Synthesis and luminescence properties of biphenyl-type firefly luciferin analogs with a new,near-infrared light-emitting bioluminophore

New firefly luciferin analogs of the 4,4′-substituted biphenyl-type were synthesized. One analog with a 4′-dimethylamino group possessed bioluminescence activity, emitting near-infrared biological window light at 675 nm suitable for deep-site bioimaging of living animals. The chemiluminescence light-emission maximum of the corresponding methyl ester of the bioluminescence active analog was 500 nm, implying that biphenyl and thiazolinone rings in the light emitter might be placed in a coplanar conformation at the polar luciferase active site.     

Palladium Enolate Umpolung: Cyclative Diacetoxylation of Alkynyl Cyclohexadienones Promoted by a Pd/SPRIX Catalyst

A novel palladium‐catalyzed reaction involving an unusual nucleophilic attack on a palladium enolate was developed using a spiro‐bis(isoxazoline) (SPRIX) ligand. Treatment of alkynyl cyclohexadienone substrates with a Pd/SPRIX catalyst in acetic acid under an oxygen atmosphere furnished diacetoxylated benzofuranone derivatives in good yields. This cyclative diacetoxylation proceeded enantioselectively in the presence of an optically pure SPRIX ligand.     

One‐Pot Halogen Dance/Negishi Coupling of Dibromothiophenes for Regiocontrolled Synthesis of Multiply Arylated Thiophenes

One‐pot halogen dance/Negishi cross‐coupling of readily available 2,5‐dibromothiophenes is described. A lithium diisopropylamide (LDA)‐mediated halogen dance reaction resulted in the formation of thermodynamically stable α‐lithiodibromothiophenes, which were transmetalated with ZnCl₂ and subjected to Negishi cross‐coupling to provide the corresponding arylated dibromothiophenes in one pot. The resultant β‐bromo group was much less reactive than the remaining α‐bromo group, which was used in a one‐pot double Suzuki–Miyaura cross‐coupling, enabling facile synthesis of multiply arylated thiophenes.     

Synthesis of benzofurazan derivatization reagents for short chain carboxylic acids in liquid chromatography/electrospray ionization‐tandem mass spectrometry (LC/ESI‐MS/MS)

Benzofurazan derivatization reagents, 4‐[2‐(N,N‐dimethylamino)ethylaminosulfonyl]‐7‐(2‐aminopentylamino)‐2,1,3‐benzoxadiazole (DAABD‐AP) and 4‐[2‐(N,N‐dimethylamino) ethylaminosulfonyl]‐7‐(2‐aminobutylamino)‐2,1,3‐benzoxadiazole (DAABD‐AB), for short‐chain carboxylic acids in liquid chromatography/electrospray ionization tandem mass spectrometry (LC/ESI‐MS/MS) were synthesized. These reagents reacted with short chain carboxylic acids in the presence of the condensation reagents at 60°C for 60 min. The generated derivatives were separated on the reversed‐phase column and detected by ESI‐MS/MS with the detection limits of 0.1–0.12 pmol on column. Upon collision‐induced dissociation, a single and intense product ion at m/z 151 was observed. These results indicated that DAABD‐AP and DAABD‐AB are suitable as the derivatization reagents in LC/ESI‐MS/MS analysis. Copyright © 2008 John Wiley & Sons, Ltd.     

Onboard determination of submicromolar nitrate in seawater by anion-exchange chromatography with lithium chloride eluent.

Ion-exchange chromatography using a high-capacity anion exchanger with UV detection was applied to the determination of nitrate in seawater. Major ions in seawater samples did not affect the peak shape and the retention time of the nitrate when an alkaline metal cation-chloride solution was used as an eluent at high concentrations (0.5-2 mol/l). At a wavelength of 220 nm, the peak of bromide was very small because of low absorption, while its separation from the nitrate peak was good at high concentrations. Among the eluents tested, lithium chloride gave the best separation of nitrate from bromide. It was estimated that the lithium ion had the least potential for ion-pair formation with nitrate, and its retention time was prolonged compared with the retention times when using other cations; with bromide and nitrite, such an effect was not observed. The results of shipboard seawater nitrate determination by our method in the South Pacific Ocean and Antarctic Sea showed good agreement with those by the conventional photometric method using continuous flow.     

A conversion of an SDP having free variables into the standard form SDP

This paper deals with a semidefinite program (SDP) having free variables, which often appears in practice. To apply the primal–dual interior-point method, we usually need to convert our SDP into the standard form having no free variables. One simple way of conversion is to represent each free variable as a difference of two nonnegative variables. But this conversion not only expands the size of the SDP to be solved but also yields some numerical difficulties which are caused by the non-existence of a primal–dual pair of interior-feasible solutions in the resulting standard form SDP and its dual. This paper proposes a new conversion method that eliminates all free variables. The resulting standard form SDP is smaller in its size, and it can be more stably solved in general because the SDP and its dual have interior-feasible solutions whenever the original primal–dual pair of SDPs have interior-feasible solutions. Effectiveness of the new conversion method applied to SDPs having free variables is reported in comparison to some other existing methods.     

Temperature dependence of thermoelectric properties of Ni-doped CoSb3

Temperature dependences of the Hall coefficient, Hall mobility and thermoelectric properties of Ni-doped CoSb₃ have been characterized over the temperature range from 20 to 773 K. Ni-doped CoSb₃ is an n-type semiconductor and the conduction type changes from n-type to p-type at around 450 K. The temperature for the transition from n-type to p-type increased with increasing Ni content x. The Seebeck coefficient reaches a maximum value near the transition temperature. The electrical resistivity indicates that Co_1−xNi_xSb₃ is a typical semiconductor when x≤0.03 and a degenerate semiconductor when x>0.03. Thermal conductivity analyses show that the lattice component is predominant at lower temperatures and carrier and bipolar components become large at temperatures higher than the transition temperature. The thermoelectric figure of merit reaches a maximum value close to the transition temperature and the largest value, 4.67×10⁻⁴ K⁻¹ at 600 K, was obtained for x=0.05.     

XPS study of silicon surface after ultra-low-energy ion implantation

Ultra-low-energy ion implantation of silicon with a hydrogen-terminated (0 0 1) surface was carried out using a mass-separated ³¹P⁺ ion beam. The ion energy was 30 eV, the displacement energy of silicon, and the ion doses were 6 × 10¹³ ions/cm². Annealing after the implantation was not carried out. The effects of ion implantation on the surface electrical state of silicon were investigated using X-ray photoelectron spectroscopy (XPS). The Si 2p peak position using XPS depends on the doping conditions because the Fermi level of the hydrogen-terminated silicon surface is unpinned. The Si 2p peak position of the specimen after ion implantation at a vacuum pressure of 3 × 10⁻⁷ Pa was shifted to the higher energy region. It suggested the possibility of phosphorus doping in silicon without annealing. In the case of ion implantation at 5 × 10⁻⁵ Pa, the Si 2p peak position was not shifted, and the peak was broadened because of the damage by the fast neutrals. Ultra-low-energy ion doping can be achieved at ultra-high-vacuum conditions.     

Electrical transport characteristic of carbon nanotube after mass-separated ultra-low-energy oxygen ion beams irradiation

Mass-separated ultra-low-energy oxygen ion beams were irradiated to the single-walled carbon nanotubes (SWCNTs) under an ultra-high-vacuum pressure of 10⁻⁷ Pa for the purpose of achieving n-type conduction of nanotubes. The ion beam energy was 25 eV, which was close to the displacement energy of graphite. The incident angle of the ion beam was normal to the target nanotube. The ion dose ranged from 3.3 × 10¹¹ to 3.8 × 10¹² ions/cm². The structure of SWCNTs after the ion irradiation was investigated. The CNTs still have a clear single-walled structure after the ion irradiation. The graphite structure is distorted and some defects are induced in the nanotube by the oxygen irradiation. The oxygen ions with the ion energy of 25 eV are irradiated to the field effect transistor (FET) device with the nanotube channel. The n-type characteristic appears upon the oxygen ion irradiation, and the device exhibits ambipolar behavior. The defects induced by the ion irradiation may act as the n-type dopants.