Design and synthesis of benzo-18-crown-6 carboxylic acids and diazadibenzo crown ethers and lariat ethers with neutral and proton-ionizable side arms

A series of proton-ionizable benzo-18-crown-6 lariat ethers has been prepared to probe the optimal host structure for a ferrioxamine B guest. Host-guest supramolecular assembly formation constants involving second-sphere complexation of the siderophore ferrioxamine B by a lariat ether carboxylic acid host were obtained from liquid-liquid extractions at high and low pH. The formation constant, Ka, determined at pH = 3.2 is compared to those from other lariat ether carboxylic acids of different chain lengths. These constants are similar to the parent crown ether. At pH = 9.3, the lariat ethers are ionized and this results in a more stable complexes. According to the comparison of formation constants at pH =9.3, an optimal host structure for the complexation of ferrioxamine B guest is determined.

To study the complexation behavior of nitrogen containing macrocyclic ligands toward transition metal cations, series of diazadibenzocrown ethers and diazadibenzo lariat ethers with neutral side arms and proton-ionizable side arms were synthesized. Solvent extraction and membrane transport studies were performed with 1,13- diazadibenzo-15-crown-5, 1,13-diazadibenzo-18-crovra-6, 1,13-diazadi(?er^butylbenzo)- 18-crown-6 and l,13-diazadibenzo-18-crown-6 diester and showed that 1,13-diazadi (?ert-butylbenzo)-18-crown-6 and a l,13-diazadibenzo-18-crown-6 diester selectively forms complexes with Pb^2+ in the presence of Cd^2+ and Zn^2+.