Biologically Active Substances Distribution And Transfer Of Liquid - Liquid Interface In The Microemulsion

Biological membrane is quite a broad area in living organism. Membrane phenomena almost completely control the transfer of ions and neutral molecules from the exterior of living cells to the interior or vice versa. The liquid-liquid interface formed by the surfactant aggregation, such as the water in oil (W/O) - oil in water (O/W) interface or W/O - bicontinuous (BI) interface, can be taken as half a model of biological membrane. Studies of the electric properties of a liquid-liquid interface, as well as the mass transfer behavior via the interface, are of great significance to the thermodynamic and dynamic foundations for the simulation of the mass transfer through the biological membrane. In this paper, we have studied the distribution and transfer of functional substances, such as drugs, amino acids and protein, through the W/O-O/W and W/O-BI interface in SDS/n-C₅H₁₁OH/H₂O system. The results will provide theoretical basis for the transport behavior of the biologically active substance across membrane, and the design of functional biomaterials. This paper include the following three parts:1. Transfer and distribution of drugs through the W/O-O/W and W/O-BI interfaceMany processes during the biological system occur at the biological membrane, and many physiological phenomena are relative to the changes of electric signals. The change of electric properties of biological membrane can provide theoretic guidance for the interactions of drugs and biological membrane and the transport of drugs through biological membrane. At the weight ratio of n-C₅H₁₁OH/H₂O = 50/50, when the total content of SDS is less than 6.0%, the ternary mixture of SDS/n-C₅H₁₁OH/H₂O is the coexistence of two immiscible microemulsions. Surfactant molecules not only adsorb at the liquid-liquid interface, but also assemble into micelles in the bulk solution to form W/O, O/W or BI microemulsion. When the total SDS content is less than 3.0%, with the increase of the total SDS content, the SDS contents in both phases increase, and that of the lower phase (O/W) increases faster. After the total SDS content reaches 3.0%, the increase of SDS content in the upper phase slows down, the composition of which is still in the W/O region. But the SDS content increases at almost the same rate in the lower phase, the composition of which is in the bicontinuous (BI) region. In this chapter, the distribution and transfer of gatifloxacin (GTFX) between the two phases in SDS/n-C₅H₁₁OH/H₂O system was studied by UV-vis spectroscopy, the effects of GTFX and SDS on the interphase electric properties of the system were studied by the method of AC impedance, and the effect of GTFX on the structures of the different microemulsion phases was studied by the method of rheometer. The results show that the addition of GTFX does not change the structures of the two different phases fundamentally, but results in the transfer and redistribution of SDS. At the weight ratio of n-C5H11OH/ H2O=50/50, with the increase of the total SDS content at a total GTFX concentration of 1.0×10-5 mol/L, GTFX transfers from the upper phase (W/O) to the lower phase (O/W or BI). The capacitance and interphase charge-transfer current of the system increase, while the resistivity decreases with the increase of the total SDS content. But when the total SDS content is greater than 3.0%, the change tendencies of all the electric properties slow down. With the increase of the total GTFX concentration at a constant total content of SDS, the concentrations of GTFX in both the upper and lower phases increase, and a small amount of SDS transfers from the lower phase to the upper phase correspondingly, namely the distribution coefficient of SDS between the upper and lower phases increases. These result in the change of the electric properties: the capacitance in the upper phase, the interphase capacitance, the resistivity in the lower phase and the interphase charge-transfer current increase, while the capacitance in the lower phase, the resistivity in the upper phase and the interphase resistivity decrease.We also select methylene blue (MB), which has positive charge in SDS/n-C₅H₁₁OH/H₂O system contrary to GTFX. In the same way, the distribution of MB between the two phases with different structures was determined by UV-vis spectroscopy. And the research of the effect of MB on the interphase electric properties studied by the method of AC impedance provides further evidence for it. The results show that, with the increase of the total SDS content at the constant weight ratio of n-C₅H₁₁OH/H₂O = 50/50 and the total MB concentration of 1.2×10-5 mol/L, MB transfers from the upper phase (W/O) to the lower phase (O/W or BI). At the constant content of SDS, with the increase of the total MB concentration, the concentrations of MB in the upper and lower phases increase, which results in the transfer of SDS from the upper phase to the lower phase. So the capacitance and the interphase charge-transfer current increase, whereas the resistivity decreases. The research will provide the valuable information for the study of the interactional mechanism of drugs at the liquid-liquid interface.2. Transfer and distribution of amino acids through the W/O-O/W and W/O-BI interfaceThe distributions of L-phenylalanine (L-Phe) and L-tryptophan (L-Trp) between W/O phase (the upper phase) and O/W or bicontinuous phase (the lower phase) in the SDS/n-C₅H₁₁OH/H₂O system were determined by UV-vis spectroscopy, respectively. The effects of L-Phe and L-Trp on the interphase electric properties were investigated by the method of AC impedance. In addition, the effects of L-Phe and L-Trp on the structures of the different microemulsion phases were studied by the methods of freeze-fracture transmission electron microscopy (FF-TEM) and rheometer. The results show that at the constant weight ratio of n-C₅H₁₁OH/H₂O = 50/50 and the total L-Phe concentration is 6.0×10⁽-3(mol/L (or the total L-Trp concentration is 1.0×10^-4 mol/L), with the increase of the total SDS content in the system, the microstructure transition of microemulsions at the SDS content of 3.0% makes the changes of the capacitance, interphase charge-transfer current and resistivity apparently slow down with further increase of SDS content. L-Phe or L-Trp transfers from the lower phase to the upper phase with the increase of the total SDS content. In addition, the addition of L-Phe or L-Trp cannot change the structures of the upper and lower phases ultimately, but results in the transfer and redistribution of SDS between the two phases. At the constant content of SDS, with the increase of the total L-Phe or L-Trp concentration, the concentrations of L-Phe or L-Trp in both the upper and lower phases increase, the SDS content in the upper phase decreases while that in the lower phase increases. So the capacitance and the interphase charge-transfer current increase, whereas the resistivity decreases. The above results indicate that the structure of membrane can be adjusted by constitutes of the upper and lower phases, and accordingly it can control the transfer and distribution of amino acids between the inside and outside of the membrane.3. Distribution and conformational behavior of hemoglobin between the two different microemulsion phases in SDS/n-C₅H₁₁OH/H₂O systemThe distribution and structural behavior of hemoglobin (Hb) between the upper and lower phases in SDS/n-C₅H₁₁OH/H₂O system were studied by UV-vis and circular dichroism (CD) spectroscopy. The effects of Hb and SDS on the interphase electric properties of the system were studied by the method of AC impedance. The results indicate that different structures of the two phases bring the different conformational change of Hb. In the lower phase, the content ofα-helix of Hb decreases, but the content ofβ-sheet increases, which indicates unambiguously thatα-helicity of hemoglobin subunits is gradually lost. The formerly compact structure becomes relax. Combined the CD spectra with UV-vis adsorption spectra, we know that it mostly exists as heme monomer in the upper phase, and in the lower phase hemichrome induced by SDS is partly converted to heme. At a constant content of SDS, with the increase of the total concentration of Hb, the concentrations of Hb in both the upper and lower phases increase, a small amount of SDS transfers from the lower phase to the upper phase. The changes of Hb and SDS contents in both the upper and lower phases result in the change of the electric properties. The study provides important information for the mechanism of interactions between protein and cell membrane.