Liposomes are artificially prepared vesicular lipid nanoparticles with a bilayer structure, resembling cell membrane. Their ability to encapsulate various molecules along with excellent biocompatibility makes them ideal delivery vehicles for pharmaceuticals. They can also serve as platforms for membrane proteins to elucidate the structure and function in lipid membranes. Nascent high-density lipoproteins are discoidal lipid nanoparticles with a bilayer structure, which can be reconstituted with their constituents. Such reconstituted nanoparticles, nanodisks, were originally generated in terms of elucidation for mechanisms of lipoprotein metabolisms. At the same time, like liposomes, nanodisks have been developed as delivery vehicles and platforms for membrane proteins in structural biology. From a developmental background, apolipoproteins, their analogs, or fragment peptides were initially used as scaffolding molecules to wrap around the edge of the disk-shaped lipid bilayer. Since the discovery that styrene-maleic acid copolymers produce nanodisks instead of apolipoproteins, variously modified or novel polymers have been synthesized to broaden the applications of polymer nanodisks. This review provides an overview of the types of synthetic polymers used to produce nanodisks, and the biomedical applications of nanodisks to the developments of delivery vehicles and to the structural studies of membrane proteins.

Membrane cholesterol is an essential and abundant component of eukaryotic cell membranes. The unique chemical structure of cholesterol significantly influences the physicochemical properties of phospholipid bilayers, such as hydrophobic thickness and lateral pressure profile. However, the mechanisms by which these alterations regulate the balance of protein–lipid interactions in lipid bilayer environments remain unclear. To experimentally assess basic and common driving forces for helix associations in membranes, the self-associations of a de novo designed simple transmembrane helix (AALALAA)₃ and its derivative helices were examined. Single-pair fluorescence resonance energy transfer (sp-FRET) experiments were performed to monitor the thermodynamic and kinetic stabilities of helix associations in single liposomes. The addition of cholesterol exerted both stabilizing and destabilizing effects on these associations, up to a change in ΔG_a of approx. 10 kJ mol⁻¹, and these effects were dependent on the association topology, amino acid sequence, and number of helices. These results demonstrate that cholesterol in the membrane regulates the stability of transmembrane proteins in a protein context-dependent manner through physicochemical mechanisms.

Lipid transbilayer movement (flip-flop) is regulated by membrane proteins that are involved in homeostasis and signaling in eukaryotic cells. In the plasma membrane, an asymmetric lipid composition is maintained by energy-dependent unidirectional transport. Energy-independent flip-flop promotion by phospholipid scramblases disrupts the asymmetry in several physiological processes, such as apoptosis and blood coagulation. In the endoplasmic reticulum, rapid flip-flop is essential for bilayer integrity because phospholipids are synthesized only in the cytoplasmic leaflet. Phospholipid scramblases are also involved in lipoprotein biogenesis, autophagosome formation, and viral infection. Although several scramblases have been identified and investigated, the precise flip-flop promotion mechanisms are not fully understood. Model transmembrane peptides are valuable tools for investigating the general effects of lipid–peptide interactions. We focus on the development of model transmembrane peptides with flip-flop promotion abilities and their mechanisms.

P4-ATPases, which are subfamily members of P-type ATPase superfamily, translocate membrane lipids from the exoplasmic/luminal leaflet to the cytoplasmic leaflet, thus regulating trans-bilayer lipid asymmetry. Mammalian P4-ATPases localize to the specific subcellular organelles or the plasma membrane where they translocate the specific lipids. Although recent advances in the structural analysis of P4-ATPases have improved our understanding of lipid transporting machinery, the mechanism of substrate specificity and the regulatory mechanism of the enzymes remain largely unknown. Recent studies have uncovered several specific localization and regulatory mechanisms of P4-ATPases. Here, we review the current understanding of the regulatory mechanism of P4-ATPase activity and localization in mammalian cells.

The ATP-binding cassette (ABC) transporters are one of the largest families of membrane-bound proteins and exist in almost all living organisms from eubacteria to mammals. They transport diverse substrates across membranes utilizing the energy of ATP hydrolysis as a driving force and play an essential role in cellular homeostasis. In humans, four ABC transporters classified as subfamily D have been identified. ABCD1–3 are localized to peroxisomal membranes and involved in the transport of various acyl-CoAs from the cytosol to the peroxisomal lumen. ABCD4 functions on the lysosomal membranes and transports vitamin B₁₂ (cobalamin) from lysosomes into the cytosol. The mutation of genes encoding ABCD1, ABCD3, and ABCD4 are responsible for genetic diseases called X-linked adrenoleukodystrophy, congenital bile acid synthesis defect 5, and cobalamin deficiency, respectively. In this review, we summarize the targeting mechanism and physiological functions of the ABCD transporters and discuss insights that have been obtained on the transport mechanism based on disease-causing mutations and cryo-electron microscopy (EM) structural studies.

Herein, we developed secondary-alcohol-selective C–H alkylation of 1,3-butane diol by combining an acridinium photoredox catalyst and a thiophosphoric acid hydrogen atom transfer (HAT) catalyst. The use of non-coordinating solvent such as dichloromethane (DCM) improved secondary α-alkoxy C–H selectivity by lowering bond dissociation energy (BDE) through intramolecular hydrogen bonding.

Fatty acid biosynthesis is essential for bacterial survival. Of these promising targets, β-ketoacyl-acyl carrier protein (ACP) synthase III (FabH) is the most attractive target. FabH would trigger the initiation of fatty acid biosynthesis and it is highly conserved among Gram-positive and -negative bacteria. A series of novel amide derivatives bearing dioxygenated rings were synthesized and developed as potent inhibitors of FabH. These compounds were determined by ¹H-NMR, ¹³C-NMR, MS and further confirmed by crystallographic diffraction study for compound 19. Furthermore, these compounds were evaluated strong broad-spectrum antibacterial activity. Some compounds with potent antibacterial activities were tested for their Escherichia coli (E. coli) FabH inhibitory activity. Especially, compound 19 showed the most potent antibacterial activity with minimum inhibitory concentration (MIC) values of 1.56–3.13 mg/mL against the tested bacterial strains and exhibited the most potent E. coli FabH inhibitory activity with IC₅₀ of 2.4 µM. Docking simulation was performed to position compound 19 into the E. coli FabH active site to determine the probable binding conformation.

The crystalline state of ibuprofen (IBU) confined in mesoporous silica was characterized using low-field time-domain nuclear magnetic resonance (TD-NMR). IBU was loaded into ordered (Santa Barbara Amorphous-15 [SBA-15]; SBA) or nonordered mesoporous silica (Sylysia 320; SYL) using a well-known incipient wetness impregnation method. The dissolution profile of IBU from the silica was measured. The IBU-loaded SBA showed a relatively higher drug concentration at 10 and 20 min, which was typical of a supersaturated solution. However, it did not maintain that concentration. By contrast, the IBU-loaded SYL did not show such a dissolution profile in the early stage. To characterize the crystalline state of IBU confined in silica, the T₁ relaxation time of IBU-loaded silica powder was measured and analyzed by curve fitting. Monophasic T₁ relaxation was observed for IBU-loaded SBA. This may indicate that the amorphous phase, which has various molecular mobilities, was close to within the length of ¹H spin diffusion. The TD-NMR technique, even if the sample is powder, can rapidly and easily measure NMR relaxation. Therefore, it can be useful toward fully characterizing the crystalline state of drugs confined in mesopores.

Hardness is a critical quality characteristic of pharmaceutical oral jelly. In this study, the hardness was determined by using the T₂ relaxation curves measured by time-domain NMR. For sample preparation, kappa- and iota-carrageenans, and locust bean gum, were used as gel-forming agents. Ten test jellies with different gel-forming agent composition were prepared, and their hardness and T₂ relaxation curves were measured by a texture analyzer and time-domain NMR (TD-NMR). A negative correlation between T₂ relaxation time (T₂) and hardness was observed; however, it was difficult to determine the hardness directly from the T₂ value. That is probably because the T₂ relaxation curve contains information about molecular states, not only of water but also of the solute, and T₂ values calculated by single-exponential curve fitting only express one property of the test jelly. By considering this issue, partial least squares (PLS) regression analysis was performed on the T₂ relaxation curves for hardness determination of the test jellies. According to the analysis, an accurate and reliable PLS model was created that enabled accurate assessment of the hardness of the test jellies. TD-NMR enables the measurement of samples nondestructively and rapidly with low cost, and so could be a promising method for evaluation of the hardness of pharmaceutical oral jellies.

We report aryne generation from 2-triazenylarylboronic acids using an activator such as Brønsted acids, Lewis acids, and solid acids. With the use of (±)-Camphorsulfonic acid [(±)-CSA], the aryne precursors provided cycloadducts with a range of arynophiles in high yields. Aryne generated under the acidic conditions underwent chemoselective cycloaddition with a furan in the presence of a basic arynophile, namely an amine. Hammett plot analyses revealed that an aryne generation mechanism induced by (±)-CSA is distinct from the mechanism induced by silica gel.

The atropisomeric properties of N-alkyl and N-aryl 4-substituted 5H-dibenz[b,f]azepines were investigated. The N-alkylation and N-arylation of 4-Cl or 4-Me substituted compounds was performed; however, none of the atropisomers produced were separated by chiral HPLC. Notably, we observed that the rotation of the four axes (ax. 1–4) in the 4-substituted 5H-dibenz[b,f]azepine structure is so rapid that N-alkylation or N-arylation is not sufficient to freeze it at room temperature. Additionally, the X-ray crystal structures of N-aryl compounds 13b and 14a indicated that the N atom in the triphenyl amine moiety in their structures shows sp²-like property.

The MeOH extract from dried roots of Oxypetalum caeruleum (Apocynaceae) plants yielded seventeen new pregnane glycosides, some of which had the acylated-ramanone or -isoramanone type aglycone. The structures of these compounds were established using NMR, MS spectroscopic analysis and chemical evidence.

Some terpenyl 2,3,4-tri-O-acetyl-α-D-glucuronide methyl esters were facilely synthesized from commercially available methyl 1,2,3,4-tetra-O-acetyl-β-D-glucuronate and terpenoid alcohols in the presence of bis(trifluoromethanesulfonyl)imide (Tf₂NH) in dichloromethane (DCM) in good yields. The predominant α-selectivity at the anomer position is caused via transition state in which the neighboring group participation of the methoxycarbonyl group at C-6 stabilizes the oxonium intermediate by forming ¹C₄ conformation. The intermediate accelerates the glucuronidation reaction despite the use of the acetyl group, which is not a good activating group in general glycosylation reactions, as the activating group.