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The average conformation of the methyl-branched chains of archaeal lipid phosphatidyl glycerophosphate methyl ester (PGP-Me) was examined in a hydrated bilayer membrane based on the 2H nuclear magnetic resonance (NMR) of enantioselectively 2H-labeled compounds that were totally synthesized for the first time in this study. The NMR results in combination with molecular dynamics simulations revealed that the PGP-Me chain appeared to exhibit behavior different from that of typical membrane lipids such as dimyristoylphosphatidylcholine (DMPC). The C-C bonds of the PGP-Me chain adopt alternative parallel and tilted orientations to the membrane normal as opposed to a DMPC chain where all of the C-C bonds tilt in the same way on average. This characteristic orientation causes the intertwining of PGP-Me chains, which plays an important role in the excellent thermal and high-salinity stabilities of archaeal lipid bilayers and membrane proteins.

Aluminum electrodeposition using ionic liquids or deep eutectic solvents has attracted significant interest for coating applications. Although Al electrodeposition is usually carried out in a nitrogen- or argon-filled glove box, there may be a potential for process cost reduction if the Al electrodeposition process could be carried out in a dry atmosphere. In this study, we examined two commonly used baths, namely a 1-ethyl-3-methylimidazolium chloride (EMImCl)–AlCl3 ionic liquid and an acetamide (AcAm)–AlCl3 deep eutectic solvent, to determine their respective feasibilities for the electrodeposition of a uniform Al film in dry air. Electrodeposition in dry air using the AcAm–AlCl3 bath produced uniform Al films even after the bath had been used for more than 10 weeks, whereas electrodeposition in dry air using the EMImCl–AlCl3 bath failed to produce an Al film covering the entire substrate. The current efficiency was almost 100% in the AcAm–AlCl3 bath, whereas the value decreased to 50% in EMImCl–AlCl3 bath in dry air. The findings of this study therefore reveal that AcAm–AlCl3 is a suitable bath for Al electrodeposition in dry air.

Diphytanoylphosphatidylcholine (DPhPC) is a synthetic phospholipid in which two methyl-branched acyl chains are introduced into the glycerol moiety, mimicking phospholipids of eukaryotic and eubacterial origins. The lipid bilayers of DPhPC reproduce the outstanding physical properties of methyl-branched lipids that occur in archaeal membranes. DPhPC is commonly used as the base lipid in biophysical experiments, particularly for recording ion-channel currents. However, the dynamics of lipid molecules that induces their useful physical properties is still unclear. In this study, we examined the conformation and orientation of the methyl-branched acyl chain of DPhPC in a membrane using

Medium-sized lactams are important structural motifs found in a variety of bioactive compounds and natural products but are challenging to prepare, especially in optically active form. A Michael addition/proton transfer/lactamization organocascade process is described that delivers medium-sized lactams, including azepanones, benzazepinones, azocanones, and benzazocinones, in high enantiopurity through the intermediacy of chiral α,β-unsaturated acylammonium salts. An unexpected indoline synthesis was also uncovered, and the benzazocinone skeleton was transformed into other complex heterocyclic derivatives, including spiroglutarimides, isoquinolinones, and δ-lactones.

The clinically important antibiotic amphotericin B (AmB) is a membrane-active natural product that targets membrane sterol. The antimicrobial activity of AmB is generally attributed to its membrane permeabilization, which occurs when a pore is formed across a lipid bilayer. In this study, the molecular orientation of AmB was investigated using solid-state nuclear magnetic resonance (NMR) to better understand the mechanism of antifungal activity. The methyl ester of AmB (AME) labeled with NMR isotopes, d3-AME, and its fluorinated and/or 13C-labeled derivatives were prepared. All of the AmB derivatives showed similar membrane-disrupting activities and ultraviolet spectra in phospholipid liposomes, suggesting that their molecular assemblies in membranes closely mimic those of AmB. Solid-state 2H NMR measurements of d3-AME in a hydrated membrane showed that the mobility of AME molecules depends on concentration and temperature. At a 1:5:45 AME:Erg:dimyristoylphosphatidylcholine ratio, AME became sufficiently mobilized to observe the motional averaging of quadrupole coupling. On the basis of the rotational averaging effect of 19F chemical shift anisotropy, 2H quadrupolar splitting, and 13C-19F dipolar coupling of 14β-F-AMEs, we deduced that the molecular axis of AME is predominantly parallel to the normal of a lipid bilayer. This result supports the barrel-stave model as a molecular assembly of AmB in membranes.

The electrodeposition of Al has been studied in various ionic liquids represented by the 1-ethyl-3-methylimidazolium chloride-AlCl3 system. However, AlCl3-based (chloroaluminate) ionic liquids are generally handled in an inert atmosphere of nitrogen or argon because they are highly hygroscopic and susceptible to hydrolysis through the reaction with moisture in the air. To maintain an inert atmosphere, a closed system that typically uses a glove box is required, but operation in a closed system leads to low productivity and high cost. Therefore, electrodeposition in an inert atmosphere is unsuitable for mass production on an industrial scale. To alleviate this problem, we have previously studied the feasibility of Al electrodeposition in dry air using chloroaluminate ionic liquids. Because the electrodeposition process in dry air does not require a glove box, it is considered to be more productive than the electrodeposition process under an inert atmosphere. In our previous study, four different chloroaluminate ionic liquids consisting of different organic cations ([cation]Cl-AlCl3) with a molar ratio of [cation]Cl : AlCl3 = 1 : 2 were used as Al electrodeposition baths to study Al electrodeposition behavior in dry air. The cations used were 1-ethyl-3-methylimidazolium (EMI+), 1-butylpyridinium (BP+), 1-butyl-1-methylpyrrolidinium (BMP+), and trimethylphenylammonium (TMPA+). We found that electrodeposition in dry air using the bath composed of EMI+ or BP+ could not produce an Al film covering the entire surface of the substrate, whereas electrodeposition using the bath composed of BMP+ or TMPA+ could produce an Al film covering the entire surface of the substrate in dry air as well as in an inert atmosphere. The reason for the difference in the results of Al electrodeposition in dry air according to cationic species has not yet been ascertained, but it is speculated that dissolved oxygen has some influence on the Al electrodeposition. In the present study, we measured the concentration of oxygen dissolved in four types of ionic liquids in dry air. For measuring the dissolved oxygen concentration, ionic liquids with a composition of [cation] Cl: AlCl3 = 1: 0.9 were used. This composition was chosen because only AlCl4 −, which is an ionic species that is difficult to be reduced to Al metal, is present in the bath when the AlCl3 mole fraction is less than 50 mol% (Lewis base)in chloroaluminate ionic liquids. Consequently, Al electrodeposition does not occur, and low extent of electrochemical reaction other than Al electrodeposition at a potential of 0 V vs. Al / Al (III) or less can be investigated. The concentration of dissolved oxygen was measured by chronoamperometry using two types of electrodes, a macroelectrode and a microelectrode, both of which have a circular active area with a diameter in the order of millimeter and micrometer, respectively. In the case of chronoamperometric measurement with a macroelectrode, the reduction current of oxygen follows the equation in the upper row in Table 1, assuming that the reaction rate is controlled by the planar diffusion of oxygen from the bulk electrolyte to the surface of the electrode. Upon measuring the current–time response, two unknowns remain, namely, the concentration and the diffusion coefficient of dissolved oxygen; and it is not possible to determine the dissolved oxygen concentration through the chronoamperometric measurement using the macroelectrode alone. In the case of chronoamperometric measurement with a microelectrode, the geometry of the diffusion of the reactant to the electrode surface changes to semi-spherical, and the reduction current of oxygen thus follows the equation in the lower row in Table 1. The concentration and diffusion coefficient of dissolved oxygen can thus be determined through the two chronoamperometric measurements. The chronoamperometric measurements revealed that there was no significant difference in the oxygen concentrations of the ionic liquids with different cationic species. The results that we have obtained so far are as follows: 1) In an inert atmosphere, an Al film covering the entire surface of the substrate can be electrodeposited from a bath containing any cation species. 2) In dry air, an Al film covering the entire surface of the substrate can only be electrodeposited from some baths composed of specific cation species. 3) There is no significant difference in the dissolved oxygen concentrations of the baths in dry air, even though the cation species in the baths are different. In consideration of these results, the reason for the different results of Al electrodeposition in dry air according to the cationic species is neither dissolved oxygen alone nor cationic species alone but the combined action of both dissolved oxygen and the cation. Figure 1

Phosphatidylglycerophosphate methyl ester (PGP-Me), a major constituent of the archaeal purple membrane, is essential for the proper proton-pump activity of bacteriorhodopsin (bR). We carried out the first synthesis of the bisphosphate head group of PGP-Me using H-phosphonate chemistry that led to the production of a simplified PGP-Me analogue with straight alkyl chains. To investigate the role of this head group in the structural and functional integrity of bR, the analogue was used to reconstitute bR into liposomes, in which bR retained the original trimeric structure and light-induced photocycle activity. Enhanced ordering of an alkyl chain of the (2)H-labelled analogue was observed in (2)H NMR spectra upon interaction with bR. These results together suggest that the bisphosphate moiety plays a role in the proper functioning of bR through the lipid-protein interaction.

Correction for ‘Stereoselective synthesis of the head group of archaeal phospholipid PGP-Me to investigate bacteriorhodopsin–lipid interactions’ by Jin Cui, et al., Org. Biomol. Chem., 2015, DOI: 10.1039/c5ob01252j.