Anion recognition by silanetriol in acetonitrile.

The anion recognition ability of 2,4,6-triisopropylphenylsilanetriol 5 has been evaluated by 1H NMR titrations in MeCN-d3. The anion recognition ability of silanetriol 5 was greater than those of the structurally related silanediols and silanemono-ol, although less effective than those of 1,3-disiloxane-1,3-diol and 1,3-disiloxane-1,1,3,3-tetraol. From the comparison of the association constants and DFT calculations, all three silanol groups of 5 cooperatively hydrogen bonded to anionic species. The catalytic ability of silanetriol 5 for the addition of indole to ß-nitrostyrene in CH2Cl2 has also been evaluated. Silanetriol 5 acts as a more effective organocatalyst than the corresponding silanediol in this reaction.

Synthesis of a chiral metallo-capsule composed of concave molecules and chirogenesis upon fullerene binding.

An enantiopure molecular capsule was synthesized quantitatively using complexation of four phosphangulenes as concave molecules with four Zn2+ ions and applied to fullerene binding and chirogenesis. The capsule encapsulated selectively fullerene and its derivatives based on the size of cavity. The fullerene C60 incorporated in the capsule exhibited induced-CD signals at the transitions of C60.

Correction: Synthesis of figure-of-eight helical bisBODIPY macrocycles and their chiroptical properties.

Correction for 'Synthesis of figure-of-eight helical bisBODIPY macrocycles and their chiroptical properties' by Makoto Saikawa et al., Chem. Commun., 2016, 52, 10727-10730.

Correction: A facile and high-yield formation of dipyrrin-boronic acid dyads and triads: a light-harvesting system in the visible region based on the efficient energy transfer.

Correction for 'A facile and high-yield formation of dipyrrin-boronic acid dyads and triads: a light-harvesting system in the visible region based on the efficient energy transfer' by Masaki Yamamura et al., Org. Biomol. Chem., 2015, 13, 2574-2581.

Activation of invariant natural killer T cells stimulated with microbial α-mannosyl glycolipids.

Some synthetic and bacterial glycolipids presented by CD1d specifically activate invariant NKT (iNKT) cells bearing an invariant Vα14-Jα18 (mouse) or Vα24-Jα18 (human) TCR. The antigenic glycolipids identified to date consist of two hydrophobic chains and an α-glycoside in which the 2'-OH group is in the cis orientation toward the anomeric group, namely, either an α-galactoside or an α-glucoside. Several microbial α-mannosyl glycolipids, in which the 2'-OH group is in the trans orientation, were herein examined to establish whether they have potential to activate iNKT cells. We found that α-mannnosyl1-3 (6'-O-acyl α-mannosyl)-1-1 monoacylglycerol and cholesteryl 6'-O-acyl α-mannoside, found in Saccharopolyspora and Candida albicans, respectively, induced the activation of iNKT cells, dependent on CD1d. In contrast, α-mannosyldiacylglycerol found in Streptococcus suis or α-mannosylceramide demonstrated markedly less antigenicity for iNKT cells. The potentially antigenic α-mannosyl glycolipids contributed to the protection of mice against infection with S. pneumoniae in which iNKT cells have previously been found to participate. Furthermore, these glycolipids induced the production of proinflammatory cytokines by macrophages, thereby suggesting their recognition by specific pattern recognition receptors (PRRs). Collectively, these results suggest that these microbial α-mannosyl glycolipids are capable of being recognized by both the invariant TCR and PRRs and inducing immune responses.

An efficient synthetic method for organometallic radicals: structures and properties of gold(i)-(nitronyl nitroxide)-2-ide complexes.

One-pot synthesis of (nitronyl nitroxide)-gold(i)-phosphine (NN-Au-P) complexes has been developed using chloro(tetrahydrothiophene)gold(i), phosphine ligands, nitronyl nitroxide radicals, and sodium hydroxide. The NN-Au-P complexes can be easily handled because they were quite stable under aerated conditions in both solution and crystalline states. They showed weak absorption bands with vibrational structures in the 450-650 nm region. The oxidation potentials assigned to the NN moieties of NN-Au-P complexes with aromatic phosphines were observed around -0.1 V vs. Fc/Fc+ (-0.11 V for NN-Au-1, -0.08 V for NN-Au-2, -0.13 V for NN-Au-5, and -0.07 V for NN-Au-6), somewhat lower than that of NN-Au-P complexes with aliphatic phosphines (-0.25 V for NN-Au-3 and -0.17 V for NN-Au-4).

m-Phenylene-Linked Dipyrrins and Their Boron-Difluoride Complexes as Variously Shaped Macrocyclic Oligomers.

The effectiveness of a m-phenylene linker, which has rigidity as well as rotational flexibility, is presented to produce a series of variously shaped macrocyclic oligomers of dipyrrins and BODIPYs, whose structures were revealed by X-ray crystallography and 1H NMR analysis. Although the chemical structures of the repeating units are the same for dipyrrin/BODIPY oligomers, their absorbance and emission properties changed significantly depending on the size and shape of the macrocycles.

Synthesis of figure-of-eight helical bisBODIPY macrocycles and their chiroptical properties.

A macrocyclic bisBODIPY (bis(boron-dipyrromethene)) complex [1B2] with a figure-of-eight helicity was synthesized and successfully resolved. [1B2] was proven to be one of the most efficient red-emitting CPL (circularly polarized luminescence) fluorophores reported to date (λ = 663 nm, |glum| = 9 × 10(-3), ΦF = 0.58).

Regioselective and Stereospecific Dehydrogenative Annulation Utilizing Silylium Ion-Activated Alkenes.

Treatment of dialkylbenzylsilanes (1) with trityl tetrakis(pentafluorophenyl)borate (TPFPB) afforded the corresponding silylium ions in equilibrium with their intra- or intermolecular π-complexes, which underwent dehydrogenative annulation with various alkenes to form 1,2,3,4-tetrahydro-2-silanaphthalenes (4) in up to 82% isolated yield. Sterically bulkier substituents on the silicon atom tended to increase the yield of cyclic products 4. The annulation products retained the stereochemistry in cases of the reactions using internal alkenes. The use of diisopropyl(1-naphthyl)silane (2) instead of 1 also resulted in annulation to obtain the 2,3-dihydro-1-sila-1H-phenalene derivatives 6. Electrophilic aromatic substitution at the 8-position was predominant, despite the two potentially reactive positions on the naphthyl group. The steric hindrance of the naphthyl group prevented addition of the cis-alkene to the silylium ion, which would considerably decrease yields of the desired products from 2 compared to those from 1.

Synthesis and Chiroptical Properties of a Ring-Fused BODIPY with a Skewed Chiral π Skeleton.

A twisted chiral boron-dipyrrin complex (BODIPY) was synthesized by oxidative annulation of the biphenyl units at the ß positions. The chiral BODIPY has two asymmetric carbons in the large planar skeleton, which were generated upon the ring-fused reaction. Its π-elongated and twisted structure resulted in the Cotton effect in the red region (λmax = 614 nm, Δε = 60 M(-1)·cm(-1)) as well as the strong fluorescence (ΦF = 0.73) and circularly polarized luminescence (CPL).

Synthesis of a new family of ionophores based on aluminum-dipyrrin complexes (ALDIPYs) and their strong recognition of alkaline earth ions.

Mononuclear and dinuclear aluminum-dipyrrin complexes (ALDIPYs) were synthesized as a new family of ionophores. They exhibited colorimetric and fluorometric responses to alkaline earth ions in an aqueous mixed solvent. The strong recognition was achieved via multipoint interactions with the oxygen atoms appropriately incorporated into the ligand framework.

Chiroptical switching caused by crystalline/liquid crystalline phase transition of a chiral bowl-shaped molecule.

The liquid crystal of a chiral bowl-shaped molecule having a central-phosphorus atom and long alkyl chains was developed. The DSC and XRD analyses suggested the formation of columnar liquid crystals of both the enantiopure and racemic compounds. The condensed phase of the enantiopure compound in a thin film exhibited a significant signal in CD spectra, which was switched by a reversible phase transition between the crystalline and liquid crystalline states.

Synthesis of Phosphorus-Centered and Chalcogen-Bridged Concave Molecules: Modulation of Bowl Geometries and Packing Structures by Changing Bridging Atoms.

A series of phosphorus-centered concave molecules having oxygen and sulfur as bridging atoms, C3v-symmetric P4 and Cs-symmetric P2 and P3, were newly synthesized. The packing diagrams of the concave molecules P1-P4 are dependent on the bridging atoms, columnar structures for P1 and P4, and zigzag structures for P2 and P3. The bowl depth becomes shallower in the order of P1, P2, P3, and P4 as the number of bridging sulfur atoms increases.

A Hierarchical Self-Assembly System Built Up from Preorganized Tripodal Helical Metal Complexes.

The hierarchical organization strategy has realized elaborate supramolecular structures that are difficult to achieve by a one-pot thermodynamically driven self-assembly. Self-assembly via Schiff base formation of the preorganized tripodal helical unit 2(2+), which is composed of the tris(bipyridyl) ligand 1 and octahedral metal ion (Ru(II) and Fe(II)), lead to two supramolecular structures, i.e., a macrobicyclic dimer and an interlocked helicate. Notably, the interlocked helicate had a unique motif with an elongated shape (∼ 58 Å) and linearly aligned metal centers with homochiral configurations (all-Δ or all-Λ), which shows potential for allosteric regulation based on the long-range transmittance of the structural information.

2,2'-Disilylazobenzenes featuring double intramolecular nitrogen∙∙∙silicon coordination: a photoisomerizable fluorophore.

(E)-4,4'-Dimethyl-2,2'-disilylazobenzenes were synthesized. Double intramolecular N∙∙∙Si coordination in the bis(fluorodimethylsilyl) and bis(trifluorosilyl) derivatives was confirmed using X-ray crystallographic analysis and (29)Si NMR spectroscopy. In the absorption bands, due to the π,π* transitions, introduction of silyl groups was found to cause a bathochromic shift. In contrast to most azobenzenes, which do not fluoresce at all, the (E)-2,2'-bis(trifluorosilyl)azobenzene derivative with the N∙∙∙Si coordination fluoresced a yellow-green colour at room temperature. Methyl and trifluorosilyl groups lowered the n and π* orbitals, as revealed by DFT calculations. As a result, the lowest singlet excitation energy state is found to be the allowed π,π* transition, different from the forbidden n,π* transition in general azobenzenes, as revealed by TD-DFT calculations. The allowed transition character of the lowest singlet excited state and moderately rigid conformation of the azo moiety, provided by the double N∙∙∙Si coordination, account for the fluorescence emission. Nevertheless, the N∙∙∙Si coordination is weak enough to be cleaved upon photoexcitation, and thus the (E)-2,2'-disilylazobenzenes undergo photoisomerization to the (Z)-isomers. Both the photoisomerization and fluorescence emission properties of the azobenzene moiety have been achieved for the first time. After photoisomerization of the (E)-2,2'-disilylazobenzenes to the corresponding (Z)-isomer, they do not fluoresce. This change in the fluorescence intensity upon photoisomerization is useful for the regulation of fluorescence properties. Therefore, this compound can be recognized as a unique photoisomerizable fluorophore to regulate the fluorescence intensity using a single light source.

Tuning the depth of bowl-shaped phosphine hosts: capsule and pseudo-cage architectures in host-guest complexes with C60 fullerene.

Bowl-shaped phosphine molecules, whose bowl geometry can be controlled by a variation of the axial substituent, were synthesized, and used as host molecules to encapsulate C60. Host molecules with relatively shallow bowls formed a chiral capsule, while hosts with deeper bowls formed an achiral pseudo-cage.

Zwitterionic N2O2-Type Protonated Dipyrrin Bearing a Phosphate Anionic Moiety as a pH-Responsive Fluorescence Indicator.

Zwitterionic protonated-dipyrrin 1 bearing a phosphate unit was synthesized from the N2O2-type tetradentate dipyrrin ligand. Compound 1 is in equilibrium with the deprotonated form 1' with a pKa value of 5.8. Compound 1 exhibited a pH-responsive fluorescence under physiological conditions; the fluorescence intensity increased in aqueous media as the pH increased. In living cells, 1 also exhibited emission responsive to pH. Thus, 1 should be applicable as a pH probe for detecting tumor cells.

Detection of ethanol in alcoholic beverages or vapor phase using fluorescent molecules embedded in a nanofibrous polymer.

An alcohol sensor was developed using the solid-state fluorescence emission of terphenyl-ol (TPhOH) derivatives. Admixtures of TPhOH and sodium carbonate exhibited bright sky-blue fluorescence in the solid state upon addition of small quantities of ethanol. A series of terphenol derivatives was synthesized, and the effects of solvent polarities and the structures of these π-conjugated systems on their fluorescence were systematically investigated by using fluorescence spectroscopy. In particular, π-extended TPhOHs and TPhOHs containing electron-withdrawing groups exhibited significant solvatochromism, and fluorescence colors varied from blue to red. Detection of ethanol contents in alcohol beverages (detection limit ∼ 5 v/v %) was demonstrated using different TPhOHs revealing the effect of molecular structure on sensing properties. Ethanol contents in alcoholic beverages could be estimated from the intensity of the fluorescence elicited from the TPhOHs. Moreover, when terphenol and Na2CO3 were combined with a water-absorbent polymer, ethanol could be detected at lower concentrations. Detection of ethanol vapor (8 v/v % in air) was also accomplished using a nanofibrous polymer scaffold as the immobilized sensing film.

Crystal structure of the one-dimensional metal-organic polymer catena-poly[[tris(µ-2,4,6-tri-methyl-benzoato-κ(2) O:O')dizinc]-µ-2,4,6-tri-methyl-benzoato-κ(2) O:O'].

The title complex, [Zn2(C10H11O2)4] n , has a one-dimensional polymeric structure. The asymmetric unit consists of two zinc atoms bridged by three 2,4,6-tri-methyl-benzoate anions and one bidentate bridging 2,4,6-trimethylbenzoate anion. The [Zn2(C9H11CO2)3] cluster units are inter-molecularly linked to form a one-dimensional polymer, which propagates in the direction of the crystallographic b axis. The Zn atoms adopt a tetra-hedral geometry. The Zn-O bond lengths in the intra-molecular bridges are slightly shorter than those in the inter-molecular bridges.

A facile and high-yield formation of dipyrrin-boronic acid dyads and triads: a light-harvesting system in the visible region based on the efficient energy transfer.

Artificial light-harvesting systems, Ar,O-BODIPY dyads and triads conjugated with a light harvester, were synthesized in high yield by the reaction of an N2O2-type dipyrrin with boronic acids. Dyad 2 having a pyrene unit underwent quantitative Förster resonance energy transfer (FRET) from the antenna unit, pyrene, to the fluorophore unit, Ar,O-BODIPY. Triads 3·5 and 4·5 were quantitatively prepared by mixing pyridine-appended compounds 3 and 4 with saloph·Zn complex 5, respectively. Triad 4·5 underwent efficient FRET from the saloph·Zn complex unit to the fluorophore unit at the rate of 2.0 × 10(11) s(-1). Interestingly, the fluorescence quenching process in the excited state of the triad 3·5 took place following the energy transfer event. Thus, appropriate positioning of the energy donor and acceptor is necessary to construct a highly efficient FRET system.