Induction of Chiral Recognition with Lipid Nanodomains Produced by Polymerization

Probing Orientational Dynamics of Magnetic Nanoparticles in Opaque Samples Using Near-Infrared Magnetic Linear Birefringence

We demonstrated the advantage of magnetic linear birefringence (MLB) measurement for studying the orientation dynamics of magnetic nanoparticles (MNPs) in various environments. It is expected that MNPs will be utilized as active probes of nanoscale measurements, such as nanorheology and homogeneous bioassay. The optical anisotropy induced in MNP suspensions under an AC magnetic field, including MLB, reflects the physical rotation of the MNP itself. MLB is measurable with near-infrared light, which can reduce undesirable extinction due to the scattering or absorption by the sample suspension. In this study, we built an apparatus for precise MLB measurement by refurbishing the previous one to measure magnetic linear dichroism under an AC magnetic field and confirmed the relationship between the MLB signal and the orientation of MNP. Then, two systems that were opaque for visible light were examined to show the unique advantage of the MLB measurement of MNPs: (1) MLB measurement applied to the MNP suspension with a wide concentration range, and the effect of the interparticle interaction on the orientation dynamics could be detected from MLB frequency spectra. (2) Magneto-liposomes (ML), small vesicles containing MNPs, could be measured, and the frequency spectra could provide information on the condition of MNPs in ML. Furthermore, it was possible to detect the phase transition of the lipid bilayer from the gel to the liquid crystal phase.

Investigating the impact of 2-OHOA-embedded liposomes on biophysical properties of cancer cell membranes via Laurdan two-photon microscopy imaging

2-Hydroxyoleic acid (2-OHOA) has gained attention as a membrane lipid therapy (MLT) anti-cancer drug. However, in the viewpoint of anti-cancer drug, 2-OHOA shows poor water solubility and its effectiveness still has space for improvement. Thus, this study aimed to overcome the problems by formulating 2-OHOA into liposome dosage form. Furthermore, in the context of MLT reagents, the influence of 2-OHOA on the biophysical properties of the cytoplasmic membrane remains largely unexplored. To bridge this gap, our study specifically focused the alterations in cancer cell membrane fluidity and lipid packing characteristics before and after treatment. By using a two-photon microscope and the Laurdan fluorescence probe, we noted that liposomes incorporating 2-OHOA induced a more significant reduction in cancer cell membrane fluidity, accompanied by a heightened rate of cellular apoptosis when compared to the non-formulated 2-OHOA. Importantly, the enhanced efficacy of 2-OHOA within the liposomal formulation demonstrated a correlation with its endocytic uptake mechanism. In conclusion, our findings underscore the significant influence of 2-OHOA on the biophysical properties of cancer plasma membranes, emphasizing the potential of liposomes as an optimized delivery system for 2-OHOA in anti-cancer therapy.

Significance of in situ quantitative membrane property-morphology relation (QmPMR) analysis

Deformation of the cell membrane is well understood from the viewpoint of protein interactions and free energy balance. However, the various dynamic properties of the membrane, such as lipid packing and hydrophobicity, and their relationship with cell membrane deformation are unknown. Therefore, the deformation of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) and oleic acid (OA) giant unilamellar vesicles (GUVs) was induced by heating and cooling cycles, and time-lapse analysis was conducted based on the membrane hydrophobicity and physical parameters of "single-parent" and "daughter" vesicles. Fluorescence ratiometric analysis by simultaneous dual-wavelength detection revealed the variation of different hydrophilic GUVs and enabled inferences of the "daughter" vesicle composition and the "parent" membrane's local composition during deformation; the "daughter" vesicle composition of OA was lower than that of the "parents", and lateral movement of OA was the primary contributor to the formation of the "daughter" vesicles. Thus, our findings and the newly developed methodology, named in situ quantitative membrane property-morphology relation (QmPMR) analysis, would provide new insights into cell deformation and accelerate research on both deformation and its related events, such as budding and birthing.

Guest-Induced Planar-Chiral Pillar[5]arene Surface for Selectively Adsorbing Protein Based on Host-Guest Chemistry

In living systems, the adsorption of a protein on biointerfaces is a universal phenomenon, such as the specific binding of an antibody and antigen, which plays an important role in body growth and life maintenance. The exploration of a protein-selective adsorption on the biointerface is of great significance for understanding the life process and treatment in vitro. Herein, on the basis of biomimetic strategies, we fabricated a planar-chiral NH₂-pillar[5]arene modified silicon surface (pR-/pS-NP5 surfaces) for a highly enantioselective adsorption of protein by taking advantage of the guest-induced planar chirality of pillar[5]arenes. Results from practical experiments and theoretical calculations show that the pR-NP5 surface possesses a high adsorption capacity and chiral selectivity for bovine serum albumin (BSA). Moreover, it was identified that the guest-induced chiral effect the generation and amplification of planar chirality, which was much beneficial for enhancing the interaction between planar-chiral pillar[5]arene host and BSA. The binding capacity of pR-NP5 and BSA is stronger than that of pS-NP5, thus promoting the chiral selective adsorption of BSA. This work affords a deeper understanding of the chiral influence of protein adsorption on biointerfaces and meanwhile provides a new perspective for chiral-sensing applications.

Characterization of Phase Separated Planar Lipid Bilayer Membrane by Fluorescence Ratio Imaging and Scanning Probe Microscope

The lipid membrane forms nanodomains (rafts) and shows heterogeneous properties. These nanodomains relate to significant roles in various cell functions, and thus the analysis of the nanodomains in phase-separated lipid membranes is important to clarify the function and role of the nanodomains. However, the lipid membrane possesses small-sized nanodomains and shows a small height difference between the nanodomains and their surroundings at certain lipid compositions. In addition, nanodomain analysis sometimes requires highly sensitive and expensive apparatus, such as a two-photon microscope. These have prevented the analysis by the conventional fluorescence microscope and by the topography of the scanning probe microscope (SPM), even though these are promising methods in macroscale and microscale analysis, respectively. Therefore, this study aimed to overcome these problems in nanodomain analysis. We successfully demonstrated that solvatochromic dye, LipiORDER, could analyze the phase state of the lipid membrane at the macroscale with low magnification lenses. Furthermore, we could prove that the phase mode of SPM was effective in the visualization of specific nanodomains by properties difference as well as topographic images of SPM. Hence, this combination method successfully gave much information on the phase state at the micro/macro scale, and thus this would be applied to the analysis of heterogeneous lipid membranes.

Preferential adsorption of L-tryptophan by L-phospholipid coated porous polymer particles

Chiral selective adsorption of L-amino acid, tryptophan (Trp) was achieved using phospholipid membrane-coated porous polymer particles (PPPs). PPPs with numerous pores were prepared by in situ polymerization of divinylbenzene, and then coated with 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC, L-phospholipid) via the impregnation method. Elemental mapping of energy dispersive X-ray (EDX) analysis revealed that DPPC molecules were distributed to the surface and the inner part of PPPs, where almost all the DPPC molecules applied for impregnation were deposited on PPPs. The phospholipid membrane properties of DPPC-PPPs were characterized using the fluorescence probe 6-lauroyl-2-dimethylaminonaphthalene (Laurdan). The results show that DPPC-PPPs possessed a lipid membrane-like environment similar to pure DPPC liposomes, especially at temperatures below 35 °C. DPPC-PPPs slightly adsorbed L-Trp and D-Trp at 45 °C, while DPPC-PPPs significantly adsorbed L-Trp but not D-Trp at 30 °C: enantio excess (e.e.) was 75.0%. The time course of Trp adsorption was investigated: for both enantiomers, similar adsorption behaviors were observed for 30 h, thus suggesting surface adsorption onto DPPC-PPPs. L-Trp adsorption continued after 30 h, suggesting that L-Trp could be distributed in the inner part of DPPC-PPPs. Interestingly, the reused DPPC-PPPs featured improved adsorption performance, suggesting that the deposited DPPC membranes on PPPs could act as chiral selectors for L-Trp. The optical resolution of L-/D-Trp was performed using DPPC-PPPs, resulting in the e.e. of D-Trp was > 60%. Thus, DPPC-PPPs have the potential of chiral selective adsorption of L-amino acid, which can be used as chiral separation materials.

Probing the Role of Chirality in Phospholipid Membranes

Nucleotides, amino acids, sugars, and lipids are almost ubiquitously homochiral within individual cells on Earth. While oligonucleotides and proteins exist as one natural chirality throughout the tree of life, two stereoisomers of phospholipids have separately emerged in archaea and bacteria, an evolutionary divergence known as "the lipid divide". Within this review, we focus on the emergence of phospholipid homochirality and compare the stability of synthetic homochiral and heterochiral membranes in vitro. We discuss chemical probes designed to study the stereospecific interactions of lipid membranes in vitro. Overall, we aim to highlight studies that help elucidate the determinants of stereospecific interactions between lipids, peptides, and small molecule ligands. Continued work in understanding the drivers of favorable interactions between chiral molecules and biological membranes will lead to the design of increasingly selective chemical tools for bioorthogonal labeling of lipid membranes and safer membrane-associating pharmaceuticals.

A layer-by-layer assembled D/L-arginine-calix[4]arene-Si-surface for macroscopic enantio-selective discrimination of (R)/(S)-ibuprofen

Chiral arginine was introduced by layer-by-layer assembly onto a calix[4]arene-diacid modified silica surface to control the adsorption of different kinds of ibuprofen droplets. The droplet of (S)-ibuprofen slid off rapidly, whereas the droplet of (R)-ibuprofen absorbed on the modified surface.

Investigation of Quercetin interaction behaviors with lipid bilayers: Toward understanding its antioxidative effect within biomembrane

Quercetin (QCT), existing in common dietary sources, is an abundant bioflavonoid with planar structure and exerts multiple pharmacological effects. Herein, four kinds of liposomes were prepared as model biomembranes, and then the partition coefficient, distribution in lipid membrane and influence of the QCT on the membrane properties were evaluated. The partition of QCT to lipid membranes was affected by both membrane phase state and the interference of QCT on membrane properties. The location of QCT in lipid membrane was related to the phase state of lipid membrane. In addition, influence of QCT on the compaction of the hydrocarbon tail in lipid membranes was dependent on the unsaturation degree of lipid molecules. Finally, about its antioxidant activity, from the results of 2,2-diphenyl-1-picrylhydrazyl radical scavenging assay, it can be concluded that the interaction of QCT with lipid membrane greatly influences on QCT reductive activity in lipid membrane. Furthermore, mass spectrometry of DOPC molecule showed no lipid oxidation in the presence of QCT, indicating that in addition to the QCT ability toward radical scavenging, the ordering effect of QCT in unsaturated lipid membrane would be helpful to protect lipid membrane from oxidation by inhibiting radical diffusion (synergy effect). Based on lipid membrane analysis, our study made it clear that the effect of QCT on various lipid membrane and its relation with the antioxidant effect of QCT within lipid membrane. Therefore, our analytical method and findings would be also helpful for understanding the mechanism of other antioxidants effects on biomembrane.

Changes Caused by Liposomes to the Belousov-Zhabotinsky Reaction

The Belousov-Zhabotinsky (BZ) reaction has been applied to give autonomous dynamic behaviors to artificial systems. This reaction is conducted in an aqueous system, but it produces some hydrophobic intermediates, such as bromine. On the basis of previous works about reactions in the lipid bilayer, we investigated how liposome membranes (water-oil interface) affect the BZ reaction. Herein diacylglycerophosphocholine (PC) molecules with a variety of hydrocarbon tails were selected as components of liposomes, and the BZ reaction in the presence of the liposomes was characterized. As a result, membrane fluidity was the main characteristic leading to changes in the reaction behavior. The decrease of the frequency of oscillations was relevant to membrane fluidity, suggesting the interaction of bromine species in the hydrophobic site of the liposomes. In addition, the heterogeneous membrane (s_o+l_d) of DMPC showed a fast decrease in the amplitude of oscillations. Conclusively, characteristics of the hydrophobic environment play a role in the reaction.

3D Printing of Polydiacetylene Photocomposite Materials: Two Wavelengths for Two Orthogonal Chemistries

Polydiacetylene (PDA) materials are appealing and gaining increasing research interest due to their outstanding chromatic transition and fluorescence enhancement effects upon exposure to various environmental stimuli. However, despite the photomask method, there are very few reports about the spatial controllable photopolymerization and subsequent 3D printing of PDA until now. Herein, for the first time, we reported the preparation of PDA photocomposite materials based on polyacrylate through the strategy of dual-wavelength polymerization and orthogonal chemistry. First, diacetylene (DA) monomers were homogeneously dispersed in acrylate resin. Then a violet light emitting diode (LED) (or laser diode) was used for the free radical polymerization of polyacrylate. Finally, UV irradiation was utilized to induce the 1,4-topopolymerization of PDA, which could show a successive blue to purple to red color transition in response to the gradient increment of temperature. Interestingly, instead of photomasks, we applied a 3D printing approach directly to this composite material and fabricated some macroscopic stereo patterns, which also illustrated thermochromic properties. This novel kind of functional photocomposite material would demonstrate a huge application prospect in many potential fields, including colorimetric sensing, information encryption, anticounterfeiting, and so on.