Potentiometric Titration Measurements Research Articles

Effective Dye Degradation by Graphene Oxide Supported Manganese Oxide

Graphene oxide (GO) was used as a support for manganese oxide (MnO2) for the preparation of a nanocomposite catalyst for the degradation of an azo dye, Reactive Black 5 (RB5). The nanocomposite was characterized for the structure by XRD, for the morphology with SEM, and for the surface chemistry with FTIR and potentiometric titration measurements. The GO-MnO2 nanocomposite presented a high catalytic activity for the degradation/oxidation of RB5 at ambient conditions, which was higher than that of the pure MnO2 and could be attributed to the beneficial contribution of the manganese oxide and the graphene oxide.

Anionic polyacrylamide efficiency in goethite removal from aqueous solutions: goethite suspension destabilization by PAM

The main aim of the study was to investigate the anionic polyacrylamide (PAM) efficiency as a flocculant relative to goethite particles. This mineral is a toxic waste produced during hydrometallurgical processes and, as a result, poses a threat to the environment. In the experiments, the following analytical methods were applied: potentiometric titration, zeta potential and adsorption amount measurements, nitrogen adsorption/desorption isotherms, Fourier transform infrared spectroscopy, differential centrifugal sedimentation, UV/Vis spectrophotometry. The result analysis showed that polyacrylamide adsorbs on the goethite surface; however, its adsorption amount depends on the pH value. Due to the adsorbent–adsorbate electrostatic repulsion, the smallest number of macromolecules adsorbs at pH 9. The PAM adsorption affects the goethite surface charge and zeta potential values. It makes these parameters more negative. What is more regardless of pH value, the polymer addition contributes to clear aggregation of solid particles (suspension destabilization). Thus, PAM can be considered as a potential flocculant improving the goethite removal from aqueous wastes.

Synthesis and Aqueous Solution Properties of an Amino Bisphosphonate Methacrylate Homopolymer via RAFT Polymerization.

The present contribution reports on the synthesis via reversible addition-fragmentation chain transfer (RAFT) polymerization of a methacrylate derivative bearing an aminobisphosponate moiety as a pendant group, namely, ethyl N,N-tetramethylbis(phosphonate)-bis(methylene) amine methacrylate (MAC2NP2). The polymerization was performed by the use of cyanoisopropyl dithiobenzoate as chain transfer agent at 70 °C in various solvents with different polarities including N,N-dimethylformamide, acetonitrile, tetrahydrofuran, and in bulk. Best results were obtained in N,N-dimethylformamide where higher conversions and polymerization rates were noticed. The successful hydrolysis of the phosphonate ester groups was performed using bromotrimethylsilane with excellent yields leading to the formation of highly water soluble and pH-responsive polymers. Finally, a preliminary solution behavior study was carried out by investigating the aqueous solution properties of synthesized amino bisphosphonate methacrylate homopolymers and their phosphonic acid analogs via potentiometric titration and zeta potential measurements.

Acidic activated carbons as catalysts of biodiesel formation

Biodiesel is recognized as one of the most attractive motor vehicle fuels of the future. Therefore, technologies of its production are continuously improved and optimized. The research work reported concerns the process of biodiesel production via transesterification of vegetable oil over modified carbon catalysts obtained from waste material. In order to introduce strongly acidic groups into the carbon structure, the initial sample was treated with concentrated or fuming sulfuric acid, sodium sulfide, 4-aminobenzenesulfonic acid, phosphoric acid, or H2SO4/HNO3 mixture. The carbon materials prepared in this way were thoroughly characterized (elemental and textural analysis, potentiometric titration, TG, NMR, SEM, and XPS measurements) and then used in transesterification of rapeseed oil in the presence of methanol at 130 °C under elevated pressure. The results obtained revealed that not only sulfonic groups are capable of catalyzing transesterification reaction (FAME yield up to 60% for the best SO3H bearing sample), but also materials containing phosphate groups can successfully catalyze this process (FAME yield 43%). It was established that the carboxyl functionalities, which can be generated on the catalyst surface upon its reaction with some modification agents (e.g., H2SO4 or H2SO4/HNO3 mixture), block the active sites of the process and reduce the reaction effectiveness. The stability of the catalysts was rather poor, as they underwent deactivation in subsequent reaction cycles (mainly due to neutralization of —SO3H groups but also by their leaching); however, the catalyst regeneration was possible.

Surface Properties of Al-Functionalized Mesoporous MCM-41 and the Melting Behavior of Water in Al-MCM-41 Nanopores.

We report an experimental investigation of structural and adhesive properties for Al-containing mesoporous MCM-41 and MCM-41 surfaces. In this work, highly ordered hexagonal mesoporous structures of aluminosilica with two different Si/Al molar ratios equal to 50 and 80 and silica samples were studied; Al was incorporated into the MCM-41 structures using the direct synthesis method, with CTAB as a surfactant. The incorporation of aluminum was evidenced simultaneously without any change in the hexagonal arrangement of cylindrical mesopores. The porous materials were examined by techniques such as low-temperature nitrogen sorption, energy-dispersive spectroscopy, and scanning and transmission electron microscopy. Surface properties were determined through X-ray photoelectron spectroscopy, potentiometric titration, and static contact angle measurements. It was shown that an increase in surface acidity leads to an increase in the wetting energy of the surface. To investigate the influence of acidity on the confinement effects, the melting behavior of water in Al-MCM-41 and MCM-41 with the same pore size was determined by using dielectric relaxation spectroscopy and differential scanning calorimetry methods. We found that the melting-point depression of water in pores is larger in the functionalized pores than in pure silica pores of the same pore diameter.

Kinetic and Equilibrium Reactions of a New Heterocyclic Aqueous 4-Aminomethyltetrahydropyran (4-AMTHP) Absorbent for Post Combustion Carbon Dioxide (CO2) Capture Processes

Aqueous amine absorbent processes remain at the forefront of existing technologies for the removal of CO2 from industrial and large-scale power generation flue gas streams. It is essential that improvements in amine-based absorbent technologies are made in order to reduce both capital and operational costs. Intimate understanding of the fundamental chemical behavior of new amine absorbent systems is an intelligent pathway toward higher efficiency amine-based CO2 capture processes. Herein, we investigate and report for the first time the complete temperature-dependent kinetic and equilibrium behavior of a new heterocyclic amine 4-aminomethyltetrahydropyran (4-AMTHP), with CO2, in aqueous solutions. Stopped-flow spectrophotometry, 1H NMR spectroscopy, and potentiometric titration measurements performed over the temperature range 25.0–45.0 °C and the corresponding rate constants for the reversible formation of the carbamic acid, together with equilibrium constants describing the stability of the carbamate, and the protonation of the amine are reported here. Thermodynamic analysis of the resulting constants using the Eyring, Arrhenius, and van’t Hoff relationships has revealed the activation energies, enthalpies, and entropies for the reactions, allowing a comparison to the industrial standard monoethanolamine (MEA). From the kinetic data, the performance of 4-AMTHP was found to be superior to MEA and in line with the established Brønsted relationship between the second-order rate constant and the protonation constant or basicity of the amine. The largely negative protonation enthalpy (−47 kJ/mol), among the key chemical drivers for CO2 regeneration, is again superior to MEA (−41 kJ/mol). Together, a combination of kinetic and equilibrium properties of 4-AMTHP strongly position 4-AMTHP as a promising candidate for more intensive evaluations as a CO2 capture absorbent.

Synthesis of pH-sensitive self-assembled amphiphilic graft copolymers containing 4,4,4,3,3,2-hexafluorobutyl side chains

Novel amphiphilic graft copolymers containing 4,4,4,3,3,2-hexafluorobutyl side chains were designed and synthesized via radical polymerizaion of acrylic acid (AA), poly (ethylene glycol) methyl ether methacrylate (PEGMA) and homemade fluorinated macromonomer (PHFBMA-GMA) and the physicochemical properties of polymeric micelles prepared therefrom were investigated. GPC, FTIR and 1H NMR were employed to characterize the structures of the copolymers. Potentiometric titration measurement confirmed that the pH-sensitive segments were successfully incorporated and the copolymer performed pKa similar to the reported values. A series of random copolymers with the same chemical composition were employed to make comparisons with the graft copolymers. The critical micelle concentrations (CMC) of the copolymers at different pH (5.0 and 9.0) were determined by fluorescence spectroscopy and surface tension measurements. CMC values showed a high degree of consistency between these two methods. The results showed that CMC values for random copolymers were one magnitude order higher than that of graft copolymers. Graft copolymers performed lower CMC larger particle size compared to random copolymers. No significant difference was observed among graft or random copolymers. CMC values and particle size increased while zeta potential values showed significant decrement with increasing pH, indicating significant pH-sensitivity of the copolymers. With regard to the influence of the amount and the molecular weight of PHFBMA-GMA on the properties, increasing the amount and molecular weight of PHFBMA-GMA was prone to lower CMC, larger particle size while zeta potential performed no significant change. Transmission electron microscopy (TEM) showed that the morphological shapes of the copolymers performed spherical micelles. The cytotoxicity test showed that the comb-shaped copolymers performed extremely low cytotoxicity.The pH-sensitive self-assembled amphiphilic graft copolymers containing 4,4,4,3,3,2-hexafluorobutyl side chains could be potential candidates for nanotanks, hydrophobic drug carriers or surfactants and their facile preparation might fit for large scale industrialization.

Effect of the reduction degree of graphene oxide on the adsorption of Bisphenol A

Graphite oxide (GO) was reduced to different reduction degrees by using hydrazine hydrate and finally to graphene using NH4OH. The obtained materials were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), nitrogen adsorption (BET), Fourier transform infrared spectroscopy (FTIR) and potentiometric titration measurements. Their adsorption performance for Bisphenol A (BPA) was evaluated taking into account pH, ionic strength, kinetics initial ion concentration and thermodynamics of adsorption. The adsorption capacities were increased with increasing the reduction degree of GO with the maximum adsorption capacity (Qmax=94.06mg/g) to be presented by Graphene that was the result of the optimum reduction degree. The adsorption followed pseudo-second order kinetics and the thermodynamic analysis indicated that it was spontaneous and endothermic. The increase in the degree of GO reduction reduced the amount of oxygen-containing functional groups on the surface of reduced samples, resulting to the increase of the π–π interaction between sorbent–adsorbate and to linear increase of adsorption capacity.

Theoretically nanoscale study on ionization of muscimol nano drug in aqueous solution

In the present work, acid dissociation constant (pKa) values of muscimol derivatives were calculated using the Density Functional Theory (DFT) method. In this regard, free energy values of neutral, protonated and deprotonated species of muscimol were calculated in water at the B3LYP/6-31G(d) basis sets. The hydrogen bond formation of all species had been analyzed using the Tomasi's method. It was revealed that the theoretically calculated pKa values were in a good agreement with the existing experimental pKa values, which were determined from capillary electrophoresis, potentiometric titration and UV-visible spectrophotometric measurements.

Concentration-related response potentiometric titrations to study the interaction of small molecules with large biomolecules.

In the present paper, the utility of a special potentiometric titration approach for recognition and calculation of biomolecule/small-molecule interactions is reported. This approach is fast, sensitive, reproducible, and inexpensive in comparison to the other methods for the determination of the association constant values (Ka) and the interaction energies (ΔG). The potentiometric titration measurement is based on the use of a classical polymeric membrane indicator electrode in a solution of the small-molecule ligand. The biomolecule is used as a titrant. The potential is measured versus a reference electrode and transformed into a concentration-related signal over the entire concentration interval, also at low concentrations, where the millivolt (y-axis) versus log canalyte (x-axis) potentiometric calibration curve is not linear. In the procedure, Ka is calculated for the interaction of cocaine with a cocaine binding aptamer and with an anticocaine antibody. To study the selectivity and cross-reactivity, other oligonucleotides and aptamers are tested, as well as other small ligand molecules such as tetrakis(4-chlorophenyl)borate, metergoline, lidocaine, and bromhexine. The calculated Ka compared favorably to the value reported in the literature using surface plasmon resonance. The potentiometric titration approach called "concentration-related response potentiometry" is used to study molecular interaction for seven macromolecular target molecules and four small-molecule ligands.

New insights into the early stages of silica-controlled barium carbonate crystallisation.

Recent work has demonstrated that the dynamic interplay between silica and carbonate during co-precipitation can result in the self-assembly of unusual, highly complex crystal architectures with morphologies and textures resembling those typically displayed by biogenic minerals. These so-called biomorphs were shown to be composed of uniform elongated carbonate nanoparticles that are arranged according to a specific order over mesoscopic scales. In the present study, we have investigated the circumstances leading to the continuous formation and stabilisation of such well-defined nanometric building units in these inorganic systems. For this purpose, in situ potentiometric titration measurements were carried out in order to monitor and quantify the influence of silica on both the nucleation and early growth stages of barium carbonate crystallisation in alkaline media at constant pH. Complementarily, the nature and composition of particles occurring at different times in samples under various conditions were characterised ex situ by means of high-resolution electron microscopy and elemental analysis. The collected data clearly evidence that added silica affects carbonate crystallisation from the very beginning (i.e. already prior to, during, and shortly after nucleation), eventually arresting growth on the nanoscale by cementation of BaCO3 particles within a siliceous matrix. Our findings thus shed light on the fundamental processes driving bottom-up self-organisation in silica-carbonate materials and, for the first time, provide direct experimental proof that silicate species are responsible for the miniaturisation of carbonate crystals during growth of biomorphs, hence confirming previously discussed theoretical models for their formation mechanism.

Effect of layer (calcium phosphate–chitosan)-by-layer (mesquite gum) matrix on carotenoids-in-water-emulsion properties

Layer-by-layer calcium phosphate (CP)–chitosan (Ch)/mesquite gum (MG) matrixes were designed for protecting and stabilizing red chili oleoresin-in-water emulsions. Potentiometric titration, turbidity and ζ-potential measurements were used for establishing the interaction windows for obtaining CP–Ch complexes. The CP–Ch mass ratio of 1.24 showed the maximum soluble complex formation and a positive charge (∼18.5 mV) for allow the interaction with MG. Then, red chili oleoresin-in-water emulsions were formed by a layer-by-layer deposition of MG/CP–Ch complexes (C/WRMG/CP–Ch). The results show that high mass ratio of MG was required to form a dense interfacial layer to improve the stability of the system. The droplet size distribution remained unchanged up to 720 h. Rheological measurements of C/WRMG/CP–Ch indicate that both, the storage (G′) and loss (G″) moduli showed increasing values with frequency (∼0.4–11.0 Hz) independently of shear strain applied (1, 5, 10%), attributed to the formation of MG/CP–Ch interlinked network in the continuous phase. The emulsion providing best stability and protection against carotenoid degradation was that made with CP–Ch mass ratio of 1.24 and MG/CP–Ch mass ratio of 10. The mean half-time life of the C/W10 was 502 days compared to 0.24 days for the free unprotected carotenoids.

The impact of two –GlyProGly– motifs on formation of di-copper complexes by His4-cyclopeptides

The interactions of copper(II) ions with the macrocyclic peptide, c(HKHGPG)2, were investigated in aqueous solution as a function of pH by potentiometric titration, spectroscopic (UV-Vis, CD, and EPR) and mass spectrometry (ESI-MS) measurements. The experiments were conducted for two different ligand to metal ratios: 1 : 1 and 1 : 2. The present study reveals that below pH 6 only mononuclear complexes exist in the case of both systems (L : Cu(II) = 1 : 1, L : Cu(II) = 1 : 2). However, in an alkaline medium dinuclear forms are preferred, which are dominant in the system containing two equiv. of copper(II). Under basic conditions the {2NIm, 2Nam−} coordination mode is favored. Furthermore, a molecular modeling study was performed in order to characterize structural aspects of the formation of di-copper(II) complexes by His4-cyclopeptides. The comparison of coordination properties of c(HKHP)2 and c(HKHGPG)2 allowed to characterize the impact of two –GlyProGly– motifs on formation of di-copper complexes by His4-cyclopeptides.

Application of the zeta potential measurements to explanation of colloidal Cr2O3 stability mechanism in the presence of the ionic polyamino acids.

In the presented paper, the influence of the molecular weight and the type of polyamino acid functional groups on the electrokinetic properties and the stability of chromium (III) oxide suspension were examined. Analysis of the data obtained from the adsorption, potentiometric titration, zeta potential, and stability measurements allows to propose stabilization or destabilization mechanism of the studied systems. In the studies, there were used polyamino acids with different ionic characters: anionic polyaspartic acid and cationic polylysine. The measurements showed that the zeta potential depends on the concentration and molecular weight of the applied polymer. Stability of the chromium (III) oxide suspensions in the presence of ionic polyamino acids increases compared to the results obtained in the absence of polymers. The exception is LYS 4,900 at pH = 10. Under these conditions, the decrease in stability is observed due to formation of polymer bridges between the polymer chains adsorbed on different colloidal particles. Determination of the stabilization/destabilization mechanism of the polyamino acid/chromium (III) oxide system and examination of the effects of polymer molecular weight on the stabilization properties can contribute to a wider use of this group of compounds as potential stabilizers or flocculants in many industrial suspensions.

Preparation and characterization of carboxymethyl derivatives of yeast mannans in aqueous solutions

Novel carboxymethyl derivatives of yeast mannans of different degrees of substitution (DS) were prepared by optimized reaction of concentrated polysaccharides in alkaline aqueous solution. Mannans from various yeasts differing in size and degree of branching show similar reactivity. Strong alkaline conditions during carboxymethylation caused degradation of the polysaccharides. The degree of substitution (DS) of Candida albicans mannan and dextran were proportional to the amount of monochloroacetate added. However, degrees of carboxymethylation of Candida albicans mannan (0.30, 0.41, 0.73) were lower than those of dextran (DS=0.33, 0.6, 1.1) using the same amounts of monochloroacetate. Evidently the resulted polyanionic derivatives have higher hydrodynamic sizes than the original polysaccharides. Non-uniform, variable position of substitutions results to non-proportional change of optical rotation and increase of complexity of NMR spectra. Basic physico-chemical characteristics of novel carboxymethyl mannans obtained by potentiometric titration, FT-IR, UV, HPLC, 1H NMR and optical rotation measurements are presented here.

Characterization of sulfhydryl sites within bacterial cell envelopes using selective site-blocking and potentiometric titrations

In this study, a novel approach was developed to estimate the concentration and acidity constants of sulfhydryl sites within bacterial cell envelopes, and we apply the approach to compare sulfhydryl site concentrations of Bacillus licheniformis, Bacillus subtilis, Bacillus cereus, Shewanella oneidensis and Pseudomonas fluorescens. The experiments involved the selective blocking of sulfhydryl sites using a thiol-specific molecule, coupled with total site concentration comparisons of blocked and un-blocked bacterial samples by potentiometric titration measurements to determine sulfhydryl concentrations. All five species studied contained measureable concentrations of sulfhydryl sites, ranging from 16.6±3.3μmol/g for B. cereus to 33.1±7.6μmol/g for S. oneidensis. No significant difference was found between sulfhydryl site concentrations on Gram-positive species relative to those on Gram-negative bacteria. However, the proportion of sulfhydryl sites relative to the total sites on each species was the highest for the thermophilic bacterium B. licheniformis with 14±3%, and the four mesophilic species exhibited an average of 8±2%. All species contained sulfhydryl sites with a pKa of 9.2–9.4, but B. subtilis and P. fluorescens exhibited significant concentrations of sulfhydryl sites with much lower pKa values as well. Our results suggest that sulfhydryl sites are present in relatively low concentrations over a wide range of bacterial diversity, but that their concentrations are high enough to control the binding of metals onto bacteria under low metal-loading conditions.

Acid–base behavior and Al3+ complex formation of synthesized 2,3-dihydroxyterephthalic acid (DHTPA) at pH 3 as a model compound of Inogashira fulvic acid (IFA)

The interaction between the aluminum ion (Al3+) and Inogashira fulvic acid (IFA) at pH 3 was investigated using the calibration curve method for 27Al NMR spectra. The average conditional stability constant (logK) can be calculated to be 2.00–2.04 (M−1) (bidentate–monodentate) from the results of 27Al NMR measurements. In addition, because IFA has various coordination sites, including COOH, phenolic and/or alcoholic OH groups, we attempted to synthesize 2,3-dihydroxyterephthalic acid (DHTPA) as a model compound with the functional groups of IFA for the investigation of the microscopic coordination mechanism between Al3+ and IFA by potentiometric titration and 27Al NMR measurements. The pKai values of DHTPA could be determined successfully (pKa1=2.3, pKa2=3.4 and pKa3=7.2; pKa4 was not determined), and these values indicate that DHTPA can act as a powerful chelating ligand, even at pH 3. DHTPA can interact with Al3+, and it predominantly forms 1:1 and 2:1 Al–DHTPA complexes. The calculated average conditional formation constant (logK1 and K2) of each complex can be determined as 1.09 (1:1) and 4.81 (M−1) (2:1). The results obtained showed that both the 1:1 and 2:1 Al–DHTPA complexes are formed and Al3+ interacts with IFA at pH3.

Experimental investigation on chloride diffusion and binding in concrete containing metakaolin

In this paper, the effects of metakaolin addition on the compressive strength and chloride penetrability were studied. The study focused on the diffusion of the free and total chloride in concrete containing metakaolin (MK), which was measured by a potentiometric titration measurement. Effect of MK and sulphate on chloride binding capability was investigated, and Friedel’s salt was identified by X-ray diffraction and differential scanning calorimetry. The compressive strength increased with the addition of MK. Metakaolin decreased both the permeability of concrete and the free chloride, and increased the chloride binding capability greatly. The mechanism is that MK reduced the porosity and optimised the pore structure. The addition of MK favoured the formation of Friedel’s salts. However, sulphate decreased the chloride binding capability of concrete containing MK due to the formation of ettringite.

Studies of conformational preferences of derivatives fragments of protein G (1IGD) using temperature dependent potentiometric titration methodology

The pKa values of charged amino-acid groups present in the sequences of the peptide excised from the C terminal hairpin of B3 domain of the immunoglobulin binding protein G from Streptococcus (1IGD 51-56): Ac-DDATKT-NH2 (Dag1) and its variants: Ac-DVATKT-NH2 (Dag2) and Ac-OVATKT-NH2 (Dag3), where D, A, T, K, V, and O denote aspartic acid, alanine, threonine, lysine, valine, and ornithine, respectively, were determined by potentiometric titration measurements at three different temperatures. Our previous studies have shown that the presence of charged amino acid residues at opposite ends of a short peptide chain can stabilize the structure. The values of ΔH and ΔS and the folding-unfolding transition temperatures calculated from the CD are in good agreement with those obtained from the DSC measurements, which indicates that the major conformational transition is associated with turn formation. The measured pKa values of Dag1, Dag2 and Dag3, except for pKa1 of Dag2, decrease with increasing temperature as expected, because deprotonation in water of these groups is an endothermic process. For Dag1 and Dag2, the pKa1 values are lower than that of the reference compound (acetic acid), which suggests the formation of a salt bridge in both peptides. The folding-unfolding transition enthalpy of Dag1 is remarkably greater than those of Dag2 and Dag3, which suggests that this compound has the most stable structure in water.

Influence of surface conductivity on the apparent zeta potential of amorphous silica nanoparticles

Zeta potential is a physicochemical parameter of particular importance in describing ion adsorption and double layer interactions between charged particles. However, for metal-oxide nanoparticles, the conversion of electrophoretic mobility measurements into zeta potentials is difficult. This is due to their very high surface electrical conductivity, which is inversely proportional to the size of the particle. When surface conductivity is similar to or higher than the electrical conductivity of bulk water, it can significantly lower the electrophoretic mobility of the particles. It follows that the magnitude of the apparent zeta potential determined from the Smoluchowski equation (disregarding surface conductivity) can be grossly underestimated. We use a basic Stern model to describe the electrochemical properties and to calculate the true zeta potential of amorphous silica nanoparticles immersed in NaCl solution. The parameters of our surface complexation model are adjusted by potentiometric titration and electrophoretic mobility measurements at high salinity (10−1M NaCl). Electrophoretic mobilities are calculated using Henry’s electrokinetic transport model with specific surface conductivities and zeta potentials estimated by our surface complexation model. The very good agreement of calculated and measured electrophoretic mobilities confirms that the true zeta potential corresponds to the electrical potential at the outer Helmholtz plane (OHP). Consequently, the shear plane might be located close to the OHP. The assumption of the presence of a stagnant diffuse layer at the amorphous silica/water interface is therefore not required.