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Journal of Colloid And Interface Science (v.308, #2)

Editorial Board (pp. ofc).

Adsorption of poly(ethylene oxide)– block–polylactide copolymers on polylactide as studied by ATR-FTIR spectroscopy by Štěpán Popelka; Lud'ka Machová; František Rypáček (pp. 291-299).
In this study, the adsorption of amphiphilic poly(ethylene oxide)– block–polylactide (mPEO–PLA) copolymers from a selective solvent onto a polylactide surface was studied as a method of polylactide surface modification and its effect on nonspecific protein adsorption was evaluated. A series of well defined mPEO–PLA copolymers was prepared to investigate the effect of copolymer composition on the resulting PEO chain density and on the surface resistance to protein adsorption. The copolymers contained PEO blocks with molecular weights ranging between 5600 and 23,800 and with 16–47 wt% of PLA. The adsorption of both the copolymers and bovine serum albumin was quantified by attenuated total reflection FTIR spectroscopy (ATR-FTIR). In addition to the adsorbed copolymer amount, its actual composition was determined. The PEO chain density on the surface was found to decrease with the molecular weight of the PEO block and to increase with the molecular weight of the PLA block. The adsorbed copolymers displayed the ability to reduce protein adsorption. The maximum reduction within the tested series (by 80%) was achieved with the copolymer containing PEO of MW 5600 and a PLA block of the same MW.Layers of amphiphilic PEO– b–PLA copolymers were deposited on polylactide surface by adsorption from aqueous solutions. The effect of molecular weight of copolymer blocks on the layer resistance to nonspecific adsorption of bovine serum albumin was investigated.

Keywords: ATR-FTIR spectroscopy; Copolymer adsorption; Poly(ethylene oxide); Poly(ethylene oxide)–; block; –polylactide; Polylactide; PEO surface density; Protein adsorption

Effect of chain length and charge density on the construction of polyelectrolyte multilayers on colloidal particles by Viktoria Milkova; Tsetska Radeva (pp. 300-308).
Two combinations of sodium poly(4-styrene sulfonate) (PSS) and poly(allylamine hydrochloride) (PAH) of different chain length and charge density are employed to construct multilayer films. The polyelectrolytes are assembled layer-by-layer on colloidal particles in the absence of salt. We have investigated the formation and electrical characteristics of the films by using electric light scattering technique. The results show that the film thickness is independent of the chain length when fully charged PAH (at pH 4.6) is combined with fully charged PSS. When the films are prepared with less charged PAH (at pH 6.7) and fully charged PSS, lower thickness is found for the film with shorter polymer chains. In all cases, the thickness increment realized on addition of the polymer with lower molar concentration is partially lost on exposure to the solution with higher concentration of the oppositely charged partner. When the film growth is regular (at equal molar concentrations of the fully charged polyelectrolytes), the ratio of PSS to PAH charge, estimated from the electro-optical effect values, exceeds 1. The electro-optical effect is also higher for the films ending with PSS when fully charged PSS is combined with less charged PAH (at pH 6.7). This reveals the key role of the charge in the last-adsorbed layer for the electro-optical behavior of the whole film.The influence of charge density and chain length on formation of multilayer films from sodium poly(4-styrene sulfonate) and poly(allylamine hydrochloride) is investigated by electro-optics.

Keywords: Polyelectrolyte multilayers; Multilayers buildup; Multilayers on colloidal particles; Electrical properties of multilayers; Electro-optics of multilayers

Polypeptide multilayer films on colloidal particles: An in situ electro-optical study by Tsetska Radeva; Kamelia Kamburova (pp. 309-317).
The buildup of poly(l-glutamic acid) (PGA) and poly(l-lysine) (PLL) multilayers on β-FeOOH colloidal particles was investigated by means of electro-optics and electrophoresis. The films were built at different (acidic) pH in the absence of salt. We found that the thickness of the film grows linearly when the fully charged PLL (at pH 5.5) is combined with almost fully charged PGA (at pH 6.5), with a thickness of about 2 nm per single layer. When the fully charged PLL is combined with weakly charged PGA (at pH 4.5), the film thickness increases exponentially with the number of deposited layers. The thickness of the exponentially growing film increases to 300 nm after deposition of 16 layers. The exponential film growth is attributed to the ability of the PLL to diffuse “in” and “out” of the film bulk at each deposition step. The variation in the electrical polarizability of the film-coated particles was also monitored as a function of the number of adsorbed layers. The result reveals that the PLL chains, which can diffuse into the film bulk, have no measurable contribution to the electro-optical effect of the films terminated with PLL. It is only due to the polarization of counterions of the PLL adsorbed on the film surface.The formation of polypeptide film based on the alternate deposition of poly(l-glutamic acid) and poly(l-lysine) on β-FeOOH particles is investigated as a function of pH by electro-optics.

Keywords: Polypeptide multilayers; Electro-optics of multilayers; Multilayers on colloidal particles; Mechanism of multilayer growth; Electrical polarizability of multilayers

Real dispersion of isolated fumed silica nanoparticles in highly filled PMMA prepared by high energy ball milling by P.D. Castrillo; D. Olmos; D.R. Amador; J. González-Benito (pp. 318-324).
Fumed silica nanoparticles with 14 nm of diameter were blended with poly(methylmethacrylate), PMMA, by means of a high energy ball milling process. AFM analysis revealed how this process of blending allows obtaining a very homogeneous dispersion of the nanoparticles within the PMMA. Furthermore, it was observed that the properties of the composite are highly dependent on the active milling time: (i) SEM inspection showed that the particle size of the silica–PMMA nanocomposite decreases and (ii) DSC analysis demonstrated that theTg also decreases due to a reduction in the molecular weight of the PMMA caused by chain scission during the high energy blending process. TwoTg's were obtained in the case of the nanocomposite when milling times were higher than 6 h, one of them being even higher than that of the PMMA without being subjected to the HEBM process. This result was assigned to surface-induced molecular weight segregation near the nanoparticles surface. It has been demonstrated the possibility of preparing transparent nanocomposites with excellent moldability.High (left) and phase contrast (right) AFM images of fumed silica nanoparticles/PMMA composite showing real dispersion of isolated nanoparticles.

Keywords: Nanoparticle dispersion; Nanocomposites; Fumed silica; PMMA; Ball milling

DNA–DNA interaction on dendron-functionalized sol–gel silica films followed with surface plasmon fluorescence spectroscopy by Sung Hong Kwon; Bong Jin Hong; Hye Young Park; Wolfgang Knoll; Joon Won Park (pp. 325-331).
Since we observed that dendron-assembled surface provided high single nucleotide polymorphism discrimination efficiency for DNA microarrays, and that the binding yield for streptavidin increased when biotin was immobilized on top of it, the nanoscale-controlled surface is examined for surface plasmon field-enhanced fluorescence spectroscopy (or SPFS). Firstly, a silica film was coated onto a gold substrate using the sol–gel technique, followed by the covalent immobilization of a layer of second-generation dendrons with a DNA catcher strand at their apex. The thickness of the inorganic interlayer (d=33 nm) was effectively suppressing fluorescence quenching. Thus, the kinetics and affinity characteristics of DNA hybridization could be investigated very sensitively by SPFS. The kinetic rate constants found for DNA hybridization on the dendron-modified surface were larger than those reported for a streptavidin-modified surface by one order of magnitude, except for dissociation rate constant for a single mismatched case. In addition, we observed that the DNA on the cone-shaped linker maintained its capability to capture DNA target strands even after extended storage at ambient conditions.We investigated the kinetics and affinity characteristics of DNA hybridization by surface plasmon fluorescence spectroscopy on dendron-functionalized sol–gel silica films for the generation of nanoscale-controlled surface architectures providing regular lateral spacing between the immobilized biomolecules.

Keywords: Dendron; Self-assembly; DNA hybridization; Kinetics; SPFS; Sol–gel

Controllable preparation of magnetic polymer microspheres with different morphologies by miniemulsion polymerization by Ying Sun; Biao Wang; H.P. Huaping Wang; J.M. Jianming Jiang (pp. 332-336).
Magnetic poly(styrene-co-acrylic acid-co-acrylamide) microspheres were prepared by water-in-oil-in-water (W/O/W) miniemulsion polymerization of monomers in the presence of Fe3O4 nanoparticles. The copolymerizable monomers of acrylic acid and acrylamide were used not only to modify the surfaces of the microspheres with functional groups, but also to act as viscosity regulators to control the morphology and size of these microspheres. It was experimentally observed that the surfaces of these microspheres were functionalized withNH2 groups produced by copolymerization, the morphologies (sphere, ringlike, and one-hole) of the microspheres were controlled by the concentration of copolymerizable monomers, and all samples prepared were superparamagnetic. The possible mechanism of formation of these magnetic microspheres is also discussed.Magnetic poly(styrene-co-acrylic acid-co-acrylamide) microspheres with ringlike or one-hole structures were prepared by miniemulsion polymerization of monomers in the presence of Fe3O4 nanoparticles. The morphology and size of these microspheres can be controlled by the viscosity of the water phase.

Keywords: W/O/W miniemulsion; Magnetic polymer microspheres; Preparation; Morphology; Particle size; Magnetic properties

Formation and stability of a suspended biomimetic lipid bilayer on silicon submicrometer-sized pores by A. Simon; A. Girard-Egrot; F. Sauter; C. Pudda; N. Picollet D'Hahan; L. Blum; F. Chatelain; A. Fuchs (pp. 337-343).
We report the fabrication of a thin silicon membrane with an array of micrometer and submicrometer pores that acts as a scaffold for suspending a lipid bilayer. We successfully deposited a lipid bilayer by the Langmuir–Blodgett method on a synthetic silicon membrane bearing arrays of pores with sizes of 1000, 650, and 300 nm. Topographic images obtained by AFM showed a suspended lipid film spanning the pores, whatever the pore size. Higher stability of bilayers supported on smaller pores was shown by AFM characterization. These results represent an important first step to creating a biomimetic environment to study cell membrane dynamics and/or in developing a biosensor.Part of AFM images of (left) silicon surface bearing pore and (right) lipid bilayer containing free-standing area, spanning pore, obtained by Langmuir–Blodgett method.

Keywords: Lipid bilayer; Pore-spanning bilayer; Membrane-mimetic; Langmuir–Blodgett film; Atomic force microscopy (AFM)

A novel method of measuring electrophoretic mobility of gas bubbles by Aref Seyyed Najafi; Jaroslaw Drelich; Anthony Yeung; Zhenghe Xu; Jacob Masliyah (pp. 344-350).
Accurate measurement of electrophoretic mobility for gas bubbles is a challenging task as it requires the creation of a desired number of very small air bubbles to ensure negligible rise velocities during the course of the measurement. Here, we report a simple and reliable method for generating stable dispersions of “nano-bubbles.” Preparation of such dispersions relies on the nucleation of nano-bubbles in solutions supersaturated with gas. Electrophoretic mobility of these nano-bubbles is determined by the ZetaPALS technique (Brookhaven Instruments) using Uzgiris electrodes coated with palladium. The Smoluchowski limit is assumed in the calculation of zeta potentials. In regard to reproducibility and reliability, this novel method shows a clear advantage over other existing techniques of zeta potential measurement for bubbles.A simple and a reliable method of bubble electrophoretic mobility measurement is reported. This method is based on generating of stable dispersions of nano-bubbles.

Keywords: Bubbles; Electrophoretic mobility; Oil sand; Process water; Zeta potential

Synthesis and self-assembly of monodisperse silver-nanocrystal-doped silica particles by Dong Chen; L.L. Linlin Li; J.S. Jianshu Liu; Shuo Qi; F.Q. Fangqiong Tang; X.L. Xiangling Ren; Wei Wu; Jun Ren; Lin Zhang (pp. 351-355).
A simple method based on the Stöber reaction was developed to prepare silver-nanocrystal-doped silica composite particles. The silane coupling agent N-[3-(trimethoxysilyl)dropyl]ethylene diamine (TSD) incorporated Ag+ into a siloxane framework and a further chemical reducer reduced Ag+ to silver nanoparticles. TEM images showed that, in the presence of TSD, silver nanocrystals (fcc) of 2–8 nm were homogeneously doped in the silica particles, which showed a typical surface plasmon resonance (SPR) peak. The as-prepared Ag/SiO2 composite particles can be self-assembled into long-range ordered lattices (or photonic crystals) over large areas.

Keywords: Silane coupling agent; Surface plasmon resonance; Composite particles; Photonic crystals

Structural control of peptide-coated gold nanoparticle assemblies by the conformational transition of surface peptides by Masahiro Higuchi; Kae Ushiba; Masami Kawaguchi (pp. 356-363).
Gold nanoparticles having peptide chains on the surfaces have been prepared yb ring-opening polymerization of γ-methyll-glutamate N-carboxyanhydride with fixed amino groups on the nanoparticle surface as an initiator. The number of peptide chains on the surface was adjusted to ca. 2 molecules per gold nanoparticle by controlling the number of fixed amino groups on the surface. The peptide chains on the surface were partially saponified to obtain poly( γ-methyll-glutamate- co-l-glutamic acid) with 28 mol% of glutamic acid residues. The number-average molecular weight of the peptide was 73,000. We described structural control of the peptide-coated gold nanoparticle assembly by conformational transition of the surface peptides. In deionized water, the peptide chains on the nanoparticle took a random coil conformation, and the individual nanoparticles existed in dispersed globular species. On the other hand, the peptide chains on the nanoparticle took an α-helical conformation in trifluoroethanol. Under this condition, the α-helical peptide chains on distinct gold nanoparticles connected the nanoparticles to form a fibril assembly owing to the dipole–dipole interaction between the surface peptide chains. The morphology of the peptide-coated gold nanoparticle assembly could be controlled by the conformational transition of surface peptides, which was attended by solution composition changes.The morphology of the peptide-coated gold nanoparticle assembly could be controlled by the conformational transition of surface peptides, which was attended by solution composition changes.

Keywords: Peptide-coated gold nanoparticles; Conformational transition; Self-assembly; Structural control

The rennet coagulation mechanism of skim milk as observed by transmission diffusing wave spectroscopy by S. Sandra; Marcela Alexander; Douglas G. Dalgleish (pp. 364-373).
The technique of forward-scattering diffusing wave spectroscopy has been used to study the rennet-induced gelation of skim milk. The results allow the comparison of a colloidal suspension at a realistic concentration (Φ∼10%) compared with well-established measurements made on highly-diluted milk samples. It is shown that the partially renneted casein micelles do not begin to approach one another until the extent of breakdown of κ-casein has reached about 70%; above this point, they interact increasingly strongly with the extent of proteolysis. This interaction initially restricts the diffusive motion of the particles rather than causing true aggregation. Only after more extensive removal of the protective κ-casein does true aggregation occur, with the appearance of a space-filling gel (defined by rheology as having a value oftanδ<1). The results show in greater detail than hitherto the progress of interactions between the particles in a system where the steric stabilization is progressively destroyed, and suggest that the renneting of milk at its normal concentration cannot be described simply by reactions between freely-diffusing particles.Changes in light scattering (radius,l∗, mean square displacement) and rheological parameters during the enzyme-induced destabilization of casein micelles.

Keywords: Casein micelles; Diffusing wave spectroscopy; Renneting; Milk coagulation

Mesoporous silica spheres from colloids by Jenny Ho; Wei Zhu; Huanting Wang; Gareth M. Forde (pp. 374-380).
A novel method has been developed to synthesize mesoporous silica spheres using commercial silica colloids (SNOWTEX) as precursors and electrolytes (ammonium nitrate and sodium chloride) as destabilizers. Crosslinked polyacrylamide hydrogel was used as a temporary barrier to obtain dispersible spherical mesoporous silica particles. The influences of synthesis conditions including solution composition and calcination temperature on the formation of the mesoporous silica particles were systematically investigated. The structure and morphology of the mesoporous silica particles were characterized via scanning electron microscopy (SEM) and N2 sorption technique. Mesoporous silica particles with particle diameters ranging from 0.5 to 1.6 μm were produced whilst the BET surface area was in the range of 31–123 m2 g−1. Their pore size could be adjusted from 14.1 to 28.8 nm by increasing the starting particle diameter from 20–30 nm up to 70–100 nm. A simple and cost effective method is reported that should open up new opportunities for the synthesis of scalable host materials with controllable structures.A novel method has been developed to synthesize dispersible mesoporous silica spheres using commercial silica colloids (SNOWTEX) as precursors and electrolytes (ammonium nitrate and sodium chloride) as destabilizers, and crosslinked polyacrylamide hydrogel as a temporary barrier in the process.

Keywords: Mesoporous silica; Colloidal silica; Electrolyte; Sphere; Polyacrylamide hydrogel

A facile synthesis of aliphatic thiol surfactant with tunable length as a stabilizer of gold nanoparticles in organic solvents by Xiaoli Zhou; Jouliana M. El Khoury; Liangti Qu; Liming Dai; Quan Li (pp. 381-384).
Three new aliphatic thiol surfactants were synthesized by reacting alkyl bromide with hexamethyldisilathiane under a mild condition. This approach provides an easy access for the direct synthesis of various different length thiol surfactants which play a crucial role in tuning the properties of gold nanoparticles. Gold nanoparticles encapsulated with one of our synthetic thiols were prepared and well characterized by H NMR, UV–vis, FT-IR, and TEM. The hybrid nanoparticles are very stable in both organic solvents and the solid state.Gold nanoparticles encapsulated with the thiol surfactants with tunable length are stable in both organic solvents and the solid state.

Keywords: Synthesis; Thiol; Surfactant; Gold nanoparticles

Preparation and characterization of polyaniline/manganese dioxide composites and their catalytic activity by Ali H. Gemeay; Rehab G. El-Sharkawy; Ikhlas A. Mansour; Ahmed B. Zaki (pp. 385-394).
This paper is devoted to the preparation of polyaniline/MnO2 (PANI/MnO2) composites via chemical oxidation of aniline in H2SO4 medium using β-MnO2 as an oxidant. The parameters affecting the polymerization reaction are considered. These parameters are [aniline], amount of β-MnO2, stirring time, and polymerization temperature. SEM, FT-IR, XRD, and TGA techniques are used to characterize the resulting composites. XRD measurements reveal the distortion of the crystal structure of β-MnO2 after the polymerization reaction. Thus, the XRD pattern of PANI is predominating. The crystalline composites are obtained using higher molar ratio of [Ox]/[ANI] and at higher temperature. Increasing the amount of β-MnO2 led to an increase in the acidic character of the obtained composites due to adsorption of excess H+ on the oxide surface. The thermal stability of the composites decreased with increasing both [aniline] and stirring time, while it increased with increasing amount of β-MnO2. The applications of the composites in the oxidative degradation of Direct Red 81, Acid Blue 92, and Indigo Carmine dyes exhibited good catalytic activity in the presence of H2O2 as an oxidant. The reactions followed first-order kinetics and the rate constants were determined. The degradation reaction involved the catalytic action of the PANI counterpart of the composite toward H2O2 decomposition, which can lead to the generation of HO radicals as a highly efficient oxidant attacking the target dyes. The detailed kinetic studies and the mechanism of these catalytic reactions are under consideration in our group.Well-characterized PANI/MnO2 composites exhibited a good catalytic activity for the oxidative degradation of the target dyes using H2O2 as an oxidant.

Keywords: Polyaniline; β; -MnO; 2; Composite; Catalytic activity; Hydrogen peroxide; Wastewater; Textile dyes

Surface acid–base properties and hydration/dehydration mechanisms of aluminum (hydr)oxides by Xiaofang Yang; Zhongxi Sun; Dongsheng Wang; Willis Forsling (pp. 395-404).
In this paper, surface physiochemical properties of three typical aluminas, γ-Al(OH)3, γ-Al2O3, and α-Al2O3, were investigated by means of XRD, SEM, TEM, BET surface area, TG/DTA, and potentiometric titration techniques. Based on the titration data, surface protonation and deprotonation constants were determined using the constant capacitance model (CCM). The emphasis of this research was laid on the comparison of the crystal structure, surface hydration/dehydration and acid–base properties of these three typical alumina minerals. The calculation results revealed that the surface acidity of the aluminas is in the order ofα-Al2O3>γ-Al(OH)3>γ-Al2O3 after being hydrated for 1 h. The correlation between the hydration/dehydration mechanisms of alumina and its acid/base properties is discussed.The surface hydration process of α-Al2O3 may be regarded as a reversible process of gibbsite dehydration. At the last stage of the hydration the gibbsite surface may form.

Keywords: Acid–base properties; Aluminum (hydr)oxides; Surface hydration; Crystal structure

Surface characterization of hydroxyapatite: Potentiometric titrations coupled with solubility measurements by Kyriaki Skartsila; Nikos Spanos (pp. 405-412).
The acid–base properties of synthetically prepared and well-characterized hydroxyapatite (HAP) in contact with KNO3 solutions were investigated at 25 °C, through potentiometric titrations, ζ-potential measurements, and surface complex modeling. Aliquots of suspension were withdrawn every 0.5 pH unit during the titration procedure and analyzed for calcium and phosphate. It was found that, even for rapid titration experiments, a remarkable amount of H+ ions (H+dissol.) is consumed in the bulk solution in reacting with species coming from the dissolution of HAP. These H+ ions must be taken into account in the H+ mass balance, in order for true value for the point of zero charge (pzc=6.5±0.2) and consequently true value for the surface charge (σ0) to be obtained. Besides the conventional potentiometric titration technique, it was found that pzc may be determined much more easily as the intersection point of the suspension titration curve and the blank one modified to include the amount of H+dissol. obtained at one ionic strength. Finally, a surface complexation model was proposed for the development of surface charge. Experimental data were satisfactorily fitted by using the value of 4.2 F m−2 for the capacitance.

Keywords: Potentiometric titrations; Solubility; Hydroxyapatite; pzc; Surface complexation model

A study on electrophoretic deposition of Ni nanoparticles on pitted Ni alloy 600 with surface fractality by Gyoung-Ja Lee; Su-Il Pyun; Chang-Kyu Rhee (pp. 413-420).
In the present work, the electrophoretic deposition of Ni nanoparticles used for self-repairing of pits in organic suspension was investigated on pitted fractal Ni alloy 600 with respect to surface fractality of the pits. For this purpose, Ni nanoparticles prepared by levitation–gas condensation were dispersed into an ethanol solution with the addition of a dispersant. Four kinds of pitted fractal specimens with different surface fractal dimensionsdF,surf were prepared by applying various anodic potentials above pitting potential to alloy 600 in aqueous 0.1 M NaCl solution. From the scanning electron microscopy (SEM) images, it was observed that the pits repaired under applied electric field E of 100 V cm−1 comprised more agglomerates of Ni nanoparticles than those repaired under E of 20 V cm−1. This suggests that the higher the value of E is, the more agglomerates of Ni nanoparticles are deposited on the specimen due to more depletion of OH in suspension near the specimen surface. Moreover, the specimen with higherdF,surf gave a higher value of electrophoretic currentIp than one with lowerdF,surf due to the increased electrochemical active areaAea of the specimen. From the above, it is concluded that the surface irregularities of the pit enhance the deposition of Ni nanoparticles on pitted fractal specimen during electrophoretic deposition.The higher the value of applied electric field E is, the more agglomerates of Ni nanoparticles are deposited on the specimen due to more depletion of OH in suspension near the specimen surface.

Keywords: Pitting corrosion; Electrophoretic deposition; Ni nanoparticle; Ionic depletion; Surface fractal dimension; Perimeter–area method

Heterogeneous nucleation and growth of calcium carbonate on calcite and quartz by Maria G. Lioliou; Christakis A. Paraskeva; Petros G. Koutsoukos; Alkiviades C. Payatakes (pp. 421-428).
The precipitation of calcium carbonate as a binding salt for the consolidation of loose sand formations is a promising approach. The heterogeneous nucleation and growth of calcite were investigated in supersaturated solutions. The ionic activities in the solutions tested were selected so that they included both supersaturations in which crystal growth took place only following the introduction of seed particles and supersaturations in which precipitation occurred spontaneously past the lapse of induction times. In the latter case the supersaturation conditions were sufficiently low to allow the measurement of induction times preceding the onset of precipitation. The stability domain of the calcium carbonate system was established at pH 8.50, 25 °C, measuring the induction times in the range between 30 min and 2 h. The rates of precipitation following the destabilization of the solutions were measured from the pH and/or concentration–time profiles. The induction times were inversely proportional and rates proportional to the solution supersaturation as expected. The high-order dependence of the rates of precipitation on the solution supersaturation suggested a polynuclear growth mechanism. Fitting of the induction time–supersaturation data according to this model yielded a value of 64 mJ/m2 for the surface energy of the calcite nucleus. In the concentration domain corresponding to stable supersaturated solutions, seeded growth experiments at constant supersaturation showed a second-order dependence on the rates of crystal growth of calcite seed crystals. Inoculation of the stable supersaturated solutions with quartz seed crystals failed to induce nucleation. Raising supersaturation to reach the unstable domain showed interesting features: calcite seed crystals yielded crystal growth kinetics compatible with the polynuclear growth model, without any induction time. The presence of quartz seed crystals reduced the induction times and resulted in nucleation in the bulk solution. The kinetic data in the latter case were consistent with the polynuclear growth model and the surface energy for the newly forming embryo was calculated equal to 31.1 mJ/m2, because of the dominantly heterogeneous nature of the process.The precipitation of calcium carbonate in supersaturated solutions was investigated both in the labile (L) domain and in the stable domain through seeded growth experiments using calcite and quartz seed crystals.

Keywords: Calcium carbonate; Spontaneous precipitation; Kinetics of precipitation; Seeded growth; Calcite; Quartz

Transformations of γ-alumina in aqueous suspensions by Xavier Carrier; Eric Marceau; Jean-François Lambert; Michel Che (pp. 429-437).
Hydration of γ-Al2O3 is often reported to occur via the superficial transformation of the alumina surface into aluminum hydroxide-like layers. However, very little evidence has been given so far to support this hypothesis. It is demonstrated here by X-ray diffraction, TEM, electron diffraction, and solubility studies that a second process of hydration takes place that involves the dissolution of alumina and subsequent precipitation of well-shaped Al(OH)3 particles from supersaturated alumina aqueous solution. This process can be observed on a macroscopic scale (XRD, TEM) for anypH⩾5, provided that the contact time between alumina and water exceeds 10 h. The least thermodynamically stable phase of aluminum hydroxide, bayerite, becomes favored compared with gibbsite when the pH of the solution is increased. It is assumed that the rate of formation of bayerite germs is greater than that of gibbsite due to variations in aluminum speciation in solution as a function of pH.It is demonstrated here that the hydration of γ-Al2O3 involves the dissolution of alumina and the subsequent precipitation of well-shaped Al(OH)3 particles from supersaturated alumina aqueous solution.

Keywords: Alumina; Aluminum hydroxide; Dissolution; Hydration; Chemical weathering; Oxide support

Identification of selective ion-exchange resin for fluoride sorption by S. Meenakshi; Natrayasamy Viswanathan (pp. 438-450).
The defluoridation capacity (DC) of a chelating resin, namely Indion FR 10 (IND), and Ceralite IRA 400 (CER), an anion-exchange resin, were compared under various equilibrating conditions for the identification of selective sorbent. The results showed that chelating resin is more selective than an anion-exchange resin for fluoride removal. The fluoride sorption was reasonably explained using Freundlich and Langmuir isotherms. The surface morphology of resins before and after fluoride sorption was observed using scanning electron microscopy (SEM). Fourier transform infrared spectroscopy (FTIR) was used for the determination of functional groups responsible for fluoride sorption. Various thermodynamic parameters such asΔG0,ΔH0,ΔS0, andEa have been calculated to understand the nature of sorption. The sorption kinetic mechanism was studied with reaction-based and diffusion-based models. The sorption process was found to be controlled by pseudo-second-order and particle diffusion models. The performance of the resins studied has been tested with field samples collected from a fluoride-endemic area. The adsorption mechanism is more selective for fluoride removal than the ion-exchange process even from the dilute solutions of fluoride ion, as the ion-exchange mechanism depends on the concentrations of ions, which are normally present in water with excess of fluoride.Display OmittedDisplay Omitted

Keywords: Fluoride; Sorption; Indion FR 10; Ceralite IRA 400; Freundlich; Langmuir; Pseudo-first order; Pseudo-second order; Particle diffusion; Pore diffusion

Advective flow in spherical floc by Z. Yang; X.F. Peng; D.J. Lee; S. Ay (pp. 451-459).
Numerous structural models of flocs, such as homogeneous model or radially-varying model, were proposed in literature for predicting the extent of advective flow on the intrafloc transport processes. This work probed the three-dimensional structure of original and chemically flocculated wastewater flocs using the fluorescence in situ hybridization (FISH) and the confocal laser scanning microscope (CLSM) techniques, from which the spherical mesh model on real floc structure was constructed. Simulation results revealed that if an average characteristic of sludge floc, such as porosity or drag force correction factor of sludge floc is of concern, both homogeneous or radially-varying models may be able to apply, particularly for those flocs that were closely compacted. However, the detailed flow patterns inside real floc are much more tortuous than those of the homogeneous or radially-varying models. If local hydrodynamic environment within the floc is of interest, then only the complicated structural model with real floc could be applicable.The advective flow pattern generated from structural model from real wastewater floc that is applied to justify the use of literature models.

Keywords: Floc model; Advective flow; FISH; CLSM

3-D ordered macroporous cuprous oxide: Fabrication, optical, and photoelectrochemical properties by Xun Li; Feifei Tao; Yuan Jiang; Zheng Xu (pp. 460-465).
Cuprous oxide 3-D ordered macroporous material was constructed by electrochemical deposition using a polystyrene colloidal crystal as template. The highly ordered macroporous structure with a hexagonal array can be extended over hundreds of square micrometers. The photonic stop bands of both the PS colloidal crystal and Cu2O 3DOM were found. Due to the highly ordered porous structure, the optical absorption and the charge carrier transportation are better in Cu2O 3DOM than in bulk Cu2O, which makes the reduction of oxygen faster on Cu2O 3DOM than on bulk Cu2O under visible light illumination. The higher photocurrent efficiency under visible light illumination makes the 3DOM Cu2O more suitable for solar applications.The optical absorption and the charge carrier transportation are better in Cu2O 3DOM than in bulk Cu2O, due to the highly ordered porous structure.

Keywords: Cuprous oxide; Macroporous; Photonic stop band; Photoelectrochemistry; Visible light; Reduction of oxygen

Adsorption and aggregation properties of amino acid-based N-alkyl cysteine monomeric andN,N′-dialkyl cystine gemini surfactants by Tomokazu Yoshimura; Ayako Sakato; Koji Tsuchiya; Takahiro Ohkubo; Hideki Sakai; Masahiko Abe; Kunio Esumi (pp. 466-473).
An amino acid-based gemini surfactant derived from cystine (2C nCys, where n represents the hydrocarbon chain lengths of 8, 10, and 12) was synthesized by reacting cystine with n-alkyl bromide, and its adsorption and aggregation properties were characterized by measurements of equilibrium and dynamic surface tension and dynamic light scattering. The properties of 2C nCys were compared with those of an amino acid-based monomeric surfactant derived from cysteine (C nCys). Forn=8 and 10, when compared to C nCys, 2C nCys exhibited excellent surface activities, such as a lower critical micelle concentration (cmc), greater efficiency in lowering the surface tension of water, and smaller area occupied per molecule. Adsorption rate at air/water interface decreased with an increase in hydrocarbon chain length, chain number, and concentration of respective compounds. Further, the kinetics were discussed using the monomer diffusion coefficient obtained from short and long time scales in dynamic surface tension plots. In addition, the aggregation properties of 2C nCys forn=8 and 10 differed from those in the case ofn=12. In other words, relatively larger micelles with diameters of approximately 7 nm were formed by 2C nCys forn=8 and 10 in comparison to those formed by C nCys (2–3 nm). On the other hand, for a 0.832 mmol dm−3 2C12Cys solution, the aggregation structure investigated by cryogenic transmission electron microscopy (cryo-TEM) and small-angle neutron scattering (SANS) revealed the coexistence of small unilamellar vesicles and small rods.N,N′-Dialkyl cystine gemini surfactant forn=12 showed coexistence of small unilamellar vesicles and rods, whereas those forn=8 and 10 formed micelles.

Keywords: Gemini surfactant; Amino acid-based surfactant; Cmc; Surface tension; Adsorption; Aggregation

Surface characterization and platelet compatibility evaluation of the binary mixed self-assembled monolayers by Meng-Yen Tsai; Yu-Ting Sun; Jui-Che Lin (pp. 474-484).
This report describes a technique that used mixed self-assembled monolayer (SAM) as a model surface to evaluate the effect of steric hindrance on the SAM packing quality and its platelet compatibility. Two series of binary mixed SAMs were formed by mixing the bulky terminated alkanethiol (HS(CH2)10PO3H2) with a smaller terminated one (HS(CH2)9CH3 and HS(CH2)11OH) respectively. Surface characterization results showed the hydrophilicity on these two series of mixed SAMs changed with the solution mole fraction ofPO3H2 terminated thiol, χPO3H2,soln, and reached to a nearly constant value as χPO3H2,soln was 0.6 for PO3H2+CH3 SAM and 0.4 for PO3H2+OH SAM. This finding should be due to the gradual saturation of surfacePO3H2 functionality on these mixed SAMs. The XPS analysis indicated the addition of theCH3 andOH terminated thiol could reduce the steric hindrance effect ofPO3H2 functionality on monolayer formation and, henceforth, improve the SAM packing quality. In vitro platelet adhesion assay revealed the platelet compatibility on the PO3H2+OH SAMs was better than that on the PO3H2+CH3 and the purePO3H2 ones. Moreover, the PO3H2+OH SAM with a low χPO3H2,soln value exhibited the least platelet activating property of these two mixed SAM systems. These findings suggested that material's surface wettability and surface charge density should act collectively in affecting its platelet compatibility.

Keywords: Mixed self-assembled monolayers; Phosphonic acid; Surface characterization; X-ray photoelectron spectroscopy; Platelet compatibility

The sponge phase of a mixed surfactant system by A. Maldonado; R. Ober; T. Gulik-Krzywicki; W. Urbach; D. Langevin (pp. 485-490).
We study the sponge phase of the mixed non-ionic/ionic surfactant system C14DMAO–TTAB–hexanol–brine. Our aim is to determine if this phase exists in this mixed system and if it preserves or changes its structure when the relative amount of the charged surfactant is increased in the mixture. SAXS, FFEM, and conductivity results show that for the same bilayer volume fraction the sponge phase preserves its global structure. We propose a method to determine the geometrical obstruction factor from electrical conductivity measurements in ionic sponge phases. Analysis of lamellar phases in the same system shows that the bilayer thickness increases when the ionic surfactant concentration is increased.

Keywords: Surfactant; Sponge phase; Lamellar phase; SAXS; FFEM; Electrical conductivity

Formation of nanoparticles in water-in-oil microemulsions controlled by the yield of hydrated electron: The controlled reduction of Cu2+ by Qingde Chen; Xinghai Shen; Hongcheng Gao (pp. 491-499).
In the water-in-oil (W/O) microemulsions based on nonionic surfactants, i.e., Brij 30, Brij 56, or Triton X-100, the ω value (molar ratio of water to surfactant), anion, and surfactant could remarkably affect the radiolytic reduction of Cu2+ and the morphologies of the reduction products simultaneously. The addition of toluene or naphthalene could transform the reduction products from copper to cuprous oxide in the Brij 56-based microemulsion, and the efficiency of naphthalene was obviously higher than that of toluene. After the effects of pH value and cosurfactant were excluded, it could be concluded that the effects of the ω value, the anion, and the structure of the surfactant on the yield of hydrated electrons (eaq−) play a key role in the radiolytic reduction of Cu2+. It was also suggested that the morphology of the reduction product may be controlled by the yield ofeaq−.In the water-in-oil microemulsions, the ω value, anion and surfactant can affect the yield ofeaq−, which plays a key role in the radiolytic reduction of Cu2+ and the morphologies of the reduction products.

Keywords: Microemulsion; Hydrated electrons; γ; -Irradiation; Cuprous oxide; Copper nanoparticles; Controlled reduction

A new standardized lipolysis approach for characterization of emulsions and dispersions by M. Brogård; E. Troedsson; K. Thuresson; H. Ljusberg-Wahren (pp. 500-507).
A new standardized lipolysis approach is presented where the focus is on the initial rate of lipolysis. An advantage is that data obtained in this way reflect degradation before growing amounts of lipolysis products retard the process. The method can be used to rank different lipase substrates. In particular, the method can be used to obtain information about the susceptibility to degradation of various emulsions and dispersions that are used in technical applications. We present how the method is standardized to facilitate comparison of various substrates. This involves (i) lipase substrate in excess, i.e., the amount of lipase is rate limiting, and (ii) expressing rate of degradation relative to that of a reference substrate, tributyrin. Under such conditions, with the amount of lipase substrate held constant, an increase in enzymatic activity will generate a proportional increase in the lipolysis rate. This enables comparison of results obtained from different enzyme batches and corrects for day-to-day variability. Examples illustrating the potential of the method to discriminate and rank different lipase substrates with regard to enzymatic degradation are presented.A standardized method that utilizes the initial lipolysis rate to facilitate comparison of various substrates is presented. This involves (i) lipase substrate in excess, i.e., the amount of lipase being rate-limiting, and (ii) expressing rate of degradation relative to that of a reference substrate.

Keywords: Structured lipids; Lamellar; Lipid-based drug delivery; Lipid digestion; Lipolysis; Self-emulsifying drug delivery systems (SEDDS); Triglyceride; Dispersion; Emulsion

Adsorption of hydrophobically modified anionic starch at oppositely charged oil/water interfaces by Lars Nilsson; Björn Bergenståhl (pp. 508-513).
In this paper we study the adsorption at cationic emulsion droplets of starch which had been hydrophobically modified with octenyl succinic anhydride (OSA), a modification which also renders the starch anionic. Emulsions were formed with didodecyldimethylammonium bromide (DDAB) after which the OSA-starch was added. The emulsions were separated by centrifugation and the surface load of OSA-starch was determined through serum depletion. The results show the adsorbed amounts can become very high, in some cases reaching approximately 40 mg/m2. The surface load correlates positively with the surface charge density of the starch which depends on the degree of substitution, rms radius and molar mass. Furthermore, the surface load obtained depends on the ratio between polymer surface charge density and the interface charge density which could be varied experimentally by combining various amounts of DDAB and dioleoyl phosphatidylcholine (DOPC) in the formation of the emulsion. The very high surface loads should correspond to very thick adsorbed layers. Thus, OSA-starch should be appropriate for encapsulation applications provided a suitable adhesion substance is employed.Adsorption of hydrophobically modified anionic starch at oppositely charged oil/water interfaces can result in high surface loads reaching 40 mg/m2, depending on the physico-chemical properties of the starch.

Keywords: Encapsulation; Hydrophobically modified starch; Octenyl succinic anhydride starch; Adsorption; Emulsions; Polyelectrolytes

An HII liquid crystal-based delivery system for cyclosporin A: Physical characterization by Dima Libster; Abraham Aserin; Ellen Wachtel; Gil Shoham; Nissim Garti (pp. 514-524).
In the present study we demonstrate that large quantities of cyclosporin A and three dermal penetration enhancers (phosphatidylcholine, ethanol, or Labrasol) can be solubilized into reverse hexagonal (HII) liquid crystalline structures composed of monoolein, tricaprylin, and water. The microstructural characteristics of these complex multi-component systems were elucidated by rheological, SAXS, and DSC measurements. Addition of up to 20 wt% phosphatidylcholine improved significantly the elastic properties of the systems (lower values oftanδ) and increased the thermal stability of the mesophases enabling us to solubilize up to 6 wt% cyclosporin A and two other enhancers (Labrasol and ethanol) to obtain stable mesophases at physiological temperature. Rheological measurements revealed that solubilization of cyclosporin A alone has a destabilizing effect on the reverse hexagonal phases: it caused a deterioration in the elastic properties of the systems, leading to more liquid-like behavior and resulting in very short relaxation times (0.04–0.1 s). Labrasol, solubilized at high concentrations (up to 12 wt%) into the liquid crystals, also demonstrated a destabilizing effect on the HII structure: the decreasing elasticity of the system was attributed to Labrasol's presumed locus at the interface and its ability to bind water, as shown by DSC measurements. Ethanol had a destabilizing effect similar to that of Labrasol, yet the effect appeared to be more pronounced, probably due to its higher water-binding capability.In this study we solubilized large quantities of cyclosporin A and three dermal penetration enhancers (phosphatidylcholine, ethanol, and Labrasol) into HII liquid crystalline structures. Using rheological, SAXS and DSC measurements, we have characterized microstructural properties of these systems.

Keywords: Solubilization; Cyclosporin A; Labrasol; Liquid crystals; Reverse hexagonal phase; Rheology

Aggregation behavior of polypropylene oxide end-capped by positive charges by Tohru Inoue; Kohei Yamashita (pp. 525-531).
We investigated the aggregation behavior of poly(propylene oxide) with positive charges at both ends in aqueous solution by means of solution turbidity, dynamic light-scattering, solubilization of fluorescence probe, and optical microscopic observation. The positive charges were produced by protonation of terminal NH2 groups attached to the polymer composed of 33 PO units. It was found that the polymer exists as unimers at low temperature and as micelles at high temperature, whereas at intermediate temperature, there appear different aggregation states depending on the polymer concentration; i.e., 100-nm size aggregates which might be vesicles, 1-μm size particles (oil droplets), and a certain turbid phase showing a characteristic texture under optical microscopic observation. Filtration experiments to remove the oil droplets showed that the insoluble components with less hydrophilic property included in the polymer sample are responsible for the formation of oil droplets. Comparison of the phase diagrams obtained for the polymer/H2O mixtures before and after the filtration treatment suggests that the formation of 100 nm size aggregates and some unidentified phase in between unimer and micellar regions is an intrinsic property of the poly(propyrene oxide) chain end-capped by electrical charges.In between unimer and micellar regions of the polymer, there appear 100-nm size aggregates which might be vesicles, 1-μm size oil droplets, and a certain turbid phase.

Keywords: Amphiphilic polymer; Polypropylene oxide; Aggregation behavior; Micelle formation; Phase diagram

Rheology and orientational distributions of rodlike particles with magnetic moment normal to the particle axis for semi-dense dispersions (analysis by means of mean field approximation) by Akira Satoh; Yasuhiro Sakuda (pp. 532-541).
We have considered a semi-dense dispersion composed of ferromagnetic rodlike particles with a magnetic moment normal to the particle axis to investigate the rheological properties and particle orientational distribution in a simple shear flow as well as an external magnetic field. We have adopted the mean field approximation to take into account magnetic particle–particle interactions. The basic equation of the orientational distribution function has been derived from the balance of the torques and solved numerically. The results obtained here are summarized as follows. For a very strong magnetic field, the magnetic moment of the rodlike particle is strongly restricted in the field direction, so that the particle points to directions normal to the flow direction (and also to the magnetic field direction). This characteristic of the particle orientational distribution is also valid for the case of a strong particle–particle interaction, as in the strong magnetic field case. To the contrary, for a weak interaction among particles, the particle orientational distribution is governed by a shear flow as well as an applied magnetic field. When the magnetic particle–particle interaction is strong under circumstances of an applied magnetic field, the magnetic moment has a tendency to incline to the magnetic field direction more strongly. This leads to the characteristic that the viscosity decreases with decreasing the distance between particles, and this tendency becomes more significant for a stronger particle–particle interaction. These characteristics concerning the viscosity are quite different from those for a semi-dense dispersion composed of rodlike particles with a magnetic moment along the particle direction.

Keywords: Ferromagnetic colloidal dispersion; Aggregation phenomena; Simple shear flow; Spheroidal particle; Orientational distribution function; Rheological properties; Viscosity; Diffusion coefficient

Chemical shift imaging of molecular transport in colloidal systems: Visualization and quantification of diffusion processes by Anna Salvati; Iseult Lynch; Carin Malmborg; Daniel Topgaard (pp. 542-550).
Magnetic resonance imaging with chemical shift resolution is demonstrated to provide detailed information about molecular transport on the macroscopic scale in complex colloidal systems. The concentrations of species with distinct1H resonance lines can be quantified from spatially resolved, high-resolution,1H nuclear magnetic resonance spectra. The method is demonstrated by experiments on three systems with multiple simultaneous transport processes where the diffusion coefficients depend on position and/or on the concentration of other species: (1) release of poly(ethylene glycol) and imidazole from a hydrogel into an external reservoir of water, (2) migration of acetic acid and tetramethylammonium ions in a highly concentrated water-in-oil emulsion with initially non-uniform concentration of solutes, and (3) release of tetramethylammonium ions loaded into a hydrogel triggered by the diffusion of methyl green into the gel matrix.

Keywords: MRI; NMR; CSI; Pure phase-encoding; Controlled release

A general contact mechanical formulation of multilayered structures and its application to deconvolute thickness/mechanical properties of glue used in surface force apparatus by Souvik Math; Roger Horn; Vikram Jayaram; Sanjay Kumar Biswas (pp. 551-561).
Currently data obtained from surface force apparatus experiments are convoluted with the mechanical response of glue of unknown thickness, used to bond mica sheets to the substrates. This paper describes a formulation to precisely deconvolute out the forces between the mica sheets by determining the thickness of glue, knowing the mechanical properties of the glue. The formulation consists of a general solution based on the noniterative Hankel transform of the Laplace equation. The generality is achieved by treating all the layers except the one in contact as an effective lumped system consisting of a set of springs in series, where each spring represents a layer. The solution is validated by nanoindentation of trilayer systems consisting of layers with widely diverse mechanical properties, some differing from each other by three orders of magnitude. SFA experiments are done with carefully metered slabs of glue. The proposed method is validated by comparing the actual glue thicknesses with those determined using the present analysis.

Keywords: Trilayer; Effective modulus; Nanoindentation; Surface force apparatus

Comments on “A study of the collisional fragmentation problem using the gamma distribution approximation” by Saralees Nadarajah (pp. 562-563).
M. Kostoglou and A.J. Karabelas [J. Colloid Interface Sci. 303 (2006) 419–429] proposed using a gamma distribution approximation to study a collisional fragmentation problem. This approximation involved two types of integrals and the use of continued fraction expansions for their computation. In this Comment, explicit expressions are derived for computing the integrals.

Keywords: Gamma distribution; Collisional fragmentation problem

Direct synthesis of fct-structured FePt nanoparticles at low temperature with assistance of poly( N-vinyl-2-pyrrolidone) by Takashi Iwamoto; Kinya Matsumoto; Yoshitaka Kitamoto; Naoki Toshima (pp. 564-567).
Direct synthesis of fct-structured FePt nanoparticles was successfully achieved by using poly( N-vinyl-2-pyrrolidone) as a protective reagent at lower temperature than the case using low molecular weight ligands as a protective reagent. Experimental data suggest that a transformation of FePt nanoparticles from face-centered cubic to face-centered tetragonal (fct) structure takes place at reaction temperature of 261 °C. The results of XRD and the magnetic properties exhibit that the FePt nanoparticles synthesized at 261 °C have partially ordered fct-structure and a ferromagnetic behavior at room temperature.Magnetic hysteresis loops at 300 K of PVP-protected FePt nanoparticles synthesized at various reaction temperatures without refluxing. FePt nanoparticles synthesized at reaction temperatures above 261 °C show a ferromagnetic behavior.

Keywords: FePt nanoparticles; Direct synthesis; Poly(; N; -vinyl-2-pyrrolidone); XRD pattern; fct-Structure; Phase transformation; Coercivity; Ferromagnetism

Preparation of Pt/Rh bimetallic colloidal particles in polymer solutions using borohydride-reduction by Masafumi Harada; Hisahiro Einaga (pp. 568-572).
Colloidal dispersions of Pt/Rh bimetallic particles have been synthesized by the reduction of Pt(IV)/Rh(III) ionic solutions by using borohydride-reduction in the presence of poly( N-vinyl-2-pyrrolidone). The size and the structure of the synthesized particles have been examined by transmission electron micrograph (TEM) and extended X-ray absorption fine structure (EXAFS). We have succeeded in producing the bimetallic Pt/Rh particles with an average diameter of 2.8 nm in polymer solutions by the stepwise addition of sodium borohydride aqueous solution. The distribution of different metallic species in a particle tended to be “cluster-in-cluster” structure, in contrast to the bimetallic particle with an average diameter of 1.4 nm synthesized by alcohol-reduction which have a core–shell structure.The “cluster-in-cluster” structure is appropriate model for the Pt/Rh(1/1) bimetallic particle.

Keywords: Colloidal dispersions; Nanoparticles; Platinum; Rhodium; Platinum/rhodium bimetallic nanoparticles; Borohydride-reduction

Kinetics of N-glutaryl-l-phenylalanine p-nitroanilide hydrolysis catalyzed by α-chymotrypsin in aqueous solutions of alkyltrimethylammonium bromides by Elsa Abuin; Eduardo Lissi; Cristian Calderón (pp. 573-576).
The rate of N-glutaryl-l-phenylalanine p-nitroanilide hydrolysis catalyzed by α-chymotripsin has been measured in aqueous solutions of cetyltrimethylammonium bromide, tetradecyltrimethylammonium bromide, and dodecyltrimethylammonium bromide at concentrations below and above their critical micellar concentrations (CMC). For the three surfactants considered superactivity was observed, with maximum catalytic efficiencies taking place near the corresponding CMCs. The effect of the surfactants after the CMCs is mostly due to a decreased thermodynamic activity of the substrate due to its incorporation into the micelles. After addition of the surfactants, the Michaelis constant values (corrected to take into account the free substrate concentration) tend to decrease, passing through an ill defined minimum, afterwards reaching a constant value. The catalytic rate constants show the same profiles that the catalytic efficiency, being maxima near the surfactants CMCs. This maximum is more important for the surfactant having the shorter tail. This result is explained by considering that the hydrophobicity of the surfactant influences more the CMC than its association to the enzyme.A study has been made on the effect of the surfactant chain length upon the kinetics of the hydrolysis of N-glutaryl-l-phenylalanine p-nitroanilide (GPNA) catalyzed by α-chymotrypsin in aqueous solutions of alkyltrimethylammonium bromides.

Keywords: Alkyltrimethylammonium bromides; α; -Chymotrypsin; N; -glutaryl-; l; -phenylalanine; p; -nitroanilide

No Title by Arthur Hubbard (pp. 577-577).
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