1110 Research Article Received: 4 November 2008 Accepted: 26 January 2009 Published online in Wiley Interscience: 3 March 2009 (www.interscience.wiley.com) DOI 10.1002/jrs.2240 Hydrogen bonding in amylose/DMSO complexes studied by vibrational spectroscopy and density functional theory calculations Alberto Milani, a* Nur Aiman Fadel, a Luigi Brambilla, a Mirella Del Zoppo, a Chiara Castiglioni, a Giuseppe Zerbi a and Riccardo Stradi b The intermolecular interactions in amylose/dimethyl sulfoxide (DMSO) complexes are discussed both experimentally and theoretically by means of Raman and infrared spectroscopies. The study is based on a preliminary analysis of well known systems such as pure liquid DMSO or DMSO in mixture with water: for such systems, an analysis of the CS stretching region is carried out both by means of Raman and infrared spectra. In particular, Raman spectra reveal a high sensitivity to the strength and to the type of interaction involving the DMSO molecules. These results, applied to the investigation of amylose-DMSO complexes, show the presence of different hydrogen-bonded complexes which coexist in this compound. In particular, DMSO molecules are identified both on the external surface of the V-amylose helix, where they can interact via one hydrogen bond and in the inner channel of the helix where they can interact via two hydrogen bonds. The present findings open the possibility of applying vibrational spectroscopy to the characterization of inclusion compounds of amylose which are currently being involved in many fields of nanosciences. Copyright c  2009 John Wiley & Sons, Ltd. Keywords: hydrogen bonding; first-principles calculations; host-guest compounds; intermolecular interactions Introduction Amylose and amylose complexes have attracted the interest of sci- entists in many different fields. Their importance is not restricted only to research in biology, food sciences or macromolecular structure, [1 – 18] but recently proved to be interesting systems in many other fields, such as nanotechnology [19 – 25] and pharmaceu- tical science. [26 – 29] Amylose complexes are host-guest systems where many different kinds of molecules can be included in the helical structure of V-amylose, thus affecting their environmental properties. [5 – 11] In the field of organic nanotechnology, complexes of amylose and conjugated oligomers have been recently prepared for possible applications as optical devices, [19 – 23] or complexed with carbon nanotubes [24,25] ; furthermore, complexes of amylose and drugs are currently investigated for applications in drug delivery. [26 – 29] A reliable chemical and physical characterization is required in order to understand the morphology and the molecular structure of these systems, first of all as proof of the existence of the inclusion complexes. The peculiar properties of amylose, either in the solid state or in solution with different solvents, have been already investigated. [5 – 18] In particular, the properties of amylose dis- solved in dimethyl sulfoxide (DMSO) or in water/DMSO mixtures have seeded much interest. This solvent interacts strongly with amylose, significantly affecting its molecular and supramolecular organization, and possibly promoting the formation of inclu- sion complexes. Indeed, amylose/DMSO solutions are used in the preparation of many complexes which have been carefully analyzed in the past. [12 – 18] From the point of view of vibrational spectroscopy, the intermolecular properties of DMSO in different environments have been analyzed in many works, both by infrared and Raman spectroscopies. [30 – 41] The vibrational dynamics of these molecules were found to be sensitive to intermolecular interactions, and the related spectroscopic features were identified. In this paper, the Raman spectra of amylose/DMSO complexes are investigated on the basis of the spectroscopic markers identified by the analysis of the spectra of simpler systems such as pure DMSO and mixtures of DMSO with water or benzene. The study of the spectra in the CS stretching region has allowed to find evidence of the existence of different kinds of intermolecular interactions, thus offering a spectroscopic marker which has been almost completely overlooked in previous studies. [30 – 32] The reliability of our interpretation, and the validity of the markers identified, are further supported by the infrared spectra. The comparison of DMSO-H 2 O, DMSO-benzene solutions and DMSO-amylose complexes indicates that it is possible to identify different types of complexation. In previous papers by Winter and Sarko, [12,13] on the basis of X-ray diffraction data, it was found that DMSO molecules inside the ∗ Correspondence to: Alberto Milani, Politecnico di Milano, Dip. di Chimica, Materiali, Ing. Chimica ‘‘G.Natta’’ Piazza Leonardo da Vinci 32, Milano - Italy. E-mail: alberto.milani@polimi.it a Politecnico di Milano, Dipartimento di Chimica, Materiali e Ingegneria Chimica, G. Natta, Piazza Leonardo da Vinci 32, I-20133 Milan, Italy b Universit` a di Milano Facolt` a di Farmacia, Istituto di Chimica Organica ‘‘Alessandro Marchesini’’ Via Giacomo Venezian 21, 20133 Milan, Italy J. Raman Spectrosc. 2009, 40, 1110–1116 Copyright c  2009 John Wiley & Sons, Ltd.