Spectroscopic and Theoretical Studies on Conformational Stability of Benzyl Methyl Ether.

Conformer-selected electronic and vibrational spectra of benzyl methyl ether and its terminal methyl group-substituted derivative in a supersonic jet have been measured using ultraviolet (UV)-UV hole burning and fluorescence-detected infrared spectroscopy to investigate the conformational stability of flexible molecules. Various quantum chemical calculations as well as experimental observations reveal the coexistence of three conformers with different CCOC dihedral angles and side-chain orientations relative to the benzene ring plane. Vibrational analysis in the excited state with time-dependent density functional theory and IR simulations containing anharmonic coupling sufficiently reproduce the experimental results, suggesting that these three conformers can be distinguished into one gauche-conformer and two trans-ones with respect to the CCOC dihedral angle. We also observe that the gauche conformer exhibits higher-frequency CH2 modes. The natural bond orbital analysis indicates that this phenomenon is attributed to the electron delocalization from the non-bonding orbitals and the C-O orbitals associated with the neighboring oxygen atom, which leads to a conformer dependence of the methylene C-H bond strength.

Photo-induced Morphological Changes of Lipid Bilayer Vesicles Enabled by a Visible-Light-Responsive Azo Compound.

Living cells and organelles are separated by a lipid membrane bilayer. It is possible to induce morphological changes in this membrane by disturbing the order of the membrane using external stimuli and understanding the details of this mechanism is expected to be applicable to intracellular transport. DBA (DBAB-BODIPY-aminopropyl), which contains (1) a DBAB (4-[di(biphenyl-4-yl)amino]azobenzene) moiety that undergoes photo-isomerization under visible light irradiation, and (2) a BODIPY (borondipyrromethene) fluorophore was synthesized. The π-π* transition absorptions of both the azo moiety and that of BODIPY moiety in DBA were observed, independently. The photo-isomerization rate constant of the DMSO solution of DBA at 299K is 5.5 ×10-3/s. The structure of the fluorescent group in DBA did not readily influence the isomerization. Upon introducing DBA into the lipid bilayer membranes of a vesicle suspension and irradiating the vesicles with visible light to isomerize the azo group, a morphological change in of the vesicles was observed due to the disturbance of the membrane order. Thus, DBA is a useful molecule for artificial modulation of the lipid membrane morphology.

Thiopyrylium Scaffolds from the Lewis/Brønsted-Acid-Promoted Cyclization of Thioethers.

A series of acene- or heteroacene-fused thiopyrylium salts was synthesized from diarylthioethers that contain formyl groups via an intramolecular Friedel-Crafts cyclization. The reaction, promoted by a Lewis or Brønsted acid, afforded the new thiopyrylium salts in good yield. Kinetic investigations and density functional theory calculations were used to explore the mechanism of the reaction. The electronic structures of the thiopyrylium salts were examined by UV-vis absorption spectroscopy, which afforded insight into the electronic transitions within these molecules.

Reaction of ketone hydrazones with TeCl4: isolation and reactions of novel divinyl telluride.

The reaction of acetophenone hydrazones with TeCl4 in the presence of DBU gave a mixture of divinyl ditellurides and divinyl tellurides, which easily reacted with Cu powder in refluxing toluene to afford divinyl tellurides in good yields. The reaction of divinyl tellurides with bromine (1.2 eq.) gave the corresponding tellurium dibromide rather than the addition of the double bond whereas 3 molar amount of bromine gave excess brominated and oxidized products. The reaction of divinyl tellurides with 2-(trimethylsilyl)phenyl triflate in the presence of CsF gave (E)-2-alkenyldiaryl tellurides in good yields.

Synthesis and Properties of Thiophene-Fused Thiopyrylium Salts.

A new family of thiophene-fused thiopyrylium salts has been synthesized via Lewis-acid-induced Rieche formylation, followed by an intramolecular Friedel-Crafts cyclization of a series of diarylthioethers. Moreover, in the case of diarylthioethers that bear formyl groups, Lewis-acid-promoted intramolecular cyclizations afforded novel thiophene-fused bisthiopyrylium salts in good yield. The electronic structures of the new compounds were determined experimentally by NMR and UV-vis absorption spectroscopy and theoretically investigated by density functional theory calculations. The results of our examinations revealed effective conjugation of the π-electrons over the entire linearly fused heteroacene framework.

Buchwald-Hartwig Amination of Phosphinines and the Effect of Amine Substituents on Optoelectronic Properties of the Resulting Coupling Products.

The Buchwald-Hartwig amination of a phosphinine bearing a bromophenyl moiety was carried out using a dinuclear Ni catalyst. A variety of monoarylamines, diarylamines, and alkylamine, as well as heterocycles, were successfully converted into novel phosphinines bearing amine units. The photophysical properties of these novel phosphinines were examined, including the substituent-dependent absorption/emission features and intramolecular charge-transfer interactions.

2,5-Diaryltellurophenes: Effect of Electron-Donating and Electron-Withdrawing Groups on their Optoelectronic Properties.

The transformation of 1,2-bis(1-arylvinyl)ditellurides into 2,5-diaryltellurophenes by sequential ditelluride exchange and thermal intramolecular cyclization reactions is presented, and the optoelectronic properties of a series of 2,5-diaryltellurophenes with both electron-donating and electron-withdrawing aryl substituents are disclosed. Furthermore, the multicolored emissive tellurophenes in solution at room temperature have been demonstrated.

Small fluorescent molecules for monitoring autophagic flux.

We have developed two types of fluorescent probes, DALGreen and DAPGreen, for monitoring autophagy, that exhibit fluorescence upon being incorporated into autophagosomes. DALGreen enhances its fluorescence at acidic pH, which is favorable for monitoring late-phase autophagy, whereas DAPGreen remains fluorescent with almost constant brightness during the autophagic process. With these probes that stain autophagosomes as they are being formed, the real-time change of autophagic phenomena of live cells may be traced, which is an advantage over conventional approaches with small molecules that stain mature autophagosomes. The use of both dyes allows monitoring of the membrane dynamics of autophagy in any type of cell without the need for genetic engineering, and therefore, will be useful as a tool to study autophagic phenomena.

Live Cell Imaging of Mitochondrial Autophagy with a Novel Fluorescent Small Molecule.

There has been a growing interest in mitophagy, mitochondria-selective autophagy, which plays an essential role in maintaining intracellular homeostasis. We have developed a small-molecule fluorescent probe, Mtphagy Dye, for visualizing mitophagy, which was readily synthesized from a known perylene derivative, perylene-3,4-dicarboxylic anhydride. Mtphagy Dye has suitable fluorescent properties for detecting mitochondrial acidification during mitophagy in the long-wavelength region that does not damage mitochondria. Using Mtphagy Dye, we were able to visualize mitophagy with both cases of Parkin-dependent and -independent HeLa cells.

Stable 1H-Benzo[c]thio- and 1H-Benzo[c]selenophen-2-ium Tetrafluoroborates: Insight into Electronic Structures, Electrochemical Behavior, and Reactivity.

The synthesis of 1H-benzo[c]thio- and 1H-benzo[c]selenophen-2-ium tetrafluoroborates by the reaction of triphenylcarbenium tetrafluoroborate with 1-ethylidene-1,3-dihydrobenzo[c]thiophene or 1-ethylidene-1,3-dihydrobenzo[c]selenophene, respectively, is reported. The electronic structure of these novel 1H-benzo[c]chalcogenophenium salts was examined on the basis of their electronic spectra, whereby transitions were assigned in agreement with theoretical calculations. Electrochemical measurements revealed irreversible one-electron reduction waves for these 1H-benzo[c]chalcogenophenium salts.

First Isolation of Bicyclic Ditellurides from the Reaction of Camphor Hydrazone with Tellurium Tetrachloride.

Reaction of camphor hydrazone with TeCI4 under basic conditions gave an isomeric mixture of vinyl ditelluride and Wagner-Meerwein rearranged ditelluride. Initially formed tellurocamphor enolized and oxidized to give vinyl telluride, whereas tellurocamphor complexed with TeC4 to afford carbocation, which rearranged in a Wagner-Meerwein manner to afford the rearranged ditelluride. Photolysis of ditelluride in methyl methacrylate solution gave the radical polymerization product, PMMA, in which ditelluride acted as a radical initiator.

One-pot synthesis of dibenzo[b,h][1,6]naphthyridines from 2-acetylaminobenzaldehyde: application to a fluorescent DNA-binding compound.

Dibenzo[b,h][1,6]naphthyridines were synthesized in one pot by reacting 2-acetylaminobenzaldehyde with methyl ketones under basic conditions via four sequential condensation reactions. This method was also applied to the synthesis of 1,2-dihydroquinolines. 6-Methyl-1,6-dibenzonaphthyridinium triflates showed strong fluorescence, and the fluorescence intensities were changed upon intercalation into double-stranded DNA.

Tandem carbon-carbon bond insertion and intramolecular aldol reaction of benzyne with aroylacetones: novel formation of 4,4'-disubstituted 1,1'-binaphthols.

An efficient route to 4-aryl-2-naphthols from arynes and aroylacetones was developed by carbon-carbon bond insertion followed by an intramolecular aldol reaction and dehydration. Benzyne derived from 2-(trimethylsilyl)phenyl triflate reacted with benzoylacetones in refluxing acetonitrile to give 4-aryl-2-naphthols and 3-aryl-1-naphthols.

Reaction of arynes with amino acid esters.

An efficient route to a variety of 2-phenylindolin-3-ones from amino acid methyl esters has been developed. The reaction of amino acid methyl esters with benzyne prepared from 2-(trimethylsilyl)phenyl triflate and CsF gave 2-phenylindolin-3-ones in moderate to good yields.

Synthesis and properties of stable 2-metallanaphthalenes of heavier group 14 elements.

The first stable neutral stannaaromatic compound, 2-stannanaphthalene , was synthesized by taking advantage of an extremely bulky and efficient steric protection group, 2,4,6-tris[bis(trimethylsilyl)methyl]phenyl (Tbt). The molecular structure and aromaticity of were discussed on the basis of X-ray crystallographic analysis, NMR, UV-vis, and Raman spectroscopy, cyclic voltammetry, and theoretical calculations. 2-Germanaphthalene , which has a framework similar to that of , was synthesized for comparison, and systematic elucidation was made for the properties of 2-metallanaphthalene systems containing a heavier group 14 element (Si, Ge, or Sn).

One-electron reduction of kinetically stabilized dipnictenes: synthesis of dipnictene anion radicals.

The redox behavior of kinetically stabilized dipnictenes, BbtE=EBbt [E = P, Sb, Bi; Bbt = 2,6-bis[bis(trimethylsilyl)methyl]-4-[tris(trimethylsilyl)methyl]phenyl], was systematically disclosed using cyclic voltammetry and theoretical calculations. It was found that they showed reversible one-electron redox couples in the reduction region. The anion radical species of the Bbt-substituted diphosphene and distibene were successfully synthesized by the reduction of the corresponding neutral dipnictenes (BbtP=PBbt and BbtSb=SbBbt). Their structures were reasonably characterized by ESR, UV-vis, and Raman spectroscopy, and the distibene anion radical was structurally characterized by X-ray crystallographic analysis.

A kinetically stabilized ferrocenyl diphosphene: synthesis, structure, properties, and redox behavior.

A new, stable ferrocenyl diphosphene [Tbt-P==P-Fc] (1) (Tbt=2,4,6-tris[bis(trimethylsilyl)methyl]phenyl, Fc = ferrocenyl) was synthesized by the dehydrochlorination reaction of the corresponding diphosphane, [Tbt-P(H)-P(Cl)-Fc] (8), with 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) in good yield. Diphosphene 1 is very stable in the solid state and also in solution. In the 31P NMR spectrum (C6D6), diphosphene 1 showed a low-fielded AB quartet at delta 501.7 and 479.5 ppm with the coupling constant 1J(PP)=546 Hz, which is characteristic of an unsymmetrically substituted trans-diphosphene. The molecular structure of 1 was established by X-ray crystallographic analysis, which showed a trans-diphosphene with a C-P-P-C torsion angle of 177.86(17) degrees . The phosphorus-phosphorus bond length of 1 [2.0285(15) A] which is considerably shorter than the typical P-P single-bond lengths (ca. 2.22-2.24 A) and within the range of reported P=P double-bond lengths (1.985-2.051 A) for diaryl diphosphenes, evidenced the P=P double-bond character of 1 in the solid state. In addition, the cyclic voltammograms of 1 showed reversible reduction and oxidation couples at -1.95 and +0.34 V versus SCE, respectively. The electrochemical results for 1 were reasonably supported by the DFT calculations, which suggested that the LUMO and HOMO orbitals should be mainly pi* orbital of the diphosphene moiety and d orbitals of the iron(II) atom, respectively.

Novel multi-chalcogen ring systems with three different chalcogen atoms: synthesis, structure and redox property of five-membered trichalcogenaheterocycles.

The molecular structure of novel five-membered trichalcogenaheterocycles with three different chalcogen atoms, sulfur, selenium and tellurium, has been determined by crystallographic studies.