23. - 25. 10. 2012, Brno, Czech Republic, EU STRUCTURE ANALYSIS OF THE INTERLAYER SPACE OF VERMICULITE/CHLORHEXIDINE NANOCOMPOSITE USING MOLECULAR MODELING Dominik HLAVÁČ, Jonáš TOKARSKÝ IT4INNOVATIONS CENTRE OF EXCELLENCE, VŠB-TECHNICAL UNIVERSITY OF OSTRAVA, 17. listopadu 15, 708 33 Ostrava-Poruba, Czech Republic, dominik.hlavac@vsb.cz Abstract The aim of this work is to give closer information about structure of Na-vermiculite/chlorhexidine diacetate antibacterial nanocomposite. Special attention has been paid to the orientation of the molecules of chlorhexidine in the vermiculite interlayer space. Molecular modeling using empirical force field in Accelrys Materials Studio modeling environment was performed in this study and obtained results were confronted with available experimental data of real samples. Molecular modeling revealed that increasing interlayer distance of vermiculite in dependence on increasing number of chlorhexidine cations in the vermiculite interlayer space is not caused by simply higher amount of chlorhexidine cations but by the different space arrangement. Molecular modeling results also led to the conclusion that it is the vermiculite surface which is primarily responsible for the modulation of antibacterial properties of vermiculite/chlorhexidine diacetate nanocomposite. Keywords: Molecular modeling, structure, chlorhexidine, vermiculite 1. INTRODUCTION Chlorhexidine (CH) is an organic compound belonging to the bis(biguanide) family. Due to the basic character it forms stable salts with several acids, i.e. in presence of acetic acid it forms a chlorhexidine diacetate (CA) [1,2]. The CH is nowadays one of the most widely used biocides in dental and hand washing antiseptic products [3]. The mechanism of CH action involves destabilization of the outer bacterial membrane which is penetrated by two chlorophenyl guanide groups [4]. Because the question of CH toxicity in higher concentrations remains open [5], the possible risks must be restrained. A simple method how to minimize these risks is a stabilization of CH with appropriate matrix. Montmorillonite [6] or silica [7] was used in some previous works. Holešová and her co-workers [8] decided to use vermiculite (VMT) matrix because the VMT is layered phyllosilicate with large specific surface area and high negative layer charge which causes the presence of greater amount of interlayer cations than in other clay minerals [9]. This novel synthesized vermiculite/chlorhexidine (VMT/CH) nanocomposite has a significant antibacterial activity at low concentrations against Gram-negative Escherichia coli and Gram-positive Enterococcus faecalis. In addition, the VMT/CH nanocomposite with higher CH concentrations succesfully inhibited the growth of a very resistant Pseudomonas aeruginosa. Although the work of Holešová et al. [8] confirmed the antibacterial activity of VMT/CH nanocomposite, the question of structural arrangement of chlorhexidine on VMT matrix remained unanswered. Because only the combination of instrumental analytical methods and computer molecular modeling can provide the clear answer, the molecular modeling study based on the experimental data (elementary analysis, X-ray powder diffraction, thermogravimetry and IR spectroscopy) published in [8] was carried out. The main goal of present work was to describe the interlayer structure of VMT/CA nanocomposite, especially the space arrangement of the CH molecules in dependence on their number. Attention has also been paid to the influence of substitutions in the VMT structure on this arrangement.