Nanostructures in n-Octanol Equilibrated with Additives and/or Water

Abstract

Fluid fatty alcohols are believed to be nanostructured but broadly amorphous (i.e., noncrystalline) fluids and solvents, including the most popular fatty tissue mimetic, hydrated n-octanol (i.e., hydro-octanol). To check this premise, we studied dry octanol and hydro-octanol as a model of relatively short fluid n-alkanols with small-angle X-ray scattering (SAXS). We also combined this alkanol with the matching alkane (i.e., octane) and with a common anti-inflammatory pain killer (ketoprofen). This revealed that (hydro-)octanol and arguably any other short fatty alcohol form a mesophase. Its basic structural motif are regularly packed polar nanoclusters, reflected in the inner peak in the SAXS diffractogram of (hydro-)octanol and other fluid n-alkanols. The nanoclusters arguably resemble tiny, (inverse) hydrated bilayer fragments, located on a thermally smeared para-crystalline lattice. Additives to hydro-octanol can change the nanoclusters only moderately, if at all. For example, octane and the drug ketoprofen added to hydro-octanol enlarge the nanoclusters only little because of the mixture's packing frustration. To associate with and to bring more water into hydro-octanol, an additive must hence transform the nanoclusters: it expands them into irregularly distributed aqueous lacunae that form a proto-microemulsion, reflected in the previously unknown Guinier's SAXS signal. A "weak" (i.e., a weakly polar or nonpolar) additive can moreover create only size-limited lacunae. Coexistence of nanoclusters and lacunae as well as size variability of the latter in hydro-octanol subvert the concept of octanol-water partition coefficient, which relies on the studied compartment homogeneity. In turn, it opens new possibilities for interfacial catalysis. Reinterpreting "octanol-water partition coefficient" data in terms of octanol-water association or binding constant(s) could furthermore diminish the variability of molecular lipophilicity description and pave the ground toward a more precise theoretical quantification and prediction of molecular properties.

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Interactions of amphiphiles with plasticisers used in polymers: Understanding the basis of health and environmental challenges

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Electrical Conductivity and Viscosity in Binary Organic Liquid Mixtures: Participation of Molecular Interactions and Nanodomains

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“…Thus, Figure 1a shows that the dipole moment increases at the highest concentrations [16], which is attributed to an increase in the concentration of associated species, such as chains of octanol molecules (e.g., Figure 1b [39]). Furthermore, it is found that the addition of n-octane to octanol (6:1 octanol:octane, i.e., 87 wt% octanol, equivalent to ≈0.86 mole fraction) results in the formation of a mesophase [6,40], thereby relieving the nanocluster packing stress. Assuming that the same mole ratio is applicable to other alkanes, this would be equivalent to 82 wt% dodecane, which is relevant to the present work.…”

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