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[Display omitted] Nonionic surfactants can counter the deleterious effect that anionic surfactants have on proteins, where the folded states are retrieved from a previously unfolded state. However, further studies are required to refine our understanding of the underlying mechanism of the refolding process. While interactions between nonionic surfactants and tightly folded proteins are not anticipated, we hypothesized that intermediate stages of surfactant-induced unfolding could define new interaction mechanisms by which nonionic surfactants can further alter protein conformation. In this work, the behavior of three model proteins (human growth hormone, bovine serum albumin, and β-lactoglobulin) was investigated in the presence of the anionic surfactant sodium dodecylsulfate, the nonionic surfactant β-dodecylmaltoside, and mixtures of both surfactants. The transitions occurring to the proteins were determined using intrinsic fluorescence spectroscopy and far-UV circular dichroism. Based on these results, we developed a detailed interaction model for human growth hormone. Using nuclear magnetic resonance and contrast-variation small-angle neutron scattering, we studied the amino acid environment and the conformational state of the protein. The results demonstrate the key role of surfactant cooperation in defining the conformational state of the proteins, which can shift away or toward the folded state depending on the nonionic-to-ionic surfactant ratio. Dodecylmaltoside, initially a non-interacting surfactant, can unexpectedly associate with sodium dodecylsulfate-unfolded proteins to further impact their conformation at low nonionic-to-ionic surfactant ratio. When this ratio increases, the protein begins to retrieve the folded state. However, the native conformation cannot be fully recovered due to remnant surfactant molecules still adsorbed to the protein. This study demonstrates that the conformational landscape of the protein depends on a delicate interplay between the surfactants, ultimately controlled by the ratio between them, resulting in unpredictable changes in the protein conformation. [ABSTRACT FROM AUTHOR]

The self-assembly of long-tail surfactants results in the formation of nanoscale structures, e.g. worm-like micelles, with the ability to modify the rheology of the system. However, micelle formation, and thus the alteration of the rheology, is subject to the high Krafft temperature of saturated long-tail surfactants. Hexadecylmaltosides are sustainable surfactants that, in solution, form tailorable viscoelastic fluids. The preparation of monounsaturated sugar-based surfactants is hypothesised to reduce the Krafft point compared to the saturated analogues, therefore increasing the temperature range where the surfactant remains in the micellar form. Here we report the synthesis and characterisation of a novel sugar-based surfactant with an unsaturated C16-tail, namely palmitoleyl-β- d -maltoside (β-C 16-1 G 2). Differential scanning calorimetry was used to probe the temperature stability of the system. The rheology of β-C 16-1 G 2 solutions was investigated by means of rotational and oscillatory rheology, and these results were connected to the mesoscopic structure of the system as shown by small-angle neutron and X-ray scattering, and dynamic light scattering. The presence of a double bond on the alkyl chain moiety leads to a depression in the Krafft point, allowing the surfactant to form a thermodynamically stable micellar solution over a wide range of temperatures, i.e. 5–95 °C. The surfactant self-assembles into worm-like micelles which, upon entanglement in the semi-dilute regime, result in the formation of a non-Newtonian, viscoelastic fluid. These observations have important implications in the development of new sustainable formulated products, enabling the preparation of surfactant phases with remarkable thermal resilience. [ABSTRACT FROM AUTHOR]

The self-assembly of ionic surfactants in deep eutectic solvents has recently been demonstrated, opening up new possibilities in terms of the development of formulated products and templating of nanostructured materials. As it occurs in an aqueous environment, the solvophobic effect drives the formation of micelles in these solvents and specific-ion interactions alter the resulting structures. We hypothesized that the presence of hydrotropic salts would greatly affect the micellar structure in deep eutectic solvents, ultimately leading to the formation of worm-like aggregates. A systematic investigation performed on hydrotrope-surfactant assemblies in neat and hydrated 1:2 choline chloride:glycerol is presented. The effect of choline salicylate on the micellization of hexadecyltrimethylammonium chloride at different hydrotrope-to-surfactant ratios was probed by contrast variation small-angle neutron scattering. Here the first investigation on salt-induced micellar growth in deep eutectic solvents is presented. The microscopic characterization of the system shows that the micelle-hydrotrope interaction in pure and hydrated deep eutectic solvents results in a significant increase in micelle elongation. The condensation of the hydrotrope on the micelle, which alters the effective monomer packing, leads to the formation of worm-like micelles with tunable morphology and flexibility. The results presented here present new possibilities in terms of self-assembly and co-assembly in neoteric solvents, where micelle morphology can be controlled through surfactant-salt interactions. [ABSTRACT FROM AUTHOR]

The anomeric configuration (α or β) of n -hexadecyl- d -maltopyranoside (C 16 G 2) has been shown to affect the morphology of the micelle, from elongated for α-C 16 G 2 to worm-like micelles for β-C 16 G 2. The entanglement of worm-like micelles often leads to strong modifications of the rheological behavior of the system and, as such, the anomeric configuration of C 16 G 2 could also provide the possibility of controlling this. Furthermore, mixing these surfactants are hypothesized to result in mixed micelles allowing to finely tune the rheology of a system containing these sustainable surfactants. The rheology of α- and β-C 16 G 2 , and mixtures of those, was determined by rotational and oscillatory rheology at different temperatures and surfactant concentrations. Micelle structure and composition for these systems were characterized using contrast variation small-angle neutron scattering and small-angle X-ray scattering. The results from these were connected in order to elaborate a molecular understanding of the rheological response of the system. The self-assembly of these surfactants have been found to result in different rheological properties. β-C 16 G 2 show a high viscosity with a non-Newtonian viscoelastic behavior, which was linked to the formation of worm-like micelles. In contrast, α-C 16 G 2 self-assembled into short cylindrical micelles, resulting in a Newtonian fluid with low viscosity. Furthermore, mixtures of these two surfactants lead to systems with intermediate rheological properties as a result of the formation of micelles with intermediate morphology to those of the pure anomers. These results also show that the rheological properties of the system can be tuned to change the micelle morphology, which in turn depends on the anomeric configuration of the surfactant. Also, surfactant concentration, temperature of the system, and micelle composition for surfactant mixtures provide control over the rheological properties of the system in a wide temperature range. Therefore, these results open new possibilities in the development of sustainable excipients for formulation technology, where the characteristics of the system can be easily tailored through geometric variations in the monomer structure whilst maintaining the chemical composition of the system. [ABSTRACT FROM AUTHOR]