pKa Of Acid Research Articles

Linear Free Energy Relationships and Transition State Analysis of CO2 Reduction Catalysts Bearing Second Coordination Spheres with Tunable Acidity.

In molecular catalysts, protic functional groups in the secondary coordination sphere (SCS) work in conjunction with an exogenous acid to relay protons to the active site of electrochemical CO2 reduction; however, it is not well understood how the acidity of the SCS and exogenous acid together determine the kinetics of catalytic turnover. To evaluate the relative contributions of proton transfer driving forces, we synthesized a series of modular iron tetraphenylporphyrin electrocatalysts bearing SCS amides of tunable pKa (17.6 to 20.0 in dimethyl sulfoxide (DMSO)) and employed phenols of variable acidity (15.3 to 19.1) as exogenous acids. This system allowed us to (1) evaluate contributions from proton transfer driving forces associated with either the SCS or exogenous acid and (2) obtain mechanistic insights into CO2 reduction as a function of pKa. A series of linear free-energy relationships show that kinetics become increasingly sensitive to variations in SCS pKa when more acidic exogenous acids are used (0.82 ≥ Brønsted α ≥ 0.13), as well as to variations in exogenous acid pKa when SCS acidity is increased (0.62 ≥ Brønsted α ≥ 0.32). An Eyring analysis suggests that the rate-determining transition state becomes more ordered with decreasing SCS acidity, which is consistent with the proposal that SCS acidity modulates charge accumulation and solvation at the rate-limiting transition state. Together, these insights enable the optimization of activation barriers as a function of both SCS and exogenous acid pKa and can further guide the rational design of electrocatalytic systems wherein contributions from all participants in a proton relay are considered.

The effect of a preparation containing glycocholic acid on the biocidal efficacy of sodium hypochlorite in a biofilm laboratory model.

This study assessed the antimicrobial effect of sodium hypochlorite (NaOCl) mixtures combined with Keratobacter (KB) using an engineered biofilm root canal model. Clinical and reagent grade NaOCl were mixed with KB (9:1-vol/vol) to assess pH values over 1 min to select the ideal solution with a pH just below the pKa of hypochlorous acid. The samples were randomly divided into five groups: 1% and 4% NaOCl reagents, a mixture of NaOCl:KB using 1% and 4% NaOCl reagents and distilled water. Outcome measures were colony-forming units (CFUs/mL) and positive/negative cultures. No significant differences were observed in the pairwise comparisons between 1%, 4% NaOCl and 4% NaOCl+KB for the outcome CFUs/mL. Only 4% NaOCl presented with negative cultures in all samples, whereas 1% NaOCl and 4% NaOCl+KB had similar results (54% vs. 40%). The addition of KB has a limited effect on the antimicrobial efficacy of 4% NaOCl in this laboratory model.

Adsorptive recovery of volatile fatty acids from wastewater fermentation broth

This work developed an adsorptive separation and recovery process for anaerobically generated volatile fatty acids (VFAs) from swine wastewater fermentation. Batch adsorption studies were conducted using several weak anion exchange resins and synthetic adsorbent resins to identify a suitable candidate. Relite RAM2 with a tertiary amine functional group showed the highest adsorption (over 98%) of hexanoic acid. Under the different pH values (1.8–7.5) and extraction temperatures (30–50 °C), the highest adsorption was observed at a pH of 3.2, which is below the pKa of hexanoic acid, at all the evaluated temperatures. A full factorial design was used to optimize the resin and VFA concentrations, wherein over 99% adsorption could be achieved when the ratio of VFA to resin was below 0.23 (g/g) for model solution (VFAs in water). The adsorption equilibrium could be achieved within 30 min of contact time and 0.5% w/v NaOH was identified as a suitable desorption agent. Under the optimal conditions, 65–72% of VFAs present in fermentation broth was adsorbed, which was increased to 72–76% by using fresh resins. The VFAs adsorption and recovery efficiency were maintained for 9 successive cycles without requiring extensive resin washing and regeneration for both model solution and fermentation broth. Overall, the work presents a comprehensive study for resin adsorption to recover VFAs and provides a potential industrial-relevant process to recover VFAs from fermentation broth.

Recent Progress in Diboronic-Acid-Based Glucose Sensors.

Non-enzymatic sensors with the capability of long-term stability and low cost are promising in glucose monitoring applications. Boronic acid (BA) derivatives offer a reversible and covalent binding mechanism for glucose recognition, which enables continuous glucose monitoring and responsive insulin release. To improve selectivity to glucose, a diboronic acid (DBA) structure design has been explored and has become a hot research topic for real-time glucose sensing in recent decades. This paper reviews the glucose recognition mechanism of boronic acids and discusses different glucose sensing strategies based on DBA-derivatives-based sensors reported in the past 10 years. The tunable pKa, electron-withdrawing properties, and modifiable group of phenylboronic acids were explored to develop various sensing strategies, including optical, electrochemical, and other methods. However, compared to the numerous monoboronic acid molecules and methods developed for glucose monitoring, the diversity of DBA molecules and applied sensing strategies remains limited. The challenges and opportunities are also highlighted for the future of glucose sensing strategies, which need to consider practicability, advanced medical equipment fitment, patient compliance, as well as better selectivity and tolerance to interferences.

Modular Design and Bonding Mechanism of Internal Boron–Nitrogen Coordinated Boronic Ester Hydrogels with Alkaline pH Responsiveness and Tunable Gelation pH

Boronic ester hydrogels have been widely used in biomedical fields for their stimuli responsiveness to multiple disease-related triggers. However, the restricted pH for gelation and the poor hydrolysis stability limit their application in variable physiological microenvironments. Here, we report a modular conjugation method for designing internal boron–nitrogen coordinated boronic ester (IBNCB) hydrogels by constructing polymers with phenylboronic acid or N,N-bis(2-hydroxyethyl) moieties based on amides. Eight distinct IBNCB hydrogel models composed of polymer/polymer or polymer/micromolecule were prepared, exhibiting a unique pH responsiveness in the alkaline environment, an enhanced hydrolysis stability, bidirectional pH-tunable mechanical properties, and a lowered and tunable pH for gelation. In addition, the IBNCB hydrogels maintained a sol–gel transitional responsiveness to reactive oxygen species (ROS), glucose, and temperature. Especially, we found that the pH required to form an ideal IBNCB hydrogel should be greater than the pKa of phenylboronic acid but lower than the pKa of N,N-bis(2-hydroxyethyl), and reducing the pKa of phenylboronic acid could lower the gelation pH. The pKa of the tertiary amine in N,N-bis(2-hydroxyethyl) was shown to be important in the creation of the B–N coordination bond, which influenced the formation of the IBNCB bond. Finally, we explored the effect of the main chain’s charge on gelability and proposed the dynamic equilibrium mechanism of IBNCB bonds in the hydrogel. We expect that the multi-stimuli-responsive IBNCB hydrogels will provide a new strategy for designing smart materials sensitive to physicochemical signals. Furthermore, the amide-based modular conjugation could be exploited to generate a theoretically limitless number of novel IBNCB materials including microgels, polymer vesicles, and micro–nano particles.

Rapid LC-MS/MS quantification of Organophosphate non-specific metabolites in hair using alkaline extraction approach

Assessing human exposure to commonly used, highly toxic, but non-persistent organophosphates (OPs) is challenging because these toxicants are readily biotransformed into dialkyl phosphates (DAPs) and other metabolites. Growing hair accumulates toxicants and their metabolites, which makes hair a valuable non-invasively sampled matrix that can be used to retrospectively examine chemical exposure. However, the efficient quantification of hydrophilic DAP compounds in hair is challenging due to complex hair matrix effects. To improve upon existing methods, we first examined the acid dissociation constants (pKa) of DAPs and amino acids (major components in hair) and identified the best pH conditions for minimizing matrix effects. We hypothesized that under basic pH conditions DAPs and amino acids would be negatively charged and have weak interactions favorable to DAP dissociation from the matrix. To test this, we compared the efficiency of various pH conditions of suitable solvents to extract six DAPs from hair samples, and we quantified these DAPs using liquid chromatography-tandem mass spectroscopy (LC-MS/MS). As expected, a basic extraction (methanol with 2% NH4OH) approach had the highest extraction efficiency and yielded satisfactory recoveries for all six DAPs (72%-152%) without matrix effects. Additionally, the alkaline extract can be directly injected into the LC-MS/MS. This relatively rapid and simple procedure allowed us to process up to 90 samples per week with reproducible results. To our knowledge, this is the first method to quantify all six DAPs simultaneously in hair using LC-MS/MS with electrospray ionization (ESI) in negative ion mode. Finally, we demonstrated the feasibility of measuring DAP levels in hair samples from patients affected with amyotrophic lateral sclerosis (ALS), a neurodegenerative disease potentially linked to OP exposure. Due to our optimized solvent extraction process, the method we have developed is compatible with the rapidity and sensitivity needed for hair analysis applied to population biomonitoring.

Tripeptide Self-Assembled Monolayers as Biocompatible Surfaces for Cytochrome c Electrochemistry.

Biocompatible tripeptide self-assembled monolayers (SAMs) are designed with a carboxylate group on the terminal amino acid (glutamate, aspartate, or amino adipate) to electrostatically attract the lysine groups around the heme crevice in horse heart cytochrome c (cyt c), creating an electroactive protein/tripeptide/Au interfacial structure. Exposing the peptide/Au electrode to cyt c resulted in an 11 ± 3 pmol/cm2 electroactive protein surface coverage. Topographical images of the interfacial structure are obtained down to single-protein resolution by atomic force microscopy. Uniform protein monolayer assemblies are formed on the Au electrode with no major surface roughness changes. The cyt c/peptide/Au electrode systems were examined electrochemically to probe surface charge effects on the redox thermodynamics and kinetics of cyt c. Neutralization of protein surface charge due to adsorption on anionic COOH-terminated SAMs was found to change the formal potential, as determined by cyclic voltammetry. The cyt c/peptide/Au electrodes exhibit formal potentials shifted to more positive values, have a surface carboxylic acid pKa of 6 or higher, and produce effective cyt c surface charges (Zox) of -6 to -14. The Marcus theory is utilized to determine the protein electron transfer rates, which are ∼5 times faster for cyt c/tripeptide/Au compared to cyt c/11-mercaptoundecanoic acid SAMs of similar chain lengths.

Formic and acetic acid pKa values increase under nanoconfinement.

Organic acids are prevalent in the environment and their acidity and the corresponding dissociation constants can change under varying environmental conditions. The impact of nanoconfinement (when acids are confined within nanometer-scale domains) on physicochemical properties of chemical species is poorly understood and is an emerging field of study. By combining infrared and Raman spectroscopies with molecular dynamics (MD) simulations, we quantified the effect of nanoconfinement in silica nanopores on one of the fundamental chemical reactions-the dissociation of organic acids. The pKa of formic and acetic acids confined within cylindrical silica nanopores with 4 nm diameters were measured. MD models were constructed to calculate the shifts in the pKa values of acetic acid nanoconfined within 1, 2, 3, and 4 nm silica slit pores. Both experiments and MD models indicate a decrease in the apparent acid dissociation constants (i.e., increase in the pKa values) when organic acids are nanoconfined. Therefore, nanoconfinement stabilizes the protonated species. We attribute this observation to (1) a decrease in the average dielectric response of nanoconfined aqueous solutions where charge screening may be decreased; or (2) an increase in proton concentration inside nanopores, which would shift the equilibrium towards the protonated form. Overall, the results of this study provide the first quantification of the pKa values for nanoconfined formic and acetic acids and pave the way for a unifying theory predicting the impact of nanoconfinement on acid-base chemistry.

PKa prediction of per- and polyfluoroalkyl acids in water using in silico gas phase stretching vibrational frequencies and infrared intensities.

To successfully understand and model the environmental fate of per- and polyfluoroalkyl substances (PFAS), it is necessary to know key physicochemical properties (PChPs) such as pKa; however, measured PChPs of PFAS are scarce and of uncertain reliability. In this study, quantitative structure-activity relationships (QSARs) were developed by correlating calculated (M062-X/aug-cc-pVDZ) vibrational frequencies (VF) and corresponding infrared intensities (IRInt) to the pKa of carboxylic acids, sulfonic acids, phosphonic acids, sulfonamides, betaines, and alcohols. Antisymmetric stretching VF of the anionic species were used for all subclasses except for alcohols where the OH stretching VF performed better. The individual QSARs predicted the pKa for each subclass mostly within 0.5 pKa units from the experimental values. The inclusion of IRInt as a pKa predictor for carboxylic acids improved the results by decreasing the root-mean-square error from 0.35 to 0.25 (n > 100). Application of the developed QSARs to estimate the pKa of PFAS within each subclass revealed that the length of the perfluoroalkyl chain has minimal effect on the pKa, consistent with other models but in stark contrast with the limited experimental data available.

Zwitterion-neutral form equilibria and binding selectivity of pyridineboronic acids.

A 11B NMR study of 3-pyridineboronic acid at variable pH in water and 50 vol% aqueous dioxane confirms that the tautomeric equilibrium of the acid is shifted to the zwitterionic form in water, but to the molecular form in the mixed organic solvent. Interactions of 3- and 4-pyridineboronic acids with sialic acid, fructose and several other diols were studied by potentiometric titrations in a wide range of pH in water and water-organic mixtures. In all reaction media the stability of boronate complexes increases upon an increase in pH for neutral low acidic diols such as fructose and glucose but has the opposite trend for highly acidic sialic and lactic acids occurring as anionic species. The selectivity of pyridineboronic acids to sialate anions in an acidic medium is interpreted quantitatively by combining the pH-profiles with Brønsted type correlations for binding constants. In addition, mathematical expressions allowing one to predict the optimum pKa value of a boronic acid for the strongest binding of a given diol (sialic acid or fructose) at a given pH are suggested. The shifts in the tautomeric equilibrium induced by changing the solvent polarity in aqueous-organic mixtures are manifested in the magnitude of relative shifts of pKa of pyridineboronic acids induced by diol complexation.

Relationships between the Reversible Oxidation of the Single Cysteine Residue and the Physiological Function of the Mitochondrial Glutaredoxin S15 from Arabidopsis thaliana.

Glutaredoxins (GRXs) are widespread proteins catalyzing deglutathionylation or glutathionylation reactions or serving for iron-sulfur (Fe-S) protein maturation. Previous studies highlighted a role of the Arabidopsis thaliana mitochondrial class II GRXS15 in Fe-S cluster assembly, whereas only a weak glutathione-dependent oxidation activity was detected with the non-physiological roGFP2 substrate in vitro. Still, the protein must exist in a reduced form for both redox and Fe-S cluster binding functions. Therefore, this study aimed at examining the redox properties of AtGRXS15. The acidic pKa of the sole cysteine present in AtGRXS15 indicates that it should be almost totally under a thiolate form at mitochondrial pH and thus possibly subject to oxidation. Oxidizing treatments revealed that this cysteine reacts with H2O2 or with oxidized glutathione forms. This leads to the formation of disulfide-bridge dimers and glutathionylated monomers which have redox midpoint potentials of -304 mV and -280 mV, respectively. Both oxidized forms are reduced by glutathione and mitochondrial thioredoxins. In conclusion, it appears that AtGRXS15 is prone to oxidation, forming reversible oxidation forms that may be seen either as a catalytic intermediate of the oxidoreductase activity and/or as a protective mechanism preventing irreversible oxidation and allowing Fe-S cluster binding upon reduction.

Desulfurization characteristics of limestone slurry with added organic acid

In this study, a desulfurization experiment was performed in a bubbling reactor to investigate the effects of adding organic acids, such as formic, acetic, propionic, lactic, oxalic and adipic acid, to limestone slurries. The limestone slurries added these organic acids were referred to as FAS, AAS, PAS, LAS, OAS, and ADS, respectively. Flue-gas desulfurization characteristics varied with the acidity of organic acid additives. The T99 of slurries increased with pKa of the organic acids because slurry pH was high in the early phase of absorption which increased the time to reach the slurry pH range (4.1–4.6) required for the T99 end. During SO2 absorption, the sulfate ion fraction was ≥0.5 in PAS, AAS, and ADS, with pKa > 4, but <0.5 in LAS and FAS with pKa < 4. PAS, AAS, and ADS supported the oxidation of sulfite ions, whereas LAS and FAS suppressed it. [H+] × [A−] increases with decreasing pKa of organic acids. Therefore, [H+]slurry and [A−]slurry in the slurry may be engaged in the oxidation of sulfite ions; consequently, increasing [H+] × [A−] inhibited the oxidation of sulfite ions. The sulfate ion fraction affected gypsum dehydration following completion of SO2 absorption. After drying at 60 °C, LAS and FAS (sulfate ion fraction < 0.5) formed only gypsum, whereas PAS, AAS, and ADS (sulfate ion fraction ≥ 0.5) formed both gypsum and anhydrite. Accelerated oxidation of sulfite ions with sulfate ion fraction ≥ 0.5 during slurry drying after reaction completion produced a sulfuric acid solution with a high sulfate ion concentration, which reduced the temperature of gypsum dehydration.

ALipSol: An Attention-Driven Mixture-of-Experts Model for Lipophilicity and Solubility Prediction.

Lipophilicity (logD) and aqueous solubility (logSw) play a central role in drug development. The accurate prediction of these properties remains to be solved due to data scarcity. Current methodologies neglect the intrinsic relationships between physicochemical properties and usually ignore the ionization effects. Here, we propose an attention-driven mixture-of-experts (MoE) model named ALipSol, which explicitly reproduces the hierarchy of task relationships. We adopt the principle of divide-and-conquer by breaking down the complex end point (logD or logSw) into simpler ones (acidic pKa, basic pKa, and logP) and allocating a specific expert network for each subproblem. Subsequently, we implement transfer learning to extract knowledge from related tasks, thus alleviating the dilemma of limited data. Additionally, we substitute the gating network with an attention mechanism to better capture the dynamic task relationships on a per-example basis. We adopt local fine-tuning and consensus prediction to further boost model performance. Extensive evaluation experiments verify the success of the ALipSol model, which achieves RMSE improvement of 8.04%, 2.49%, 8.57%, 12.8%, and 8.60% on the Lipop, ESOL, AqSolDB, external logD, and external logS data sets, respectively, compared with Attentive FP and the state-of-the-art in silico tools. In particular, our model yields more significant advantages (Welch's t-test) for small training data, implying its high robustness and generalizability. The interpretability analysis proves that the atom contributions learned by ALipSol are more reasonable compared with the vanilla Attentive FP, and the substitution effects in benzene derivatives agreed well with empirical constants, revealing the potential of our model to extract useful patterns from data and provide guidance for lead optimization.

The Ability of Acid-Based Natural Deep Eutectic Solvents to Co-Extract Elements from the Roots of Glycyrrhiza glabra L. and Associated Health Risks.

The roots of licorice (Glycyrrhiza glabra L.) have been widely used in traditional and officinal medicines for the treatment of different diseases. Natural deep eutectic solvents (NADES) have become popular for the extraction of active principles from medicinal plants. However, the ability of NADES to co-extract trace elements during the isolation of target active compounds is rarely investigated. The aim of this study was to analyze the content of trace elements in acid-based NADES extracts from the roots of G. glabra and the health risks associated with them. In this study, we have tested for the first time the ability of several acid-based NADES to co-extract glycyrrhizic acid (GA) and trace elements from the roots of G. glabra. GA has been identified as the dominant phytochemical in G. glabra NADES extracts (0.145-0.495 mg/g). Due to the close pKa of lactic acid and GA, the yield of GA in lactic acid-based NADES was higher in comparison with other tested NADES. The yield of GA in NADES3-NADES5 was statistically significant and surpassed the yield of GA in water. The recovery of all elements (except Li) by all tested NADES was low (less than 6%). According to an ANOVA test, the hydrogen bond donor type plays a decisive role in the extraction of elements. A strong positive correlation between the recovery of GA and MPI was noted. The metal pollution index, hazard quotient, hazard index, and chronic daily intake were calculated and suggest that all tested NADES extracts of G. glabra roots were nontoxic and possess no health risk for both ingestion and topical application.

Titrimetric‐comparable BN results determined for in‐service lubricants using quantitative FTIR spectroscopy

AbstractA new stoichiometric FTIR Base Number (BN) method of significant utility and analytical benefit to the tribology sector has been developed, providing ASTM D4739‐comparable BN results in lieu of titration in a fraction of the time. Thirty‐six new/in‐service oils analysed by both methods were linearly related with a between‐method accuracy of ~±1.0 BN and a within‐FTIR method reproducibility of ~±0.50 BN. Acid pKa differences and the comparative similarity of the FTIR results to HCl titration are discussed, including analytical benefits. It provides a rapid means of producing quality ASTM‐comparable results, taking ~1 min/sample for spectral analysis versus 30–40 min for potentiometric titration. Method protocols are best suited to an open architecture FTIR accessory but can be readily adapted to flow cell equipped FTIRs. As structured, ASTM‐like results are obtained rapidly with a major analytical environmental/maintenance footprint reduction, being ideally suited for in‐service lubricant or research labs analysing 20–50 samples/day.

Cyclic voltammetry of heavy metal/amino acid in Jordanian water

Amino acids make up about 20% of our bodies or about 50% of our solid body mass; they are the next largest component in our bodies after water. The body of a person who weighing 50 kg has about 10 kg of amino acids in their body make up. The pH at the equivalence point in titrations of weak acids or weak bases, on the other hand, is more or less than 7.0, respectively. In titrations of weak acids and weak bases, the pH changes more slowly until the equivalence point is reached than in titrations of strong acids and strong bases. The pH at the midpoint, which is midway between the weak acid and the weak base on the titration curve, is equal to the pKa of the weak acid or the pKb of the weak base. As a result, titration methods can be used to measure a weak acid's concentration as well as its pKa (or pKb) (or a weak base). Acid-base indicators are substances that change color when exposed to a specific pH. They are usually weak acids or bases whose color changes correspond to the indicator's deprotonation or protonation.

Study on the Effect of Electrolyte pH during Kolbe Electrolysis of Acetic Acid on Pt Anodes

AbstractKolbe already discovered in 1849 that electrochemical oxidative decarboxylation of carboxylic acids is feasible and leads to formation of alkanes and CO2, via alkyl radical intermediates. We now show for Pt electrodes that Kolbe electrolysis of acetic acid is favored in electrolytes with a pH similar to, or larger than the pKa of acetic acid, suppressing the formation of O2. However extended duration of electrolysis of acetate at basic pH results in loss of Faradaic efficiency to ethane, compensated by the formation of methanol. This change in selectivity is likely caused by the dissolution of CO2 near the electrode‐electrolyte interface, resulting in enlarged concentration of bicarbonate/carbonate. On the positively polarized, and oxidized Pt surface, these anions seem to inhibit homocoupling of methyl radicals to ethane. These results demonstrate that reaction selectivity in acetic acid (acetate) oxidation using oxidized Pt electrodes is determined by the pH and the anionic composition of the electrolyte.

Two Different Strategies Based on Three‐Way Analysis Models of UV Spectroscopic and Spectrochromatographic Measurements to Quantify the Acidity Constant of Acetylsalicylic Acid

AbstractA comparative study to quantify acid dissociation constant (pKa) of acetylsalicylic acid by applying the parallel factor analysis (PARAFAC) to three‐way data arrays of UV spectroscopic and spectrochromatographic measurements was presented. In data recording and data collection stages, the spectrochromatograms of 20 μg/mL acetylsalicylic acid in different mobile phases having seven different pH levels were recorded, and a cubic data set was created with time x wavelength x pH dimensions. UV spectra of the analyte in the concentration range of 10–30 μg/mL and in seven different pH media were recorded and arranged as a three‐way array with dimensions, wavelength x concentration x pH. To estimate the pKa by two different chemometric strategies, the cubic data sets were decomposed into trilinear components, which allowed to predict the pKa in the pH profiles. In practice, the three‐way analysis‐based UV spectroscopic and spectrochromatographic methods didn't include a titration procedure and had a second‐order advantage over traditional pKa determination methods. As a result, this investigation on the rapid and accurate estimation of the acidity constant of acetylsalicylic acid provided alternative and practical ways to determine the pKa of active pharmaceutical ingredients in the future.

Effects of Non-Ionic Micelles on the Acid-Base Equilibria of a Weak Polyelectrolyte.

Weak polyelectrolytes (WPEs) are widely used as pH-responsive materials, pH modulators and charge regulators in biomedical and technological applications that involve multi-component fluid environments. In these complex fluids, coupling between (often weak) interactions induced by micelles, nanoparticles and molecular aggregates modify the pKa as compared to that measured in single component solutions. Here we investigated the effect of coupling between hydrogen bonding and excluded volume interactions on the titration curves and pKa of polyacrylic acid (PAA) in solutions comprising PEO-based micelles (Pluronics and Brij-S20) of different size and volume fraction. Titration experiments of dilute, salt-free solutions of PAA (5 kDa, 30 kDa and 100 kDa) at low degree of polymer ionization (α < 0.25) drive spatial re-organization of the system, reduce the degree of ionization and consequentially increase the pKa by up to ~0.7 units. These findings indicate that the actual degree of ionization of WPEs measured in complex fluids is significantly lower (at a given pH) than that measured in single-component solutions.

Prediction of acid pKa values in the solvent acetone based on COSMO-RS.

In this contribution we extent the use of the conductor-like screening model for realistic solvation (COSMO-RS) to the prediction of pKa values in acetone, a commonly used dipolar aprotic solvent. For this, we calculated the Gibbs free energy of dissociation of 120 organic acids (nine acrylic acids, 87 benzoic acids, nine phenols, and 15 benzenesulfonamides) using COSMO-RS at the two levels BP-TZVP and BP-TZVPD-FINE and determined the parameters for a linear free energy relation for the prediction by performing linear fits to experimental values. Our results suggest that the data set dissects into two groups, with the phenols being different from the other three subsets. The acrylic and benzoic acids and the sulfonamides can be treated together and yield an excellent linear correlation ( ) with an RMSD of only ~0.3. The slope is found to be significantly smaller than the theoretical value ( ), only 45% of it, which is in accordance with findings in the literature. The phenols, however, while similarly well correlated in their own subset with an RMSD of 1.7-1.9, exhibit a slope larger than one. We discuss both a higher uncertainty in the reference values as well as physical origins as possible reasons.