Supramolecular-directed novel superparamagnetic 5′-adenosine monophosphate templated β-FeOOH hydrogel with enhanced multi-functional properties

Abstract

The present work describes the synthesis and properties of 5′-AMP mediated porous superparamagnetic β-FeOOH hydrogel with biocompatible components. For the optimized 5′-AMP mediated β-FeOOH hydrogel containing 2.5 mM of 5′-AMP (SP4H), initially colloidal nanoparticles are produced, which in the process of self-assembly reorganize to form hydrogel. The process of gelation is found to be controlled by the change in the concentration of 5′-AMP, pH and temperature. The presence of β-FeOOH in the hydrogel sample is indicated by Raman, UV-Vis-NIR, and IR spectroscopy, XPS and SAED analyses. FESEM, AFM and TEM analyses of this sample reveal it to be porous, which is also indicated by its high BET surface area (215 m² g⁻¹) as compared to that of the untemplated β-FeOOH. Zeta potential (ζ) measurements show the fresh nanoparticles to be fairly stable with a ζ-value of ∼45 mV, which upon gelation becomes negatively charged with a change in the ζ value to ∼−35 mV. The occurrence of gelation is assigned to the change in the interaction between the core-β-FeOOH and 5′-AMP in the shell. The FTIR analysis shows that interactions through the pyrimidine ring, in plane C(8)H and PO₃²⁻ are responsible for gelation. The 5′-AMP templated β-FeOOH hydrogel exhibits superparamagnetic behavior from 300 to 50 K associated with a more than 75% increase for room temperature magnetization (3.4 emu g⁻¹) as compared to the bare β-FeOOH (1.9 emu g⁻¹) at 7 T. Unlike the bare 5′-AMP mediated hydrogel, the as-synthesized 5′-AMP templated β-FeOOH hydrogel employs more than an order of magnitude lower concentration of 5′-AMP and displays enhanced multifunctional properties. The use of non-toxic precursors for synthesizing 5′-AMP mediated β-FeOOH hydrogel in aqueous medium having potential for biomedical applications makes it a green material.