Quantitative studies of the effect of some metal ions on the reaction of glycyl-glycine (gg) in the pH ranges 0.3–1.0 and 3.8–6.0 and temperatures ranging from 364 to 387 K are reported. In the pH range 0.3–1.0, Co(II), Mn(II), Cu (II) and Ni(II) do not affect the rate of hydrolysis of gg. A previous report by Lawrence and Moore that Co(II) increases the rate of hydrolysis by 40–70 % is spurious. In the pH range 3.8–6.0 the metal ions Co(II), Ni(II), Zn(II) and Mn(II) catalyze both hydrolytic cleavage and diketopiperazine formation. The reaction scheme proposed for the metalion-catalyzed hydrolysis requires that the rate of hydrolysis be directly proportional to the metal ion concentration and inversely proportional to the hydrogen ion concentration. The experimental results are in accord with these predictions. There is also evidence that the mechanism for Zn(II)-catalyzed hydrolysis is different from that for the other metal ions.
The solid-state (powder) i.r. (1000–40 cm–1) and Raman (1000–130 cm–1) spectra of sodium, potassium, and ammonium chromate(VI) and dichromate(VI) are reported and compared with the previously reported solution Raman spectra. Considerable splittings of the degenerate modes are observed and an attempt is made to account for these splittings by site- and factor-group analysis.
A quantitative study of the kinetics of simultaneous hydrolysis and reversible sequence-inversion of the dipeptides L-leucyl-L-tyrosine, L-tryosyl-L-leucine, L-leucyl-glycine, glycyl-L-leucine, L-alanyl-glycine, glycyl-L-alanine, L-valyl-glycine and gylcyl-L-valine in 2 M HCl is reported. Values of the first-order rate constants for both processes have been determined at several temperatures in the range 84.2–114.2°C and values of ΔH≠ and ΔS≠ calculated. The results are discussed in terms of conformation effects of the dipeptide side chains. Revised values of the rate constants for the acid-catalyzed hydrolysis of L-leucyl-glycyl-L-leucine and glycyl-L-leucyl-glycine are also reported.
D. A. Long and J. E. Lillycrop, Trans. Faraday Soc., 1963, 59, 907 DOI: 10.1039/TF9635900907
D. A. Long, R. B. Gravenor and D. C. Milner, Trans. Faraday Soc., 1963, 59, 46 DOI: 10.1039/TF9635900046
Vibrational spectra are reported for fumaronitrile (infrared and Raman) maleonitrile (infrared), tetracyanoethylene (infrared and Raman) and the 2-dicyanomethylene-1,1,3,3-tetracyano-propanediide ion (infrared and Raman). A complete assignment is proposed for fumaronitrile and partial assignments made for the other three compounds.
D. A. Long and J. Y. H. Chau, Trans. Faraday Soc., 1962, 58, 2328 DOI: 10.1039/TF9625802328
D. A. Long and J. Y. H. Chau, Trans. Faraday Soc., 1962, 58, 2325 DOI: 10.1039/TF9625802325
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