Hybrid conjugates have been obtained by "click chemistry" (azide-alkyne coupling) of well controlled xylo-oligosaccharides (XOS), obtained by mild hydrolysis of hardwoods xylans, and two model fatty acids, namely methyl ricinoleate (MeRic) and methyl oleate (MeOl) (Figure 1). Evidences of self-assembling of the conjugates were firstly obtained by recording NMR in polar (D2O) or non-polar (CDCl3). XOS protons signals were not visible in CDCl3 spectra, while those of fatty acids were only poorly resolved in D2O. Dynamic light scattering (DLS) and transmission electron microscopy (TEM) were used to point out the nature and dimensions of objects formed by dissolving the two conjugates (XOS-MeRic and XOS-MeOI) either in water or chloroform, in different concentrations (from 0.1 to 10 g/L). The results obtained show that the nature of the self-assembly properties considerably depends on the polarity of the solvent, the solution concentration and the chemical structure of the fatty acids. Both conjugates form nano-objects whose dimensions increases with concentration in chloroform (~700 nm at 0,1 g/L, ~ 1500 nm at 1 g/L, and ~ 2500 nm at 10 g/L as measured by DLS), clearly demonstrating the formation of aggregates. However, at 1 g/L the combined use of TEM and DLS allows observing that the size and populations of the objects depends on the fatty acid moiety. XOS-Ol presents important concentration of aggregates. After the elimination of these later over a 0.45 µm filter, regular objects of diameter between 40 and 90 nm are observed. For XOS-MeRic, no differences were observed before and after filtering. Spherical nanoparticles of around 30 nm diameter were evidenced by TEM. In water, XOS-Ol also form aggregates. After filtering, poorly controlled particles measuring around 30 nm diameter were obtained, whereas for XOS-MeRic, very well controlled spherical nanoparticles of 30 nm diameter were evidenced by TEM before and after filtering. An overview of the different objects obtained from the two different conjugates in both polar and non-polar solvents is also presented in Figure 1. These observations will be useful for the future different applications (encapsulation, emulsion stabilizers, coatings, etc) envisaged for these hybrid systems.

Nanoscale self-assembling properties of hybrid materials obtained from hemicelluloses oligomers and fatty acids in polar and non-polar media

253rd National Meeting (2017)

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