Trace elements in tobacco and tobacco smoke by X-ray fluorescence technique

Trace elements in tobacco and tobacco smoke of a large number of commonly available brands of cigarettes were analyzed by energy dispersive X-ray fluorescence. This work supplements the data on same samples gathered by INAA and reported earlier. Data on some toxic elements like Pb, Cu and Ni that could not be measured by INAA are presented here. A number of chewing and snuff tobacco samples were also analyzed. The concentrations of Ca, K, Cl, Br, Cu, Fe, Ni, Pb, Rb, Sr, Ti and Zn in all these samples are presented and their relative hazards are discussed.     

NaIO4/LiBr-mediated diastereoselective dihydroxylation of olefins: a catalytic approach to the Prevost-Woodward reaction

[reaction: see text] LiBr catalyzes efficiently the dihydroxylation of alkenes to afford syn and anti diols with excellent diastereoselectivity depending upon the use of NaIO(4) (30 mol %) or PhI(OAc)(2) (1 equiv), respectively, as the oxidants. The oxidation of non-benzylic halides has been achieved for the first time to afford the corresponding diols in excellent yields.     

Structural and electrical properties of hexavalent-substituted BIMEVOX synthesized by a microwave-assisted route

The microwave (MW)-assisted solid synthesis route was employed to prepare a new Aurivillius-type compound with the general formula Bi₂Cr _x V_1?x O_5.5+x?δ; 0≤x≤0.20 (BICRVOX). This novel synthesis method revealed that polycrystalline products of the BICRVOX system can effectively be obtained after being irradiated for 25 min rather than for the many hours of high-temperature heating needed in other conventional routes. The phase structure of MW-prepared samples was characterized by comparison with those obtained from the conventional solid-state reaction, using powder X-ray diffraction, FT-IR and differential thermal analysis techniques. Importantly, the substitution of Cr(VI) for V(V) in the parent compound resulted in stabilization of only the α - and β -phases. AC impedance spectroscopy confirmed that the MW-prepared samples possess slightly lower oxide-ion performance compared with the conventionally-prepared ones; it did, however, evidence the significant role of powerful dielectric heating of MWs in lowering the charge carrier accumulation.     

Highly Efficient Method for Synthesis of Bis(Indolyl)Methanes Catalyzed by FeCl3−based Ionic Liquid

A simple and highly efficient green protocol for synthesis of bis(indolyl)methanes was carried out by the reaction of indole with aldehydes and ketones in the presence of FeCl_3?based ionic liquid. These liquids serve as efficient media as well as Lewis acid catalysts.     

A novel and efficient total synthesis of (±)-physostigmine

Application of the Wittig olefination-Claisen rearrangement protocol for the total synthesis of (±)-physostigmine.     

Determination of benzene at trace levels in air by a novel method based on solid-phase microextraction gas chromatography/mass spectrometry.

A new method for the determination of benzene at trace levels in air is presented. The method consists of the collection of air samples on adsorbent cartridges with simultaneous adsorption of pre-established amounts of D6-labeled internal standard. Desorption from the cartridge is performed by solid-phase microextraction (SPME) with analysis by gas chromatography/mass spectrometry (GC/MS) using an ion trap mass spectrometer. The influence of several parameters (type of SPME fiber, temperature, time, for example) was investigated, and good linearity in the range 10-400 ng of C6D6, with a coefficient of variance (CV) around 3-5%, was obtained. The method was tested by sampling air in a town center in Italy, and a benzene concentration of approximately 50 microg/m(3) was determined. The maximum limit recommended by the European Community is 10 microg/m(3).     

The stereochemistry of 1,3-dipolar cycloaddition of internally H-bonded chiral methylenenitrones

A study of diastereoselectivity in the cycloaddition reactions of a series of mono- and disubstituted alkenes with two chiral, internally H-bonded methylenenitrones has been carried out. The high degree of stereochemical control in the presence of anhydrous magnesium bromide has been explained in terms of a metal chelated transition state. Intramolecular cycloaddition involving a methylenenitrone containing an alkene moiety linked to a nitrogen gave a stereoselective addition product.     

Stable,Reactive, and Orthogonal Tetrazines: Dispersion Forces Promote the Cycloaddition with Isonitriles

The isocyano group is a structurally compact bioorthogonal functional group that reacts with tetrazines under physiological conditions. Now it is shown that bulky tetrazine substituents accelerate this cycloaddition. Computational studies suggest that dispersion forces between the isocyano group and the tetrazine substituents in the transition state contribute to the atypical structure–activity relationship. Stable asymmetric tetrazines that react with isonitriles at rate constants as high as 57 L mol^?1 s^?1 were accessible by combining bulky and electron‐withdrawing substituents. Sterically encumbered tetrazines react selectively with isonitriles in the presence of strained alkenes/alkynes, which allows for the orthogonal labeling of three proteins. The established principles will open new opportunities for developing tetrazine reactants with improved characteristics for diverse labeling and release applications with isonitriles.