Unsymmetrically substituted disilyne Dsi(2)(i)PrSi-Si≡Si-SiNpDsi(2) (Np = CH(2)(t)Bu): synthesis and characterization

The unsymmetrically substituted disilyne, Dsi(2)(i)PrSi-Si≡Si-SiNpDsi(2) (Np = CH(2)(t)Bu) 2, was synthesized and characterized by X-ray crystallography to show a trans-bent structure with a silicon-silicon triple bond length of 2.0569(12) ?. The (29)Si chemical shifts of the triply bonded silicon atoms of 2 are quite different, being observed at 62.6 ppm for the Dsi(2)(i)PrSi side and 106.3 ppm for the Dsi(2)NpSi side, indicating different hybridizations on the triply bonded silicon atoms at each site.     

(tBu2MeSi)2Sn=Sn(SiMetBu2)2: a distannene with a >Sn=Sn< double bond that is stable both in the solid state and in solution

((t)Bu(2)MeSi)(2)Sn=Sn(SiMe(t)Bu(2))(2) 1, prepared by the reaction of (t)Bu(2)MeSiNa with SnCl(2)-diox in THF and isolated as dark-green crystals, represents the first example of acyclic distannene with a Sn=Sn double bond that is stable both in the crystalline form and in solution. This was proved by the crystal and NMR spectral data of 1. Distannene 1 has these peculiar structural features: a shortest among all acyclic distannenes Sn=Sn double bond of 2.6683(10) A, a nearly planar geometry around both Sn atoms, and a highly twisted Sn=Sn double bond. The reactions of 1 toward carbon tetrachloride and phenylacetylene also correspond to the reactivity anticipated for the Sn=Sn double bond. The one-electron reduction of 1 with potassium produced the distannene anion radical, the heavy analogue of alkene ion radicals, for which the particular crystal structure and low-temperature EPR behavior are also discussed.     

Agesamides A and B, bromopyrrole alkaloids from sponge Agelas species: application of DOSY for chemical screening of new metabolites

Diffusion-ordered NMR spectroscopy (DOSY) is a versatile and powerful NMR technique and a noninvasive analytical method for mixture analysis that does not require prior physical separation of the analytes. In our search for new metabolites from natural resources, DOSY was applied for constituent analysis of crude bromopyrrole fractions separated from an Okinawan marine sponge Agelas sp. so that two new bromopyrrole alkaloids, agesamides A (1) and B (2), have been isolated. The structures and relative stereochemistry of 1 and 2 were elucidated from spectroscopic data.     

Determination of 3,6-dinitrobenzo[e]pyrene in surface soil and airborne particles by high-performance liquid chromatography with fluorescence detection

We developed a sensitive analytical method and an efficient clean-up method to quantify 3,6-dinitrobenzo[e]pyrene (3,6-DNBeP) in surface soil and airborne particles. After purification using a silica gel column and two reversed-phase columns, 3,6-DNBeP was reduced to 3,6-diaminobenzo[e]pyrene by a catalyst column and analyzed by high-performance liquid chromatography (HPLC) with a fluorescence detector. 3,6-DNBeP was detected in all of the soil samples and airborne particles examined. The concentration of 3,6-DNBeP in surface soil and airborne particles was determined in the ranges of 347-5007 pg/g of soil and 137-1238 fg/m3, respectively.     

Analysis of sugar phosphates in plants by ion chromatography on a titanium dioxide column with pulsed amperometric detection

This paper describes the development of a practical method for the analysis of sugar phosphates from the model higher plant Arabidopsis thaliana by high-performance anion-exchange chromatography with pulsed amperometric detection (HPAEC-PAD). The extraction method of sugar phosphates from higher plants was first optimized for HPAEC-PAD analysis. In order to improve the resolution in HPAEC-PAD, a column packed with titanium dioxide resin was used. The titanium dioxide column was used as a trap-column for sugar phosphates and nucleotides, for the removal of sample matrices. Sample pretreatment was achieved in-line and automatically using a six-port valve placed after the injection valve.     

Decomposition of protonated formic acid: One transition state—Two product channels

The unimolecular chemistry of protonated formic acid, [HCOOH]H(+), has been investigated by analyzing the fragmentation of metastable ions (MI) during flight in a sector mass spectrometer, and by proton transfer to formic acid in a Fourier-transform ion cyclotron resonance (FT-ICR) mass spectrometer. High level ab initio calculations have been used to model the relevant parts of the potential energy surface (PES). In addition, ab initio direct dynamics calculations have been conducted, tracing out 60 different reaction trajectories. The only stable isomer in the mass spectrometric experiments is HC(OH)(2)(+), which is the precursor to both observed ionic products, HCO(+) and H(3)O(+), via the same saddle point of the potential energy surface. The detailed motion of the dissociating molecule during passage of the post-transition state region of the PES therefore determines which product ion is formed. After passing the TS a transient HC(O)OH(2)(+) molecule is first formed. High total energy increases the probability that the nascent water molecule will have sufficient speed to escape the HCO(+) moiety. Otherwise, typically at low energies, the two units recombine, upon which intra-complex proton transfer is very likely. Eventually, this will give the more stable H(3)O(+).     

Hyrtioseragamines A and B, new alkaloids from the sponge Hyrtios species

Two novel alkaloids with a furo[2,3-b]pyrazin-2(1H)-one moiety and a guanidino group, hyrtioseragamines A (1) and B (2), have been isolated from an Okinawan marine sponge Hyrtios species. The structures of 1 and 2 were elucidated on the basis of spectroscopic data and chemical conversions. Compounds 1 and 2 are the first natural products possessing a furo[2,3-b]pyrazine-related moiety.     

Thermal membrane potential across cation-exchange membranes for various halide solutions

Thermal membrane potential across cation-exchange membranes was measured for various halide solutions. Linear relationships between thermal membrane potential () and temperature difference (T) were observed, and the temperature coefficient of thermal membrane potential (/T) decreases with increase in the molality of the external solution as predicted by a theory reported. When counterions of membranes are hydrogen ions, the sign of the coefficients turns into minus near 0.01 mol/kg of the external solution for all membranes, although the coefficients are always positive for all the other forms. The dependence of the coefficients on the molality of the external solutions sometimes deviated slightly from the theory. This deviation is attributed to some change in water content of the membranes. A reproducible method of measuring water content of membranes was applied to discuss the change in the state of the membranes.