Kováts' coefficients for predicting polarities in silicone stationary phases and their mixtures

Summary A correlation between the retention polarity and the Kováts' coefficient has been found for a number of commercial stationary phases used in gas chromatography. The correlation has been used to predict the polarity of a few mixed stationary phase columns prepared as binary mixtures of OV-101 with OV-25, DC-550 or Carbowax 20M, and also mixtures of OV-225 with SP-2340. A linear relationship was found between polarity and mixture composition. The temperature dependence of the Kováts' coefficient was investigated and found to increase linearly with temperature, the rate of increase depending on the polarity of the stationary phase, with greater increases for more polar stationary phases.     

Synthesis,structural analysis,and photophysical properties of bi-1,2,3-triazoles

Structural Chemistry - Structural insights of a group of bi-1,2,3-triazoles derived from oxidative CuAAC are described through an X-ray crystallography study, distinguishing a dihedral angle which...     

Spectroscopic elucidation of reaction pathways of acetaldehyde on platinum and palladium in acidic media

The electrochemical behavior of acetaldehyde on palladium and platinum electrodes in acidic media was comparatively studied by means of differential electrochemical mass spectrometry (DEMS) and in situ Fourier transform infrared spectroscopy (FTIRS) combined with cyclic voltammetry. It was observed that acetaldehyde decomposition depends on the catalyst material, applied potential, and reactant concentration. Additionally, it was detected that acetaldehyde adsorbs and dissociates at potentials lower than 0.60 V vs RHE, producing methane and adsorbed CO on Pd; while C₂-species, CH_x and CO_ad are formed on Pt. Besides carbon dioxide, acetic acid and adsorbed acetate were observed at E?>?0.6 V, and their contribution increased with acetaldehyde concentration. Differences between Pt and Pd in potential dependence of the products and intermediates were established. Calibration of the mass spectrometer, together with the use of labeled acetaldehyde and IR spectra, allows establishment of the nature of adsorbed species and products for both Pt and Pd at different potentials, elucidating global reaction pathways for acetaldehyde on these two noble metals.     

Ion binding to polyelectrolytes: Monte Carlo simulations versus classical mean field theories

The influence of ion size and surface charge model in titrations of ionizable polyelectrolytes is studied by means of the Semi Grand Canonical Monte Carlo simulation method in the context of the primitive model. Three models describing a discrete distribution of charged functional groups on the polyelectrolyte and different values for the radius of the background electrolyte spanning from ionic to hydrated radii values were analyzed. The polyelectrolyte titrations were simulated by calculating the degree of ionization versus pH curves at two ionic strengths. The results allow us to quantify the impact of the sizes of the background salt ions and surface functional groups of the polyelectrolyte on the dissociation degree. This influence is explained in terms of the effectiveness of the screening of the charged surface sites. Finally, by comparison with the Non-Linear Poisson–Boltzmann model, the influence of ionic correlations and finite size of the solution ions is assessed.     

Adsorption micro calorimeter

In this work, it is described an innovative heat flux micro calorimeter Tian-Calvet type designed to measure adsorption heats and reactions as well as adsorption isotherms. It consists in an adsorption instrument for volumetric gases, which is coupled to the micro calorimeter. The changes in the pressure are monitored by means of high sensitivity and high precision pressure transducers. The micro calorimeter has thermo elements that work by a Seebeck effect, in a twin cells system. The cells are inside a box in which the temperature can be adjusted from 77 to 300 K. The sensitiveness of the calorimeter is established by applying a perfectly known electric work. The results corresponding to the electric calibration, the base line stability determination and the time constant in the equipment are shown.     

Addressing selectivity criteria in binding equilibria

Chemical systems, in particular those involving biological and environmental backgrounds, develop through selective processes which are determined by multiple equilibria. Several methods that have been developed to assess thermodynamic selectivity in binding equilibria, including the analysis of selectivity coefficients, the use of calculated species distribution diagrams, selectivity diagrams, and conditional stability constants, are reviewed in this paper with reference to examples mainly related to chemical systems of biological and/or environmental concern. Also the concept of binding affinity has been dealt with, since binding selectivity in equilibrium systems relates to the different affinities with which chemical species bind to each other.     

Synthesis and functionalization of new polyhalogenated BODIPY dyes. Study of their photophysical properties and singlet oxygen generation

A theoretical and experimental study on the iodination of BODIPY dyes with different degrees of substitution has been developed. Polyhalogenated BODIPYs synthesized in this work are the first examples of this type of dyes with more than two halogen atoms in the BODIPY core and they can be selectively functionalized. Surprisingly, the position in which halogen is attached has a marked effect in the photophysical properties and modulates the fluorescence capacity of the resulting BODIPY. These iodinated BODIPYs are efficient singlet oxygen generators.     

Multivariate optimization of the Kharasch–Sosnovsky allylic oxidation of olefins

The multivariate optimization method known as simplex is applied to the Kharasch–Sosnovsky allylic oxidation of double bonds. By applying this method, the amounts of three variables (copper source, oxidant, and additive) are optimized at the same time. Under the conditions thus obtained the reaction takes place in a considerable shorter time, being the alkene the limiting reagent. These conditions are applied to some monoterpenes and sesquiterpenes leading regioselectively to the corresponding benzoate esters, opening a route to the employment of this reaction in the synthesis of more complex molecules.