International Journal of Pharmaceutics 325 (2006) 99–107 Effects of dirhamnolipid on the structural properties of phosphatidylcholine membranes Antonio Ortiz a , Jos´ e A. Teruel a , Mar´ ıa J. Espuny b , Ana Marqu´ es b , ´ Angeles Manresa b , Francisco J. Aranda a,∗ a Departamento de Bioqu´ ımica y Biolog´ ıa Molecular ‘A’, Facultad de Veterinaria, Universidad de Murcia, Campus de Espinardo, E-30100 Murcia, Spain b Laboratorio de Microbiolog´ ıa, Facultad de Farmacia, Universidad de Barcelona, Joan XXIII s/n, E-08028 Barcelona, Spain Received 21 April 2006; received in revised form 14 June 2006; accepted 17 June 2006 Available online 23 June 2006 Abstract Rhamnolipids are biosurfactants produced by Pseudomonas aeruginosa which are well known for their potential industrial and environmental uses. Rhamnolipids have gained considerable interest in recent years due to their potential use in cosmetics and pharmaceutics. They also show broad biological activities and have potential applications as therapeutic agents. The amphiphilic nature of rhamnolipids points to the membrane as their hypothetical site of action. We have purified dirhamnolipid and studied its interaction with phosphatidylcholine membranes, using differential scanning calorimetry, X-ray diffraction and infrared spectroscopy. It has been found that dirhamnolipid greatly affects the gel to liquid crystalline phase transition of phosphatidylcholines, broadening and shifting the transition to lower temperatures. Dirhamnolipid increases the interlamellar repeat distance of phosphatidylcholines and reduces the long-range order of the multilamellar systems. The phospholipid hydrocarbon chain conformational disorder is increased and the packing of the phospholipid molecules is perturbed in the presence of dirhamnolipid. The above evidence supports the idea that dirhamnolipid intercalates into the phosphatidylcholine bilayers and produces structural perturbations which might affect the function of the membrane. © 2006 Elsevier B.V. All rights reserved. Keywords: Dirhamnolipid; Model membranes; DSC; X-ray diffraction; Infrared spectroscopy 1. Introduction Biosurfactants constitute a diverse group of surface- active molecules synthesized by microorganisms. Pseudomonas aeruginosa produces rhamnose containing glycolipids also called rhamnolipids when grown on a number of water immis- cible substrates (Benincasa et al., 2002). The structure of the rhamnose containing glycolipids produced by the genus Pseu- domonas has been widely studied (Sim et al., 1997; Desai and Banat, 1997; Lang and Wagner, 1993). The surfactant properties Abbreviations: DiRL, dirhamnolipid; DMPC, 1,2-dimiristoyl-sn-glycero- 3-phosphocholine; DPPC, 1,2-dipalmitoyl-sn-glycero-3-phosphocholine; DSC, differential scanning calorimetry; DSPC, 1,2-distearoyl-sn-glycero-3-phospho- choline; SAXD, small angle X-ray diffraction; WAXD, wide angle X-ray diffrac- tion ∗ Corresponding author. Tel.: +34 968 364760; fax: +34 968 364147. E-mail address: fjam@um.es (F.J. Aranda). of rhamnolipids are well documented. They reduce the surface tension of water and the interfacial tension of water/oil systems (Lang and Wullbrandt, 1999). Rhamnolipids have gained con- siderable interest due to their low toxicity, biodegradable nature and diversity. Their range of potential industrial applications includes enhanced oil recovery, crude oil drilling, lubricants and bioremediation of water insoluble pollutants (Banat et al., 2000). Besides the environmental and industrial use of rhamno- lipids, a significant potential application is emerging for them as fine and specialty chemicals (Ishigami, 1997). In this regard, the use of rhamnolipids as emulsifiers, penetrating agents and drug delivery systems in cosmetics and pharmaceutics is a great developing area of research. Rhamnolipids show a great vari- ety of biological activities as they have been shown to have antimicrobial action (Itoh et al., 1971; Benincasa et al., 2004), antiphytoviral effect (Haferburg et al., 1987) and zoosporici- dal activity (Stanghellini and Miller, 1997). There is increasing interest in the effect of rhamnolipids on human and animal cells 0378-5173/$ – see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.ijpharm.2006.06.028