Photoluminescence properties of Ag2S semiconductor clusters synthesized in micropores and mesopores

Silver sulfide (Ag₂S) clusters were synthesized in microporous zeolites and mesoporous AlMCM-41 by the sulfurization of Ag⁺ ions exchanged within the pores of the host. Characterization was performed by means of XRD, UV-Vis Ag K-edge XAFS and photoluminescence. The pore size of the host has great effects on the photoluminescence properties. Ag₂S/AlMCM-41 showed photoluminescence at the longer wavelengths than Ag₂S/zeolites. The photoluminescence band of Ag₂S in the zeolite with 1-dimensional channels was narrow in comparison to the Ag₂S in zeolites with 2- or 3-dimensional channels.     

Specific interactions between silver(I) ions and cytosine-cytosine pairs in DNA duplexes

Very specific binding of the Ag(i) ion unexpectedly stabilized DNA duplexes containing the naturally occurring cytosine-cytosine (C-C) mismatch-base pair; because the C-C pair selectively binds to the Ag(i) ion, we developed a DNA-based Ag(i) sensor that employed an oligodeoxyribonucleotide containing C-C pairs used for Ag(i) binding sites.     

Realization of anti-SN2' selective allylation of 4-cyclopentene-1,3-diol monoester with aryl- and alkenyl-zinc reagents

Anti-SN2' mode of allylation of the monoester of 4-cyclopentene-1,3-diol with aryl and alkenyl anions was achieved, for the first time, with the MeOCH2CO2- group as a leaving group to which R-ZnBr and CuCl (as a catalyst) were best fitted. The aryl groups successfully installed were Ph, o- and p-MeC6H4, o-MOMOC6H4, o-MeOC6H4, and p-F-C6H4, while cis and trans alkenyl groups were attached with retention of the olefinic stereochemistries.     

Rhodium-catalyzed borylative cyclization of 2-alkynylaryl isocyanates with bis(pinacolato)diboron

2-alkynylaryl isocyanates reacted with bis(pinacolato)diboron in the presence of a cationic rhodium(I) catalyst to produce borylated 3-alkylideneoxindoles stereoselectively. The carbon-boron linkage formed was further transformed via reactions such as a cross-coupling and a halogenation reaction.     

Novel One-pot Three-component Coupling Reaction with Trimethylsilylmethyl-phosphonate, Acyl Fluoride, and Aldehyde through the Horner-Wadsworth-Emmons Reaction

A novel three-component coupling between trimethylsilylmethylphosphonate, acyl fluoride, and aldehyde has been developed. A sequential nucleophilic addition of lithio-trimethylsilylmethylphosphonate to the acyl fluoride and Horner-Wadsworth-Emmons reaction of an aldehyde with the lithio-β-ketophosphonate generated in situ by desilylation at the α-position of the α-silyl-β-ketophosphonate by fluoride took place cleanly in a one-pot operation. Various E- and Z-enones were obtained in high yields with high stereoselectivities by this one-pot procedure.     

Role of intracellular contents to facilitate supercooling capability in beech (Fagus crenata) xylem parenchyma cells

In order to find the possible role of intracellular contents in facilitating the supercooling capability of xylem parenchyma cells, changes in the temperature of supercooling levels were compared before and after the release of intracellular substances from beech xylem parenchyma cells by DTA. Various methods were employed to release intracellular substances from xylem parenchyma cells and all resulted in a reduction of supercooling ability. It was concluded that the reduction of supercooling ability primarily resulted from changes of intracellular conditions, including the release of intracellular contents or their mixing with extracellular solutions, rather than due to changes of cell wall structures. It is therefore suggested that any unidentified intracellular contents may function to facilitate supercooling capability in xylem parenchyma cells.     

Solvent and ligand partition reaction pathways in nickel-mediated carboxylation of methylenecyclopropanes

Methylenecyclopropanes are carboxylated with gaseous carbon dioxide in the presence of a stoichiometric amount of a nickel complex; the reaction pathways are significantly influenced by the reaction solvent and the amine ligand.     

Effective detection of peptides containing cysteine sulfonic acid using matrix-assisted laser desorption/ionization and laser desorption/ionization on porous silicon mass spectrometry

Cysteine sulfonic acid-containing peptides, being typical acidic peptides, exhibit low response in matrix-assisted laser desorption/ionization (MALDI) mass spectrometry. In this study, matrix conditions and the effect of diammonium hydrogencitrate (DAHC) as additive were investigated for ionization of cysteine sulfonic acid-containing peptides in MALDI. A matrix-free ionization method, desorption/ionization on porous silicon (DIOS), was also utilized to evaluate the effect of DAHC. When equimolar three-component mixtures of peptides carrying free cysteine, cysteine sulfonic acid, and carbamidomethyl cysteine were measured by MALDI using a common matrix, alpha-cyano-4-hydroxycinnamic acid (CHCA), no signal corresponding to cysteine sulfonic acid-containing peptide could be observed in the mass spectrum. However, by addition of DAHC to CHCA, the peaks of cysteine sulfonic acid-containing peptides were successfully observed, as well as when using 2,4,6-trihydroxyacetophenone (THAP) and 2,6-dihydroxyacetophenone with DAHC. In the DIOS mass spectra of these analytes, the use of DAHC also enhanced the peak intensity of the cysteine sulfonic acid-containing peptides. On the basis of studies with these model peptides, tryptic digests of oxidized peroxiredoxin 6 were examined as a complex peptide mixture by MALDI and DIOS. In MALDI, the peaks of cysteine sulfonic acid-containing peptides were observed when using THAP/DAHC as the matrix, but this was not so with CHCA. In DIOS, the signal from cysteine sulfonic acid-containing peptides was suppressed; however, the use of DAHC significantly enhanced the signal intensity with an increase in the number of observed peptides and increased signal-to-noise ratio in the DIOS spectra. The results show that DAHC in the matrix or on the DIOS chip decreases discrimination and suppression effects in addition to suppressing alkali-adduct ions, which leads to a beneficial effect on protonation of peptides containing cysteine sulfonic acid.     

Allylcyanation of alkynes: regio- and stereoselective access to functionalized di- or trisubstituted acrylonitriles

Allyl cyanides are found to add across alkynes in the presence of a nickel catalyst prepared from Ni(cod)2 and P(4-CF3-C6H4)3 in situ to give variously functionalized di- or trisubstituted acrylonitriles in highly stereoselective manners possibly via a pi-allylnickel species as an intermediate. alpha-Siloxyallyl cyanides also react at the gamma-position of a cyano group with both internal and terminal alkynes having various functional groups to give silyl enol ethers, which give the corresponding aldehydes or ketones upon hydrolysis.     

Synthesis of trifluoro- or difluoromethylated olefins by regio- and stereocontrolled S(N)2' reactions of gem-difluorinated vinyloxiranes

This paper presents a highly stereoselective synthesis of trifluoro- or difluoromethylated olefins via an S(N)2' type fluorination or reductions of gem-difluorinated vinyloxiranes. Their fluorination with HF-Py furnished trifluoromethylated allylic alcohols with exclusive E selectivity. On the other hand, their reduction with DIBAL-H afforded difluoromethylated E-allylic alcohols predominantly, whereas the corresponding Z isomers were formed exclusively by treatment with BH3.THF.