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In this work a sample of SBA-15 mesoporous silica was synthesized and characterized by TEM, XRD, and N2 adsorption. The sample had a high value of specific surface area (1007 m² g^-1) and total pore volume (2.1 cm³ g^-1). The pore diameter was 67 Å, so it was large enough to accommodate protein molecules inside the channels. Immobilization by physical adsorption of a commercial lipase preparation from Mucor javanicus was performed at different pH values (pH 5−8). pH 6 gave the highest lipase loading and hydrolytic activity of the corresponding biocatalyst. Chemical modification of the SBA-15 via glutardialdehyde allowed also the enzyme immobilization through chemical adsorption. This preparation was active toward tributyrin hydrolysis. On the contrary, very low activity toward triolein hydrolysis was observed. The reduction of the size of the channels due the immobilization process has been suggested as a possible explanation.

The antiseptic, antibacterial, and antifungal properties of the essential oil of Melaleuca alternifolia, commonly called tea tree oil (TTO), are well-known. This mixture of monoterpenes, sesquiterpenes, and their alcohols is utilized in many therapeutic and cosmetic applications, directly as essential oil or in different kinds of formulations. The terpinen-4-ol, which is present in the commercial essential oil samples in the minimum amount of 30 wt %, is recognized as the main active agent of TTO. Considering the good performance of lipid-based liquid crystalline phases as drug delivery systems, the monoolein/water system has been assessed for both terpinen-4-ol and TTO formulations. The phase behavior of the ternary systems has been investigated by means of optical microscopy and ²H NMR quadrupolar splitting. ¹³C NMR spin−lattice relaxation times and self-diffusion coefficients (measured by ¹³C NMR PGSE technique) of the lipid matrix and the active agent have been determined to give insights on the dynamic and localization of the molecules in the different microstructures.

¹⁴N NMR relaxation rates were measured in ternary DDAB water-in-oil microemulsions to investigate structural transitions along oil dilution lines. A two-step model of relaxation was used to estimate the slow correlation times of the surfactant interface. The interpretation of the ¹⁴N slow correlation times in terms of the percolation theory gave critical exponents in agreement with static and dynamic regimes, depending either on the volume fraction of the dispersed phase or on the oil type.

Monoolein (GMO) forms a bicontinuous cubic phase that can coexist in equilibrium with a water phase, and this phase can be dispersed into colloidal particles. Poloxamer is an efficient stabilizer for dispersions of this phase. By adding a small amount of triolein to GMO, a reversed hexagonal phase is formed at room temperature. This phase can be dispersed into submicron particles in water in the same way. The inner molecular arrangement of these dispersions was investigated by ¹³C NMR relaxation. The ¹³C NMR relaxation rates of the various GMO carbon atoms obtained from the dispersed particles compared to those obtained from the nondispersed phases indicate that the lipid organization and dynamic properties of the original nondispersed phases are retained. It is also demonstrated that the cubic phase is transformed into the reversed hexagonal phase, within six months, due to hydrolysis of GMO. A remarkable observation is that no significant hydrolysis occurs during this time in the corresponding dispersed samples. This indicates that solubilization of a few wt % of Poloxamer into the GMO bilayer provides protection against degradation.

The ternary phase diagram of two nonionic polar lipids, glycerol monooleate (GMO) and diglycerol monooleate (DGMO), in water has been characterized through NMR, polarizing optical microscopy, SAXS, and rheological measurements. GMO in water forms a lamellar and two types of bicontinuous cubic phases. The diamond type exists in equilibrium with water. DGMO, with its bulky polar group, forms only lamellar structures that also coexist with water. In the ternary GMO/DGMO/water system, the regions of lamellar and cubic phases are significantly enlarged, and a swollen cubic phase of the gyroid type exists in equilibrium with water. Measurement of the viscoelastic properties revealed that the cubic phases are elastic, independent of the sample composition. The cubic phases become softer (the G‘ storage modulus decreases) with increasing water and DGMO content. A discontinuity is observed in the G‘ versus water content graph at the transition between the gyroid and the diamond cubic phases.

The water-in-oil (w/o) microemulsion regions formed by the double-chained DDAB surfactants with the two aromatic oils toluene and trifluoromethylbenzene have been investigated with the highlight on the microstructural features. A remarkable finding is that DDAB is soluble up to ~30 wt % in these oils. The phase diagrams of DDAB/water/aromatic oil systems show a microemulsion region near the oil−DDAB axis, with a maximum water uptake of ~15 wt %. Along the oil dilution line, the water/surfactant (w/s) mass ratio is 0.16; at high surfactant concentrations, the lamellar region is seen to melt gradually into the isotropic microemulsion through a very small two-phase region. ¹⁴N NMR relaxation times and conductivity measurements, collected along water and oil dilution lines, have suggested the existence of flexible bilayers at high volume fractions of the dispersed phase (φd), whereas at low φd, self-association of the oil highly perturbs the expected w/o organization of DDAB molecules, which become almost molecularly dispersed. The interpretation of the slow ¹⁴N NMR correlation times in terms of the percolation theory gives critical exponents in agreement with a dynamic regime at intermediate φd and with a static regime at high φd in the proximity of the lamellar phase.

The microstructural features of ternary microemulsions in the CaAOT/water/isooctane system are investigated by conductivity and NMR self-diffusion measurements. The results are compared with the corresponding NaAOT system. Experimental data are collected along water and oil dilution lines with the aim of investigating the interactions among the surfactant aggregates. Previous studies on the microemulsion regions of CaAOT/water/decane are also considered in order to evaluate the influence of the oil (branched or linear) on the microstructural transitions. Water-in-oil spherical droplets with a hard-sphere behavior are likely to occur in a very limited region of the L2 phase, namely, at low volume fractions of the disperse phase, φd. Both conductivity and water self-diffusion demonstrate the occurrence of important modifications of the water-in-oil droplet organization and suggest the occurrence of transient fusion−fission processes among the droplets. These processes become more and more important with increasing φd. The microstructure of the system is discussed in view of different approaches based on percolation theory, attractive interactions among discrete particles, and a multiconnected water network.

Didodecyldimethylammonium bromide (DDAB) in water has been reported to form two coexisting lamellar phases. Here, the phase diagrams of DDAB in H2O and in D2O are reinvestigated focusing on the isotopic effect, on the coexistence of two different types of surfactant bilayers at room temperature, and on the structural transition from vesicles to lamellar liquid crystals, observed at low surfactant concentration with increasing temperature. Only at high temperature DDAB forms a monophasic lamellar liquid crystalline structure in the whole range of composition, with critical points located around 84 °C in D2O and 74 °C in H2O. The higher energy (zero-point stretching) associated with the O−D···O bond not only increases the transition temperature but also causes the formation of a regular lamellar phase, at room temperature, at a slightly higher surfactant/water molar ratio than in H2O. ²H NMR data for the DDAB−D2O system evidentiate the temperature dependent structural transition from a Lα1 phase, where lamellar liquid crystals coexist with multilayer vesicles, to a more ordered and apparently homogeneous Lα2 lamellar phase. At 85 °C the water molecules, close to the interface, appear to be significantly affected by the surfactant interface, thus displaying a much higher order parameter than at 25 °C. The analysis of ⁸¹Br and ¹⁴N NMR data reveals details related to this structural transition which should occur through two main steps. In the range of temperature 30−50 °C bromine dissociation plays a crucial role in unsettling the vesicle arrangement whereas in the range 60−85 °C the charged bilayers evolve toward a regular lamellar packing. The significant increase of the ¹⁴N quadrupolar splittings with increasing surfactant concentration is interpreted in terms of an increased order of the nitrogen nuclei, which reflects the tendency of the surfactant molecules to assume a more symmetric conformation with respect to the aggregate surface, thus allowing for a higher chain compressibility. The existence of two different stable microstructures, at room temperature, implies that two minima of the self-association energy occur for two different compositions, which, in turn, satisfy two packing requirements, namely, 0.5 < v/al < 1 (for vesicles) and v/al ≈ 1 (for lamellae).

The microstructural features of the ternary microemulsion CaAOT/water/n-decane are investigated by viscosity, conductivity, dynamic light scattering, and NMR self-diffusion measurements. The phase diagram shows a significant shrinkage of the microemulsion region, compared with the corresponding NaAOT system, which implies a decrease of the capability of water uptake. This is also observed for the Lα phase of the binary CaAOT/water system. A preliminary analysis of viscosity data suggests the occurrence of nonspherical particles at high volume fraction of the disperse phase, φd, whereas the conductivity measurements show a percolative behavior at a critical φd^c = 0.142, along an oil dilution line at constant molar ratio w/s = 26.4. The percolation threshold is not temperature dependent in the range 15−30 °C, thus suggesting the possibility of a static percolation. The comparison between the diffusion coefficients calculated from composition and those obtained by DLS and NMR measurements reveals that spherical droplets with a hard-sphere behavior are likely to occur in a very limited region of the L2 phase, namely, at low φd. The conductivity measurements and the NMR self-diffusion coefficients of water, measured along several water dilution lines, display significant maxima, appearing at w° ([H2O]/2[CaAOT]) between 6 and 13 (conductivity, diffusion, and w° values, at the maximum, increase with increasing the s/o ratio), in evident conflict with a hard-sphere model. All experimental data demonstrate the occurrence of important modifications of the water-in-oil droplet organization. The microstructure of the system is discussed in view of different approaches based on percolation theory, attractive interactions among discrete particles, and multiconnected water network. Microstructural evolutions can be justified in terms of transient fusion−fission processes among the droplets occurring over time scales that are comparable with the experimental (conductivity and NMR) observation times. Similar results have been obtained by considering the geometrical DOC model set up to interpret the transition from a bicontinuous to a water-in-oil droplet microstructure in DDAB microemulsions.

The solubilization of vitamin K1 (VK1), a highly hydrophobic molecule, into a 1-monoolein/water (MO/W) system, is investigated by NMR self-diffusion, small angle X-ray scattering (SAXS), optical microscopy, and electrochemical methods. The various MO/W phases, namely L2, Lα, CG, and CD, can accommodate different amounts of VK1. In particular, the Lα and the cubic CG phases can solubilize up to 8 and 5 wt % VK1, respectively, without modifing the microstructure substantially. By contrast, the cubic CD phase can accommodate only about 1 wt % VK1. Larger addition of VK1 produces a transition from the lamellar and cubic phases to a reverse hexagonal phase HII, which in the MO/W binary system occurs only for the cubic phases and at temperatures above 80 °C. In practice the solubilization of VK1 induces almost the same phase transitions as would a temperature increase in the binary system. The SAXS and NMR self-diffusion data strongly suggest that the VK1 molecules are well intermingled with the MO hydrophobic chains. Consequently the swelling of the CG and Lα phases does not seem to be affected by the amount of VK1 present. However, if a sufficient number of VK1 molecules has penetrated into the lipid bilayer, the local change of the bilayer curvature is so large that a transition from cubic or Lα phase to a reverse hexagonal phase will occur. Electrochemical measurements indicate that, when solubilized in the cubic phase, the naphthoquinone group of VK1 reaches the bilayer/aqueous interface during the redox cycle, as the formal redox potential of the group is pH-dependent. The potential use of MO/W cubic phases with electrochemically active bilayer components in bioanalytical systems is discussed.