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Keywords: acidity; delignification; Hammett acidity function; trifluoromethanesulfonic acid EN acidity delignification Hammett acidity function trifluoromethanesulfonic acid 722 731 10 08/09/22 20220801 NES 220801 1 Introduction Acidolysis is one of the most fundamental chemical reactions of lignin and traditionally applied to the isolation of structurally altered lignin ([12]), its structural analysis ([1]; [3]; [2]; [6]; [7]; [11]; [16]), its quantification ([9]), and the saccharification of carbohydrates, as well as the recently reported biorefinery of woody biomass ([10]). The lack of condensation in the aqueous 90 mol% Diox solution differs from the result obtained by [14], in which condensation products were detected in aqueous 90, 95, and 98 mol% Diox solutions and a 100% Diox solution. All solvent systems appear to show a common trend, in that I k i SB obs sb is larger in low mol% solutions than in the 100% H SB 2 sb O solution, decreases with increasing mol% to the minima in the intermediate mol% range, and increases again with increasing mol%. [Extracted from the article]

• For the first time the Hammett acidity function (H 0) has been measured for phosphoric acid in glacial acetic acid using nitrobenzene as indicator. • H 0 was determined over the wide concentration range of phosphoric acid at room temperature. For the first time, the Hammett acidity function (H 0) has been measured for phosphoric acid in glacial acetic acid using nitrobenzene as an indicator. The H 0 was determined over the wide concentration range of phosphoric acid at room temperature. [ABSTRACT FROM AUTHOR]

• For the first time the Hammett acidity function (H 0) has been measured for phosphoric acid in glacial acetic acid using nitrobenzene as indicator. • H 0 was determined over the wide concentration range of phosphoric acid at room temperature. For the first time, the Hammett acidity function (H 0) has been measured for phosphoric acid in glacial acetic acid using nitrobenzene as an indicator. The H 0 was determined over the wide concentration range of phosphoric acid at room temperature. [ABSTRACT FROM AUTHOR]

Abstract Pyrazine‑2‑amidoxime (PAOX) is a prototypical sp2-hybridized amidoxime. Although, we described first time in details PAOX structure in solid state, the profile of PAOX behavior in aqueous solution still needs to be improved. While, acid-base properties of PAOX have been tried to define just once, the presented description was not complete and based only on the results of potentiometry during complexometric studies. The selection of method gives rise problems to observation the protonation or deprotonation processes of compound studied. Due to above, the presented studies show first time the complete description of PAOX acid-base properties by obtaining its pKa, solubility, partition (P) and distribution (D) coefficients using various methods. Among them, experiments: potentiometry; UV spectrophotometry by using Hammett's function and pH-metric titrations; cyclic voltammetry (CV) with glassy carbon electrode (GCE) and with GCE electropolymerized by poly‑ l ‑glycine (PGGCE); 1H NMR and theoretical calculations (DFT). Generally, combined four types of experimental and theoretical methods were used to estimate PAOX macro acidic-dissociation constants values. Moreover, log P and log D were determined spectrophotometrically and calculated also by DFT methods. No previous reports were found in the presented form regarding the complete drug-like properties, including negative together with positive values of pKa. Additionally, we proved by our electrochemical results that the quantitative analysis of PAOX do not need the special conditions of the electrode used in research. Hence, the comparison of our results to those described in the literature about analysis made for others, amidoxime derivatives. Graphical abstract Unlabelled Image Highlights • The biochemical profile of pyrazine‑2‑amidoxime was obtained by multi-methods. • Drug-like properties of amidoxime derivative were described in details. • Preferred protonation and deprotonation sites in molecule studied were established. • Pyrazine‑2‑amidoxime ionization states were confirmed and discussed. [ABSTRACT FROM AUTHOR]

[Display omitted] Citrate buffers are commonly utilized in the field of biomolecule stabilization. We investigate their applicability in the frozen state within a range of initial pHs (2.5 to 8.0) and concentrations (0.02 to 0.60 M). Citrate buffer solutions subjected to various cooling and heating temperatures are examined in terms of the freezing-induced acidity changes, revealing that citrate buffers acidify upon cooling. The acidity is assessed with sulfonephthalein molecular probes frozen in the samples. Optical cryomicroscopy combined with differential scanning calorimetry was employed to investigate the causes of the observed acidity changes. The buffers partly crystallize and partly vitrify in the ice matrix; these processes influence the resulting pH and allow designing the optimal storage temperatures in the frozen state. The freezing-induced acidification apparently depends on the buffer concentration; at each pH, we suggest pertinent concentration, at which freezing causes minimal acidification. [ABSTRACT FROM AUTHOR]

The goal was to evaluate the effects of acidity, expressed as the Hammett acidity function, on chemical reactivity in freeze-dried materials (lyophiles). Dextran–sucrose–citrate and polyvinyl pyrrolidone (PVP)–sucrose–citrate aqueous solutions, adjusted to pH values of 2.6, 2.8, and 3.0 were freeze dried, and characterized by X-ray powder diffractometry, DSC, isothermal microcalorimetry, and Karl Fischer titrimetry. Lyophiles were also prepared from identical solutions but containing bromophenol blue (BB). Diffuse reflectance-visible spectroscopy was used to measure the extent of BB protonation from which the Hammett acidity functions were determined. The stability studies were performed at 60°C. All the freeze-dried samples were observed to be X-ray amorphous with <0.15% w/w water content. The Tg of dextran lyophiles were approximately 20°C higher than that of PVP lyophiles whereas enthalpy relaxation rates at 60°C were similar. The Hammett acidity functions were significantly lower (i.e., higher acidity) for dextran systems (<2.2–2.6) when compared with PVP systems (3.3–3.9). The rate of sucrose inversion was significantly (an order of magnitude) higher in dextran lyophiles. This study showed that in amorphous matrices with comparable water content and structural relaxation times, chemical reactivity could be significantly different depending on the matrix “acidity”. © 2007 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 97:274–286, 2008 [ABSTRACT FROM AUTHOR]

“pH memory,” i.e., correlation between pH of solution before freeze-drying and chemical reactivity in the freeze-dried state, has been reported in many systems. In this study, the “pH memory” is explored by comparing the extent of protonation of sulfonephthalein probe molecules, bromophenol blue, bromocresol green, and chlorophenol red, in aqueous solution in the pH range of 3.4–6.0 and in the resulting freeze-dried amorphous matrix (lyophile) containing trehalose and sodium citrate buffer. The protonation of the probe molecules was measured in the lyophiles by diffuse reflectance visible spectroscopy, and compared with that in the solution before drying. The protonation of the indicators in the amorphous matrix correlated with solution pH, that is, an increase in solution pH resulted in a progressive decrease in the indicator protonation in the corresponding lyophile. However, the protonation was consistently higher in the lyophile than in the corresponding solution. The Hammett acidity function of lyophiles was calculated based on the extent of protonation of the probe molecules. Protonation of the probe molecules and the Hammett acidity function depended not only on prelyophilization solution pH, but also on the residual water content and the presence of amorphous sugar in the lyophile. © 2006 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 95: 1498–1510, 2006 [ABSTRACT FROM AUTHOR]

Abstract: In this work the Hammett acidity function has been measured to assess the relative acidity of excipients used in the preparation of pharmaceutical solid dosage forms. A systematic series of experiments is reported which illustrates how the selection of the measurement conditions can influence the results of such determinations. Although the technique is somewhat empirical and relies on several key assumptions it is shown that very consistent results can be achieved by carefully controlling the measurement conditions. It is also shown that by taking this approach laboratory-to-laboratory variation can be reduced to a negligible level and the influences of subtle changes in the acidity of pharmaceutical excipients due to intrinsic variations in their physical properties or due to different processing histories can be detected and quantified. [Copyright &y& Elsevier]

Abstract: The 2,2,4-trimethylpentane (2,2,4-TMP) decomposition kinetics in the presence of trifluoromethane sulfonic acid (TfOH) and acid soluble oil (ASO) was studied at the temperatures of 15–35°C in a wide concentration range. 2,2,4-TMP partially undergoes isomerization during the reaction. The adequate kinetic model is designed for isooctane sum decomposition including light ends, heavy ends, and ASO formations. In this model heavy ends are the intermediate in ASO formation. Light ends’ evolving accompanies both heavy ends and ASO formations. Rate equations are first order in catalyst concentration and its Hammett proton activity controlled by ASO content. In particular the heavy ends formation rate is first order in isooctanes concentration, slowed down by light ends and auto-accelerated by heavy ends. The ASO formation rate is 0.6 orders in heavy ends’ concentration, slowed down by light ends, and accelerated by isooctanes and heavy ends. The reaction mechanism explaining all these phenomena is proposed and discussed in connection with practice of commercial isobutane alkylation with olefins. [Copyright &y& Elsevier]

Solutions of three Good's buffers (HEPES, MOPS, and MES), both pure and mixed with sodium phosphate buffers (Na-P), are investigated in terms of the freezing-induced acidity changes in their operational pH ranges. The Good's buffers have the tendency to basify upon freezing and, more intensively, at lower pHs. The acidity varies most prominently in MES, where the change may reach the value of two. Importantly, the Good's buffers are shown to mitigate the strong acidification in the Na-P buffer. Diverse concentrations of the Good's buffers are added to cancel out the strong, freezing-induced acidity drop in 50 mM Na-P that markedly contributes to the solution's acidity; the relevant values are 3 mM HEPES, 10 mM MOPS, and 80 mM MES. These buffer blends are therefore proposed to be applied in maintaining approximately the acidity of solutions even after the freezing process and, as such, should limit the stresses for frozen chemicals and biochemicals. [ABSTRACT FROM AUTHOR]