A DFT investigation of the addition reaction of monomeric lithium enolate derived from propiophenone to propene oxide: examination of the possible transition structures

The addition reaction of monomeric lithium enolate (Z)-1, derived from propiophenone, to propene oxide 2, was examined to clarify the exact geometry of the transition state (TS) involved in this type of reaction. The eight possible TSs and the corresponding pathways, four leading to syn gamma-hydroxy ketone (gamma-HK) 3 and four leading to anti gamma-HK 4, were compared, using the B3LYP/6-31+G(d)//B3LYP/6-31+G(d) theory level in vacuo and in the presence of the reaction solvent (toluene/hexane). In every case, the favored pathway involves a TS where the enolate C=C and the epoxide C-C are in a gauche relationship and where the Li(+) is stabilized by some C-C and C-H sigma bonds of epoxide 2.     

Dynamic processes in the Venice region outlined by environmental isotopes

Research carried out in the last 40 years has shown the scientific importance of groundwater circulation both in the Northern Adriatic sea bed and within the uppermost sedimentary layers of the Venice lagoon and of the Venice plain. Hydrodynamic processes are strictly controlled by a well-cemented sedimentary horizon lying under and around Venice ('caranto'), which plays the role of regional aquitard. This layer was attributed to the subaerial cementation of the Flandrian (8-10 ka Before Present) sedimentary surface. The caranto is generalised as a continuum horizon, being an easy explanation for several environmental, hydrogeological and geotechnical problems, e.g., a base layer for landfills, a confining layer for deep aquifers and the best substratum for locating the oak wooden pile-dwelling needed to support the largest buildings. The preservation of the isotope signal within the deep aquifers and aquiclude system records the changes in surface and groundwater characteristics and suggests the present and past recharge regimes. In this region, the heavily perturbed hydrodynamic conditions do not allow for the use of isotopic signals to derive a correct reconstruction of the present recharge. The perturbations induced by the intensive anthropogenic activity force to follow climate evolution by considering deep groundwater and pore waters. In addition, the presence of carbonatic rocks inside terrigeneous sediments affects the reconstruction of the past. Results indicate that carbonatic rocks are created by seepage, through the sediments, of gaseous carbon compounds from decaying organic layers. The gas interactions with the intra-sedimentary saline and fresh waters produce CO2, inducing the cementation of the sediments.     

EPR spectroscopy of protein microcrystals oriented in a liquid crystalline polymer medium

Correlation of the g-tensor of a paramagnetic active center of a protein with its structure provides a unique experimental information on the electronic structure of the metal site. To address this problem, we made solid films containing metalloprotein (Desulfovibrio gigas cytochrome c(3)) microcrystals. The microcrystals in a liquid crystalline polymer medium (water/hydroxypropylcellulose) were partially aligned by a shear flow. A strong orientation effect of the metalloprotein was observed by EPR spectroscopy and polarizing optical microscopy. The EPR spectra of partially oriented samples were simulated, allowing for molecular orientation distribution function determination. The observed effect results in enhanced sensitivity and resolution of the EPR spectra and provides a new approach towards the correlation of spectroscopic data, obtained by EPR or some other technique, with the three-dimensional structure of a protein or a model compound.     

Sol-Gel Synthesis of Transparent Alumina Gel and Pure Gamma Alumina by Urea Hydrolysis of Aluminum Nitrate

-Alumina was synthesized by a sol-gel method with the aluminum ion hydrolysis control performed by urea. The initial saturated Al³⁺/urea solution presented urea coordinated with the aluminum ion, as shown in the ¹³C NMR and ²⁷Al NMR spectra and longitudinal relaxation times, T ₁, from the latter. The substitution of water molecules in the Al³⁺ coordination shell by urea controlled the hydrolysis process and provided an extensive nucleation during the initial steps of the aluminum hydroxide formation due to urea thermolysis at 90°C. The resulting sol, composed of Al(OH)₃ nanoparticles, coalesced and became a transparent gel permeated by a solution of urea and the polycation ion [Al₁₃O₄(OH)₂₄(H₂O)₁₂]⁷⁺. The freshly prepared gel was transformed, under heating at 300°C, directly to -alumina, characterized by FTIR, ²⁷Al-MAS-NMR and S_BET techniques, without - or -phases, as a consequence of the high degree of homogeneity of the -alumina precursor.     

Preliminary results on the immobilisation of radionuclides from waters with specific adsorbers based on phosphate salts

The present paper is focused on the ability of aluminium phosphate (ALPC), magnesium ammonium phosphate (MGPC), magnesium hydrogen phosphate (MGHPC), and calcium hydrogenphosphate (CAHPC), adsorbed onto charcoal, to immobilise actinides by adsorption from natural waters. The objective of this process is to evaluate the environmental pollution due to the actinides. Europium, thorium, protactinium, neptunyl, and uranyl ions were chosen to simulate actinides in the +3, +4, +5 and +6 oxidation state. The adsorbers were tested using natural waters samples. The adsorption trends and capacities were analysed. ALPC and MGPC exhibited a similar behaviour and adsorbed demonstrating that the +5, +4 and +3 actinide ions can be easily immobilised from natural waters and may be successfully used at pH 7-8. MGHPC may be used at a higher pH, whereas CAHPC is effective in the whole pH range. In all cases, thorium, protactinium and europium were strongly     

Determination of creatinine in human serum by short-end injection capillary zone electrophoresis

A new ultra-rapid free-solution capillary zone electrophoresis method to measure serum creatinine is presented. Procedural parameters such as injection mode, concentration and pH of phosphate running buffer and acidic deproteinization of serum samples were investigated. Short-end injection permits a decrease of the analysis time by injecting samples at the outlet end of a silica capillary closest to the detection window, so reducing the migration distance. Thus, when a capillary with an effective length of 10.2 cm and a 40 mmol/L sodium phosphate buffer pH 2.35 was used, the obtained migration time of the creatinine peak was the shortest never described before, about 1.1 min. These conditions give a good reproducibility of the migration times (coefficient of variation, CV% < 0.5) and the peak areas (CV% < 2.8). Intra- and interassay CV were 3.06 and 6.26%, respectively, and analytical recovery was 99.4%. We compared our proposed method to Jaffé colorimetric assay, by measuring serum creatinine in 128 normal subjects. The obtained data were analyzed by the Passing and Bablok regression and Bland-Altman test. Creatinine concentration in healthy subjects was also used to investigate on its relationships with plasma thiols levels.     

Synthesis of a first thiophene containing analog of the HIV protease inhibitor nelfinavir

A stereoselective and efficient preparation of a thiophene containing intermediate 2 from ethyl 3-thienyl propenoate 4 as the core of new possible HIV protease inhibitors is described. The chiral intermediate has been successfully used for the preparation of the analog 1 of the potent HIV inhibitor nelfinavir.     

Subphthalocyanines: tuneable molecular scaffolds for intramolecular electron and energy transfer processes

A series of four subphthalocyanine-C(60) fullerene dyads have been prepared through axial functionalization of the macrocycle with m-hydroxybenzaldehyde and a subsequent dipolar cycloaddition reaction. The subphthalocyanine moiety has been peripherally functionalized with substituents of different electronic character, namely fluorine or iodine atoms and ether or amino groups, thus reaching a control over its electron-donating properties. This is evidenced in cyclic voltammetry experiments by a progressive shift to lower potentials, by ca. 200 mV, of the first oxidation event of the SubPc unit in the dyads. As a consequence, the energy level of the SubPc(*)(+)-C(60)(*)(-) charge-transfer state may be tuned so as to compete with energy transfer deactivation pathways upon selective excitation of the SubPc component. For instance, excitation of those systems where the level of the radical pair lies high in energy triggers a sequence of exergonic photophysical events that comprise (i) nearly quantitative singlet-singlet energy transfer to the C(60) moiety, (ii) fullerene intersystem crossing, and (iii) triplet-triplet energy transfer back to the SubPc. On the contrary, the stabilization of the SubPc(*)(+)-C(60)(*)(-) radical pair state by increasing the polarity of the medium or by lowering the donor-acceptor redox gap causes charge transfer to dominate. In the case of 1c in benzonitrile, the thus formed radical pair has a lifetime of 0.65 ns and decays via the energetically lower lying triplet excited state. Further stabilization is achieved for dyad 1d, whose charge-transfer state would lie now below both triplets. The radical pair lifetime consequently increases in more than 2 orders of magnitude with respect to 1c and presents a significant stabilization in less polar solvents, revealing a low reorganization energy for this kind of SubPc-C(60) systems.     

Peak compression effects in capillary electrochromatography

Peak compression in CEC is a phenomenon that can generate very narrow peaks with extremely high efficiencies that defy current chromatographic theory. This review article summarises the content of publications in this area up to this date. Two main types of peak compression effects have been observed in the literature. First, an irreproducible and hard to control focusing effect of unclear origin, observed on strong cation exchangers. Second, a reproducible continuous stacking effect caused by sample composition induced system zones demonstrated on several types of stationary phases.     

Motion of spheres along a fluid-gas interface

A system of many spherical particles, suspended in a quiescent fluid and touching a planar free fluid-gas interface, is considered. Stick fluid boundary conditions at the sphere surfaces are assumed. The free surface boundary conditions are taken into account with the use of the method of images. For such a quasi-two-dimensional system, the one-sphere resistance operator is calculated numerically. Moreover, the corresponding friction and mobility tensors are constructed from irreducible multipole expansion. Finally, the long-distance terms of the two-sphere mobility tensor are evaluated explicitly up to the order of 1/r3, where r is the interparticle distance. Experiments which have motivated this work are outlined.