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

Authors: Bouzid Menaa, Corrado Montoneri, Farid Menaa, Enzo Montoneri, Vittorio Boffa, Olga Nick Sharts

Addresses: Fluorotronics, Inc., 2453 Cades Way, Bldg C, Vista, CA 92081, USA. ' Dimorfipa, Universita di Bologna, Via Tolara di Sopra, 50, 40064 Ozzano dell'Emillia, Bologna, Italy. ' Fluorotronics, Inc., 2453 Cades Way, Bldg C, Vista, CA 92081, USA. ' Dipartimento di Chimica Generale e Chimica Organica, Universita di Torino, Corsa Massimo d'Azeglio 48, 10125 Torino, Italy. ' Dipartimento di Chimica Generale e Chimica Organica, Universita di Torino, Corsa Massimo d'Azeglio 48, 10125 Torino, Italy. ' Fluorotronics, Inc., 2453 Cades Way, Bldg C, Vista, CA 92081, USA

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.

Keywords: nanoporous sol-gel glasses; fluorine; phosphonate groups; silica-based biomaterials; protein folding; circular dichroism spectroscopy; nanotechnology; protein helical structures; biocompatibility.

DOI: 10.1504/IJNT.2011.040189

International Journal of Nanotechnology, 2011 Vol.8 No.6/7, pp.471 - 491

Available online: 19 May 2011 *

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