The acidic dissociation constant of N-(2-acetamido)-iminodiacetic acid monosodium (ADA) has been determined at 12 temperatures from 278.15 to 328.15 K by electromotive-force (emf) measurements of hydrogen-silver chlor...The acidic dissociation constant of N-(2-acetamido)-iminodiacetic acid monosodium (ADA) has been determined at 12 temperatures from 278.15 to 328.15 K by electromotive-force (emf) measurements of hydrogen-silver chloride cells without liquid junction. At 298.15 K, the value of the dissociation constant (pK2) is 6.8416 ± 0.0004. In response to the need for new physiological pH standards, buffer solutions of NaADA and its disodium salt, Na2ADA would be useful for pH control in the biological region of pH 6.5 to 7.5. The pK2 values over the experimental temperature range are given as a function of the thermodynamic temperature (T) by the equation pK2 = 2943.784/T - 47.05762 + 7.72703 ln T. At 298.15 K, standard thermodynamic quantities for the dissociation process have been derived from the temperature coefficients;ΔH° = 12,252 J·mol-1, ΔS° = -89.9 J·K-1·mol-1 and = -148 J·K-1·mol-1. The results are interpreted and compared with those of structurally related derivatives of GLYCINE.展开更多
The second acidic dissociation constants of protonated piperazine-N,N′-bis-2-hydroxypropane-sulfonic acid (POPSO sesquisodium salt) have been determined at 12 different temperatures from (278.15 to 328.15) K includin...The second acidic dissociation constants of protonated piperazine-N,N′-bis-2-hydroxypropane-sulfonic acid (POPSO sesquisodium salt) have been determined at 12 different temperatures from (278.15 to 328.15) K including 310.15 K. Electromotive-force measurement technique was used employing hydrogen-silver chloride cells without liquid junction. The results of pK2 are given by the equation: pK2 = -1041.77/T + 51.0459 - 6.97646lnT. The uncertainty of the fit is ±0.0008. At 289.15 K, pK2 = 7.8029;whereas, at 310.15 K (body temperature), pK2 = 7.6862. Thus, the buffer solutions of POPSO and its sodium salt are useful for pH control in the physiological pH region of (7.0 to 8.5). The changes of Gibbs free energy (G°), enthalpy (H°), entropy (S°) and heat capacity Cp° were computed from the temperature derivative of the pK2 for the dissociation of the zwitterionic acid POPSO±-3 = POPSO-4 + H+ in the standard state. At 298.15 K, these results are compared with those of similar components, which are the derivatives of the parent compounds TAURINE, PIPERAZINE and MORPHOLINE.展开更多
Values of the second thermodynamic dissociation constant pK2 of the protonated form of monosodium 1,4-piperazinediethanesulfonate (PIPES) have been determined at twelve different temperatures in the temperature range ...Values of the second thermodynamic dissociation constant pK2 of the protonated form of monosodium 1,4-piperazinediethanesulfonate (PIPES) have been determined at twelve different temperatures in the temperature range from (278.15 to 328.15) K including the body temperature 310.15 K by measurement of the electromotive-force for cells without liquid junction of the type: Pt (s), H2 (g), 101.325 kPa|Na-PIPES (m1) + Na 2-PIPES (m2) + NaCl (m3)|AgCl (s), Ag (s), where m1, m2 and m3 indicate the molalities of the corresponding species at 1 atm = 101.325 kPa in SI units. The pK2 values for the dissociation of Na-PIPES are represented by the equation: pK2 = -1303.76/T + 48.369 - 6.46889 lnT with an uncertainty of ± 0.001. The values of pK2 for Na-PIPES were found to be 7.1399 ± 0.0004 at 298.15 K and 7.0512 ± 0.0004 at 310.15 K, respectively, and indicate that this buffer would be useful as pH standard in the range of physiological application. Standard thermodynamic quantities for the acidic dissociation process of Na-PIPES have been derived from the temperature coefficients of the pK2. These values are compared with those of structurally related N-substituted PIPERAZINE and TAURINE at 298.15 K.展开更多
Thermodynamic dissociation constants pKa of 2,2-bis(hydroxymethyl)-2,2’,2”-nitrilotriethanol have been determined at 12 temperatures from (278.15 to 328.15) K including the body temperature 310.15 K by the electromo...Thermodynamic dissociation constants pKa of 2,2-bis(hydroxymethyl)-2,2’,2”-nitrilotriethanol have been determined at 12 temperatures from (278.15 to 328.15) K including the body temperature 310.15 K by the electromotive-force measurements (emf) of hydrogen-silver chloride cells without liquid junction of the type: Pt(s), H2(g), 101.325 kPa|BIS-TRIS (m) + BIS-TRIS·HCl (m)| AgCl(s), Ag(s), where m denotes molality. The pKa values for the dissociation process of BIS-TRIS·H++ H2O = H3O+ + BIS-TRIS given as a function of T in Kelvin (K) by the equation pKa = 921.66 (K/T) + 14.0007-1.86197 ln(T/K). At 298.15 and 310.15 K, the values of pKa for BIS-TRIS were found to be 6.4828 ± 0.0005 and 6.2906 ± 0.0006 respectively. Thus buffer solutions composed of BIS-TRIS and its hydrochloride would be useful as secondary pH buffer standards and for control of acidity in the pH range 6 to 8. At 298.15 K the thermodynamic functions G°, H°, S° and Cp° for the dissociation process of BIS-TRIS·H+ are G°=37,005 J·mol-1, H° = 28,273 J·mol-1, S°= 29.3 J·K-1·mol-1 and Cp° = 36 J·K-1·mol-1. These results are compared with the dissociation of protonated bases structurally related to BIS-TRIS·H+.展开更多
文摘The acidic dissociation constant of N-(2-acetamido)-iminodiacetic acid monosodium (ADA) has been determined at 12 temperatures from 278.15 to 328.15 K by electromotive-force (emf) measurements of hydrogen-silver chloride cells without liquid junction. At 298.15 K, the value of the dissociation constant (pK2) is 6.8416 ± 0.0004. In response to the need for new physiological pH standards, buffer solutions of NaADA and its disodium salt, Na2ADA would be useful for pH control in the biological region of pH 6.5 to 7.5. The pK2 values over the experimental temperature range are given as a function of the thermodynamic temperature (T) by the equation pK2 = 2943.784/T - 47.05762 + 7.72703 ln T. At 298.15 K, standard thermodynamic quantities for the dissociation process have been derived from the temperature coefficients;ΔH° = 12,252 J·mol-1, ΔS° = -89.9 J·K-1·mol-1 and = -148 J·K-1·mol-1. The results are interpreted and compared with those of structurally related derivatives of GLYCINE.
文摘The second acidic dissociation constants of protonated piperazine-N,N′-bis-2-hydroxypropane-sulfonic acid (POPSO sesquisodium salt) have been determined at 12 different temperatures from (278.15 to 328.15) K including 310.15 K. Electromotive-force measurement technique was used employing hydrogen-silver chloride cells without liquid junction. The results of pK2 are given by the equation: pK2 = -1041.77/T + 51.0459 - 6.97646lnT. The uncertainty of the fit is ±0.0008. At 289.15 K, pK2 = 7.8029;whereas, at 310.15 K (body temperature), pK2 = 7.6862. Thus, the buffer solutions of POPSO and its sodium salt are useful for pH control in the physiological pH region of (7.0 to 8.5). The changes of Gibbs free energy (G°), enthalpy (H°), entropy (S°) and heat capacity Cp° were computed from the temperature derivative of the pK2 for the dissociation of the zwitterionic acid POPSO±-3 = POPSO-4 + H+ in the standard state. At 298.15 K, these results are compared with those of similar components, which are the derivatives of the parent compounds TAURINE, PIPERAZINE and MORPHOLINE.
文摘Values of the second thermodynamic dissociation constant pK2 of the protonated form of monosodium 1,4-piperazinediethanesulfonate (PIPES) have been determined at twelve different temperatures in the temperature range from (278.15 to 328.15) K including the body temperature 310.15 K by measurement of the electromotive-force for cells without liquid junction of the type: Pt (s), H2 (g), 101.325 kPa|Na-PIPES (m1) + Na 2-PIPES (m2) + NaCl (m3)|AgCl (s), Ag (s), where m1, m2 and m3 indicate the molalities of the corresponding species at 1 atm = 101.325 kPa in SI units. The pK2 values for the dissociation of Na-PIPES are represented by the equation: pK2 = -1303.76/T + 48.369 - 6.46889 lnT with an uncertainty of ± 0.001. The values of pK2 for Na-PIPES were found to be 7.1399 ± 0.0004 at 298.15 K and 7.0512 ± 0.0004 at 310.15 K, respectively, and indicate that this buffer would be useful as pH standard in the range of physiological application. Standard thermodynamic quantities for the acidic dissociation process of Na-PIPES have been derived from the temperature coefficients of the pK2. These values are compared with those of structurally related N-substituted PIPERAZINE and TAURINE at 298.15 K.
文摘Thermodynamic dissociation constants pKa of 2,2-bis(hydroxymethyl)-2,2’,2”-nitrilotriethanol have been determined at 12 temperatures from (278.15 to 328.15) K including the body temperature 310.15 K by the electromotive-force measurements (emf) of hydrogen-silver chloride cells without liquid junction of the type: Pt(s), H2(g), 101.325 kPa|BIS-TRIS (m) + BIS-TRIS·HCl (m)| AgCl(s), Ag(s), where m denotes molality. The pKa values for the dissociation process of BIS-TRIS·H++ H2O = H3O+ + BIS-TRIS given as a function of T in Kelvin (K) by the equation pKa = 921.66 (K/T) + 14.0007-1.86197 ln(T/K). At 298.15 and 310.15 K, the values of pKa for BIS-TRIS were found to be 6.4828 ± 0.0005 and 6.2906 ± 0.0006 respectively. Thus buffer solutions composed of BIS-TRIS and its hydrochloride would be useful as secondary pH buffer standards and for control of acidity in the pH range 6 to 8. At 298.15 K the thermodynamic functions G°, H°, S° and Cp° for the dissociation process of BIS-TRIS·H+ are G°=37,005 J·mol-1, H° = 28,273 J·mol-1, S°= 29.3 J·K-1·mol-1 and Cp° = 36 J·K-1·mol-1. These results are compared with the dissociation of protonated bases structurally related to BIS-TRIS·H+.
