DOI: 10.1021/la1005067 6177 Langmuir 2010, 26(9), 6177–6183 Published on Web 03/31/2010 pubs.acs.org/Langmuir © 2010 American Chemical Society Synthesis and Physicochemical Characterization of New Twin-Tailed N-Oxide Based Gemini Surfactants Federico Bordi, † Giorgio Cerichelli,* ,‡ Nadia de Berardinis, ‡ Marco Diociaiuti, § Luisa Giansanti, ^ Giovanna Mancini,* ,^, ) and Simona Sennato # † Dipartimento di Fisica and INFM-CRS SOFT, Universit  a degli Studi di Roma “La Sapienza”, Piazzale A. Moro 5, 00185 Roma, Italy, ‡ Dipartimento di Chimica, Ingegneria Chimica e Materiali, Universit  a degli Studi de L’Aquila, UdR INCA, Via Vetoio, 67010 Coppito Due, L’Aquila, Italy, § Dipartimento di Tecnologie e Salute, Istituto Superiore di Sanit  a, V. le Regina Elena 299, 00161 Roma, Italy, ^ CNR, Istituto di Metodologie Chimiche;Sezione Meccanismi di Reazione and Dipartimento di Chimica, Universit  a degli Studi di Roma “La Sapienza”, P. le Aldo Moro 5, 00185 Roma, Italy, ) Centro di Eccellenza Materiali Innovativi Nanostrutturali per Applicazioni Cliniche, Fisiche e Biomediche, and # Dipartimento di Fisica and CNISM, Universit  a degli Studi di Roma “La Sapienza”, Piazzale A. Moro 5, 00185 Roma, Italy Received July 17, 2009. Revised Manuscript Received March 15, 2010 New gemini surfactants (GSs) constituted by two double alkyl chain (from 7 to 17 methylenic units) N-oxide monovalent surfactants joined by a PEG spacer of different length (from 3 to 21 ethylene glycol units), thus combining the properties of both N-oxide and GS surfactants, were synthetized and characterized. The different hydrophilic/ hydrophobic balance of the molecular structure strongly influences the morphology and the electrical features of the aggregates. Despite the zwitterionic nature of the polar head groups, all the aggregates are characterized by positive potential thus suggesting protonation at the interface; however, the extent of protonation was shown to strongly depend on the length of the alkyl chain and of the spacer. Introduction Gemini surfactants 1,2 (GSs) are amphiphilic molecules that con- tain two head groups and two aliphatic chains, linked by a rigid 3-6 or flexible 7,8 spacer. Their molecular structure confers them very peculiar physicochemical properties compared to the correspond- ing monovalent surfactants. In fact, they typically show highly superior surfactant properties with respect to the corresponding conventional amphiphiles; for example, surface activity can be increased 1000-fold. Moreover, GSs are characterized by lower critical micellar concentration (cmc) values, higher solubilization power, and hydrotropy with respect to the corresponding mon- ovalent surfactants. The higher surface activity of GSs is advan- tageous for their applications in the industry for detergency and emulsification and involves the use of smaller amounts of raw material for synthesis and the handling of less manufacturing and byproduct, thus ending in a minor environmental impact. 9 All these advantages make them of special interest also for biomedical applications, where they have been investigated as drug delivery systems 10 and DNA carriers in transfection studies. 11 Because of these features, though the family of GSs is relatively young (actually, they were first reported ∼40 years ago, 12 but a large interest for these surfactants has spread ∼20 years later), there already are a large number of species for a whole range of applications. So far over 10000 international patents on GSs have been filled, and investigations on many different applica- tions are currently being reported. The manipulation of the basic structure of gemini can give an almost unlimited number of potential molecules, thus allowing extensive structure-activity studies aimed at identifying structural features necessary for the successful exploitation of GSs. Here we report the preparation of the new GSs (Scheme 1), composed of two (from 7 to 17 methylenic units) N-oxide monovalent surfactants bearing two alkyl chains and joined by a PEG spacer of different length (from 3 to 21 ethylene glycol units), and the physicochemical characterization of the aggregates they form in water. N-Oxide surfactants are in general biodegrad- able, show a low-to-moderate toxicity, and show good antiox- idant 13 and antimicrobial activity 14 (both depending on the alkyl chain length). N-oxide surfactants are used in many cleaning formulations, in liquid bleach products, as antistatic agent in textile industry, as foam stabilizer in the rubber industry, as polymerization catalysts in polymer industry, in anticorrosion compositions, as lime soap dispersants, and as antibacterial agents in deodorant bars due to their compatible synergistic effect and environment friendly nature. 15 The absence of counterions in *Corresponding authors. (G.M.) Telephone: 00390649913078. Fax: 003906490421. E-mail: giovanna.mancini@uniroma1.it. (G.C.) Telephone: 0039 0862433784. Fax: 0039 0862433753. E-mail: cerichel@univaq.it. At the time of publication, G.C.’s telephones were not working, as the Chemistry building cannot be used due to an earthquake; reconstruction is in course. (1) Menger, F. M.; Keiper, J. S. Angew. Chem. 2000, 112, 1980–1996. (2) Menger, F. M. Angew. Chem., Int. Ed. 2000, 39, 1906. (3) Menger, F. M.; Littau, C. A. J. Am. Chem. Soc. 1993, 115, 10083. 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