Interactions of vanadates with carbohydrates in aqueous solutions

Spatiotemporal characterization of vanadium at the sediment-water interface of a multi-ecological lake

As an emerging environmentally harmful metal, vanadium (V) deserves significant research attention due to its hazardous concentrations in aquatic environments. However, the research on the characterization of V in sediment-water interface (SWI) remains limited. In this study, seasonal sampling was conducted in algal- and macrophyte-dominated zones via the method of in situ high-resolution diffusive gradients in thin films (DGT). The concentration of dissolved V in water in algal-dominated regions (12 sites) exceeded the long-term ecotoxicology limit of 1.2 μg⋅L-1. Seasonal variations of chemical speciation of V were observed in three ecological sites. DGT-labile V at the SWI exhibited two basic patterns associated with eutrophic status, one showing sharply decreasing gradients in the vicinity of the SWI and the other showing the absence of diffusion gradient. Positive correlations were observed between the water-dissolved V and the DGT-labile V, indicating DGT-labile V is a sensitive indicator for the release of V from sediment into water. Moreover, the mobility of V was influenced by the reduction of Fe(hydr)oxides and complexation with organic matter, in particular, during periods of algal blooms. It is suggested that V contamination at the SWI of algal-dominated zones deserves additional attention.

Hierarchically organized Li–Al-LDH nano-flakes: a low-temperature approach to seal porous anodic oxide on aluminum alloys

Li-LDH sealing is accounted for being highly competitive to standard hot-water sealing as referred to reduced treatment temperature and higher corrosion protection efficiency.

Self-assembled systems of water soluble metal 8-hydroxyquinolates with surfactants and conjugated polyelectrolytes

We have studied the interaction of 8-hydroxyquinoline-5-sulfonate (8-HQS) with the metal ions Al(iii) and Zn(ii) in aqueous solution in the presence of tetraalkylammonium surfactants using UV/vis absorption, fluorescence, NMR spectroscopy and electrical conductivity measurements, complemented by DFT calculations and molecular dynamics (MD) simulations. Under appropriate conditions, complexes between 8-HQS and metal ions form rapidly, and have similar electronic, spectroscopic and photophysical properties to the corresponding metal quinolates, such as Alq3. These interact with the cationic surfactants, leading to marked increases in fluorescence intensity. However, significant differences are seen in the behavior of the two metal ions. With aluminium, a stable [Al(8-QS)3](3-) anion is formed, and interacts, predominantly through electrostatic interactions, with the surfactant, without disrupting the metal ion coordination sphere. In contrast, with Zn(ii), there is a competition between the metal ion and surfactants in the interaction with 8-HQS, although the [Zn(8-QS)2(H2O)2](2-) species is stable at appropriate pH and surfactant concentration. The studies are extended to systems with the conjugated polyelectrolyte (CPE) poly-(9,9-bis(6-N,N,N-trimethylammonium)hexyl)-fluorene-phenylene bromide (HTMA-PFP), which has a similar alkylammonium chain to the surfactants. Mixing metal salt, 8-HQS and HTMA-PFP in the presence of a nonionic surfactant leads to the formation of a metal complex/CPE supramolecular assembly between the conjugated polyelectrolyte and the metal/8-HQS complex, as demonstrated by electronic energy transfer. The potential of these systems in sensing, light harvesting, and electron injection/transport layers in organic semiconductor devices is discussed.

Interactions of a zwitterionic thiophene-based conjugated polymer with surfactants

Structural organization and photoluminescence properties of zwitterionic conjugated polymer–surfactant assemblies depend on specific and non-specific polymer–surfactant interactions within the aggregate.

NMR, DFT and luminescence studies of the complexation of V(v) oxoions in solution with 8-hydroxyquinoline-5-sulfonate

The complexation of vanadium(v) with 8-HQS is accompanied by marked changes in the multinuclear NMR and UV/visible absorption spectra of 8-HQS, but does not lead to a significant increase in fluorescence.

Effect of metal ion hydration on the interaction between sodium carboxylates and aluminum(III) or chromium(III) ions in aqueous solution

The interaction between sodium octanoate, decanoate, and dodecanoate and aluminum(III) and chromium(III) has been studied in water at natural pH values, starting well below the surfactant critical micelle concentration, using electrical conductivity, turbidity, and potentiometric measurements. With decanoate or dodecanoate, maximum interaction occurs at 3:1 stoichiometry, corresponding to charge neutralization. Although the solutions become turbid with both metal ions, indicating phase separation, differences are observed and attributed to the fact that aluminum(III) is relatively labile to substitution and rapidly replaces its water ligands, whereas chromium(III) is substitution inert. This shows up in well-defined floc formation with Al(3+), whereas Cr(3+) suspensions do not precipitate, probably because that replacement of coordinated water by carboxylate ligands is impeded. This can be overcome by increasing temperature, and differences in the thermal behavior with Al(3+) and Cr(3+) are suggested to be due to increased involvement of substitution reactions in the latter case. The effect of octanoate on the trivalent metal ions is less clear, and with Cr(3+) interaction only occurs when the carboxylate is in excess. Hydrophobic interactions between alkyl chains play a major role in driving phase separation. At high surfactant concentrations, the solid phases do not dissolve, in contrast to what is observed with the corresponding alkylsulfates. This has implications for use of these systems in metal separation through froth flotation. The concentration of metal ions in supernatant solution has been determined for sodium dodecanoate and sodium dodecylsulfate with Al(3+) and Cr(3+) over the whole surfactant concentration range by inductively coupled plasma-mass spectrometry (ICP-MS). From this, association constants have been determined and are found to be larger for the carboxylate than the alkylsulfate, in agreement with the greater Lewis basicity of the -CO(2)(-) group.

Solubilization of poly{1,4-phenylene-[9,9-bis(4-phenoxy-butylsulfonate)]fluorene-2,7-diyl} in water by nonionic amphiphiles

In the presence of the nonionic alkyloxyethylene surfactant n-dodecylpentaoxyethylene glycol ether (C12E5), the anionic conjugated polyelectrolyte (CPE) poly{1,4-phenylene-[9,9-bis(4-phenoxy-butylsulfonate)]fluorene-2,7-diyl} (PBS-PFP) dissolves in water, leading to a blue shift in fluorescence and dramatic increases in fluorescence quantum yields above the surfactant critical micelle concentration (cmc). No significant changes were seen with a poly(ethylene oxide) of similar size to the surfactant headgroup, confirming that specific surfactant-polyelectrolyte interactions are important. From UV-visible and fluorescence spectroscopy, dynamic light scattering (DLS), small-angle X-ray scattering (SAXS), cryogenic transmission electron microscopy (cryo-TEM), and electrical conductivity, together with our published NMR and small-angle neutron scattering (SANS) results, we provide a coherent model for this behavior in terms of breakup of PBS-PFP clusters through polymer-surfactant association leading to cylindrical aggregates containing isolated polymer chains. This is supported by molecular dynamics simulations, which indicate stable polymer-surfactant structures and also provide indications of the tendency of C12E5 to break up polymer clusters to form these mixed polymer-surfactant aggregates. Radial electron density profiles of the cylindrical cross section obtained from SAXS results reveal the internal structure of such inhomogeneous species. DLS and cryo-TEM results show that at higher surfactant concentrations the micelles start to grow, possibly partially due to formation of long, threadlike species. Other alkyloxyethylene surfactants, together with poly(propylene glycol) and hydrophobically modified poly(ethylene glycol), also solubilize this polymer in water, and it is suggested that this results from a balance between electrostatic (or ion-dipole), hydrophilic, and hydrophobic interactions. There is a small, but significant, dependence of the emission maximum on the local environment.

Aggregation and micellization of sodium dodecyl sulfate in the presence of Ce(III) at different temperatures: a conductometric study

Aggregation properties of sodium dodecyl sulfate (SDS) in the presence of cerium(III) chloride, at various temperatures (298.15-323.15 K) have been measured by the electrical conductance technique. The experimental data on aqueous solutions as a function of SDS concentration show the presence of two inflexion points indicating the presence of two distinct interaction mechanisms: the first, occurring at SDS concentrations below the critical micelle concentration of the pure surfactant, which can be explained by the formation of aggregates between dodecyl sulfate (DS-) and Ce(III), while the second one, at SDS concentrations around the critical micelle concentration (cmc) of the pure surfactant which is due to the SDS micellization. The aggregation between DS- and Ce(III) was confirmed by static light scattering. The binding ratio of DS-/Ce(III) changes from 6 to 4, shows a slight dependence on the Ce(III) concentration and is independent of the temperature. The thermodynamic micellization parameters, Gibbs energy, enthalpy and entropy of micellization were calculated on the basis of the experimental data for the aggregation concentration, and the degree of counterion dissociation of the micelles. The SDS micellization is energetically favoured by increasing either the concentration of CeCl3 or the temperature. Such behaviour is clearly dominated by a decrease of the micellization (exothermic) enthalpy. The entropy of micellization approaches zero as the cerium(III) chloride concentration and temperature increase.

NMR diffusometry and conductometry study of the host–guest association between β-cyclodextrin and dodecane 1,12-bis(trimethylammonium bromide)

Surfactants form association complexes with cyclodextrins. In the present investigation we have used NMR-diffusometry and electrical conductivity to follow the interactions which take place between beta-cyclodextrin and a bolaform surfactant: dodecane 1,12-bis(trimethylammonium bromide). Both (1)H NMR self-diffusion and conductometry data indicate the formation of a 1:1 inclusion complex. Assuming this stoichiometry, it was possible to calculate the association constant; from the analysis of the self-diffusion coefficients of free beta-cyclodextrin and the bolaform surfactant an association constant K=3x10(3)M(-1) was obtained while the analysis of conductivity data gave a comparable value of K=2.5x10(3)M(-1).