Effect of Periodic Replacement of the Heteroatom on the Spectroscopic Properties of Indole and Benzofuran Derivatives

Sb-Phenyl-N-methyl-5,6,7,12-tetrahydrodibenz[c,f][1,5]azastibocine Induces Perlecan Core Protein Synthesis in Cultured Vascular Endothelial Cells

Vascular endothelial cells synthesize and secrete perlecan, a large heparan sulfate proteoglycan that increases the anticoagulant activity of vascular endothelium by inducing antithrombin III and intensifying fibroblast growth factor (FGF)-2 activity to promote migration and proliferation in the repair process of damaged endothelium during the progression of atherosclerosis. However, the exact regulatory mechanisms of endothelial perlecan expression remain unclear. Since organic-inorganic hybrid molecules are being developed rapidly as tools to analyze biological systems, we searched for a molecular probe to analyze these mechanisms using a library of organoantimony compounds and found that the Sb-phenyl-N-methyl-5,6,7,12-tetrahydrodibenz[c,f][1,5]azastibocine (PMTAS) molecule promotes the expression of perlecan core protein gene without exhibiting cytotoxicity in vascular endothelial cells. In the present study, we characterized proteoglycans synthesized by cultured bovine aortic endothelial cells using biochemical techniques. The results indicated that PMTAS selectively induced perlecan core protein synthesis, without affecting the formation of its heparan sulfate chain, in vascular endothelial cells. The results also implied that this process is independent of the endothelial cell density, whereas in vascular smooth muscle cells, it occurred only at high cell density. Thus, PMTAS would be a useful tool for further studies on the mechanisms underlying perlecan core protein synthesis in vascular cells, which is critical in the progression of vascular lesions, such as those during atherosclerosis.

Supramolecular Chalcogen‐Bonded Semiconducting Nanoribbons at Work in Lighting Devices

This work describes the design and synthesis of a π‐conjugated telluro[3,2‐β][1]‐tellurophene‐based synthon that, embodying pyridyl and haloaryl chalcogen‐bonding acceptors, self‐assembles into nanoribbons through chalcogen bonds. The ribbons π‐stack in a multi‐layered architecture both in single crystals and thin films. Theoretical studies of the electronic states of chalcogen‐bonded material showed the presence of a local charge density between Te and N atoms. OTFT‐based charge transport measurements showed hole‐transport properties for this material. Its integration as a p‐type semiconductor in multi‐layered Cu^I‐based light‐emitting electrochemical cells (LECs) led to a 10‐fold increase in stability (38 h vs. 3 h) compared to single‐layered devices. Finally, using the reference tellurotellurophene congener bearing a C−H group instead of the pyridyl N atom, a herringbone solid‐state assembly is formed without charge transport features, resulting in LECs with poor stabilities (<1 h).

Systematic Study of Pnictogen-Fused Heterofluorenes

Heteroatom-fused π-conjugated molecules have attracted considerable attention, and various elements for such fusion have been investigated. Herein, we focused on pnictogen-fused heterofluorenes. The structures, reactivity with O₂ and I₂, coordination ability to AuCl, and photophysical properties were systematically studied to better understand the effects of pnictogen atoms on the nature of π-conjugated molecules.

A tellura-Baeyer-Villiger oxidation: one-step transformation of tellurophene into chiral tellurinate lactone

Baeyer-Villiger (BV) oxidation is a fundamental organic reaction, whereas the hetero-BV oxidation is uncharted. Herein, a tellura-BV oxidation is discovered. By oxidizing a tellurophene-embedded and electron-rich polycycle (1) with mCPBA or Oxone, an oxygen atom is inserted into the Te-C bond of the tellurophene to form tellurinate lactone mono-2. This reaction proceeds as follows: (i) 1 is oxidized to the tellurophene Te-oxide form (IM-1); (ii) IM-1 undergoes tellura-BV oxidation to give mono-2. Moreover, the hybrid trichalcogenasumanenes 7 and 8 are, respectively, converted to tellurinate lactones mono-9 and mono-10 under the same conditions, indicating that tellura-BV oxidation shows high chemoselectivity. Due to the strong secondary bonding interactions between the Te[double bond, length as m-dash]O groups on tellurinate lactones, mono-2, mono-9, and mono-10 are dimerized to form U-shaped polycycles 2, 9, and 10, respectively. Notably, mono-2, mono-9, mono-10, and their dimers show chirality. This work enables one-step transformation of tellurophene into tellurinate lactone and construction of intricate polycycles.

2,3-Diarylbenzo[b]arsole: Structural Modification and Polymerization for Tuning of Photophysical Properties

2,3-Diarylbenzo[b]arsoles were synthesized from zirconacycles and diiodophenylarsine. The structural modification to the luminophore was attained through diarylacetylene precursors, Suzuki-Miyaura coupling, and oxidation of the arsenic atom. The emission properties were controlled according to these modifications. The 2,3-diarylbenzo[b]arsoles showed aggregation-induced emission enhancement; the stronger emission was observed in the solid states than in solutions. In addition, Suzuki-Miyaura polycondensation and olefin metathesis polymerization produced main- and side-chain polymers, respectively. The resultant polymers showed different emission behaviors such as aggregation caused quenching and aggregation induced emission enhancement.

Steric effects on the intramolecular charge transfer fluorescence of benzo[b]thiophene-1,1-dioxide bridged macrocages

Intramolecular charge transfer (ICT) fluorescence has been widely investigated and exploited in sensor molecules. However, steric effects on the ICT fluorescence properties have rarely been reported so far, although research in this area would promote an understanding of the basics of solvation. Herein, we report the detailed fluorescence properties of bis(trimethylsilyl)benzo[b]thiophene-1,1-dioxide (TMSBTO2) and its caged cyclophanes and non-cage isomers, which demonstrate ICT fluorescence in various solutions. The fluorescence band maxima for these benzo[b]thiophene-1,1-dioxides (BTO2s) showed a red-shift with increasing solvent polarity, confirming ICT fluorescence characteristics. The linearity of the Lippert-Mataga plots was confirmed for all ICT fluorescence measured in hexane, toluene, AcOEt, CH2Cl2, and EtOH. The slopes of the plots decreased in the following order: TMSBTO2, non-cage isomers, and caged BTO2s. It is concluded that the Onsager radii for these BTO2s were increased in the abovementioned order, assuming that the difference in the dipole moments between the excited and ground states for these BTO2s was identical.

2-Arylbenzo[b]arsoles: an experimental and computational study on the relationship between structural and photophysical properties

Benzo[b]arsole derivatives, being arsenic analogues of indole, were synthesized by utilizing a safely prepared arsenic precursor. The structural and photophysical properties of the obtained 2-arylbenzo[b]arsoles were experimentally and computationally studied in comparison with those of 1,2,5-triarylarsoles and 9-phenylarsafluorene. It was found that the emission color and/or quantum yield were significantly affected by substituents on the luminescent center and metal-coordination to the arsenic atom. This is the first study on the structure-property relationship of benzo[b]arsole derivatives.

Zn(ii)2,9-dimethyl-1,10-phenanthroline stimulates cultured bovine aortic endothelial cell proliferation

Vascular endothelial cells cover the luminal surface of blood vessels in a monolayer. Proliferation of these cells is crucial for the repair of damaged endothelial monolayers. In the present study, we identified a zinc complex, Zn(ii)2,9-dimethyl-1,10-phenanthroline (Zn-12), that stimulates the proliferation of bovine aortic endothelial cells in a culture system. No such stimulatory activity was observed for the ligand alone or in combination with other metals; however, the ligand combined with iron weakly stimulated the proliferation, as evidenced by the [³H]thymidine incorporation assay. Inorganic zinc weakly but significantly stimulated proliferation, and intracellular accumulation of zinc was similar between inorganic zinc and Zn-12 treatment, suggesting that the mechanisms by which Zn-12 stimulates vascular endothelial cell proliferation contain processes that differ from those by which inorganic zinc stimulates proliferation. Although expression of endogenous fibroblast growth factor-2 (FGF-2) and its receptor FGFR-1 was unchanged by Zn-12, both siRNA-mediated knockdown of FGF-2 and FGFR inhibition partly but significantly suppressed the stimulation of vascular endothelial cell proliferation by Zn-12, indicating that the zinc complex activates the FGF-2 pathway to stimulate proliferation. Phosphorylation of ERK1/2 and MAPKs was induced by Zn-12, and PD98059, a MEK1 inhibitor, significantly suppressed the stimulatory effect of Zn-12 on vascular endothelial cell proliferation. Therefore, it is suggested that Zn-12 activates the FGF-2 pathway via activation of ERK1/2 signaling to stimulate vascular endothelial cell proliferation, although FGF-2-independent mechanisms are also involved in the stimulation. Zn-12 and related compounds may be promising molecular probes to analyze biological systems of vascular endothelial cells.

Stimulation of vascular endothelial cell proliferation by Zn-12 can be mediated by the ERK1/2 activation independently of the FGF-2-FGFR pathway. Additionally, there may be other pathways involved in the Zn-12 stimulation.

The Dawn of Functional Organoarsenic Chemistry

Organoarsenic chemistry was actively studied until the middle of 20th century. Although various properties of organoarsenic compounds have been computationally predicted, for example, frontier orbital levels, aromaticity, and inversion energies, serious concern to the danger of their synthetic processes has restricted experimental studies. Conventional synthetic routes require volatile and toxic arsenic precursors. Recently, nonvolatile intermediate transformation (NIT) methods have been developed to safely access functional organoarsenic compounds. Important intermediates in the NIT methods are cyclooligoarsines, which are prepared from nonvolatile inorganic precursors. In particular, the new approach has realized experimental studies on conjugated arsenic compounds: arsole derivatives. The elucidation of their intrinsic properties has triggered studies on functional organoarsenic chemistry. As a result, various kinds of arsenic-containing π-conjugated molecules and polymers have been reported for the last few years. In this minireview, progress of this recently invigorated field is overviewed.

Synthesis, structure and aromaticity of carborane-fused carbo- and heterocycles

The results of molecular structures, NMR data, and NICS (nucleus-independent chemical shift) and ISE (isomerization stabilization energy) values as well as molecular orbital analyses clearly suggest the presence of considerable aromatic character in the exo five-membered ring of carborane-fused carbo- and heterocycles and considerable conjugation between a 3-D carborane and a fused 2-D π-ring system.

Conjugation between a 3-D icosahedral carborane and a fused 2-D π-ring system is ambiguous. To address this issue, we prepared several carborane-fused carbo- and heterocycles. Detailed studies on their molecular structures, NMR data, and NICS (nucleus-independent chemical shift) and ISE (isomerization stabilization energy) values as well as molecular orbital analyses clearly suggest the presence of (1) considerable aromatic character in the exo five-membered ring of carborane-fused carbo- and heterocycles and (2) considerable conjugation between a 3-D carborane and a fused 2-D π-ring system. These results will shed some light on the design of new carborane-based materials.

Versatile telluracycle synthesis via the sequential electrophilic telluration of C(sp2)-Zn and C(sp2)-H bonds

We report herein a new approach for the synthesis of tellurium-bridged aromatic compounds based on the sequential electrophilic telluration of C(sp2)-Zn and C(sp2)-H bonds with tellurium(iv) chlorides. A combination of transition metal-catalyzed (migratory) arylmetalation of alkynes and sequential telluration allows for the expedient construction of a library of functionalized benzo[b]tellurophenes. Furthermore, a variety of heteroarene-fused benzotellurophenes and other novel tellurium-embedded polycyclic aromatics can be readily synthesized from the corresponding 2-iodoheterobiaryls.

Toxicology of organic-inorganic hybrid molecules: bio-organometallics and its toxicology

Bio-organometallics is a research strategy of biology that uses organic-inorganic hybrid molecules. The molecules are expected to exhibit useful bioactivities based on the unique structure formed by interaction between the organic structure and intramolecular metal(s). However, studies on both biology and toxicology of organic-inorganic hybrid molecules have been incompletely performed. There can be two types of toxicological studies of bio-organometallics; one is evaluation of organic-inorganic hybrid molecules and the other is analysis of biological systems from the viewpoint of toxicology using organic-inorganic hybrid molecules. Our recent studies indicate that cytotoxicity of hybrid molecules containing a metal that is nontoxic in inorganic forms can be more toxic than that of hybrid molecules containing a metal that is toxic in inorganic forms when the structure of the ligand is the same. Additionally, it was revealed that organic-inorganic hybrid molecules are useful for analysis of biological systems important for understanding the toxicity of chemical compounds including heavy metals.

Synthesis and characterization of heterofluorenes containing four-coordinated group 13 elements: theoretical and experimental analyses and comparison of structures, optical properties and electronic states

Herein, we report the series of heterofluorenes containing four-coordinated group 13 elements.

Tellurophenes with delocalized π-systems and their extended valence adducts

The π-conjugated 2,5-substituted tellurophene compounds 2,5-bis(2-(9,9-dihexylfluorene))tellurophene (1) and 2,5-diphenyltellurophene (3) were synthesized through ring closing reactions of 1,4-substituted butadiyne. The oxidative addition of Br(2) to tellurophene compounds 1 and 3 was studied through absorption spectroscopy, NMR, electrochemistry, X-ray crystallography, and density functional theory (DFT) calculations. When Br(2) adds to the tellurium center the absorption spectrum shifts to a lower energy. From electrochemistry and DFT calculations we show that this is caused by lowering the lowest unoccupied orbital. The highest occupied orbital is also lowered, but to a lesser extent. This shift in absorption spectrum and lowering of the oxidation potential can provide a method to modify tellurophene containing materials. The two-electron oxidative addition is promising for catalyzing energy storage reactions.

Boron in disguise: the parent "fused" BN indole

"Fused" BN indoles are an emerging class of boron-containing indole mimics, featuring geometric structure and electophilic aromatic substitution reactivity similar to those of indoles but exhibiting distinct electronic structure, leading to unique optoelectronic properties. Herein we report the synthesis of the parent N-H BN indole and provide a head-to-head comparison of the structural features, pK(a) values, and optoelectronic properties of this hybrid organic/inorganic indole with the classic natural indole.