Abstract:To understand the behavior of cellular interfaces, it is important to clarify the effect of chemical compounds on artificial cell membranes. In this study, an aqueous acetonitrile solution was mixed with a suspension of lipid vesicles, and the changes in vesicle behavior arising as a result of acetonitrile application were observed. The fast Fourier transformations (FFTs) of the membrane waviness/crinkliness of the vesicles were carried out, and the membrane thermal fluctuations were analyzed. The experimental results show that the addition of acetonitrile molecules enhances the fluctuation of lipid membranes. In particular, the k = 2 mode fluctuation was significantly enhanced. This finding is expected to lead us to a further understanding of the fundamental properties of living cells.
We show the bursting process of dioleoylphosphatidylcholine (DOPC) liposomes in response to the addition of acetonitrile, a small toxic molecule widely used in the fields of chemistry and industry. The percentage of destroyed liposomes is reduced upon decreasing the acetonitrile fraction in the aqueous solution and vesicle bursting is not observed at volume ratios of 4:6 and below. This indicates that a high fraction of acetonitrile causes the bursting of liposomes, and it is proposed that this occurs through insertion of the molecules into outer leaflet of the lipid bilayer. The elapsed time between initial addition of acetonitrile and liposome bursting at each vesicle is also measured and demonstrated to be dependent on the volume fraction of acetonitrile and the vesicle size.
Abstract:In order to construct the artificial cells and to understand the physicochemical properties of living cells, it is important to clarify the cell-sized confinement effect on the behaviours of bio-inspired polymers. We report the dynamic behaviours of aqueous hydroxypropyl cellulose (HPC) solution coated with phospholipids in oil (water-in-oil droplets, W/O droplets), accompanied by an increase in the temperature. We directly observed the beginning of phase separation of HPC solution using a fluorescence microscope and confirmed the dependence of such phenomena on droplet size. The results indicate that the start time of phase separation is decreased with an increase in droplet size. The experimental results suggest that the confinement situation accelerates the phase separation of aqueous HPC solutions.
Most organelles, such as the endoplasmic reticulum, are enclosed by biological membranes, although there are some membrane‐less organelles, such as stress granules. The mechanisms by which membrane‐less organelles form and keep their shape are akin to phase separation. Such organelles are located inside cell membranes. However, interactions between cell membranes, phase separations in polymer solutions and lipid head groups, directed towards the inside of the cell have not been investigated. Here we directly observed aqueous hydroxypropyl cellulose (HPC) droplets coated with lipids in mineral oil during an increase in temperature from 10 °C to 65 °C to elucidate the effect of lipid head groups located at the interfaces on dynamic phase behaviours of HPC solutions encapsulated in the cell‐sized droplets. The water molecules inside the droplets are aggregated to the interfaces during an increase in temperature due to the effect of lipid head groups with the separation into water‐ and HPC‐rich phases.
The lipid bilayer structure is the main component of cell membranes, therefore, the physical properties of such structure have been studied for many years. Recently, the applications of lipid bilayers have been studied, in addition to fundamental studies. For instance, a transistor-like device was developed (Ma et al., ACS Omega, 2019). As a part of such studies, we show the 2D and 3D control of lipid bilayer membranes. The first one is the effect of local anesthetics, Dibucaine hydrochloride molecules, on the phase behavior of ternary lipid membranes, which corresponds to the 2D control of lipid bilayer membranes (Yoshida et al., MedChemComm, 2015). The lipid membranes composed of a saturated phospholipid, unsaturated phospholipid, and cholesterol induce lateral phase separation. We revealed that the phase behavior is affected by the insertion of local anesthetic molecules into bilayer structures. Another one is the effect of toxic polar molecules, acetonitrile molecules, on the shape of lipid bilayer vesicles, which corresponds to the 3D control of lipid bilayer membranes (Yoshida et al., Colloids Interfaces, 2018). Insertion of acetonitrile molecules induces the membrane deformation. We are trying to utilize such behaviors for soft and bio-inspired molecular sensors. We show the trials for such applications.
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