Hydrogen ion buffers for biological research.

A study of some problems in determining the stoicheiometric proton dissociation constants of complexes by potentiometric titrations using a glass electrode

Computer calculation of equilibrium concentrations in mixtures of metal ions and complexing species.

Isolation and some properties of human metallothionein.

Complexing agents of the type: (HOOCCH2)(2=N(CH2))n N = (CH2COOH)2 with n-values from 2–8 have been investigated. The stability constants of the 1:1 complexes of Ca2+, Cd2+ and Hg2+ have been determined for nearly the whole series of these complexons and a few values have been obtained also for the complexes of Mg2+, Sr2+, Ba2+ and Go2+. There is generally a strong decrease in complex stability when n is increased from 2 t o 4, where an almost constant value is reached which does not alter anymore to an appreciable extent hy a further increase of the chain length 11. The mercury complexes behave exceptionally. Replacement of one or two CH2-groups in the chain connecting the two nitrogens by O, S, and N(CH2) increases the complex stability to a great extent if new 5-membered chelate rings can be formed by coordination of this heteroatom.

Komplexone XXIX. Ein grosser Chelateffekt besonderer Art

Substituted iminodiacetic acids of the general formula RN(CH2-COOH)2 have been synthesized and their coordination tendency with 12 different metal cations investigated. The groups R of the 13 different complexing agents are tabulated on page 1147–1148 of this paper. Most of them carry donor atoms in such a position, that a third chelate ring may be formed when the anion of the iminodiacetic acid combines with the metal. It could be proved that the oxygen, the sulfur and the nitrogen atom of aliphatically bound HO, CH3O, HS, CH3S, (−)S, NH2, (−)OOC, H2NCO are actually coordinated in this manner, raising thereby the stability of the metal complex considerably. The carbonamide group coordinates probably by its oxygen atom rather than by its nitrogen atom. The negatively charged mercaptide sulfur is a very powerful donor for the heavy metals and there is a linear relation between the logarithm of the solubility product of the metal sulfide and the logarithm of the stability constant of the metal complex of (−)SCH2CH2N(CH2COO(−))2. The trimethylammonium group in of course lowers the complex stability, its effect however is much less important than expected. Also the cyano group in NCCH2-N(CH2-COO(−))2 weakens the metal binding much less than the addition of the proton to the nitrogen of the iminodiacetate group.

W. Schneider

Papers

Komplexone XXVI. Über die Koordinationstendenz von N-substituierten Iminodiessigsäuren