1,2]- or [2,3]-rearrangement of onium ylides of allyl and benzyl ethers and sulfides via in situ-generated iodonium ylides

Iodonium ylides, generated in situ with bisacetoxyiodobenzene, are converted to allyl- or benzyl-substituted oxonium or sulfonium ylides via rhodium- or copper-catalyzed carbene transfer. Except for the S-benzyl example, the resulting ylides undergo rearrangement to the corresponding 2-substituted heterocycles. This demonstrates the first use of iodonium ylides as diazoketone surrogates for the generation and rearrangement of onium ylide intermediates. This abbreviated one-step method proceeds in comparable yields relative to the corresponding two-step route employing diazoketone intermediates.     

Reinforced self-assembly of hexa-peri-hexabenzocoronenes by hydrogen bonds: from microscopic aggregates to macroscopic fluorescent organogels

Hexa-peri-hexabenzocoronene derivatives (HBCs) that have hydrogen-bonding functionalities (either amido or ureido groups) adjacent to the aromatic cores have been synthesized to study the effects of intracolumnar hydrogen bonds on the self-assembly behavior of HBCs. The hydrogen bonds effectively increased the aggregation tendency of these compounds in solution. In the bulk state, the typical columnar supramolecular arrangement of HBCs was either stabilized substantially (1 a, 1 b, 2 a, and 2 b), or suppressed by dominant hydrogen-bonding interactions (3). For some of the compounds (1 a, 2 a, and 2 b), the supramolecular arrangement adopted in the liquid-crystalline state was even retained after annealing, presumably owing to the reinforcement of the pi-stacking interactions by the hydrogen bonds. Additionally, the combined effect of the hydrogen bonds and pi-stacking of the aromatic moieties led to the formation of fluorescent organogels, whereby some derivatives were further investigated as novel low molecular-mass organic gelators (LMOGs).     

Thermodynamic and biodistribution studies of Zn(II), Ca(II), Gd(III) and Cu(II) complexes of 3,3,9,9-tetramethyl-4,8-diazaundecane-2,10-dione dioxime

The thermodynamic equilibria of copper(II), zinc(II), calcium(II) and gadolinium(III) with 3,3,9,9-tetramethyl-4,8-diazaundecane-2,10-dione dioxime (L1) have been studied at 25 degrees C and an ionic strength of 0.15 mol dm(-3). Copper and gadolinium form stable complexes with the ligand while the corresponding zinc species are more than 9 log units less stable. No complexes between calcium and the ligand were detected. The low binding strength of L1 towards zinc is attributed to the square-planar coordination geometry forced on the metal ion by the ligand as revealed by molecular mechanics calculations and molecular dynamics simulations. Speciation calculations, using a computer model of blood plasma, indicate that, despite the high concentration of zinc(II) and calcium(II) in vivo, L1 is able to increase the low-molecular-mass fraction of copper in plasma. Octanol/water partition coefficient of [CuL1H(-1)] indicates that although this species is largely hydrophilic, approximately 6% of the complex goes into the octanol phase and hence may promote dermal absorption of copper by the same amount. The dermal penetration rate is calculated to be 4.0 x 10(-4) mm h(-1). The [CuL1H(-1)] complex, which predominates at pH 7.4, is a poor mimic of native copper-zinc superoxide dismutase. Biodistribution experiments using the 64Cu-labelled [CuL1H(-1)] complex indicate an initial high uptake of this species in the liver followed by redistribution into muscle. Only a small amount is excreted through the urine.     

A study of mesoamerican obsidian sources using activation analysis

An extensive study of Mesoamerican obsidian source samples from 37 sites has been begun to better differentiate and define the trace element content at known Mesoamerican obsidian quarries, with particular emphasis on those in Mexico. This paper reports on the first results in that study as well as studies of sample contamination by grinding and results for the new National Bureau of Standards No. 278 Obsidian SRM.     

Reduction of nitroaromatics to arylnitrenium ions by vinyl halide cations

The title reduction of nitroaromatics ArNO(2) by vinyl halide radical cations CH(2)[double bond]CH-X(+*)(X = Cl or Br) to form arylnitrenium ions ArNH(+) involves a change in oxidation number of nitrogen from +3 to -1. This novel reaction provides a new route for the generation of arylnitrenium ions, a highly selective method for the detection of explosives in mixtures, and offers clues to the carcinogenic activity of nitroaromatics in vivo.     

Direct and quantitative analysis of underivatized acylcarnitines in serum and whole blood using paper spray mass spectrometry

A simple protocol for rapid quantitation of acylcarnitines in serum and whole blood has been developed using paper spray mass spectrometry. Dried serum and whole blood containing a mixture of ten acylcarnitines at various concentrations were analyzed as spots from paper directly without any sample pretreatment, separation, or derivatization. The composition of the spray solvent was found to be a critical factor: for serum samples, spray solvent of methanol/water/formic acid (80:20:0.1) gave the best signal intensity while for blood samples which contain more matrix components, acetonitrile/water (90:10) was a much more suitable spray solvent. For the paper type and size used, 0.5 μL of sample provided an optimal signal for both serum and whole blood samples. For quantitative profiling, the limits of quantitation obtained from both serum and blood were much lower than the clinically validated cutoff values for diagnosis of fatty acid oxidation disorders in newborn screening. Linearity (R(2) > 0.95) and reproducibility (RSD ~10 %) were achieved in the concentration ranges from 100 nM to 5 μM for the C2 acylcarnitine, and for other acylcarnitines, these values were from 10 to 500 nM. Acylcarnitine profiles offer an effective demonstration of the fact that paper spray mass spectrometry is an appropriate, simple, rapid method with high sensitivity and high reproducibility applicable to newborn screening tests.     

Accelerated Chemical Reactions and Organic Synthesis in Leidenfrost Droplets

Leidenfrost levitated droplets can be used to accelerate chemical reactions in processes that appear similar to reaction acceleration in charged microdroplets produced by electrospray ionization. Reaction acceleration in Leidenfrost droplets is demonstrated for a base‐catalyzed Claisen–Schmidt condensation, hydrazone formation from precharged and neutral ketones, and for the Katritzky pyrylium into pyridinium conversion under various reaction conditions. Comparisons with bulk reactions gave intermediate acceleration factors (2–50). By keeping the volume of the Leidenfrost droplets constant, it was shown that interfacial effects contribute to acceleration; this was confirmed by decreased reaction rates in the presence of a surfactant. The ability to multiplex Leidenfrost microreactors, to extract product into an immiscible solvent during reaction, and to use Leidenfrost droplets as reaction vessels to synthesize milligram quantities of product is also demonstrated.     

Nucleophilic Addition of Nitrogen to Aryl Cations: Mimicking Titan Chemistry

The reactivity of aryl cations toward molecular nitrogen is studied systematically in an ion trap mass spectrometer at 10² Pascal of nitrogen, the pressure of the Titan main haze layer. Nucleophilic addition of dinitrogen occurs and the nature of aryl group has a significant influence on the reactivity, through inductive effects and by changing the ground state spin multiplicity. The products of nitrogen activation, aryldiazonium ions, react with typical nitriles, aromatic amines, and alkynes (compounds that are relevant as possible Titan atmosphere constituents) to form covalently bonded heterocyclic products. Theoretical calculations at the level [DFT(B3LYP)/6-311++G(d,p)] indicate that the N₂ addition reaction is exothermic for the singlet aryl cations but endothermic for their triplet spin isomers. The –OH and –NH₂ substituted aryl ions are calculated to have triplet ground states, which is consistent with their decreased nitrogen addition reactivity. The energy needed for the generation of the aryl cations from their protonated precursors (ca. 340 kJ/mol starting with protonated aniline) is far less than that required to directly activate the nitrogen triple bond (the lowest energy excited state of N₂ lies ca. 600 kJ/mol above the ground state). The formation of aza-aromatics via arene ionization and subsequent reactions provide a conceivable route to the genesis of nitrogen-containing organic molecules in the interstellar medium and Titan haze layers.

Cyclisations of alkynoic acids using copper(I) arylspiroborate complexes

In this study we have studied the synthesis, characterization and catalytic activity of phosphinocopper(I) complexes [Cu(PPh₃)₃(NCCH₃)][B(O₂C₆H₄-4-R)₂] (3a: R?=?H; 3b: R?=?Me; 3c: R?=?NO₂) and [Cu(PPh₃)₃(NCCH₃)][B(O₂C₆H₃-3,5-di-^tBu)₂] (3d) containing weakly coordinating arylspiroborate ligands bearing various electronic and sterically defined characteristics. All new compounds have been characterized fully including single crystal X-ray diffraction studies for 3a and 3c and confirm that the arylspiroborate ligands do not coordinate to the copper atoms. Using these new metal complexes as precatalysts in the cyclisation of short chain alkynoic acids gave the corresponding exo-dig cyclic lactones exclusively.     

2-(1-Azulyl)ethyl tosylate methylene scrambling in the gas phase. Similarities to solution chemistry

The methylene groups in 2-(1-azulyl)ethyl tosylate are largely scrambled prior to formation of fragment ions in the mass spectrometer. This process also occurs in the 3-nitro analog, where it is dependent on sample residence time in the source and independent of electron energy. It could not be observed with the isomeric 6-substituted tosylates, the 1-substituted acetates or alcohols, or with 2-(p-anisyl)ethyl tosylate. Scrambling occurs in the neutral molecule prior to ionization and a mechanism involving absorption onto the metal surface and formation of a complexed ethylenazulonium ion is suggested.