Syntheses of polymerizable viologens bearing a terminal vinyl group

Viologens that bore a terminal vinyl group were synthesized by four sequences of reactions: (1) N-vinylbenzyl-N′-n-propyl-4,4′-bipyridinium bromide chloride (V) was synthesized by the reaction of 4-(4′-pyrodyl)-N-n-propyl pyridinium bromide (III) with vinylbenzyl chloride; (2) N-β-acrylamidoethyl-N′-n-propyl-4,4′-bipyridinium dibromide (IX) was synthesized by the Menschutkin reaction of III with 2-aminoethyl bromide hydrobromide and subsequent reaction with acryloyl chloride; (3) N-β-methacryloyloxyethyl-N′-n-propyl-4,4′-bipyridinium dibromide and its analogs (XI) were synthesized by the reactions of III with the corresponding acyloxyalkyl bromides; and (4) N-vinyloxycarbonylmethyl-N′-n-propyl-4,4′-bipyridinium bromide chloride (XIII) was synthesized by the reaction of III with vinyl chloroacetate. With the exception of monomer XIII in which hydrolysis in large extent was observed during attempted polymerization, the synthesized monomers polymerized smoothly in aqueous solutions by a conventional radical procedure. Comparisons of the absorption peaks of the radical cations produced by reductions in aqueous solutions with those produced in films by ultraviolet (UV) irradiation indicate that the radical cations of polymers are associated intramolecularly in aqueous solutions.     

Convergent total syntheses of gambierol and 16-epi-gambierol and their biological activities

The convergent total syntheses of gambierol (1) and 16-epi-gambierol (2) have been achieved. The ABC and FGH ring segments 4 and 5 were prepared from known compounds 6 and 13, respectively, by linear manners. The fragments prepared were connected by our own synthetic strategy including the intramolecular allylation of alpha-acetoxy ether followed by ring-closing metathesis to furnish the octacyclic ether 3. The diiodoalkene 45, prepared from 3, was converted to the Z-iodoalkene 50 via a novel and stereoselective hydrogenolysis followed by deprotection. Construction of the triene side chain was performed by the modified Stille coupling of 50 with the Z-vinylic stannane 41 to afford 1. The similar transformations were carried out on the epimeric octacycle 34 to give 2, which showed no toxicity against mice at the concentration of 14 mg/kg.     

Do Anionic π Molecules Aggregate in Solution? A Case Study with Multi-interactive Ligands and Network Formation

An anionic π molecule can form an aggregate when a multi-interactivity is introduced, in sharp contrast to common anionic molecules that are generally difficult to stack on each other. We found that a multi-interactive ligand, 2,5,8-tri(4′-pyridyl)-1,3,4,6,7,9-hexaazaphenalenate (TPHAP⁻) exhibited a large Stokes shift and an intramolecular charge transfer, both of which were sensitive to hydrogen-bonding media. An anionic potassium salt of TPHAP⁻ in methanol formed various aggregation states depending on the concentration examined; this was revealed by steady-state spectroscopic and fluorescence lifetime measurements. Self-assembling cadmium ions and the ligands can create several morphological crystals that are controlled by the ligand concentration, among which three new structures were determined by single-crystal analysis. The X-ray structures obtained suggest that the aggregation states of the ligand in solution can be transferred to the solid system of the porous coordination networks.     

Crystal Structure of Europium C60 Compounds

Abstract

We have studied crystal structures of europium C₆₀ compounds by high resolution x-ray diffraction measurements. In the systematic synthesis of Eu _x C₆₀ for x (0 ≤ x ≤ 6), two stable phases appear at x = 3 and 6. Eu₆C₆₀ has a bcc structure, which is an isostructure to M ₆C₆₀ (M represents an alkali or alkaline earth metal). Eu₃C₆₀ has a superstructure derived by doubling the fcc pristine C₆₀ crystal along three principal axes. This superstructure comes from an ordering of cation vacancies, which is analogous to Yb_2.75C₆₀.     

Femtosecond laser-induced cleaving of protein crystal in water solution

For precise X-ray diffraction (XRD) measurement giving the three-dimensional structure of proteins, it is important to prepare high-quality single crystals with suitable shape. As a new processing technique to obtain such protein crystals, we employed femtosecond laser-induced cleaving of protein crystal in a growth vessel containing water solution. An intact protein crystal was precisely processed without mechanical contact in its sealed growth vessel by focusing femtosecond laser pulses. We confirmed that three-dimensional processing of the crystal in its supersaturated solution was realized using multiphoton absorption and that the processing was efficiently enhanced by the cleaving behavior attributed to a photomechanical mechanism of the femtosecond laser ablation.     

Solid–Gas Phase Synthesis of Coordination Networks by Using Redox-Active Ligands and Elucidation of Their Oxidation Reaction

Formation of coordination networks is a complex process affected by a multitude of factors. Many synthetic strategies have been developed that attempt to control these factors and direct the structure of the final product. Coordination bond formation and structural assembly processes, however, typically take place either in the solution or solid states. In comparison, gas-phase network synthesis remains largely unexplored. Herein, two new two-dimensional coordination networks are obtained from the solid–gas phase reaction between ZnX₂ (X=I, Br) and the redox-active 2,5,8-tri(4-pyridyl)1,3-diazaphenalene (HTPDAP) ligand. Their structures were solved by ab initio powder X-ray diffraction analysis and feature a novel Zn halide trimeric cluster. This strategy is contrasted with a conventional solvothermal synthesis, which led to a one-dimensional coordination polymer instead. The intrinsic electroactive properties of these materials were probed by solid-state cyclic voltammetry measurements, which revealed the presence of HTPDAP and halide-based processes. Chemical oxidation of the two-dimensional networks by using NOPF₆ agent, unexpectedly, led to the formation of a nitrated analog of HTPDAP, the PF₆⁻ salt of diprotonated 4,6,7,9-tetranitro-2,5,8-tris(4-pyridyl)diazaphenalene cation (denoted N-TPDAP), which was isolated and characterized. These results provide deeper insights into the oxidation process of HTPDAP-containing networks and uncover unique redox-induced chemical transformations.     

Periodic Oscillatory Motion of a Self-Propelled Motor Driven by Decomposition of H2O2 by Catalase

A self-propelled motor driven by the enzymatic reaction of catalase adsorbed onto a filter paper floating on an aqueous solution of H₂O₂ was used to study nonlinear behavior in the motor's motion. An increase in the concentration of H₂O₂ resulted in a change from no motion to irregular oscillatory motion, periodic oscillatory motion, and continuous motion. The mechanisms underlying oscillation and mode bifurcation are discussed based on experimental results on O₂ bubble formation and growth on the underside of the motor.