Microwave‐assisted synthesis of 2‐(2‐pyridyl)azoles. Study of their corrosion inhibiting properties

An efficient and fast procedure for the synthesis of 2‐(2‐pyridyl)azoles is described using ionic liquids as catalysts under microwave irradiation. The X‐ray crystallographic analyses for three of the four synthesized compounds are presented. Potentiodynamic polarization studies were carried out to analyze the electrochemical behavior of the compounds in corrosive acidic media. Of the four derivatives, one compound was detected to be an effective corrosion inhibitor prototype for oil refinery environments.     

Interactions between gemini surfactants and polymers: thermodynamic studies

Aqueous mixtures containing a homopolymer, poly(vinylpyrrolidone) (PVP), or a hydrophobically modified graft copolymer, HM-pullulan, (PULAU9, where 9 stands for the nominal substitution degree), and different Gemini surfactants have been investigated at 25.0 degrees C. A wide variety of experimental conditions were addressed by changing the amount of polymer and of surfactant. The Gemini surfactants were synthesized, purified, and characterized by routine methods. They differ from each other in polar head groups (two sulfonate-, two quaternary ammonium-, or two arginine-based groups), in alkyl chain length (11 or 12 carbon atoms), and in the distance between the polar head groups. The spacers consist of 2, 3, and 6 methylene units or 3 oxyethylene units. Surface activity and solution calorimetry measurements yield some physicochemical features inherent to micelle formation and polymer-surfactant interactions. The data are supported by ionic conductivity, detecting the critical thresholds and quantifying the modifications in binding associated with critical association (CAC) and micelle formation (CMC*). The Gibbs energy of transfer from the micelles to a polymer-binding site, DeltaGtrans, was evaluated from the CAC/CMC* ratios versus the amount of added polymer. A similar procedure determined the enthalpy of transfer, DeltaHtrans. DeltaGtrans decreases with added polymer, whereas DeltaHtrans becomes more negative on increasing the amount of polymer in the medium. According to the selected data presented here, cationic Geminis do not interact with PVP, while significant interactions have been observed in other surfactants. In mixtures with PULAU9, the interaction is significant for all Geminis. This effect is due to interactions between the surfactants and the hydrophobic alkyl groups on the main polymer chain. The pendent groups facing away from the polysaccharide chain act as binding sites for aggregates onto such polymers.     

Ligand effects in the non-alternating CO-ethylene copolymerization by palladium(II) catalysis

In this paper we report on a comparative study of the non-alternating CO-C(2)H(4) copolymerization catalyzed by neutral Pd(II) complexes with the phosphine-sulfonate ligands bis(o-methoxyphenyl)phosphinophenylenesulfonate and bis(o-methoxyphenyl)phosphino-ethylenesulfonate. The former ligand, featuring a lower skeletal flexibility, has been found to form more active catalysts as well as produce polyketones with higher molecular weight and higher extra-ethylene incorporation. Operando high-pressure NMR studies have allowed us to intercept, for the first time, Pd(II)(phosphine-sulfonate) beta-chelates in the non-alternating copolymerization cycle, while model organometallic reactions have contributed to demonstrate that Pd(II) (phosphine-sulfonate) fragments do not form stable carbonyl complexes. The opening of the beta-chelates has been found to be a viable process by either comonomer, which contrasts with the behaviour of Pd(II) (chelating diphosphine) catalysts for the perfectly alternating copolymerization.     

Correlation between rheological properties of zinc carboxylate liquids and molecular structure

Using Fourier transform infrared spectroscopy (FTIR), the viscosity of zinc 2-ethylhexanoate liquid has been found to correlate with the intensity of an asymmetric COO stretching resonance at 1632 cm-1. This is consistent with the presence of the zinc carboxylate polymer, catena-2-ethylhexanato-(O,O')-tri-micro-2-ethylhexanato-(O,O')-dizinc(II) as the origin of the viscosity, a conclusion that is further supported by theoretical predictions. Density functional theory has been used to assign the IR spectra of the zinc carboxylate dimer, catena-2-ethylhexanato-(O,O')-di-(tri-micro-2-ethylhexanato-(O,O')-dizinc(II)-formic) acid, and the model of the molecular liquid, micro-4-oxo-hexakis-(micro-2-ethylhexanato)-tetrazinc(II). The predicted spectra indicate that the decreased symmetry of the polymer relative to the zinc 2-ethylhexanoate liquid increases the intensity of the asymmetric carboxylate stretch at 1632 cm-1 and leads to the observed correlation.     

Unexpected inverse correlations and cooperativity in ion-pair phase transfer

Liquid/liquid extraction is one of the most widely used separation and purification methods, where a forefront of research is the study of transport mechanisms for solute partitioning and the relationships that these have to solution structure at the phase boundary. To date, organized surface features that include protrusions, water-fingers, and molecular hinges have been reported. Many of these equilibrium studies have focused upon small-molecule transport – yet the extent to which the complexity of the solute, and the competition between different solutes, influence transport mechanisms have not been explored. Here we report molecular dynamics simulations that demonstrate that a metal salt (LiNO₃) can be transported via a protrusion mechanism that is remarkably similar to that reported for H₂O by tri-butyl phosphate (TBP), a process that involves dimeric assemblies. Yet the LiNO₃ out-competes H₂O for a bridging position between the extracting TBP dimer, which in-turn changes the preferred transport pathway of H₂O. Examining the electrolyte concentration dependence on ion-pair transport unexpectedly reveals an inverse correlation with the extracting surfactant concentration. As [LiNO₃] increases, surface adsorbed TBP becomes a limiting reactant in correlation with an increased negative surface charge induced by excess interfacial NO₃⁻, however the rate of transport is enhanced. Within the highly dynamic interfacial environment, we hypothesize that this unique cooperative effect may be due to perturbed surface organization that either decreases the energy of formation of transporting protrusion motifs or makes it easier for these self-assembled species to disengage from the surface.

A forefront of research in separations science (specifically liquid–liquid extraction) is the study of transport mechanisms for solute partitioning, and the relationships that these have to solution structure at the phase boundary.     

Cooperative motions in PVC studied by thermally stimulated currents: Comparison with A.C. dielectric derivative analysis

The thermally stimulated current–thermal sampling (TSC–TS) technique was used to study the broadened glass transition in conventional “atactic” poly(vinyl chloride), PVC. The activated parameters obtained from the TSC–TS data, mainly the apparent activation energy (E_a), characterize the breadth of glass transitions in a very sensitive way. These results are compared with those values of E_a obtained from the literature, using a recently proposed method of analyzing a.c. dielectric constants and their derivatives, over the temperature range of −100–130°C. Both techniques detect weak cooperative glass transition-like relaxations well below the main glass transition of ca. 80°C. As is the case with “atactic” PMMA, the data suggest that compositional heterogeneity related to a small fraction of predominantly isotactic sequences contribute to the broad glass transition extending ca. 60°C below the main glass transition in atactic PVC. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 913–918, 1998     

An approximated principal component prediction model for continuous-time stochastic processes

In this paper, a linear model for forecasting a continuous-time stochastic process in a future interval in terms of its evolution in a past interval is developed. This model is based on linear regression of the principal components in the future against the principal components in the past. In order to approximate the principal factors from discrete observations of a set of regular sample paths, cubic spline interpolation is used. An application for forecasting tourism evolution in Granada is also included. © 1997 by John Wiley & Sons, Ltd.     

Surface tension and adsorption behavior of mixtures of diacyl glycerol arginine-based surfactants with DPPC and DMPC phospholipids

The binary surface interactions of some novel cationic diacyl glycerol arginine-based surfactants with model phospholipids, which are often used as model membrane components, are studied at 25 °C in aqueous solutions of 0.1 M sodium chloride. The surfactants are 1,2-dimyristoyl-rac-glycero-3-O-(N^α-acetyl-l-arginine) hydrochloride (1414RAc) and 1,2-dilauroyl-rac-glycero-3-O-(N^α-acetyl-l-arginine) hydrochloride (1212RAc), and they are important as potential antimicrobial agents which are biodegradable and with less toxicity than other cationic surfactants. The phospholipids are 1,2-dipalmitoyl-sn-glycero-3-phosphatidylcholine (DPPC) and 1,2-dimyristoyl-sn-glycero-3-phosphatidylcholine (DMPC). The equilibrium and dynamic surface tension of each surfactant, each phospholipid, and some of their binary mixtures are studied using the bubble surfactometry method at constant area or pulsating area conditions. In addition, the surface densities of pure and mixed monolayers of these compounds at the air/water interface are probed with infrared reflection–absorption spectroscopy (IRRAS). Steady state and dynamic surface tension synergism, or antisynergism in one case, and synergistic adsorption effects are detected for the mixed dispersions studied. The enhanced adsorption detected with IRRAS, and the enhanced dynamic and steady state surface tension lowering indicate strong miscibility and net attractive interactions between the compounds in the adsorbed mixed monolayers.     

Structure modulated electronic contributions to metalloenediyne reactivity: synthesis and thermal Bergman cyclization of MLX2 compounds

The synthesis of novel metalloendiyne complexes MLRX(2) (where L = 1,4-dibenzyl/diethyl-1,4-diaza-cyclododec-8-ene-6,10-diyne, X = halogen) are reported with their X-ray crystal structures and thermal Bergman cyclization temperatures. Two distinct types of constructs are obtained; the Zn(II) compounds are tetrahedral, while the Cu(II) and the Pd(II) compounds are all distorted- or square-planar. Each possesses structurally similar enediyne conformations and critical distances (3.75-3.88 A). The tetragonal Cu(II) species all exhibit Bergman cyclization temperatures between 140 and 150 degrees C in the solid state, while the square-planar Pd(II) analogues possess similar critical distances but cyclize at significantly higher temperatures (205-220 degrees C). In contrast, the Zn(II) derivatives show a marked halogen dependence, with X = Cl having the highest Bergman cyclization temperature, which is comparable to the Pd(II) square-planar set, while the ZnLX(2) compound with X = I shows the lowest Bergman cyclization temperature (144 degrees C), similar to the Cu(II) derivatives. Moreover, for the planar constructs, the R group has little influence on the cyclization temperatures; however, for the tetrahedral ZnLX(2) compounds, the steric influence of the R group plays a more significant role in the cyclization reaction coordinate by influencing the stability of the precyclized intermediate. This complex set of results is best interpreted by a combination of steric contributions and electronic interactions between the halogen through space (in the case of Zn(II)) and through bonds (in the case of Pd(II)) and the pi orbitals of the endiyne fragment. In contrast, for Cu(II) systems, the distorted square-planar geometry permits neither direct through space nor symmetry-allowed through bond communication between the orbital partners, and thus little variation in Bergman cyclization reactivity is observed.