Soichiro Kyushin

An organosilicon cluster with an octasilacuneane core: a missing silicon cage motif.

Cagey silicon: A silicon cluster, consisting of sixteen silicon atoms and composed of an octasilacuneane core (red, see picture) fused with cyclotetrasilanes (orange), was synthesized by reductive tetramerization of tetrachlorocyclotetrasilane. Analytical and theoretical studies reveal the unique structural and electronic features of this organosilicon cluster.

Silylation Improves the Photodynamic Activity of Tetraphenylporphyrin Derivatives In Vitro and In Vivo

The effects of silyl and hydrophilic groups on the photodynamic properties of tetraphenylporphyrin (TPP) derivatives have been studied in vitro and in vivo. Silylation led to an improvement in the quantum yield of singlet oxygen sensitization for both sulfo and carboxy derivatives, although the silylation did not affect other photophysical properties. Silylation also improved the cellular uptake efficiency for both sulfo and carboxy derivatives, enhancing the in vitro photodynamic activity of the photosensitizer in U251 human glioma cells. The carboxy derivative (SiTPPC4 ) was found to show higher cellular uptake efficiency and in vitro photodynamic activity than the corresponding sulfo derivative (SiTPPS4 ), which indicates that the carboxy group is a more promising hydrophilic group than the sulfo group in the silylated porphyrin. SiTPPC4 was found to show high selective accumulation efficiency in tumors, although almost no tumor selectivity was observed for the nonsilylated porphyrin. The concentration of SiTPPC4 in tumors was 13 times higher than that in muscle 12u2005h after drug administration. We also studied tumor response after treatment and found that silylation enhanced in vivo photodynamic activity significantly. SiTPPC4 shows higher photodynamic activity than NPe6 with white light irradiation.

Tetrasilane-Bridged Bicyclo[4.1.0]heptasil-1(6)-ene

Tetrasilane-bridged bicyclo[4.1.0]heptasil-1(6)-ene 1 was synthesized by the reduction of 1,1,2,2-tetrachlorocyclohexasilane 2 in 12% yield as red-orange crystals. The structure and properties of 1 were studied by spectroscopy, X-ray crystallography, and theoretical calculations. The linkage of the cyclotrisilene moiety with two tetrasilane chains with tert-butyl groups remarkably affects its structure and (29)Si NMR spectrum.

Two Pentasilahousanes Fused Together

The organosilicon cluster 1 with two pentasilahousanes fused together was synthesized by the reduction of 1,1,3-trichlorocyclotetrasilane. This reaction involves dimerization and rearrangement of the silicon skeleton. The structure and properties of 1 were studied by X-ray crystallographic and spectroscopic analyses.

The Radical Anion of Cyclopentasilane‐Fused Hexasilabenzvalene

The radical anion of cyclopentasilane-fused hexasilabenzvalene was synthesized by the reduction of the corresponding neutral compound. X-ray crystallographic analysis showed a more trans-bent structure of the disilene moiety than the neutral compound. Theoretical calculations showed that the highly trans-bent structure is attributed to the hexasilabenzvalene structure. The EPR spectrum showed that an unpaired electron exists mainly at the disilene moiety. In the UV/Vis spectrum, a large bathochromic shift was observed compared with the neutral compound.

An Isolable Radical Anion of an Organosilicon Cluster Containing Only σ Bonds

The radical anion of octa-tert-butyloctasilacubane was generated and isolated. The EPR spectrum showed the satellites due to the tertiary (13)C nuclei of the eight tert-butyl groups. The X-ray crystallographic analysis showed that the Si-Si bonds are shortened and the Si-C bonds are elongated compared with those of octa-tert-butyloctasilacubane. These results are well explained by the distribution of an unpaired electron in the singly occupied molecular orbital (SOMO).