Chlorogenic acid/PEG-based organic-inorganic hybrids: A versatile sol-gel synthesis route for new bioactive materials

New organic-inorganic hybrid materials were synthesized by an acid catalysed sol-gel approach, using silicon alkoxide and low molecular weight polyethylene glycol (PEG400) as inorganic and organic precursor, respectively. Chlorogenic acid (CGA), an antioxidant natural phenol compound, enriched further the organic component. Hybrids synthesized, all identical in terms of their starting materials, but differing in terms of their relative proportions, were characterized by means of Fourier Transform InfraRed (FTIR) measurements, UV-Vis spectroscopy, and UHPLC-HRMS analysis. The preservation of the intrinsic chlorogenic acid ability to scavenge, in a dose-dependent manner, radical species was investigated by directly exposing the hybrids to DPPH radical and ABTS radical cation. The relative ratio of both the natural compound and PEG heavily affected the antiradical response, suggesting that chemical interactions in the established network were able, based on components' ratio, to differently mask and/or display the CGA moieties, commonly deemed relevant for antioxidant power exerting. Cell culture MTT assay was used to assess the biocompatibility of hybrid materials towards fibroblast NIH-3 T3 cells and neuroblastoma SH-SY5Y cells. Cells tested appeared differently responsive. In particular, a marked cell viability increase was observed when hybrids with low PEG amount (6%) and high CGA (15%) were directly exposed to fibroblast cells, whose mitochondrial redox activity was negatively affected by hybrid synthesized using the highest organic component rate (both PEG and CGA). Cell viability and morphology of human neuroblastoma SH-SY5Y cells were broadly compromised regardless of organic/inorganic starting materials ratio, suggesting the ability of hybrids to exert pro-oxidant effect towards tumour cells and to selectively interfere with their growth. The hybrids, able to elicit cleverly anti- or proliferative effects, were also shown to be bioactive. In fact, a biologically active hydroxyapatite layer was observed to be formed on the surface of the smart synthesized materials. This feature, which makes them a valuable bonding interface with tissues, opens new scenario aiming at further investigating the employment of natural phenol compounds in versatile sol-gel synthesis routes.