Reversible Vesicle-to-Disk Transitions of Liposomes Induced by the

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Reversible Vesicle-to-Disk Transitions of Liposomes Induced by Self-Assembly of Water-Soluble Porphyrins Kouta Sugikawa, Yutaro Takamatsu, Kazuma Yasuhara, Masafumi Ueda, and Atsushi Ikeda Langmuir, Just Accepted Manuscript • DOI: 10.1021/acs.langmuir.6b02723 • Publication Date (Web): 05 Jan 2017 Downloaded from http://pubs.acs.org on January 10, 2017

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Reversible Vesicle-to-Disk Transitions of Liposomes Induced by Self-Assembly of WaterSoluble Porphyrins Kouta Sugikawa,*,† Yutaro Takamatsu,† Kazuma Yasuhara,‡ Masafumi Ueda,† and Atsushi Ikeda*,†

†

Department of Applied Chemistry, Graduate School of Engineering, Hiroshima University,

Higashi-Hiroshima 739-8527, Japan ‡

Graduate School of Materials Science, Nara Institute of Science and Technology, Nara 630-

0192, Japan

ABSTRACT: Structural control of lipid membranes is important for mechanisms underlying biological functions and for creating high-functionality soft materials. We demonstrate reversible control of vesicle structures (liposomes) using supramolecular assemblies. Specifically, watersoluble anionic porphyrin molecules interact with positively charged lipid membrane surfaces to form one-dimensional self-assembled structures (J-aggregates) under acidic conditions. Cryogenic transmission electron microscopy revealed that porphyrin J-aggregates on the membrane surface induced an extensive structural change from vesicles to layered disks.

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Neutralization of the solution deformed the porphyrin J-aggregates, thereby reforming nanosized liposomes from the layered disks.

INTRODUCTION Molecular self-assembly is one of the most important techniques in nanotechnology,1 and has been the focus of shape and function manipulation at the nanoscale. Small perturbations or interactions at the molecular level can lead to profound changes in organized nanostructures. Thus, it is critical to construct or manipulate soft matter in a noncontact and reversible manner to better understand self-assembly mechanisms and to create highly functional nanomaterials. Self-assembled lipid membranes form a bilayer interface with hydrophobic tails oriented towards the interior.2-5 Lipid bilayer vesicles, or “liposomes”, are used as biomimetic membranes because they are controllable and enable elucidation of biological processes. In particular, they exhibit flexible structural changes when interacting with flat substrates,6,7 macromolecules,8-12 or surfactants.13,14 This enables applications such as binding of biomolecules, surface patterning, and drug-delivery systems. Solid-supported lipid bilayers6 are formed by adhesion of liposomes on substrates that results in a structural transition to a disk or sheet structure. Recently, Milanesi et al. directly visualized lipid membrane disruption induced by the interaction with the fibrous protein aggregate amyloid β.9 Aida et al. prepared stable bilayer micelles (bicelles) via in situ polymerization of surfactants on the edge of the bicelle.14 However, reversible structural transitions of liposomes, especially at the molecular level, remain a difficult challenge because it is difficult to control interactions of membranes with substrates or macromolecules. Here, we


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demonstrate reversible structural transformations of nanoscale vesicles to layered-disk structures, induced by interactions with anionic supramolecular porphyrin nanofibers (Figure 1). 5,10,15,20-Tetrakis(4-sulfonatephenyl)porphyrins (H2TPPS4–) have the diacid form (H4TPPS2– ) below pH 3.0 (Figure 1a), where the pKa for H2TPPS4– is 4.9. H4TPPS2– forms a well-ordered fibrous J-aggregate via electrostatic intermolecular interactions at certain concentrations, low pH, and/or high ionic strength. Furthermore, J-aggregate formation is induced or accelerated by the interaction of cationic molecules and macromolecules.10,15,16 Thus the supramolecular nanofibers have anionic charges arising from sulfonate groups.15-17 Anionic materials, such as nanoparticles, can adsorb on the surface of zwitterionic lipid membranes via multisite electrostatic or dipoleanionic interactions.20-23 Therefore, supramolecular H4TPPS2– nanofibers should similarly interact with liposomes. Furthermore, conformational changes in H4TPPS2– assemblies via pH changes may induce structural changes in the liposomes. The resulting composite would acquire reversible properties because of conformational changes in the self-assembled porphyrins (Figure 1c).

EXPERIMENTAL Materials. 1,2-Dipalmitoyl-sn-glycero-phosphatidylcholine (DPPC) was purchased from NOF Corp. (Tokyo, Japan). 5, 10, 15, 20-Tetrakis(4-sulfonatephenyl)porphyrins were purchased from Tokyo Chemical Industry Co., Ltd. (Tokyo, Japan). Sodium hydroxide (NaOH) and hydrochloric acid (HCl) were purchased from Wako Pure Chemical Industries, Ltd. (Tokyo, Japan). All reagents were used as received.


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Preparation of Liposomes and Porphyrin-Liposome Composites. DPPC liposomes were prepared by extrusion. A 130-mM DPPC solution was dissolved in chloroform and then evaporated to dryness under a flow of nitrogen gas. It was then re-hydrated with MilliQ water (1 mL) and vortexed for 1 min. The suspension was subjected to eight freeze/thaw cycles using liquid nitrogen and a water bath, respectively, and then extruded eleven times above the phase transition temperature through a polycarbonate membrane with 50-nm pores. Subsequently, a 1.0-mM aqueous H2TPPS4– solution was mixed with the liposomes at various molar ratios below the phase transition temperature (Tm) of the mixture. The pH was adjusted by adding 1-M aqueous HCl or NaOH. Calcein-Release Studies. Calcein-loaded DPPC liposomes (cal-DPPC) were prepared in MilliQ water as described above, except that the dried lipids were hydrated with 60-mM calcein (pH 8.0). Non-encapsulated calcein was removed by size-extrusion chromatography on a Sephacryl S-400 column (GE Healthcare Technologies, Uppsala, Sweden) using a 0.9-wt% NaCl aqueous solution. The fluorescence intensity of the cal-DPPC was low because of self-quenching. When H2TPPS4– was introduced and incubated for 10 min at 25 °C after the pH was adjusted to 6.0 or 2.0, the change in fluorescence intensity from calcein released from ruptured liposomes was monitored with a luminescence spectrometer (Perkin-Elmer, LS-55, MA, USA). The pH for all the samples was adjusted to 8.0 before acquiring fluorescence spectra. The excitation wavelength was 480 nm. Complete release of the dye was achieved by adding 100 µL of a 5-wt% solution of TritonX-100 to 3 mL of each solution. The corresponding fluorescence intensity was defined as 100% leakage. The amount of calcein released, RF, was calculated by:


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where I0, I, and Imax are the fluorescence intensities measured without H2TPPS4–, at 10 min after the addition of HCl, and after the addition of TritonX-100, respectively. Porphyrin absorption at emission and excitation wavelengths was taken into account. Calculation of spectroscopic aggregation number (N). The spectroscopic aggregation number, N, was calculated using the following equation,

where ∆ν and ∆ν1/2 are the full-width at half-maximum in absorption peaks of the porphyrin monomer (433 nm) and J-aggregate (491 nm), respectively. UV-Vis Absorption and Circular Dichroism (CD). All samples were thoroughly dispersed using a vortex mixer before obtaining UV-vis absorption and CD spectra over the range of 300–800 nm at 25 °C, using a spectrophotometer (SHIMADZU, UV-2550, Kyoto, Japan) and a CD spectrometer (JASCO, J-1500, Tokyo, Japan), respectively. Dynamic Light Scattering. The hydrodynamic diameter of the DPPC liposomes was measured via electrophoretic light scattering in a laser Doppler apparatus (Zetasizer Nano ZS, Malvern Instruments Ltd, Malvern, UK). The data were fit with a non-negative least squares method and a scattering geometry of 173°. Cryogenic Transmission Electron Microscopy (Cryo-TEM). Cryo-TEM samples were prepared using a universal cryogenic fixation and -preparation system (Leica EM CPC, Wetzlar, Germany). To prevent water evaporation from the sample, an isolated chamber was humidified to near saturation prior to introduction of the sample. Sample droplets (2–3 µL) were placed on a


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micro-perforated cryo-TEM grid and then absorbed with filter paper, forming a 10–300-nm-thick liquid film that spanned the micro-pores in a carbon-coated, lace-like polymer layer supported by the metal mesh grid. After a minimum holding time of 30 s, the sample grid assembly was rapidly vitrified in liquid ethane at −163 to −170 °C. The holding time was adopted to relax any possible flow deformation that may have resulted from the blotting process. The vitreous specimen was maintained in liquid nitrogen until it was loaded into a cryogenic sample holder (Gatan 626-DH). Imaging was performed using a JEOL JEM-3100 FEF instrument operating at 300 kV (Tokyo, Japan). The minimal dose system was necessitated by the electron radiation sensitivity of the sample probe. Images were recorded using a Gatan 794 multi-scan digital camera and processed using version 3.8.1 DigitalMicrographs software. Background optical density gradients were digitally corrected with a custom-made subroutine compatible with DigitalMicrographs. RESULTS AND DISCUSSION The interaction of anionic porphyrins with DPPC liposomes (Figure 1b) was investigated with ultraviolet-visible (UV-vis) absorption and circular dichroism (CD). The liposomes had an average diameter of 68 nm (Table S1 and Figure S1a), determined by dynamic light scattering (DLS).24,25 To 5.0-µM H2TPPS4– aqueous solutions, various amounts (0–100 µM) of DPPC liposomes were added and the pH was adjusted to 6.0 or 2.0. At pH 6.0, apart from an increase in solution turbidity caused by the liposomes, the absorption spectra derived from monomeric H2TPPS4– remained constant (Figure S2), and no change was observed in the CD spectra over the DPPC concentration range. At pH 2.0, the UV-vis spectrum of monomeric H4TPPS2– in the absence of DPPC liposomes has a characteristic Soret band at 433 nm (Figure 2a). Upon addition of DPPC liposomes, the Soret band was significantly red-shifted to 491 nm, which indicates


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formation of H4TPPS2– J-aggregates (Figure 2a).17 Furthermore, the CD spectra displayed Cotton effects at the split bands around 490 nm, where the intensity increases upon DPPC addition (Figure 2b). Cationic L-isomers usually induce negative Cotton effects.26 However, the CD data at 490 nm have a positive Cotton effect for the L-isomer of DPPC. According to previous reports, Cotton effect reversal can be attributed to the fractal morphology of the hierarchical, chiral Jaggregation of H4TPPS2–.15,26,27 This suggests that H4TPPS2– and DPPC liposome interaction forms hierarchical H4TPPS2– J-aggregates.15 The ζ-potential of DPPC liposomes at various pH values yields important information on interactions with the J-aggregates. The zwitterionic DPPC liposome exhibited an almost neutral 4.4 or 3.3 ζ-potential at pH 6.0 or 7.5, respectively (Table S2). As the pH decreased, the ζ-potential increased, and was 32.2 at pH 2.0 (Table S2). This indicates that the liposome surface is positively charged at low pH, which might be attributed to protonation of phosphate groups.28 Thus, the H4TPPS2– electrostatically interacts with the positively charged liposome surface to form J-aggregates. Changes in the UV-vis absorption spectra were almost saturated for 50-µM DPPC ([porphyrin]/[DPPC)=0.1, Figure S3a). The intensity of CD was maximized for 50-µM DPPC but decreased in the presence of 500-µM DPPC (Figure S3b) This is because, in the presence of excess DPPC (500 µM), the number of porphyrin molecules per J-aggregate decreases with the increased lipid membrane surface area. Similar results have been reported previously.15,16 Structural changes in liposomes usually cause the release of captured molecules such as calcein.23,29,30. For cal-DPPC (50 mM calcein),30 the release of dye in the absence or presence of H4TPPS2– at pH 2.0 was monitored using fluorescence (Figure S4). As noted in the Experimental Section, the pH of all the samples was adjusted to 8.0 immediately prior to the acquisition of fluorescence spectra to eliminate pH effects on the fluorescence intensity. In the absence of


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porphyrins, the cal-DPPC fluorescence intensity after 10-min incubation at pH 2.0 was low because of self-quenching (Figure S4a); the RF was 0.43. Thus the DPPC lipid membrane remained intact at pH 2.0. In the presence of H4TPPS2– ([porphyrin]/[DPPC]=0.1), a pronounced increase in fluorescence intensity was observed (Figure S4b) after incubation for 10 min at pH 2.0. Moreover, the RF was 75, which was calculated for the absorption of H4TPPS2–. There was no increase in fluorescence intensity at pH 6.0, even in the presence of H2TPPS4–. Thus, the formation of H4TPPS2– J-aggregates increases the fluorescence by releasing and diluting the calcein molecules via disruption of the lipid membrane. Cryo-TEM was performed on DPPC liposomes in the presence of H4TPPS2– J-aggregates. Images of liposomes were acquired for [porphyrin]/[DPPC]=0.1. At pH 6.0, the liposomes were vesicles (Figure 3a) with a polyhedral structure that is common because of the high bending modulus of the DPPC lipid membrane below Tm.31 At pH 2.0, a layered disk-like structure with a uniform contrast was observed (Figure 3b). The average periodicity of the layers was 7.1 nm (Figure 3c), which is very consistent with several thicknesses of gel-phase DPPC bilayers (the distance between head groups is 4.42 nm)32 and the widths of H4TPPS2– J-aggregates (1.9 nm).33 The small difference may be attributed to water molecules. Structures layered with dozens of sheets were also observed with scanning electron microscopy (SEM) (Figure 3d). The size of the layered structure observed with SEM is much larger than those imaged with cryo-TEM (Figure 3b) because the SEM sample was dried on a micro-grid before imaging. DPPC liposomes maintained their vesicle structures at pH 2.0 in the absence of H4TPPS2– (cryo-TEM images in Figure S1b, and DLS data in Table S1). Furthermore, cryo-TEM images of H4TPPS2– in the absence of DPPC at pH 2.0 did not reveal any specific structures except nanoscale spherical ice


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particles (Figure S5). These images support the notion that interactions of H4TPPS2– J-aggregates induce the transformation of vesicles to layered-disk structures. The dynamics of the vesicle-disk transformation were investigated with cryo-TEM. Images were acquired of DPPC liposomes in the presence of anionic porphyrins 3 min after adjusting the pH from 6.0 to 2.0. They were distorted vesicles, or disk-like structures, instead of layered structures (Figure 3e). After 2 h of incubation, the vesicles were depleted and some layered structures were observed (Figure 3f). Finally, after 3 days' incubation, the vesicles were gone and mostly layered disks were observed (Figure 3b). Time-dependent UV-vis absorption measurements revealed that J-aggregates formed on the lipid membrane surfaces in a few minutes (Figure 4). After 3 days of incubation, no J-aggregates were formed in 5-µM porphyrin concentrations. This was confirmed by the time dependence of the 491-nm absorption band of H4TPPS2– in the absence of DPPC liposomes (Figure S6). These observations suggest that H4TPPS2– immediately formed J-aggregates on the DPPC vesicles and flattened them into disk structures that gradually aggregated into layered disks. The average diameter of the disk structures observed from the sample 3 min after adjusting the pH from 6.0 to 2.0 (Figure 3e) was 125±36 nm, which is consistent with the expected 136-nm diameter formed from one 68-nm diameter liposome. Slight differences between calculated and ideal values might be attributed to the inclination of disk structures in the cryo-TEM images. The results indicate that at [porphyrin]/[DPPC]=0.1, each liposome transformed to one disk layer without fusing or decomposition. To understand the transformation mechanism, effects of the ratio [porphyrin]/[DPPC] on the structures was investigated. When an excess of H4TPPS2– was present ([porphyrin]/[DPPC]=1), no layered disks were observed; instead, there were large sheet structures with diameters in the


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micrometer

range

(Figure

5a).

In

contrast,

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only

vesicles

were

observed

for

[porphyrin]/[DPPC]=0.04, and regions of the vesicles were flat (Figure 5b). These observations indicate that J-aggregates were present on the flat faces of the disks and bridged the disks to form a layered structure (Figure 1c). Below Tm, a DPPC membrane has a high bending modulus and tends to form flat disks or sheets. Typically, phospholipids with different acyl chains length are mixed to minimize the energy cost in the vesicle curvature required to form flat structures.34,35 Here, we assume that the interaction with rigid nanofibers of J-aggregates compensates for the energy required to form hydrophobic edges of disk- or sheet-like lipid structures.14,15,36,37 UV-vis absorption spectra of porphyrin/DPPC composites support this idea. The spectroscopic aggregation number N for each J-aggregate was calculated from the full-width at half-maximum of the 491-nm J-aggregate absorption peak and the 433-nm monomer peak.38 For [porphyrin]/[DPPC]=0.1

at

pH

2.0

after

3

days

of

incubation,

N=10.8.

For

[porphyrin]/[DPPC]=1, N=17.4. Therefore, the J-aggregate formed on a large sheet ([porphyrin]/[DPPC]=1,

Figure

5a)

is

longer

than

that

formed

on

a

layered-

disk([porphyrin]/[DPPC]=0.1, Figure 3b). The formation of J-aggregates on the membrane surface thus flattens the liposome via multipoint electrostatic interactions, and further Jaggregation induces the formation of larger sheets to minimize the edge area. To reconfirm that H4TPPS2– J-aggregates are integral to the structural changes in DPPC liposomes, NaOH was added to a solution containing layered disks ([porphyrin]/[DPPC]=0.1) to dissociate the J-aggregates. At pH 6.0, the UV-vis spectrum revealed that one third of the Jaggregates did not dissociate (Figure 6a), while J-aggregates prepared overnight in a 50-µM porphyrin solution in the absence of DPPC liposomes immediately and completely converted into monomeric H2TPPS4– after pH adjustment to 6.0 (Figure S7). The J-aggregates in


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porphyrin/DPPC composites at pH 6.0 completely disappeared after the addition of NaCl, or after heating above the 41 °C DPPC phase transition temperature (Figure 6b). The J-aggregates also completely dissociated at pH 7.5 (Figure 6a). Overall, these results indicate that the multipoint interaction of the anionic porphyrin J-aggregate and the cationic lipid membrane under acidic conditions is required for the quick transformation of the vesicles to flat structures. Cryo-TEM images provided evidence of structural changes in the lipid bilayer during dissociation of J-aggregates. As shown in Figures 6c and S8, both vesicles and layered disks coexisted at pH 6.0. Furthermore, complexes of vesicles and layered disks were observed where the vesicle appeared to peel away from the layered disk. At pH 9.6, only vesicles were observed (Figure 6d), suggesting that dissociation of J-aggregates induced vesicle reconstruction. Thus, for phosphatidylcholine lipid membranes, disks or sheets are energetically unfavorable relative to vesicles because more hydrophobic edge structures are exposed to water. Therefore, it is reasonable that vesicles reformed when there were no more interactions with J-aggregates. DLS also indicated vesicle reconstruction from layered disks. Mixed solutions of porphyrin and DPPC liposomes at pH 6.0 had an average hydrodynamic diameter of 68 nm, with a low polydispersity index (PDI) of 0.01. The narrow size distribution (Figure S9a) indicated that the DPPC liposomes maintained monodispersity in the presence of porphyrins at pH 6.0. When the pH was adjusted to 2.0, the average hydrodynamic diameter became 531 nm, with a high PDI of 0.41 and a broadened size distribution (Table S1 and Figure S9b). A PDI >0.3 indicates the presence of various sizes and/or structures; thus, a calculated hydrodynamic diameter is not meaningful. This is consistent with cryo-TEM images where the number of layered disks was not constant in the layered-disk structures (Figure 3b). When the pH was increased from 2.0 to 6.0, the PDI remained at 0.55, and the size distribution revealed two separate peaks (Figure S9c).


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This is also in good agreement with cyro-TEM images exhibiting both vesicle and layered disks and their complexes at pH 6.0 (Figures 6c and S8). At pH 6.5 (PDI=0.90) and pH 7.5 (PDI=0.51), the size distributions were more complex (Figures S9d,e), indicating various large structures. At pH 9.5 and pH 11.4, peaks assignable to 68- and 91-nm structures were detected with PDIs of 0.17 and 0.13, respectively (Table S1, Figures S9f,g). Note that at pH values between 2.0 and 11.4, the average hydrodynamic diameters of the DPPC liposomes were almost constant with low PDI values (Table S1). This is in good agreement with cryo-TEM images where only nanoscale vesicles were observed at pH 9.6 (Figure 6d). The fact that similar vesicles sizes were reformed from the layered disks indicates that each disk was formed from one vesicle, and vice versa, without fusion or decomposition. Finally, the dynamics for the reverse transformation were investigated. H4TPPS2–/DPPC composites at pH 2.0 were incubated for 10 min to induce J-aggregates and the subsequent transformation of DPPC vesicles into layered disks. Cryo-TEM images of the composites 3 min after adjusting the pH from 2.0 to 9.8 revealed only vesicles (Figure 7). Time-dependent UV-vis absorption also revealed that the J-aggregates completely disassembled into monomeric H2TPPS4– immediately after the pH change (Figure 4). Thus, the breakdown of the J-aggregates transformed the layered disks into vesicles. These results clearly support the view that multipoint interactions between anionic porphyrin J-aggregates and the lipid membrane surface are the key for reversible liposome transformations.

CONCLUSIONS The formation of rigid supramolecular fibers on the surface of lipid membranes induced a marked structural change from vesicles to layered disks. The final structure was strongly


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dependent on the ratio of anionic porphyrins to lipids, as were large sheets or attached vesicles. The reversible structural changes were controlled by the formation or dissociation of the supramolecular fibers, depending on the pH. The formation of porphyrin J-aggregates on a DPPC lipid membrane surface via multipoint interactions flattened the membrane and the Jaggregates bridged the membranes to form layered structures. The pH is an efficient tool for controlling the structure or shape of soft matter because it is an important parameter in biological systems, especially in vivo. It is also an example of engineered supramolecular membrane systems for specific functions.


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Figure 1. Structures of (a) free-base (H2TPPS4–) and diacid (H4TPPS2–) forms of anionic porphyrins, and (b) DPPC. (c) Structural transformation of vesicles to layered-disks induced by the self-assembly of anionic porphyrins.


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Figure 2. (a) UV-vis and (b) CD spectral changes of H4TPPS2– upon addition of DPPC liposomes. [porphyrin]=5 µM, [DPPC]=0–100 µM. T=25 °C.


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Figure 3. Cryo-TEM images of DPPC liposomes at pH 6.0 (a) and 2.0 (b), in the presence of anionic porphyrins ([porphyrin]/[DPPC]= 0.1). Scale bars are 100 nm. (c) Magnified image of (b) and extracted periodic patterns. Scale bar is 20 nm. (d) Magnified SEM image of layered-disk structure. Scale bar is 100 nm. Cryo-TEM images of DPPC liposomes in the presence of H4TPPS2–: incubated for (e) 3 min, and (f) 2 h, after adjusting the pH from 6.8 to 2.0. Scale bars are 100 nm.


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Figure 4. 491-nm absorbance vs. time, after adjusting the pH from 6.8 to 2.0 (forward, blue points), and from 2.0 to 8.5 (reverse, red points). [porphyrin]=5 µM, [DPPC]=50 µM, T=25 °C.

Figure 5. Cryo-TEM images of DPPC liposomes at pH 2.0 for a [porphyrin]/[DPPC] ratio of (a) 1 and (b) 0.04. Scale bars are 100 nm.


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Figure 6. (a) UV-vis absorbance changes of layered-disk structures at pH 2.0 (red), pH 6.0 (orange), pH 6.5 (yellow), pH 7.5 (green), pH 9.6 (blue), and pH 11.4 (purple). (b) UV-vis absorbance changes of layered disks at pH 6.0 before (solid line) and after (dashed line) the addition of 0.8-M NaCl, or after heating to 50 °C (dotted line). [porphyrin]=50 µM, [DPPC]=500 µM. Cryo-TEM images of reconstructed vesicles at (c) pH 6.0 and (d) pH 9.6. Scale bars are 50 nm.


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Figure 7. Cryo-TEM image of reconstructed vesicles 3 min after adjusting the pH from 2.0 to 9.6. Scale bar is 100 nm.


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ASSOCIATED CONTENT Supporting Information. The Supporting Information is available free of charge on the ACS Publications website at DOI: XXX Table S1, S2 and Figures S1 – S9 (PDF)

AUTHOR INFORMATION Corresponding Author * E-mail: [email protected] * E-mail: [email protected] Author Contributions The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript. Notes The authors declare no competing financial interest.

ACKNOWLEDGMENT This work was supported by the Electric Technology Research Foundation of Chugoku and a Grant-in-Aid for Scientific Research (B) (Grant no. 25288037). The authors would like to express their deepest gratitude to Ms S. Fujita, Graduate School of Materials Science, Nara Institute of Science and Technology, for providing technical assistance with the cryo-TEM imaging.


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ABBREVIATIONS DPPC,

1,2-dipalmitoyl-sn-glycero-3-phosphocholine;

H2TPPS4–,

5,10,15,20-Tetrakis(4-

sulfonatephenyl)porphyrins; H4TPPS2–, di-protonated H2TPPS4–; CD, circular dichroism; calDPPC, calcein-loaded DPPC liposome; cryo-TEM, cryo-transmission electron microscopy; DLS, dynamic light scattering; PDI, polydispersity index REFERENCES 1. 2. 3. 4. 5. 6. 7. 8.

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Insert Table of Contents Graphic and Synopsis Here. A reversible structure control system for lipid vesicles, also called liposomes, using supramolecular assemblies has been developed. The formation of porphyrin J-aggregates on the lipid membrane surface induced a reversible extensive structural change in liposomes from vesicles to a layered-disk structure.


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Reversible Vesicle-to-Disk Transitions of Liposomes Induced by the

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