Ethynylpyrene Linked Benzocrown Ethers as Fluorescent Sensors for Metal Ions

Substances containing ethynylpyrenes linked to either one or four benzocrown ethers were synthesized, and their absorption and fluorescence spectroscopic responses to metal ions were assessed. Addition of metal perchlorates to solutions of these substances promotes short wavelength shifts in their absorption and fluorescence maxima and increases in their fluorescence intensities. The magnitudes of the fluorescence intensity increases are dependent on the ring size and number of the crown ether and the nature of the metal cation. Association constants for complex formation were calculated using fluorescence intensity versus concentration data. Analysis using Job's plots showed that the substances containing one benzocrown ether moiety form 1:1 complexes with metal ions. Results of experiments employing repeated addition and removal of Mg(ClO₄)₂ demonstrate that the ON‐OFF fluorescence response can be repeated at least three times. Results of molecular orbital calculations show that complexation with metal ions lowers the energies of both the π and π* levels of the ethynylpyrene moiety and that in some cases the vacant orbital on the metal becomes the LUMO of the complex. An explanation of the spectroscopic changes promoted by metal ions is proposed in terms of electrostatic repulsion and structural regulation.     

Trunculins X and Y from an Okinawan sponge Sigmosceptrella sp.

Two new norsesterterpenoid cyclic peroxides, trunculins X and Y, were isolated from an Okinawan sponge Sigmosceptrella sp. Their structures were determined by spectroscopic analyses on intact molecules and derivatives and also by crystallographic study. The compounds showed cytotoxicity in a range of IC₅₀ 0.32–20 μM against three cell lines.     

Chichibabin pyridinium synthesis

Chichibabin pyridine synthesis involves the reaction of three aldehydes and ammonia to form 2,3,5-trisubstituted pyridines. This study examined the synthesis of tetrasubstituted pyridinium from aldehydes and an amine hydrochloride in the presence/absence of Pr(OTf)₃. Important insights into the reaction mechanisms of Chichibabin pyridinium synthesis were proposed through the investigation of reaction intermediates along with quantitative GC–MS analysis.     

Helical foldamer-catalyzed enantioselective 1,4-addition reaction of dialkyl malonates to cyclic enones

The introduction of a five-membered ring α,α-disubstituted α-amino acid into l-Leu-based heptapeptides preferentially induced right-handed (P) helical structures. Using 5 ～ 20 mol% of a single helical foldamers-catalyst, enantioselective 1,4-addition reactions of dialkyl malonates to cycloalk-2-enones (5 ～ 7 rings) proceeded to give chiral 3-substituted cycloalkanones with 94 ～ 99% ee in moderate chemical yields, regardless of the ring size of substrates.     

Disulfide‐Unit Conjugation Enables Ultrafast Cytosolic Internalization of Antisense DNA and siRNA

Development of intracellular delivery methods for antisense DNA and siRNA is important. Previously reported methods using liposomes or receptor‐ligands take several hours or more to deliver oligonucleotides to the cytoplasm due to their retention in endosomes. Oligonucleotides modified with low molecular weight disulfide units at a terminus reach the cytoplasm 10 minutes after administration to cultured cells. This rapid cytoplasmic internalization of disulfide‐modified oligonucleotides suggests the existence of an uptake pathway other than endocytosis. Mechanistic analysis revealed that the modified oligonucleotides are efficiently internalized into the cytoplasm through disulfide exchange reactions with the thiol groups on the cellular surface. This approach solves several critical problems with the currently available methods for enhancing cellular uptake of oligonucleotides and may be an effective approach in the medicinal application of antisense DNA and siRNA.     

Dibenzoarsepins: Planarization of 8π‐Electron System in the Lowest Singlet Excited State

Dibenzo[b,f]arsepins possessing severely distorted cores compared to those of other heteropins were synthesized. These derivatives exhibited dual photoluminescence in the green‐to‐red region (500–700 nm) and the near‐ultraviolet region (<380 nm), which could be attributed to the planarization of the arsepin core in the lowest singlet excited (S₁) state. The computational approach for the assessment of the aromatic indices revealed that the dibenzoarsepins studied show aromaticity (8π system) in the S₁ states in line with Baird's rule. The lone pair electrons of the arsenic atoms play a crucial role in the aromaticity in the S₁ states.     

Stereochemical Dichotomy in Two Competing Cascade Processes: Total Syntheses of Both Enantiomers of Spiroxin A

The first total synthesis of the marine antibiotic spiroxin A has been achieved for both enantiomeric forms. The discovery of two competing cascade processes triggered by two orthogonal stimuli, photo‐irradiation or acid/base treatment, enabled the divergent conversion of a single chiral, nonracemic bis‐quinone into both enantiomers of an advanced intermediate en route to both (?)‐ and (+)‐spiroxin A. The mechanism of the enantiodivergence is discussed.     

Molecular understanding of the adhesive interactions between silica surface and epoxy resin: Effects of interfacial water

The molecular mechanism of the adhesion between silica surface and epoxy resin under atmospheric conditions is investigated by periodic density-functional-theory (DFT) calculations. Slab models of the adhesion interface were built by integrating a fragment of epoxy resin and hydroxylated (0 0 1) surface of α-cristobalite in the presence of adsorbed water molecules. Effects of adsorbed water on the adhesion interaction are evaluated on the basis of geometry-optimized structures, adhesion energies, and forces. Calculated results demonstrate that adsorbed water molecules significantly reduce both the adhesion energies and forces of the silica surface–epoxy resin interface. The reduction of adhesion properties can be associated with structural deformation of water molecules confined in the tight space between the adhesive and adherend as well as structural flexibility of the hydrogen-bonding network in the interfacial region during detachment of the epoxy resin from the hydrophilic silica surface. © 2018 Wiley Periodicals, Inc.     

Synthesis,Structures, and Near‐IR Absorption of Heterole‐Fused Earring Porphyrins

A reaction sequence of regioselective peripheral bromination, Suzuki–Miyaura coupling with 2‐borylated thiophene or pyrrole, and oxidative ring‐closure with FeCl₃ allowed the synthesis of heterole‐fused earring porphyrins 4Pd and 9Pd from the parent earring porphyrin 1 . Differently pyrrole‐fused porphyrins 5H and 6H and their Pd^II complexes 5Pd and 6Pd were also synthesized. The structures of 4Pd , 5H, 6Pd , and 8Pd have been revealed by X‐ray analysis to be slightly twisted owing to constraints imposed by heterole‐fused structures. 5Pd exhibits an intensified band at 1505 nm, while 4Pd and 9Pd display small but remarkably red‐shifted absorption bands reaching around 2200 nm.     

Long-Range Lateral Correlation between Self-Assembled Domains of Fluorocarbon-Hydrocarbon Tetrablocks by Quantitative GISAXS

The structure and lateral correlation of fluorocarbon-hydrocarbon tetrablock di(F10Hm) domains at the air/water interface have been determined by quantitative analysis of grazing incidence small-angle X-ray scattering (GISAXS) data. The measured GISAXS signals can be well represented by the full calculation of the form and structure factors. The form factor suggests that di(F10Hm) domains take a hemiellipsoid shape. Both major and minor axes of the hemiellipsoids monotonically increased in response to the elongation of the hydrocarbon blocks, which can be explained by the concominant increase in van der Waals interaction. The structure factor calculated from the GISAXS signals suggests that the domains take an orthorhombic lattice. Remarkably, the lateral correlation can reach over a distance that is more than 14 times longer than the distance to the nearest neighbors. Our data suggest that quantitative GISAXS enables the optimal design of mesoscopic self-assemblies at the air/water interface by fine-tuning of the structures of molecular building blocks.