Contents lists available at ScienceDirect Chemistry and Physics of Lipids journal homepage: www.elsevier.com/locate/chemphyslip Influence of structurally related micelle forming surfactants on the antioxidant activity of natural substances Sara Battista, Patrizio Campitelli, Armando Carlone, Luisa Giansanti ⁎ Dipartimento di Scienze Fisiche e Chimiche, Università degli Studi dell’Aquila, Via Vetoio 10, 67100 Coppito, AQ, Italy ARTICLE INFO Keywords: (+)-usnic acid L-ascorbic acid antioxidant activity L-prolinol derivatives N-oxide moiety structure-properties relationship ABSTRACT Physicochemical properties of micelles, like other lipid aggregates, mostly depend on the composition and on the structure of the surfactants used as monomers. The preparation and the characterization of three cationic L- prolinol derivative surfactants with different chain lengths and their corresponding N-oxide are described. UV measurements were carried out to investigate the effect of the inclusion in micelles on the degradation of L- ascorbic acid and (+)-usnic acid. An influence on antioxidant activity was exerted to an extent strictly de- pendent on i) surfactant chain length, ii) charge, iii) pH (in the case of (+)-usnic acid) and iv) on the hydro- philicity of the solute, determinant parameter for their location in the aggregates. In general the extent of the antioxidant activity of the system in the case of N-oxides micelles depends on surfactant chain length. On the other hand, cationic micelles formed by the surfactant with the shortest chain behave more like N-oxides ones rather than those formed by its relative structural homologues featuring longer alkyl chains, probably as a consequence of a concentration effect. 1. Introduction It is well known that the structural characteristics of the compo- nents of lipidic self-assembled systems influence the morphology and physicochemical behavior of the aggregates (Israelachvili et al., 1976; Oliver et al., 2013) and are strictly related to their “classical” perfor- mance properties (i.e. wetting and foaming ability, solubilization and detergency) (Azira et al., 2008; Sehgal et al., 2003; Lichtenberg et al., 1983). For example, the length of the surfactant can significantly affect the properties of the aggregates it forms (Ceccacci et al., 2013; Costas- Costas et al., 2005; Wang and Gao, 2018; Ceccacci et al., 2008). Moreover, the charge of the polar headgroup of the surfactants plays a crucial role in determining the interaction of their aggregates with the solute and with the counterions in solution (Fuangswasdi et al., 2006; Demissie and Duraisamy, 2016; Joshi et al., 2002; Sinha and Bahadur, 2002; Vlachy et al., 2008). In general, a polar headgroup featuring a pyrrolidine ring is characterized by a lower conformational freedom with respect to the corresponding acyclic analogue, together with a different balance as a whole between the hydrophilic and the hydro- phobic region of the molecules (Karukstis and McDonough, 2005). The possibility of modifying the pyrrolidine skeleton and the length of the alkyl chains, thus the physicochemical properties of the surfactant, makes pyrrolidinium based surfactants interesting in many research fields (Zhao and Zheng, 2011; Cai et al., 2012, Tian2016; Bombelli et al., 2008). Furthermore, N-oxide based surfactants (N-ox) show very interesting properties and are involved in a wide variety of industrial applications such as cleaning products (washing-up and laundry de- tergents), foaming and wetting agents, fabric softeners and thickeners in hair and body care products (Sauer, 1990; Vaikunth, 2019; Gunstone and Padley, 2018). In fact, they are zwitterionic (at physiological pH) amphiphilic molecules characterized by a strong polar NeO bond (and a high electron density on the oxygen) (Łukomska et al., 2015). Moreover, they are environmentally friendly (often they are classified as soft surfactants) (Lewińska et al., 2014) and very easy to prepare. Thanks to a number of peculiarities, such as pH-sensitivity, higher emulsifying ability and biodegradability, lower irritant action and toxicity, gelating and antioxidant properties, N-ox are regarded as very interesting molecules that could find application in a range of areas. Several reports describe the effect of changes in the molecular structure of mono- and di-twin (Lewińska et al., 2014; Piasecki et al., 2009) tailed and gemini (Bordi et al., 2010) N-ox on their self-aggregation behavior, their catalytic activity (Katritzky et al., 1988; Karlovská et al., 2006) and their influence on entrapped solutes (Niedziółka et al., 2012). In particular, it was described that the antioxidant activity of L-ascorbic acid (AA), well known for its reducing properties, increases in a dose- dependent manner in the presence of N-ox micelles in pure water https://doi.org/10.1016/j.chemphyslip.2019.104818 Received 18 July 2019; Received in revised form 22 August 2019; Accepted 4 September 2019 ⁎ Corresponding author. E-mail address: luisa.giansanti@univaq.it (L. Giansanti). Chemistry and Physics of Lipids 225 (2019) 104818 Available online 04 September 2019 0009-3084/ © 2019 Elsevier B.V. All rights reserved. T