Temperature dependence of thermodynamic properties of a polarizable potential model of water

The temperature dependence of several thermodynamic properties of water is determined at atmospheric pressure by a set of computer simulations with a polarizable potential model. It is found that the maximum of the density occurs at the correct temperature, but the decrease in density with increasing temperature is more rapid than expected for real water. Consequently, the temperature dependence of other quantities, especially that of the thermal expansion coefficient, is reproduced with some inaccuracies. The model, however, turns out to be a definitive improvement over similar non-polarizable ones, for which the density maximum is either missing or found to be shifted considerably with temperature.     

Simple(r) algebraic equation for transition moments of fundamental transitions in vibrational second-order perturbation theory

Rayleigh–Schrödinger perturbation theory is applied in second order to obtain an expression for the transition moment of vibrational fundamentals. The reported equation is considerably simpler than previous ones. Applications for H₂O and HFCO are reported using force fields and dipole functions calculated at the CCSD(T) level of theory with different basis sets.     

Theoretical investigations of the vapour-liquid equilibrium and dielectric properties of dipolar Yukawa fluids in an external field

In a low field approximation, using the dipolar Yukawa fluid model (in mean spherical approximation as a reference system) a consistent field-dependent free energy expression is proposed for the calculation of the vapour-liquid equilibrium of polar fluids in an applied electric field. A perturbation theory high field approximation expression of the free energy is also proposed to study the field-dependent properties of fluids. In the high field approximation, equations for the field-dependent polarization and for the nonlinear dielectric constant (or Piekara constant) are also predicted. It has been discussed that our approximations are appropriate to describe the vapour-liquid-like phase equilibria and the magnetization curves of magnetic fluids.     

Experimental and theoretical study of the far-infrared spectra of HCl dissolved in liquid Ar,Kr, and Xe

New experimental results are reported on the relative absorption intensity distribution in the FIR spectra of HCl dissolved in liquefied Ar, Kr, and Xe at several temperatures along the liquid—vapour coexistence curve. These are treated further by applying a previously developed quantum-statistical spectral theory, which accounts for the line mixing and memory effects. Theoretical spectra are given in terms of the anisotropic potential time autocorrelation functions obtained from classical MD simulations using several empirical analytical potentials with density-adjusted well depths. Globally fair agreement between the theoretical and experimental spectra is demonstrated, except in the high frequency wings, where the theory underestimates the observed intensities. The choice of a particular radial form for the anisotropic HCl/RG potentials is found to be not critical for reproducing the experimental absorption profiles.     

Iron(I) in Negishi cross-coupling reactions

Herein we demonstrate both the importance of Fe(I) in Negishi cross-coupling reactions with arylzinc reagents and the isolation of catalytically competent Fe(I) intermediates. These complexes, [FeX(dpbz)(2)] [X = 4-tolyl (7), Cl (8a), Br (8b); dpbz = 1,2-bis(diphenylphosphino)benzene], were characterized by crystallography and tested for activity in representative reactions. The complexes are low-spin with no significant spin density on the ligands. While complex 8b shows performance consistent with an on-cycle intermediate, it seems that 7 is an off-cycle species.     

Synthesis of conformationally-constrained thio(seleno)hydantoins and α-triazolyl lactones from d-arabinose as potential glycosidase inhibitors

We have explored the rich structural diversity provided by an α-azido ester derived from d-arabinose as the source of sugar templates with reduced conformational flexibility. Using transient α-thioureido(selenoureido) esters we have prepared spiranic thio(seleno)hydantoins at the C-3 position of the sugar moiety. In this context, the first example of a stable spiranic α-lactam (or aziridinone) was isolated as a by-product in the hydrogenolysis of the starting α-azido ester. Furthermore, using copper(I)-catalyzed azido–alkyne cycloaddition (click chemistry), we have accessed bicyclic cis-fused α-triazolyl lactones fixed in the furanose form. Spiranic thiohydantoins turned out to be moderate, though selective, inhibitors of glycosidases, whereas their selenium isosters behaved as good free radical scavengers.     

Dispersive liquid-liquid microextraction of pesticides and metabolites from soils using 1,3-dipentylimidazolium hexafluorophosphate ionic liquid as an alternative extraction solvent

In this work, the use of the ionic liquid (IL) 1,3-dipentylimidazolium hexafluorophosphate ([PPIm][PF?]) as an alternative extractant for IL dispersive liquid-liquid microextraction (IL-DLLME) of a group of pesticides and metabolites (2-aminobenzimidazole, carbendazim/benomyl, thiabendazole, fuberidazole, carbaryl, 1-naphthol, and triazophos) from soils is described. After performing an initial ultrasound-assisted extraction (USE), the IL-DLLME procedure was applied for the extraction of these organic analytes from soil extracts. Separation and quantification was achieved by high-performance liquid chromatography (HPLC) with fluorescence detection (FD). Calibration, precision, and accuracy of the described USE-IL-DLLME-HPLC-FD method using [PPIm][PF?] as an alternative extractant was evaluated with two soils of different physicochemical properties. Accuracy percentages were in the range 93-118% with RSD values below 20%. A comparison of the performance of [PPIm][PF?] versus that of the so-common 1-hexyl-3-methylimidazolium hexafluorophosphate ([HMIm][PF?]) was accomplished. Results indicate a comparable extraction efficiency with both ILs, being slightly higher with [HMIm][PF?] for the metabolite 2-aminobenzimidazole, and slightly higher with [PPIm][PF?] for triazophos. In all cases, LODs were in the low ng/g range (0.02-14.2 ng/g for [HMIm][PF?] and 0.02-60.5 ng/g for [PPIm][PF?]). As a result, the current work constitutes a starting point for the use of the IL [PPIm][PF?] for further analytical approaches.     

Smart portable electrophoresis instrument based on multipurpose microfluidic chips with electrochemical detection

A second generation of a battery-powered portable electrophoresis instrument for the use of ME with electrochemical detection was developed. As the first-generation, the main unit of the instrument (150 mm × 165 mm × 95 mm) consists of four-outputs high-voltage power supply (HVPS) with maximum voltage of 3 KV and acquisition system (bipotentiostat) containing 2-channels for dual electrochemical detection. A new reusable microfluidic platform was designed in order to incorporate the microchips with the portable instrument. In this case, the platform is integrated to the main unit of the instrument so that it is not necessary to have any external cable for the interconnection of both parts, making the use of the complete system easier. The new platform contains all the electrical connections for the HVPS and bipotentiostat, as well as fluidic ports for driving the solutions. The microfluidic electrophoresis instrument is controlled by means of a user-friendly interface from a computer. The possibility of wireless connection (Bluetooth?) allows the use of the instrument without any external cable improving the portability. Therefore, the second generation brings a more compact and integrated electrophoresis instrument for "in situ" applications using microfluidic chips in an easy way. The performance of the electrophoresis system was initially evaluated using single- and dual-channel SU-8/Pyrex microchips with different models of integrated electrodes including microelectrodes and interdigitated arrays. The method was tested in different analytical applications such as separation of neurotransmitters, chlorophenols, purine derivatives, vitamins, polyphenolic acids, and flavones.     

Alpha 1-antitrypsin: a novel tumor-associated antigen identified in patients with early-stage breast cancer

Several studies have demonstrated that sera from patients with cancer contain antibodies that recognize a unique group of autologous antigens called tumor-associated antigens (TAA). In the current study, we employed an immunoproteomic approach, combining 2DE, Western blot, and MALDI-MS to identify TAA in the sera of patients diagnosed with infiltrating ductal or in situ carcinoma breast cancer. Sera obtained from 25 newly diagnosed patients with stage II breast cancer and 20 healthy volunteers was evaluated for the presence of novel TAA. Alpha 1-antitrypsin (A1AT) antibodies were detected in 24 of 25 patients with breast cancer (96%) and in 2 of 20 controls (10%). Sensitivity of detection of autoantibodies against A1AT in patients with breast cancer was 96%. Our preliminary results suggest that A1AT and autoantibodies against alpha 1 antitrypsin may be useful serum biomarkers for early-stage breast cancer screening and diagnosis.