High-Field Nuclear Magnetic Resonance Studies Reveal New Structural Landscape of Sulfur-Vulcanized Natural Rubber.

Despite intensive research efforts over the past 3 decades, the structural analysis of sulfur-vulcanized natural rubber (NR) remains challenging owing to the complexity and low population of its sulfur moieties. Herein, solid vulcanized NR samples and NR samples reacted with sulfur and other reactants in an organic solvent were analyzed by solid-state NMR with fast magic-angle spinning and solution NMR, respectively. The present high-field two-dimensional NMR analysis revealed six novel sulfur moieties in these samples, including cyclic sulfides, cyclic di/polysulfides, and crosslinked structures with a vinylidene group.

Helix-helix inversion of an optically-inactive π-conjugated foldamer triggered by concentration changes of a single enantiomeric guest leading to a change in the helical stability.

A preferred-handed helicity induced in an optically-inactive poly(phenyleneethynylene)-based foldamer bearing carboxylic acid pendants upon complexation with a single enantiomeric diamine was subsequently inverted into the opposite helix upon further addition of the diamine, accompanied by a remarkable change in the stability of the helices.

Chiral tether-mediated stabilization and helix-sense control of complementary metallo-double helices.

A series of novel Pt-linked double helices were prepared by inter- or intrastrand ligand-exchange reactions of the complementary duplexes composed of chiral or achiral amidine dimer and achiral carboxylic acid dimer strands joined by -Pt-acetylide complexes with PPh ligands using chiral and achiral chelating diphosphines. The structure and stability of the Pt-linked double helices were highly dependent on the diphosphine structures. An interstrand ligand exchange took place with chiral and achiral 1,3-diphosphine-based ligands, resulting in -Pt-bridged double helices, whose helical structures were quite stable even in dimethyl sulfoxide (DMSO) due to the interstrand cross-link, whereas a 1,2-diphosphine-based ligand produced non-cross-linked -Pt-linked duplexes, resulting from an intrastrand ligand-exchange that readily dissociated into single strands in DMSO.

Synthesis of nickel(II) azacorroles by Pd-catalyzed amination of α,α'-dichlorodipyrrin Ni(II) complex and their properties.

Synthesis of nickel(II) complexes of meso-aryl-substituted azacorroles was performed by Buchwald-Hartwig amination of a dipyrrin Ni(II) complex with benzylamine through C-N and C-C coupling. The highly planar structure of Ni(II) azacorroles was elucidated by X-ray diffraction analysis. (1)H NMR analysis and nucleus independent chemical shift (NICS) calculation on Ni(II) azacorrole revealed its distinct aromaticity with [17]triaza-annulene 18π conjugation.