Protein helical structure enhancement in biocompatible fluoro-phosphonate-based nanoporous silica glasses assessed by circular dichroism spectroscopy

Abstract

The role of fluorine and phosphonate groups on protein structure and biocompatibility has been probed by protein encapsulation in tetramethoxysilane (TMOS)-based sol-gel glass and assessed by circular dichroism spectroscopy (CD). Apomyoglobin (apoMb) is known as a model protein for the study of protein folding. Thus, we demonstrated the increase of apoMb helicity in phosphonate and fluorinated phosphonate-based sol-gel glasses via the addition of methane diphosphonic acid (MDPA) and difluoromethane diphosphonic acid (DFMDPA) during the hydrolysis/polycondensation of TMOS precursor forming a nanoporous sol-gel glass host matrix for the protein. Alternatively to silica surface functionalisation using organosilane modifiers, functional organic molecules or nano-agents can be doped directly during the sol-gel process. Since TMOS is not functionalised, we can probe the role of some organic molecules as intermediates as well as their surface hydration effect contributing to the protein folding process. The presence of both fluorine and phosphonate groups in TMOS glass folded the protein to its native state as function of its molar content. The protein ellipticity has been enlightened by CD with signals observable at 222 nm characterising the secondary protein structure at the far UV. The incorporation of these groups to the sol-gel glass systems to mimic the behaviour and conformation of protein as function of its surrounding environment brings both steric and hydrophobic properties to enhance the protein folding. These results are important from the point of view of potential applications in bio-nanotechnology with the design of efficient biomaterials but also to probe the role of fluorine and phosphonate groups in protein folding for the human healthcare.