Journal of Colloid and Interface Science 283 (2005) 555–564 www.elsevier.com/locate/jcis Aggregation behaviors of gemini nucleotide at the air–water interface and in solutions induced by adenine–uracil interaction Yujie Wang a , Bernard Desbat b , Sabine Manet a , Carole Aimé a , Thomas Labrot a , Reiko Oda a,∗ a Institut Européen de Chimie et Biologie, 2 rue Robert Escarpit, 33607 Pessac Cedex, France b Laboratoire de Physico-Chimie Moléculaire, 351 cours de la libération, 33405 Talence Cedex, France Received 27 May 2004; accepted 2 September 2004 Available online 9 December 2004 Abstract Cationic gemini surfactants having nucleotides as counterions (called nucleo-gemini hereafter) were synthesized and their aggregation behavior at air–water surfaces as well as in bulk solutions were studied. Fluid solutions of these nucleo-gemini surfactants show transitions to hydrogels upon addition of complementary nucleoside bases or other nucleo-gemini surfactants having complementary bases as counterions. The FTIR-ATR measurements show that the carboxylate groups of uridine form hydrogen bonds with the amine groups of adenosine. The aggregation behavior was also confirmed at the air–water interface by Brewster angle microscopy as well as surface pressure measurements; the monolayer of a gemini nucleotide was observed to undergo a transition to multilayers when nucleosides with complementary bases were added into the subphase. Isotherm curves of surface pressure monitored in parallel show a decrease in molecular area upon addition of such nucleosides.  2004 Elsevier Inc. All rights reserved. Keywords: Hydrogels; Molecular recognition at air–water interface; Gemini surfactants 1. Introduction Molecular recognition is an essential process for the con- struction of biological assemblies; the double helical struc- ture of DNA provides the ultimate example. Such subtly tuned molecular recognition tools have attracted attention for their potential use in materials science, for example, as biosensors. However, the elementary constituents of such biological polymers, mononucleotides, do not show base pairing recognition in solution, since this particular recog- nition is driven by hydrogen bonds, and in aqueous solution specific intermolecular interactions are in competition with nonspecific hydrogen bonds with water molecules [1]. For- mation of an isolated base pair is therefore energetically unfavorable. Cooperative processes where the pairing for- mation is influenced by neighboring constituents are im- * Corresponding author. Fax: +33(0)540-00-30-66. E-mail address: r.oda@iecb.u-bordeaux.fr (R. Oda). portant. Pörschke has shown that nucleotides have to be at least tetramers in order to exhibit recognition behavior in solution between complementary strands [2]. Extensive syn- thetic procedures are required to obtain very small amounts of such materials for materials science applications. Alterna- tive systems to covalently bonded oligonucleotides are nu- cleotides which interact with each other via noncovalent in- teractions. The use of nucleo-amphiphiles has been proposed in such a context. The objective is to confine nucleo-bases at the surfaces of amphiphilic aggregates to give effects similar to those of covalent bonds between nucleotides [3]. To investigate molecular recognition between comple- mentary bases of nucleo-lipids, the most common config- urations are at interfaces, such as spectroscopic studies or monolayer isotherm measurements at the air–water inter- face [4,5], water–solid interface [6], or Langmuir–Blodgett films [7]. Complex formation between complementary bases can increase (or decrease) the molecular area at the air– water interface, while the formation of hydrogen bonds be- tween the nucleobases can be detected by FTIR. The surface 0021-9797/$ – see front matter  2004 Elsevier Inc. All rights reserved. doi:10.1016/j.jcis.2004.09.003