Effects of long-range interactions on the dynamics of ions in aqueous solution

Molecular dynamics simulations have been carried out for a Br⁻ ion in aqueous solution in order to establish the effect of truncation of long-range interactions on the dynamical properties of the ion. Simulations using smooth truncation of the potential at different cutoff radii were carried out and compared to results using the Ewald summation method. It is shown that when small cutoffs are applied (i.e. R_c = 8Å), the calculations yield low ionic diffusion coefficients relative to experiment, as well as short-time dynamical behavior which is inconsistent with the Ewald calculations. As the cutoff is increased, the results approach both the Ewald and the experimental results. In contrast to the results with the truncated potential, the short-time dynamical behavior of the hydrated bromide ion obtained with the Ewald method can be described by simple Langevin dynamics.     

Study of the extraction of uranium (VI) by bis-(di-n-butylphosphate) compounds including a polyheteroatomic chain from nitrate solutions

Compounds 1–4 with two di-n-butylphosphate groups linked by a polyheteroatomic chain BuO)₂P(O)OCH₂(CH₂XCH₂)_nCH₂OP(O)(OBu)₂ (1: n = 0; 2: n = 1, X = 0; 3: n = 2, X = 0; 4: n = 1, X = S) were prepared respectively by action of chlorodi-n-butylphosphate on ethyleneglycol, di and triethyleneglycol, and thiodiethyleneglycol under phase transfer conditions.The extraction of uranium (VI) from aqueous nitrate phase with these compounds, in toluene diluent, was studied. Distribution ratios with compounds 1–3 are somewhat greater than those obtained with tri-n-butyl-phosphate. Extraction studies reveal that polyoxygenated chain of these compounds takes part in U(VI) complexation. The general expression for the complexes is assumed to be UO₂(NO₃)₂L_m in which L is extractant compound and m the number of molecules coordinated to uranyl cation. Extraction stoichiometry is dependent upon extractant compound and its concentration in organic phase. For the compounds 1–3, m = 1.5 when extractant concentration is higher than 0.1 M; m takes the different values 0.5, 1.0 and 1.5 when extractant concentration is lower than 0.1 M For the compound in which X is sulfur atom, m= 2.0 over all studied concentration range.It was found that in the solvent extraction of uranium (VI) with these compounds, di-n-butylphosphoric acid exhibits a synergistic effect increasing the distribution ratio of U(VI) by a factor of 100.     

A two step synthesis of 2-oxo-2-vinyl 1,3,2-dioxaphospholanes and -dioxaphosphorinanes

The title compounds are prepared via a two step procedure involving a transesterification between a diol and diethyl phosphite followed by a palladium-catalyzed coupling of the so-obtained cyclic phosphite with vinyl bromide. Theoretical DFT calculations have been performed on phosphonate and phosphite anions models in order to estimate stereoelectronic effects in five-membered and six-membered ring compounds.     

Palladium-catalyzed Heck reaction on 1-alkoxy-1,3-dienes: a regioselective gamma-arylation of alpha,beta-unsaturated carbonyl compounds

[reaction: see text] alpha,beta-Unsaturated acetals afford, in the presence of the LIC-KOR superbase, 1-alkoxybuta-1,3-dienes. These substrates cross couple with aryl derivatives in the presence of Pd catalyst (Heck conditions) in a regio- and stereoselective mode. With dialkyl acetals, the reaction affords arylated dienes; on the other hand, in the case of 1,3-dioxane derivatives, the final outcome of the process formally corresponds to the direct gamma-arylation reaction of the starting alpha,beta-unsaturated material.     

Detection of nitroaromatic and cyclic nitramine compounds by cyclodextrin assisted capillary electrophoresis quadrupole ion trap mass spectrometry

An Agilent 3DCE capillary electrophoresis system using sulfobutylether-beta-cyclodextrin (SB-beta-CD)-ammonium acetate separation buffer pH 6.9 was coupled to a Bruker Esquire 3000+ quadrupole ion trap mass detector via a commercially available electrospray ionization interface with acetonitrile sheath flow. The CE-MS system was applied in negative ionization mode for the resolution and detection of nitroaromatic and polar cyclic or caged nitramine energetic materials including TNT [2,4,6-trinitrotoluene, formula mass (FW) 227.13], TNB (1,3,5-trinitrobenzene, FW 213.12), RDX (hexahydro-1,3,5-trinitro-1,3,5-triazine, FW 222.26) HMX (octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine, FW 296.16), and CL-20 (2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane, FW 438.19). The CE-MS system conformed to the high-performance liquid chromatography with ultraviolet absorbance detection (HPLC-UV) and HPLC-MS reference methods for the identification of energetic contaminants and their degradation products in soil and marine sediment samples.     

UNUSUAL CRYSTALLIZATION AND MELTING PROCESSES OF AN OPTICALLY ACTIVE POLYOLEFIN： ISOTACTIC POLY（（S）-4-METHYL-HEXENE-1）

Polyolefins that bear a chiral side chain (typically an isobutyl group) experience a so-called macromolecular amplification of chirality: the chiral side-chain induces a slight preference for either tg or tg- main chain conformation. This slight conformational bias is amplified cooperatively along the chain, and results in preferred chirality of the main chain helical conformations. As a result, these polymers display a liquid-crystal (LC) phase both in solution and, in the melt as a transient phase on the way to crystallization. The existence of two processes (melt-LC and LC-crystal transitions) results in unconventional behaviors that were first analyzed by Pino and collaborators back in 1975. These polymers also offer a means to test the structural consequences of recently introduced crystallization schemes. These schemes postulate the formation of a transient liquid-crystal phase as a general scheme for polymer crystallization.     

Existence and uniqueness for p-Laplace equations involving singular nonlinearities

We consider quasilinear elliptic equations involving the p-Laplacian and singular nonlinearities. We prove comparison principles and we deduce some uniqueness results.     

A simple route to chiral phosphinous acid-boranes

We report a simple one-pot synthesis of enantiomerically enriched alkyl- and arylphenylphosphinous acid-borane starting from readily available (R(P))-(-)-menthylhydrogenophenylphosphinate and organolithium reagents.     

N-metalated imines by reaction of 1,1-diethoxybut-2-ene with aromatic nitriles, as useful intermediates for the synthesis of substituted pyrimidines and cyclopentenones

A new approach to the synthesis of pyrimidines and cyclopentenones is described. The method exploits the reactivity of alpha,beta-unsaturated acetals with aromatic nitriles in the presence of the Schlosser's superbase LIC-KOR.     

Insights into palladium-catalyzed cyanation of bromobenzene: additive effects on the rate-limiting step

Kinetic studies using reaction calorimetry were conducted under synthetically relevant conditions to study the effect of additives in the cyanation of bromobenzene catalyzed by palladium complexes. This work demonstrates that the addition of a catalytic amount of ZnBr(2) facilitates the reaction with an elimination of the induction period observed without additive. This study afforded a qualitative assessment of the effect of water on the rate-limiting step and the apparent reaction order in bromobenzene.