THE ability of metal chelates derived from copper and dimethylglyoxime or platinum, palladium and 6-mercaptopurine to inhibit the growth of tumour cells has been demonstrated by Takamiya (1960) and Kirschner, Yung-Kang Wei and Francis (1962) respectively. Further, Lenta and Riehl (1960) have demonstrated the ability of metal chelates derived from ethylene diamine tetraacetic acid (E.D.T.A.) to influence oxidative processes in liver mitochondria isolated from the mouse hepatoma 98/15. Consequently, it seemed likely that other types of metal chelate would have similar actions, especially those derived from the transition metals, Ru, Os, Ni, Fe, Cu, Co, Zn, Cd, and Mn, and substituted 1,10-phenanthroline or related bases, since these substances have been shown to exert marked effects on a wide variety of biological systems including HeLa cells in culture (White, Harris and Shulman, 1963;Shulman and Dwyer, 1964).The present work reports the effect of the following three metal chelates on the growth of the Landschutz ascites tumour in B alb C+ male or C female mice. The marked stability of cations like Ru 2, both to chemical treatment and under biological conditions, suggests that their biological effects are due to the cation as a whole and not to its constituents, the metal and the ligand (Koch, Rogers, Dwyer and Gyarfas, 1957). While it is likely that Cu 1 also acts as the cation, it is possible, since its stability is lower than that of Ru 2, that the constituents of Cu 1 also contribute to its biological action. Further ternary chelates, formed from these constituents and physiological ligands or metals, could likewise contribute to these biological effects (Shulman and Dwyer, 1964). Since stable coordinately-saturated metal chelates are unable to form covalent bonds, their biological actions must be mediated by physical means following their attachment

During earlier work carried out in this Institute on carcinogenic mixtures obtained from coal-tar, a study of the fluorescence spectra of such mixtures gave useful indications of the type of compound present, and subsequently assisted in the separation of one of them, 1 : 2-benzpyrene. Very small quantities of material may often be detected by the study of fluorescence spectra, but the results are as a rule only qualitative. In general, at room temperature, the fluorescence spectra of hydrocarbons in solution consist of diffuse bands, and the total emitted energy is often very small and consequently difficult to measure. Moreover, the absolute amount of radiated energy depends on Ike energy distribution in the incident radiation, and on such experimental details as concentration of solutions, and size and shape of containing vessels. On the other hand, a quantitative measurement of the ultra-violet absorption spectrum of a solution of a pure compound can be made relatively easily, and not only furnishes a method of identification of the substance but serves as a basis for a theoretical treatment of its molecular structure.

Evidence for the existence of a reactive triplet excited state of lumiflavin has been obtained by the flash-photolysis technique. The triplet state is formed in high yield on the irradiation of flavin solutions in water or chloroform by visible light, and it has been demonstrated that it can transfer its energy to a second molecular species. The flavin-sensitised oxidation of two purine nucleotides, adenylic and guanylic acids, has been studied by flashphotolysis and by long-term irradiation, and the results suggest a triplet-triplet mechanism for the transfer of energy from the excited flavin to the nucleotide.Approximate absorption spectra of the triplet state and of a semiquinone of the flavin have been calculated from the complex transient absorption curves observed on flashing the flavin solution. The triplet decays by a first-order process where k, = 1.1 X 104 sec-' and the semiquinone by a second-order process where &, = 0.75 X lo8 I .m-l sec-l. The rate constants and extinction coefficients obtained enable decay curves to be calculated which fit satisfactorily those measured with the kinetic-flash apparatus.

Ultra-violet Absorption 8pectra of trans-and cis-Stilbenes and Their Derivatives. Part I. trans-and cis-Xtilbenes.

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