Thermodynamic Quantities for the Ionization Reactions of Buffers

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268 GOLDBERG, KISHORE, AND LENNEN Values adjusted to TÄ298.15 K and IÄ0—Continued pK rH°/(kJ mol 1 ) rC p /(J K 1 mol 1 ) Reference 4.761 2.45 178 49BAT/PIN 4.66 51HEI 4.77 2.01 80ARE/CAL 4.751 90DAN/DER 4.777 3.85 150 90DER/DES 4.759 2.19 192 97BEN/PAL Reaction „3…: HL À ÄL 3À ¿H ¿ 6.42 28KOL/BOS 6.26 28SIM 6.399 2.5 29BJE/UNM 6.396 3.40 254 49BAT/PIN 6.38 51HEI 6.42 3.35 80ARE/CAL 6.418 90DAN/DER 6.412 1.75 225 90DER/DES 6.397 3.58 231 97BEN/PAL Comments: The careful investigation of Bates and Pinching 49BAT/PIN was performed using an electrochemical cell without liquid junction and is judged to be the most carefully done study. It is in agreement with most of the other studies where pK values were adjusted to I0. The values of rH° determined in the calorimetric study of Arena et al. 80ARE/CAL are in good agreement with the results obtained from the temperature dependance of the pK values determined by Bates and Pinching 49BAT/PIN. We have adopted the average of the rH° values from these two studies 49BAT/PIN, 80ARE/CAL. Direct heat capacity measurements would be useful. Many additional studies, performed under a variety of conditions, are cited by Martell et al. 2001MAR/SMI and by Pettit and Powell 2000PET/POW. TABLE 7.23. L-Cysteine Other names S--cysteine; L--mercaptoalanine; Cys; C; cysteine; 2-amino-3-mercaptopropanoic acid; CySH; -2-amino-3mercaptopropionic acid; L--cysteine; 3-mercapto-L-alanine; thioserine; R-2-amino-3-mercaptopropanoic acid; R-2amino-3-mercaptopropanoic acid; Half-cystine; CAS No. 52-90-4 Empirical formula C 3H 7NO 2S Molecular weight 121.16 Ionization reactions H 3L H H 2L (1) H 2LH HL (2) HL H L 2 (3) where H 2LC 3H 7NO 2S Selected values at TÄ298.15 K and IÄ0: pK1.71, rG°/(kJ mol 1 )9.76, and rH°/(kJ mol 1 )0.6 for reaction 1 pK8.36, rG°/(kJ mol 1 )47.72, rH°/(kJ mol 1 )36.1, and rC p /(J K 1 mol 1 )66 for reaction 2 pK10.75, rG°/(kJ mol 1 )61.36, rH°/(kJ mol 1 )34.1, and rC p /(J K 1 mol 1 )204 for reaction 3 Evaluation: reaction 1, CD; reaction 2, BBD; reaction 3, BBD Structure: J. Phys. Chem. Ref. Data, Vol. 31, No. 2, 2002
Values from literature pK rH°/(kJ mol 1 ) T/K I Methods and comments Reference Reaction „1…: H 3L ¿ ÄH 2L¿H ¿ 1.71 298.15 0 Potentiometric titration—glass electrode. 37BOR/ELL 2.44 0.3 298.15 3.0 M Potentiometric titration—glass electrode; calorimetry. The first set of 72GRA/WIL 2.4 1.4 298.15 3.0 M pK and rH° values is based on calorimetry; the second set is based on the potentiometric titration data. The same values are also given in a subsequent publication 76COR/WIL. Reaction „2…: H 2LÄHL À ¿H ¿ 8.33 298.15 0 Potentiometric titration—glass electrode. 37BOR/ELL 8.53 293.15 0.01 M Potentiometric titration—glass electrode. 53PER 8.39 36.1 298.15 0 Potentiometric titration—glass electrode; calorimetry. 64WRA/IZA 8.15 28.9 303.15 0.1 M Potentiometric titration—glass electrode. 66WAL/STR 8.84 278.15 0 Potentiometric titration—glass electrode. The value of rH° given 8.58 288.15 0 8.37 35.3 298.15 0 8.17 308.15 0 7.98 318.15 0 7.85 328.15 0 7.69 338.15 0 7.52 348.15 0 7.38 358.15 0 7.28 368.15 0 IONIZATION REACTIONS OF BUFFERS here was calculated from pKs measured at several temperatures. The value rC p /(J K 1 mol 1 )66 was also calculated from the temperature dependency of their 69COA/MAR reported pKs. 69COA/MAR 32.3 ? ? Calorimetry. 71MAR/BER 8.78 38.8 298.15 3.0 M Potentiometric titration; calorimetry. The same values were also given in a subsequent publication 76COR/WIL. 72GRA/WIL Reaction „3…: HL À ÄL 2À ¿H ¿ 10.78 298.15 0 Potentiometric titration—glass electrode. 37BOR/ELL 10.53 293.15 0.01 M Potentiometric titration—glass electrode. 53PER 10.76 34.1 298.15 0 Potentiometric titration—glass electrode; calorimetry. 64WRA/IZA 10.47 22.6 303.15 0.1 M Potentiometric titration—glass electrode. 66WAL/STR 11.20 278.15 0 Potentiometric titration—glass electrode. The value of rH° given here was calculated from pKs measured at several temperatures. The value rC p /(J K 1 mol 1 )204 was also calculated from the temperature dependency of their 69COA/MAR reported pKs. 69COA/MAR 10.89 288.15 0 10.70 34.9 298.15 0 10.50 308.15 0 10.34 318.15 0 10.23 328.15 0 10.08 338.15 0 9.93 348.15 0 9.85 358.15 0 9.76 368.15 0 35.9 ? ? Calorimetry. 71MAR/BER 10.71 40.4 298.15 3.0 M Potentiometric; calorimetry. The same values were also given in a subsequent publication 76COR/WIL. 72GRA/WIL Values adjusted to TÄ298.15 K and IÄ0 pK rH°/(kJ mol 1 ) rC p /(J K 1 mol 1 ) Reference Reaction „1…: H 3L ¿ ÄH 2L¿H ¿ 1.71 37BOR/ELL 2.4 0.6 72GRA/WIL Reaction „2…: H 2LÄHL À ¿H ¿ 8.33 37BOR/ELL 8.51 53PER 8.39 36.1 64WRA/IZA 8.47 28.6 66WAL/STR 8.37 35.3 66 69COA/MAR 32.3 71MAR/BER 37.4 72GRA/WIL 269 J. Phys. Chem. Ref. Data, Vol. 31, No. 2, 2002
Page 1 and 2: Thermodynamic Quantities for the Io
Page 3 and 4: 2. Thermodynamic Background Of prim
Page 5 and 6: cal cells both with and without liq
Page 7 and 8: 7. Tables of Thermodynamic Quantiti
Page 9 and 10: IONIZATION REACTIONS OF BUFFERS Val
Page 11 and 12: TABLE 7.3. ADA Other names N-2-acet
Page 13 and 14: TABLE 7.4. 2-Amino-2-methyl-1,3-pro
Page 15 and 16: Values adjusted to TÄ298.15 K and
Page 19 and 20: Values from literature pK rH°/(kJ
Page 21 and 22: TABLE 7.10. Barbital Other names ba
Page 31 and 32: TABLE 7.17. Cacodylate Other names
Page 33 and 34: Values from literature—Continued
Page 35 and 36: Values from literature pK rH°/(kJ
Page 37: Values from literature—Continued
Page 45 and 46: TABLE 7.26. 3,3-Dimethylglutarate O
Page 47 and 48: TABLE 7.28. Ethanolamine Other name
Page 57 and 58: TABLE 7.33. Glycylglycine Other nam
Page 65 and 66: TABLE 7.38. HEPPSO Other names N-2-
Page 75 and 76: TABLE 7.42. Maleate Other names mal
Page 79 and 80: TABLE 7.44. MES Other names 2-N-mor
Page 85 and 86: TABLE 7.49. MOPSO Other names 3-N-m
Page 89 and 90:
Values from literature—Continued
Page 91 and 92:
TABLE 7.51. Phosphate Other names p
Page 93 and 94:
Values from literature—Continued
Page 95 and 96:
IONIZATION REACTIONS OF BUFFERS Val
Page 97 and 98:
Values from literature pK rH°/(kJ
Page 99 and 100:
Values adjusted to TÄ298.15 K and
Page 101 and 102:
Page 103 and 104:
TABLE 7.55. POPSO Other names piper
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TABLE 7.60. TABS Other names N-tris
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TABLE 7.68. Tris Other names 2-amin
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IONIZATION REACTIONS OF BUFFERS 8.
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IONIZATION REACTIONS OF BUFFERS 27C
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IONIZATION REACTIONS OF BUFFERS 57N
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IONIZATION REACTIONS OF BUFFERS 68V
Page 137 and 138:
IONIZATION REACTIONS OF BUFFERS 76W
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IONIZATION REACTIONS OF BUFFERS 90D
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Thermodynamic Quantities for the Ionization Reactions of Buffers

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