References
- Albert , A. 1953 . Biochem. J. , 54 : 646
- Harkins , T. R. and Freiser , H. 1958 . J. Am. Chem. Soc. , 80 : 1132
- Cheney , G. E. , Freiser , H. and Fernando , Q. 1959 . J. Am. Chem. Soc. , 81 : 2611
- Taqui Khan , M. M. and Krishnamoorthy , C. R. 1971 . J. Inorg. Nucl. Chem. , 33 : 1417
- Taqui Khan , M. M. and Krishnamoorthy , C. R. 1974 . J. Inorg. Nucl. Chem. , 36 : 711
- Janson , C. A. and Cleland , W. W. 1973 . J. Biol. Chem. , 249 : 2572 and earlier papers in this series
- Depamphilis , M. L. and Cleland , W. W. 1973 . Biochem. , 12 : 37 3714
- Brummond , D. O. and Cleland , W. W. 1974 . Fed. Proc. , 33 : 1565
- Ritchie , C. D. , Wright , D. J. , Huang , Der-Shing and Kamego , A. A. 1975 . J. Am. Chem. Soc. , 97 : 1163 Courtesy of C. D. Ritchie of this Department. See for details
- Rollinson , C. L. and Bailar , J. C. Jr. , eds. 1956 . Chemistry of the Co-ordination Compounds , New York : Reinhold . Ch. 13. The tris-hydroxo bridge is well-known in cobalt(III) chemistry Evidence for chromium(III) species of this type has been adduced in early studies (see A. G. Sykes and J. A. Weil, Prog. Inorg. Chem., 13, 77 (1977))
- Analysis performed by Instranal Laboratories , New York : Rensselaer .
- Bjerrum , J. 1941 . Metal Ammine Formation in Aqueous Solution , Copenhagen : Haak and Son .
- Izatt , R. M. , Christensen , J. J. and Rything , J. H. 1971 . Chem. Rev. , 71 : 439
- Rajan , K. S. and Martell , A. E. 1965 . Inorg. Chem. , 4 : 462 (Note that the factor 2 appearing in Eqs. (6) and (7) in this paper is incorrect and should be deleted.)
- This assumption is borne out by the titration curves of Figure 2, where an immediate decrease in pH is seen to occur when chromium(III) is added to the adenine solution, in keeping with the reaction H2 L + M → H+ + MHL even at low pH
- Hodgson , D. J. 1977 . Prog. Inorg. Chem. , 23 : 211
- Marzilli , L. G. 1977 . Prog. Inorg. Chem. , 23 : 255
- Above pH 5.5, precipitate formation begins to complicate the process during rather early stages of the reaction. In the equilibrium studies, precipitation became a problem even at pH 4.5 due to the higher chromium(III) concentration employed in those studies
- For the runs in which adenine was not in greater than five-fold excess (3.5 × 10−3 M), the values of kobs were deduced from the initial portions of the rate data only, where reasonable first-order kinetics prevailed
- The existence of the reverse path was further supported by the spectral data, which indicated that the higher the ligand concentration, the more complete the reaction becomes, as shown by the final absorbance
- Two independent sets of data were obtained at pH 4.4 and 60°, and both are plotted in Figure 6. These confirm the good reproducibility of the experiments
- Schenk , C. , Stieger , H. and Kelm , H. 1972 . Zeit. anorg. allg. Chemie. , 391 : 1 Various authors agree on a value of 4.0 ± 0.1 for pK1 at 25° in media up to I = 1 molar (see Chem. Soc. Special Publication, 17, 48 1964); see Chem. Soc. Special Publication, 25, 20(1971)), and temperature dependence studies suggest 3.4 as a reasonable estimate for pK1 at 60°. Few determinations have been made of pK2, but we have accepted the figure of 5.6 at 25° reported by Assuming the same temperature variation for K2 as for K1, we adopt the value of 5.0 at 60° for pK2
- Izatt and co-workers (see Ref. 10) have measured ΔH° = 4.8 kcal mol−1 for the first deprotonation of adenine. We have used this figure to adjust our measured value for pK1a at 50° (Table IA) to a value at 60° of 3.9. In the pH range of our experiments, pK2a is not involved
- A further test that the k2A path makes a small contribution to the process is that the quantity k2 ([H+] + K3) shows no trend in values and is constant within the range 1.7 × 0.2 M sec−1 for each of the k2 and [H+] values of Table IIIA
- These are readily obtained from Eq. (12), setting k2A [H+] = 0
- Since the ligand concentration is in excess in all these runs, the significant reactants are [Cr(H2 O) 5OH · HL]2+ and [Cr(H2 O)4 (OH)2 · HL]+ which will be present in equilibrium amounts dictated by K1a, K1 and K2, but independent of the magnitude of KA
- Nothing definitive can be said concerning the parent acidic form Cr(H2 O)6 3+ in this respect since there appears to be no measurable substitution of adenine for water in this species, so no kinetic evidence is available from which to deduce KA
- Kruse , W. and Taube , H. 1961 . J. Am. Chem. Soc. , 83 : 1280
- Plumb , W. and Harris , G. M. 1964 . Inorg. Chem. , 3 : 542
- Hunt , J. P. and Plane , R. A. 1954 . J. Am. Chem. Soc. , 76 : 5960
- Espenson , J. A. 1969 . Inorg. Chem. , 8 : 1554
- Stranks , D. R. and Swaddle , T. W. 1971 . J. Am. Chem. Soc. , 93 : 2783
- Inskeep , R. G. and Bjerrum , J. 1961 . Acta Chem. Scand. , 15 : 62
- It is noteworthy that our value for ΔH1 # which relates to the adenine-for-ligand water substitution reaction is considerably smaller than 25 kcal mol−1, even after adding in the ΔH for the association reaction. The slowness of the adenine reaction is a result of the very negative ΔS# value, a possible indication of a highly structured transition state
- Schenk , C. , Stieger , H. and Kelm , H. 1972 . Zeit, anorg. allg. Chemie. , 391 : 1 The authors quote a rate constant of 2.4 × 10−3 M−1 min−1 at 25°, pH = 2.7 and I = 1.0 M, with ΔH# = 26.6 kcal mol−1. At the pH specified most of the oxalate exists as HC2 O4 − and the chromium(III) as Cr(H2 O)6 3+