Effect of temperature on n-tetradecane emulsion in the presence of phospholipid DPPC and enzyme lipase or phospholipase A2

Interfacial Interactions of a Myoglobin/DOPC Hybrid System at the Air-Water Interface and Its Physicochemical Properties

In the present study, the intermolecular interactions between a water-insoluble phospholipid (DOPC) and water-soluble protein (myoglobin) and the interaction among themselves were investigated at the air-water interface using the Langmuir and Langmuir-Blodgett techniques. The effects of changes in physicochemical factors, like pH and temperature, on these interactions were also examined. Surface pressure-molecular area (π-A) isotherms of the DOPC monolayer at the air-water interface, with and without myoglobin (Myo) revealed the evolution of various physical properties, such as elastic, thermodynamic, and hysteric properties, in response to changes in subphase pH and temperature. With the increment of subphase pH from 5 to 7 at a fixed temperature (20 °C), the DOPC isotherm expanded, and the in-plane elasticity (CS-1) decreased, but no significant presence of hysteresis was encountered in either of the pH values. On the other hand, a diminution of temperature (from 20 to 5 °C) leads to an expansion of monolayers yielding low elasticity and significant hysteresis. The incorporation of Myo molecules within the DOPC monolayer decreased the CS-1 value of the DOPC monolayer. Such a decrement in CS-1 was also encountered while increasing the pH and decreasing the temperature (T) of the subphase in the absence of Myo. Systematic expansion of DOPC isotherm and increased hysteric area with the increase in Myo proportion were observed and the atomic force microscopy (AFM) observations suggested a strong conjugation between Myo and DOPC in the mixed monolayer. The denaturation effect of Myo molecules was studied using AFM at different temperatures. Furthermore, the Myo molecules were found to be most surface active at pH = 7, which is very close to its isoelectric point. These observations come up with the interaction mechanism between biomolecules under dynamically varied conditions.

Comparison of Different Protein Emulsifiers on Physicochemical Properties of β-Carotene-Loaded Nanoemulsion: Effect on Formation, Stability, and In Vitro Digestion

In this study, β-carotene-loaded nanoemulsions are emulsified using four biomacromolecular proteins-peanut protein isolate (PPI), soy protein isolate (SPI), rice bran protein isolate (RBPI), and whey protein isolate (WPI)-in order to explore their emulsion stability and in vitro digestion characteristics. All four nanoemulsions attained high encapsulation levels (over 90%). During the three-stage in vitro digestion model (including oral, gastric, and small intestine digestion phases), the PPI-emulsified nanoemulsion showed the highest lipolysis rates (117.39%) and bioaccessibility (37.39%) among the four nanoemulsions. Moreover, the PPI-emulsified nanoemulsion (with the smallest droplet size) also demonstrated the highest stability during storage and centrifugation, while those for the RBPI-emulsified nanoemulsion (with the largest droplet size) were the lowest. In addition, all four nanoemulsions showed superior oxidation stability when compared with the blank control of corn oil. The oxidation rates of the PPI- and WPI-stabilized groups were slower than the other two groups.

Dry Two-Step Self-Assembly of Stable Supported Lipid Bilayers on Silicon Substrates

Artificial membranes are models for biological systems and are important for applications. We introduce a dry two-step self-assembly method consisting of the high-vacuum evaporation of phospholipid molecules over silicon, followed by a subsequent annealing step in air. We evaporate dipalmitoylphosphatidylcholine (DPPC) molecules over bare silicon without the use of polymer cushions or solvents. High-resolution ellipsometry and AFM temperature-dependent measurements are performed in air to detect the characteristic phase transitions of DPPC bilayers. Complementary AFM force-spectroscopy breakthrough events are induced to detect single- and multi-bilayer formation. These combined experimental methods confirm the formation of stable non-hydrated supported lipid bilayers with phase transitions gel to ripple at 311.5 ± 0.9 K, ripple to liquid crystalline at 323.8 ± 2.5 K and liquid crystalline to fluid disordered at 330.4 ± 0.9 K, consistent with such structures reported in wet environments. We find that the AFM tip induces a restructuring or intercalation of the bilayer that is strongly related to the applied tip-force. These dry supported lipid bilayers show long-term stability. These findings are relevant for the development of functional biointerfaces, specifically for fabrication of biosensors and membrane protein platforms. The observed stability is relevant in the context of lifetimes of systems protected by bilayers in dry environments.

Particle condition change in emulsion admixture evaluated by in situ flow particle imaging analysis

We evaluated the particle state change in emulsion admixtures using in situ flow particle imaging analysis (FPIA). Ropion® intravenous (flurbiprofen axetil: Ropion®) served as the model emulsion formulation. A binary mixture of Ropion® and normal saline (NS), and a ternary admixture of Ropion®, NS, and Gaster® injection (famotidine: Gaster®) or Primperan® injection (metoclopramide hydrochloride: Primperan®) were prepared and the change in emulsion particle state was analyzed using FPIA under in situ condition. The effect of storage on pH change and the chemical stability of flurbiprofen axetil were also investigated. In Ropion®, various particle images (mean diameter: 2.4 µm) were obtained. From our analysis of changes in scattergrams and particle images, changing behaviors of emulsion particles as a function of storage time depended on the systems of admixture samples. In Ropion®/NS and Ropion®/Gaster®/NS systems, mean particle size and particle number increased with lengthening storage time; however, these values were dramatically increased beyond 6 h in the Ropion®/Primperan®/NS system, corresponding to a decrease in measured pH. The decomposition of flurbiprofen axetil due to incompatibility was not observed in all systems. Detailed information on the change in emulsion particle state was obtained using FPIA, indicating that this method is useful to evaluate state changes in emulsion admixtures under in situ condition.

Comparison of n-tetradecane/electrolyte emulsions properties stabilized by DPPC and DPPC vesicles in the electrolyte solution

The properties of n-tetradecane/electrolyte emulsions with DPPC or DPPC vesicles in the electrolyte solution were investigated. The DPPC molecules form different aggregates, which possess different surface affinity, size and structure, and therefore we assumed some differences in the adsorption at the oil droplet/water interface. The n-tetradecane emulsions in 1:1, 1:2 and 1:3 electrolytes were prepared by mechanical stirring in the presence of DPPC at natural pH. Electrokinetic properties of the systems were investigated taking into account the effective diameter and multimodal size distribution of the droplets as well as the zeta potentials using the dynamic light scattering technique. The zeta potential of the droplets was negative in all systems with NaCl. In the emulsions with CaCl(2) at a higher concentration of electrolyte and emulsions with LaCl(3) with all investigated concentrations, positive values were observed. Similar measurements were performed for DPPC vesicles in the electrolyte solution. The pH and ionic strength changes induce those in the electrical charge of DPPC layer or vesicle surface. This is due to the fact that the DPPC molecule contains -PO(-) and -N(CH(3))(3) groups, which are in equilibrium with H(+) and OH(-), as well as other ions present in the solution, i.e. Na(+), Ca(2+), La(3+) or Cl(-). In the n-tetradecane/electrolyte emulsion stabilized by DPPC or DPPC vesicles the zeta potential may be also related to acid-base interactions. The effect of the ions from the solution on the DPPC layer adsorbed on n-tetradecane droplets or DPPC vesicles is discussed.

Surface modification of glass plates and silica particles by phospholipid adsorption

The effect of phospholipid adsorption on the hydrophobicity of glass plates and on the surface charge of silica particles using contact angle and electrophoretic mobility measurements, respectively, was investigated. Deposition of successive statistical monolayers of dipalmitoylphosphatidylcholine (DPPC) on the glass surface showed zig-zag changes of water contact angle, especially on the first few monolayers. This behavior is qualitatively coherent with the oscillations observed in zeta potential values for increasing DPPC concentration. The results indicate that the phospholipid is adsorbed vertically on the plates, exposing alternately its polar head and non-polar hydrocarbon chains in successive layers. On the other hand, experiments conducted on glass plates prior hydrophobized by contact with n-tetradecane suggest that DPPC molecules may to some extent dissolve in the relatively thick n-alkane film and then expose their polar heads over the film surface thus producing polar electron-donor interactions. The effect of both DPPC and dioleoylphosphatidylcholine (DOPC) on the electrokinetic potential of silica spheres confirms adsorption of the phospholipids, leading to a decrease in the (originally negative) zeta potential of silica and even reversal of its sign to positive at acidic pH. Hydrophobic interactions between phospholipid molecules in the medium and those already adsorbed may explain the overcharging. The adsorption of neutral phospholipids may reduce the zeta potential as a consequence of the shift of the electrokinetic or slip plane. The effect is more evident in the case of DOPC, suggesting a less efficient packing of this phospholipid because of the presence of double bonds in its molecule, which in fact is well known.