The polarographic determination of stability constants of urea/crown ether complexes in methanol

Abstract

SUMMARYA general method for determination of the stability constants of complexes of crown ethers and related compounds with small organic molecules in polar solvents is described, based on an indirect polarographic procedure. Computerized evaluation of the data forms an essential part of the procedure.Since the publication of the pioneering paper of Pedersen in 1967 [l] , interest in the chemistry of crown ethers and related compounds has steadily increased, not only from a purely scientific point of view, but also with regard to possible applications of crown ethers in (organic) synthesis, analytical chemistry and in the field of physiological processes and pharmacology i&31.Apart from the abundance of data on complexes of various crown ethers with metal ions and other cations that can be found in the literature, complexes with neutral molecules are also mentioned [4]. Complexation of (uncharged) molecules plays an essential role in many biological processes such as enzyme-substrate and pharmacon-receptor interactions. In this respect, the study of the interactions between crown ethers and neutral molecules could eventually lead to the design of specific host molecules for compounds of biological significance like neurotransmitters, drugs and toxic compounds.For a number of complexes of crown ethers with neutral molecules, the crystal structure has been elucidated (Table l), but crystalline complexes for which the crystalline structure has not yet been resolved have been reported for many other compounds [ 41. In this Department, interest in these neutral compound complexes was aroused during consideration of the possibility of using crown ethers in the selective removal of urea from dialysis fluid, one of the major problems in the current practice of kidney dialysis.In order to obtain guidelines for the synthesis of possible urea-selective crown-type ligands, it was necessary to have information concerning the 0003-2670/84/$03.00 Q 1984 Elsevier Science Publishers B.V.

Neutral water-soluble aluminum complex of neurological interest

“…The disorder causes Al-0(5) and Al-0(6) to be averaged up and down, respectively, from those distances observable if 0(5) was exclusively a hydroxy oxygen and 0(6) exclusively a keto oxygen. The observed bond distances are consistent with this averaging, Al-0 (5) being slightly shorter than Al-0(6). The bond angles are consistent with a somewhat distorted octahedron with all the m-O-Al-O angles being 90 ± 5.5°and the ligands are quite planar.…”

Ion-transfer Polarographic Determination of Successive Formation Constants of Rubidium and Cesium Complexes with Benzo-15-crown-5 and -18-crown-6 Ethers in Nitrobenzene

“…1,2 We have determined the stability constants of these complex ions by ion-transfer polarographic measurements. [3][4][5] In one of these studies, the DeFord-Hume method was applied for the analysis of polarographic waves 6,7 arising from ion transfer facilitated by L across a w/nitrobenzene (NB)-interface. Then, the overall stability constants of 1:1 and 1:2 (metal to ligand) complexes in the NB solution saturated with water were determined using Cs + and dibenzo-18-crown-6 ether (DB18C6).…”