Formation Constants Research Articles

Recognition of halide anions by N,N’-bis(4-nitrophenyl)urea in the gas-phase and solution: a computational study

ABSTRACT This study investigates the recognition of halide anions by N,N’-bis(4-nitrophenyl)urea using computational methods in both gas-phase and solution. It examines interaction, stabilization, and deformation energies, revealing a gas-phase selectivity trend of [L⋯F]−>[L⋯Cl]−>[L⋯Br]−>[L⋯I]−. NBO, QTAIM, and EDA-NOCV analyses highlight N-H∙∙∙X hydrogen bonds, with electrostatic forces contributing around 60% to the total interaction. Despite unfavorable solvation energy changes, the intrinsic affinity remains the main factor for selectivity, which aligns with experimental data. The strong correlation between theoretical and experimental formation constants supports the reliability of the computational findings.

Dual‐Phase Enabled Sinusoidal Current Anodizing for Efficient Preparation of High Specific Capacitance Anode Aluminum Foils

The anodized aluminum oxide prepared by anodizing is the core of aluminum electrolytic capacitors, and its quality determines the performance of aluminum electrolytic capacitors. The traditional direct current (t‐DC) anodizing method commonly used in industrial production today with low current density has the problems of low anodizing efficiency, poor crystallinity, and high formation constants of the oxide film. However, high current density direct current anodizing has the problems of severe defects of the oxide film and much thermal dissolution of aluminum foil. Herein, the dual‐phase enabled sinusoidal current (DESC) anodizing method is proposed for the preparation of 200 V anodized aluminum foil with much higher efficiency and performance. After testing, it is found that the alumina prepared by the DESC method has higher crystallinity and fewer defects. Consequently, the specific capacitance of the DESC sample is 23% greater than that of the t‐DC anodized sample, while the former displays a lower loss angle tangent and leakage current. Meanwhile, DESC anodizing takes 60% time less than t‐DC anodizing due to its high current density. The DESC anodizing method has been identified as a promising avenue for further investigation, exhibiting high efficiency and performance.

Synthesis and Preliminary Studies for In Vitro Biological Activity of Two New Water-Soluble Bis(thio)carbohydrazones and Their Copper(II) and Zinc(II) Complexes

Research in the field of metallodrugs is continually increasing. However, it is often limited by the poor solubility in water of the metal complexes. To try to overcome this problem, the two new ligands bis-(sodium 3-methoxy-5-sulfonate-salicylaldehyde)thiocarbohydrazone (bis-TCH, Na2H4L1) and bis-(sodium 3-methoxy-5-sulfonate-salicylaldehyde)carbohydrazone (bis-CH, Na2H4L2) were synthesized and characterized, both achieving high solubility in water. The speciation of the ligands and their coordinating behaviour towards the biologically relevant Cu(II) and Zn(II) ions were studied spectroscopically and potentiometrically, determining the pKas of the ligands and the formation constants of the complex species. The monometallic and bimetallic Cu(II) and Zn(II) complexes were isolated, and the single-crystal X-ray structure of [Cu2(NaHL1)(H2O)7].3.5H2O was discussed. Finally, preliminary studies of the in vitro cytotoxic properties of the new compounds were started on normal (Hs27) and cancer (U937) cell lines. bis-TCH was able to induce a growth inhibition effect between 40% and 45% in both cell lines; bis-CH did not produce a reduction in cell viability in Hs27 cells but revealed mild antiproliferative activity after 72 h of treatment in U937 cancer cells (GI50 = 46.5 ± 4.94 μg/mL). Coordination of the Cu(II) ions increased the toxicity of the compounds, while, in contrast, Zn(II) complexes were not cytotoxic.

Synthesis of an Ethylenediaminetetraacetic Acid-like Ligand Based on Sucrose Scaffold and Complexation and Proton Relaxivity Studies of Its Gadolinium(III) Complex in Solution.

Sucrose constitutes a non-toxic, biodegradable, low-cost and readily available natural product. To expand its utility, we developed total synthesis for a ligand based on a sucrose scaffold for potential use as a metal chelation agent. The designed target (compound 2) has a metal-chelating functionality at both the C-6 and C-6' positions, which can provide a first coordination sphere of eight valencies. The designed total synthesis was highly efficient. To demonstrate the utility of the ligand, we studied its complexation with Gd(III). Using potentiometric titration and high-resolution mass spectrometry, we confirmed the formation of a 1:1 complex with Gd(III), which has a respectable formation constant of ~1013.4. Further NMR relaxivity studies show that the Gd(III) complex has a relaxivity (r1) of 7.6958 mmol-1 s-1.

Speciation and formation constants of aqueous lanthanum (III) chloride complexes from 5 to 80 °C by Raman spectroscopy

Lanthanum chloride solutions were studied both computationally and by polarized Raman spectroscopy to determine the aqueous species present and their equilibrium constants. Four species were predicted from Gaussian 16 computations using density functional theory: La(H2O)9 3+, LaCl(H2O)8 2+, LaCl2(H2O)6 2+, and LaCl3(H2O)4 0. Both LaCl(H2O)8 2+ and LaCl2(H2O)6 + were identified in the reduced isotropic solvent-subtracted Raman spectra from their La–Cl vibrational bands at 234 and 221 cm−1, respectively. The spectra did not change significantly with temperature from 5 to 80 °C, and the Raman bands for each species could not be fitted with sufficient accuracy to determine the scattering coefficients directly from the experimental data. Instead, the computed scattering coefficients from Gaussian 16 (B3LYP with the Los Alamos National Laboratory 2-double-zeta effective core potential and 6-311+G(d,p) basis set) were to be used to obtain the equilibrium concentrations of LaCl(H2O)8 2+ and LaCl2(H2O)6 +, from which the concentration of La(H2O)9 3+ was determined. The concentration dependent formation quotients were fitted with the specific ion interaction (SIT) activity coefficient model to determine the stepwise formation constants K0, 1 and K1, 2, from 5 to 80 °C. Both K0, 1 and K1, 2 showed minor increases with temperature.

Mononuclear high-spin iron(III) phthalocyanines

2,9(or 10),16(or 17), 23(or 24)-Tetradecyloxycarbonylphthalocyaninatoiron, FeTDPc, and 2,3,9,10,16,17,23,24-octadecyloxycarbonylphthalocyaninatoiron, FeODPc, were synthesized and characterized. These compounds seem to be in trivalent iron high-spin state in solvents such as chloroform, dichloromethane, benzene, and chlorobenzene, although their counter anion could not be detected by elemental analyses. They react with strong bases such as pyridine and imidazoles to form their mono- and subsequently their di-base complexes with formation constant of >106 and < 200 dm3 mol−1, respectively, in dichloromethane at 20 °C. The resultant mono-adducts appear to be trivalent iron low-spin while the di-base adducts are bivalent iron low-spin state complexes. The addition of ca. 10–30 equivalent of tetrabutylammonium-chloride or -bromide (electrolyte) to the solution containing FeTDPc or FeODPc, causes their spin-state change from iron(III) high to low-spin state. In a solid power state, however, both FeTDPc and FeODPc exist as a mixture of high-spin iron(III)- and intermediate-spin iron(II) species. Strangely, when these compounds are dissolved in polystyrene, i.e. each molecules are isolated from each other, the signals originated from the iron(II) component disappear.

Assessing the structural, antibacterial, and dissolution properties of 1:1 doxycycline/β-cyclodextrin complexes

A 1:1 β-cyclodextrin (βCD) inclusion complex with doxycycline (DO) as the guest molecule was prepared using kneading (KN) and coprecipitation (CoP) methods, along with a physical mixture (PM) . The complex was characterized through FTIR, ¹H NMR, UV–Vis spectroscopy, and DSC analysis. Semi-empirical quantum mechanical calculations confirmed the inclusion of DO within βCD's hydrophobic cavity. The formation constant, determined by a modified Benesi-Hildebrand equation at 25 °C, was 116.22 M⁻¹ for the βCD-DO complex. Dissolution studies revealed that the CoP method significantly enhanced DO's dissolution kinetics compared to the KN, PM methods, and free DO, highlighting CoP's effectiveness. Molecular docking indicated a stable βCD-DO complex, with binding energies from -5.9570 to -6.1423 kcal/mol, driven by hydrophilic and hydrophobic interactions. Antibacterial testing against E. coli, P. aeruginosa, S. aureus, B. cereus, and B. subtilis showed CoP had the highest efficacy, with MIC values of 5–10 µg/ml and MBC values of 10–20 µg/ml, better than KN, DO, and βCD.

Plutonium Speciation and Oxidation State Distributions in the Presence of Citrate.

We explored the speciation and kinetics of the Pu(VI)-citrate and Pu(III)-citrate systems (pHm = 2.5-11.0, I = 0.1 M NaCl, T = 23 °C, O2(g) < 2 ppm) using ultraviolet-visible-near-infrared (UV-vis-NIR) spectrophotometry, solvent extraction, and PHREEQC modeling. Formation constants were determined for PuO2(HcitH)(aq) (log K°1,1 = 1.09 ± 0.05) and PuO2(HcitH)(citH)3- (log K°1,2 = -0.20 ± 0.07), and evidence for (PuO2)m(citH-k)n(OH)x2m(3+k)n-x was identified under alkaline conditions. Pu(VI) species were found to be less stable in the presence of citrate than in the absence of citrate (t ≤ 168 days); the rate of reduction increased with increasing pH. The direct reduction of Pu(VI) to Pu(IV) was required to fit experimental data in the presence of citrate but did not improve the fit for Pu in the absence of citrate. We also observed increased Pu(III) stability in the presence of citrate (t ≤ 293 days), with higher concentrations of Pu(III) favored at lower pH. Finally, we provide evidence of a radiolysis-driven mechanism for the citrate-mediated reduction of plutonium that involves electron transfer from the oxidative breakdown of citrate. Our work highlights the need to investigate the redox effect of organic ligands on plutonium oxidation states under repository-relevant conditions.

Factorial design-aided derivatization-free fluorimetric ultrasensitive assay of vonoprazan with application in uniformity of dosage units and plasma samples analysis: Comprehensive and comparative greenness and whiteness assessment

This study presents a novel derivatization-free spectrofluorimetric method for the quantification of vonoprazan (VPZ) that is characterized by its high sensitivity, environmental friendliness, and cost-effectiveness. Notably, this method eliminates the requirement for pre-derivatization, extraction procedures, large amounts of organic solvents, and/or expensive instrumentation, which distinguishes it from previous approaches. The approach employed in this study relies on the formation of an association complex between VPZand the xanthene dye acid red 87 (AR87) under acidic conditions. The stability of the VPZ-AR87 complex was determined to be remarkably high, with a complex formation constant (Kf) value exceeding 2 x 106 M−1. The fluorimetric measurements rely on the quantitative and selective quenchingof the dye’s native fluorescence emission at 545 nm. The experimental parameters were optimized utilizing a quality-by-design 23 full factorial design. This strategy yielded a highly favorable linearity range of 10.0 to 400.0 ng/mL, with a correlation coefficient (r) of 0.9997. The presented methodology exhibited a high level of sensitivity, as evidenced by its ability to detect concentrations as low as 1.2 ng/mL. This sensitivity enabled its successful application for the estimation of VPZ in human plasma samples with high %recoveries (98.21–101.67) and low %RSD values (<1.52). Furthermore, content uniformity testing of low-dose VPZ tablets was performed according to United States Pharmacopeia guidelines. Greenness and whiteness metrics analysis showed a significant advantage of the proposed method over previously reported fluorimetric methods. Validation of the developed approach was carried out in accordance with ICHQ2 (R1) guidelines.

SODIUM, MONOETHANOLAMMONIUM AND POLYETHYLENE POLYAMMONIUM CITRATES AQUEOUS SOLUTIONS ELECTROCHEMICAL PROPERTIES

pH and conductometric study of aqueous (0.1 ÷ 9.0)⋅10-3 mol/l solutions of sodium (Na3Cit), monoethanolammonium (H3Cit⋅3MEA) and polyethylenepolyammonium (kH3Cit⋅3PEPA) citrates was carried out. Features of the electrochemical behavior of monoethanolamine and polyethylenepolamine ammonium citrates aqueous solutions were revealed in comparison with Na3Cit. As the temperature increases from 293 to 303 K, the pH values and Na3Cit solutions molar electrical conductivity increase. Due to hydrolytic processes, when diluting H3Cit⋅3MEA solutions, a change in pH is observed from slightly acidic to slightly alkaline, in contrast to Na3Cit. An increase in temperature (in the region of 293–308 K) leads to an increase in the medium acidity, in contrast to sodium citrate solutions, which is accompanied by an atypical decrease in molar electrical conductivity at the same H3Cit⋅3MEA content. It has been shown that an increase in temperature in the range of 293-308 K leads to a decrease in H3Cit⋅3MEA aqueous solutions pH, in contrast to Na3Cit and kH3Cit⋅3PEPA solutions, which is accompanied by an atypical decrease in molar electrical conductivity at the same H3Cit⋅3MEA content. The component composition of Na3Cit, H3Cit⋅3MEA and kH3Cit⋅3PEPA aqueous solutions was calculated. The probability of the existence of negatively charged ion-molecular complexes in H3Cit⋅3MEA and kH3Cit⋅3PEPA aqueous solutions is shown. The concentration and temperature dependence of citrate ions hydrolysis constant was obtained. The concentration and temperature dependence of these complexes was assessed. The atypical negative effect of heating on H3Cit⋅3MEA aqueous solutions molar electrical conductivity is associated with a change in the radius of the ion-molecular complex and its stability. The value of the limiting molar electrical conductivity of sodium, monoethanolammonium and polyethylenepolyammonium citrates aqueous solutions in the range of 293–313 K was estimated. Correlations were revealed between the values of the limiting electrical conductivity and ion-molecular complexes formation constants in H3Cit⋅PEPA aqueous solutions. The values of energy, enthalpy and entropy of activation of molar electrical conductivities of aqueous solutions were calculated. For the solutions studied, compensation effects were noted in the activation parameters of molar electrical conductivity.

Tungsten speciation in hydrothermal fluids

Understanding the speciation and thermodynamic properties of aqueous tungsten (W) complexes under various conditions is essential for predicting W transport in hydrothermal fluids relevant to ore formation and geothermal systems. Although previous experimental and geochemical modelling studies have provided insights into W solubility in hydrothermal systems, a comprehensive molecular-level understanding of W in hydrothermal fluids remains elusive.In this study, we employed ab initio molecular dynamics (MD) simulations to determine the speciation and coordination geometries of W(VI) complexes in NaCl, NaHS, and NaF-bearing brines at temperatures up to 600 °C and pressures up to 2 kbar. These theoretical calculations were complemented by synchrotron in-situ X-ray Absorption Spectroscopy measurements of W(VI) in chloride-, sulfide-, and fluoride-rich solutions under pressures of 600 bar and temperatures ranging from 25 to 429 °C. The speciation and geometrical properties obtained from ab initio MD simulations are in reasonably good agreement with the in-situ X-ray Absorption Spectroscopy data. Our study reveals that W-Cl complexes are not stable, and W is transported as tungstates (H2WO4(aq), HWO4− and WO42−)in NaCl-rich fluids. In sulfur-rich fluids under near-neutral pH and reduced conditions (sulfide predominant), S2− ions gradually replace O2− in tungstates to form thiotungstate complexes (WO4-xSx2−, where x = 1, 2, 3, 4). The MD results suggest that fluoride (F−) plays a significant role in W transport by forming WO3F− and WO3F22− complexes, or their hydrated ions. We employed thermodynamic integration to determine the formation constants of the WO3F− and WO3F22− complexes at temperatures up to 600 °C and 2 kbar, and extrapolated these properties across a broader range of temperatures and pressures. This study underscores the significance of W-F complexes in W transportation in fluoride-bearing, acidic to neutral (pH < 8) hydrothermal fluids. In contrast, W is most likely transported as thiotungstate complexes in sulfur-bearing hydrothermal fluids within a neutral to alkaline pH range (e.g., pH 5–8.5 at 300 °C) under reduced (sulfide-stable) conditions in the Earth’s crust. Existing models for W transport in hydrothermal ore fluids need to consider the influence of W-F and thiotungstate species.

Metronidazole Interaction with Cu2+ and Zn2+: Speciation Study in Aqueous Solution and Biological Activity Evaluation.

Metronidazole (2-methyl-5-nitro-1H-imidazole-1-ethanol, MNZ) is a well-known and widely used drug for its excellent activity against various anaerobic bacteria and protozoa. The purpose of this study is to elucidate the ability of MNZ to form metal complexes with Cu2+ and Zn2+ and to demonstrate that complexation increases its bioactivity profile against different pathogenic microorganisms. The interaction of MNZ with Cu2+ and Zn2+ was investigated in NaCl aqueous solution under different conditions of temperature (15, 25, and 37 °C) and ionic strength (0.15, 0.5, and 1 mol L-1) by potentiometric and spectrophotometric titrations. The obtained speciation models include two species for the Cu2+-containing system, namely, CuL and CuL2, and three species for the Zn2+-containing system, namely, ZnLH, ZnL, and ZnLOH. The formation constants of the species were calculated and their dependence on temperature and ionic strength evaluated. Comparison of the sequestering ability of MNZ under physiological conditions revealed a capacity toward Cu2+ higher than that toward Zn2+. A simulation under the same conditions also showed a significant percentage of the Cu2+-MNZ species. The biological assessments highlighted that the complexation of MNZ with Cu2+ has a relevant impact on the potency of the drug against two Trypanosoma spp. (i.e., T. b. brucei and T. b. rhodesiense) and one gram-(-) bacterial species (i.e., Escherichia coli). It is noteworthy that the increased potency upon complexation with Cu2+ did not result in cytotoxicity against MRC-5 human fetal lung fibroblasts and primary peritoneal mouse macrophages.

Chelation of rare earth metals by perfluorinated β-diketones bearing nitrogen heterocycles rings

Aqueous equilibria of three substituted perfluorinated 1,3-diketones with pyrrole, pyrazole, and pyridine rings have been extensively studied in aqueous solutions. Thermodynamic characteristics of dissociation, protonation, and chelation processes have been investigated by UV–Vis spectroscopy using non-linear regression analysis. Acid-base parameters were discovered in the acidity range from highly acidic media (C(HCl) = 10 M) to alkaline pH region. Dissociation constants (pKa) have been determined in glycine-HCl, phosphate-citrate, and TRIS-HCl buffered media. Protonation activities were studied by the Cox-Yates approach in concentrated hydrochloric acid solutions. First formation constants of ML complex species with trivalent ions of Sc3+, Y3+, La3+, Ce3+, Pr3+, Nd3+, Sm3+, Eu3+, Gd3+, Dy3+, Tb3+, Ho3+, Er3+, Tm3+, Yb3+, and Lu3+ have been obtained in the pH within 3.0–5.6 (I = 0.5 M, NaCl). True stability constants have been calculated using determined acid-base parameters considering side reactions. The “True” formation constants lie from 3.7 to 6.9 logarithmic units and have a linear relationship with the ionic (Coulomb) potential of metals. DFT and TD-DFT simulations have been performed for the modeling of the data obtained.

Methods of Preparation and Characterization of Cyclodextrin Encapsulated Inclusion Complex : Review

Inclusion Complex is supramolecular system which is formed by inclusion of the guest molecules into the cavity of host molecule and these molecules are held by intermolecular forces but not by covalent bond. The special characteristic of Cyclodextrins is the ability to form an inclusion complex with viable compounds. This article focuses on the various preparation methods for inclusion complexes, their formation constant, experimental and spectral approaches to demonstrate host-guest interaction. Phase solubility diagram indicated that the solubility of guest molecule increases linearly with CD concentration in AL-type and a stoichiometry of 1:1. The inclusion complex formed by various techniques was characterized by various spectroscopic methods. The study offers a variety of studies that demonstrate how cyclodextrins can be used to enhance the solubility, stability, and effectiveness of synthetic pharmaceuticals as well as their physical, chemical, and biological properties.

P‐253: Late‐News Poster: The Evaluation on the Stability of Electroluminescent Materials Using Polaron Pair Formation Kinetics

We developed the method for evaluation of the stability of electroluminescent materials by using QEMS (quantum efficiency measurement system). Relative PL (photoluminescence) intensity decay of BDs (blue dopants) with BHs (blue hosts) in solution under UV light irradiation were measured and the rate constants for polaron pair formation by electron transfer were determined through first‐order kinetics analyses. The rate constants of polaron pair formation (6.487E‐04 –1.805E‐03 min‐1 ) were inversely proportional to the lifetime of OLED (organic light‐emitting diode) devices. We expect that this evaluation method can be applied to the development of new OLED materials and longer lifetime OLED devices.

Binding ability of chloride ion with platinum and rhodium dinuclear complex containing ethylenediamine as co-ligand

In this study, the binding capability for Cl− ion was investigated with amidate-bridged platinum–rhodium dinuclear complex axially coordinated PPh3 to the rhodium atoms containing ethylenediamine (=en) as co-ligand. Mixing [PtRhCl3(piam)2(en)]·3H2O (2Cl) with PPh3 and NaPF6 provided [PtRhCl2(piam)2(en)(PPh3)]PF6 (2(PPh3)·PF6) which can bind Cl− ion at the axial position of platinum atom to be [PtRhCl2(piam)2(en)(PPh3)]Cl (2(PPh3)·Cl), where both crystal structures were determined by single-crystal X-ray analyses. UV–vis titration demonstrated that the formation constant of 2(PPh3)·PF6 with Cl− is 1.6 × 103 M−1, significantly smaller than that with NH3 as a co-ligand, which suggests that multinucleation is necessary for effective hydrogen bonds as well as the affinity of metals.

Enhancing bioavailability of resveratrol through complexation with π-acceptors: A spectroscopic investigation

Polyphenols, including the highly effective resveratrol, have garnered attention due to their potential as drug candidates for COVID-19 prevention and treatment, as well as their diverse biological activities. However, clinical application is hindered by limited bioavailability. To address this, complexation of resveratrol (RES) with electron-accepting compounds, such as TCNE and DDQ, was investigated. A spectroscopic and thermodynamic study of these charge transfer complexes was conducted in methanol and ethanol using UV-visible spectrophotometry. The composition of the charge transfer complexes (CTC) were determined using molar ratio method and Job's continuous variation method. Benesi–Hildbrand equation was used to calculate the formation constants KCT and the molar extinction coefficient ɛCT of the formed complexes. Thermodynamic parameters (∆G°), (∆H°), (∆S°) and other physical factors, transition energy (ECT), ionization potential (IP), resonance energy (RN), oscillator strength (ƒ) and dipole moment (μ) were determined too.Solid CTC were characterized by FT-IR and NMR spectroscopy. CTC formed in the reaction of resveratrol with both π -acceptors have high formation constants KCT indicating the high stability of these complexes. The solvent nature was identified as a factor influencing KCT values. Specifically, the KCT values for [RES-DDQ] CTC formed in ethanol surpassed those of the same complex formed in methanol. Conversely, the KCT values of [RES-TCNE] CTC formed in methanol were higher than those of the same complex formed in ethanol.This research offers insights into enhancing the properties of resveratrol through charge transfer complex formation, paving the way for potential applications in anticancer therapeutics.

Single versus multiple metabolite quantification of in vitro starch digestion: A comparison for the case of pulse cotyledon cells

Different quantification methods for in vitro amylolysis were compared for individual chickpea and lentil cotyledon cells (ICC) as a relevant case study. For the first time, much-applied spectrophotometric methods relying on the quantification of certain functional groups (i.e., DNS, GOPOD) were compared to chromatographic quantification of starch metabolites (HPLC-ELSD). The estimated rate constant and linked initial rates of amylolysis were highly correlated for DNS, GOPOD, and HPLC-ELSD. However, absolute amylolysis levels depended on the applied method and sample-specific metabolite formation patterns. Multiresponse modelling was employed to further investigate HPLC-ELSD metabolite formation patterns. This delivered insight into the relative importance of different amylolysis reactions during in vitro digestion of pulse ICC, proving that maltotriose and maltose formation determined the overall amylolysis rate in this case. Multiresponse reaction rate constants of maltotriose and maltose formation were highly correlated to single response amylolysis rate constants (and initial rates) obtained for all three quantification methods.

Study on An Interaction between Titan Yellow and Orange S Indicators in Water and Ethanol by using Spectroscopy Technique

Charge transfer complex (CTC) of Orange S (donor) and Titan Yellow (acceptor) has been studied in ethanol, and water solvents at room temperature (20°C) using absorption spectrophotometer. The results indicate that formation of CTC in high polar solvent is high. The stoichiometry of the complex was found to be 1:1 ratio by straight-line method between donor and acceptor with maximum absorption bands and present of isosbestic point suggest this fact. The data are discussed in terms of formation constant (KCT), molar extinction coefficient (εCT), standard free energy (ΔGo), transition energy (ECT), and ionization potential (IP). The formation constant (KCT) for the complex was shown to be dependent upon the polarity of solvents that were used. Electronic absorption spectra, which indicate the CT interaction, associated with proton migration from the acceptor to the donor followed by hydrogen bonding.

Colloidal titration: from the perspective of stability constants between oppositely charged polyelectrolytes

Abstract Colloidal titration is a unique method to measure the concentration of charged groups based on the association between cationic and anionic colloids. Titrimetry must involve a unidirectional reaction with a large formation constant. However, the underlying polyelectrolyte complex (PEC) for colloidal titration lacks sufficient data regarding the stability constants (KI). To date, the stoichiometry of colloidal titration has not been discussed in relation to KI. Thus, in this paper, we reviewed PEC studies by focusing on KI and discuss colloidal titration comprehensively. The topics include the history of its establishment, the method to calculate KI, and the special characteristics of PEC compared with ion association reactions, the practical use of colloid titration, and the condition by which the stability constant can be increased. In terms of analytical reagents, polyelectrolytes are similar to (but positioned as a subspecies of) ion association reagents. Ionic strength strongly affects KIs values. Excluding coaggregation effects, the maximum values of log10 KI obtained from reliable data were found to decrease linearly as ionic strength increases logarithmically. The critical line connected with the maximum KI value at each ionic strength can be used as an empirical reference value and facilitate the analytical design of colloidal titration.