ORIGINAL ARTICLE Host–guest system of Vitamin B10 in b-cyclodextrin: characterization of the interaction in solution and in solid state Irina Kacso ´ • Gh. Borodi • S. I. Farcas • A. Hernanz • I. Bratu Received: 23 October 2009 / Accepted: 24 February 2010 Ó Springer Science+Business Media B.V. 2010 Abstract Conventional drugs are usually formulated for the immediate release of the medicinal substances and for obtaining the desired therapeutic effect. The aim of this paper was to investigate the possible interactions between Vitamin B10 and b-cyclodextrin (b-CD), to determine the physical-chemical characteristics and the interactions present in the corresponding inclusion compound. The so- obtained compounds were characterized by X-ray diffrac- tion, DSC and FTIR spectroscopy. 1 H NMR and UV–vis spectroscopic methods were employed to study the inclu- sion process in aqueous solution. The X-ray powder dif- fraction patterns demonstrate the inclusion compound formation, especially for the lyophilized product where the amorphous phase dominates. The existence of the inclusion compounds obtained by different methods was confirmed by comparing with DSC and FTIR data of the pure com- pounds and the (1:1) Vitamin B10:b-CD physical mixture (pm). 1 H NMR measurements on aqueous solutions of Vitamin B10 and b-CD in D 2 O allowed us to establish the corresponding Vitamin B10’s and cyclodextrin’s protons implied in the complexation process. 2D NMR spectros- copy established the geometry of the inclusion complex. 1 H NMR, UV–Vis and fluorescence data were used to obtain the stoichiometry and the stability constant of the complex. Keywords Inclusion compound  p-Amino benzoic acid  Cyclodextrin  Molecular spectroscopy (FTIR, UV–vis, fluorescence, 1 H NMR)  DSC  X-ray powder diffraction Introduction A series of researches will conduct in the field of controlled drug release (release of Vitamin included in cyclodextrin). Para-amino benzoic acid (PABA) or Vitamin B10 (see Fig. 1a), is an intermediate in bacterial synthesis of folate [1], the microorganisms in the intestines are capable of synthesizing folic acid (an important factor in the protein use) from this compound, and humans lack this ability. Vitamin B10 is sometimes marketed as an essential nutri- ent for use whenever normal Vitamin B10 synthesis by intestinal bacteria is insufficient. The compound is used as a UV filter in sunscreen formulations [2], as a drug against fibrotic skin disorders, in treating irritable bowel syndrome [3, 4]. CDs are cyclic oligosaccharides consisting of six, seven or eight units of a-D-(?)-glucopyranose, referred to as a-, b- and c-CD respectively [5] (see Fig. 1b) obtained from starch by enzymatic reaction, that may encapsulate a wide variety of guest molecules (completely, or at least partially) in their hydrophobic cavity. Through controlled release, these systems ensure control of the release and of the absorption of the medicinal sub- stances from the respective system. The aim of this paper was to obtain an inclusion com- pound (IC) of Vitamin B10 with b-cyclodextrin (b-CD) and to characterize it by FT IR, X-ray powder diffraction, DSC, 1 H NMR, UV–Vis and spectrofluorimetry. Molecular modeling technique was employed to obtain the spatial architecture of this supramolecular assembly. I. Kacso ´  Gh. Borodi  S. I. Farcas  I. Bratu (&) National Institute for R&D of Isotopic and Molecular Technologies Dona ´th, 65-103 Cluj-Napoca, Romania e-mail: ibratu@gmail.com A. Hernanz Depto de CC y TT Fı ´sico Quimicas, UNED Madrid, Senda del Rey 9, 28040 Madrid, Spain 123 J Incl Phenom Macrocycl Chem DOI 10.1007/s10847-010-9763-y