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Spontaneous transfer of discrete colloidal silica particles from water into 2,6-dimethyl-4-heptanone (DH) is obtained upon preliminary adsorption of dodecylbenzyldimethylammonium bromide (DBDAB) from the aqueous phase onto the solid. Partitioning of the surfactant between the silica surface and both liquid phases is evaluated through the determination of the isotherm in the aqueous phase, taking into account their mutual solubility. The organosol particles are found to be covered by a statistical monolayer of surfactant molecules presumably hydrated to the extent of 20% on a mole ratio basis. Monodispersion of this stable suspension is ascertained by dynamic light scattering. Evidence of DBDAB association in the monolayer emerges from the conductimetric behavior of the amphiphile in DH and from the reversal of the silica native charge in the organosol, as shown by electrophoretic mobility determinations. Disorganization of the water layer contacting silica upon adsorption of DBDAB is argumented to originate from the presence of sparsely distributed dodecyl chains. Copyright 1998 Academic Press.
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PMID:Surfactant-Mediated Transfer of Colloidal Silica Particles from Water into an Immiscible Weakly Polar Solvent. 982 Jul 60

1. The effects of external anions on the decay kinetics of Ca2+-activated Cl- currents (ICl(Ca)) were studied in smooth muscle cells isolated from rabbit portal vein using the perforated patch whole-cell voltage clamp technique. 2. In normal NaCl-containing external solution the decay of spontaneous Ca2+-activated Cl- currents (STICs) and Ca2+-activated Cl- 'tail' currents (Itail) was described by a single exponential with a time constant (tau) that was prolonged by external anions which are more permeable than Cl- (Br-, I- and SCN-) and accelerated by less permeant anions. However, intracellular I- did not affect the tau of STICs and Itail. 3. There was a positive correlation between the ability of an external anion to affect the decay tau of ICl(Ca) and its permeability relative to Cl-. 4. The voltage dependence of STIC and Itail decay was not affected by external or internal anions. 5. External permeating anions were not obligatory for activation of ICl(Ca) and STIC tau was not altered in Cl--free external solution. 6. Modulation of tau by mole fractions of SCN- and Cl- ions was fitted by a logistic curve, suggesting competition between SCN- and Cl- ions for a binding site. 7. In conclusion, external anions affect the decay of ICl(Ca) by a mechanism compatible with an interaction with a binding site which modulates Cl- channel kinetics.
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PMID:Modulation of the decay of Ca2+-activated Cl- currents in rabbit portal vein smooth muscle cells by external anions. 1008 37

Extent of binding (gamma 2(1)) of cationic surfactants cetyltrimethyl ammonium bromide (CTAB), myristyltrimethyl ammonium bromide (MTAB) and dodecyl trimethyl ammonium bromide (DTAB) to calf-thymus DNA, bovine serum albumin (BSA) and to their binary mixture respectively have been measured as function of bulk concentration of the surfactant by using equilibrium dialysis technique. Binding of CTAB has been studied at different pH, ionic strength (mu), temperature and biopolymer composition and with native and denatured states of the biopolymers. The chain-length of different long chain amines plays a significant role in the extent of binding under identical solution condition. The binding ratios for CTAB to collagen, gelatin, DNA-collagen and DNA-gelatin mixtures respectively have also been determined. The conformational structures of different biopolymers are observed to play significant role in macromolecular interactions between protein and DNA in the presence of CTAB. From the experimental values of the maximum binding ratio (gamma 2m) at the saturation level for each individual biopolymer, ideal values (gamma 2m)id have been theoretically calculated for binary mixtures of biopolymers using additivity rule. The protein-DNA-CTAB interaction in mixture has been explained in terms of the deviation (delta) of (gamma 2m) from (gamma 2m)id in the presence of a surfactant in bulk. The binding of surfactants to biopolymers and to their binary mixtures are compared more precisely in terms of the Gibbs' free energy decrease (-delta G degree) for the saturation of the binding sites in the biopolymers or biopolymer mixtures with the change of the bulk surfactant activity from zero to unity in the rational mole fraction scale.
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PMID:Binding of cationic surfactants to DNA, protein and DNA-protein mixtures. 1065 Jul 15

Extent of binding (gamma 2(1)) of sodium dodecyl sulphate (SDS) to the binary complex formed between calfthymus DNA and cetyltrimethylammonium bromide (CTAB) has been measured in mole per mole of nucleotide in the complex as function of concentration of SDS by using equilibrium dialysis technique at different temperatures and pH. Binding of SDS to thermally denatured DNA-CTAB complex has also been studied. The most interesting aspect to be noted in this experiment is that the water insoluble DNA-CTAB binary complex gets solubilized in the ternary mixture in presence of SDS but when DNA is thermally denatured, the ternary system DNA-CTAB-SDS remains insoluble. Significant change in the extent of binding has been noted with the variation of the relative composition of DNA and CTAB in their binary mixture. The data of binding of SDS to DNA-CTAB complex are compared more precisely in terms of the standard Gibbs' free energy decrease (-delta G degree) for the saturation of the binding sites in the complex with the change of SDS activity from zero to unity in the rational mole fraction scale.
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PMID:Solubilization and binding of DNA-CTAB complex with SDS in aqueous media. 1065 Jul 24

The conductances of trimethyltetradecylammonium bromide (TTAB)+triphenyltetradecylphosphonium bromide (TTPB) and TTAB+trimethylhexadecylammonium bromide (HTAB) over the entire mole fraction range of TTAB (alpha(TTAB)) were measured in water and in beta-cyclodextrin+water (CD+W) mixtures at fixed 4 and 8 mM of CD at 30 degrees C. The conductivity plots for both binary mixtures show a single break from which the mixed critical micelle concentration (cmc) and degree of micelle ionization (chi) were computed. From the slopes of the conductivity curves, the equivalent ionic conductivities of the monomeric (Lambda(m)), associated (Lambda(ass)), and the micelle (Lambda(mic)) states were calculated and discussed with respect to the surfactant-CD complexation in the whole mole fraction range of both surfactant binary mixtures. The association constant (K) between the respective monomeric surfactant and CD cavity of fixed 4 mM CD was computed by considering 1:1 association from the surface tension measurements. A comparison among the K values for HTAB-CD, TTAB-CD, and TTPB-CD shows that the former complexation is significantly stronger in comparison to the other ones due to the longer hydrophobic tail. The nonideality in mixed micelle formation in pure water was evaluated by using the regular solution theory, and it was observed that both binary mixtures exhibit close to ideal behavior. Copyright 2000 Academic Press.
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PMID:Cationic Mixed Micelles in the Presence of beta-Cyclodextrin: A Host-Guest Study. 1086 May 97

1. Anion binding within the pores of wild-type and mutant cystic fibrosis transmembrane conductance regulator (CFTR) Cl- channels, expressed in two different mammalian cell lines, was assayed using patch clamp recording. Specifically, experiments measured both the conductance of different anions and the ability of other permeant anions to block Cl- permeation through the pore. 2. Under symmetrical ionic conditions, wild-type CFTR channels showed the conductance sequence Cl- > NO3- > Br- > or = formate > F- > SCN- congruent to ClO4-. 3. High SCN- conductance was not observed, nor was there an anomalous mole fraction effect of SCN- on conductance under the conditions used. Iodide currents could not be measured under symmetrical ionic conditions, but under bi-ionic conditions I- conductance appeared low. 4. Chloride currents through CFTR channels were blocked by low concentrations (10 mM) of SCN-, I- and ClO4-, implying relatively tight binding of these anions within the pore. 5. Two mutations in CFTR which alter the anion permeability sequence, F337S and T338A, also altered the anion conductance sequence. Furthermore, block by SCN-, I- and ClO4- were weakened in both mutants. Both these effects are consistent with altered anion binding within the pore. 6. The effects of mutations on anion permeability and relative anion conductance suggested that, for most anions, increased permeability was associated with increased conductance. This indicates that the CFTR channel pore does not achieve its anion selectivity by selective anion binding within the mutated region. Instead, it is suggested that entry of anions into the region around F337 and T338 facilitates their passage through the pore. In wild-type CFTR channels, anion entry into this crucial pore region is probably dominated by anion hydration energies.
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PMID:Relationship between anion binding and anion permeability revealed by mutagenesis within the cystic fibrosis transmembrane conductance regulator chloride channel pore. 1117 91

The aqueous solutions of mixtures of various conventional surfactants and dimeric anionic and cationic surfactants have been investigated by electrical conductivity, spectrofluorometry, and time-resolved fluorescence quenching to determine the critical micelle concentrations and the micelle aggregation numbers in these mixtures. The following systems have been investigated: 12-2-12/DTAB, 12-2-12/C(12)E(6), 12-2-12/C(12)E(8), 12-3-12/C(12)E(8), Dim3/C(12)E(8), and Dim4/C(12)E(8) (12-2-12 and 12-3-12=dimethylene-1,2- and trimethylene-1,3-bis(dodecyldimethylammonium bromide), respectively; C(12)E(6) and C(12)E(8)=hexa- and octaethyleneglycol monododecylethers, respectively; Dim3 and Dim4=anionic dimeric surfactants of the disodium sulfonate type, Scheme 1; DTAB=dodecyltrimethylammonium bromide). For the sake of comparison the conventional surfactant mixtures DTAB/C(12)E(8) and SDS/C(12)E(8) (SDS=sodium dodecylsulfate) have also been investigated (reference systems). Synergism in micelle formation (presence of a minimum in the cmc vs composition plot) has been observed for the Dim4/C(12)E(8) mixture but not for other dimeric surfactant/nonionic surfactant mixtures investigated. The aggregation numbers of the mixed reference systems DTAB/C(12)E(8) and SDS/C(12)E(8) vary monotonously with composition from the value of the aggregation number of the pure C(12)E(8) to that of the pure ionic component. In contrast, the aggregation number of the dimeric surfactant/C(12)E(8) mixtures goes through a minimum at a low value of the dimeric surfactant mole fraction. This minimum does not appear to be correlated to the existence of synergism in micelle formation. The initial decrease of the aggregation number of the nonionic surfactant upon addition of ionic surfactant, up to a mole fraction of ionic surfactant of about 0.2 (in equivalent per total equivalent), depends little on the nature the surfactant, whether conventional or dimeric. The results also show that the microviscosity of the systems containing dimeric surfactants is larger than that of the reference systems. Copyright 2001 Academic Press.
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PMID:Mixed Micellization of Dimeric (Gemini) Surfactants and Conventional Surfactants. 1123 50

Dendrimeric polyphenylsulfides, -selenides, and -tellurides are prepared in high yield using propyloxy spacers to connect the phenylchalcogeno groups to the dendrimeric core. The selenides and tellurides catalyze the oxidation of bromide with hydrogen peroxide to give positive bromine species that can be captured by cyclohexene in two-phase systems. The corresponding sulfides show no catalytic activity. The increase in the rate of catalysis followed statistical effects for 1, 6, and 12 phenyltelluro groups. However, the increase in the rate of catalysis exceeds statistical contributions for the first few generations with 1, 3, 6, and 12 phenylseleno groups and suggested cooperativity among phenylseleno groups. The increase in catalytic rate was lost upon replacing all but one phenylseleno group with phenoxy groups. On the basis of H2O2 consumed, the dendrimer with 12 phenylseleno groups has a turnover number of >60 000 mol of H2O2 consumed per mole of catalyst.
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PMID:Dendrimeric organochalcogen catalysts for the activation of hydrogen peroxide: improved catalytic activity through statistical effects and cooperativity in successive generations. 1127 1

The formation and speciation of disinfection byproducts (DBPs) resulting from chlorination of nanofilter permeates obtained from various source water locations and membrane types are examined. Specific ultraviolet absorbance and bromide utilization are shown to decrease following nanofiltration. Both dissolved organic carbon (DOC) concentration and ultraviolet absorbance at 254 nm were found to correlate strongly with trihalomethane (THM), haloacetic acid (HAA), and total organic halide (TOX) concentrations in chlorinated nanofilter permeates, suggesting that they can be employed as surrogates for DBPs in nanofiltered waters. Because smooth curves were obtained for individual THM and HAA species as well as bromine and chlorine incorporation into THMs and HAAs as a function of Br-/DOC molar ratio, it is likely that mole fractions of these DBPs are more strongly influenced by chlorination conditions, Br-, and DOC concentrations than NOM source and membrane type. Mole fractions of mono-, di-, and trihalogenated HAAs were found to be independent of Br-/DOC. Even at a very low Br-/DOC of 2.9microM/mM, the mixed bromochloro- and tribromoacetic acids constituted 20% of total HAAs on a molar basis. This increased to approximately 50% as Br-/DOC increased to approximately 25microM/mM or more, proving that a large fraction of HAAs may not be covered under existing federal regulations. Total THM and HAA9 concentrations decreased in permeate waters with increasing Br-/DOC suggesting that nanofilter permeates are limited with respect to DBP precursors.
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PMID:Disinfection byproduct relationships and speciation in chlorinated nanofiltered waters. 1164 67

We report principles for microscale separations based on selective solubilization and deposition of sparingly water-soluble compounds by an aqueous solution of a redox-active surfactant. The surfactant, (11-ferrocenylundecyl)trimethylammonium bromide, undergoes a reversible change in micellization upon oxidation or reduction. This change in aggregation is exploited in a general scheme in which micelles of reduced surfactant are formed and then put in contact with a mixture of hydrophobic compounds leading to selective solubilization of the compounds. The micelles are then electrochemically disrupted, leading to the selective deposition of their contents. We measured the selectivity of the solubilization and deposition processes using mixtures of two model drug-like compounds, o-tolueneazo-beta-naphthol (I) and 1-phenylazo-2-naphthylamine (II). By repeatedly solubilizing and depositing a mixture that initially contained equal mole fractions of each compound, we demonstrate formation of a product that contains 98.4% of I after six cycles. Because the aggregation states of redox-active surfactants are easily controlled within simple microfabricated structures, including structures that define small stationary volumes (e.g., wells of a microtiter plate) or flowing volumes of liquids (e.g., microfabricated channels), we believe these principles may be useful for the purification or analysis of compounds in microscale chemical process systems. When used for purification, these principles provide separation of surfactant and product.
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PMID:Principles for microscale separations based on redox-active surfactants and electrochemical methods. 1168 55


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