Synthesis of 5′-GMP-mediated porous hydrogel containing β-FeOOH nanostructures: optimization of its morphology, optical and magnetic properties

Abstract

The present manuscript reports 5′-GMP-mediated β-FeOOH nanostructures with varied morphologies ranging from nanorods to porous structures via the formation of spherical nanoparticles (NPs). For the optimized 5′-GMP-mediated β-FeOOH nanostructures (containing 2.5 × 10⁻³ mol dm⁻³ of 5′-GMP), the freshly prepared colloidal solution contained nanochains consisting of spherical NPs with an average diameter of 8 nm as measured by TEM, which upon aging produced porous hydrogels. Similar morphological changes were also evidenced by AFM. The change in morphology is controlled by the concentration of 5′-GMP, pH and the period of aging, which is clearly demonstrated by the ζ-potential measurements. Changing interactions in the hydrogel are clearly indicated by IR spectroscopy, where the functionalities of 5′-GMP (CO, –NH₂, –CN–, imidazole, pyrimidine, –C–O– of the sugar, PO₃²⁻, sugar ring and P–O–5′-sugar) interact with β-FeOOH. Specific interactions of β-FeOOH through the N and P of 5′-GMP are also supported by XPS studies. These nanostructures exhibit superparamagnetism at room temperature, exhibiting a magnetization of 3.2 emu g⁻¹, which upon the formation of the hydrogel is increased to 4.8 emu g⁻¹. The superparamagnetic behavior is retained by these nanostructures in the hydrogel up to <50 K. The observed morphology and stability of the 5′-GMP–β-FeOOH nanohybrid at about pH 7.0, the low toxicity of β-FeOOH and the biocompatiblity of 5′-GMP suggests the potential of these nanostructures for biomedical applications.