Single‐Line EPR Spectra from Radicals Encapsulated in Aggregates of Amphiphilic Block Copolymers with Hydrophobic Dendritic Pendants in Water

Summary: A water‐insoluble organic 1,1‐diphenyl‐2‐picrylhydrazyl (DPPH) radical is solubilized in aqueous solutions of aggregates of amphiphilic block copolymers with hydrophobic dendritic pendants. The number (100–200) of DPPH molecules solubilized in an aggregate, which is evaluated from UV‐visible absorption spectra, is in agreement with that of the DPPH radicals determined from electron paramagnetic resonance (EPR) spectroscopy. The DPPH radicals are stably solubilized without decomposition in the polymer aggregates. The radicals exhibit a single‐line EPR absorption, which is narrowed by the interspin interaction, and indicates the assembly formation of DPPH radicals in polymer aggregates. These results suggest the effective utilization of the DPPH radical as a spin‐probe indicator in aqueous solutions.

When DPPH is solubilized in aqueous solutions of NaAMPS‐b‐G2(n3), the polymer solutions become purple colored, which is characteristic of the DPPH radical.     

A Combined Experimental and Computational Study on the Cycloisomerization of 2‐Ethynylbiaryls Catalyzed by Dicationic Arene Ruthenium Complexes

Ruthenium‐catalyzed cycloisomerization of 2‐ethynylbiaryls was investigated to identify an optimal ruthenium catalyst system. A combination of [η⁶‐(p‐cymene)RuCl₂(PR₃)] and two equivalents of AgPF₆ effectively converted 2‐ethynylbiphenyls into phenanthrenes in chlorobenzene at 120 °C over 20 h. Moreover, 2‐ethynylheterobiaryls were found to be favorable substrates for this ruthenium catalysis, thus achieving the cycloisomerization of previously unused heterocyclic substrates. Moreover, several control experiments and DFT calculations of model complexes were performed to propose a plausible reaction mechanism.     

Hydrostatic pressure effects on polymer cholesteric liquid-crystalline structure. I. Equilibrium structure of hydroxypropyl cellulose aqueous solution

Abstract

The effect of pressure on the polymer cholesteric liquid-crystalline structure of hydroxypropyl cellulose aqueous solutions was studied using reflection spectra measurements. Pressures applied to the polymer liquid crystals ranged from 1 to 2000 bar. The equilibrium reflection spectrum of the cholesteric structure shifted to longer wavelengths, showing that the cholesteric pitch of the liquid-crystalline structure increases as the applied pressure increases. At pressures higher than 200 bar the maximum wavelength of reflection shifted linearly with the increase in applied pressure. At lower pressures, the cholesteric structure was influenced by the surface plane of the quartz window.     

Quinolone Analogues 12: Synthesis and Tautomers of 2‐Substituted 4‐Quinolones and Related Compounds

The 4‐quinolone‐2‐carboxylates 4a,b were converted into the 4‐quinolone‐2‐carbohydrazides 5a,b , hydrazones 6,7,10 , and related compounds 8,9,11 . The 4‐methoxyquinoline‐2‐carboxylate 12 was also transformed into the 4‐methoxyquinoline‐2‐carbohydrazide 13 , which was modified to the hydrazone 14 and related compound 15 . The antimicrobial activities of compounds 6b and 14 are described together with the 4‐oxo and 4‐hydroxy tautomers of compounds 4‐11 in deuteriodimethyl sulfoxide and deuteriotrifluoroacetic acid.     

Palladium(Ti)-Catalyzed Claisen Rearrangement of 1-Phenylethenyl 2-Propenyl Ethers

Allyl vinyl ethers containing phenyl group at a position of vinyl ether readily undergo the Claisen rearrangement in the presence of a palladium(II) catalyst to give phenyl homoallyl ketones in good yields.     

Synthetic Approach Toward Antibiotic Tunicamycins, 4. X-Ray Crystal Structure Analysis of a Higher-Carbon Nitro Sugar

Abstract

A higher-carbon carbohydrate, a derivative of undecose has been synthesized by the potassium fluoride-catalyzed addition of a nitro sugar to a sugar aldehyde. The addition of methyl 5-de-oxy-2,3-O-isopropylidene-5-nitro-β-D-ribofuranoside to methyl 2-benzyloxycarbonylamino-2-deoxy-3,4-O-isopropylidene-α-D-galacto-dialdopyranoside-(1, 5) yielded a single diastereomer of the nitro undecose derivative. The absolute configuration of two chiral centers of the derivative has been established by the X-ray crystal structure analysis.     

Terminal Redox‐Site Effect on the Long‐Range Electron Conduction of Fe(tpy)2 Oligomer Wires on a Gold Electrode

This article completes our comprehensive understanding of the electron transport properties of our original π‐conjugated redox‐active molecular wires comprising Fe bridged by p‐phenylene linkers (tpy=2,2′:6′,2′′‐terpyridine). The Fe(tpy)₂ oligomer wires comprise three types of tpy ligands: the anchor tpy ligand ( A series) makes a junction between the wire and electrode, the bridging bis‐tpy ligand ( L series) connects the Fe(tpy)₂ units, and the terminal tpy ligand ( T series) possesses a redox site as a probe for the long‐range electron transport ability. Taking advantage of the precise tunability of the composition of the Fe(tpy)₂ oligomer wires, thus far we investigated how A and L impacted on the electron‐transport ability. The excellent long‐range electron transport ability with ultrasmall attenuation constants (β^d, 0.002 Å^?1 as the minimum) depends on L significantly [Chem. Asian J. 2009 , 4, 1361], whereas A is unrelated to the β^d value, but influences the zero‐distance electron‐transfer rate constant, k_et⁰ [J. Am. Chem. Soc. 2010 , 132, 4524]. Herein we study the influence of terminal ligand T ^x (x=1–3). β^d is independent of T , however, T³ , with a cyclometallated Ru complex as the redox site, gives rise to a k_et⁰ value greater than T¹ and T² with ferrocene. This series of simple but definitive conclusions indicates that we have reached the stage of being able to precisely design molecular wires to attain desirable single‐molecule electron conduction.