysis established that the B-form of DNA was maintained before and after the metallization process. After successful metallization, Pd–DNA–Fe3O4 was utilized as a nanobiocatalyst for Suzuki coupling reaction and reduction of nitrobenzene to aniline. The metallized DNA showed remarkable catalytic activity and efficiency for sustainable Suzuki coupling reaction in DES. Under optimized conditions, 100% conversion of the substrates was recorded with 100% selectivity of the desired C–C coupled product. Taking advantage of the high temperature stability of DNA in DES, the recyclability (up to 6 cycles) potential of both metallized DNA and DES toward C–C coupling was explored without significant loss in the catalytic activity, thus demonstrating the green aspects of the process. When utilized as a catalyst for the reduction of nitrobenzene to aniline, ∼90% conversion of nitrobenzene was achieved with 66% selectivity of aniline which suggested that the overall assembly of metallized DNA is a very efficient system to carry out facile nitrobenzene reduction. Overall, the present study demonstrates a general process for metallization of DNA in DES and the applications of the metallized DNA as a catalyst in different organic reactions.