Journal of Colloid And Interface Science (v.371, #1)
Measurement and analysis of forces in bubble and droplet systems using AFM
by Rico F. Tabor; Franz Grieser; Raymond R. Dagastine; Derek Y.C. Chan (pp. 1-14).
Display Omitted► Atomic force microscopy measures forces between drops and bubbles. ► Modelling frameworks for quasi-equilibrium and dynamic forces are presented. ► Highlights of recent experimental advances in forces from soft matter AFM. ► Van der Waals, electrical double-layer, structural and hydrodynamic forces.The use of atomic force microscopy to measure and understand the interactions between deformable colloids – particularly bubbles and drops – has grown to prominence over the last decade. Insight into surface and structural forces, hydrodynamic drainage and coalescence events has been obtained, aiding in the understanding of emulsions, foams and other soft matter systems. This article provides information on experimental techniques and considerations unique to performing such measurements. The theoretical modelling frameworks which have proven crucial to quantitative analysis are presented briefly, along with a summary of the most significant results from drop and bubble AFM measurements. The advantages and limitations of such measurements are noted in the context of other experimental force measurement techniques.
Keywords: Atomic force microscope; Deformable; Drops; Bubbles; Dynamics; Surface forces
Single-step synthesis of layered double hydroxides ultrathin nanosheets
by Yanxia Yan; Qi Liu; Jun Wang; Jinbo Wei; Zan Gao; Tom Mann; Zhanshuang Li; Yang He; Milin Zhang; Lianhe Liu (pp. 15-19).
Display Omitted► A novel single-step approach is developed to prepare MgAl–LDHs ultrathin nanosheets. ► Large-scale MgAl–LDHs nanosheets with thickness of about 1.44nm are obtained. ► The weight loss of these nanosheets at 500°C is very low.A novel single-step approach was developed to prepare large-scale MgAl–LDHs ultrathin nanosheets. The key point of the successful realization was that we employed a high concentration of H2O2. Oxygen molecules, derived from in situ decomposition of H2O2, were speculated to be the decisive factor leading to complete separation of LDHs layers. The ultrathin nanosheets were characterized by XRD, TEM, AFM, FT-IR, and TG–DSC. The results indicated that the thickness of these nanosheets was about 1.44nm, which was almost in perfect agreement with the theoretical thickness of two LDHs layers. From the TG–DSC curves, the weight loss of these exfoliated MgAl–LDHs ultrathin nanosheets at 500°C was 18.5%, which was much smaller compared to the 32.3% weight loss of unexfoliated MgAl–LDHs.
Keywords: Nanosheet; Exfoliation; Layered double hydroxides; Single-step; H; 2; O; 2
Concentration and size dependence of nano-silver dispersed water based nanofluids
by G. Paul; S. Sarkar; T. Pal; P.K. Das; I. Manna (pp. 20-27).
Display Omitted► Nano-Ag dispersed water based nanofluids (NFs) are synthesized by one-step method. ► Concentration and size of Ag nanoparticles (NPs) are main variables. ► Microstructure (of NPs) and thermal conductivity ( k) of NFs are characterized. ► A maximum 21% enhancement in k at 0.001M concentration and 55nm size is noted. ► Brownian motion and clustering of nanoparticles closely predict experimental data.Nanometric silver dispersed water based nanofluids have been prepared by a single-step chemical process. The crystallite/particle size, morphology and purity of nanoparticles were characterized using standard microscopic, diffraction and spectroscopic techniques. The thermal conductivity enhancement (with respect to the base fluid) has been determined as a function of concentration and size of silver particles using transient hot-wire technique. The accurate fitting of the experimental data of thermal conductivity enhancement with a theoretical model developed by Patel et al. predicts that high specific surface area of the particles, layering at the liquid–solid interface and Brownian motion may be responsible for enhancement.
Keywords: Nanofluid; Transient hot-wire; Concentration; Particle size; Brownian motion
Simple fabrication of snowman-like colloids
by Neetu Chaturvedi; Bala Krishna Juluri; Qingzhen Hao; Tony Jun Huang; Darrell Velegol (pp. 28-33).
Display Omitted► Fabrication of anisotropic colloidal particles bearing a snowman-like shape. ► Tunable structure by adjusting the size ratio between the constituent colloids. ► Technique is adjustable in surface coverage of the substrate by changing the ionic strength of the solution. ► Simple, reproducible and cost-effective technique.Anisotropic colloidal particles consisting of different compositions and geometry are useful for various applications. These include optical biosensing, antireflective coatings and electronic displays. In this work we demonstrate a simple and cost-effective method for fabricating anisotropic colloidal particles bearing a snowman-like shape. This is achieved by first settling the positively-charged polystyrene latex (PSL) colloids and negatively-charged silica colloids in deionized water onto a glass substrate, forming heterodoublets. The temperature is then raised above the glass transition temperature of the polymer. As a result, the silica particle spontaneously rises to the top of the PSL particle forming a snowman like structure. We have extended this method to different sizes and shown that the structure of the hybrid particles can be tuned by adjusting the size ratio between the silica and the PSL colloids. The surface coverage of the PSL, and hence of the snowman particles, on the glass substrate can also be varied by changing the ionic strength of the solution during the adhesion of PSL to the glass.
Keywords: Snowman; Heterodoublets; Anisotropic colloids; Controlled self-assembly; Lithographed patch
Probing quenched dye fluorescence of Cy3–DNA–Au-nanoparticle hybrid conjugates using solution and array platforms
by Judy M. Obliosca; Pen-Cheng Wang; Fan-Gang Tseng (pp. 34-41).
Display Omitted► Au–DNA–Cy3 prepared using 10-nm AuNPs and ds-DNA with disulfide-modified target and Cy3-labeled probe. ► Quenching of Au–DNA–Cy3 in solution and array platforms assessed using ligand exchange by ME. ► High quenching efficiency observed for the shortest Au-to-Cy3 gap.Tuning the luminescence intensity of fluorophores using nanoparticles has shown great potential for the detection of inorganic metal ions, viruses, and proteins. The enhancement or quenching of a dye’s fluorescence intensity is strongly dependent on the spatial separation of the dye from the nanoparticle surface. To extend luminescence probing from the solution platform to the solid-state platform, we explored and performed dye quenching assessment using an array format in this study. We report the distance-dependent fluorescence behavior of Au–DNA conjugates prepared by equilibrating phosphine-stabilized gold nanoparticles (AuNPs) of 10-nm size with the designed spacer ds-DNA consisting of thiol-modified target and Cy3-labeled complementary probe of different lengths (5–20nm). The Cy3-labeled products were immobilized onto MPTMS (3-mercaptopropyltrimethoxysilane)-modified glass substrates and then excited with a 532-nm laser source. Quenching efficiency of AuNPs with increasing Au-to-dye distance was assessed using ligand exchange of the thiolated oligonucleotide by 2-mercaptoethanol (ME) to obtain free Cy3–DNA probe, thus eliminating nanoparticle effect on the dye’s luminescence intensity. Effective exchange, revealed by UV–vis absorption and fluorescence profiles, was achieved in a few minutes. It was observed that fluorescence quenching of Au–DNA–Cy3 assessed using the array format was consistent with the result in solution phase for the conjugates with up to 10-nm Au-to-Cy3 separation distance.
Keywords: Fluorescence quenching; Gold nanoparticles; Surface functionalization; Microarray; DNA
Perfluorinated polymer colloids: Controlling the size, shape, and surface charge
by Stephen M. Budy; S. Suresh; Stephen H. Foulger; Dennis W. Smith Jr. (pp. 42-45).
Display Omitted► First account of perfluorocyclobutyl (PFCB) aryl ether polymer colloids. ► Size of perfluorinated polymer colloids controlled by concentration. ► Surface charge of colloids modified by post-functionalized sulfonic acid groups. ► Different self-assembly morphologies were observed on four different substrates; spherical (Al), clover-like (Cr), flower-like (C), and “squalloid” (Si).The first report of perfluorocyclobutyl (PFCB) aryl ether polymer colloids is presented herein. The biphenyl rings were post-functionalized with chlorosulfonic acid modification in the backbone of the perfluoropolymer, thereby changing the zeta potential ( ζ) of the colloids across the pH range (2–12). Self-assembly of the colloids was observed by scanning electron microscopy (SEM) on four separate surfaces which led to different morphological changes for each surface; spherical on Al substrate, clover-like on Cr substrate, flower-like on carbon substrate, and “squalloid” on Si substrate.
Keywords: Perfluorocyclobutyl (PFCB) aryl ether polymer; Colloids; Shape
Size-controlled and monodisperse enzyme-encapsulated chitosan microspheres developed by the SPG membrane emulsification technique
by Kazuki Akamatsu; Yuto Ikeuchi; Aiko Nakao; Shin-ichi Nakao (pp. 46-51).
Display Omitted► Prepared lysozyme-encapsulated chitosan microspheres by SPG membrane emulsification. ► Achieved monodispersity and size-controllability of the microspheres. ► Could predict the average diameters of the microspheres with no fitting parameters. ► Controlled the amount of encapsulated lysozyme. ► Elucidated the maintenance of the activities of the encapsulated lysozymes.Lysozyme-encapsulated chitosan microspheres with micron-size diameters were successfully prepared for the first time by employing the Shirasu porous glass (SPG) membrane emulsification technique followed by cross-linking with glutaraldehyde, and the relationships between the preparation conditions and characteristics of the microspheres were studied in detail. This preparation method provided size-controllability and monodispersity of the microspheres, owing to the sharpness of the pore sizes of the SPG membranes. It was also possible to predict the average diameters of the enzyme-encapsulated microspheres using no fitting parameters, on the basis that each microsphere is prepared in an emulsion containing chitosan and lysozyme, without any collisions or aggregation occurring. X-ray photoelectron spectroscopy measurements indicated that the amount of encapsulated lysozyme was controlled by the concentrations of chitosan and lysozymes in the dispersion phase used for preparing the emulsions from which the enzyme-encapsulated microspheres are formed. Finally, the apparent activity of the encapsulated lysozymes was measured by the viscosimetric method, using ethyleneglycolchitin. Results showed that about half of the activity of the encapsulated lysozymes was maintained during the preparation procedure when employing the SPG membrane emulsification technique.
Keywords: Abbreviations; FE-SEM; field-emission scanning electron microscopy; SPG; Shirasu porous glass; TGCR; tetraglycerol condensed ricinoleate; XPS; X-ray photoelectron spectroscopyMembrane emulsification; Microspheres; Shirasu porous glass (SPG) membranes; Chitosan; Lysozyme; Activity
Aggregation behavior of pyridinium based ionic liquids in water – Surface tension,1H NMR chemical shifts, SANS and SAXS measurements
by Nandhibatla V. Sastry; Nilesh M. Vaghela; Pradip M. Macwan; Saurabh S. Soni; Vinod K. Aswal; Alain Gibaud (pp. 52-61).
Display Omitted► The short alkyl chain pyridinium ionic liquids (IL) are surface active in water. ► The morphological features of the aggregates are concentration dependent. ► The IL aggregates exhibit a cubic packing of molecules.The aggregation behavior of short alkyl chain ionic liquids (ILs), namely 1-butyl, or 1-hexyl or 1-octylpyridinium and 1-octyl-2-, or -3-, or -4-methylpyridinium chlorides, in water has been assessed using surface tension, electrical conductance,1H NMR, small angle neutron scattering (SANS) and small angle X-ray scattering (SAXS) measurements. Critical aggregation concentrations (CACs), adsorption (at air/water interface) and thermodynamic parameters of aggregation have been reported. The values of CAC and area per adsorbed molecule decrease with the number of carbon atoms in the alkyl chain. The aggregation process is driven by both favorable enthalpy and entropy contributions. An attempt was made to examine the morphological features of the aggregates in water using SANS and SAXS methods. SANS and SAXS curves displayed diffuse structural peaks that could not be model fitted, and therefore, we calculated the mean aggregation numbers from the Qmax assuming that IL molecules typically order into cubic type clusters.
Keywords: Pyridinium based ionic liquids; Critical aggregation concentration; Surface active parameters; Thermodynamic parameters of aggregation; 1; H NMR; SANS and SAXS
Interfacial concentrations of chloride and bromide in zwitterionic micelles with opposite dipoles: Experimental determination by chemical trapping and a theoretical description
by Tereza Pereira de Souza; Hernan Chaimovich; Alfred Fahr; Bianca Schweitzer; Augusto Agostinho Neto; Iolanda Midea Cuccovia (pp. 62-72).
Display Omitted► Anion concentrations in zwitterionic micelles determined by chemical trapping. ► Poisson Boltzmann description used to fit experimental anion concentrations in zwitterionic micelles. ► Assuming translational freedom of ions in the micellar adsorbing plane gives the best description.Interfacial concentrations of chloride and bromide ions, with Li+, Na+, K+, Rb+, Cs+, trimethylammonium (TMA+), Ca2+, and Mg2+ as counterions, were determined by chemical trapping in micelles formed by two zwitterionic surfactants, namely N-hexadecyl-N,N-dimethyl-3-ammonio-1-propanesulfonate (HPS) and hexadecylphosphorylcholine (HDPC) micelles. Appropriate standard curves for the chemical trapping method were obtained by measuring the product yields of chloride and bromide salts with 2,4,6-trimethyl-benzenediazonium (BF4) in the presence of low molecular analogs (N,N,N-trimethyl-propane sulfonate and methyl-phosphorylcholine) of the employed surfactants. The experimentally determined values for the local Br− (Cl−) concentrations were modeled by fully integrated non-linear Poisson Boltzmann equations. The best fits to all experimental data were obtained by considering that ions at the interface are not fixed at an adsorption site but are free to move in the interfacial plane. In addition, the calculation of ion distribution allowed the estimation of the degree of ion coverage by using standard chemical potential differences accounting for ion specificity.
Keywords: Ionic selectivity; Chemical trapping; Zwitterionic micelles; Poisson–Boltzmann
Effect of hydrocarbon structure of the headgroup on the thermodynamic properties of micellization of cationic gemini surfactants: An electrical conductivity study
by Qi Zhang; Zhinong Gao; Feng Xu; Shuxin Tai (pp. 73-81).
Display Omitted► The headgroup alkyl chain affects the thermodynamic properties of gemini surfactants. ► The temperature of the minimum of cmc ( Tmin) increases with increasing the headgroup alkyl chain length. ► Log (cmc) does not vary linearly with carbon number of the headgroup alkyl chain. ► The enthalpy–entropy compensation plots exhibit excellent linearity.A series of cationic gemini surfactants butanediyl-1,4-bis(dodecyldialkylammonium bromide), C12H25N+(C mH2 m+1)2C4H8N+(C mH2 m+1)2C12H25·2Br−, where m=1, 2, 3, 4, referred to as C12C4C12(Me), C12C4C12(Et), C12C4C12(Pr), and C12C4C12(Bu), respectively, were synthesized, and their thermodynamic properties of micellization were studied by electrical conductivity measurements. There existed a minimum critical micelle concentration (cmc) in the curve of cmc versus temperature, and the temperature of the minimum of cmc ( Tmin) increased with increasing the headgroup alkyl chain length. The values of log (cmc) depended linearly on carbon number of the alkyl chains, but that was not true for the carbon number of the headgroup substituents. The temperature dependence of cmc and degree of counterion association ( β) were used to calculate the Gibbs free energy (Δmic G°), enthalpies (Δmic H°) and entropies (Δmic S°) of micelle formation for these gemini surfactants, and well correlated enthalpy–entropy compensation was observed. The analyses showed C12C4C12(Me) and C12C4C12(Et) behaved similarly in terms of thermodynamics of micellization, but they behaved differently from C12C4C12(Pr) and C12C4C12(Bu), which could be ascribed to the hydrophobicity and the location of the headgroup alkyl chains in the aggregates. These initial results indicate the headgroup alkyl chain plays an important role in influencing the thermodynamic properties of gemini surfactants.
Keywords: Gemini surfactants; Headgroup; Micellization; Thermodynamic properties; Enthalpy–entropy compensation
Novel ethoxylated inositol derivatives – Hybrid carbohydrate/oligoethylene oxide surfactants
by Gabriela Catanoiu; Dirk Blunk; Cosima Stubenrauch (pp. 82-88).
Display Omitted► Synthesis of two nonionic ethoxylated inositol-based surfactants C12E3I1 and C12I1E3. ► Properties are driven by the way the head group is attached to the alkyl chain. ► Recipe to tailor-make effective surfactants with hybrid head groups.Carbohydrate- and oligoethylene oxide-based surfactants behave quite differently despite the fact that they are both classes of nonionic surfactants. Intensive studies of a mixture at fixed molar ratio (1:1) of two very common sugar- and oligoethylene oxide-based surfactants, namely n-dodecyl-β-d-maltoside (β-C12G2) and n-dodecyl hexaethylene oxide (C12E6), revealed that most properties of the mixture are similar to those of the oligoethylene oxide-based surfactant. In the present work, this mixture is compared to respective “hybrid surfactants”. Such hybrid surfactants are surfactants whose head group contains chemically linked carbohydrate and oligoethylene oxide units. In order to study the behaviour of this sort of compounds, we synthesised a new class of surfactants whose head group consists of one carbohydrate-like unit ( myo-inositol) and three ethylene oxide units. New regiochemically defined ethoxylated inositol derivatives (referred to as C12I1E3 and C12E3I1 in the following) were synthesised and studied for their thermotropic and lyotropic liquid crystalline properties as well as for their surface activities. The results are compared with those of the reference systems β-C12G2 and C12E6, and their 1:1 mixture, respectively, and are discussed in terms of structure–property relations.
Keywords: New inositol-based surfactants; Hybrid surfactants; Surface properties; Phase diagrams; Thermotropic and lyotropic liquid crystals; Surfactant mixtures
Cyclodextrins adsorbed onto activated carbons: Preparation, characterization, and effect on the dispersibility of the particles in water
by Nicolas Kania; Sébastien Rio; Eric Monflier; Anne Ponchel (pp. 89-100).
Display Omitted► Adsorption equilibrium studies of selected cyclodextrins on activated carbons. ► Activated carbons could spontaneously adsorb high contents of cyclodextrins. ► Use of modified cyclodextrins may improve the dispersion of the carbon particles. ► New insights into the role of cyclodextrins in the dispersion of carbon suspensions.We have investigated the adsorption equilibrium of selected cyclodextrins onto activated carbons. A number of parameters were examined including the type of carbon material, the size of macrocyclic cavity, and the chemical nature of the oligosaccharide (e.g., neutral, anionic, or cationic cyclodextrin). Adsorption isotherm studies revealed that the maximum amount of cyclodextrin immobilized on the carbon surface is obtained for the native β-CD, while the adsorption capacity of the ionic cyclodextrins derivatives strongly depends on the net surface charge of the activated carbon. The affinity of cyclodextrins for activated carbons was further utilized to prepare modified activated carbons containing controlled amounts of cyclodextrins through an adsorption process. The resulting materials were characterized by N2 adsorption–desorption volumetric measurements, FTIR and Raman spectroscopy, while the quantitative determination of the oligosaccharide content on activated carbons was performed by gravimetric measurements. On the basis of the Turbiscan results, it was found that the chemical structure of cyclodextrins, which are incorporated in the carbon framework, had significant influence on the dispersibility and stabilization of the solid particles in water. Agglomeration and precipitation of the carbon particles were markedly suppressed with substituted cyclodextrins whose hydroxyl groups were partially substituted by methyl or alkylammonium groups.
Keywords: Cyclodextrin; Adsorption; Activated carbon; Turbiscan analysis; Aqueous carbon dispersion
Photo-catalyzed degradation of hazardous dye methyl orange by use of a composite catalyst consisting of multi-walled carbon nanotubes and titanium dioxide
by Tawfik A. Saleh; Vinod K. Gupta (pp. 101-106).
Preparation of MWCNT/TiO2 composite.Display Omitted► Catalytic activity of MWCNT/TiO2 has been investigated. ► The MWCNT/TiO2 composite showed better performance. ► MWCNT acts as dispersing agent preventing TiO2 from agglomeration.The high rate of electron/hole pair recombination reduces the quantum yield of the processes with TiO2 and represents its major drawback. Adding a co-adsorbent increases the photocatalytic efficiency of TiO2. In order to hybridize the photocatalytic activity of TiO2 with the adsorptivity of carbon nanotube, a composite of multi-walled carbon nanotubes and titanium dioxide (MWCNT/TiO2) has been synthesized. The composite was characterized by means of X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), Fourier transform infrared absorption spectroscopy (FTIR), and diffuse reflectance UV–vis spectroscopy. The catalytic activity of this composite material was investigated by application of the composite for the degradation of methyl orange. It was observed that the composite exhibits enhanced photocatalytic activity compared with TiO2. The enhancement in photocatalytic performance of the MWCNT/TiO2 composite is explained in terms of recombination of photogenerated electron–hole pairs. In addition, MWCNT acts as a dispersing agent preventing TiO2 from agglomerating activity during the catalytic process, providing a high catalytically active surface area. This work adds to the global discussion of how CNTs can enhance the efficiency of catalysts.
Keywords: Carbon nanotube; Titanium oxide; Methyl orange; Photo catalyst
Dynamics of a climbing surfactant-laden film – I: Base-state flow
by A. Mavromoustaki; O.K. Matar; R.V. Craster (pp. 107-120).
Display Omitted► We model the dynamics of a surfactant-laden film climbing up an inclined plane. ► Using lubrication theory we obtain a 2-D evolution equation for the film height. ► The base flow is examined by carrying out a parametric study on the 1-D solutions. ► Competition between 2 forces is observed: Marangoni forces and gravity effects. ► The spreading of the surface-tension-induced ridges exhibits a power–law relation.The dynamics of a surfactant-laden film climbing up an inclined plane is investigated through a two-dimensional (2-D), nonlinear evolution equation for the interface coupled to convective-diffusion equations for the surfactant, derived using lubrication theory. One-dimensional (1-D) solutions, representing the base-state flow, are investigated for constant flux and constant volume configurations; these flows are parameterised by capillarity, gravity, convection–diffusion ratios (represented by Péclét numbers at the surface and bulk), a solubility parameter, sorption kinetics constants, the number of surfactant monomers in a micelle, and the nonlinearity of the surfactant equation of state. In both configurations studied, a front develops spreading up the substrate against the direction of gravity whereby the leading edge of the front follows a power–law as a function of time. The effect of system parameters on the base-state flow is explored through an extensive parametric study, while the stability of the above-mentioned system to spanwise perturbations is the focus of Part II .
Keywords: Thin film; Soluble surfactant; Marangoni effect; Fingering; Critical micelle concentration
Dynamics of a climbing surfactant-laden film II: Stability
by A. Mavromoustaki; O.K. Matar; R.V. Craster (pp. 121-135).
Display Omitted► We examine the spanwise stability of a surfactant-laden film climbing up a plane. ► Small-amplitude disturbances are introduced in the linearised base-state equations. ► In the constant-flux case the thinnest region is unstable to finger formation. ► For finite-volume spreading, the gravity-force-induced capillary ridge is unstable. ► Increasing the initial micellar concentration leads to stabilising effects.The linear and nonlinear stability of a spreading film of constant flux and a drop of constant volume, discussed in , are examined here. A linear stability analysis (LSA) is carried out to investigate the stability to spanwise perturbations, by linearisation of the two-dimensional (2-D) evolution equations derived in for the film thickness and surfactant concentration fields. The latter correspond to convective–diffusion equations for the surfactant, existing in the form of monomers (present at the free surface and in the bulk) and micelles (present in the bulk). The results of the LSA indicate that the thinning region, present upstream of the leading front in the constant flux case, and the leading ridge in the constant volume case, are unstable to spanwise perturbations. Numerical simulations of the 2-D system of equations demonstrate that the above-mentioned regions exhibit finger formation; the effect of selected system parameters on the fingering patterns is discussed.
Keywords: Thin film; Soluble surfactant; Marangoni effect; Fingering; Critical micelle concentration
Protonation enthalpies of metal oxides from high temperature electrophoresis
by Victor Rodriguez-Santiago; Mark V. Fedkin; Serguei N. Lvov (pp. 136-143).
Display Omitted► High temperature electrophoresis data are summarized for a variety of metal oxides. ► Surface protonation enthalpies were extracted via two alternative models. ► Two groups of oxides are identified based on their protonation enthalpy behavior. ► Relative permittivity, Me–OH bond length are found to affect protonation enthalpy.Surface protonation reactions play an important role in the behavior of mineral and colloidal systems, specifically in hydrothermal aqueous environments. However, studies addressing the reactions at the solid/liquid interface at temperatures above 100°C are scarce. In this study, newly and previously obtained high temperature electrophoresis data (up to 260°C) – zeta potentials and isoelectric points – for metal oxides, including SiO2, SnO2, ZrO2, TiO2, and Fe3O4, were used in thermodynamic analysis to derive the standard enthalpies of their surface protonation. Two different approaches were used for calculating the protonation enthalpy: one is based on thermodynamic description of the 1-p Ka model for surface protonation, and another one – on a combination of crystal chemistry and solvation theories which link the relative permittivity of the solid phase and the ratio of the Pauling bond strength and bond length to standard protonation enthalpy. From this analysis, two expressions relating the protonation enthalpy to the relative permittivity of the solid phase were obtained.
Keywords: Protonation; Electrophoresis; Zeta potential; High temperature; Metal oxides
Characterizing N-acetylcysteine (NAC) and N-acetylcysteine amide (NACA) binding for lead poisoning treatment
by Weiqing Chen; Nuran Ercal; Tien Huynh; Anatoliy Volkov; Charles C. Chusuei (pp. 144-149).
Display Omitted► Pb(II) binds more strongly to NACA than to NAC. ► Surface electrostatic interactions play a partial role in Pb–antioxidant binding. ► Supermolecular interaction energies account for enhanced Pb(II) binding to NACA.Using antioxidants is an important means of treating lead poisoning. Prior in vivo studies showed marked differences between various chelator antioxidants in their ability to decrease both blood Pb(II) levels and oxidative stress resulting from lead poisoning. The comparative abilities of NAC and NACA to Pb(II) were studied in vitro, for the first time, to examine the role of theOH/NH2 functional group in antioxidant binding behavior. To assay the antioxidant–divalent metal interaction, the antioxidants were probed as solid surfaces, adsorbing Pb(II) onto them. Surface characterization was carried out using X-ray photoelectron spectroscopy (XPS) analysis to quantify Pb(II) in the resulting adducts. XPS of the Pb 4f orbitals showed that more Pb(II) was chemically bound to NACA than NAC. In addition, the antioxidant surfaces probed via point-of-zero charge (PZC) measurements of NAC and NACA were obtained to gain further insight into the Pb–NAC and Pb–NACA binding, showing that Coulombic interactions played a partial role in facilitating complex formation. The data correlated well with solution analysis of metal–ligand complexation. UV–vis spectroscopy was used to probe complexation behavior. NACA was found to have the higher binding affinity as shown by free Pb(II) available in the solution after complexation from HPLC data. Electrospray ionization mass spectrometry (ESI-MS) was applied to delineate the structures of Pb–antioxidant complexes. Experimental results were further supported by density functional theory (DFT) calculations of supermolecular interaction energies ( Einter) showing a greater interaction of Pb(II) with NACA than NAC.
Keywords: Lead poisoning; N; -acetylcysteine; N; -acetylcysteine amide; Isoelectric point; Density functional theory
Tantalum oxide/carbon nanotubes composite coatings on titanium, and their functionalization with organophosphonic molecular films: A high quality scaffold for hydroxyapatite growth
by A. Maho; S. Linden; C. Arnould; S. Detriche; J. Delhalle; Z. Mekhalif (pp. 150-158).
.Display Omitted► Sol–gel elaboration of thin composite films made of Ta2O5 and MWCNTs on Ti. ► Optimization of the sol composition (acid catalyst), hydrolysis and drying steps. ► Functionalization of the coatings with organophosphonic acid molecular films. ► Obtained deposits are free of defects, very homogeneous, and resistant to corrosion. ► Effects of inorganic and organic layers on in vitro HAp growth are highly beneficial.Nowadays, titanium is a very commonly used biomaterial for the preparation of orthopedic and dental implants. Its excellent mechanical and biochemical bulk properties are nevertheless counterbalanced by its propensity to long term degradation in physiological conditions and its weak osseointegrative capacities. In this context, surface modifications can significantly hinder titanium weaknesses.The approach considered in this work relies on the preparation of thin composite coatings based on tantalum oxide and carbon nanotubes by sol–gel process. Tantalum is particularly interesting for its high biocompatibility and bioactivity, as well as its strong resistance to bio-corrosion. Carbon nanotubes are exploited to reinforce the compactness and homogeneity of the coatings, and can act as a favorable factor to strengthen the interaction with bone components by biomimicry. The composite layers are further modified with specific organophosphonic acid molecular films, able to chemically bind the tantalum oxide surface and improve the hydroxyapatite formation process.The characteristics and the qualities of these hybrid inorganic/organic coatings are evaluated by XPS, SEM, TEM, peeling tests, contact angle measurements, and electrochemical characterizations (free potential, polarization curves).
Keywords: Titanium-based biomaterials; Tantalum oxide; Carbon nanotubes; Sol–gel co-deposition; Amino-tris-methylene phosphonic acid; Hydroxyapatite