The ferric form of the haem undecapeptide, derived from horse cytochrome c by peptic digestion, undergoes at least three pH-induced transitions with pK values of 3.4, 5.8 and 7.6. Temperaturejump experiments suggest that the first of these is due to the binding of a deprotonated imidazole group to the ferric iron while the second and third arise from the binding of the two available amino groups present (the a-NH2 of valine and the E -N H~ of lysine).Molecular models indicate that steric restraints on the peptide dictate that these amino groups may only coordinate to iron atoms via intermolecular bonds, thus leading to the polymerization of the peptide.Cyanide binding studies are in agreement with these conclusions and also yield a value of 3.6 x lo6 M-' s-' for the intrinsic combination constant of CN-anion with the haem.A model is proposed which describes the pH-dependent properties of the ferric undecapeptide.

The mercuriation of a series of aromatic derivatives by mercury(l1) trifluoroacetate in trifluoroacetic acid has been studied using titrirnetric and spectrophotornetric methods. The latter method has revealed the presence of a rapidly formed x-complex intermediate and values of the thermodynamic parameters of its formation have been computed. Only small kinetic isotope effects were found for the complex-forming step in contrast to the large values obtained for the slow step. The effect of added salts was investigated and the mechanism of the reaction discussed in detail in the light of these results. Mercuriation by a readily synthesised mixed acetate, Hg(OCOCF,)-(OCOCH,), is also reported as well as some preliminary studies of triptycene derivatives.

o-Phthalaldehyde, as well as the a,a'-dideuterio isomer, has been shown to undergo a Cannizzaro reaction in water containing base, while partially hydrated and ionised. The reaction of the monoanion of the hydrate is intramolecular and of the first order in the monoanion of the hydrate, and either first or zero order in the base. The rate coefficients have been measured at several temperatures and activation paramaters evaluated. The kinetic isotope effect, k,/k,, for the first and second order processes were found to be ca. 1.9 and 1.8, respectively. The alkaline hydrolysis of the corresponding lactone, phthalide, has also been studied under the same conditions. The evidence for the intramolecular Cannizzaro reaction indicates a mechanistic pathway involving rate-determining hydride transfer from the chain tautomers of both monoanion and dianion of the hydrate.

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Upper and lower critical solution temperatures have been determined for acetone solutions of cellulose acetate samples with varying degrees of substitution. The Patterson-Delmas theory of corresponding states, based on the Prigogine theory, has been used to describe the molecular weight dependence of these critical temperatures. This method is most successfully applied to the primary acetate, but the data for the secondary acetate are less amenable to this theoretical approach, possibly because of the copolymeric nature of such samples.