Studies on pyrazines. 15. A convenient synthesis of 2,5-dihydroxypyrazines

The reaction of 2,5-dimethoxypyrazines with iodotrimethylsilane followed by hydrolysis was investigated to prepare the title compounds.     

INDO Studies on the structure of benzosemiquinone radicals

The spin densities of the radical anions from 4-methylcatechol, 4-carboxylic catechol, and 3-methylcatechol were calculated by means of the INDO method with the geometrical parameter adjusting method. The observed protion hyperfine coupling constants were exactly reproduced.     

Discovery of deeply bound π− states in the 208Pb(d,3He) reaction

Zeitschrift für Physik A Hadrons and nuclei - Narrow lines were observed around 133 MeV excitation energy in the 208Pb(d,3He) reaction at T d = 300 MeV/u using the Fragment Separator System at...     

Synthesis of (1-substituted piperidin-4-yl)-1H-benzimidazoles and (1-substituted piperidin-4-yl)-3,4-dihydroquinazolines as possible antihypertensive agents

Structural modifications of 4-piperidylbenzimidazolinones (I) by replacing the benzimidazolinone group with other heterocycles (2-cyanoamino, 2-ethoxy, and 2-methylbenzimidazole and 2-cyanoamino-3,4-dihydroquinazoline) has been made and a number of new piperidines (II) were synthesized as potential antihypertensive agents.     

Synthesis and biological activity of novel mitomycin C analogs derived from mitomycin A

A variety of mitomycin C analogs were synthesized from mitomycin A and their biological activities were studied. Mitomycin A ( 1 ) underwent nucleophilic displacement reactions involving intramolecular hydrogen migrations upon treatment with nitrogen nucleophiles bearing mobile hydrogens, but the mode of hydrogen migration depended on the nature of the nucleophiles. The reaction with alkoxyamines gave compounds 6 and 7 which have the 5H-6-alkoxyimino-4,7-dione structure in ring A of 1 . However, the reaction with hydroxylamine and benzoylhydrazine afforded compounds 11 and 13 which have the 4-hydroxy-6-hydroxyimino-7-one structure and the 4-hydroxy-6-hydrazono-7-one structure, respectively, in ring A of 1 . These products were converted into various types of mitomycin C derivatives by methylation with methyl iodide or dimethyl sulfate. The mechanistic features of these reactions are discussed. The in vitro and in vivo biological activities were tested by using P388 leukemia and Sarcoma 180 tumor cells. Several of the synthesized compounds exhibited better activity than that of mitomycin C.     

Antiferromagnetism and phase diagram in ammoniated alkali fulleride salts

Intercalation of neutral ammonia molecules into trivalent face-centered-cubic (fcc) fulleride superconductors induces a dramatic change in electronic states. Monoammoniated alkali fulleride salts (NH3)K3-xRbxC60, forming an isostructural orthorhombic series, undergo an antiferromagnetic transition, which was found by the electron spin resonance experiment. The Neel temperature first increases with the interfullerene spacing and then decreases for (NH3)Rb3C60, forming a maximum at 76 K. This feature is explained by the generalized phase diagram of Mott-Hubbard transition with an antiferromagnetic ground state.     

Evaluation of Morphology and Size Distribution of Silicon and Titanium Oxide Nanoparticles Generated by Laser Ablation

Nanometer-sized particles of silicon and titanium oxide were generated by irradiating solid targets using a nanosecond pulsed-Nd : YAG laser in a low pressure atmosphere. A low pressure differential mobility analyzer (LP-DMA) was used to classify the size of the generated particles. The LP-DMA and electron microscopes (SEM and TEM) were used to measure the change in the size distribution and morphology of the generated particles with laser power density and system pressure. The size distribution of both silicon and titanium oxide ranged from two to one hundred nanometers in diameter depending on the laser power density and pressure. From the high resolution TEM observation and electron diffraction, it was found that the generated titanium oxide nanoparticles were composed of a core of faceted metallic single crystals with an oxide layer 'shell.     

Stimuli-Responsive Molecular Photon Upconversion

The addition of stimuli-responsiveness to anti-Stokes emission provides a unique platform for biosensing and chemosensing. Particularly, stimuli-responsive photon upconversion based on triplet–triplet annihilation (TTA-UC) is promising due to its occurrence at low excitation intensity with high efficiency. This Minireview summarizes the recent developments of TTA-UC switching by external stimuli such as temperature, oxygen, chemicals, light, electric field, and mechanical force. For the systematic understanding of the underlying general mechanisms, the switching mechanisms are categorized into four types: 1) aggregation-induced UC; 2) assembly-induced air-stable UC; 3) diffusion-controlled UC; and 4) energy-transfer-controlled UC. The development of stimuli-responsive smart TTA-UC systems would enable sensing with unprecedented sensitivity and selectivity, and expand the scope of TTA-UC photochemistry by combination with supramolecular chemistry, materials chemistry, mechanochemistry, and biochemistry.