Unique incorporation behavior of amino acid-type surfactant into phospholipid vesicle membrane

Abstract

The incorporation behavior of some anionic surfactants, including amino acid-type surfactants, on phospholipid vesicles was investigated. This was done by measuring the release of a vesicle-entrapped fluorescence probe and the scattered light intensities of vesicle particles in the surfactant solution as a function of surfactant concentration and time. Sodium dodecyl sulfate, sodium dodecanesulfonate, sodium dodecanoyl sarcosinate, and sodium dodecanoyl glutaminate were employed in this study. All surfactants ruptured the phospholipid vesicle at around each critical micelle concentration by mixed micelle formation with phospholipid. While leakage of the fluorescence probe took place at a very low concentration in the sulfate-or sulfonate-type surfactant systems, it occurred at the concentration just below the CMC in the amino acid-type surfactant systems. Kinetic analysis of the release of the probe from the vesicles showed that the former surfactants adsorbed independently and homogeneously onto the phospholipid vesicles, while the latter surfactants were cooperatively incorporated.

Effect of Functional Groups on Incorporation Behavior of Amino Acid-Type Surfactant into Phospholipid Vesicle Membrane

“…For the SDS system, on the other hand, the enthalpy values deviated from the curve for the DPPC-free solution at very low concentration. This result supports our previous finding that the SDS molecules were adsorbed homogeneously on DPPC vesicles even at very low concentrations below C*= 0.1, while the amino acid surfactants hardly affect the property of membrane in the low concentration range 27) . However when the surfactant concentration approached to the CMC, the endothermic peak appeared on the differential enthalpy vs concentration curve, and then the enthalpy value of the peak top increased with increasing DPPC concentration for all surfactant systems.…”

“…Although a number of surfactant molecules bound to the DPPC vesicle membrane, the environment around DPPC in the vesicle was not changed so much by the adsorption as demonstrated by polarization result. This result supports our depiction, in which the amino acid-type surfactant molecules are organized in the DPPC vesicle membrane 27,34) . On the other hand, R value of SDS system is almost unity, though SDS molecules affect the DPPC vesicle at even lower reduced concentration compared with the amino acid-type surfactant systems.…”

“…These results suggest that the solubilization of liposome is not the only mechanism of dye leakage induced by amino acid surfactants. In the previous study, we have reported that several amino acid type surfactants interact with DPPC vesicles cooperatively to form pore structure in the vesicle membrane, which is large enough for CF molecules to pass through the membrane 27,34) . Karatekin et al have reported the toroidal membrane pore formed by surfactant molecules 35,36) .…”

“…In our previous study, the incorporation behaviors of sodium N-dodecanoyl-sarcosinate and -L-glutamate into phospholipid vesicle were examined, and the results were compared with those of sodium dodecyl sulfate (SDS) and sodium dodecanesulfonate 27) . This study revealed the unique behaviors of amino acid-type surfactants; i.e., the cooperative adsorption on the vesicle membrane occurs for amino acid-type surfactant systems, and these surfactant molecules are organized on the vesicle.…”

Structural and morphological transition of long-chain phospholipid vesicles induced by mixing with short-chain phospholipid

“…Since the short-chain DHPC behaves like a surfactant [9][10][11], DMPC-DHPC mixtures are also of great interest from the standpoint of the interaction between the vesicle membranes and surfactant molecules [12][13][14][15][16][17][18]. In a series of the studies, the three-stage model was proposed by Lichtenberg in the 1980s [19]; in the first stage, surfactant molecules are distributed into vesicle membranes and mixed vesicles are formed, in the second stage, the mixed micelles are formed and coexist with the mixed vesicles, and in the third stage, all of the lipid molecules are solubilized into the mixed micelles.…”