Thermodynamics of the Second Dissociation Constant and Standards for pH of 3-(NMorpholino) Propanesulfonic Acid (MOPS) Buffers from 5 to 55°C

The second dissociation constant pK2 of 3-(N-morpholino)propanesulfonic acid (MOPS) has been determined at eight temperatures from 5 to 55°C by measurements of the emf of cells without liquid junction, utilizing hydrogen electrodes and silver–silver chloride electrodes. The pK2 has a value of 7.18 ± 0.001 at 25°C and 7.044 ± 0.002 at 37°C. The thermodynamic quantities G°, H°, S°, and C _p ^o have been derived from the temperature coefficients of the pK ₂. This buffer at ionic strength I = 0.16 mol-kg^–1 close to that of blood serum, has been recommended as a useful secondary pH standard for measurements of physiological fluids. Five buffer solutions with the following compositions were prepared: (a) equimolal mixture of MOPS (0.05 mol-kg^–1) + NaMOPS, (0.05 mol-kg^–1); (b( MOPS (0.05 mol-kg^–1) + NaMOPS (0.05 mol-kg^–1) + NaCl (0.05 mol-kg^–1); (c) MOPS (0.05 mol-kg^–1) + NaMOPS (0.05 mol-kg^–1); + NaCl (0.11mol-kg^–1); (d) MOPS (0.08 mol-kg^–1) + NaMOPS (0.08 mol-kg^–1); and (e)MOPS (0.08 mol-kg^–1) + NaMOPS (0.08 mol-kg^–1) + NaCl (0.08 mol-kg^–1).The pH values obtained by using the pH meter + glass electrode assembly are compared with those measured from a flow–junction calomel cell saturated with KCl (cell B), as well as those obtained from cell (A) without liquid junction at 25 and 37°C. The conventional values of the liquid junction potentials E _j have been obtained at 25 and 37°C for the physiological phosphate reference solution as well as for the MOPS buffers (d) and (e) mentioned above.     

Second Dissociation Constants of 4-[N-morpholino]butanesulfonic Acid and N-[2-hydroxyethyl]piperazine-N′-4-butanesulfonic Acid from 5 to 55°C

The values of the second dissociation constant, pK ₂, for the dissociation of the NH⁺ charge center of the zwitterionic buffer compounds 4-(N-morpholino)butanesulfonic acid (MOBS), and N-(2-hydroxyethyl)piperazine-N-4-butanesulfonic acid (HEPBS) have been determined from 5 to 55°C, including, 37°C at intervals of 5°C. The electromotive-force (emf) measurements have been made utilizing hydrogen electrodes and silver–silver chloride electrodes. The value of pK ₂ for MOBS was found to be 7.702 ± 0.0005, and 8.284 ± 0.0004 for HEPBS, at 25°C, respectively. The related thermodynamic quantities, G ^o, H ^o, S ^o, and C _p ^o for the dissociation processes of MOBS and HEPBS have been derived from the temperature coefficients of pK ₂. Both the MOBS and HEPBS buffer materials are useful as primary pH standards for the control of pH 7.3 to 8.6 in the region close to that of physiological fluids.     

The Second Dissociation Constant of Carbonic Acid in Ethanol–Water Mixtures from 5 to 45°C

The determination of the second dissociation constant of carbonic acid K ₂ in 5, 15, and 25 mass% ethanol—water mixed solvents has been made using cell of the type:

Raman-Spectroscopic Measurements of the First Dissociation Constant of Aqueous Phosphoric Acid Solution from 5 to 301 °C

Dilute aqueous phosphoric acid solutions have been studied by Raman spectroscopy at room temperature and over a broad temperature range from 5 to 301?°C. R-normalized spectra (Bose?CEinstein correction) have been constructed and used for quantitative analysis. The vibrational modes of H₃PO₄(aq) (pseudo C_3v symmetry) have been assigned. The band with the highest intensity, the symmetric stretch ?? _s{P(OH)₃}(?? ₁(a ₁)) is strongly polarized while ?? ₄(e), the antisymmetric stretch ?? _asP(OH)₃) is depolarized. The stretching mode of the phosphoryl group (?CP=O), ?? ₂(a₁) occurs at 1178?cm^?1 and is polarized. In the range between 300 and 600?cm^?1, the deformation modes are observed. The deformation mode, ??{PO?CH}, involving the O?CH group has been detected at 1250?cm^?1 as a very weak and broad mode. In addition to the modes of phosphoric acid, modes of the dissociation product $\mathrm{H}_{2}\mathrm{PO}_{4}^{ -}(\mathrm{aq})$ have been observed. The mode at 1077?cm^?1 has been assigned to ?? _s{PO₂}, and the mode at 877?cm^?1 to ?? _s{P(OH)₂} which is overlapped by ?? _s{P(OH)₃} of H₃PO₄(aq). The modes of $\mathrm{H}_{2}\mathrm{PO}_{4}^{ -} \mathrm{(aq)}$ have been measured in dilute solution and were assigned and presented as well. H₃PO₄ is hydrated in aqueous solution, which can be verified with Raman spectroscopy by following the modes ?? ₂(a₁) and ?? ₁(a₁) as a function of temperature. These modes show a strong temperature dependency. The mode ?? ₁(a₁) broadens and shifts to lower wavenumbers. The mode ?? ₂(a₁) on the other hand, shifts to higher wavenumbers and broadens considerably with increases in temperature. At 301?°C the phosphoric acid is almost molecular in nature. In very dilute H₃PO₄ solutions at room temperature, however, the dissociation product, $\mathrm{H}_{2}\mathrm{PO}_{4}^{ -} \mathrm{(aq)}$ is the dominant species. In these dilute H₃PO₄(aq) solutions no spectroscopic features could be detected for a hydrogen bonded dimeric species of the formula $\mathrm{H}_{5}\mathrm{P}_{2}\mathrm{O}_{8}^{ -}$ (or the neutral dimeric acid H₆P₂O₈). Pyrophosphate formation, although favored at high temperatures, could not be detected in dilute solution even at 301?°C due to the high water activity. In highly concentrated solutions, however, pyrophosphate formation is observable and in hydrate melts the formation of pyrophosphate is already noticeable at room temperature. Quantitative Raman measurements have been carried out to follow the dissociation of H₃PO₄(aq) over a very broad temperature range. In the temperature interval from 5.0 to 301.0?°C the pK ₁ values for H₃PO₄(aq) have been determined and thermodynamic data have been derived.     

Buffers for the Physiological pH Range: Thermodynamics of the Second Dissociation of N-(2-Hydroxyethyl)piperazine-N′-2-hydroxypropanesulfonic Acid From 5 to 55°C

The second acidic dissociation constants pK ₂ of the ampholyte N-(2-hydroxyethyl) piperazine-N-2-hydroxypropanesulfonic acid (HEPPSO) have been determined at seven temperatures from 5 to 55°C from emf measurements utilizing hydrogen and silver–silver chloride cells without liquid junction. The thermodynamic quantities, G°, H°,S°, and C _p ^o have been calculated from the temperature coefficient of pK ₂. At 25°C, the pK ₂ = 8.042 and at 37°C, pK ₂ = 7.876; hence, buffer solutions of HEPPSO and NaHEPPSOate are important for pH control in the region close to that of clinical fluids (blood serum). Conventional pH values from 5 to 55°C as well as those obtained from liquid junction correction at 25 and 37°C have been reported for three buffer solutions with the compositions (molality scale): (1) equimolal mixture of HEPPSO (0.04 m) + NaHEPPSOate (0.04 m) + NaCl (0.12 m); (2) HEPPSO (0.08 m) + NaHEPPSOate (0.08 m); and (3) HEPPSO (0.08 m) + NaHEPPSOate (0.08 m) + NaCl (0.08 m).     

Buffers for the Physiological pH Range: Studies of 4-(N-Morpholino)butanesulfonic Acid (MOBS) from 5 to 55 °C

In this study, we report the pH values of two buffer solutions without chloride ion and eight buffer solutions with NaCl with an ionic strength I=0.16 mol?kg^?1. Electromotive force (emf) techniques have been used to get the cell potentials at 12 temperatures from 5 to 55?°C, including 37?°C. An extended form of the Bates-Guggenheim convention is used in the entire ionic strength range, 0.04 to 0.16?mol?kg^?1. The residual liquid junction potentials (??E _j ) of the buffer solutions of MOBS have been estimated from previous measurements with a flowing junction cell. These values of ??E _j have been used for correction in order to ascertain the operational pH values of four buffer solutions of MOBS at 25 and 37?°C. These solutions are recommended as pH standards for physiological application in the pH range 7.4 to 7.7.     

Thermodynamics of nucleic acid bases and nucleosides in water from 25 to 55°C

Specific heat capacities, apparent molar heat capacities, densities, and apparent molar volumes have been determined for cytosine, uracil, thymine, adenine, cytidine, 2-deoxycytidine, uridine, thymidine and adenosine at temperatures from 25°C to 55°C. The results of these measurements have been used to calculate for the first time, the thermodynamic quantities:C _p,2 ^o , (C _p,2 ^o /T)_p, (² C _p,2 ^o T ²)_p,V ₂ ^o , (V ₂ ^o /T)_p, and (² V ₂ ^o /T ²)_p. The-CH₂-group contribution has been calculated at different temperatures. It has also been observed from the data for the nucleic acid bases and nucleosides that the additivity ruleC _p,2 ^o (nucleoside)-C _p,2 ^o (base) +C _p,2 ^o (water)=C _p,2 ^o (ribose) does not hold in these cases.     

Thermodynamics of the System HCl + SmCl3 + H2O from 5 to 55°C. Application of Harned's Rule and the Pitzer Formalism

A comprehensive array of electrochemical cell measurements for the system HCl +SmCl₃ + H₂O was made from 5 to 55°C using a cell without liquid junction ofthe type:Pt; H₂(g, 1 atm)|HCl (m _A) + SmCl₃ (m _B)|AgCl, Ag (A)The present study, unlike previous studies of trivalent ions, are not complicatedby hydrolysis reactions. Measurements of the emf were performed for solutionsat constant total ionic strengths of 0.025, 0.05, 0.1, 0.25, 0.5, 1.0, 1.5, 2.0, 2.5,and 3.0 mol-kg^–1. The mean activity coefficients of HCl (_HCl) in the mixtureswere calculated using the Nernst equation. All the experimental emf measurements(about 850) were first treated in terms of the simpler Harned's rule. Harnedinteraction coefficients (_AB and _AB) were calculated. The linear form of Harned'srule is valid for most ionic strengths, but quadratic terms are needed at I = 1.5and 3 mol-kg^–1. The Pitzer model was used to evaluate the activity coefficientsusing literature values, ⁽⁰⁾, ⁽¹⁾, and C , for HCl from 0 to 50°C and 25°C forSmCl₃. The effect of temperature on the parameters for SmCl₃ has been estimatedusing enthalpy and heat-capacity data. The mixing parameter _H,Sm wasdetermined at 25°C. The addition of the _H,Sm,Cl coefficient did not improve the fitsignificantly and no temperature dependence was found to be significant. Thevalue of _H,Sm = 0.2 ± 0.01 represented the values of _HCl with a standarddeviation of = 0.009 over the entire range of temperatures and ionic strength.The use of higher-order electrostatic effects (^E_H,Sm, ^E_H,Sm) was included as itgave a better fit of the activity coefficients of HCl.     

Thermodynamics of protonation of amino acid carboxylate groups from 50 to 125°C

Flow calorimetry has been used to study the interaction of glycine, DL--alanine, DL-2-aminobutyric acid, -alanine, 4-aminobutyric acid, and 6-aminocaproic acid with protons in aqueous solutions from 323.15 K to 398.15 K and at 1.52 MPa. LogK, H°, S°, and C _p ^° for the protonation of the carboxylate groups of these amino acids have been obtained at each temperature studied. Equations are given expressing these values as functions of temperature. The protonation reactions are exothermic at lower temperatures and become endothermic as temperature increases. The logK, H°, and S° values are close together over the temperature range studied for the protonation of -amino acids, i.e., glycine, DL--alanine, and 2-aminobutyric acid. At each temperature, the magnitudes of these thermodynamic quantities increase as the number of methylene groups between the amino group and the carboxylate group increases. The C _p ^° value for the protonation of the carboxyl group is found to lie between those of an isocoulombic reaction and a charge reduction reaction. At 323.15 K, the protonation reactions of the carboxylate groups have larger C _p ^° values which approach those associated with charge reduction reactions. As the temperature increases, C _p ^° decreases and approaches those found for isocoulombic reactions. This result is explained by considering long-range and short-range solvent effects. The trend in H° and S° with temperature and with charge separation in the zwitterions is interpreted in terms of solvent-solute interactions and the electrostatic interaction of the two oppositely charged groups within the molecule.     

Potentiometric Determination of the First Hydrolysis Constant of Gallium(III) in NaCl Solution to 100°C

The hydrolysis equilibrum of gallium (III) solutions in aqueous 1 mol-kg^–1 NaCl over a range of low pH was measured potentiometrically with a hydrogen ion concentration cell at temperatures from 25 to 100°C at 25°C intervals. Potentials at temperatures above 100°C increased gradually because of further hydrolysis of the gallium(III) ion, followed by precipitation. The results were treated with a nonlinear least-squares computer program to determine the equilibrium constants for gallium(III)–hydroxo complexes using the Debye–Hückel equation. The log K (mol-kg^–1) values of the first hydrolysis constant for the reaction, Ga³⁺ + H₂O GaOH²⁺ + H⁺ were –2.85 ± 0.03 at 25°C, –2.36 ± 0.03 at 50°C, –1.98 ± 0.01 at 75°C, and –1.45 ± 0.02 at 100°C. The computed standard enthalpy and entropy changes for the hydrolysis reaction are presented over the range of experimental temperatures.     

Dissociation Constant of Acetic Acid in (N,N-Dimethylformamide + Water) Mixtures at the Temperature 298.15 K

In the present work the thermodynamic dissociation constants of acetic acid were determined in (N,N-dimethylformamide (DMF) + water) mixtures over the DMF mole fraction range from 0 to 0.65 at the temperature 298.15 K by the potentiometric titration method. The dissociation constant in pure DMF was obtained by extrapolation and comparative calculation methods. The dependence of the acetic acid dissociation constant on the mixed solvent composition was fitted with linear multiple regression of the solvatochromic parameters of (DMF + water) mixtures at every studied composition.     

Thermodynamics of protonation of AMP,ADP, and ATP from 50 to 125°C

The interaction of adenosine 5-monophosphate (AMP), adenosine 5-diphosphate (ADP), and adenosine 5-triphosphate (ATP) ions with protons in aqueous solution has been studied calorimetrically from 50 to 125°C and 1.52 MPa. At each temperature, the reaction of acidic AMP with tetramethylammonium hydroxide was combined with the heat of ionization for water to obtain the enthalpy of protonation of AMP, while the reactions of HCl with deprotonated tetramethylammonium salts of ADP and ATP were used to obtain the enthalpies of protonation of ADP and ATP. Equilibrium constant K, enthalpy change H^o, entropy change S^o, and heat capacity change C _p ^o values were calculated for the stepwise protonation reactions as a function of temperature. The reactions involving the first protonation of AMP, ADP, and ATP and the third protonation of ADP and ATP were endothermic over the temperature range studied, while that involving the second protonation is exothermic for AMP and ADP, but is exothermic below 100°C and endothermic at 125°C in the case of ATP. Consequently, log K values for the first and third protonation reactions (phosphate groups) increase while those for the second protonation reaction (N₁-adenine) decrease in the cases of AMP and ADP and go through a minimum in the case of ATP as temperature increases. The H^o values for all protonation reactions increase with temperature. The magnitude and the trend for the H^o, S^o, and C _p ^o values with temperature are discussed in terms of solvent-solute interactions. The magnitude of the C _p ^o values for the second protonation is consistent with little interaction between the phosphate ion and the protonated N₁ site of the adenine moiety in AMP, but indicates moderate interaction between these groups in ADP, and strong interaction in ATP.     

Extraction of Cesium from the Irradiated Nuclear Waste by 4(5),4''''(5'''')-Bis[1-hydroxyalkylbenzo]-21-crown-7

The fission product 137Cs accounts for a large fraction of the radioactivity in high-levelnuclear waste (HLW). Because of the hazard to environment and the widespreadapplication of 137Cs gamma radiatior1, a need has arisen to develop improved methods forthe removal and recovery of radiocesium from these wastes. Reports have shown thatsome calixcrown compounds may be highly selective for Cs cation2, but, since thesynthesis of them is difficult and the cost is high, it might obviate their use…     

Addition of Hypophosphorous Acid to N,N′-Terephthalylidene-bis[1-(alkoxycarbonyl)alkylamines]

The preparation of 1,4-phenylene-bis[1-(alkoxycarbonyl)alkylamino-methanephosphonous acids] by the addition of hypophosphorous acid to terephthalylidene-bis[1-(alkoxycar bonyl)alkylamines] is described. Despite expectations, no chiral assistance of the amino acid ester moiety is observed.     

5-[4-amino(1,2,5)oxadiazolyl]-5H-[1,2,3]tri-azolo [4,5-c][1,2,5]oxadiazole from 4,4′-diamino-3,3′-azofurazane

4,4-Diamino-3,3-azofurazane undergoes intramolecular oxidative cyclization to give 5-[4-amino(1,2,5)oxadiazolyl]-5H-[1,2,3]triazolo[4,5-c][1,2,5]oxadiazole upon heating with Pb(OAc)₄ in chlorobenzene oro-dichlorobenzene or with thionyl chloride.Deceased.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 2, pp. 253–254, February, 1996.     

Dimer of Bis[trans-5-methyl-2-[2-(4-methoxylphenyl) ethenyl]-benzoxazole]di-μ-nitratosilver(I)

The title complex [AgNO3(C17H15NO2)2]2 was synthesized and characterized by X-ray diffraction analysis. The compound crystallizes in triclinic, space group Pī with a = 11.226(7), b = 11.906(7), c = 12.144(7) (A。), α = 99.796(10), β = 91.631(10), γ = 101.225(10)°, V = 1565.6(16)(A。)3, Z = 1, Mr = 1400.96, Dc = 1.486 g/cm3, F(000) = 716 and μ(Mo-Kα) = 0.697 mm-1. The final R and wR are 0.0401 and 0.0995, respectively for 5492 independent observable reflections with I > 2σ(I). The results show that the central Ag atom is four-coordinated with two O atoms from two distinct NO3- anions and two N atoms from two trans-5-methyl-2-[2-(4-methoxylphenyl)ethenyl]- benzoxazole ligands, and the two Ag atoms bridged with two O atoms give an interesting Ag-O-Ag-O parallelogram structure. The coordination sphere of Ag atom exhibits a heavily distorted tetrahedral geometry and the coordination angles lie in the range of 66.73(12)～129.59(10)°. The intra- molecular dihedral angles between the benzoxazolyl and phenyl planes are 4.1(3) and 2.9(3)°, respectively.     

Cadmium Malonate Complexation in Aqueous Sodium Trifluoromethanesulfonate Media to 75°C; Including Dissociation Quotients of Malonic Acid

The molal formation quotients for cadmium–malonate complexes were measured potentiometrically from 5 to 75°C, at ionic strengths of 0.1, 0.3, 0.6 and 1.0 molal in aqueous sodium trifluoromethanesulfonate (NaTr) media. In addition, the stepwise dissociation quotients for malonic acid were measured in the same medium from 5 to 100°C, at ionic strengths of 0.1, 0.3, 0.6, and 1.0 molal by the same method. The dissociation quotients for malonic acid were modeled as a function of temperature and ionic strength with empirical equations formulated such that the equilibrium constants at infinite dilution were consistent, within the error estimates, with the malonic acid dissociation constants obtained in NaCl media. The equilibrium constants calculated for the dissociation of malonic acid at 25°C and infinite dilution are log K _1a=-2.86 ± 0.01 and log K _2a=-5.71 ± 0.01. A single Cd–malonate species, CdCH₂C₂O₄, was identified from the complexation study and the formation quotients for this species were also modeled as a function of temperature and ionic strength. Thermodynamic parameters obtained by differentiating the equation with respect to temperature for the formation of CdCH₂C₂O₄ at 25°C and infinite dilution are: K = 3.45 ± 0.09, S° = 7 ± 6 kJ-mol^-1, S° = 91 ± 22 J-K^--mol^-1, and C _p ^o =400±300 J­K^-1­mol^-1.     

Thermodynamics of the Dissociation of Carbonic Acid in Mixed Solvent.4. The System of NaHCO_3-Na_2CO_3-NaCl-Ethanol-Water

Theeffectofethanol-watermixtureontheseconddissociationconstantofcarbonicacidwasofinterestnotonlyforbiologistsbutalsoforchefestsandchemicalengineers,becauseitmayprovideusefulinformationinregardtotheidentificationofthenatureofthesesolute-solventinteractionpatternsinbinarysolventsystem"'.ThispaperreportStheseconddissociationconstantsofcarbonicacid,K,,atfivetemperaturesfrom278.15to318.15Kin5,15,25mass%ethanol-water"dxedsolventsdeterminedfrompreciseelnfmeasurementsincell(A)withoutliquidjunction:Pt…     

Quantitative evaluation of the biosynthetic pathways leading to δ-aminolevulinic acid from the Shemin precursor glycine via the C5 pathway in Arthrobacter hyalinus by analysis of 13C-labeled coproporphyrinogen III biosynthesized from [2-13C]glycine, [1-13C]acetate, and [2-13C]acetate using 13C NMR spectroscopy

The biosynthetic pathways leading to δ-aminolevulinic acid (ALA) from the Shemin precursor glycine via the C5 pathway in Arthrobacter hyalinus were quantitatively evaluated by means of feeding experiments with [2-¹³C]glycine, sodium [1-¹³C]acetate, and sodium [2-¹³C]acetate, followed by analysis of the labeling patterns of coproporphyrinogen III (Copro’gen III) (biosynthesized from ALA) using ¹³C NMR spectroscopy. Two biosynthetic pathways leading to ALA from glycine via the C5 pathway were identified: i.e., transformation of glycine to l-serine catalyzed by glycine hydroxymethyltransferase, and glycine synthase-catalyzed catabolism of glycine to N ⁵,N ¹⁰-methylene-tetrahydrofolic acid (THF), which reacts with another molecule of glycine to afford l-serine. l-Serine is transformed to acetyl-CoA via pyruvic acid. Acetyl-CoA enters the tricarboxylic acid cycle, affording 2-oxoglutaric acid, which in turn is transformed to l-glutamic acid. The l-glutamic acid enters the C5 pathway, affording ALA in A. hyalinus. A ¹³C NMR spectroscopic comparison of the labeling patterns of Copro’gen III obtained after feeding of [2-¹³C]glycine, sodium [1-¹³C]acetate, and sodium [2-¹³C]acetate showed that [2-¹³C]glycine transformation and [2-¹³C]glycine catabolism in A. hyalinus proceed in the ratio of 52 and 48 %. The reaction of [2-¹³C]glycine and N ⁵,N ¹⁰-methylene-THF, that of glycine and N ⁵,N ¹⁰-[methylene-¹³C]methylene-THF generated from the [2-¹³C]glycine catabolism, and that of [2-¹³C]glycine and N ⁵,N ¹⁰-[methylene-¹³C]methylene-THF transformed the fed [2-¹³C]glycine to [1-¹³C]acetyl-CoA, [2-¹³C]acetyl-CoA, and [1,2-¹³C₂]acetyl-CoA in the ratios of 42, 37, and 21 %, respectively. These labeled acetyl-CoAs were then incorporated into ALA. Our results provide a quantitative picture of the pathways of biosynthetic transformation to ALA from glycine in A. hyalinus.