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.     

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.     

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.     

Thermodynamics of the Second Dissociation Constant of N-tris[Hydroxymethyl]-4-amino-butanesulfonic Acid (TABS) from 5 to 55°C

N-tris[Hydroxymethyl]-4-aminobutanesulfonic acid (TABS) has been investigated for the determination of the values of the second dissociation constant, pK ₂, in water at 12 temperatures in the range 5–55°C, including 37°C. This zwitterionic compound is useful as a secondary pH standard in the range of pH (7–9) for physiological applications. The electromotive force (emf) measurements have been carried out using a hydrogen gas electrode and a silver–silver chloride electrode. The values of pK ₂ are fitted as a function of temperature with the following results: pK ₂ = 1671.305/T+14.8737–2.04383 ln T, where T is the thermodynamic temperature in Kelvins. The experimental values of pK ₂ are 8.834 ± 0.0005 and 8.539 ± 0.0004 at 25 and 37°C, respectively. The related thermodynamic quantities, G°, H°, S°, and C _p ° characterizing the dissociation process have been derived from the pK ₂ and its temperature coefficients.     

Buffer Standards for pH Measurement of N-(2-Hydroxyethyl)piperazine-N′-2-ethanesulfonic Acid (HEPES) for I=0.16 mol⋅kg−1 from 5 to 55 °C

The values of the second dissociation constant, pK ₂, of N-(2-hydroxyethyl) piperazine-N′-2-ethanesulfonic acid (HEPES) have been reported at twelve temperatures over the temperature range 5 to 55 °C, including 37 °C. This paper reports the results for the pa _H of eight isotonic saline buffer solutions with an I=0.16 mol⋅kg⁻¹ including compositions: (a) HEPES (0.01 mol⋅kg⁻¹) + NaHEPES (0.01 mol⋅kg⁻¹) + NaCl (0.15 mol⋅kg⁻¹); (b) HEPES (0.02 mol⋅kg⁻¹) + NaHEPES (0.02 mol⋅kg⁻¹) + NaCl (0.14 mol⋅kg⁻¹); (c) HEPES (0.03 mol⋅kg⁻¹) + NaHEPES (0.03 mol⋅kg⁻¹) + NaCl (0.13 mol⋅kg⁻¹); (d) HEPES (0.04 mol⋅kg⁻¹) + NaHEPES (0.04 mol⋅kg⁻¹) + NaCl (0.12 mol⋅kg⁻¹); (e) HEPES (0.05 mol⋅kg⁻¹) + NaHEPES (0.05 mol⋅kg⁻¹) + NaCl (0.11 mol⋅kg⁻¹); (f) HEPES (0.06 mol⋅kg⁻¹) + NaHEPES (0.06 mol⋅kg⁻¹) + NaCl (0.10 mol⋅kg⁻¹); (g) HEPES (0.07 mol⋅kg⁻¹) + NaHEPES (0.07 mol⋅kg⁻¹) + NaCl (0.09 mol⋅kg⁻¹); and (h) HEPES (0.08 mol⋅kg⁻¹) + NaHEPES (0.08 mol⋅kg⁻¹) + NaCl (0.08 mol⋅kg⁻¹). Conventional pa _H values, for all eight buffer solutions from 5 to 55 °C, have been calculated. The operational pH values with liquid junction corrections, at 25 and 37 °C have been determined based on the NBS/NIST standard between the physiological phosphate standard and four buffer solutions. These are recommended as pH standards for physiological fluids in the range of pH = 7.3 to 7.5 at I=0.16 mol⋅kg⁻¹.     

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.     

Buffer Standards for the Physiological pH of the Zwitterionic Compound, HEPPSO from 5 to 55 °C

The values of the thermodynamic second dissociation constant, pK ₂, and related thermodynamic quantities of N-(2-hydroxyethyl)piperazine-N′-2-hydroxypropanesulfonic acid (HEPPSO) have already been reported from 5 to 55?°C, including 37?°C, by the emf method. This paper reports the results for the pH of one chloride-free buffer solution containing the composition: (a) HEPPSO (0.08 mol?kg^?1)+NaHEPPSO (0.04 mol?kg^?1). The remaining seventeen buffer solutions contain a saline medium of ionic strength I=0.16 mol?kg^?1, matching closely that of physiological fluids. Conventional pH values, denoted as pa _H, for all eighteen buffer solutions from 5 to 55?°C have been calculated. The operational pH values, designated as pH, with residual liquid-junction corrections for five buffer solutions, one without NaCl, and four with buffer solutions in saline media of I=0.16 mol?kg^?1 are recommended as pH standards in the range of physiological application. These are based on the NBS/NIST standard scale for pH measurements.     

Buffer Standards for the Physiological pH of the Zwitterionic Compound,DIPSO, from 5 to 55 °C

The values of the second dissociation constant, pK ₂, and related thermodynamic quantities of 3-[N,N-bis (2-hydroxyethyl)amino]-2-hydroxypropanesulfonic acid (DIPSO) have already been reported over the temperature range 5 to 55 °C including 37 °C. This paper reports the pH values of four NaCl-free buffer solutions and four buffer composition containing NaCl salt at I=0.16 mol⋅kg⁻¹. Conventional pa _H values are reported for all eight buffer solutions. The operational pH values have been calculated for four buffer solutions recommended as pH standards, at 25 and 37 °C after correcting the liquid junction potentials with the flowing junction cell.     

Buffer Standards for the Physiological pH of the Zwitterionic Compound, ACES, from 5 to 55 °C

The values of the second dissociation constant, pK ₂, and related thermodynamic quantities of [N-(2-acetamido)-2-aminoethanesulfonic acid] (ACES) have already been reported over the temperature range 5 to 55 °C including 37 °C. This paper reports the pa _H values of four chloride ion free buffer solutions and eight buffer solutions with I=0.16 mol⋅kg⁻¹, matching closely that of the physiological sample. Conventional pa _H values for all twelve buffer solutions from 5 to 55 °C are reported. The residual liquid-junction potential correction for two widely used temperatures, 25 and 37 °C, has been made. The flowing-junction calomel cell method has been utilized to measure E _j , the liquid-junction potential. The operational pH values for four buffer solutions at 25 and 37 °C are calculated using the physiological phosphate buffer standard based on the NBS/NIST convention. These solutions are recommended as pH standards in the pH range of 6.8 to 7.2 for physiological fluids.     

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.     

Phosphomolybdic Acid: An Efficient and Recyclable Solid Acid Catalyst for the Synthesis of 4,4′-(Arylmethylene)bis(1H-pyrazol-5-ols)

An efficient and environmentally friendly method has been developed for synthesis of 4,4′-(arylmethylene)bis(1H-pyrazol-5-ols) by condensation reaction of aromatic aldehydes with 3-methyl-l-phenyl-5-pyrazolone in the presence of phosphomolybdic acid as a recyclable catalyst in ethanol at ambient temperature in excellent yields.     

Structural Relationships Afforded by the Coordination of 2,2′-Bipyridine to the (Iminodiacetato)Copper(II) Chelate: Synthesis,Structure and Properties of (2,2′-Bipyridine) (N-(2-Hydroxyethyl)Iminodiacetato) Copper(II)Tetrahydrate

Abstract

The stoichiometric reaction of copper(II) hydroxycarbonate, N-(2-hydroxyethyl)iminodiacetic acid [H₂heida?HOCH₂CH₂N(CH₂CO₂H)₂)] and 2,2′-bipyridine (bipy) in water yields crystalline (2,2′-bipyridine)(N-(2-hydroxyethyl)iminodiacetato)copper(II) tetrahydrate, [Cu(heida)-(bipy)] · 4H₂O (compound I). This was studied by TG analysis (with FT-IR study of evolved gases), IR, electronic and ESR spectra, magnetic susceptibility data and single crystal X-ray diffraction methods. The compound crystallises in the triclinic system, space group P1, a = 7.011(2), b = 12.586(3), c = 13.052(3) Å, α = 62.14(1), β = 80.51(2), γ = 77.09(2)°, Z = 2, final R ₁ = 0.051 for 3900 independent reflections. The Cu(II) atom exhibits an asymmetric, elongated, octahedral coordination (type 4+1 + 1), and bipy acts as an N,N-bidentate ligand supplying two among the four closest donor atoms of the metal (Cu-N bond lengths of 1.994(2) and 2.053(2) Å); heida plays an N,O,O′,O″-tetradentate chelating role (bond lengths Cu?N = 2.075(2), Cu-O(carboxyl) = 1.958(2), Cu-O′(carboxyl) = 2.337(2) and Cu-O″(hydroxyl) = 2.459(2) Å). The effective bidentate chelation of bipy imposes fac-chelation to the iminodiace-tate moiety of heida in I, as previously reported in mixed-ligand complexes having a 1:1:2 Cu(II)/IDA/N(heterocyclic) or a 1/1/(1 + 1) Cu/IDA/(N-heterocyclic + N-aliphatic) donor ratio. The tetradentate role of heida in I reveals its noticeable conformational flexibility. The crystal features a hydrogen bond network forming supra-molecular chains extending along the a axis. These are linked by two symmetry-related hydrogen bonds of the type O(hydroxyl)-H…O′(carboxyl) between two adjacent complex units (symmetry code i=-x, -y+1, -z+1), related to each other by an inversion centre.     

Synthesis and Biological Evaluation of (2-Hydroxyethyl) 2-Deoxy-α-D-Threo-Pyranoside 3,4,2′-Trisphosphate,A Mimic of the Second Messenger Inositol 1,4,5-Trisphosphate

ABSTRACT

(2-Hydroxyethyl) 2-deoxy-α-D-threo-pentopyranoside 3,4,2′-trisphosphate (3) has been prepared starting from allyl-α-D-xylopyranoside. The suitably protected 2-deoxy intermediate obtained by judicious selective protection and deprotection has been phosphorylated using the phosphoramidite methodology. Final deprotection gave the expected analogue of myo-inositol 1,4,5-trisphosphate.     

Activity Coefficients for the System HCl +GaCl3 + H2O from 5 to 55°C

Activity coefficients for HCl in HCl + GaCl₃ + H₂O at eleven different temperatures from 5 to 55°C have been determined at total experimental ionic strengths from 0.01 to 3.0 mol-kg^–1 using a cell of the type: Pt; H₂(g, 1 atm)|HCl (m_A) + GaCl₃(m_B)|AgCl, Ag (A) The results for the 770 experimental emf data points have been used to determine the variation of the activity coefficients of HCl with the change in molality of GaCl₃ in the solution. It is found that the linear form of Harned's rule is not obeyed for this system.     

Thermodynamics of Aqueous Diethylenetriaminepentaacetic Acid (DTPA) Systems: Apparent and Partial Molar Heat Capacities and Volumes of Aqueous H2DTPA3−, DTPA5−, CuDTPA3−, and Cu2DTPA− from 10 to 55°C

Apparent molar heat capacities and volumes have been determined for aqueous solutions of the mixed electrolytes Na₅DTPA + NaOH, Na₃CuDTPA + NaOH, and NaCu₂DTPA + NaOH, and the single electrolyte Na₃H₂DTPA (DTPA=diethylenetriaminepentaacetic acid) at temperatures from 10 to 55°C. The experimental results have been analyzed in terms of Young's rule with the Guggenheim form of the extended Debye–Hückel equation and the Pitzer ion-interaction model. These calculations led to standard partial molar heat capacities and volumes for the species H₂DTPA^3–(aq), DTPA^5–(aq), CuDTPA^3–(aq), and Cu₂DTPA^–(aq) at each temperature. The partial molar properties at 0.1 m ionic strength were also calculated. The standard partial molar properties were extrapolated to elevated temperatures with the revised Helgeson–Kirkham–Flowers (HKF) model. Values for the partial molar heat capacities from the HKF model have been combined with the literature data to estimate the ionization constants of H₂DTPA^3–(aq) and the formation constant of the CuDTPA^3–(aq) copper complex at temperatures up to 300°C.     

Silica Sulfuric Acid,an Efficient and Recyclable Solid Acid Catalyst for the Synthesis of 4,4′-(Arylmethylene)bis (1H-pyrazol-5-ols)

Silica sulfuric acid (SSA) is employed as a recyclable catalyst for the condensation reaction of aromatic aldehydes with 3-methyl-l-phenyl-5-pyrazolone. This condensation reaction is performed in a mixture (1:1 v/v) of water–ethanol at 70 °C, giving 4,4′-alkylmethylene-bis(3-methyl-5-pyrazolones) in 75–93% yields.

Xanthan Sulfuric Acid: An Efficient,Biosupported, and Recyclable Solid Acid Catalyst for the Synthesis of 4,4′-(Arylmethylene)bis(1H-pyrazol-5-ols)

A simple and efficient method has been developed for the synthesis of 4,4′-(arylmethylene)bis(1H-pyrazol-5-ols) by the condensation reaction between substituted aldehydes, and 1-phenyl-3-methylpyrazol-5-one in the presence of xanthan sulfuric acid (XSA) as a solid acid catalyst. This method is simple and cost-effective with short reaction times. Yields are excellent with high purity, and the catalyst could be easily recycled.     

Thermodynamics of the hydrolysis reactions of adenosine 3′,5′-(cyclic)phosphate(aq) and phosphoenolpyruvate(aq); the standard molar formation properties of 3′,5′-(cyclic)phosphate(aq) and phosphoenolpyruvate(aq)

Molar calorimetric enthalpy changes Δ_rH_m(cal) have been measured for the biochemical reactions {cAMP(aq) + H₂O(l)=AMP(aq)} and {PEP(aq) + H₂O(l)=pyruvate(aq) + phosphate(aq)}. The reactions were catalyzed, respectively, by phosphodiesterase 3^′,5^′-cyclic nucleotide and by alkaline phosphatase. The results were analyzed by using a chemical equilibrium model to obtain values of standard molar enthalpies of reaction Δ_rH_m^∘ for the respective reference reactions {cAMP⁻(aq) + H₂O(l)=HAMP⁻(aq)} and {PEP³⁻(aq) + H₂O(l)=pyruvate⁻(aq) + HPO²⁻₄(aq)}. Literature values of the apparent equilibrium constants K^′ for the reactions {ATP(aq)=cAMP(aq) + pyrophosphate(aq)}, {ATP(aq) + pyruvate(aq)=ADP(aq) + PEP(aq)}, and {ATP(aq) + pyruvate(aq) + phosphate(aq)=AMP(aq) + PEP(aq) + pyrophosphate(aq)} were also analyzed by using the chemical equilibrium model. These calculations yielded values of the equilibrium constants K and standard molar Gibbs free energy changes Δ_rG_m^∘ for ionic reference reactions that correspond to the overall biochemical reactions. Combination of the standard molar reaction property values (K, Δ_rH_m^∘, and Δ_rG_m^∘) with the standard molar formation properties of the AMP, ADP, ATP, pyrophosphate, and pyruvate species led to values of the standard molar enthalpy Δ_fH_m^∘ and Gibbs free energy of formation Δ_fG_m^∘ and the standard partial molar entropy S_m^∘ of the cAMP and PEP species. The thermochemical network appears to be reasonably well reinforced and thus lends some confidence to the accuracy of the calculated property values of the variety of species involved in the several reactions considered herein.     

Synthesis and Structure Determination of (2S, 2′S)-3-Phenyl-2-(pyrrolidin-2′-yl)- propionic Acid

Abstract

Aβ²,β³-homoproline derivative, (2S, 2′S)-3-phenyl-2-(pyrrolidin-2′-yl)propionic acid, was synthesized starting from l-proline. After preparation of the (4S, 4aS)-4-benzyl-4a,5,6,7-tetrahydro-pyrrolo-[1,2-c]pyrimidine-1,3-dione under a mild condition, the absolute configuration of target compound was assigned using 2D H-H COSY and H-H NOESY technologies.