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Journal articles on the topic 'Acid base equilibrium'

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Published: 4 June 2021
Last updated: 30 July 2024

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1

Segstro, Edward Paul, Kerry Davie, Xiaoling Huang, and Alexander Frank Janzen. "Article." Canadian Journal of Chemistry 76, no. 5 (May 1, 1998): 518–21. http://dx.doi.org/10.1139/v98-072.

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The equilibrium in the Ph2P(O)OC6H4OH-base system may be shifted by varying the base concentration, where base = imidazole, triethylamine, dimethyl sulfoxide, pyridine, and 1,4-dioxane. This equilibrium was studied by 31P and 1H NMR, and information about the symmetry of phosphorus-containing intermediates is provided by the 1H NMR spectrum of the catecholyl ring, with its ABCD spin system. The equilibrium is also affected by trifluoroacetic acid. A mechanism is proposed that involves protonation-deprotonation, cyclic-acyclic equilibria, and selective P-O bond cleavage, with all steps occurring rapidly on the NMR time scale.Key words: Ph2P(O)OC6H4OH-base system, cyclic-acyclic equilibrium, and selective P-O bond cleavage.
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2

Grifoni, Emanuele, GiovanniMaria Piccini, and Michele Parrinello. "Microscopic description of acid–base equilibrium." Proceedings of the National Academy of Sciences 116, no. 10 (February 14, 2019): 4054–57. http://dx.doi.org/10.1073/pnas.1819771116.

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Acid–base reactions are ubiquitous in nature. Understanding their mechanisms is crucial in many fields, from biochemistry to industrial catalysis. Unfortunately, experiments give only limited information without much insight into the molecular behavior. Atomistic simulations could complement experiments and shed precious light on microscopic mechanisms. The large free-energy barriers connected to proton dissociation, however, make the use of enhanced sampling methods mandatory. Here we perform an ab initio molecular dynamics (MD) simulation and enhance sampling with the help of metadynamics. This has been made possible by the introduction of descriptors or collective variables (CVs) that are based on a conceptually different outlook on acid–base equilibria. We test successfully our approach on three different aqueous solutions of acetic acid, ammonia, and bicarbonate. These are representative of acid, basic, and amphoteric behavior.
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3

Pálla, Tamás, Arash Mirzahosseini, and Béla Noszál. "Species-Specific, pH-Independent, Standard Redox Potential of Selenocysteine and Selenocysteamine." Antioxidants 9, no. 6 (June 1, 2020): 465. http://dx.doi.org/10.3390/antiox9060465.

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Microscopic redox equilibrium constants and standard redox potential values were determined to quantify selenolate-diselenide equilibria of biological significance. The highly composite, codependent acid-base and redox equilibria of selenolates could so far be converted into pH-dependent, apparent parameters (equilibrium constants, redox potentials) only. In this work, the selenolate-diselenide redox equilibria of selenocysteamine and selenocysteine against dithiothreitol were analyzed by quantitative nuclear magnetic resonance (NMR) methods to characterize the interfering acid-base and redox equilibria. The directly obtained, pH-dependent, conditional redox equilibrium constants were then decomposed by our method into pH-independent, microscopic constants, which characterize the two-electron redox transitions of selenocysteamine and selenocysteine. The 12 different, species-specific parameter values show close correlation with the respective selenolate basicities, providing a tool to estimate otherwise inaccessible site-specific selenolate-diselenide redox potentials of related moieties in large peptides and proteins.
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4

Petersen, V. Posborg. "Acid-Base Equilibrium during Ether Anaesthesia." Acta Pharmacologica et Toxicologica 3, no. 4 (March 13, 2009): 385–94. http://dx.doi.org/10.1111/j.1600-0773.1947.tb02667.x.

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5

Wolf, Matthew B., and Edward C. DeLand. "A mathematical model of blood-interstitial acid-base balance: application to dilution acidosis and acid-base status." Journal of Applied Physiology 110, no. 4 (April 2011): 988–1002. http://dx.doi.org/10.1152/japplphysiol.00514.2010.

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We developed mathematical models that predict equilibrium distribution of water and electrolytes (proteins and simple ions), metabolites, and other species between plasma and erythrocyte fluids (blood) and interstitial fluid. The models use physicochemical principles of electroneutrality in a fluid compartment and osmotic equilibrium between compartments and transmembrane Donnan relationships for mobile species. Across the erythrocyte membrane, the significant mobile species Cl−is assumed to reach electrochemical equilibrium, whereas Na+and K+distributions are away from equilibrium because of the Na+/K+pump, but movement from this steady state is restricted because of their effective short-term impermeability. Across the capillary membrane separating plasma and interstitial fluid, Na+, K+, Ca2+, Mg2+, Cl−, and H+are mobile and establish Donnan equilibrium distribution ratios. In each compartment, attainment of equilibrium by carbonates, phosphates, proteins, and metabolites is determined by their reactions with H+. These relationships produce the recognized exchange of Cl−and bicarbonate across the erythrocyte membrane. The blood submodel was validated by its close predictions of in vitro experimental data, blood pH, pH-dependent ratio of H+, Cl−, and HCO3−concentrations in erythrocytes to that in plasma, and blood hematocrit. The blood-interstitial model was validated against available in vivo laboratory data from humans with respiratory acid-base disorders. Model predictions were used to gain understanding of the important acid-base disorder caused by addition of saline solutions. Blood model results were used as a basis for estimating errors in base excess predictions in blood by the traditional approach of Siggaard-Andersen (acid-base status) and more recent approaches by others using measured blood pH and Pco2values. Blood-interstitial model predictions were also used as a basis for assessing prediction errors of extracellular acid-base status values, such as by the standard base excess approach. Hence, these new models can give considerable insight into the physicochemical mechanisms producing acid-base disorders and aid in their diagnoses.
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6

WEN, Yan. "Relationship between Acid-Base Titration Curve and Acid-Base Equilibrium Curve." University Chemistry 33, no. 12 (2018): 76–82. http://dx.doi.org/10.3866/pku.dxhx201804014.

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7

Boulebd, Houssem, Adam Mechler, Nguyen Thi Hoa, and Quan V. Vo. "Insights on the kinetics and mechanisms of the peroxyl radical scavenging capacity of caftaric acid: the important role of the acid–base equilibrium." New Journal of Chemistry 46, no. 16 (2022): 7403–9. http://dx.doi.org/10.1039/d2nj00377e.

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8

Nguyen, Minhtri K., Liyo Kao, and Ira Kurtz. "Calculation of the equilibrium pH in a multiple-buffered aqueous solution based on partitioning of proton buffering: a new predictive formula." American Journal of Physiology-Renal Physiology 296, no. 6 (June 2009): F1521—F1529. http://dx.doi.org/10.1152/ajprenal.90651.2008.

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Upon the addition of protons to an aqueous solution containing multiple buffers, the final H+concentration ([H+]) at equilibrium is determined by the partitioning of added H+among the various buffer components. In the analysis of acid-base chemistry, the Henderson-Hasselbalch equation and the Stewart strong ion formulation can only describe (rather than predict) the equilibrium pH following a proton load since these formulas calculate the equilibrium pH only when the reactant concentrations at equilibrium11 The term “equilibrium” refers to the steady state proton and reactant concentrations when the buffering of excess protons by the various buffers is complete. are already known. In this regard, it is simpler to directly measure the equilibrium pH rather than measure the equilibrium reactant concentrations to calculate the equilibrium pH. As these formulas cannot predict the final equilibrium [H+] following a proton load to a multiple-buffered aqueous solution, we developed a new quantitative approach for predicting the equilibrium [H+] that is based on the preequilibrium22 The term “preequilibrium” refers to the initial proton and reactant concentrations immediately upon addition of protons and before the buffering of excess protons by the various buffers. concentrations of all buffers in an aqueous solution. The mathematical model used to derive our equation is based on proton transfer buffer equilibria without requiring the incorporation of electroneutrality considerations. The model consists of a quartic polynomial equation that is derived based solely on the partitioning of H+among the various buffer components. We tested the accuracy of the model using aqueous solutions with various buffers and measured the equilibrium pH values following the addition of HCl. Our results confirmed the accuracy of our new equation ( r2= 1; measured pH vs. predicted pH), indicating that it quantitatively accounts for the underlying acid-base phenomenology.
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9

Kofránek, Jiří, and Filip Ježek. "ACID-BASE EQUILIBRIUM MODELING BASED ON THE BALANCE CONCEPT." Medsoft 2018 30, no. 1 (March 10, 2018): 26–43. http://dx.doi.org/10.35191/medsoft_2018_1_30_26_43.

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Two approaches are applied to the clinical evaluation of acid--base equilibria: one is the traditional “Danish school” approach of Siggaard-Andersen et al., the other is the “modern” approach by Stewart and Fencl. The two theories are interlinked by what is called the balance approach, described in detail in [1]. A simulation model can be applied in order to model various pathogeneses of acid-base disorders and to monitor their mani-festations from both the traditional and the modern acid-base theory aspects.
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10

Imai, Hirokazu, and Wataru Kitagawa. "2. New Approach to Acid-base Equilibrium." Nihon Naika Gakkai Zasshi 97, no. 5 (2008): 1044–47. http://dx.doi.org/10.2169/naika.97.1044.

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11

Aristizábal-Salazar, Raúl E., Felipe L. Calvo-Torres, Luis Alfonso Valencia-Arango, Mauricio Montoya-Cañon, Oscar Barbosa-Gantiva, and Vanessa Hincapié-Baena. "Acid-base equilibrium: The best clinical approach☆." Colombian Journal of Anesthesiology 43, no. 3 (2015): 219–24. http://dx.doi.org/10.1097/01819236-201543030-00008.

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12

Aristizábal-Salazar, Raúl E., L. Felipe Calvo-Torres, Luis Alfonso Valencia-Arango, Mauricio Montoya-Cañon, Oscar Barbosa-Gantiva, and Vanessa Hincapié-Baena. "Acid–base equilibrium: The best clinical approach." Colombian Journal of Anesthesiology 43, no. 3 (July 2015): 219–24. http://dx.doi.org/10.1016/j.rcae.2015.05.002.

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13

Kozachkova, Oleksandra, Nataliya Tsaryk, Vasyl Pekhnyo, Volodymyr Trachevskij, Olga Kocharovska, and Oleksii Palchyk. "ACID-BASE PROPERTIES OF ALKYLENE­DIAMINETETRA (METHYLENEPHOSPHONIC) ACIDS." Ukrainian Chemistry Journal 89, no. 3 (April 28, 2023): 3–14. http://dx.doi.org/10.33609/2708-129x.89.03.2023.3-14.

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The acid-base characteristics of ethylenediaminetetra(methylenephosphonic) (edtmp), tetramethylenediaminetetra(methylenephosphonic) (tetdtmp) and pentamethylenediaminetetra(methylenephosphonic) (pendtmp) acids were investigated by means of pH-potentiometry and 31P NMR spectroscopy. Calculated and estimated values of acid dissociation constants (pK) for edtmp (рК1<2, рК2<2, рК3=3.07, рК4=5.17, рК5=6.52, рК6=7.97, рК7=9.65, рК8=10.94), for tetdtmp (рК1<2, рК2=4.48, рК3=5.34, рК4=6.13, рК5=6.66, рК6=10.08, рК7~11.4, рК8~11.5) and for pendtmp (рК1<2, рК2=4.22, рК3=5.56, рК4=6.16, рК5=7.66, рК6=10.99, рК7~11.5, рК8~11.6) were obtained. The values of the acid dissociation constants indicate a decrease in the acidity of phosphonic groups and an increase in the basicity of amino groups with increasing hydrocarbon chain length between the two nitrogen atoms in the edtmp, tetdtmp, and pendtmpseries. Based on the values of the calculated constants for the formation of anions of tetra­phosphonic acids, diagrams of the distribution of their equilibrium concentrations depending on pH were constructed, which indicate the state of acid-base equilibrium, the charge and the ratio of concentrations between anions with different degrees of protonation at certain pH values. According to the data of 31P NMR spectro­scopy, the formation of intramolecular hydrogen bonds between the deprotonated oxygen atoms of one amino(methylphosphonic) group with protonated nitrogen atom of another amino(methylphosphonic) group was established in the case of edtmp. In the case of pendtmp and tetdtmp, the formation of intermolecular hydrogen bonds between distant amino(me­thyl­phosphonic) groups is impossible due to the presence of steric hindrances.
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14

Lin, Yun, Yuemeng Ji, Yixin Li, Jeremiah Secrest, Wen Xu, Fei Xu, Yuan Wang, Taicheng An, and Renyi Zhang. "Interaction between succinic acid and sulfuric acid–base clusters." Atmospheric Chemistry and Physics 19, no. 12 (June 18, 2019): 8003–19. http://dx.doi.org/10.5194/acp-19-8003-2019.

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Abstract. Dicarboxylic acids likely participate in the formation of pre-nucleation clusters to facilitate new particle formation in the atmosphere, but the detailed mechanism leading to the formation of multicomponent critical nuclei involving organic acids, sulfuric acid (SA), base species, and water remains unclear. In this study, theoretical calculations are performed to elucidate the interactions between succinic acid (SUA) and clusters consisting of SA-ammonia (AM)∕dimethylamine (DMA) in the presence of hydration of up to six water molecules. Formation of the hydrated SUA⚫SA⚫ base clusters is energetically favorable, triggering proton transfer from SA to the base molecule to form new covalent bonds or strengthening the preexisting covalent bonds. The presence of SUA promotes hydration of the SA⚫AM and SA⚫AM⚫DMA clusters but dehydration of the SA⚫DMA clusters. At equilibrium, SUA competes with the second SA molecule for addition to the SA⚫ base clusters at atmospherically relevant concentrations. The clusters containing both the base and organic acid are capable of further binding with acid molecules to promote subsequent growth. Our results indicate that the multicomponent nucleation involving organic acids, sulfuric acid, and base species promotes new particle formation in the atmosphere, particularly under polluted conditions with a high concentration of diverse organic acids.
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15

Arman-Zubic, Lucijana, Nada Perisic-Janjic, and Marija Lazarevic. "A study of the behaviour of some substituted 1,2,4-triazoline-3-thiones in different media." Journal of the Serbian Chemical Society 65, no. 9 (2000): 619–30. http://dx.doi.org/10.2298/jsc0009619a.

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The acid-base behaviour of 4-phenyl-5-(4-R-benzyl)-1,2,4-triazoline-3-thione (1(R = OH); 2(R = OC2H5)) was studied in aqueous sulfuric acid and sodium hydroxide solutions. Three ionisation equilibria of compound 1 (pKBH3+ = -4.64, pKBH2 = 7.50, pKBH- = 10.06) and two ionisation equilibria of compound 2 (pKBH2+ = -4.82, pKBH = 7.45) were found. The first equilibrium belongs to the protonation of 1,2,4-triazoline-3-thione, while the second belongs to the dissociation of the same part of the molecule. The third equilibrium represents the dissociation process of the phenolic OH group of compound 1. The kinetics of hydrolysis of compounds 1 and 2 were studied in high concentrated sulfuric acid solutions. The hydrolysis follows an irreversible first-order consecutive reaction path.
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16

Shaw, Amy. "Bicarbonate and Chloride Equilibrium and Acid-Base Balance in the Neonate." Neonatal Network 27, no. 4 (July 2008): 261–66. http://dx.doi.org/10.1891/0730-0832.27.4.261.

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MAINTENANCE OF ACID-BASE equilibrium in the neonate is a challenge in the face of illness or prematurity. Neonatal growth and development and the proper functioning of all organ systems of the body are dependent on maintaining a normal serum pH. Neonates encounter in the normal transitional period many stresses that can cause acid-base imbalance. In addition, premature neonates are more susceptible to acid-base imbalance because their compensatory responses are limited. Factors associated with acid-base imbalance seen in the newborn period include respiratory distress, sepsis, hypovolemia, perinatal stressors, and prematurity.1–4
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17

Santa Cruz, Francisco Vicente. "Acid-Base equilibrium and hydroelectrolytic disorders Learning by clinical cases." Anales de la Facultad de Ciencias Médicas (Asunción) 53, no. 2 (August 30, 2020): 171–72. http://dx.doi.org/10.18004/anales/2020.053.02.171.

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18

Kuznetsova, Rimma T., Yulia V. Aksenova, Georgii V. Mayer, and E. V. Antina. "The Interactions with Proton-Donor Solvents and Stability of some Borondipyrrinates." Advanced Materials Research 1088 (February 2015): 386–90. http://dx.doi.org/10.4028/www.scientific.net/amr.1088.386.

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The constants of acid-base equilibrium were estimated with spectroscopic method at the ground (S0) and at the fluorescent (S1fl) states. The constants of acid-base equilibrium for Franck-Condon excited states (S1F-C) were estimated from spectral shifts for basic and acid forms. This results are compared with quantum yields of photostability of complexes in neutral solvents. The mechanisms of complexes protonation are discussed dependence from the structure of ligands.
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19

Kowalchuk, John M., and Barry W. Scheuermann. "Acid-Base Balance: Origin of Plasma [H+] During Exercise." Canadian Journal of Applied Physiology 20, no. 3 (September 1, 1995): 341–56. http://dx.doi.org/10.1139/h95-027.

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According to physicochemical principles, the plasma concentration of hydrogen ions ([H+]), bicarbonate ([HCO3−]), and other acid-base-dependent variables are determined by the plasma PCO2; the strong ion difference ([SID+] = Σ[strong cations] − Σ[strong anions]); and the concentration of weak acids ([ATOT] = [HA] + [A−]). The physicochemical interactions between the acid-base-independent and dependent variables must recognize the constraints imposed by the law of electrical neutrality, dissociation equilibrium of weak acids and water, and the conservation of mass. This review demonstrates the usefulness of the physicochemical approach in studying plasma acid-base control during progressive exercise to exhaustion where the work rate was increased as either a slow (8 W/min) or fast (65 W/min) ramp function. The factors contributing to changes in the concentration of the acid-base-independent variables, and the contribution of the acid-base-independent variables to the plasma [H+] and [HCO3−] during exercise, will be discussed. Key words: PCO2, strong ion difference, weak acids, lactate, potassium
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20

Abdel-Mottaleb, M. S. A., H. R. Galal, A. F. M. Dessouky, M. El-Naggar, D. Mekkawi, S. S. Ali, and G. M. Attya. "Fluorescence and photostability studies of anthracene-9-carboxylic acid in different media." International Journal of Photoenergy 2, no. 1 (2000): 47–53. http://dx.doi.org/10.1155/s1110662x00000076.

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Electronic absorption and fluorescence spectra of anthracene-9-carboxylic acid (ANCA) were studied in different homogeneous solvents, binary protic/aprotic solvent mixtures and in heterogeneous solutions of the cationic cetyltrimethyl ammonium bromide (CTAB) micelle. Different chemical species of ANCA were identified spectroscopically in different media. The results are discussed on the basis of a mechanism that involves two equilibria: acid-base equilibrium and monomer-dimer equilibrium. These equilibria were found to be very sensitive to the nature of the medium and the concentration of ANCA.Moreover, while it is photostable in most solvents studied, the ANCA was found to be photolabile in aqueous media of different pHs. The acid-base catalyzed photodegradation rate was studied by following up absorption and/or fluorescence intensities as a function of illumination dose. The determined rate of the photochemical degradation of ANCA depends on the nature of the medium. The first order degradation rate constant is remarkably enhanced in heterogeneous medium of CTAB. As expected, the determined activation energy is low (∼3.2 kJ.mol-1). This result favors photooxidation process. Anthraquinone was the main photodegradation product obtainedvia9,9′-dicarboxylic head-to-head dimer of anthracene that was identified by GC-Mass technique.
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21

Madias, Nicolaos E., Charles J. Wolf, and Jordan J. Cohen. "Regulation of acid-base equilibrium in chronic hypercapnia." Kidney International 27, no. 3 (March 1985): 538–43. http://dx.doi.org/10.1038/ki.1985.44.

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22

Ilich, Predrag-Peter, and Kristina K. Streb. "Acid–Base Equilibrium in a Lipid/Water Gel." Journal of Chemical Education 80, no. 12 (December 2003): 1464. http://dx.doi.org/10.1021/ed080p1464.

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23

Xi, Juqun, and Rong Guo. "Acid–base equilibrium of puerarin in CTAB micelles." Journal of Pharmaceutical and Biomedical Analysis 43, no. 1 (January 2007): 111–18. http://dx.doi.org/10.1016/j.jpba.2006.06.028.

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24

Mchedlov-Petrossyan, Nikolay O. "Protolytic equilibrium in lyophilic nanosized dispersions: Differentiating influence of the pseudophase and salt effects." Pure and Applied Chemistry 80, no. 7 (January 1, 2008): 1459–510. http://dx.doi.org/10.1351/pac200880071459.

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The so-called apparent ionization constants of various acids (mainly indicator dyes) in versatile organized solutions are analyzed. Aqueous micellar solutions of colloidal surfactants and related lyophilic colloidal systems display a strong differentiating influence on the acidic strength of indicators located in the dispersed pseudophase, i.e., non-uniform changes of pKa on going from water to the given system. This concept allows the influence of such media on acid-base properties of dissolved reagents to be rationalized. It is demonstrated that the differentiating phenomenon is the main reason for limitation of the common electrostatic model of acid-base interactions, and is the principal hindrance to exact evaluations of the interfacial electrical potentials of ionic micelles by means of acid-base indicators. Salt effects, i.e., the influence of supporting electrolytes on the apparent ionization constants of acid-base indicators in the Stern region of ionic micelles, are considered. These salt effects can be conventionally divided into two kinds, namely, general (normal) and special (specific) effects. While the first type adds up to screening of the surface charge, the second one consists in micellar transitions caused by hydrophobic counterions.
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25

Tanganov, B. B. "Applied aspects of acid-base interactions and modelling equilibrium concentrations in two-component acid mixtures." Proceedings of Universities. Applied Chemistry and Biotechnology 10, no. 3 (October 8, 2020): 393–400. http://dx.doi.org/10.21285/2227-2925-2020-10-3-393-400.

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Fundamental and applied research into aqueous and non-aqueous solutions of strong and weak electrolytes remains to be highly relevant, which fact is confirmed by a large number of Russian and foreign publications. In almost all such publications, acid-base interactions are considered exclusively with regard to changes in hydrogen ion concentrations. However, the ionic strength of solutions is determined by all ions present in the system, the concentration of which varies during interactions. This is particularly true for potentiometric titration of strong and weak electrolytes not only in aqueous, but also in more complex non-aqueous solutions, which differ significantly in their basic properties (dielectric constant, ionic product, dipole moment, viscosity, etc.). In the study of equilibria, it is more feasible to develop model representations that would greatly simplify and facilitate the computation and evaluation of certain properties of the system under consideration. In this work, acid-base interactions are presented in the form of equations based on mass action laws and those describing equilibrium processes, solvent ionic product, electroneutrality and material balance in electrolyte systems. The proposed equations consider the effect of the concentrations of all charged particles in the system (not only of hydrogen ions – pH) on the ionic strength of the solution, activity coefficients and, as a consequence, the thermodynamic dissociation constant. In addition, these equations allow the dependence between the equilibrium concentrations of all charged particles and the solution acidity determined by the potentiometric method to be expressed in convenient and objective logarithmic coordinates, thus facilitating estimation of the concentration of all particles at any moment of titration.
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Xiang, Tao, and Keith P. Johnston. "Acid-base behavior in supercritical water: β-naphthoic acid-ammonia equilibrium." Journal of Solution Chemistry 26, no. 1 (January 1997): 13–30. http://dx.doi.org/10.1007/bf02439441.

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27

Al Ajmi, Muna, Ahoud AL- Hamadani, Anteneh Mesfin Yeneneh, and Tahereh Jafary. "Removal of Oil from Contaminated Wastewater Using Thermo-Chemically Modified Lignocellulosic Biomass." Materials Science Forum 1059 (April 25, 2022): 157–70. http://dx.doi.org/10.4028/p-j9vcgc.

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The volume of oil-contaminated wastewater generated from petrochemical industries and various oil fields is significant. The discharge of such oily wastewater endangers terrestrial and aquatic ecosystems due to the high organic load and toxicity of the oily components. Currently, there are several technologies available for the treatment of oily wastewater among which adsorption was observed to be a promising technique for the removal of oil emulsions from wastewater. In this study, acid modified and base modified pyrolyzed date seed was investigated for the removal of oil and oil emulsions from contaminated water. The effect of pH in the range of (2-12), temperature (30°C-70°C), date seed dose of (0.1-1 g) and contact time of (1-240 mins) was investigated for both the acid modified and base modified activated date seeds samples. Equilibrium sorption was attained after a contact time of 120 minutes. It was observed that base modified activated date seed resulted in 83% removal of oil. Both acid and base modified activated date seed showed a high percentage removal of 92.9 % and 94.3 % respectively at a lower acidic pH of 2. Concerning the equilibrium sorption kinetics, Pseudo-Second-order kinetic Model showed better fit as compared to pseudo first order kinetic model. Therefore, the adsorption of oily wastewater onto both acid and base modified activated date seeds are consistent with the second-order kinetic model. The Langmuir isotherm was found to be linear with high correlation coefficient values over the entire concentration range, which confirms that the Langmuir isotherm is more accurate to represent sorption by acid modified date seed unlike the case of base modified activated date seed where Freundlich isotherms were found to better fit the adsorption equilibrium data for base modified date seed. Keywords: Pyrolyzed date seeds; chemically modified activated date seeds; thermo-chemically modified lignocellulosic biomass; kinetics; equilibrium isotherms.
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28

Al Ajmi, Muna, Ahoud AL- Hamadani, Anteneh Mesfin Yeneneh, and Tahereh Jafary. "Removal of Oil from Contaminated Wastewater Using Thermo-Chemically Modified Lignocellulosic Biomass." Materials Science Forum 1059 (April 25, 2022): 157–70. http://dx.doi.org/10.4028/p-j9vcgc.

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The volume of oil-contaminated wastewater generated from petrochemical industries and various oil fields is significant. The discharge of such oily wastewater endangers terrestrial and aquatic ecosystems due to the high organic load and toxicity of the oily components. Currently, there are several technologies available for the treatment of oily wastewater among which adsorption was observed to be a promising technique for the removal of oil emulsions from wastewater. In this study, acid modified and base modified pyrolyzed date seed was investigated for the removal of oil and oil emulsions from contaminated water. The effect of pH in the range of (2-12), temperature (30°C-70°C), date seed dose of (0.1-1 g) and contact time of (1-240 mins) was investigated for both the acid modified and base modified activated date seeds samples. Equilibrium sorption was attained after a contact time of 120 minutes. It was observed that base modified activated date seed resulted in 83% removal of oil. Both acid and base modified activated date seed showed a high percentage removal of 92.9 % and 94.3 % respectively at a lower acidic pH of 2. Concerning the equilibrium sorption kinetics, Pseudo-Second-order kinetic Model showed better fit as compared to pseudo first order kinetic model. Therefore, the adsorption of oily wastewater onto both acid and base modified activated date seeds are consistent with the second-order kinetic model. The Langmuir isotherm was found to be linear with high correlation coefficient values over the entire concentration range, which confirms that the Langmuir isotherm is more accurate to represent sorption by acid modified date seed unlike the case of base modified activated date seed where Freundlich isotherms were found to better fit the adsorption equilibrium data for base modified date seed. Keywords: Pyrolyzed date seeds; chemically modified activated date seeds; thermo-chemically modified lignocellulosic biomass; kinetics; equilibrium isotherms.
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29

Le-Thanh, Hoa, and D. Vocelle. "1H NMR studies of proton transfer in Schiff base and carboxylic acid systems." Canadian Journal of Chemistry 68, no. 10 (October 1, 1990): 1909–16. http://dx.doi.org/10.1139/v90-295.

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When the unconjugated Schiff base, isobutylidene isopropylamine (2), reacts with acids such as the mineral acids HCl, HBr, and HI, or the carboxylic acids trichloroacetic, monochloroacetic, and propionic acid, in CDCl3, several complexes are formed. In this study, 1H NMR allows us to differentiate between several possibilities. With the mineral acids, only 1:1 structures are seen and the chemical shift of the [Formula: see text] proton varies according to the strength of the hydrogen bond between the protonated Schiff base and its counterion. With the carboxylic acids, 1:1 and 1:2 structures are present in rapid equilibrium. In the presence of an excess of acid, protonation of the Schiff base increases considerably. Extrapolation of the results is given in terms of the molecular mechanism of vision. Keywords: protonation, proton nuclear magnetic resonance, proton transfer, rhodopsins, Schiff base.
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30

Anderson, John C., and A. Douglas Broadbent. "The influence of pH in the tautomerism of 9,10-anthracenediols and 1,3-diketones." Canadian Journal of Chemistry 64, no. 1 (January 1, 1986): 127–32. http://dx.doi.org/10.1139/v86-022.

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Equations have been derived to describe how the ratio of the total concentration of all keto forms to that of all enolic forms (K′) varies with changing pH, for a tautomeric system in which the enol and ketone are polyprotic acids. The influence of pH on the tautomerism of 2-amino-9,10-anthracenediol, 2,9,10-anthracenetriol, 2,4-pentanedione, and 1-(3-pyridyl)-1,3-butanedione was examined. The equilibrium constants for all the acid–base equilibria involved were calculated from the dependence of K′ on pH.
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31

Rys, Paul, Ruth Weber, and Qinglan Wu. "Light-induced change of the molecular charge in a spironaphthoxazine compound." Canadian Journal of Chemistry 71, no. 11 (November 1, 1993): 1828–33. http://dx.doi.org/10.1139/v93-228.

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To evaluate the experimental conditions for the light-induced change of the molecular charge, the dependence of the photochromic reaction behaviour of the indolino spiro naphthoxazine compound 1,3,3-trimethyl-spiro[2H-indol 2,3′-[3H]naphth[2,1-b]-[1,4]oxazine] on the pH value of the solution is investigated. In the absence of UV light an acid–base equilibrium between the spiro form and a protonated closed form is established. By irradiation under appropriate acidic conditions the spiro form can be transformed into an open cationic form through the merocyanine form. Between the two open forms an acid–base equilibrium is established. Except for the closed protonated form the structures are confirmed by mean of NMR. The kinetics of the thermal ring-closing reaction of both forms are investigated by flash photolysis. It is shown that the ring-closing reaction proceeds exclusively via the merocyanine form. The pK values determined for both equilibria give the pH range, in which the light-induced change of the molecular charge occurs.
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32

Benko, Ján, Oľga Vollárová, and Miroslav Kovarčík. "Kinetics of oxidation of the bis(ethylenediamine)mercaptoacetatocobalt(III) and cysteinato-bis(ethylenediamine)cobalt(III) ions by hydrogen peroxide in mixed aqueous-nonaqueous solutions." Collection of Czechoslovak Chemical Communications 53, no. 3 (1988): 554–62. http://dx.doi.org/10.1135/cccc19880554.

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The kinetics of oxidation of the coordinatively bonded sulphur in the cysteinato-bis(ethylenediamine)cobalt(III) and bis(ethylenediamine)mercaptoacetatocobalt(III) complexes by hydrogen peroxide to the sulphoxides was examined in HClO4 solutions (c(HClO4) = 1 – 500 mmol l-1) with a view to obtaining data characterizing the effect of the acid-base equilibria of the reactants on the reaction rate. The reaction rate was found affected particularly by the acid-base equilibrium of the oxidant, which plays a role in strongly acid solutions. The oxidation was also studied in water-methyl alcohol, water-tert-butyl alcohol and water-ethylene glycol mixtures, and the effect of the mole fraction of the nonaqueous component on the rate constant and thermodynamic activation parameters was examined.
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33

Natsuda, Kenichiro, Takahiro Kozawa, Kazumasa Okamoto, and Seiichi Tagawa. "Study of Acid-Base Equilibrium in Chemically Amplified Resist." Japanese Journal of Applied Physics 46, no. 11 (November 6, 2007): 7285–89. http://dx.doi.org/10.1143/jjap.46.7285.

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34

Gordos, Adon A. "Chemical equilibrium: VII. pH approximations in acid-base titrations." Journal of Chemical Education 68, no. 9 (September 1991): 759. http://dx.doi.org/10.1021/ed068p759.

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35

Kipp, James E. "PHCALC: A Computer Program for Acid/Base Equilibrium Calculations." Journal of Chemical Education 71, no. 2 (February 1994): 119. http://dx.doi.org/10.1021/ed071p119.

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36

Eriksen, T. E., J. Lind, and G. Merényi. "On the acid-base equilibrium of the carbonate radical." Radiation Physics and Chemistry (1977) 26, no. 2 (January 1985): 197–99. http://dx.doi.org/10.1016/0146-5724(85)90185-2.

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37

Kawata, Hiroki, and Shigeya Niizuma. "Acid-base equilibrium in Excited State of 10-Methylacridone." Journal f�r Praktische Chemie/Chemiker-Zeitung 336, no. 5 (1994): 425–28. http://dx.doi.org/10.1002/prac.19943360508.

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38

Zhang, Wei-Ming, Jin-Long Chen, Bing-Cai Pan, and Quan-Xing Zhang. "Competitive and Cooperative Adsorption of Aromatic Acids and Bases onto a New Aminated Macroreticular Adsorbent." Adsorption Science & Technology 23, no. 9 (November 2005): 751–62. http://dx.doi.org/10.1260/026361705776316541.

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The adsorption behaviour of three aromatic acids [phenol, benzoic acid (BCA) and 2-naphthalene sulphonic acid (2-NSA)] and of one aromatic base (aniline) on an aminated macroreticular adsorbent (NDA103) were investigated employing single or binary batch systems at 293 K and 313 K, respectively. All the adsorption isotherms in the studied systems could be adequately fitted by the Langmuir model, thereby indicating the existence of an exothermic adsorption process for phenol, BCA and aniline. At low equilibrium concentrations, the individual uptakes in the single-component systems were higher than those in binary-component systems because of competition between the two types of adsorbate molecules towards the adsorption sites. On the other hand, it is noteworthy that the total molar uptakes of adsorbates in the binary-component systems at high equilibrium concentrations were larger than the uptakes in the single-component systems. In binary-component systems, a large excess of aromatic acids was noted on the adsorbent surface at saturation, presumably as a result of a cooperative effect arising primarily from acid–base interaction between the loaded adsorbates.
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39

Drazic, Branka, Gordana Popovic, Ratomir Jelic, Dusan Sladic, Dragana Mitic, Katarina Andjelkovic, and Zivoslav Tesic. "Acid-base equilibria of the Zn(II) and Fe(III) complexes with condensation products of 2-acetylpyridine and the dihydrazide of oxalic and malonic acid." Journal of the Serbian Chemical Society 74, no. 3 (2009): 269–77. http://dx.doi.org/10.2298/jsc0903269d.

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Acid-base equilibria of Zn(II) and Fe(III) complexes with N',N'2-bis- [(1E)-1-(2-pyridyl)ethylidene]ethanedihydrazide (ligand L1) and N',N'2-bis[(1E)- -1-(2-pyridyl)ethylidene]propanedihydrazide (ligand L2), i.e., [Fe(L1)Cl2(H2O)], [Fe(L2)Cl(H2O)]2+, [Zn(L1)(H2O)3]+ and [Zn(L2)(H2O)2]2+, which expressed cytotoxic activity, were investigated in aqueous media. The equilibrium constants were determined potentiometrically at 25?C at a constant ionic strength of 0.10 mol/dm3 (Na2SO4). The results showed that at pH < 8 both the Fe(III) complexes studied here have three, while [Zn(L1)(H2O)3]+ and [Zn(L2)(H2O)2]2+ have one and two titratable protons, respectively. Based on the obtained values for the equilibrium constants, protonation schemes of the examined complexes are proposed.
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40

Vojic, Mirjana, Gordana Popovic, Dusan Sladic, and Lidija Pfendt. "Protolytic equilibria in homogeneous and heterogeneous systems of ketoconazole and its direct spectrophotometric determination in tablets." Journal of the Serbian Chemical Society 70, no. 1 (2005): 67–78. http://dx.doi.org/10.2298/jsc0501067v.

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The acid-base equilibria of a diprotic, slightly hydrosoluble base ketoconazole were studied in homogeneous and heterogeneous water systems. The determinations were performed at 25?C at a constant ionic strength of M(NaCl). The acidity constant Ka1 was determined by potentiometric (pKa1 3.20) and spectrophotometric (pKa1 3.26) methods. A pKa2 constant of 6.10 was obtained based on the equilibrium constants pKs0 4.84 and pKs1 -1.26, determined in a heterogeneous ketoconazole system. The obtained values of the constants served to calculate the solubility and the distribution of the equilibrium forms of ketoconazole as a function of pH. On the basis of the distribution of the equilibrium forms of ketoconazole, a spectrophotometric method for the determination of its content in commercial tablets was developed. The determinations were performed at 225 nm in 0.1 M HCl. The method is simple and rapid and enables the direct spectrophotometric determination of the content of ketoconazole without previous isolation.
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41

Porter, Ned A., Huiyong Yin, and Derek A. Pratt. "The Peroxy Acid Dioxirane Equilibrium: Base-Promoted Exchange of Peroxy Acid Oxygens." Journal of the American Chemical Society 122, no. 45 (November 2000): 11272–73. http://dx.doi.org/10.1021/ja005648q.

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42

Ostakhov, S. S., R. R. Kayumova, A. A. Akhiyarov, S. P. Ivanov, and S. L. Khursan. "Spectral-Luminescent Study of the Acid–Base Equilibrium of 5-Aminouracil and 6-Aminouracil in Aqueous Solutions." Химия высоких энергий 57, no. 1 (January 1, 2023): 3–8. http://dx.doi.org/10.31857/s0023119323010102.

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The spectral fluorescence characteristics of 5-aminouracil (5AU) and 6-aminouracil (6AU) in neutral and alkaline aqueous solutions have been studied. With the use of the density functional theory, it has been shown that uracils preferentially dissociate at the N1–H bond. The acid–base equilibrium constants pKa1(5AU) = 9.4 and pKa1(6AU) = 8.95 were determined by a fluorescence method. It was concluded that the ultrashort lifetime of the excited singlets of 5AU and 6AU prevents the measurement of the acid–base equilibrium constant of uracils in an electronically excited state.
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43

Földényi, Rita, and Aurél Marton. "Organisation of the Analytical, Stoichiometric, and Thermodynamic Information for water Chemistry Calculations." Hungarian Journal of Industry and Chemistry 43, no. 1 (June 1, 2015): 33–38. http://dx.doi.org/10.1515/hjic-2015-0006.

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Abstract A common feature of the chemical processes of the hydrosphere and water treatment plants is that essentially the same types of chemical equilibrium reactions occur in both fields. These equilibria could be acid/base, complexation, redox, precipitation, and interfacial processes. Since these reactions may also occur in combination, the aqueous environments are unavoidably multispecies systems. Due to multiple equilibria, the state of aggregation, the state of oxidation, as well as the electric charge of the species may change dramatically. Calculation of the equilibrium concentration of the species is facilitated by the availability of analytical, stoichiometric, and thermodynamic information that are consistently organised into an ASTI matrix. The matrix makes it possible to apply a uniform algebraic treatment for all occurring equilibria even, if later on, further reactions have to be included in the chemical model. The use of the ASTI matrix enables us to set up the necessary mass balance equations and equilibrium relationships, which together form a non-linear system of equations (NLSE). The goal of our paper is to show that the use of the ASTI matrix approach in cooperation with the powerful engineering calculation software, MATHCAD14, results in fast and easy handling of the NLSE-s and, consequently, the calculations of speciation in aqueous systems. The paper demonstrates the method of application in three examples: the calculation of the pH dependence of the solubility of calcite in closed and open systems, the calculation of the pH and pε in a system where acid/base reactions, complexation equilibria, and redox equilibria occur, and a study of adsorption of lead ions on aluminium oxide.
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44

Kaválek, Jaromír, Vladimír Macháček, Gabriela Svobodová, and Vojeslav Štěrba. "Base catalyzed cyclization of substituted esters of hydantoic and thiohydantoic acids." Collection of Czechoslovak Chemical Communications 51, no. 2 (1986): 375–90. http://dx.doi.org/10.1135/cccc19860375.

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Base catalyzed cyclization rates have been measured of 22 derivatives of hydantoic and thiohydantoic acid esters in water and methanol. The cyclization of methyl and ethyl esters of hydantoic and 5-methylhydantoic acids is accompanied by hydrolysis of the ester group, whereas with the other derivatives the hydrolysis does not take place. Hydrolysis of the cyclization products (hydantoin and thiohydantoin derivatives) is not significant under the kinetic conditions. The cyclization of methyl ester of 5-phenylhydantoic acid in methanol is reversible; the equilibrium mixture contains 30% of the starting ester. In all the cases the cyclization is subject to specific base catalysis; exceptions are esters of 5-phenylthiohydantoic and 5-phenyl-2-methylthiohydantoic acids whose cyclizations are subject to general base catalysis. Substituents always accelerate the cyclization. The 3-substituents have the greatest effects, the cyclization rate being considerably increased with bulk of the substituents; similarly large effect of 5-phenyl group consists mainly in its polar effects on the pre-equilibrium. The cyclization are slower in methanol at the same concentration of the lyate ion: the greatest difference (up to 3 orders of magnitude) is observed with the 5-phenyl derivatives.
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45

Escolar, D., Ma R. Haro, A. Saucedo, J. Ayuso, A. Jimenez, and J. A. Alvarez. "Determining Acid Equilibrium Constants by Means of Chromatic Parameters." Applied Spectroscopy 50, no. 10 (October 1996): 1290–94. http://dx.doi.org/10.1366/0003702963905024.

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A method has been developed for the determination of acid-base equilibrium constants, which is applicable to compounds that absorb in the visible. The tristimulus (X, Y, Z) and the colorimetric coordinate values ( L, a, b) of the chromatic space CIELAB 1976 are calculated by means of the transmittances of the entire spectral range. The curves, in the a,b plane, of chromatic differences vs. pH intersect at a pH value agreeing with the p Ka; this configuration occurs because a chromatic equilibrium of both species takes place at this point, which corresponds to the chemical equilibrium. With this method, the acidity constants are found easily and quickly, and they yield very good results. The validity of the method has been tested with the acid-base indicator bromophenol blue, obtaining p Ka= 3.943 at 25 °C; this result is compared with those obtained through the usual spectrophotometric methods. Also, thermodynamic magnitudes obtained from p Ka values at different temperatures from 20 to 70 °C have been determined, resulting in Δ H0 = -(13.93 ± 0.88) kj mol−1 Δ S0 = -(122.6 ± 2.8) J K−1 mol−1.
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46

Brboric, Jasmina, Mirjana Jovanovic, Gordana Popovic, Vera Kapetanovic, and Sote Vladimirov. "Acid-base equilibria of 2,4-diiodo-6-methylphenylcarbamoylmethyl iminodiacetic acid and its labeling with technetium-99m." Journal of the Serbian Chemical Society 71, no. 1 (2006): 55–65. http://dx.doi.org/10.2298/jsc0601055b.

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The acid-base equilibria of a novel hepatobiliary imaging agent, 2,4-diiodo-6-methylphenylcarbamoylmethyl iminodiacetic acid (DIIODIDA) were studied. The potentiometrically determined acidity constants of the second carboxylic group, amino and amide groups were pK2 = 2.52 ? 0.02; pK3 = 5.86 ? 0.06 and pK4 = 10.9 ? 0.1. The determinations were performed at 25 ?C and an ionic strength of 0.1 mol/dm3 (NaCl). The acidity constants (pK1 = 1.3 ? 0.4) corresponding to the first carboxylic group was determined indirectly, on the basis of equilibrium constants obtained in a heterogeneous system, at 25 ?C and an ionic strength 1 mol/dm3 (HCl, NaCl). DIIODIDA was labeled with technetium-99m, and the influence of pH on the yield of labeling was investigated. It was found that labeling within the pH range from 5.5 to 6.5 provided a radiopharmaceutical of high radiochemical purity (>98 %).
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47

Ishiguro, Shin-ichi, Yasuhiro Umebayashi, Ryo Kanzaki, and Kenta Fujii. "Structure, solvation, and acid–base property in ionic liquids." Pure and Applied Chemistry 82, no. 10 (August 6, 2010): 1927–41. http://dx.doi.org/10.1351/pac-con-09-10-28.

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Ionic liquids (ILs) are expected to have specific properties as solvents for chemical reactions in view of solution chemistry. Among physicochemical properties, liquid structure, acid–base, and electron-pair donating and accepting abilities of solvent play a crucial role in ion-solvation and acid–base, metal-ion complexation, and electrochemical reactions. Various types of ILs have been developed, and among others, the bis(trifluoromethanesulfonyl)amide (TFSA–)-based ILs are extensively used. TFSA– is a flexible molecule to give two stable conformers, cis (C1) and trans (C2), which are present in equilibrium in the liquid state. The conformational equilibrium shifts upon solvation to the metal ion. This is quantitatively studied to obtain thermodynamic parameters of conformational change from C2 to C1 in the bulk and in the solvation sphere of the lithium ion. On the other hand, with ethylammonium nitrate (EAN), a typical protic IL, it is revealed that the ammonium group is hydrogen-bonded with three nitrate ions to form a heterogeneous liquid structure. The solvent acid–base property of EAN and acid dissociation reaction in EAN have been quantitatively revealed, and the results will be discussed in comparison with those in normal molecular solvents.
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48

Pálla, Tamás, Arash Mirzahosseini, and Béla Noszál. "Properties of Selenolate-Diselenide Redox Equilibria in View of Their Thiolate-Disulfide Counterparts." Antioxidants 12, no. 4 (March 28, 2023): 822. http://dx.doi.org/10.3390/antiox12040822.

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Selenium, the multifaceted redox agent, is characterized in terms of oxidation states, with emphasis on selenol and diselenide in proteinogenic compounds. Selenocysteine, selenocystine, selenocysteamine, and selenocystamine are depicted in view of their co-dependent, interfering acid-base, and redox properties. The pH-dependent, apparent (conditional), and pH-independent, highly specific, microscopic forms of the redox equilibrium constants are described. Experimental techniques and evaluation methods for the determination of the equilibrium and redox parameters are discussed, with a focus on nuclear magnetic resonance spectroscopy, which is the prime technique to observe selenium properties in organic compounds. The correlation between redox, acid-base, and NMR parameters is shown in diagrams and tables. The fairly accessible NMR and acid-base parameters are discussed to assess the predictive power of these methods to estimate the site-specific redox properties of selenium-containing moieties in large molecules.
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49

Gasanov, K. A., and V. M. Asadov. "Prediction of the spastic component of grave alcoholic abstinent syndrome." Neurology Bulletin XXV, no. 1-2 (September 20, 1993): 112–15. http://dx.doi.org/10.17816/nb105992.

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The resultes of examinations of hydroion balance (acid-base equilibrium, circulating blood volume, content of potassium and sodium in plasma and erythrocytes in 145 patients with grave forms of alcoholic abstinent syndrome are given. The data presented allow to justify the objective criteria suggesting the possibility of development of epileptic attacks within the limits of grave abstinent syndrome and underline the decisive role of the elimination of pathologic shifts of acid-base equilibrium and water-and-electrolyte balance by means of directional differented correction to prevent graver state as well as to increase the efficiency of the treatment.
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50

Smith, Bradley J., and Vincent A. Patrick. "Quantitative Determination of Aqueous Dodecatungstophosphoric Acid Speciation by NMR Spectroscopy." Australian Journal of Chemistry 57, no. 3 (2004): 261. http://dx.doi.org/10.1071/ch02037.

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The speciation and equilibria during base decomposition of α-[PW12O40]3– have been determined using 31P and 183W NMR spectroscopy over the pH range 0.7–13.5. NMR spectroscopy was used to directly observe the polytungstate species in aqueous solution at high concentration (0.25 mol L–1) and follows the progressive decomposition of [PW12O40]3– to WO42– and PO43–. It was found unexpectedly in the pH range 1.2–2.3 that [PW12O40]3– did not decompose directly to [PW11O39]7– but first formed an equilibrium with [P2W18O62]6–, [P2W21O71]6–, and some new, stable, intermediate species before converting into α-[PW11O39]7–.
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