Silver ions blocking crystallization of guanosine-based hydrogel for potential antimicrobial applications

In this work, the detailed crystallization process of 2'-deoxy-2'-fluoroguanosine ((F)G(d)) hydrogel has been studied using single crystal X-ray diffraction, variable-temperature nuclear magnetic resonance (VT-NMR), and scanning electron microscopy (SEM). Both solid and solution results indicated that the K+-mediated G-quartet structures were unstable and easily resulted in the breakdown of the hydrogel to form linear ribbon structures by forming mimic reverse Watson-Crick base pairs between the two faces with an intermolecular hydrogen-bond (N10H-O11). Accordingly, Ag+ was introduced to block the crystallization of (F)G(d) to form long lifetime stable supramolecular hydrogel (>6 months) and possible silver-ions-mediated base pair motifs were suggested via NMR, UV, and mass spectroscopy (MS) in combination with powder X-ray diffraction (PXRD) and circular dichroism spectroscopy (CD). Furthermore, (F)G(d)Ag hydrogel exhibited low toxicity for normal oral keratinocyte cells (NOK-SI) and good antibacterial activities for Fusobacterium nucleatum in vitro.