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Proteins may exhibit an unfolding or folding state in the presence of a surfactant. In the present study, the unfolding and folding pathway of hen egg white lysozyme (HEWL) induced by sodium dodecyl sulfate (SDS) is studied. The stoichiometry obtained from isothermal titration calorimetry (ITC) provides guidelines for other techniques. The fluorescence spectra and circular dichroism show that the fluorescence properties and secondary structure of proteins undergo a two-step change upon binding with SDS, in which the intensity decreases, the emission blue shifts and the helical conformation decreases at low ratios of SDS to HEWL, while all of them return to the native-like state upon the addition of SDS at higher ratios. At the end of the binding, HEWL presents a higher α-helical content but its tertiary structure is lost compared to its native state, which is namely a molten globule state. Small angle X-ray scattering (SAXS) analysis and the derived model reveal that the complexes possess a decorated core-shell structure, with the core composed of dodecyl chains and the shell consisting of SDS head groups with a protein in molten globule state. Five binding steps, including the individual details involved in the denaturation, were obtained to describe the unfolding and folding pathway of HEWL induced by SDS. The results of this study not only present details about the denaturation of protein induced by SDS and the structure of the complexes involved in each binding step, but also provide molecular insights into the mechanism of the higher helical conformation of proteins in the presence of surfactant micelles.

Two commercial exogenous pulmonary surfactants, Curosurf and Survanta, are investigated. Their thermotropic behavior and associated structural changes for the samples in bulk are characterized and described. For Survanta, the obtained results of differential scanning calorimetry showed a thermogram with three peaks on heating and only a single peak on cooling. Curosurf on the other hand, presents calorimetric thermograms with only one peak in both the heating and cooling scans. This distinct thermotropic behavior between the two pulmonary surfactants, a consequence of their particular compositions, is associated with structural changes that were evaluated by simultaneous small- and wide-angle X-ray scattering experiments with in situ temperature variation. Interestingly, for temperatures below ∼35 °C for Curosurf and ∼53 °C for Survanta, the scattering data indicated the coexistence of two lamellar phases with different carbon chain organizations. For temperatures above these limits, the coexistence of phases disappears, giving rise to a fluid phase in both pulmonary surfactants, with multilamelar vesicles for Curosurf and unilamellar vesicles for Survanta. This process is quasi-reversible under cooling, and advanced data analysis for the scattering data indicated differences in the structural and elastic properties of the pulmonary surfactants. The detailed and systematic investigation shown in this work expands on the knowledge of the structure and thermodynamic behavior of Curosurf and Survanta, being relevant from both physiological and biophysical perspectives and also providing a basis for further studies on other types of pulmonary surfactants.

In this work, we developed a coarse-grained model of sumatriptan suitable for extensive molecular dynamics simulations. First, we confirmed the interfacial distribution of this drug in bilayers through cryogenic transmission electron microscopy and small-angle X-ray scattering techniques, as was predicted by our previous atomistic simulations. Based on these simulations, we developed a coarse-grained model for sumatriptan able to reproduce its overall molecular behavior, captured by atomistic simulations and experiments. We then tested the sumatriptan model in a micellar environment along with experimental characterization of sumatriptan-loaded micelles. The simulation results showed good agreement with photon correlation spectroscopy and electrophoretic mobility experiments performed in this work. The particle size of the obtained micelles was comparable with the simulated ones; meanwhile, zeta-potential results suggest adsorption of the drug on the micellar surface. This model is a step forward in the search for a suitable drug-delivery system for sumatriptan.

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Lauric acid (LAH) strongly inhibits the growth of acne-causing bacteria. LAH is essentially water-insoluble and the solubility of laurate (LA) salts are medium and temperature dependent. Hence, LAH/LA preparations are difficult to formulate. Here we fully characterized phospholipid vesicles containing up to 50 mol% LAH. Vesicles of dipalmitoylphosphatidylcholine (DPPC) containing LAH, at pHs 7.4 and 5.0, were characterized measuring size, charge, bilayer phase transition temperature (Tm) and permeability of water-soluble probes. Small angle X-ray scattering and cryotransmission electron microscopy showed multilamellar vesicles at low LAH %. Increasing LAH % had a negligible effect on particle size. An internal aqueous compartment in all vesicle's preparations, even at equimolar DPPC: LAH fractions, was demonstrated using water-soluble probes. At pH 5.0, the interaction between DPPC and LAH increased the Tm and phase transition cooperativity showing a single lipid phase formed by hydrogen-bonded DPPC: LAH complexes. At pH 7.4, vesicles containing 50 mol% LAH exhibited distinct phases, ascribed to complex formation between LAH and LA or LAH and DPPC. LAH incorporated in the vesicles minimally permeated a skin preparation at both pHs, indicating that the primary sites of LAH solubilization were the skin layers. These results provide the foundations for developing processes and products containing DPPC: LAH.

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Candelilla wax (CW) and 12-hydroxystearic acid (12HSA) are classic solid-fiber-matrix organogelators. Despite the high number of studies using those ingredients in oily systems, there is scarce literature using a mixture of oil and antioxidants. Vitamin E (VE) is an important candidate for its lipophilicity and several applications on pharmaceutical, cosmetics, and food industries. In this work, we investigated the influences of mixtures between vegetable oil (VO) and VE on the microstructures and rheological properties of CW and 12HSA organogels. A weak gel (G′′/G′ > 0.1) with a shear-thinning behavior was observed for all samples. The presence of VE impacted the gel strength and the phase transition temperatures in a dose-dependent pattern. Larger and denser packed crystals were seen for 12HSA samples, while smaller and more dispersed structures were obtained for CW organogels. The results obtained in this work allowed the correlation of the structural and mechanical properties of the organogels, which plays an important role in the physical-chemical characteristics of these materials.