Study of inclusion compound in solution involving tetracycline and b-cyclodextrin by FTIR-ATR Frederico B. de Sousa a , Michele F. Oliveira a , Ivana S. Lula a , Maria Terezinha C. Sansiviero a , Maria E. Corte ´s b , Rube ´n D. Sinisterra a, * a Departamento de Quı ´mica, Instituto de Cie ˆncias Exatas, Universidade Federal de Minas Gerais (UFMG), Antonio Carlos 6627, Belo Horizonte, MG 31270-901, Brazil b Departamento de Odontologia Restauradora, Faculdade de Odontologia, Universidade Federal de Minas Gerais (UFMG), Belo Horizonte, MG 31270-901, Brazil Received 20 November 2006; received in revised form 24 September 2007; accepted 1 October 2007 Available online 7 October 2007 Abstract The objective of this article was to investigate the changes on the vibrations modes of the supramolecular system constituted between b- cyclodextrin (host) and the tetracycline (guest) by Fourier transform infrared attenuate total reflectance (FTIR-ATR) in aqueous solution as a new alternative probe for the host:guest complexes. To confirm the non-covalent interactions of this system, nuclear magnetic resonance spectroscopy techniques ( 1 H NMR and NOESY), were also used. In addition the complex stoichiometry was determined using the FTIR-ATR results. Comparison between the tetracycline FTIR-ATR spectra of free to the inclusion compound, it was clear that the n(C O), n(C C), d(O–H), d(C– C), n(C–C), d(N–H) and n(C–N) signals of tetracycline in the inclusion compound were disturbed by the presence of b-cyclodextrin. In addition, the intensity of b-cyclodextrin vibration mode at 1031–1082 cm À1 , corresponding to n(C–O–C), was strongly reduced when the concentration of tetracycline was increased. These results suggest the interaction between the molecules in aqueous solution. The 1 H nuclear magnetic resonance experiment demonstrated a similar result to that obtained by FTIR-ATR concerning the changes which occurred in the chemical shits of the pure tetracycline as compared to that obtained upon forming the inclusion complex. In addition, the 2D NOESY experiment also confirmed the Tetracycline interaction not only with the cavity but also with the external protons of the cyclodextrin by cross peaks correlations present in the contour map. # 2007 Published by Elsevier B.V. Keywords: FTIR-ATR; 1 H NMR; NOESY; b-Cyclodextrin; Non-covalent interaction; Inclusion compound; Tetracycline 1. Introduction The primary purpose of drug delivery systems is to transport the necessary amount of drug to the targeted site for a necessary period of time, both efficiently and precisely [1–6]. In this sense, the development of new strategies to drug delivery systems such as, hydrogels, nano- and microspheres of biodregradable polymers, lypossomes and also host:guest systems, are an important research area, since the delivery of some molecules used in pharmaceutical therapy cannot be delivered effectively through the conventional oral route [1–3]. In this case, cyclodextrins (CDs) have been considered useful drug delivery and carrier systems [4–6]. CDs are macrocyclic oligosaccharides obtained by an enzymatic transformation of starch. The most common CDs are a-CD, b-CD and g-CD, which consist of six, seven and eight glucopyranose units, respectively. The geometry of this class of compounds is often described as a truncated cone. This kind of structure provides a hydrophobic cavity that allows the formation of inclusion compounds (IC) with guest molecules in aqueous solutions and solid state [7]. CDs have attracted the attention of many formulation experts due to their improvement in the therapeutic efficacy of poorly water-soluble drugs, enhancement in physical and chemical stability and elimination of the undesired effects of drugs [7–11]. Hence, the physical- chemistry characterization of this complex is important for a www.elsevier.com/locate/vibspec Available online at www.sciencedirect.com Vibrational Spectroscopy 46 (2008) 57–62 * Corresponding author. Tel.: +55 31 3499 5778; fax: +55 31 3499 5700. E-mail address: sinisterra@ufmg.br (R.D. Sinisterra). 0924-2031/$ – see front matter # 2007 Published by Elsevier B.V. doi:10.1016/j.vibspec.2007.10.002