Detection of inorganic species by chemical reaction laser desorption ionization mass spectrometry

The oxidation numbers of metals in inorganic compounds were identified by matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) by using their acetylacetonates, which are soluble in acetone. For the MALDI analysis of inorganic species insoluble in common solvents used for matrices, such as acetone, methanol, water, etc., a suspension method of sample preparation was developed. Turbid suspensions of inorganic species in the solvent were spotted on the sample holder with chelating reagents, as in the conventional sample preparation for MALDI-MS. Chemical reaction between the inorganic species and the chelating reagents occurred in the plume after irradiation by laser light. Metal oxides were also analyzed by this method, and samples with different oxidation numbers gave different mass spectra. These results suggest that many other metal oxides with different oxidation numbers could be identified if suitable chelating reagents are chosen for sample preparation for MALDI-MS.     

1,3-Dipolar cycloadditions of anhydro-5-hydroxyoxazolium hydroxide generated from 2-piperidinecarboxylic acid. Isolation of the primary adduct and synthesis of tetrahydroindolizines

1,3-Dipolar cycloaddition reactions of anhydro-5-hydroxyoxazolium hydroxide 3 generated from 2-piperidinecarboxylic acid and acetic anhydride, with dimethyl and diethyl acetylene-dicarboxylates, dibenzoylacetylene, p-benzoquinone, and 1,4-naphthoquinone gave the corresponding tetrahydroindolizines. In the case of the reaction with p-benzoquinone, the dihydroindolizine 12 was also formed. The primary N-bridged lactone intermediate 4 was isolated from the reaction of 2 with dibenzoylacetylene. Several attempted conversions of these tetrahydroindolizines into the corresponding aromatic indolizines were fruitless.     

Stereospecific polymerization of isobutyl vinyl ether by AlR3–VCln catalysts. I. Influence of preparative conditions of the catalysts

The polymerization of isobutyl vinyl ether by the VCl_n–AIR₃ system was carefully studied. The vanadium components were prepared by the reaction between VCl₄ and AlEt₃ or n-BuLi as a reducing agent. VCl₃·LiCl and VCl₂·2LiCl are the effective catalysts for the stereospecific polymerization of isobutyl vinyl ether. When VCl₃·LiCl is combined with AlR₃, a new catalytic system is formed. The effect of the preparative conditions of the various vanadium component in the AlR₃–VCl_n system shows that the effective vanadium component is trivalent. In the polymerization by VCl₃·LiCl–Al (i-Bu)₃ system, a change of the polymerization mechanism may occur at Al(i-Bu)₃/VCl₃·LiCl ratio at around 5. When the ratio is lower than 5, a cationic polymerization by VCl₃·LiCl takes place predominantly, while at ratios higher than 5, it is suggested that the polymerization proceeds by means of a VCl₃·LiClA–Al(i-Bu)₃ complex by a coordinated anionic mechanism. The polymers obtained by these catalysts are highly crystalline. Styrene was also polymerized by using the same catalysts. VCl₃·LiCl and VCl₃·LiCl–THF complex yielded amorphous polymer by cationic polymerization. When VCl₃·LiCl was combined with 6 mole-eq of Al(i-Bu)₃, the resulting polystyrene was highly crystalline and had an isotactic structure, while the VCl₂·2LiCl–Al(i-Bu)₃ (1:6) system yielded traces of polymer of extremely low stereoregularity. The results indicate that the effective vanadium component at Al/V ≧ 6 is trivalent and that the mechanism is a coordinated anionic one.     

Preparation of micron-size monodisperse polymer particles by dispersion copolymerization of styrene with poly(2-oxazoline) macromonomer

This article describes the preparation of micron-size monodisperse polymer particles by dispersion copolymerization of styrene with a poly(2-oxazoline) macromonomer in an aqueous ethanol solution. The macromonomer acted as a comonomer as well as a stabilizer. The diameter of the particles increased as the concentration of the macromonomer decreased. The higher the molecular weight of the macromonomer, the smaller the particle size. The copolymerization in the solvent containing higher water content gave smaller polymer particles. Under the condition giving the monodisperse particles, the particles volume increased linearly with the yield of the particles. From ESCA analysis of the particle surface, poly(2-oxazoline) chains were enriched on the surface. © 1993 John Wiley & Sons, Inc.     

Synthesis and reactivity of a (mu-1,1-hydroperoxo)(mu-hydroxo)dicopper(II) complex: ligand hydroxylation by a bridging hydroperoxo ligand

A new tetradentate tripodal ligand (L3) containing sterically bulky imidazolyl groups was synthesized, where L3 is tris(1-methyl-2-phenyl-4-imidazolylmethyl)amine. Reaction of a bis(mu-hydroxo)dicopper(II) complex, [Cu2(L3)2(OH)2]2+ (1), with H2O2 in acetonitrile at -40 degrees C generated a (mu-1,1-hydroperoxo)dicopper(II) complex [Cu2(L3)2(OOH)(OH)]2+ (2), which was characterized by various physicochemical measurements including X-ray crystallography. The crystal structure of 2 revealed that the complex cation has a Cu2(mu-1,1-OOH)(mu-OH) core and each copper has a square pyramidal structure having an N3O2 donor set with a weak ligation of a tertiary amine nitrogen in the apex. Consequently, one pendant arm of L3 in 2 is free from coordination, which produces a hydrophobic cavity around the Cu2(mu-1,1-OOH)(mu-OH) core. The hydrophobic cavity is preserved by hydrogen bondings between the hydroperoxide and the imidazole nitrogen of an uncoordinated pendant arm in one side and the hydroxide and the imidazole nitrogen of an uncoordinated pendant arm in the other side. The hydrophobic cavity significantly suppresses the H/D and 16O/18O exchange reactions in 2 compared to that in 1 and stabilizes the Cu2(mu-1,1-OOH)(mu-OH) core against decomposition. Decomposition of 2 in acetonitrile at 0 degrees C proceeded mainly via disproportionation of the hydroperoxo ligand and reduction of 2 to [Cu(L3)]+ by hydroperoxo ligand. In contrast, decomposition of a solid sample of 2 at 60 degrees C gave a complex having a hydroxylated ligand [Cu2(L3)(L3-OH)(OH)2]2+ (2-(L3-OH)) as a main product, where L3-OH is an oxidized ligand in which one of the methylene groups of the pendant arms is hydroxylated. ESI-TOF/MS measurement showed that complex 2-(L3-OH) is stable in acetonitrile at -40 degrees C, whereas warming 2-(L3-OH) at room temperature resulted in the N-dealkylation from L3-OH to give an N-dealkylated ligand, bis(1-methyl-2-phenyl-4-imidazolylmethyl)amine (L2) in approximately 80% yield based on 2, and 1-methyl-2-phenyl-4-formylimidazole (Phim-CHO). Isotope labeling experiments confirmed that the oxygen atom in both L3-OH and Phim-CHO come from OOH. This aliphatic hydroxylation performed by 2 is in marked contrast to the arene hydroxylation reported for some (mu-1,1-hydroperoxo)dicopper(II) complexes with a xylyl linker.     

Preparation of gold-, gold/silver-dendrimer nanocomposites in the presence of benzoin in ethanol by UV irradiation

Gold- and gold/silver-dendrimer nanocomposites have been synthesized by UV irradiation of their salts dissolved in ethanol containing dendrimers. As dendrimers, poly(amidomaine) PAMAM dendrimers and poly(propyleneimine) PPI dendrimers of various generations were used. The photoreduction of their salts is greatly accelerated by using benzoin as a photoinitiator. The sizes of gold in the nanocomposites are affected by the concentration of benzoin as well as the concentration of dendrimers, but are hardly changed with the kind of dendrimers. For gold/silver-dendrimer nanocomposites, the absorption spectra of gold/silver nanoparticles in the nanocomposites are very similar to the theoretical spectra of gold/silver alloy nanoparticles, suggesting the formation of gold/silver alloy nanoparticles. From the comparison of TEM and DLS measurements, it is found that the metal-dendrimer nanocomposites consist of metal nanoparticles covering by dendrimer molecules.     

Accumulated detection of ethidium bromide using a UV-irradiated DNA film modified electrode and its application for electrochemical detection of an environmental pollutant

In this study, DNA was first fabricated on a glassy carbon electrode by UV-irradiation. Through this process, water-soluble DNA was converted into insoluble materials, and a stable DNA film formed on the electrode. Ethidium bromide (EtBr), a typical model substance for harmful chemicals having planer structure, was used as an electroactive intercalator. This allowed our group to investigate the electrochemical and accumulative behaviors of the intercalator in UV-irradiated DNA film on the electrode. The UV-irradiated, DNA film-modified electrode (UV-DNA-FE) made it possible to accumulate electroactive EtBr on the electrode and detect it after accumulation. The modified electrode was used to detect dibenzofuran (DBF) as an environmental pollutant. The measurements were successfully obtained by focusing on the variation of the electrode response of EtBr, based on the competitive reaction between EtBr and DBF for the intercalating sites of DNA. The results indicated the possibility of using UV-DNA film as a sensing mechanism.     

Sugar binding specificities of anti-H(O) lectins disclosed by use of fucose-containing human milk oligosaccharides as binding inhibitors

The binding to normal and sialidase-treated human erythrocytes of six 125I-labeled lectins [Ulex europeus lectin I (UEA-1) and II (UEA-II), Laburnum alpinum lectins I (LAA-I) and II (LAA-II), and Cytisus multiflorus lectins I (CMA-I) and II (CMA-II)], was studied in detail. Quantitative inhibition assays of the lectin binding to the cells were also performed with various human milk oligosaccharides as inhibitors. Based on a comparison of the inhibition constants of the inhibitors thus obtained with the association constants of the lectins to the cells, the relative activities of cell surface blood group antigens toward the lectins are discussed.     

Reactions of a platinum(III) dimeric complex with alkynes in water: novel approach to alpha-aminoketone, alpha-iminoketone, and alpha,beta-diimine via ketonyl-Pt(III) dinuclear complexes

Reaction of the platinum(III) dimeric complex [Pt(2)(NH(3))(4)((CH(3))(3)CCONH)(2)(NO(3))(2)](NO(3))(2) (1), prepared in situ by the oxidation of the platinum blue complex [Pt(4)(NH(3))(8)((CH(3))(3)CCONH)(4)](NO(3))(5) (2) with Na(2)S(2)O(8), with terminal alkynes CH[triple bond]CR (R = (CH(2))(n)CH(3) (n = 2-5), (CH(2))(n)CH(2)OH (n = 0-2), CH(2)OCH(3), and Ph), in water gave a series of ketonyl-Pt(III) dinuclear complexes [Pt(2)(NH(3))(4)((CH(3))(3)CCONH)(2)(CH(2)COR)](NO(3))(3) (3, R = (CH(2))(2)CH(3); 4, R = (CH(2))(3)CH(3); 5, R = (CH(2))(4)CH(3); 6, R = (CH(2))(5)CH(3); 7, R = CH(2)OH; 8, R = CH(2)CH(2)OH; 9, R = (CH(2))(2)CH(2)OH; 10, R = CH(2)OCH(3); 11, R = Ph). Internal alkyne 2-butyne reacted with 1 to form the complex [Pt(2)(NH(3))(4)((CH(3))(3)CCONH)(2)(CH(CH(3))COCH(3))](NO(3))(3) (12). These reactions show that Pt(III) reacts with alkynes to give various ketonyl complexes. Coordination of the triple bond to the Pt(III) atom at the axial position, followed by nucleophilic attack of water and hydrogen shift from the enol to keto form, would be the mechanism. The structures of complexes 3.H(2)O, 7.0.5C(3)H(4)O, 9, 10, and 12 have been confirmed by X-ray diffraction analysis. A competitive reaction between equimolar 1-pentyne and 1-pentene toward 1 produced complex 3 and [Pt(2)(NH(3))(4)((CH(3))(3)CCONH)(2)(CH(2)CH(OH)CH(2)CH(2)CH(3))](NO(3))(3) (14) at a molar ratio of 9:1, suggesting that alkyne is more reactive than alkene. The ketonyl-Pt(III) dinuclear complexes are susceptible to nucleophiles, such as amines, and the reactions with secondary and tertiary amines give the corresponding alpha-amino-substituted ketones and the reduced Pt(II) complex quantitatively. In the reactions with primary amines, the once formed alpha-amino-substituted ketones were further converted to the iminoketones and diimines. The nucleophilic attack at the ketonyl group of the Pt(III) complexes provides a convenient means for the preparation of alpha-aminoketones, alpha-iminoketones, and diimines from the corresponding alkynes and amines.     

Structure and properties of new ionic liquids based on alkyl- and alkenyltrifluoroborates.

A new series of low-melting, low-viscosity, hydrophilic ionic liquids, which comprise 1-ethyl-3-methylimidazolium ([EMI]+) and alkyl(alkenyl)trifluoroborate anions ([RBF3]-, R=n-C(m)H(2m+1) (m=1-5), CH2CH), were prepared and characterized. The phase-transition behavior, thermal stability, density, viscosity, conductivity, and surface tension of these salts were measured. The influence of the structural variations, such as changing the length and fluorination of the alkyl chain (R) in the anion [RBF3]-, on the above properties was extensively investigated. The low viscosity of these [RBF3]- salts suggests that a high degree of freedom and/or a somewhat flat-shaped feature in the anion make an important contribution to reducing the viscosity. The Walden products for each salt are not constant and vary with temperature, which suggests that the ions in these salts are not completely dissociated.