Synthesis of 3-substituted 2-cyclohexenones through umpoled functionalization

A new protocol to obtain 3-substituted 2-cyclohexenones, was developed by reversing the chemical reactivity of 2-cyclohexenone. One-pot synthesis of 3-substituted 2-cyclohexenones can be achieved by treatment of 3-phenylthiosilyl enol ether with a mixture of t-BuLi/HMPA that allows hydrogen-selective exchange in presence of reactive electrophiles such as aldehydes, ketones and alkyl halides. This affords the corresponding product in moderate overall yield, after silyl enol ether cleavage and concomitant thiophenol elimination initiated with TBAF.     

The importance of glyceraldehyde radiolysis in chemical evolution

Studies in chemical evolution are intended to demonstrate how compounds of biological importance are generated from substances that could have been found in abiotic conditions on the primitive Earth or in extraterrestrial environments. In this context, the aim of the present work was to examine the behavior of dl-glyceraldehyde in both aqueous solution and solid samples under gamma irradiation. We irradiated dl-glyceraldehyde at different doses and temperatures with a gamma source; even at low doses and temperature (77 K), free radicals were detected. Among the products formed were ethylene glycol and glycolaldehyde. Some sugar-like compounds were also detected.

     

Influence of the synthetic conditions on the structural diversity of extended manganese-oxalato-1,2-bis(4-pyridyl)ethylene systems

We report herein the synthesis and physicochemical characterization of eight new manganese-oxalato compounds with 1,2-bis(4-pyridyl)ethylene (bpe): {(Hbpe)(2)[Mn(2)(μ-ox)(3)]·～0.8(C(2)H(5)OH)·～0.4(H(2)O)}(n) (1), {[Mn(μ-ox)(μ-bpe)]·xH(2)O}(n) (2), [Mn(2)(μ-ox)(2)(μ-bpe)(bpe)(2)](n) (3), [Mn(μ-ox)(μ-bpe)](n) (4a and 4b), and {[Mn(4)(μ-ox)(3)(μ-bpe)(4)(H(2)O)(4)]·(X)(2)·mY}(n) with X = NO(3)(-) (5a), Br(-) (5b), and ClO(4)(-) (5c) and Y = solvation molecules. The appropriate selection of the synthetic conditions allowed us to control the crystal structure and to design extended 2D and 3D frameworks. Compound 1 is obtained at acid pH values and its crystal structure consists of stacked [Mn(2)(μ-ox)(3)](2-) layers with cationic Hbpe(+) molecules intercalated among them. Compound 2 was obtained at basic pH values with a manganese/bpe ratio of 1:1, and the resulting 3D structure consists of an interpenetrating framework in which metal-oxalato chains are bridged by bpe ligands, leading to a microporous network that hosts a variable number of water molecules (between 0 and 1) depending on the synthetic conditions. Compound 3, synthesized with a manganese/bpe ratio of 1:3, shows a 2D framework in which linear metal-oxalato chains are joined by bis-monodentate 1,2-bis(4-pyridyl)ethylene ligands. The thermal treatment of compound 3 permits the release of one of the bpe molecules, giving rise to two new 2D crystalline phases of formula [Mn(μ-ox)(μ-bpe)](n) (4a and 4b) depending on the heating rate. The open structures of 5a-5c were synthesized in a medium with a high concentration of nitrate, perchlorate, or bromide salts (potassium or sodium as cations). These anions behave as templating agents directing the crystal growing toward a cationic porous network, in which the anions placed in the voids and channels of the structure present high mobility, as inferred from the ionic exchange experiments. Variable-temperature magnetic susceptibility measurements show an overall antiferromagnetic behavior for all compounds, which are discussed in detail.     

Information theory of D‐dimensional hydrogenic systems: Application to circular and Rydberg states

The analytic information theory of quantum systems includes the exact determination of their spatial extension or multidimensional spreading in both position and momentum spaces by means of the familiar variance and its generalization, the power and logarithmic moments, and, more appropriately, the Shannon entropy and the Fisher information. These complementary uncertainty measures have a global or local character, respectively, because they are power‐like (variance, moments), logarithmic (Shannon) and gradient (Fisher) functionals of the corresponding probability distribution. Here we explicitly discuss all these spreading measures (and their associated uncertainty relations) in both position and momentum for the main prototype in D‐dimensional physics, the hydrogenic system, directly in terms of the dimensionality and the hyperquantum numbers which characterize the involved states. Then, we analyze in detail such measures for s‐states, circular states (i.e., single‐electron states of highest angular momenta allowed within an electronic manifold characterized by a given principal hyperquantum number), and Rydberg states (i.e., states with large radial hyperquantum numbers n). © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2010     

The first total synthesis of the (±)-17-methyl-trans-4,5-methyleneoctadecanoic acid and related analogs with antileishmanial activity

The first total synthesis of the marine cyclopropane fatty acid (±)-17-methyl-trans-4,5-methyleneoctadecanoic acid was accomplished in eight steps and in 9.1% overall yield starting from 1-bromo-12-methyltridecane. The cis analog (±)-17-methyl-cis-4,5-methyleneoctadecanoic acid was also synthesized but in seven steps and in 16.4% overall yield. With the two isomeric cyclopropane fatty acids at hand it was possible to unequivocally corroborate the trans relative configuration of the naturally occurring fatty acid by gas chromatographic co-elution of the corresponding methyl esters. The cis isomer was cytotoxic to Leishmania donovani promastigotes with an IC₅₀ of 300.2 ± 4.2 μM.     

Local Disorder in Hydrogen Storage Compounds: The Case of Lithium Amide/Imide

Amides and imides of alkali metals are a very promising class of materials for use as a hydrogen‐storage system, as they are able to store and release hydrogen via a chemical route at controllable temperatures and pressures. We critically revise the present picture of the atomic structure of the lightest member (LiNH₂/Li₂NH) by using a combined computational and experimental approach. Specifically, ab initio path integral molecular dynamics simulations and solid‐state ¹H NMR techniques are combined. The results show that the presently assumed local structure might be inconsistent or at least incomplete and needs considerable revision. In particular, the Li atoms turn out to be more mobile and more disordered than suggested by structural data obtained from X‐ray scattering. Also, the configuration of the hydrogen atoms, which is accessible via the NMR experiment and the corresponding first‐principles calculations, is different from the previously assumed data. The computed and experimentally observed ¹H NMR parameters are in very good mutual agreement and illustrate the unusual chemical environment of the hydrogen atoms in this system. Incorporating our results on the new lithium data, we show that the effect of nuclear quantum delocalization for the hydrogen atoms is considerably reduced compared to the perfect crystal structure.     

Determination of heterocyclic amines in urine samples by capillary liquid chromatography with evaporated light-scattering detection

A rapid and simple method for separation and detection of six heterocyclic aromatic amines (2-amino-1-methyl-6-phenylimidazo [4,5-b]-pyridine, 2-amino-1-methyl-imidazo [4,5-f]-quinoline, 2-amino-3,8-dimethyl-imidazo [4,5-f]-quinoxaline, 2-amino-3,7,8-trimethyl-imidazo [4,5-f]-quinoxaline, 2-amino-3,4,8-trimethyl-imidazo [4,5-f]-quinoxaline, and 2-amino-3,4-dimethyl-imidazo [4,5-f]-quinoline) in human urine samples is proposed to reflect daily intake and recent HAAs exposure. This method comprises previous clean-up and preconcentration of the analytes on Strata-X reversed phase extraction cartridges followed by capillary liquid chromatography (CLC) and evaporative light-scattering detection (ELSD). A mobile phase of acetonitrile and ammonium acetate 35 mM at pH 5.15 through a gradient of composition and a flow rate of 15 μL min⁻¹ resulted in good separations of the analytes. Temperature and gas pressure were optimized for detection. The CLC-ELSD allows the separation and quantification of HAAs with good resolution, precision, and sensitivity. The usefulness of the proposed method was demonstrated by the analysis of synthetic and natural human urine samples spiked with different concentration levels of heterocyclic amines.