Barrierless electron transfer bond fragmentation reactions

The ultrafast N-O bond fragmentation in a series of N-methoxypyridyl radicals, formed by one-electron reduction of the corresponding N-methoxypyridiniums, has been investigated as potentially barrierless electron-transfer-initiated chemical reactions. A model for the reaction involving the electronic and geometric factors that control the shape of the potential energy surface for the reaction is described. On the basis of this model, molecular structural features appropriate for ultrafast reactivity are proposed. Femtosecond kinetic measurements on these reactions are consistent with a kinetic definition of an essentially barrierless reaction, i.e., that the lifetime of the radical is a few vibrational periods of the fragmenting bond, for the p-methoxy-N-methoxypyridyl radical.     

Determination of low-molecular-mass quaternary ammonium compounds by capillary electrophoresis and hyphenation with mass spectrometry

The determination of quaternary ammonium ions by capillary electrophoresis (CE) is reviewed. The analytes include tetraalkylammonium and alkylbenzyldimethylammonium compounds frequently used as antiseptic and antibacterial agents as well as in various household products, several plant growth regulators and herbicides, by-products in bile acid sequestrants, and a range of anticholinergic drugs. Besides direct and indirect UV detection, hyphenation with electrospray mass spectrometry is particularly suited for quaternary ammonium ions and may lower the detection limits by two orders of magnitude. In comparison with established liquid chromatographic techniques, CE may exhibits superior separation efficiency. Applications in routine analysis have demonstrated that CE is reliable and robust enough to represent a real alternative to chromatography.     

The Henicosaphosphide Iodides of Potassium and Rubidium,K4P21I and Rb4P21I

The novel ternary polyphosphides M₄P₂₁I (M = K, Rb) have been synthesized from the elements in single crystalline form, representing further examples for the formation of mixed crystals between simple salts and binary phosphides. They form as ruby‐red platelets and dark‐red prisms, respectively, and are only slightly sensitive to moisture and oxygen. The compounds are isotypic (Ccmm (no 63); Z = 4; oP104; K₄P₂₁I: a = 12.853Å; b = 21.795Å; c = 9.748Å; 1168 hkl, R = 0.033; Rb₄P₂₁I: a = 13.281Å; b = 21.868Å; c = 9.771Å; 777 hkl, R = 0.053) and feature corrugated 2D networks formed from two different types of polymerized P₇ units. The networks form large cavities filled by M⁺ and I^‐ ions. Zigzag chains of condensed trigonal M₆ prisms, centered by the I^‐ anions, separate the polyphosphide nets. The mean homoatomic P‐P bond length (d = 2.216Å) corresponds to a P‐P single bond. However, the individual P‐P distances vary with position and function (2.126 ‐ 2.247Å) and these are compared with those of the isolated P₂₁^‐3 anion.     

Electrokinetic characterization of poly(dimethylsiloxane) microchannels

This paper characterizes the basic electrokinetic phenomena occurring within native poly(dimethylsiloxane) (PDMS) microchannels. Using simple buffers and current measurements, current density and electroosmosis data were determined in trapezoidal, reversibly sealed PDMS/PDMS and hybrid PDMS/glass channels with a cross-sectional area of 1035.5 microm(2) and about 6 cm length. This data was then compared to that obtained in an air-thermostated 50 microm inner diameter (1963.5 microm(2) cross-sectional area) fused-silica (FS) capillary of 70 cm length. Having a pH 7.8 buffer with an ionic strength (I) of 90 mM, Ohms's law was observed in the microchannels with electric field strengths of up to about 420 V/cm, which is about twice as high as for the FS capillary. The electroosmotic mobility (micro(EO)) in PDMS and FS is shown to exhibit the same general dependences on I and pH. For all configurations tested, the experimentally determined micro(EO) values were found to correlate well with the relationship micro(EO) = a + b log(I), where a and b are coefficients that are determined via nonlinear regression analysis. Electroosmotic fluid pumping in native PDMS also follows a pH dependence that can be estimated with a model based upon the ionization of silanol. Compared to FS, however, the magnitude of the electroosmotic flow in native PDMS is 50-70% smaller over the entire pH range and is difficult to maintain at acidic pH values. Thus, the origin of the negative charge at the inner wall of PDMS, glass, and FS appears to be similar but the density is lower for PDMS than for glass and FS.     

The rhombidodecahedral tessellation of 3-space and a particular 15-vertex triangulation of the 3-dimensional torus

It is well known that the unique 7-vertex triangulation of the 2-dimensional torus S¹×S¹ is a consequence of the relationship between two hexagonal lattices in the euclidean plane: it is just the quotient of the triangular tessellation of the plane by a translation group. Each vertex star is a regular hexagon and the symmetry group of this triangulation is the affine group A(1,₇) in one dimension over ₇. In this paper we describe a particular 15-vertex triangulation of the 3-dimensional torus S¹×S¹×S¹ whose symmetry group is the affine group A(1,₁₅) and which is similarly related to two lattices in euclidean 3-space: it is just the quotient of a particular tessellation of 3-space by a translation group. Each vertex star happens to be a rhombidodecahedron, the dual of a (semiregular) cuboctahedron.     

Copper—A “Modern” Bioelement

Copper is a bioessential element in biology with truly unique chemical characteristics in its two relevant oxidation states +I and +II. Significant progress has been made in recent years in the elucidation of the frequently surprising biochemistry of this trace element. Those advances were especially furthered through mutual stimulation involving results from biochemistry, molecular biology, and medicine on one hand and the synthesis as well as the structural and spectroscopic characterization of low molecular weight model complexes on the other. The most notable features of protein-bound active copper are its almost exclusive function in the metabolism of O₂ or N/O compounds (NO, N₂O) and its frequent association with oxidizing organic and inorganic radicals such as tyrosyl, semiquinones, superoxide, or nitrosyl. This unique biological role of copper can be rationalized given its chemical and assumed evolutionary background.     

Development and validation of a method for the determination of trace alkylphenols and phthalates in the atmosphere

An analytical method has been developed for the simultaneous extraction and determination of trace tertiary octylphenol (t-OP), technical nonylphenol isomers (NP), nonylphenol monoethoxylate isomers (NP1EO) and seven phthalates in the atmosphere using gas chromatography-mass spectrometry (GC-MS). High volume samples were collected using a high-volume pump equipped with a PUF/XAD-2 column for air and glass fiber filter for particles. The detection limits of the method for alkylphenols (APs) and the phthalates ranged from 0.0006 to 0.034 ng m⁻³ in air. The recoveries of t-OP, NP, NP1EO and the phthalates for the entire procedure were satisfactory (>69%). The method was successfully applied to the determination of the analytes in the atmosphere samples collected over land and the ocean. The concentrations of t-OP, NP, NP1EO showed decline trends from land to the open sea, and the phthalates present over land and the North Sea were comparable. It is suggested that the atmosphere is a significant pathway for the transport of alkylphenols and the phthalates in the environment.     

Determination of the Insect Repellent Bayrepel® in Pool and Lake Water by Gas Chromatography after Preconcentration with Solid-Phase Extraction and Stir-Bar-Sorptive Extraction

A method for the determination of the new insect repellent Bayrepel in bathing lakes and public pools is presented. Sample preconcentration is performed either by solid-phase extraction (SPE) or stir bar sorptive extraction (SBSE). Analysis of the enriched analyte using gas chromatography-mass spectrometry (GC-MS) led to almost identical limits of detection (LOD) of 25ngL^–1 for Bayrepel with both extraction methods. Because of the slightly reduced handling effort involved, the method based on preconcentration by SBSE was finally chosen for the analysis of real samples.     

A Convergent Synthesis of (±)-α- and β-Himachalenes

(±)-α and β-Himachalene, 5 and 6 , have been synthesized in a convergent manner from 3,3-dimethylacrolein ( 9 ), the ester enolate 10 and the silyloxypentadienyllithium 7 . The key steps are the regioselective γ-addition of the dienal 13 to 7 and the intramolecular Diels-Alder addition 15 → 16 . Hydrogenolysis of the diethylphosphate group and functionalization at C (5) completed the synthesis of 5 and 6 .     

A three‐dimensional framework of bis­[tris­(ethyl­enediamine)zinc] tetra­iodo­cadmate diiodide assisted by N—H⋯I hydrogen bonds

The title salt, [Zn(C₂N₂H₈)₃]₂[CdI₄]I₂, conventionally abbreviated [Zn(en)₃]₂[CdI₄]I₂, where en is ethyl­enediamine, contains discrete [Zn(en)₃]²⁺ cations and [CdI₄]²⁻ anions with distorted octa­hedral and nearly tetra­hedral geometries, respectively, as well as uncoordinated I⁻ ions. The cation and the free I⁻ anion lie on twofold rotation axes and the [CdI₄]²⁻ anion lies on a axis in the space group I2d. The structure exhibits numerous weak inter‐ionic hydrogen bonds of two types, viz. N—H⋯I⁻(free ion) and N—H⋯I([CdI₄]²⁻), which support the resulting three‐dimensional framework.