The CDW phase transformation in 1T-TaS2 observed by the doppler broadening of positron annihilation

The layered transition metal dichalcogenide 1T-TaS₂ was studied by the Doppler broadening of positron annihilation. The Doppler broadened line- shape was measured over the temperature range between 77 and 292 K. The CDW phase transformation at about 200 K is discussed in terms of the W-parameters calculated from the energy spectra.     

Enantioselective formal synthesis of (−)-aurantioclavine using Pd-catalyzed cascade cyclization and organocatalytic asymmetric aziridination

The enantioselective formal synthesis of (?)-aurantioclavine is described. The core tricyclic skeleton was synthesized using a Pd-catalyzed Heck insertion–allylic amination cascade. The stereocenter was constructed by a highly enantioselective organocatalytic asymmetric aziridination reaction.     

A short synthesis of protected 3-deoxy-d-arabino-2-heptulosonates (DAH) from shikimic acid based on silyl group migration

The reaction of (2S,3S,4R)-2,3,4,7-tetrahydroxy-6-oxoheptanals with lower alcohols produced protected 3-deoxy-d-arabino-2-heptulosonates. The key transformation is based on an 1,4-O–O silyl group migration, followed by 6-exo-trig cyclisation to give the final pyranose.     

Synthesis of new 5-bromo derivatives of indole and spiroindole phytoalexins

Electrophilic aromatic substitution is one of the most thoroughly studied reactions in organic chemistry. In the present paper, the 5-brominated spirobrassinol methyl ethers VII, VIII were obtained by electrophilic substitution of the aromatic core of indoline at the C-5 position in the presence of various brominating agents. The same products were also prepared from 5-bromoindole (IX) following the sequence for the synthesis 1-methoxyspirobrassinol methyl ether (V) from indoline. In addition, the new related 5-bromospiroindoline derivatives XX–XXIII were synthesised and their biological activity on human tumour cell lines was examined. The presence of bromine in the indole or indoline skeleton at the C-5 position resulted in the partial increase in anticancer activity on leukaemia cell lines (Jurkat, CEM). The structures of the newly prepared products were determined by ¹H and ¹³C NMR spectroscopy, including HSQC, HMBC, COSY, NOESY and DEPT measurements.     

Enhancement in thermal stability and resistance to denaturants of lipase encapsulated in mesoporous silica with alkyltrimethylammonium (CTAB)

We assembled a highly durable conjugate with both a high-density accumulation and a regular array of lipase, by encapsulating it in mesoporous silica (FSM) with alkyltrimethylammonium (CTAB) chains on the surface. The activity for hydrolyzing esters of the lipase immobilized in mesoporous silica was linearly related to the concentration of lipase, whereas that of non-immobilized lipase showed saturation due to self-aggregation at a high concentration. The lipase conjugate also had increased resistance to heating when stayed in the silica coupling with CTAB. In addition, encapsulating the enzyme with FSM coupled CTAB caused the lipase to remain stable even in the presence of urea and trypsin, suggesting that the encapsulation prevented dissociation and denaturing. This conjugate had much higher activity and much higher stability for hydrolyzing esters when compared to the native lipase. These results show that FSM provides suitable support for the immobilization and dispersion of proteins in mesopores with disintegration of the aggregates.     

Synthesis and properties of 2-azidodeoxyadenosine and its incorporation into oligodeoxynucleotides

2-Azidodeoxyadenosine (7) was conveniently synthesized from deoxyguanosine (2) by use of a combined reagent of TMSN₃–BuONO. The structure of the tautomer of the azido derivative was determined by ¹H NMR. Reaction of 7 with iPr₂NP(OEt)₂ gave an intermediate 10 of the Staudinger reaction. Incorporation of 7 into a DNA 13mer resulted in a significant decrease of the T_m value of the DNA duplex upon hybridization with the complementary strand. The thermal stability was discussed based on the hydrogen bond energy and electrostatic repulsion.     

Proton radiation effects in quantum dot lasers

Proton beams with energies of 10 and 200 MeV were irradiated onto InAs quantum dot lasers with a wavelength of 1.3 μm. The increase in threshold current by proton irradiation was small compared with those of the previously reported other quantum dot lasers with larger active region and 1.3-μm InGaAsP quantum well lasers. These results were discussed by taking account of non-ionizing energy loss and effective volume of active region.     

A Facile Access to (R)-Methyl 2-Oxocyclopentane-1-acetate via Lipase-Catalyzed Irreversible Transesterification

A highly efficient kinetic resolution of (±)-methyl trans-2-hydroxycyclopentane-1-acetate via lipase PS-catalyzed irreversible transesterification provides a facile and economical entry to (R)-methyl 2-oxocyclopentane-1-acetate of 96% ee, a starting material for the convergent synthesis of (+)-isocarbacyclin.