Thermodynamic modeling of the vapor–liquid equilibrium of the CO2/H2O mixture

In order to evaluate the feasibility of CO₂ sequestration in geological formations detailed knowledge of the mutual solubilities of the CO₂/H₂O system is required. In this work we employ three models, which all involve the well-known Peng–Robinson equation of state, to study the CO₂/H₂O phase equilibrium, with emphasis on the solubility of CO₂ in the aqueous phase and the solubility of H₂O in the CO₂-rich phase. The considered models include the Peng–Robinson equation of state coupled with the conventional van der Waals one fluid mixing rules or the universal mixing rules, and the cubic-plus-association equation of state that uses the Peng–Robinson equation of state in order to account for the usual attractive and repulsive forces and an extra association term to account for the strong hydrogen bonding interactions. The required model parameters are calibrated using experimental data up to 1500 bar for pressure, and up to 673 K for temperature. To improve the accuracy of the proposed models we consider two temperature ranges. Temperatures lower than 373 K are of interest to the geological CO₂ sequestration, while higher temperatures are of interest to fluid-inclusion studies. Good agreement is obtained between the experimental and the correlated solubilities.     

Nickel ferrocyanide modified electrodes as active cation-exchange matrices: real time XRD evaluation of overlayer structure and electrochemical behavior

The dynamic variations in the structure of nickel ferrocyanide modified electrodes was determined using in situ diffractoelectrochemical techniques. X-ray powder diffraction peaks from the nickel ferrocyanide modified electrode were recorded during electrochemical oxidation/reduction of the surface overlayer and reversible changes in the unit cell lattice parameter observed. The electrochemical changes that occur during oxidation/reduction in various alkali cation electrolytes are correlated with changes in the lattice parameter. It is postulated that micro-domains form when two cations having markedly different radii such as cesium and potassium are intercalated into the nickel ferrocyanide structure so that distinct regions of the nickel ferrocyanide layer containing cesium exist separated from regions with the lighter alkali cations.     

Temperature and Pressure Effects on Local Structure and Chain Packing in cis‐1,4‐Polybutadiene from Detailed Molecular Dynamics Simulations

Summary: We present results for the temperature and pressure dependence of local structure and chain packing in cis‐1,4‐polybutadiene (cis‐1,4‐PB) from detailed molecular dynamics (MD) simulations with a united‐atom model. The simulations have been executed in the NPT statistical ensemble with a parallel, multiple time step MD algorithm, which allowed us to access simulation times up to 1 µs. Because of this, a 32 chain C₁₂₈ cis‐1,4‐PB system was successfully simulated over a wide range of temperature (from 430 to 195 K) and pressure (from 1 atm to 3 kbar) conditions. Simulation predictions are reported for the temperature and pressure dependence of the: (a) density; (b) chain characteristic ratio, C_n; (c) intermolecular pair distribution function, g(r), static structure factor, S(q), and first peak position, Q_max, in the S(q) pattern; (d) free volume around each monomer unit along a chain for the simulated polymer system. These were thoroughly compared against available experimental data. One of the most important findings of this work is that the component of the S(q) vs. q plot representing intramolecular contributions in a fully deuterated cis‐1,4‐PB sample exhibits a monotonic decrease with q which remains completely unaffected by the pressure. In contrast, the intermolecular contribution exhibits a distinct peak (at around 1.4 Å⁻¹) whose position shifts towards higher q values as the pressure is raised, accompanied by a decrease in its intensity.

3D view of the simulation box containing 32 chains of C₁₂₈ cis‐1,4‐polybutadiene at density ρ = 0.849 g · cm⁻³ and the conformation of a single C₁₂₈ cis‐1,4‐PB chain fully unwrapped in space.     

On lifted cover inequalities: A new lifting procedure with unusual properties

Lifted cover inequalities are well-known cutting planes for 0–1 linear programs. We show how one of the earliest lifting procedures, due to Balas, can be significantly improved. The resulting procedure has some unusual properties. For example, (i) it can yield facet-defining inequalities even if the given cover is not minimal, (ii) it can yield facet-defining inequalities that cannot be obtained by standard lifting procedures, and (iii) the associated superadditive lifting function is integer-valued almost everywhere.     

Potentiometric Cholesterol Biosensor Based on ZnO Nanowalls and Stabilized Polymerized Lipid Film

A novel potentiometric cholesterol biosensor was fabricated by immobilization of cholesterol oxidase into stabilized lipid films using zinc oxide (ZnO) nanowalls as measuring electrode. Cholesterol oxidase was incorporated into the lipid film prior polymerization on the surface of ZnO nanowalls resulting in a sensitive, selective, stable and reproducible cholesterol biosensor. The potentiometric response was 57 mV/ decade concentration. The sensor response had no interferences by normal concentrations of ascorbic acid, glucose, and urea, proteins and lipids. The present biosensor could be implanted in the human body because of the biocompatibility of the lipid film.     

Fluorimetric Analysis of Five Amino Acids in Chocolate: Development and Validation

Amino acids present ergogenic action, helping to increase, protect, and restore the muscular system of young athletes. Moreover, the encapsulation of five relevant amino acids in chocolate pellet form will appeal to them, facilitating their daily consumption. A reliable HPLC fluorimetric method was developed to detect and quantitatively determine L-Leucine, L-Isoleucine, L-Histidine, L-Valine, and β-Alanine in chocolate using aniline as an internal standard. Experimental design methodology was used to investigate and optimize the clean-up procedure of the samples. Therefore, three extraction techniques (solid-phase extraction (by two different SPE cartridges) and liquid–solid extraction (LSE)) were compared and evaluated. The LOQ values in chocolate varied from 24 to 118 ng/g (recovery 89.7–95.6%, %RSD < 2.5). Amino acids were pre-column derivatized with o-phthalaldehyde (OPA), while derivatization parameters were thoroughly investigated by experimental design methodology. The analysis was performed by HPLC-fluorescence (emission: λ = 455 nm, excitation: λ = 340 nm) method using a C₁₈ column and a mixture of phosphate buffer (pH = 2.8; 20 mM)-methanol as a mobile phase in gradient elution. The method was validated (r² > 0.999, %RSD < 2, LOD: 10 ng mL⁻¹ for histidine and leucine, 2 ng mL⁻¹ for alanine and valine, and 4 ng mL⁻¹ for Isoleucine) according to the International Conference on Harmonization guidelines.     

Ion-exchange chromatography followed by ESI-MS for quantitative analysis of sugar monophosphates from glucose catabolism

The aim of this work is to establish a quantitative method to determine the ratio of [U-(13)C] labeled to unlabeled hexose monophosphates isolated from yeast extracts. This is accomplished by anion exchange chromatography and mobile phase desalting followed by electrospray (ESI) mass spectrometry. We test the method with the analysis of a sample of biological origin. Previously developed analytical techniques are not adequate to accomplish mass spectrometric analysis of these and other small monosaccharide systems because of interference from salt clusters. By lowering the ionic strength of the mobile phase and using a simplified injection system to the mass spectrometer, we were able to obtain data on the relative abundance of the hexose monophosphates.