Permeation of water as a tool for characterizing the effect of solvent, film thickness and water solubility in cellulose acetate membranes

Cellulose acetate membranes have been used in many applications; of particular interest are reverse osmosis systems, and as a neutral matrix for incorporation of different polymers (e.g., conducting polymers), inorganic ions (e.g., lanthanides) and organic (e.g., pharmaceutical) compounds. The properties of the new polymers derived from cellulose acetate or blends depend on those of cellulose acetate. This work presents an attempt to find links between thermodynamic and kinetic properties of cellulose acetate membranes in equilibrium with water. Water diffusion coefficients in cellulose acetate membranes are reported, measured with a simple water permeation technique. The comparison of these values with the percentage of water uptake and polymer thickness leads to interesting conclusions related with different polymer properties.http://www.sciencedirect.com/science/article/B6TWW-4DVBFCN-7/1/63e48f8aac1513c35feeaa6c746621e

Probing solute distribution and acid-base behaviour in water-in-oil microemulsions by fluorescence techniques

The distribution and acid-base behaviour of the four solutes harmine, chromotropic acid (4,5-dihydroxynaphthalene-2,7-disulfonate, disodium salt), 2-naphthol and 5,10,15,20-tetrakis [4-trimethylammonium)phenyl]-21H,23H-porphine tetra-p-tosylate (TTMP) have been studied in water-in-oil (w/o) microemulsions using fluorescence and absorption spectroscopy. Carbon tetrachloride is a quencher of fluorescence of these compounds, and studies using this as oil phase in microemulsions show that chromotropic acid is located in the water domain, TTMP at the surfactant-water interface, while the distribution of harmine or 2-naphthol depends on the degree of protonation. Detailed studies have been made on harmine. In water/AOT/cyclohexane microemulsions the cationic form is observed up to much higher apparent pH than in aqueous solutions. An important factor is shown to be the compartmentalisation of hydroxide ions between water pools. Similar effects are observed with the other probes, and it is suggested that compartmentalisation of hydrogen or hydroxide ions is a major effect in many acid-base reactions in microemulsions. The validity of the concept of pH in microemulsions under these conditions is questioned. Fluorescence lifetime measurements are also shown to provide information on the dynamics of the processes, and demonstrate the importance of diffusion of solutes from organic solvent to the microemulsion pool. A comparison is made of the behaviour of harmine in water/AOT/cyclohexane and water/lecithin/cyclohexane microemulsions.http://www.sciencedirect.com/science/article/B6TFR-416K8BS-12/1/1e48ace7f73afe3996e2e8a782a190d

Probing solute distribution and acid-base behaviour in water-in-oil microemulsions by fluorescence techniques

The distribution and acid-base behaviour of the four solutes harmine, chromotropic acid (4,5-dihydroxynaphthalene-2,7-disulfonate, disodium salt), 2-naphthol and 5,10,15,20-tetrakis [4-trimethylammonium)phenyl]-21H,23H-porphine tetra-p-tosylate (TTMP) have been studied in water-in-oil (w/o) microemulsions using fluorescence and absorption spectroscopy. Carbon tetrachloride is a quencher of fluorescence of these compounds, and studies using this as oil phase in microemulsions show that chromotropic acid is located in the water domain, TTMP at the surfactant-water interface, while the distribution of harmine or 2-naphthol depends on the degree of protonation. Detailed studies have been made on harmine. In water/AOT/cyclohexane microemulsions the cationic form is observed up to much higher apparent pH than in aqueous solutions. An important factor is shown to be the compartmentalisation of hydroxide ions between water pools. Similar effects are observed with the other probes, and it is suggested that compartmentalisation of hydrogen or hydroxide ions is a major effect in many acid-base reactions in microemulsions. The validity of the concept of pH in microemulsions under these conditions is questioned. Fluorescence lifetime measurements are also shown to provide information on the dynamics of the processes, and demonstrate the importance of diffusion of solutes from organic solvent to the microemulsion pool. A comparison is made of the behaviour of harmine in water/AOT/cyclohexane and water/lecithin/cyclohexane microemulsions.http://www.sciencedirect.com/science/article/B6TFR-416K8BS-12/1/1e48ace7f73afe3996e2e8a782a190d

Theoretical and experimental insights into the complexation of 8-hydroxyquinoline-5-sulfonate with divalent ions of Group 12 metals

The complexation of 8-hydroxyquinoline-5-sulfonic acid with cadmium(II) and mercury(II) has been studied in aqueous solutions using UV/visible absorption, fluorescence and 1H NMR spectroscopy, accompanied by DFT calculations. Results are compared with the behavior of zinc(II) and show in all cases the dominant formation of a 1:2 (metal:ligand) complex. DFT calculations under PCM (water) conditions indicate a preference for hexacoordinated metal centers with two ligands and two water molecules. However, while the zinc(II) complex has a square bipyramidal geometry, with the two 8-HQS ligands and metal in the same plane and two coordinated water molecules mutually trans, with cadmium(II) and mercury(II), the isomers in which the water molecules are in the cis geometry are more stable. Changes in UV–Vis absorption, fluorescence spectra and fluorescence intensity are observed on complexation. Fluorescence quantum yields follow the order Zn/8-HQS Hg/8-HQS. We believe two competing factors may be involved: an increase in fluorescence on going from Zn(II) to Cd(II) due to increased stability, and a decrease on going increasing atomic number of the metal ion due to the heavy atom effect which increases intersystem crossing. Triplet state quantum yields were measured for the Zn(II) and Cd(II) complexes, and the value for the cadmium(II) complex is higher, in agreement with the heavy atom effect. However, the sum of fluorescence and triplet quantum yields in these cases is less than unity. It is suggested that there is a competing non-radiative route for deactivation of the excited state through ligand or solvent exchange. This provides a ready explanation of increased fluorescence yields when metal/8-HQS complexes are immobilized in solid matrices

Using Lanthanides as Probes for Polyelectrolyte-Metal Ion Interactions. Hydration Changes on Binding of Trivalent Cations to Nucleotides and Nucleic Acids

http://www.sciencedirect.com/science/article/B6TFM-4SWFNW8-1/1/aadd2972e76576ca7bf5c347abd5a68

Synergistic photoluminescence enhancement in conjugated polymer-di-ureasil organic-inorganic composites.

Poly(fluorene) conjugated polyelectrolyte (CPE)-di-ureasil organic-inorganic composites have been prepared using a versatile sol-gel processing method, which enables selective localisation of the CPE within the di-ureasil matrix. Introduction of the CPE during the sol-gel reaction leads to a homogeneous distribution of the CPE throughout the di-ureasil, whereas a post-synthesis solvent permeation route leads to the formation of a confined layer of the CPE at the di-ureasil surface. The CPE and the di-ureasil both function as photoactive components, contributing directly to, and enhancing the optical properties of their composite material. The bright blue photoluminescence exhibited by CPE-di-ureasils is reminiscent of the parent CPE; however the distinct contribution of the di-ureasil to the steady-state emission profile is also apparent. This is accompanied by a dramatic increase in the photoluminescence quantum yield to >50%, which is a direct consequence of the synergy between the two components. Picosecond time-correlated single photon counting measurements reveal that the di-ureasil effectively isolates the CPE chains, leading to emissive trap sites which have a high radiative probability. Moreover, intimate mixing of the CPE and the di-ureasil, coupled with their strong spectral overlap, results in efficient excitation energy transfer from the di-ureasil to these emissive traps. Given the simple, solution-based fabrication method and the structural tunability of the two components, this approach presents an efficient route to highly desirable CPE-hybrid materials whose optoelectronic properties may be enhanced and tailored for a targeted application

Kinetics and thermodynamics of poly (9,9-dioctylfluorene) beta-phase formation in dilute solution

Poly(9,9-dioctylfluorene) (PFO) adopts a particular type of conformation in dilute solutions of the poor solvent methylcyclohexane (MCH) below 273 K, which is revealed by the appearance of a red-shifted absorption peak at 437−438 nm. The formation of this ordered conformation depends on the temperature but is independent of polymer concentration over the range studied (3−25 μg/mL). On the basis of absorption, steady-state, and time-resolved fluorescence data, the new absorption peak at 437−438 nm is assigned to a highly ordered conformation of PFO chains, analogous to the so-called β-phase first identified in PFO films. From the study of PFO solutions in MCH as a function of temperature, we conclude that these ordered segments (β-conformation) coexist with less ordered domains in the same chain. When the ordered domains are present, they act as efficient energy traps and the fluorescence from the disordered regions is quenched. The transition between the disordered and the ordered PFO conformations is adequately described by a mechanism that involves two steps:  a first, essentially intramolecular, one from a relatively disordered (α) to an ordered conformation (β), followed by aggregation of chains containing β-conformation into anisotropic ordered domains. From the temperature dependence of the 437−438 nm peak intensity, the transition temperature Tβ = 261 K, enthalpy ΔHβ = −18.0 kcal mol-1, and entropy ΔSβ = −68.4 cal K-1 mol-1 were obtained. The formation of the β-conformation domains were also followed as a function of time at 260 K. The rate constants at 260 K were determined, showing an order of magnitude around 10-3 s-1 (kα→β = 5.9 × 10-4 s-1; kβ→α = 9 × 10-4 s-1; kagg = 2.3 × 10-3 M-1 s-1; kdiss = 4.4 × 10-4 s-1). This small magnitude explains the long times required for a “complete” conversion to the β-conformation

Synthesis and characterization of new aromatic polyamides bearing crown ethers and acyclic ethylene oxide units in the pendant structure. III. Benzo-18-crown-6 systems and their open-chain counterparts

We report the synthesis and characterization of 10 novel polyamides containing the benzo-18-crown-6 subunit and its dipodal counterpart, along with their properties, and a comparison with homologous polyamides bearing benzo-12-crown-4, benzo-15-crown-5, and the corresponding dipodal systems. The anomalous polymerization of some of the diacid monomers, that leads to insoluble gels under standard Yamazaki polymerization conditions, is described. The gel formation has been attributed to the threading of cyclic oligoamides with a growing polyamide chain to yield rotaxanes, polyrotaxanes, catenanes, or polycatenanes. Polyamide macrocycles have been characterized with matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. A route to avoid gel formation, consisting of a lower initial monomer concentration, is also described, along with the polymer properties of the polyamides obtained, including the chemical characterization, mechanical behavior, water sorption, morphology, diffusion data, and permeability of membranes prepared with these polymers. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 6252-6269, 200

Effect of pH and dissolved organic matter on the photochemical fate of acetamiprid

Trabalho apresentado em 9th European Conference on Pesticides and Related Organic Micropolluants in the Environment, 4-7 de outubro 2016, Santiago de Compostela, EspanhaIn this study the effect of pH and dissolved organic matter (DOM) on the photodegradation rate of acetamiprid (ACT) was studied. Observed photodegradation rate constants in the range of 0.0010 – 0.0026 h-1 and 24 – 36 h-1 were obtained using a solar simulator (290-800 nm) and a medium pressure mercury (MP Hg) lamp, respectively. In both experiments an increase in pH from 5 to 9 did not significantly change the photodegradation rate constant of ACT. A different behaviour was found for ACT degradation in the presence of DOM. When samples were irradiated with MP Hg lamp the observed photodegradation rate constant of ACT decreased with an increase of DOM concentration.N/