Rate constant measurements for initial addition reactions of radicals at the propagation step of photo‐polymerization as studied by pulsed EPR spectroscopy

Pulsed EPR spectroscopy was employed to determine reaction rate constants at an early stage of addition reactions in radical polymerizations triggered by four initiator radicals, which were generated by photodissociation of four parent molecules. Two monomers (tert‐butylacrylate and tert‐butylmethacrylate) were examined as reactant. Stern–Volmer analysis on the measured decay time of electron spin echo intensity of reacting radicals provides rate constants for addition reactions. We focused on rate constants for the second step reaction between monomer and adduct radical that is produced by the first step addition reaction between initiator radical and monomer. The rate constant measured by pulsed EPR was evaluated by theoretical calculations in the light of (1) enthalpy difference between product radical and reactants and (2) charge transfer interaction between reacting radical and monomer. Copyright © 2016 John Wiley & Sons, Ltd.     

Simple and efficient quantum key distribution with parametric down-conversion

We propose an efficient quantum key distribution protocol based on the photon-pair generation from parametric down-conversion (PDC). It uses the same experimental setup as the conventional protocol, but a refined data analysis enables detection of photon-number splitting attacks by utilizing information from a built-in decoy state. Assuming the use of practical detectors, we analyze the unconditional security of the new scheme and show that it improves the secure key generation rate by several orders of magnitude at long distances, using a high intensity PDC source.     

Second-harmonic-generation microscope using eight-segment polarization-mode converter to observe three-dimensional molecular orientation

We developed a compact polarization-mode converter for microscopy to control three-dimensional polarization at the focus. The converter consisted of two homogeneously aligned liquid-crystal spatial light modulators with eight independently controllable electrodes (segments), and a quarter-waveplate. The converter converted a linearly polarized beam to three polarization modes: two orthogonal linear polarizations and a pseudo-radial polarization. We applied the converter to second-harmonic-generation microscopy and demonstrated the detection of three-dimensional molecular orientation.     

Acidic‐pH‐Activatable Fluorescence Probes for Visualizing Exocytosis Dynamics

Live imaging of exocytosis dynamics is crucial for a precise spatiotemporal understanding of secretion phenomena, but current approaches have serious limitations. We designed and synthesized small‐molecular fluorescent probes that were chemically optimized for sensing acidic intravesicular pH values, and established that they can be used to sensitively and reliably visualize vesicular dynamics following stimulation. This straightforward technique for the visualization of exocytosis as well as endocytosis/reacidification processes with high spatiotemporal precision is expected to be a powerful tool for investigating dynamic cellular phenomena involving changes in the pH value.     

Incorporation of Pseudo‐complementary Bases 2,6‐Diaminopurine and 2‐Thiouracil into Serinol Nucleic Acid (SNA) to Promote SNA/RNA Hybridization

Serinol nucleic acid (SNA) is a promising candidate for nucleic acid‐based molecular probes and drugs due to its high affinity for RNA. Our previous work revealed that incorporation of 2,6‐diaminpurine (D), which can form three hydrogen bonds with uracil, into SNA increases the melting temperature of SNA‐RNA duplexes. However, D incorporation into short self‐complementary regions of SNA promoted self‐dimerization and hindered hybridization with RNA. Here we synthesized a SNA monomer of 2‐thiouracil (sU), which was expected to inhibit base pairing with D by steric hindrance between sulfur and the amino group. To prepare the SNA containing D and sU in high yield, we customized the protecting groups on D and sU monomers that can be readily deprotected under acidic conditions. Incorporation of D and sU into SNA facilitated stable duplex formation with target RNA by suppressing the self‐hybridization of SNA and increasing the stability of the heteroduplex of SNA and its complementary RNA. Our results have important implications for the development of SNA‐based probes and nucleic acid drugs.     

Multiple Fused Anthracenes as Helical Polycyclic Aromatic Hydrocarbon Motif for Chiroptical Performance Enhancement

Polycyclic aromatic hydrocarbons consisting of three fused anthracene units were designed as new π‐conjugated compounds having helical structures. These expanded helicenes were synthesized by Pt‐catalyzed cycloisomerization of the corresponding ethynyl‐substituted precursors. The nonplanar and helical structure was confirmed by X‐ray analysis and DFT calculations, and the barrier to helical inversion was estimated to be 34 kJ mol^?1. The enantiomers of the diphenyl derivative were successfully resolved by chiral HPLC. Enantiopure samples showed good chiroptical performance in the CD (|Δ?| 1380 L mol^?1 cm^?1) and CPL (|g_lum| 0.013) spectra, and these values were considerably large for simple organic molecules. The unique chiroptical properties are discussed on the basis of the molecular structure and the electronic state with the aid of time‐dependent DFT calculations.     

Porosity control in nylon-6/nylon-6, 6 membranes

The possibility of porosity control in N6/N66 membranes prepared from N6/N66 blend solutions of calcium chloride – methanol mixture was investigated. For N6/N66 blend solutions at 10 °C and 20 °C, the four-phase structure of solid, gel 1, gel 2 and solution was observed clearly in the pore formation process after adding water on a solution surface. In the boundary part between gel 1 and gel 2, the phase separation of N6 and N66 was predicted. The macroscopic pores of blend membranes prepared at 10°C and 20 °C were almost spherical.     

Monte carlo simulations for blue-phase structure in liquid crystals

Blue-phase liquid crystals form three-dimensional structures in a self-organizing manner and are similar to living tissue structures such as the teeth of mice and collagen tissues. This study presents numerical results regarding the conditions under which blue-phase liquid crystals occur. The Monte Carlo simulations are performed by employing an improved Lennard–Jones potential that considers anisotropy and chirality. The conditions for the formation of the blue phase, which vary with respect to the chirality, are examined first. The relationship between the anisotropic parameters and the chiral parameter for the formation of the blue phase is discussed. Identical blue-phase structures are obtained, even when the cell size and molecular number are varied drastically. This discussion is useful for considering the scale-up problem, which is almost always a difficult issue for molecular-scale simulations.