Addition Of Counterions Research Articles

Onion-Like Structure of Viscoelastic Surfactant Solution Flow Induced by 4-Blade Paddle Impeller in a Vessel

Aqueous solutions of some kinds of surfactants and counterions are known as viscoelastic fluids. The rheological properties and fluidity of the solutions are significantly affected by the surfactant and counterion concentrations. Thus, the solution is a potential solvent for industrial applications because a drastic change in the fluidity can be realized only through the addition of counterions. In this study, we focused on the characteristics of the fluid flow of viscoelastic surfactant solutions in a mixing vessel. It was found that in the vicinity of the impeller the fluid was actively mixed and contained a large number of laminated fluid lumps, forming onion-like structure. When the elastic force becomes comparable to the viscous force, the micellar network of the surfactant was deformed. Additionally, if the elastic force was not much smaller than the inertia force, the impeller region was covered by a network-deformed fluid and an onion-like structure was then formed. Moreover, a stable onion-like structure was obtained when the impeller rotated as slowly as possible or when the elastic force of the solution was more significant than the viscous one.

Association of a Cylindrical Polyelectrolyte Brush with Tetravalent Counterions

Cylindrical poly(styrene sulfonate) brushes were combined with a tetravalent double-DABCO based counterion. With increasing addition of counterion, hydrodynamic radius and radius of gyration decrease and AFMreveals a conformation change from wormlike to curled structures. Rg/Rh changes from 1.3 to 0.9. Above charge stoichiometry, brushes become interconnected into finite size assemblies, which are stable in aqueous solution for charge ratios (ratio of the molar concentration of charged counterion groups to the molar concentration of charged monomer units of the polymer brush) 1 < l < 1.2. They are compact and consist of the brushes in curled (bent) conformation, which is in difference to network-like aggregates from cylindrical poly(styrene sulfonate) brushes with tetravalent porphyrin counterions (Gröhn et al. Macromolecules 2009) and to a wormlike - bent conformation - helix transition found for another brush counterion system (Müller et al. Soft Matter 2009).

Effect of Molecular Crowding and Ionic Strength on the Isothermal Hybridization of Oligonucleotides

The isothermal hybridization of complementary oligonucleotides, 15-mer, 25-mer, 35-mer, and a molecular beacon, was investigated under varying conditions of molecular crowding and ionic strength, using hypochromicity to follow strand pairing and polyethylene glycol as a crowding agent. Thermodynamic analysis of the results revealed the addition of counterions to the oligonucleotide backbones, DeltaPsi, to be dependent on the strand GC content and the molecular crowding. A decrease in DeltaPsi was observed, with both increasing GC% and solution PEG content. In contrast, the number of bound water molecules depended on the activity of Na(+), where two regimes were observed. At a(Na(+)) < 0.05 and increasing molecular crowding, water molecules were released into the DNA solutions, and oligonucleotide pairing was favored with both increasing hydrophobic forces, whereas at a(Na(+)) >or= 0.05, water molecules were bound to the strands, and the extent of double strand formation decreased with increasing PEG wt %.

Heterogeneous Fenton type processes for the degradation of organic dye pollutant in water — The application of zeolite assisted AOPs

Heterogeneous Fenton type processes using Fe-exchanged zeolite of ZSM5 type were investigated for the degradation of model organic pollutant, reactive azo dye C.I. Reactive Blue 137, in water. Research work was directed to compare process efficiency and to establish their advantages over corresponding homogenous Fenton type processes. The influence of UV irradiation on both heterogeneous and homogeneous processes was also studied. On the basis of decolorization and mineralization degree of dye aqueous solution the overall process efficiency was estimated. Homogeneous and heterogeneous Fenton processes yielded similar decolorization and mineralization, but the concentration of Fe ions in the bulk after the treatment was significantly lower in the latter case. Moreover, the usage of heterogeneous catalyst allows process to be operated at milder pH conditions minimizing the addition of counter ions (both anions and cations) for strong pH conditioning like in homogeneous Fenton processes. Besides that, another advantage of heterogeneous over homogeneous process is the avoidance of unnecessary additional loading of wastewater by counter ions that originated from iron salts. UV irradiation positively affected both decolorization and mineralization degree in all applied homogeneous and heterogeneous Fenton type processes.

Single chain contraction and re-expansion of polystyrene sulfonate: A study on its re-entrant condensation at single molecular level

Single chain conformation of a polyelectrolyte (polystyrene sulfonate, PSS(-)Na(+)) during its re-entrant condensation was studied by fluorescence correlation spectroscopy (FCS) with single molecule sensitivity. The contraction and re-expansion of PSS(-)Na(+) chain were observed with the addition of counterions of different valencies. The formation of aggregation and precipitation of PSS(-)Na(+) and its redissolution were observed in accordance with the chain contraction and re-expansion process for the PSS(-)Na(+) chain upon the addition of trivalent La(3+) ion. Chain contraction and re-expansion of the PSS(-)Na(+) chain were also observed with the addition of monovalent Cs(+) and divalent Ca(2+) ions, under which condition, the re-entrant condensation was not observed. The results demonstrate that the high sensitivity of FCS can really study single PSS(-)Na(+) chain under extremely dilute situation.

Importance of Counterion Reactivity on the Deactivation of Co−Salen Catalysts in the Hydrolytic Kinetic Resolution of Epichlorohydrin

Possible modes of deactivation of Jacobsen's Co-salen catalyst during the hydrolytic kinetic resolution (HKR) of epichlorohydrin were explored by UV-vis spectroscopy, X-ray absorption spectroscopy, and electrospray ionization mass spectrometry, combined with recycling studies. Although an active Co(III)-salen catalyst deactivated substantially after multiple cycles without regeneration, the catalyst maintained its +3 oxidation state throughout the runs. Thus, deactivation of Co-salen during HKR was not the result of Co reduction. The mass spectrum of a deactivated material showed that catalyst dimerization does not account for the loss of activity. Results from various catalyst pretreatment tests, as well as from catalysts containing various counterions (acetate, tosylate, chloride, iodide) indicated that the rate of addition of the Co-salen counterions to epoxide forming Co-OH during the reaction correlated with deactivation. The extent of counterion addition to epoxide was influenced by the exposure time and the nucleophilicity of the counterion. An oligo(cyclooctene)-supported Co-OAc salen catalyst, which was 25 times more active than the standard Co-salen catalyst, was recycled multiple times with negligible deactivation.

Self-Assembled Polyaniline Nanofibers/Nanotubes

A facile chemical polymerization is introduced to synthesize relatively long polyaniline nanofibers/nanotubes via self-assembly. 1-D elongation is achieved through the rapid formation of a substantial amount of dimer cation−radicals using excess initiator. 1-D nanostructures can be altered into 3-D hollow micro-/nanospheres in the presence of surfactant or counterion additives.

Computational study of ground‐state chiral induction in small peptides: Comparison of the relative stability of selected amino acid dimers and oligomers in homochiral and heterochiral combinations

The relative stabilities of homochiral and heterochiral forms of selected dipeptides, AA, AS, AC, AV, AF, AD, AK, tripeptides, AAA, AVA, and an acetylpentapeptide, AcGLSFA, have been calculated using thermodynamic integration protocols and the GROMOS 53A6 force field. Integration pathways have been designed that produce minimal disturbance to the system, including the use of soft atoms, low-energy intermediates, and chiral inversion of the smaller amino acid in the peptide. Comparison of the results obtained by thermodynamic integration between the diastereomeric forms (in explicit water, at 300 K) and from exhaustive global minimum-energy searches for the individual dipeptides (implicit water, epsilon = 78, 0 K) suggests that entropic contributions to the relative stability of the chiral forms are important. This conclusion is supported by the results of explicit calculation of the effect of temperature on the relative stability of alanylvalylalanine diastereomers. The Gibbs free energy calculations predict that at ambient temperature and pressure homochiral dipeptides with small side chains or polar groups in the vicinity of the peptide backbone, AA, AS, and AD, are more stable than their heterochiral counterparts by fractions of a kJ/mol. For bigger side chains, AC, AV, AF, and AK, the heterochiral diastereomers appear to be more stable. Predicted relative stabilities are in line with observations reported in the literature for AE and YY. Excellent agreement is found for the calculated and experimentally determined relative stabilities of the diastereomers of the dipeptide AA and of all-L AcGLSFA and its diastereomer containing D-serine in the central position. Addition of counterions to the solvent box has no significant effects on charged and neutral forms. From the present findings it would appear unlikely that the intrinsic stability difference between homo- and heterochiral dipeptides has been a driving force in a primordial selection process leading to the incorporation of amino acids with a single enantiomeric configuration in natural proteins.

Clouding phenomenon in ionic micellar solutions: Role of the counterion

AbstractClouding is rarely observed with ionic surfactants. Herein we report the occurrence of clouding in sodium dodecyl sulfate (SDS, an anionic surfactant) solutions on addition of different symmetrical and unsymmetrical quaternary phosphonium bromides (tetra‐n‐butylphosphonium, tetraphenylphosphonium, and n‐propyltriphenylphosphonium). Cloud point (CP) measurements were made with solutions having different SDS/salt combinations. The nature of the counterion had a crucial role in the occurrence of the phenomenon, whereas substitution of an alkyl chain by a phenyl ring made the salt more effective near ambient temperature. A linear relationship between the SDS and salt concentrations was obtained. It is proposed that both the electrostatic charge and the hydration state of the headgroup region are influenced by counterion addition and that the net charge or volume of the counterion has a key role to play in the overall phenomenon. The effect of the addition of some hydroxy compounds on CP variations in these SDS+salt systems was also studied, and the data were interpreted on the basis of incorporation of these compounds in the micellar headgroup region. The nature of the counterions influenced this incorporation.

Surfactant Drag Reduction Caused by a Cationic Surfactant with Excess Addition of Counter-ions

Surfactant drag reduction is a promising technology to reduce the pumping power of district heating–cooling systems. Many investigations have been reported to give a clear prospect of the drag-reducing phenomenon. However, the mechanism of surfactant drag reduction and the microstructure of surfactant micelles are still left unknown. This study aims to provide an experimental evidence of the effect of counter-ions on the micelle structure and the surfactant drag reduction in a pipe flow. The present authors have been investigating the surfactant drag reduction with a cationic surfactant with suitable counter-ions (sodium salicylate). The effect of the molar ratio of the counter-ion to the cationic surfactant is discussed using the experimental results on the drag reduction in a turbulent pipe flow, on the micelle size and on the shear thinning–thickening viscosity. These experimental results suggest that a new drag-reducing state exists at very high molar ratios of the counter-ion to the surfactant. This new state gives a remarkable drag reduction, but shows very weak viscoelasticity. The optimum molar ratio to cause a strong viscoelasticity is (surfactant):(counter-ion) = 1:1.5, but at higher molar ratios, the elongational viscosity decreases, while high drag reduction effectiveness is kept. The micelle structure could be changed at higher counter-ion molar ratio, but this new structure may also be effective for drag reduction.

Control of the viscous behavior of highly concentrated mullite suspensions for robocasting

Aqueous-mullite suspensions stabilized with an organic polyelectrolyte dispersant were characterized in terms of settling and rheological behaviors at solids concentrations as high as 60 vol.% (within 3 vol.% of the maximum consolidated density). The suspensions were cast into parts by a solid freeform fabrication technique termed robocasting and qualitatively characterized in terms of build behavior. Sedimentation and viscometry data were interpreted in view of knowledge of the interparticle forces. Through control of suspension pH and counter-ion addition, pseudoplastic mullite suspensions were created for use in the robocasting process. The suspensions were robocast at 52 vol.% solids and dried to yield a consolidated density of 55 vol.%. After firing to 1650 °C, robocast parts were greater than 96% dense.

Structural Flexibility of Multifunctional HABP1 May Be Important for Regulating Its Binding to Different Ligands

Hyaluronan-binding protein 1 (HABP1)/p32/gC1qR was characterized as a highly acidic and oligomeric protein, which binds to different ligands like hyaluronan, C1q, and mannosylated albumin. It exists as trimer in high ionic and reducing conditions as shown by crystal structure. In the present study, we have examined the structural changes of HABP1 under a wide range of ionic environments. HABP1 exhibits structural plasticity, which is influenced by the ionic environment under in vitro conditions near physiological pH. At low ionic strength HABP1 exists in a highly expanded and loosely held trimeric structure, similar to that of the molten globule-like state, whereas the presence of salt stabilizes the trimeric structure in a more compact fashion. It is likely that the combination of the high net charge asymmetrically distributed along the faces of the molecule and the relatively low intrinsic hydrophobicity of HABP1 result in its expanded structure at neutral pH. Thus, the addition of counter ions in the molecular environment minimizes the intramolecular electrostatic repulsion in HABP1 leading to its stable and compact conformations, which reflect in its differential binding toward different ligands. Whereas the binding of HABP1 toward HA is enhanced on increasing the ionic strength, no significant effect was observed with the two other ligands, C1q and mannosylated albumin. Thus, although HA interacts only with compact HABP1, C1q and mannosylated albumin can bind to loosely held oligomeric HABP1 as well. In other words, structural changes in HABP1 mediated by changes in the ionic environment are responsible for recognizing different ligands.

A Coat of Many Layers

DRUG DELIVERY Several particle-coating methods have been developed for time-released drug delivery, but few have been tested under in vivo conditions. Recently, two groups have subjected their delivery systems to some of these conditions. Qui et al. encapsulated micrometer-sized ibuprofen crystals through repeated adsorption of oppositely charged biocompatible polysaccharides. The polymer coating delayed ibuprofen release at pH 1.4 (representative of gastric fluid) but did not significantly affect release at pH 7.4 (similar to intestinal pH). Marinakos et al. used gold colloidal particles to support small molecules or enzymes. Conductive polymer coatings were formed in situ without altering the biomolecules, and then the colloidal core was dissolved away. The addition of counterions was shown to influence the diffusion rate of the encapsulated small molecules, and coated enzymes showed greater resistance to harsh solvents. When generated in this fashion, poly(pyrrole) capsules 25 to 100 nm in diameter were absorbed by mouse fibroblasts without compromising cell viability. — MSL Langmuir , 10.1021/la010201w; J. Phys. Chem. B . 10.1021/jp010820d.

Chitosan Microspheres Prepared by Emulsification and Ionotropic Gelation

An attempt was made to prepare chitosan microspheres by an emulsion-phase separation technique but without the usual use of glutaraldehyde as a cross-linking agent. Instead, ionotropic gelation was employed in a w/o emulsion. The effect of formulation factors was examined. The results showed that microspheres so formed were spherical, free-flowing, and had smooth surfaces. The rate of addition of counterions was important. Gelation of chitosan droplets should take place before the destabilizing effect of the counterions occurred. This effect is associated with the increase in aqueous phase volume when the counterion solution is incorporated.

An electrostatic approach to negatively charged substrate reactions with hydroxide ion in cationic CTAB micelles

An electrostatic treatment is presented to explain the experimental kinetic data we obtained for the basic hydrolysis of the negatively charged substrates acetylsalicylic acid and 3-acetoxy-2-naphthoic acid. This treatment, based on the non-linearized Poisson–Boltzmann equation, considers specific interactions between the counterions and the micellar surface and explains the displacement of these substrates from the micellar to the aqueous phase through bromide counterion addition. Keywords: electrostatic approach, cationic CTAB micelles.

Molecular Mechanics and Dynamics of an Abasic Frameshift in DNA and Comparison to NMR Data

In a previous publication (Ph. Cuniasse, L.C. Sowers, R. Eritja, B. Kaplan, M.F. Goodman, J.A.H. Cognet, M. Le Bret, W. Guschlbauer and G.V. Fazakerley, Biochemistry 28, 2018 (1989), we determined by two dimensional NMR studies and molecular mechanics calculations the three-dimensional structure of a non-selfcomplementary oligonucleotide: [sequence; see text] where dr, at the center of the first strand, is a model abasic site. In order to explain all the results arising from NMR measurements, we found that an equilibrium between two conformations was necessary. These conformations differ mainly by the sugar pucker of G5 which is C2' endo or C3' endo. The latter is stabilized by addition of counterions between phosphate residues P3 and P4. In this paper, we have constructed systematically, all possible structures as a function of torsion angles delta of dr4 and of G5 by molecular mechanics in the presence or absence of counterions. Since these conformations were not forced with NMR distance measurements, this method allows detailed comparisons between all possible conformations and NMR data. Maps of contour lines of the potential energy, of fits to NMR distance measurements, and of helical twist as a function of torsion angles delta of dr4 and of G5 unravel the difficulties associated with the study of the G5 sugar pucker conformation equilibrium. Sugar puckers and proton distances are very sensitive criteria to monitor molecular dynamics. Relying on these experimental criteria, we have tested many molecular dynamics preparation phases and we propose a new warm-up and equilibration procedure for molecular dynamics. Thus we show with a 290 ps molecular dynamic run that G5 is in conformational equilibrium and that all NMR data are well reproduced.

Determination of some pyridinium aldoxime compounds by means of ion-pair reversed-phase high-performance liquid chromatography: Application in biological material

Two reversed-phase high-performance liquid chromatographic systems are presented for the separation and assay of the pyridinium aldoximes benzyl-P2A, HI-6 and obidoxime in aqueous solutions and biological samples. The systems involve a 5-μm C 18 silica gel stationary phase. The eluent consists of methanol, acetic acid buffer (pH 4.80), a counter ion (perchlorate or n-octanesulphonate) and a surfactant. The compounds were detected spectrophotometrically at 304 nm. In the concentration range used, linear plots of concentration versus extinction were obtained, both in blood and in water. Detection limits, even in blood, are satisfactory (0.5–1 μ M). Evidence is presented that, at least for HI-6, the addition of counter ions to the system does not lead to the formation of ion pairs to be retained by partition, but rather to a mechanism based on adsorption chromatography.

Protamines. VII. Circular Dichroism Study of Salmine A I

Salmine A I, one of the components of the protamine from salmon, has been purified and characterized. The conformational preferences of salmine A I have been examined as a function of pH, added salts, presence of helix-supporting solvents, and temperature, using circular dichroism. It has been found that this small basic protein adopts predominantly an unordered conformation in aqueous solution. Addition of counter-ions, in particular perchlorate, and 2-chloroethanol induces to various extents the onset of the right-handed α-helical conformation. The results are discussed in comparison with those previously reported on the three main components of clupeine, the protamine from herring, and with the published conformational predictions by various statistical methods

Studies on cationic micelle inhibited transimination reactions of barbituryl-azine-indandione and azine-bis-indandione with semicarbazide

The acid cataylsed transimination reactions of barbituryl-azine-indandione (BAI)and azine-bisindandione (ABI) with semicarbazide are inhibited by n-alkyl trimethylammonium bromides. At a given detergent concentration, the efficiency of inhibition increases with increasing alkyl chain-length of the detergent. Addition of counterions and alcohols increased the cetyltrimethylammonium bromide (CTAB) inhibited rate. Extent of micellar inhibition is reduced by the addition of counterions in the order NO 3 -, > Br - > Cl - > SO 4 = and by the addition of alcohols in the order n-butanol > n-propanol > ethanol > methanol. Activation parameters for the reactions in the presence of CTAB have been evaluated and compared with those obtained in the absence of detergent.

Protamines: II. Circular dichroism study of the three main components of clupeine

The three main components YI, YII, and Z of clupeine, a protamine from herring, have been purified and characterized. The conformational preferences of clupeines have been examined as a function of pH, temperature, added salts, and presence of structure-disrupting agents and helix-supporting solvents using circular dichroism. It was found that these small basic proteins assume predominantly an unordered conformation in aqueous solution. Addition of counter ions, in particular perchlorate, and 2-chloroethanol induces in various amounts the onset of the right-handed α-helical conformation. Urea favors the statistical coil state. It was also demonstrated that in the 0.1–4.0 · 10 −1 M range, in contrast to clupeines YI and Z, the circular dichroic properties of the YII component do not seem to be sensitive to the addition of mono- and diphosphate.