Deposition of thin mesoporous silica films on glass substrates from basic solution

Transparent thin (ca. 100 nm) films of silica-surfactant mesostructured materials were deposited on borosilicate glass plates and soda-lime glass tubes from aqueous solutions containing tetraethoxysilane, alkyltrimethylammonium chloride, ammonia, and methanol. By calcination in air, the films became mesoporous (BET surface area of 700-900 m2 g-1) with pore diameter 2.0-2.8 nm.     

Efficient approach to 1,2-diazepines via formal diazomethylene insertion into the C-C bond of cyclobutenones

Efficient monocyclic 1,2-diazepine formation via a tandem electrocyclization reaction of cyclobutenones with lithiodiazoacetate is demonstrated. The reaction proceeds through an oxy anion-accelerated 4π-ring opening of cyclobutene followed by an 8π-ring closure of the resultant oxy anion-substituted diazo-diene under mild conditions to furnish a 1,2-diazepine via formal diazomethylene insertion into the C-C bond of cyclobutenone.     

Synthesis and photophysical properties of luminescent mononuclear and dinuclear gold(I) complexes with ethynyl-substituted phenanthrolines

A novel asymmetric dinuclear gold(I) complex with 3,6-diethynylphenanthroline, 3,6-bis{(PPh₃)–Au–C≡C}₂-phen, has been synthesized from Au(PPh₃)Cl (PPh₃ = triphenylphosphine) and 3,6-diethynyl-1,10-phenanthroline. The asymmetrical dinuclear gold(I) complex, 3,6-bis{(PPh₃)–Au–C≡C}₂-phen, demonstrated a weak phosphorescence assignable to the metal-perturbed ³ π–π* transition in the long wavelength region compared to an intense emission of the symmetrical dinuclear complex with 3,8-diethynylphenanthroline, 3,8-bis{(PPh₃)–Au–C≡C}₂-phen. A similar tendency of phosphorescent bands for the mononuclear gold(I) complexes with 5-ethynylphenanthroline, 5-{(PPh₃)–Au–C≡C}-phen, and 3-ethynylphenanthroline, 3-{(PPh₃)–Au–C≡C}-phen was observed. The absorption bands assignable to the π–π*(C≡Cphen) transition and phosphorescent emission assignable to the metal-perturbed ³ π–π* transition for these four gold(I) complexes were reasonably consistent with the results calculated by DFT and TD-DFT.     

Stereoselective synthesis of trisubstituted alkenylboranes by palladium-catalysed reaction of alkynyltriarylborates with aryl halides

The palladium-catalysed reaction of alkynyltriarylborates with aryl halides afforded trisubstituted alkenylboranes, in which two different aryl groups were installed across the carbon-carbon double bond in a cis arrangement.     

Forced proximity of nitroxide groups in pincer compounds with a xanthene spacer

We designed bisnitroxide compounds where the radical sites are located close to each other in a molecule. Two new pincer-type bisnitroxide compounds have been synthesized, involving xanthene-4,5-diyl as a spacer and tert-butyl phenyl nitroxides as arms. From the X-ray crystal structure analysis, the shortest intramolecular interatomic N?O and O?O distances respectively are 5.074(6) and 5.258(6) Å for the m,m′-derivative and 3.624(3) and 3.771(3) Å for the p,p′-derivative. The N?O distance in the latter satisfies the empirical criterion for possible dimerization/degradation reaction accompanied by dia-/paramagnetic transition. However, the magnetic study clarified paramagnetic behavior in all the temperature range. According to a singlet-triplet model, antiferromagnetic couplings were characterized with 2J/k_B = ?7.71(2) and ?8.83(4) K for the m,m′ and p,p′-derivatives, respectively. The present result suggests that a more flexible spacer is required for realization of possible dia-/paramagnetic transition.     

Photoreaction Cycle of Phoborhodopsin (Sensory Rhodopsin II) from Halobacterium salinarum Expressed in Escherichia coli

Phoborhodopsin (pR; also called sensory rhodopsin II, SRII) is a photoreceptor of negative phototaxis of halobacteria. The studies of photochemical properties of this pigment are not many because the amount of the pigment is small and the stability is low. Recently an expression system of phoborhodopsin from Halobacterium salinarum (called salinarum phoborhodopsin, spR; also HsSRII) in Escherichia coli and purification method has been developed (Mironova et al. [2005] FEBS Lett., 579, 3147–3151), which enables detailed studies on the photochemical properties of spR. In the present work, the photoreaction cycle of E. coli-expressed spR was studied by low-temperature spectroscopy and flash photolysis. Formations of K-, M-, O-like intermediates and P480 were reconfirmed as reported previously. New findings are as follows. (1) The K-like intermediate (P500) was a mixture of two photoproducts. (2) Formation of L-like intermediate (P482) was observed by low-temperature spectroscopy and flash photolysis at room temperature. (3) On long irradiation of spR at 20°C, formation of a new photoproduct P370 was observed and it decayed to the original spR in the dark with a decay half time of 190 min. Based on these results the similarities and dissimilarities between spR and ppR are discussed.     

Circularly polarized luminescence (CPL) characteristics of hydrophobic pyrene derivatives/γ-cyclodextrin (γ-CD) complexes in aqueous solution dissolved by grinding

Circularly polarized luminescence (CPL) organic dyes are currently receiving a great interest, but there are still not many reported observations of CPL spectra of hydrophobic dyes from aqueous solution. We have prepared hydrophobic pyrene derivatives and dissolved them into aqueous solutions with γ-cyclodextrin (γ-CD) by using grinding technique. Among these derivatives, (pyrene-1-carbonyl)serine (PySer) forms a spatially restricted dimer in the hydrophobic chiral cavity of γ-CD and exhibits excimer emission with a high quantum yield of Φ_f?=?0.68. In addition, circular dichroism and CPL signals were induced for the complex. The strong g_CPL value of g_CPL?=?+?2.2?×?10^?3 was obtained, which may be attributed to the interaction between the hydroxyl groups in the side chain of PySer with those of γ-CD and it strengthens the chiral dimeric structure.

Graphic abstract

     

Planarized Phenyldithienylboranes: Effects of the Bridging Moieties and π-Extension on the Photophysical Properties and Lewis Acidity

Two kinds of planarized phenyldithienylboranes, which contain (CH₃)₂C- or CH₂-bridging moieties, were synthesized. The difference of the bridging moieties affects their packing structures and photophysical properties. In particular, the (CH₃)₂C-bridged derivative exhibits a large Stokes shift, unusual for such planarized compounds, that results from a large structural relaxation in the excited state. A series of π-extended derivatives was synthesized, among which a p-(diphenylamino)phenyl-substituted derivative shows large solvatochromism in the fluorescence spectra, while maintaining high quantum yields even in polar solvents. The Lewis acidity of the phenyldithienylborane derivatives was also assessed by titration with pyridine. The Lewis acidity of the boron center is affected not only by the difference in the steric bulk of the bridging moieties, but also by the electronic effect of the substituents introduced at remote positions relative to the boron atom. These results demonstrate the characteristic features of planarized phenyldithienylboranes as building blocks for boron-based π-electron materials.     

Studies on palytoxins

The complete structure of palytoxin (1) was elucidated by us in 1982.¹ Our continuous interests in palytoxin led us to examine minor constituents of Okinawan Palythoa tuberculosa. In this paper, we describe successful isolation and structural elucidation of four minor toxins, which were named homopalytoxin (2), bishomopalytoxin (3), neopalytoxin (4) and deoxypalytoxin (5).