Figure‐eight Octaphyrin Bis‐Ge(IV) Complexes: Synthesis,Structures, Aromaticity,and Chiroptical Properties

Highly twisted structures of expanded porphyrin provide a prominent basis to unravel the relationship between aromaticity and chirality. Here we report the synthesis of bis‐Ge(IV) complexes of [38]octaphyrin that display rigid figure‐eight structures. Two bis‐Ge(IV) [38]octaphyrin isomers with respect to the stereochemistry of the axial hydroxy groups on the germanium ions were obtained and found to be aromatic. Upon oxidation with MnO₂, these [38]octaphyrin complexes were converted to a single syn‐type isomer of [36]octaphyrin with retained figure‐eight conformation. The enantiomers have been successfully separated by HPLC equipped with a chiral stationary phase. While aromatic [38]octaphyrin Ge(IV) complexes showed quite large molar circular dichroism of up to Δ?=1500 M^?1cm^?1 with a dissymmetry factor g_abs of 0.035, weakly antiaromatic [36]octaphyrin Ge(IV) complexes underscored moderate values; Δ?=540 M^?1cm^?1 with g_abs of 0.023. Thus, the figure‐eight octaphyrin scaffold has been proved to be an attractive platform for novel chiroptical materials with tunable aromaticity.     

Surface structure of silica gel reacted with 3-mercaptopropyltriethoxysilane and 3-aminopropyltriethoxysilane: formation of the S–S bridge structure and its characterization by Raman scattering and diffuse reflectance Fourier transform spectroscopic studies

 Silica gel samples, modified with 3-mercaptopropyltriethoxysilane, and their S–S-bridged samples have been prepared. In order to characterize the microstructure of the surface of these silica gel samples, Raman scattering and diffuse reflectance Fourier transform IR spectra of these samples have been examined by comparison with Raman spectra of various n-alkyl disulfides and their related silane polymers. The S–S and C–S stretch modes characteristic of the CH₂SSCH₂ segment, in addition to the SH and C–S stretch modes of the CH₂SH segment, have been assigned for these silica gel samples. It has been found that, even on the surface of the silica gel, a specific conformer is stabilized about the CH₂SSCH₂ segment. Received: 1 May 2001 Accepted: 16 June 2001     

Action spectrum for the suppression of arylalkylamine N-acetyltransferase activity in the two-spotted spider mite Tetranychus urticae

An action spectrum was obtained for the suppression of arylalkylamine N -acetyltransferase (NAT) activity in the two-spotted spider mite Tetranychus urticae by irradiating the mite with monochromatic lights of various wavelengths using the Okazaki Large Spectrograph at the National Institute for Basic Biology, Okazaki, Japan. Fluence–response curves were obtained for wavelengths between 300 and 650 nm by irradiating the mite for 4 h day⁻¹. The samples were frozen after the third exposure. A negative correlation between the logarithmic fluence rate and NAT activity was detected in the range of 0.01–1 μmol m⁻² s⁻¹ for wavelengths between 300 and 500 nm and in the range of 0.1–10 μmol m⁻² s⁻¹ for wavelengths between 550 and 650 nm. The constructed action spectrum indicated that the photoreceptors mediating the circadian and/or photoperiodic systems might be UV-A- and blue-type photoreceptors with absorption peaks at 350 and 450 nm.     

A concise synthesis of 3′-α-fluoro-2′,3′-dideoxyguanosine (FddG) via 3′-α-selective fluorination of 8,2′-thioanhydronucleoside

The antiviral nucleoside 3′-α-fluoro-2′,3′-dideoxyguanosine (FddG) was synthesized via 3′-α-selective fluorination of 8,2′-thioanhydronucleoside as the key step. Desulfurization of 3′-α-fluoro-3′-deoxy-8,2′-thioanhydronucleoside could be achieved by the treatment with Raney Ni in toluene. This method provides a concise route to 3′-α-fluoro-2′,3′-dideoxynucleosides that avoids the use of explosive and expensive SF₄-related fluorinating reagents.