Aqueous Bromide Solutions Research Articles

Quenching efficiency of pyrene fluorescence by nucleotide monophosphates in cationic micelles

The fluorescence behaviour of pyrene solubilized in the hexadecyltrimethylammonium bromide (CTAB) aqueous micellar solution in the presence of different nucleotide-monophosphates (NMPs) was investigated by monitoring the quenching and dequenching of pyrene steady-state fluorescence. The data clearly show that diverse nucleotide-monophosphates influence in different way the fluorescence of micellized pyrene: guanosine 5′-monophosphate (GMP), uridine 5′-monophosphate (UMP) and thimydine 5′-monophosphate (TMP) lead to a reduction in fluorescence intensity (quenching), while adenosine 5′-monophosphate (AMP) and cytosine 5′-monophosphate (CMP) induce an increment in pyrene fluorescence (dequenching). For all the NMPs the photophysical effect saturates at concentration higher than 40 mM. In the absence of micellar solution the fluorescence of pyrene follows the typical linear behaviour according to the Stern–Volmer relation. The quenching and dequenching efficiencies were analyzed according to a recently proposed model, based on the assumption that the anionic nucleotides compete with the surfactant counterion (bromide) for micelle surface. Results make available the follows of quenching efficiency order (GMP > UMP > TMP) and dequenching efficiency order (AMP > CMP). Zeta-potential measurements confirm that the predominant interaction occurs between the positively charged micellar surface and the negatively charged phosphate moieties on the nucleotides. The collected results clearly show that the fluorescence of pyrene solubilized in the CTAB micellar solution can be reduced (quenched) or enhanced (dequenched), depending on the chemical properties of the nucleobase.

Aggregation behavior of sodium deoxycholate and its interaction with cetyltrimethylammonium bromide in aqueous solution studied by NMR spectroscopy

In pure sodium deoxycholate (NaDC) dilute solution, the transverse relaxation times (T (2)) of nearly all proton signals of NaDC obey single-exponential decay, with exception for proton at 3-position (H3) that decays in a two-exponential manner. The two components with different mobility of H3 of NaDC indicate that the molecules are probably associated in head-to-tail pairs via hydrogen bonds in dilute solution. In the mixed NaDC/cetyltrimethylammonium bromide (CTAB) solutions, the T (2) values of interested NaDC protons are far less than those in pure NaDC solution, especially when the concentrations of the two components are close to equal-molar. The results of self-diffusion coefficients and the chemical shifts confirm further that the strong interaction occurs between the two components in mixed solutions, especially for equal-molar condition. The arrangement of the mixed aggregates can be speculated for the cross-peaks of proton pairs occurring between NaDC and CTAB molecules in two-dimensional and rotating frame nuclear Overhauser enhancement spectroscopy spectra.

Experimental characterization of the spreading and break-up of liquid flat-fan sheets discharging in a low-density atmosphere and application to BrLi solutions

This work presents and characterizes the existence of two different regimes in the spreading and break-up of liquid flat-fan sheets when discharging in low-density atmospheres. The motivation of the study is the improvement on the absorption phenomena of lithium bromide aqueous solution when discharging in a 600–1,500 Pa water vapor environment. This corresponds to the absorber conditions in current absorption closed-cycle cooling machines. Despite this, the dimensionless characterization obtained has universal validity. The conditions that define the change in the break-up regime, the dimensionless sheet break-up length and the break-up time are given as a function of the parameters involved. Digital particle tracking velocimetry (PTV) has been applied to measure the velocity field and additional visualization techniques have been used to further characterize the break-up process. The experiments verify the existence of critical gas-to-liquid density and viscosity ratios below which gas to liquid interaction becomes negligible. The article also offers expressions that define their values as a function of the other dimensionless parameters.

NMR Study for Self-aggregation of 1-Butyl-3-methylimidazolium Bromide in Aqueous Solution

Self-aggregation of 1-butyl-3-methylimidazolium bromide ([bmim]Br) in D(2)O has been investigated using NMR spectroscopy. The (1)H spin-lattice relaxation times (T(1)) of the [bmim](+) increased with the decrease of concentration in the range of 0.1-3.0 mol dm(-3) as expected, however, in contrast, the (1)H-T(1) decreased below 0.1 mol dm(-3). The estimated (13)C-activation energies indicated that the rotational mobility of the butyl-chain was more restricted than that of the imidazole ring at 0.1 mol dm(-3), whereas such a significant difference was not observed at 3.0 mol dm(-3). These results suggest that [bmim](+) forms micelle-like aggregations below 0.1 mol dm(-3) in D(2)O.

Volumetric and Viscometric Behaviour of some Amino Acids and their Group Contributions in Aqueous Tetramethylammonium Bromide at Different Temperatures

Abstract Densities, ρ and viscosities, η for L-serine, L-threonine, L-glutamine, L-lysine, L-arginine and L-histidine (0.05–0.25 m) in 0.20 m aqueous tetramethylammonium bromide were determined at 298.15, 303.15, 308.15, and 313.15 K. The density data was used to compute apparent molar volume, φ v . The partial molar volume, φ v 0, at infinite dilution and experimental slope, S v * were obtained from Masson´s equation and interpreted in terms of solute-solvent and solute-solute interactions, respectively. The φ v 0 values are found to vary with temperature as a power series of temperature. The structure-making/-breaking ability of solute were discussed using Hepler´s criterion. The partial molar volumes of transfer, φ v 0 (tr) of amino acid from aqueous to aqueous tetramethylammonium bromide solution were interpretedin the light of cosphere overlap model. The viscosity data was utilized to determine A- and B-coefficients of viscosity, free energy of activation of viscous flow, Δμ 1 0 * and Δμ 2 0 *, per mole of solvent and solute, respectively, and ΔH * and ΔS * were also evaluated. The linear variation of φ v 0 and B-coefficient with the number of carbon atoms in the alkyl chain of amino acids was utilized to determine the respective contributions of (NH3 +, COO–) and CH2 groups to φ v 0 and B-coefficient, respectively.

Simple one-step synthesis of water and organic media soluble gold nanoparticles with various shapes and sizes

Gold nanoparticles with an average diameter in the range 1–100 nm have been synthesized from hydrogen tetrachloroaureate (III) hydrate (HAuCl 4·3H 2O) in didodecyldimethyl ammonium bromide (DDAB) aqueous solutions at room temperature. The particle size could be controlled by the concentration of DDAB and HAuCl 4·3H 2O, and reaction temperature. An increase in DDAB concentration caused a change in the particle shape from spherical to triangular, rectangular or various shapes. Until critical concentration of DDAB, where the size of gold nanoparticles seemed to prevent particle growth from aggregation, and resulted in small particle size and narrow size distribution. And DDAB-coated nanoparticles can be dispersed well in both water and organic solvent with high colloidal stability.

New Insights into the Interactions between Dendrimers and Surfactants by Two Dimensional NOE NMR Spectroscopy

The interactions between polyamidoamine dendrimers and different surfactants including sodium dodecyl sulfate (SDS) and dodecyltrimethyl ammonium bromide in aqueous solutions have been investigated by a NOESY NMR technique. Strong NOE cross-peaks between hydrophobic chain protons of SDS and methylene protons of cationic dendrimers were found, suggesting a strong tendency for the long hydrophobic tails of SDS to associate with the hydrophobic pockets of dendrimers. The hydrophilic head of SDS localizes near the core or the boundary of each generation of dendrimers, and the hydrophobic chain of SDS localizes in the relative nonpolar pockets of dendrimers. The encapsulation of surfactant monomers by dendrimers is dependent on the charge type of the surfactants, the surface functionality, and the generation of dendrimers. The NOESY analysis provides a new insight into interactions between dendrimers and surfactants in comparison with previous investigations.

A calorimetric study on interactions of amino acids with sodium dodecylsulfate and dodecyltrimethylammonium bromide in aqueous solutions at 298.15 K

Enthalpies of solution and transfer of glycine, l-alanine, l-valine, l-serine and l-threonine from water to aqueous surfactant (sodium dodecyl sulfate or dodecyltrimethylammonium bromide) solutions have been determined at 298.15 K by isothermal calorimetry. Dehydration and ion–ion interactions are important at low concentrations of the surfactant. Hydrophobic–hydrophobic interactions become primary when the amino acid molecules insert into the hydrophobic tail groups of the micelles. These phenomena can be explained with the hydration co-sphere overlap model.

Hydrate Equilibrium Conditions for Tetra-n-butyl Ammonium Bromide

Hydrate equilibrium conditions for tetra-n-butyl ammonium bromide (TBAB) aqueous solutions were experimentally studied and reported in the mole fraction from 0.003 to 0.047 and the temperature range of (276.35 to 285.65) K at atmospheric pressure. The phase change temperature of TBAB hydrate increases with the increase of the concentration of TBAB aqueous solution when the mole fraction of TBAB aqueous solution is less than 0.044.

The wettability of polytetrafluoroethylene by aqueous solution of cetylpyridinium bromide and propanol mixtures

Measurements of advancing contact angles ( θ) were carried out for aqueous solutions of cetylpyridinium bromide (CPBr) and propanol mixtures at constant CPBr concentration equal to 1 × 10 −5, 1 × 10 −4, 6 × 10 −4, 1 × 10 −3 M, respectively, on polytetrafluoroethylene (PTFE). The obtained results indicate that the wettability of PTFE by aqueous solutions of these mixtures depends on their composition and concentration. In contrast to Zisman, there is no linear dependence between the cos θ and surface tension of aqueous solutions of CPBr and propanol mixtures ( γ LV), but a linear relationship exists between the adhesion tension and the surface tension of aqueous solutions of CPBr and propanol mixtures which have a slope equal to −1, and between cos θ and the reciprocal of the surface tension of solution. The slope equal to −1 and the intercept on the cos θ axis close to −1 suggest that adsorption of CPBr and propanol mixtures and the orientation of their molecules at aqueous solution–air and PTFE–aqueous solution interfaces are the same. This also suggests that the work of solution adhesion to the PTFE surface does not depend on the concentration of propanol and CPBr. Extrapolation of the straight line to the point corresponding to the surface tension of solution, which completely spreads over the PTFE surface, gives the value of the critical surface tension of PTFE wetting equal to 24.84 mN/m. This value is higher than PTFE surface tension (20.24 mN/m) and the values of the critical surface tension of PTFE wetting determined by other investigators from the contact angle of nonpolar liquids (e.g. n-alkanes). The differences between the value of the critical surface tension obtained here and those which can be found in the literature were discussed on the basis of the simple thermodynamic rules. Using the measured values of the contact angles and Young equation the PTFE–aqueous solution interfacial tension was determined. The values of PTFE–aqueous solution interfacial tension were also calculated from Miller and co-workers equation in which the correction coefficient of nonideality of the surface monolayer was introduced. From comparison of the obtained values it appears that good agreement exists between the values of PTFE–solution interfacial tension calculated on the basis of Young and Miller and co-workers equations in the whole range of propanol concentration.

X-ray absorption spectroscopy study of solvation and ion-pairing in aqueous gallium bromide solutions at supercritical conditions

X-ray absorption spectroscopy measurements have been performed both at the Ga and Br K-edges on aqueous GaBr 3 solutions. The isobaric experiments have been recorded at 30 MPa from ambient temperature to 670 K for two GaBr 3 concentrations (0.017 and 0.17 mol/dm 3). At room temperature, Ga 3+ and Br − ions are fully solvated, surrounded by water O atoms at 1.97 Å (Ga–O) and 3.37 Å (Br–O). When the temperature is elevated, Ga 3+ cations precipitate as gallium oxy-hydroxide colloids while Br − anions remain solvated. With a further increase in temperature, the gallium solid precipitates remarkably re-dissolved (25% and 50% for 0.017 and 0.17 mol/dm 3 respectively), due to the formation of [GaBr n (H 2O) 4 − n ] (aq) 3 − n ( n = 2, 3 or 4) tetrahedral complexes.

Kinetic studies on promazine oxidation by FeIII/CuII in acidic aqueous bromide solutions. Spectroscopic and kinetic non-additivity as evidence for the CuII–Br–FeIII-type heterobimetallic complex formation

The formation of CuII–Br–FeIII-type heterobimetallic complexes was observed spectrophotometrically, given the non-additivity of the spectra from the copper(II) and iron(III) complexes. The kinetics of the oxidation of promazine radical (ptz+•) to promazine 5-oxide, by iron(III) bromides, copper(II) bromides, and a mixture of these complexes in acidic aqueous solutions, have been studied using UV–Vis spectroscopy at I = 1.0 M (H+, Cu2+, Fe3+, Br−) and T = 318 K. Copper(II) inhibits the oxidation of the promazine radical to promazine sulfoxide using iron(III) complexes. A rate retardation effect, characterized by the dependence of the pseudo second-order rate constant (kII) on the copper(II) concentration kII = a/(1 + b[CuII]), can be rationalized as a result of CuII–Br–FeIII-type heterobimetallic complex formation.

Kinetics and Mechanisms of the Oxidation of Iodide and Bromide in Aqueous Solutions by a trans-Dioxoruthenium(VI) Complex

The kinetics and mechanisms of the oxidation of I (-) and Br (-) by trans-[Ru (VI)(N 2O 2)(O) 2] (2+) have been investigated in aqueous solutions. The reactions have the following stoichiometry: trans-[Ru (VI)(N 2O 2)(O) 2] (2+) + 3X (-) + 2H (+) --> trans-[Ru (IV)(N 2O 2)(O)(OH 2)] (2+) + X 3 (-) (X = Br, I). In the oxidation of I (-) the I 3 (-)is produced in two distinct phases. The first phase produces 45% of I 3 (-) with the rate law d[I 3 (-)]/dt = ( k a + k b[H (+)])[Ru (VI)][I (-)]. The remaining I 3 (-) is produced in the second phase which is much slower, and it follows first-order kinetics but the rate constant is independent of [I (-)], [H (+)], and ionic strength. In the proposed mechanism the first phase involves formation of a charge-transfer complex between Ru (VI) and I (-), which then undergoes a parallel acid-catalyzed oxygen atom transfer to produce [Ru (IV)(N 2O 2)(O)(OHI)] (2+), and a one electron transfer to give [Ru (V)(N 2O 2)(O)(OH)] (2+) and I (*). [Ru (V)(N 2O 2)(O)(OH)] (2+) is a stronger oxidant than [Ru (VI)(N 2O 2)(O) 2] (2+) and will rapidly oxidize another I (-) to I (*). In the second phase the [Ru (IV)(N 2O 2)(O)(OHI)] (2+) undergoes rate-limiting aquation to produce HOI which reacts rapidly with I (-) to produce I 2. In the oxidation of Br (-) the rate law is -d[Ru (VI)]/d t = {( k a2 + k b2[H (+)]) + ( k a3 + k b3[H (+)]) [Br (-)]}[Ru (VI)][Br (-)]. At 298.0 K and I = 0.1 M, k a2 = (2.03 +/- 0.03) x 10 (-2) M (-1) s (-1), k b2 = (1.50 +/- 0.07) x 10 (-1) M (-2) s (-1), k a3 = (7.22 +/- 2.19) x 10 (-1) M (-2) s (-1) and k b3 = (4.85 +/- 0.04) x 10 (2) M (-3) s (-1). The proposed mechanism involves initial oxygen atom transfer from trans-[Ru (VI)(N 2O 2)(O) 2] (2+) to Br (-) to give trans-[Ru (IV)(N 2O 2)(O)(OBr)] (+), which then undergoes parallel aquation and oxidation of Br (-), and both reactions are acid-catalyzed.

Analysis of fluorescence spectra of PRODAN in protic solvents as the superposition of two Gaussian functions

The steady-state fluorescence emission spectra of 6-propionyl-2-dimethylaminonaphthalene (PRODAN) in aqueous solutions of methanol, ethanol and 1-propanol were studied in a wide range of concentrations. The flourescence of PRODAN was also studied in aqueous solutions (from 3 × 10−3 to 21 × 10−3 mole L−1) of dodecyltrimethylammonium bromide (DTAB), a micelle-forming ionic surfactant. In all cases, experimental data, as a function of wavelength, are very well fitted by the sum of two Gaussian functions. In alcohol solutions, the maximum of lower wavelength depends linearly both on concentration and polarizability. In DTAB solutions, the maximum of higher wavelength varies smoothly with concentration, but the lower wavelength maximum changes abruptly at the Critical Micellar Concentration. Results are explained by assuming that the fluorescence emission of PRODAN is originated in transitions from two excited states which are close in energy but have dissimilar interactions with the probe environment.

Quenching and Dequenching of Pyrene Fluorescence by Nucleotide Monophosphates in Cationic Micelles

The fluorescence behavior of pyrene solubilized in the hexadecyltrimethylammonium bromide aqueous micellar solution in the presence of adenosine 5'-monophosphate (AMP) and uridine 5'-monophosphate (UMP) was investigated. AMP and UMP were found to influence oppositely the fluorescence of micellized pyrene. UMP acts as quencher, while AMP acts as dequencher. Both effects saturate at high nucleotide concentration (about 40 mM). Dequenching of micellized pyrene fluorescence is induced also by addition of disodium hydrogen orthophosphate (Na 2HPO 4), while loading with sodium bromide (NaBr) quenches the fluorescence. Furthermore, in absence of micelles, pyrene fluorescence depends on the UMP, according to the Stern-Volmer relation, but is unaffected by AMP. Dynamic light scattering experiments showed that the size and shape of aggregates is not affected by different types of nucleotide loaded into the solution; thus, we conclude that the opposite photophysical effect exploited by AMP and UMP are uncorrelated to any change in micellar microstructure. The whole fluorescence data set was successfully accounted for by assuming that the anionic nucleotides compete with the surfactant counterion (bromide) for the surface of the micelle. Accordingly, substitution of bromide with the more effective quencher UMP results in a strong decrease of the pyrene fluorescence, while the substitution of bromide with the nonquencher AMP results in an increase in the pyrene fluorescence.

Viscoelastic micellar water/CTAB/NaNO 3 solutions: Rheology, SANS and cryo-TEM analysis

Aqueous micellar solutions of the cationic surfactant hexadecyltrimethylammonium bromide (CTAB) and sodium nitrate (NaNO 3) were examined using steady and dynamic rheology, small-angle neutron scattering (SANS) and cryogenic-transmission electron microscopy (cryo-TEM). Upon addition of NaNO 3, the CTAB spherical micelles transform into long, flexible wormlike micelles, conveying viscoelastic properties to the solutions. The zero-shear viscosity ( η 0 ) versus NaNO 3 concentration curve exhibits a well-defined maximum. Likewise, upon increase in temperature, the viscosity decreases. Dynamic rheological data of the entangled micellar solutions can be well described by the Maxwell model. Changes in the structural parameters of the micelles with addition of NaNO 3 were inferred from SANS measurements. The intensity of scattered neutrons at the low q region was found to increase with increasing NaNO 3 concentration. This suggests an increase in size of the micelles and/or decrease of intermicellar interactions with increasing salt concentration. Analysis of the SANS data using prolate ellipsoidal structure and Yukawa form of interaction potential between micelles indicates that addition of NaNO 3 leads to a decrease in the surface charge of the ellipsoidal micelles and consequently an increase in their length. The structural transition from spherical to entangled threadlike micelles, induced by the addition of NaNO 3 to CTAB micelles is further confirmed by cryo-TEM.

Assessing the level of consistency between diffraction experiments and interaction potentials: A combined molecular dynamics (MD) and Reverse Monte Carlo (RMC) approach

A protocol for finding the applicability limits of interaction potential models, used in molecular dynamics (MD) computer simulations, is presented. The essence of the approach is to combine experimental structure factors and radial distribution functions from MD simulations in one single structural model, generated by Reverse Monte Carlo modeling. This way, it becomes possible to tell which parts of the structure are represented by the potential model in question. As an example, we use aqueous rubidium bromide solutions. We show that a great deal of structural information from MD may be consistent with neutron diffraction experiments at lower concentrations.

Corrosion monitoring of stainless steel 304L in lithium bromide aqueous solution using transmittance optical detection technique

We report a method based on the power ratio of transmittance for monitoring the corrosion rate in stainless steel 304L immersed in an aqueous solution of lithium bromide at 50 wt%, at 70 °C. The optical transmittance measured in the solution contaminated with corrosion oxides at different times of exposure is related to the physical degradation of the stainless steel samples. Lasers at 532 and 632 nm were utilized for monitoring the accumulation of corrosion oxides dissolved in the lithium bromide solution of the metallic samples for 480 h. The change in the optical power of transmittance was 13 μW/480 h measured at 532 nm and 3.6 μW/480 h at 632 nm. The variation of the power ratio for 532 nm was from 0.01 to 0.24, and for 632 nm, from 0.01×10 −3 to 15.61×10 −3; this is proportional to an accumulated corrosion rate of [0.0142×10 −3–0.552×10 −3 g/cm 2] for an exposure time of 432 h.

Micellar behavior of aqueous solutions of dodecyldimethylethylammonium bromide, dodecyltrimethylammonium chloride and tetradecyltrimethylammonium chloride in the presence of α-, β-, HP β- and γ-cyclodextrins

Conductivity, static fluorescence and 1H NMR measurements have been carried out to study the micellar behavior of aqueous solutions of dodecyldimethylethylammonium bromide (DDAB), dodecyltrimethylammonium chloride (DTAC) and tetradecyltrimethylammonium chloride (TDAC) in absence and presence of α-cyclodextrin ( α-CD), β-cyclodextrin ( β-CD), hydroxypropyl- β-cyclodextrin (HP β-CD) and γ-cyclodextrin ( γ-CD). The conductivity measurements were carried out at 298.15 K. The influence of cyclodextrins on the micellar parameters, such as cmc ∗ (apparent critical micellar concentration), β (degree of ionization) have been analyzed. Thermodynamics of the systems was discussed in terms of the change in standard free energy of micellization, Δ G m 0 . Micellization was found to be less spontaneous in presence of cyclodextrins. The fluorescence intensity of the surfactant solutions is enhanced by the addition of cyclodextrins. The association constants obtained from conductivity and fluorescence data suggest the binding of γ-CD with the surfactants to be strongest among all the cyclodextrins used. 1H NMR chemical shift changes provide powerful means for probing the cyclodextrin–micellar interactions and inclusion of surfactant is shown by the change in the chemical shift of some of the guest and host protons in comparison with the chemical shifts of the same protons in the free compounds.

Rheology and microstructure studies of SDS/CTAB/H2O system

Phase behavior of mixed sodium dodecyl sulfate (SDS) and cetyl trimethyl ammonium bromide (CTAB) aqueous solution was studied. The rheological properties and microstructure were investigated using a rheostat and freeze-fracture technique and are shown to be closely related to the phase behavior. Experimental investigations reveal two symmetrical aqueous two-phase systems (ATPS) in the ternary phase diagram of SDS/CTAB/H2O system. In the surfactant rich phase of ATPS or in the adjacent stoichiometric state of ATPS, the system has high viscosity because of its long range ordered structure. Lamellar phase was found in the high viscosity samples in which the cationic and anionic surfactant are in 1: 3 or 3: 1 stoichiometry. In addition, the viscosity has a tendency to increase when salt was added to the solution. The viscosity increase is due to the salt can screen the repulsion between different charged headgroups and thus reduces the effective size of surfactants and facilitates the spherical or rod likes micelles to be transformed to worm-like micelles which can form hexagonal or liquid crystal phases. Large-size salt ions like sodium sulfate (especially organic salt ions) have more significant effect on the surfactant solution viscosity.