Temperature dependence of the hyperfine quadrupolar interaction in K2ZrF6

The thermal dependence of the hyperfine quadrupolar interaction of¹⁸¹Ta at Zr sites in K₂ZrF₆ has been studied by TDPAC between RT and 511 °C. Four phases of ever increasing symmetry have been found in the range RT-437 °C. The possible existence of a healing mechanism with an activation energy of 0.187±0.040 eV is discussed for the lattice recovery in the range 270 °C–335 °C. The results at temperatures above 437 °C can be understood assuming a thermal decomposition of the compound.     

Temperature defendence of the hyperfine interaction in (NH4)2ZrF6

The thermal evolution of the hyperfine quadrupole interaction in (NH₄)₂ZrF₆ has been investigated via TDPAC from 14 to 400 K. A phase transition is detected near 370 K. The low-temperature phase exhibits two sites equally populated for¹⁸¹Ta probes. The associated electric field gradients are described by both high asymmetry parameters and high interaction frequencies. On the other hand, the high-temperature phase corresponds to an unique axially symmetric and more intense electric field gradient.     

Formation of gold branched plates in diluted solutions of poly(vinylpyrrolidone) and their use for the fabrication of near-infrared-absorbing films and coatings

Ribbon-like and branched gold nano- and microstructures were produced by simple heating of diluted aqueous solutions of poly(vinylpyrrolidone) (PVP) and HAuCl4. The reaction was carried out in a one-pot, one-step process at mild temperatures. Modification of the synthesis variables allowed the obtaining of structures with different sizes and branching degrees which formed stable hydrosols with characteristic colors. A mechanism for the growth of the crystals was proposed, based on the aggregation of metal units followed by reorientation and attachment processes facilitated by the presence of low concentrations of the polymer. These anisotropic structures were used to obtain large-area porous coatings on metallic, plastic, and glass substrates and to synthesize homogeneous polymer composites. The resulting gold-modified materials showed an important increase of absorption in the near-infrared (NIR) region of the electromagnetic spectrum, which could find interesting applications in the development of NIR-absorbing filters and coatings.     

Interaction studies of diacyl glycerol arginine-based surfactants with DPPC and DMPC monolayers, relation with antimicrobial activity

Antimicrobial agents have a major practical importance in food, pharmaceutical and cosmetic applications for preventing contamination. Our group has developed a novel class of cationic diacyl glycerol arginine-based surfactants denoted 1414RAc and 1212RAc. To assess the antimicrobial properties of these new surfactants we have studied how they interact with 1,2-dipalmitoyl-sn-glycero-3-phosphocoline (DPPC) and 1,2-dimiristoyl-sn-glycero-3-phosphocoline (DMPC) as model membranes, as well with living organisms endowed or not with external barriers, such as gram negative bacteria, the human protozoa Leishmania and mammalian cell line.

The structure and phase characteristics of mixed monolayers have been assessed through the analysis of static elasticity. The extent of component miscibility of surfactant and phospholipid in mixed monolayers has been studied using the additivity rule and the excess free energy of a mixture as a function of the phospholipid molar fraction for different surface pressure values. In all the mixtures studied, the mixed monolayer is thermodynamically favoured except for the 1212RAc/DMPC case that exhibits positive values of excess free energy.

The interaction with living cells has cytotoxic effects only in eukaryotic cells, by unspecific membrane permeabilization.     

Synthesis, primary photophysical and antibacterial properties of naphthyl ester cinoxacin and nalidixic acid derivatives

We have synthesized two naphthyl ester quinolone derivates and determined their ability to generate reactive oxygen species (ROS) such as (1)O(2), ()OH, H(2)O(2) upon photolysis with UV-A light. The ability of cinoxacin (1) and nalidixic acid (2), and their naphthyl ester derivatives (3 and 4) to generate a dose-dependent amount of singlet oxygen and ROS (()(-)O(2), ()OH) in cell-free systems was detected by histidine assay and by luminol-enhanced chemiluminescence (LCL), respectively. Their electronic absorption and emission spectra were quantified and their photostability was determined. Their tendency to generate peroxidic derivative species showed the following order: 3>4; in contrast, their ability to generate singlet oxygen was 4>3 and these were better sensitizers than their parent quinolones 1 and 2. The antibacterial activity in darkness and under irradiation of compounds 3 and 4 was tested on Escherichia coli and compared with that of their parent compounds. An enhanced antibacterial activity by irradiation of the naphthyl esters of cinoxacin and nalidixic acid on E. coli was observed.     

Poly(<Emphasis Type="SmallCaps">dl</Emphasis>-aspartic acid) and copper(II) acetate monohydrate interactions

A polychelate with poly(dl-aspartic acid) was prepared in order to study the influence of the polymer ligands on the copper(II) acetate monohydrate. This compound was characterized by elemental analysis, magnetic susceptibility measurements, spectroscopy and thermal analysis. It is suggested that in the unit Cu₂(acetate)₄ the breakage of two acetate groups occurs by the effect of polymer ligand group coordination. It coordinates through a carboxylate group, keeping the water molecules coordinated to Cu^II. A magnetic moment of the polychelate is observed which presents a value of 1.74 M.B, which corresponds to uncorrelated Cu²⁺ (S = 1/2) spins, separated by large Cu–Cu distances. According to the suggested structure, PM3 semi-empirical calculations of the polychelate of Cu^II were done.     

Seven-membered cyclic sulfite eudesmane derivatives: partial synthesis, structural determination, and enzymatic resolution

Two chromatographically inseparable, diastereomeric eudesmane cyclic sulfites have been semisynthesized from alpha-santonin. This diastereomeric mixture was resolved by enzymatic acetylation with CCL. Each cyclic sulfite derivative was individually characterized on the basis of its spectroscopic and crystallographic properties.