Unprecedented observation of days-long remnant orientation of phospholipid bicelles: a small-angle X-ray scattering and theoretical study

Nanometric bilayer-based self-assembled micelles commonly named as bicelles, formed with a mixture of long and short chains phosphatidylcholine lipids (PC), are known to orient spontaneously in a magnetic field. This field-induced orientational order strongly depends on the molecular structure of the phospholipids. Using small-angle X-ray scattering (SAXS), we performed detailed structural studies of bicelles and investigated the orientation/relaxation kinetics in three different systems: saturated-chain lipid bicelles made of DMPC (dimyristoyl PC)/DCPC (1,2-dicaproyl PC) with and without the added paramagnetic lanthanide ions Eu(3+), as well as bicelles of TBBPC (1-tetradecanoyl-2-(4-(4-biphenyl)butanoyl)-sn-glycero-3-PC)/DCPC. The structural study confirmed the previous NMR studies, which showed that DMPC bicelles orient with the membrane normal perpendicular (defined here as "nematic" orientation) to the magnetic field, whereas they orient parallel (defined here as "smectic" orientation) to the magnetic field in the presence of Eu(3+). The TBBPC bicelles also show smectic orientation. Surprisingly, the orientational order induced in the magnetic field remains even after the magnetic field is removed, which allowed us to investigate the orientation and relaxation kinetics of different bicelle structures. We demonstrate that this kinetics is very different for all three types of bicelles at the same lipid concentration; DMPC bicelles (~40 nm diameter) with and without Eu(3+) orient faster than TBBPC bicelles (~80 nm diameter). However, for the relaxation, DMPC bicelles (nematic) lose their macroscopic orientation only after one hour, whereas both DMPC bicelles with Eu(3+) and TBBPC bicelles (smectic) remarkably stay oriented for up to several days! These results indicate that the orientation mechanism of these nanometric disks in the magnetic field is governed by their size, with smaller bicelles orienting faster than the larger bicelles. Their relaxation mechanism outside the magnetic field, however, is governed by the degree of ordering. Indeed, the angular distribution of oriented bicelles is much narrower for the bicelles with smectic orientation, and, consequently, they keep aligned for much longer time (days) than those with nematic ordering (hours) outside the magnetic field. The understanding of the orientation/relaxation kinetics, as well as the morphologies of these "molecular goniometers" at molecular and supramolecular levels, allows controlling such an unprecedented long-range and long-lived smectic ordering of nanodisks and opens a wide field of applications for structural biology or material sciences.     

Chiral supramolecular thiophene fluorophore consisting of thiophenecarboxylic acid derivatives

Solid-state chiral supramolecular thiophene fluorophore has been successfully prepared by using chiral (R)-1-(2-naphthyl)ethylamine and 5-bromothiophene-2-carboxylic acid. This chiral supramolecular thiophene fluorophore is formed by assembling chiral 2₁-helical columnar network structures composed of (R)-1-(2-naphthyl)ethylamine and 5-bromothiophene-2-carboxylic acid. This supramolecular organic fluorophore exhibits circularly polarized luminescence (CPL) even in the solid state.     

Salvileucalin C, a novel rearranged neoclerodane diterpene from Salvia leucantha

Salvileucalin C (1), a novel neoclerodane diterpene having an unprecedented carbon framework and a structurally closely related salvileucalin D (2) were isolated and their absolute structures were elucidated by the vibrational circular dichroism (VCD) spectra.     

Organic Solvent‐Free Enzymatic Transformation of Poly(ϵ‐caprolactone) into Repolymerizable Oligomers in Supercritical Carbon Dioxide

The enzymatic transformation of poly(ϵ‐caprolactone) (PCL) into repolymerizable oligomers in supercritical carbon dioxide (scCO₂) using an enzyme was carried out in order to establish a sustainable chemical recycling system for PCL, which is a typical biodegradable synthetic plastic. The enzymatic conversion of PCL beads having an M̄_n of 110 000 using Candida antarctica lipase (lipase CA) in scCO₂ containing small amounts of water quantitatively afforded CL oligomers at 40°C. The CL oligomers were readily repolymerized using the same enzyme to produce high‐molecular weight PCL.     

Efficient Multiple Domain Ligation for Proteins Using Asparaginyl Endopeptidase by Selection of Appropriate Ligation Sites Based on Steric Hindrance

Three domain fragments of a multi-domain protein, ER-60, were ligated in two short linker regions using asparaginyl endopeptidase not involving denaturation. To identify appropriate ligation sites, by selecting several potential ligation sites with fewer mutations around two short linker regions, their ligation efficiencies and the functions of the ligated ER-60s were examined experimentally. To evaluate the dependence of ligation efficiencies on the ligation sites computationally, steric hinderances around the sites for the ligation were calculated through molecular dynamics simulations. Utilizing the steric hindrance, a site-dependent ligation potential index was introduced as reproducing the experimental ligation efficiency. Referring to this index, the reconstruction of ER-60 was succeeded by the ligation of the three domains for the first time. In addition, the new ligation potential index well-worked for application to other domain ligations. Therefore, the index may serve as a more time-effective tool for multi-site ligations.