Effect of the ortho Modification of Azobenzene on the Photoregulatory Efficiency of DNA Hybridization and the Thermal Stability of its cis Form

We synthesized various azobenzenes methylated at their ortho positions with respect to the azo bond for more effective photoregulation of DNA hybridization. Photoregulatory efficiency, evaluated from the change of T_m (ΔT_m) induced by trans–cis isomerization, was significantly improved for all ortho‐modified azobenzenes compared with non‐modified azobenzene due to the more stabilized trans form and the more destabilized cis form. Among the synthesized azobenzenes, 4‐carboxy‐2′,6′ ‐ dimethylazobenzene ( 2′,6′‐Me‐Azo ), in which two ortho positions of the distal benzene ring with respect to carboxyl group were methylated, exhibited the largest ΔT_m, whereas the newly synthesized 2,6‐Me‐Azo (4‐carboxy‐2,6‐dimethylazobenzene), which possesses two methyl groups on the two ortho positions of the other benzene ring, showed moderate improvement of ΔT_m. Both NMR spectroscopic analysis and computer modeling revealed that the two methyl groups on 2′,6′‐Me‐Azo were located near the imino protons of adjacent base pairs; these stabilized the DNA duplex by stacking interactions in the trans form and destabilized the DNA duplex by steric hindrance in the cis form. In addition, the thermal stability of cis‐ 2′,6′‐Me‐Azo was also greatly improved, but not that of cis‐ 2,6‐Me‐Azo . Solvent effects on the half‐life of the cis form demonstrated that cis‐to‐trans isomerization of all the modified azobenzenes proceeded through an inversion route. Improved thermal stability of 2′,6′‐Me‐Azo but not 2,6‐Me‐Azo in the cis form was attributed to the retardation of the inversion process due to steric hindrance between lone pair electrons of the π orbital of the nitrogen atom and the methyl group on the distal benzene ring.     

Construction of photoresponsive RNA for photoswitching RNA hybridization

By introducing azobenzenes into RNA using d-threoninol as a scaffold, a photoresponsive RNA was constructed for efficiently photoswitching the formation and dissociation of RNA/RNA duplexes. The difference in melting temperature (T(m)) between the trans and cis forms was so large that efficient photoregulation of RNA hybridization became possible, irrespective of the sequence adjacent to the introduced azobenzene. Compared to the corresponding photoresponsive DNA, the photoregulatory efficiency of azobenzene-modified RNA was even higher due to the drastic destabilization by cis-azobenzene. Structural analysis by NMR and molecular modeling indicated that the planar trans-azobenzene could not stabilize the RNA/RNA duplex with a rigid A-form structure by base pair stacking. However, the large steric hindrance caused by nonplanar cis-azobenzene was quite effective at distorting and destabilizing the duplex structure. We also discuss the effect of methylation of azobenzene at the ortho positions on photoregulation of RNA/RNA duplex formation. This newly constructed photoresponsive RNA has promising applications such as photoswitching of RNA functions.     

Characterization of MOVPE-grown p-InGaAs/n-InP interfaces

The low-pressure MOVPE-grown p-InGaAs-on-n-InP and n-InP-on-p-InGaAs diodes were characterized by I–V and C–V measurements to study the effects of the growth conditions on the heterointerface. The obtained band discontinuity in the conduction band ΔE_c ranged from 0.19 to 0.32 eV. It was found that ΔE_c was very sensitive to the growth interruption at the InP/InGaAs heterointerface. The n-InP-on-p-InGaAs diodes tend to show higher ΔE_c than the p-InGaAs-on-n-InP diodes. The decreased ΔE_c at InGaAs-on-InP heterointerface might be attributed to the graded layer of InGaAsP formed by intermixing at the interface. It is concluded from the estimated ΔE_c that the InP-on-InGaAs heterointerface is more abrupt than the InGaAs-on-InP heterointerface. An improvement of the InGaAs-on-InP heterointerface is mandatory for fabrication of high-performance double heterojunction bipolar transistors with InP collector layers.     

Aging effects on cerebral asymmetry: a voxel-based morphometry and diffusion tensor imaging study

The hemispheres of the human brain are functionally and structurally asymmetric. The purpose of this study was to evaluate the effects of aging on gray and white matter asymmetry. Two hundred twenty-six right-handed normal volunteers aged 21–71 years were included in this study. The effects of aging on gray matter volume asymmetry and white matter fractional anisotropy asymmetry were evaluated with use of voxel-based morphometry and voxel-based analysis of fractional anisotropy maps derived from diffusion tensor imaging (DTI), respectively. The voxel-based morphometry showed no significant correlation between age and gray matter volume asymmetry. The voxel-based analysis of DTI also showed no significant correlation between age and white matter fractional anisotropy asymmetry. Our results showed no significant effects of aging on either gray matter volume asymmetry or white matter fractional anisotropy asymmetry.     

Atomically-flat,chemically-stable,superconducting epitaxial thin film of iron-based superconductor,cobalt-doped BaFe2As2

The epitaxial growth of Fe-based superconductors such as Co-doped SrFe₂As₂ (SrFe₂As₂:Co) was reported recently, but has still insufficient properties for a device application because they have rough surfaces and are decomposed by reactions with water vapor in an ambient atmosphere. This paper reports that epitaxial films of Co-doped BaFe₂As₂ grown at 700 ^°C show the onset superconducting transition temperature of ～20 K. The transition is sharper than those observed on the SrFe₂As₂:Co films, which would originate from their improved crystallinity. These films also have atomically-flat surfaces with step-and-terrace structures and exhibit chemical stability against exposure to water vapor.     

Total Synthesis of Talatisamine

Talatisamine ( 1 ) is a member of the C₁₉‐diterpenoid alkaloid family, and exhibits K⁺ channel inhibitory and antiarrhythmic activities. The formidable synthetic challenge that 1 presents is due to its highly oxidized and intricately fused hexacyclic 6/7/5/6/6/5‐membered‐ring structure (ABCDEF‐ring) with 12 contiguous stereocenters. Here we report an efficient synthetic route to 1 by the assembly of two structurally simple fragments, chiral 6/6‐membered AE‐ring 7 and aromatic 6‐membered D‐ring 6 . AE‐ring 7 was constructed from 2‐cyclohexenone ( 8 ) through fusing an N‐ethylpiperidine ring by a double Mannich reaction. After coupling 6 with 7 , an oxidative dearomatization/Diels–Alder reaction sequence generated fused pentacycle 4 b . The newly formed 6/6‐membered ring system was then stereospecifically reorganized into the 7/5‐membered BC‐ring of 3 via a Wagner–Meerwein rearrangement. Finally, Hg(OAc)₂ induced an oxidative aza‐Prins cyclization of 2 , thereby forging the remaining 5‐membered F‐ring. The total synthesis of 1 was thus accomplished by optimizing and orchestrating 33 transformations from 8 .     

Optical and electrical properties of Tl-S glasses

The frequency and temperature dependence of ac conductivity and optical absorption have been measured for four Tl-S glasses, TlS, Tl₂S₃,TlS₂ and Tl₂S₅, prepared by a melt-quenching method. The ac conductivity has been measured over a frequency range 0.1 Hz to 1.8 GHz and a temperature range 190-273 K. The optical absorption was measured at room temperature over a wavelength range 200-2600 nm. We have determined the electrical and optical band gaps from the experimental results. For each glass, the electrical band gap is larger than the optical band gap and the difference increases with increasing sulfur concentration. The frequency dependence of ac conductivity varies with composition of the glasses. We suggest that these results are due to an increase of localized states in the band gap with increasing sulfur concentration.     

Axially chiral dicarboxylic acid-catalyzed asymmetric imino aza-enamine reaction/oxidation as a Strecker reaction surrogate

Axially chiral dicarboxylic acid-catalyzed highly enantioselective imino aza-enamine reaction was elaborated into a surrogate of the asymmetric Strecker reaction building on the fact that the N,N-dialkylhydrazone moiety can be easily converted to the cyanide moiety by treatment with peracid.