Titration Curves Research Articles

A 'poly-transfection' method for rapid, one-pot characterization and optimization of genetic systems.

Biological research is relying on increasingly complex genetic systems and circuits to perform sophisticated operations in living cells. Performing these operations often requires simultaneous delivery of many genes, and optimizing the stoichiometry of these genes can yield drastic improvements in performance. However, sufficiently sampling the large design space of gene expression stoichiometries in mammalian cells using current methods is cumbersome, complex, or expensive. We present a ‘poly-transfection’ method as a simple yet high-throughput alternative that enables comprehensive evaluation of genetic systems in a single, readily-prepared transfection sample. Each cell in a poly-transfection represents an independent measurement at a distinct gene expression stoichiometry, fully leveraging the single-cell nature of transfection experiments. We first benchmark poly-transfection against co-transfection, showing that titration curves for commonly-used regulators agree between the two methods. We then use poly-transfections to efficiently generate new insights, for example in CRISPRa and synthetic miRNA systems. Finally, we use poly-transfection to rapidly engineer a difficult-to-optimize miRNA-based cell classifier for discriminating cancerous cells. One-pot evaluation enabled by poly-transfection accelerates and simplifies the design of genetic systems, providing a new high-information strategy for interrogating biology.

Differential potentiometric precipitation titration of zinc(II) and copper(II) using carbon composite electrode

The article presents the results of investigation of potentiometric titration of the working solution containing Zn(II) and Cu(II) by sodium diethyldithiocarbamate (NaDEDC) using carbon composite electrode as the indicator electrode. The proposed method for the separate determination of copper ions (II) and zinc (II) under the joint presence was tested on data from titration model of binary mixtures and the real object. The titration curves were processed by the linearization method based on the transformation of a titration curve into the multiphase linear regression, whose parameters determine the equivalence point with high accuracy.

STUDY THE CHARACTERISTIES Of VARIABLE CHARGES OF SOME SELECTED SOILS FROM NORTHERN IRAQ

This study was carried out in three selected areas from North Iraq included (Makhmour, Shikhan and Zakho).these location Varied in annual temperature and rainfall .Nine soil samples were collected from three soil profiles (one soil profile from each location). Clay was separated without using any corrosive acid or base, except sodium acetate in order to remove calcium carbonate. Variable charge (pH-dependent charge) was measured using potentiometric titration. Results from titration curves showed a clear variations in positions of (ZPC) and the amounts of negative and positive charges from different samples. The extent of (ZPC) varies from (pH 4.4-5.8).However the amount of negative varies between(100-180) Cmole/kg. and the positive charge between(150-350) C.mole/kg. These variations in potentiometric titration curves are partially related to the presence of varying amounts of iron oxides and also the variations in type of minerals dominant in clay samples .In addition to that, there is a possibility of the presence of some calcium carbonate in clay that not completely removed by treatments with sodium-acetate.

Suboptimal stimulation by weak agonist epitope variants does not drive dysfunction of HIV-1-specific cytotoxic T lymphocyte clones.

To assess whether weakly recognized epitope variants induce anergy in HIV-1-specific CD8 T lymphocyte (CTL) clones as a mechanism of dysfunction. HIV-1-specific CTL clones were exposed to suboptimally recognized epitope variants, and screened for anergy and other T-cell dysfunction markers, and subsequent capability to kill target cells bearing index epitope. In addition to the optimally recognized index epitope, two suboptimally recognized epitope variants were selected based on titration curves for killing of peptide-labeled target cells by three HIV-1-specific CTL clones targeting the epitopes SLYNTVATL (Gag 77-85, A02-restricted), RPAEPVPLQL (Rev 66-75, B07-restricted), and KRWIIMGLNK (Gag 263-272, B27-restricted). Consequences of suboptimal stimulation were assessed by cytokine secretion, gene expression, and capacity to kill index epitope-labeled target cells upon rechallenge. Suboptimal recognition of epitope variants reduced cytokine production by CTL similarly to reduction in killing of target cells. Gene expression profiles after suboptimal stimulation demonstrated no patterns consistent with T-cell dysfunction due to anergy, exhaustion, or apoptosis. Preexposure of CTL to epitope variants had no discernable impact on their subsequent capacity to kill index epitope-bearing target cells. Our data explore the hypothesis that poorly recognized epitope variants not only facilitate HIV-1 evasion of CTL recognition, but also induce CTL dysfunction through suboptimal signaling causing anergy. However, the results do not suggest that suboptimal signaling induces anergy (or exhaustion or apoptosis), indicating that the major role of CTL epitope variation is likely viral escape.

Mechanically robust and highly methanol-resistant sulfonated poly(ether ether ketone)/poly(vinylidene fluoride) nanofiber composite membranes for direct methanol fuel cells

As a key component of direct methanol fuel cells (DMFCs), proton exchange membranes (PEMs) are required to be mechanically robust, methanol-resistant, and conductive to protons. In this work, a novel sulfonated poly(ether ether ketone) (SPEEK) impregnated poly(vinylidene fluoride) (PVDF) electrospun nanofiber membrane was prepared. To avoid the collapse of PVDF fiber framework by the solvent of SPEEK, we designed a SPEEK/solvent/nonsolvent ternary filling system through the cloud point titration curves. Meanwhile, polydopamine (PDA), an extraordinarily adhesive and hydrophilic material, was coated on the surface of PVDF nanofibers to further improve the interface bonding between SPEEK and PVDF. The introduction of PVDF nanofibers completely changed the rigidity of SPEEK thus achieving a 5.4-fold increase of toughness when compared with that of pure SPEEK at dry state. Notably, significantly improved methanol barrier ability was also obtained due to the tortuous methanol crossover pathways caused by the embedded PVDF nanofibers. In the DMFC tests, the ultra-low methanol permeability and relatively high proton conductivity of the obtained composite membrane made it could be operated with 5 M methanol fuel and showed a peak power density of 104.0 mW cm−2, which was higher than the values of 89.3 mW cm−2 (2 M methanol) and 84.0 mW cm−2 (5 M methanol) recorded with commercial Nafion 115 membrane.

Sonication-assisted Layer-by-Layer self-assembly nanoparticles for resveratrol delivery.

This paper advances the development of a novel drug nanodelivery solution to the oral administration of resveratrol (RSV), a low soluble drug whose recognized therapeutic applications are circumscribed when administered in the free compound form. Layer-by-Layer (LbL) self-assembly is an emergent nanotechnology proposed to address this concern with means to afford control over key formulation parameters, which are able to ultimately promote an improved pharmacokinetics. LbL self-assembly consists in the sequential adsorption of oppositely charged polyelectrolytes upon a low soluble drug nanoparticle (NP) template, giving rise to onion-like multilayered nanoarchitectures. In this work, RSV nanoprecipitation followed by LbL self-assembly of polyelectrolytes, led by a washless approach, was carried out by using the cationic poly(allylamine hydrochloride) (PAH) and the anionic dextran sulfate (DS) as polyelectrolytes towards the nanoencapsulation of RSV. Each saturated polyelectrolyte layer deposition involved the rigorous polyelectrolyte concentration assessment which was accomplished by tracing titration curves. This way, aqueous RSV nanocores and RSV LbL nanoformulations with a distinct number of PAH/DS bilayers were developed, including 2.5 (RSV-(PAH/DS)2.5 NPs), 5.5 (RSV-(PAH/DS)5.5 NPs) and 7.5 (RSV-(PAH/DS)7.5 NPs) bilayered nanoformulations. Homogenous particle size distributions at the desired nanoscale interval (ca. 116-220 nm; polydispersity index below 0.15), good colloidal (zeta potential magnitudes ca. ± 20-30 mV) and chemical stabilizations, high encapsulation efficiency (above 90%) together with an excellent cytocompatibility with Caco-2 cells (cell viability above 90%) were observed for all the nanoformulations. Eventfully, LbL NPs promoted a controlled release of RSV pursuant to the number of polyelectrolyte bilayers under simulated gastrointestinal conditions, particularly in the intestine medium, emphasizing their biopharmaceutical advantage. Our findings manifestly pinpoint that LbL PAH/DS NPs constitute a promising nanodelivery system for the oral delivery of RSV, providing a rational strategy to enlarge the implementation range of this interesting polyphenol, which is possibly the most actively investigated phytochemical worldwide.

Preparation and study of silica and APTES–silica-modified NiFe2O4 nanocomposites for removal of Cu2+ and Zn2+ ions from aqueous solutions

Silica and (3-aminopropyl)triethoxysilane (APTES)–silica-modified NiFe2O4 samples were successfully synthesized by a two-/three-step process, depending on the sample, including the preparation of nickel ferrite sample by hydrothermal synthesis, the coating of its surface with silica, and the subsequent functionalization with APTES. Samples were characterized by X-ray diffraction (XRD), Fourier transform-infrared (FTIR) analysis, transmission electron microscopy, and M–H curves. XRD data of the NiFe2O4 sample shows diffraction maxima that can be indexed in a cubic symmetry of space group Fd-3m with Z = 8, compatible with an inverse spinel-type structure. The estimated average crystalline size is 22 nm. All FTIR spectra show absorption bands between 600 and 400 cm−1, characteristic of spinel-type structure. Bands attributed to the vibration of O–Si–O and Si–O–Si bonds are found in the spectra of the silica-coated samples. APTES–silica-modified NiFe2O4 nanocomposites show an increase in coating thickness as the reaction time with tetraethoxysilane increases. A practically superparamagnetic behavior was found for the synthesized NiFe2O4 sample with a magnetization of 47 emu/g. This value is slightly reduced with the thickness of the nonmagnetic coating. The ultraviolet–visible spectroscopy measurements and titration curves clearly demonstrated that the APTES–silica-modified NiFe2O4 nanocomposites could be efficient materials for the removal of Cu2+ and Zn2+ ions from aqueous solutions. The best adsorption is found in the NiFe2O4@SiO2(3)–APTES(6) sample, while the NiFe2O4@SiO2(6)–APTES(12) sample seems to be the most suitable for its application, considering its better adsorption capacity and its easy separation from the aqueous solution in the presence of an external magnetic field.

Hydrophobic nanoprecipitates formed by benzoylphenylureas and β-cyclodextrin inclusion compounds: synthesis, characterization and toxicity against aedes aegypti larvae

The aim of this work was to synthesize and characterize the inclusion compounds formed by the complexation of β-cyclodextrin (βCD) with insecticides from the class of benzoylphenylureas (BPUs), named novaluron (NOV) and diflubenzuron (DIF), beyond evaluate their larvicidal activity against Aedes aegypti larvae. Solid state characterization by FTIR showed changes in the main peaks of BPUs and βCD, suggesting the formation of inclusion compounds in solid phase. DTA and TGA thermal analysis showed changes in temperatures of BPUs decomposition as result of molecular interactions. 1H NMR experiments allowed to observe the occurrence of interactions in solution through changes in chemical shifts of BPUs aromatic hydrogens. However, the presence of H–H intermolecular correlations in 2D ROESY was found only for the DIF/βCD complex, suggesting different topology for each complex. Such hypothesis was corroborated by thermodynamic analysis using ITC, which showed different profile of titration curves, beyond endothermic and exothermic interactions for NOV/βCD and DIF/βCD complexes, respectively. DLS titrations of BPUs or BPUs/βCD DMSO solutions in aqueous solution demonstrated that the spontaneously formed hydrophobic nanoprecipitates (HNPs) have different profile of sizes depending on the BPU/βCD system, corroborating also with the hypothesis about the existence of different topologies for each complex. Finally, the HNPs of inclusion compounds showed to be more efficient than free BPUs, allowing proposing a new insecticide formulation.

Measuring and simulating pH buffer capacity of calcareous soils using empirical and mechanistic models

ABSTRACTWe studied (i) the pH buffer capacity (pHBC) of calcareous soils varied widely in calcite and texture, (ii) the contribution of soil properties to pHBC and (iii) the significance of using a model based on calcite dissolution to estimate the pHBC of calcareous soils. The pHBC of soils was measured by adding several rates of HCl to soils (100–6500 mM H+ kg–1), in a 0.01 M CaCl2 background and an equilibration time of 24 h. The pHBC (mM H+ kg–1 pH−1) varied from 55 to 3383, with the mean of 1073. The pHBC of the soils was strongly correlated with soil CaCO3 equivalent (calcite) (r = 0.94), sand (r = −0.72), silt (r = 0.60), EC (r = 0.63), pH (r = 0.55), and weakly (r = 0.37) but significantly with clay content. The attained pHBC values indicated that calcite was probably the main buffer system in these soils. The chemical equilibrium model successfully predicted pH titration curves based on calcite dissolution, indicating buffering of acid inputs in the calcareous soils is dominated by calcite dissolution. The model can be used to simulate acidification of calcareous soils and to provide information for making environmental management decisions.

Comparative analysis of the metal-dependent structural and functional properties of mouse and human SMP30.

Senescence Marker Protein (SMP30) is a metalloenzyme that shows lactonase activity in the ascorbic acid (AA) biosynthesis pathway in non-primate mammals such as a mouse. However, AA biosynthesis does not occur in the primates including humans. Several studies have shown the role of SMP30 in maintaining calcium homeostasis in mammals. In addition, it is also reported to have promiscuous enzyme activity with an organophosphate (OP) substrate. Hence, this study aims to recombinantly express and purify the SMP30 proteins from both mouse and human, and to study their structural alterations and functional deviations in the presence of different divalent metals. For this, mouse SMP30 (MoSMP30) as well as human SMP30 (HuSMP30) were cloned in the bacterial expression vector. Proteins were overexpressed and purified from soluble fractions as well as from inclusion bodies as these proteins were expressed largely in insoluble fractions. The purified proteins were used to study the folding conformations in the presence of different divalent cations (Ca2+, Co2+, Mg2+, and Zn2+) with the help of circular dichroism (CD) spectroscopy. It was observed that both MoSMP30 and HuSMP30 acquired native folding conformations. To study the metal-binding affinity, dissociation constant (Kd values) were calculated from UV-VIS titration curve, which showed the highest affinity of MoSMP30 with Zn2+. However, HuSMP30 showed the highest affinity with Ca2+, suggesting the importance of HuSMP30 in maintaining calcium homeostasis. Enzyme kinetics were performed with γ-Thiobutyrolactone and Demeton-S in the presence of different divalent cations. Interestingly, both the proteins showed lactonase activity in the presence of Ca2+. In addition, MoSMP30 and HuSMP30 also showed lactonase activity in the presence of Co2+ and Zn2+ respectively. Moreover, both the proteins showed OP hydrolase activities in the presence of Ca2+ as well as Zn2+, suggesting the metal-dependent promiscuous nature of SMP30.

ExEm-FRET two-hybrid assay: FRET two-hybrid assay based on linear unmixing of excitation-emission spectra.

Simultaneous linear unmixing of excitation-emission spectra (ExEm-unmixing)-based fluorescence resonance energy transfer (FRET) two-hybrid assay method, named as ExEm-FRET two-hybrid assay, was developed for evaluating the stoichiometric ratio of macromolecular complexes in living cells. Linear unmixing of the excitation-emission spectra (SDA) of cells obtains the weight factors of donor (WD), acceptor (WA) and acceptor sensitization (WS), yielding ED and EA (donor- and acceptor-centric FRET efficiency) images. ExEm-FRET two-hybrid assay employs pixel-to-pixel titration curves of ED/EA versus the free acceptor (Ca)/donor (Cd) concentration deduced from the three weight factors to obtain EA,max and ED,max (the maximal EA and ED), thus yielding the stoichiometric ratio (EA,max/ED,max) of donor-tagged protein to acceptor-tagged protein.

A novel dual-channel Schiff base fluorescent chemo-sensor for Zn2+ and Ca2+ recognition: Synthesis, mechanism and application

A novel multifunctional chemo-sensor (RHCS-NH2), incorporating Schiff base, rhodamine B hydrazide, hydrazine hydrate group into triazine, was successfully designed and synthesized. It was found that the RHCS-NH2 sensor displays immediate multi-response toward Ca2+ in CH3CN-H2O (v/v = 9/1, Tris-HCl pH 7.0) and Zn2+ in DMF-H2O (95/5, v/v). Under the optimized conditions, the linear range of identifing Ca2+ ions are from 0.01 to 10.0 μM in CH3CN-H2O (v/v = 9/1, Tris-HCl pH 7.0), 0.03–10.0 μM for Zn2+ ions in DMF-H2O (95/5, v/v), and the detection limit were measured to be 0.10 nM for Ca2+ and 0.14 nM for Zn2+, respectively. The reaction mechanism between RHCS-NH2 and metal ions was investigated in detail based on fluorescence titration, Job's plots and 1H NMR titration curve, ESI-MS measurement and theoretical calculation respectively. Simultaneously, 3-(4,5)-dimethylthiahiazo(-z-y1)-3,5-di-phenytetrazoliumromide (MTT) assays and inverted fluorescence microscopy imaging also demonstrated that the probe has well cell membrane permeability and hypotoxicity, indicating its potential applicability in vitro.

Determination of Antioxidant Additive and its Decomposition Products in Working Motor Fuels

Sulfur compounds are formed during the oxidation of motor oil under the influence of high temperatures, and it is quite difficult to determine the residual content of an active additive. To determine the DF-11 additive the M-10G2k oil was oxidized in a thermostat. It was established that with oxidation times of 8 and 10 hours it is only possible to determine the amount of mercaptan sulfur from the potentiometric titration curve. An algorithm and some methods of determination that make it possible to predict the wear and service life of lubricating oil are proposed for complete determination of sulfur-containing compounds in oxidized oil under working conditions.

Белок-полиэлектролитные комплексы. Часть 3. Комплексы бычьего сывороточного альбумина с сульфонатсодержащими ароматическими поли- и сополиамидами

The interaction of bovine serum albumin in aqueous solution with sulfonate-containing poly- and copolyamides were studied. It was shown that, as a result of macromolecular reactions protein-polyelectrolyte complexes forms, stabilized mainly by electrostatic forces. To characterize the protein-polyelectrolyte complexes composition the r parameter used, which is defines as the ratio of mass concentration of polyelectrolyte and protein. It was shown that the main factor determining the composition and structure of forming protein-polyelectrolyte complexes is the degree of ionization of functional groups, interacting in the polyelectrolyte reaction that is determined by the nature of those groups and the pH of the solution. The presen ce of sulfonate and carboxylic groups in the copolyamide composition gives an extra opportunity to regulate the protein-polyelectrolyte interactions. Using spectrophotometry were established that, in the studied system when the aromatic polyamide and bovine serum albumin are mixed at optimal pH conditions (рН < 4.9), complexes are formed, the composition of which corresponds to the value of r ~ 0.15 g/g. The degree of conversation in protein-polyelectrolyte reactions is close to 0.8. The size of the formed particles was about 2.2 μm. In the case of aromatic copolyamides that contain both sulfonate and carboxylic groups, an increase in concentration of carboxylic groups to 42 mol. % leads to a shift of the optical density maximum on the curve of turbidimetric titration in to the higher r values (~ 0.18 g/g) at pH = 3.5, when the carboxylic groups are non-ionized. The size of the formed complex particles was about ~ 150.0 nm, the fraction of micron-sized particles is about 5%. The degree of released protein is based on the conditions under which reaction take place and varies from 93 to 99%. The result obtained during this work can serve as a base for the effective methods of isolation and purifying of the target proteins development.

Ribosomal and non-ribosomal PCR targets for the detection of low-density and mixed malaria infections

BackgroundThe unexpected high proportion of submicroscopic malaria infections in areas with low transmission intensity challenges the control and elimination of malaria in the Americas. The current PCR-based assays present limitations as most protocols still rely on amplification of few-copies target gene. Here, the hypothesis was that amplification of different plasmodial targets—ribosomal (18S rRNA) and non-ribosomal multi-copy sequences (Pvr47 for Plasmodium vivax and Pfr364 for Plasmodium falciparum)—could increase the chances of detecting submicroscopic malaria infection.MethodsA non-ribosomal real-time PCR assay targeting Pvr47/Pfr364 (NR-qPCR) was established and compared with three additional PCR protocols, two of them based on 18S rRNA gene amplification (Nested-PCR and R-qPCR) and one based on Pvr47/Pfr364 targets (NR-cPCR). The limit of detection of each PCR protocol, at single and artificial mixed P. vivax/P. falciparum infections, was determined by end-point titration curves. Field samples from clinical (n = 110) and subclinical (n = 324) malaria infections were used to evaluate the impact of using multiple molecular targets to detect malaria infections.ResultsThe results demonstrated that an association of ribosomal and non-ribosomal targets did not increase sensitivity to detect submicroscopic malaria infections. Despite of that, artificial mixed-malaria infections demonstrated that the NR-qPCR was the most sensitive protocol to detect low-levels of P. vivax/P. falciparum co-infections. Field studies confirmed that submicroscopic malaria represented a large proportion (up to 77%) of infections among asymptomatic Amazonian residents, with a high proportion of infections (~ 20%) identified only by the NR-qPCR.ConclusionsThis study presents a new species-specific non-ribosomal PCR assay with potential to identify low-density P. vivax and P. falciparum infections. As the majority of subclinical infections was caused by P. vivax, the commonest form of malaria in the Amazon area, future studies should investigate the potential of Pvr47/Pfr364 to detect mixed-malaria infections in the field.

Physicochemical Properties of the System N,N-Dimethyl-dipropylene-diamino-triacetonediamine (EvA34), Water, and Carbon Dioxide for Reactive Absorption

Aqueous solutions of N,N-dimethyl-dipropylene-diamino-triacetonediamine (EvA34) are promising solvents for CO2 capture. Therefore, in the present work, a comprehensive experimental study was carried out to determine data on physicochemical properties of EvA34 and its mixtures with H2O and CO2. The liquid density and the dynamic viscosity were studied for pure EvA34, as well as for unloaded and CO2-loaded aqueous solutions of EvA34. The liquid heat capacity was studied for pure EvA34 and unloaded aqueous solutions of EvA34. Furthermore, data on the vapor pressure of pure EvA34 was recorded. The pH value was measured for unloaded and CO2-loaded aqueous solutions of EvA34, and the dissociation constants of EvA34 were determined from titration curves. Moreover, data on the solubility of CO2 in aqueous solutions of EvA34 and data on the CO2-containing species in the liquid phase of these solutions were recorded. Most of the new data were taken at temperatures between 293 and 393 K. The mass fraction of EvA34 i...

A Simple and Rapid Method to Determine Sulfonation Degree of Lignosulfonates

Sulfonation degree is an important structural parameter of lignosulfonates which affect their water solubility, surface activity, and dispersing performance. Presently, the methods for determining sulfonation degree include elemental analysis and potentiometric titration; they have some shortcomings such as complex purification process, high equipment requirements, and time-consuming. Hence, a simple and rapid method to determine the sulfonation degree of lignosulfonates was proposed based on the electrostatic interaction between cationic surfactant (hexadecyl trimethyl ammonium bromide (CTAB)) and anionic lignosulfonates. CTAB was added and co-precipitated with lignosulfonates and then the ultraviolet absorbance of the supernatant was determined. The sulfonation degree of lignosulfonates was calculated according to the titration curve of the supernatant absorbance to the amount of CTAB. This method is applicable to lignosulfonates recovered from acid pulping as well as sulfonation products of alkali lignin. Because of the easy operation process and no purification process for lignosulfonates, this method was simple and rapid when compared to existing methods for sulfonation degree determination of lignosulfonates.

Cover Feature: Spectroelectrochemical Investigation of Cholesterol Oxidase from Streptomyces lividans at Different pH Values (ChemElectroChem 8/2019)

The Cover Feature shows the gold capillary working electrode used for the spectroelectrochemical investigation of cholesterol oxidase (ChOx). The spectral changes collected during the ongoing reduction of ChOx (by mediated electron transfer, MET) in the presence of methylene blue as redox mediator are shown. Furthermore the titration curves at 374 and 454 nm for the reduction and reoxidation as well as the possible redox states of the FAD cofactor are depicted. More information can be found in the Article by M. Heinelt et al. on page 2174 in Issue 8, 2019 (DOI: 10.1002/celc.201801416).

Capillary electrophoretic apparatus for the endpoint detection in microtitration methods

Titration methods are routinely used in the laboratories for the quantification of acids and bases, for the complexometric determination of metal ions and for the ion-pair titrations of drugs in pharmaceutical control. They also find application in a wide variety of chemical and biochemical studies. However, conventional titration methods (CTM) require large amounts of samples that are not always available. In absence of micro-titrator devices, the application of these methods for expensive samples and for small batch sizes is not possible. In this work, it was demonstrated that the commercial capillary electrophoretic apparatus (CEa) can be used, in a quick and easy way, for the end-point detection in a microtitration process. The proposed methodology exploits the change of the solutions conductivity during the titrations. The equivalent points can be easily located by plotting the change in electrical current as a function of the titrant volume added. More interestingly, only 1.1–1.5 mL of analyte solutions are required to establish the titration curves. The advantages and the limitations of the procedure are discussed in detail.

A comparative study of some kaolinites surface properties

The surface properties of five kaolinites of various origins were analyzed using potentiometric titration, electrokinetic measurements and low-pressure gas adsorption associated to derivative isotherm summation (DIS) modeling. The data show that sample structure is important in determining the surface properties. The combined analytical results clearly shows the existence of a permanent negative layer charge for all the samples. The general features that could be observed for the five kaolinites are: the titration curves are shifted to lower pH with increasing ionic strength due to the layer charge; the amount of consumed proton is influenced by the permanent layer charge; although low, the permanent charge determines the electrokinetic behavior. The shape anisotropy and the charge distribution on the basal and edge surfaces are crucial parameters to understand the behavior of kaolinite particles in aqueous media. The Cameroonian sample of the set exhibits a significant permanent charge together with large specific surface area associated to fine particle size and considerable shape anisotropy.