No abstract

The synthesis and cation binding properties of a series of macrocyclic polyethers which possess ligating arms that enhance cation binding is presented.

No abstract

No abstract

A number of carbon-pivot lariat ethers have been prepared and compared, with their counterparts having a methyl group bonded to the side-arm-bearing or pivot carbon. All of the compounds examined are 15-crown-5 derivatives, and in this series, the methyl lariats invariably show a higher affinity for sodium than do the nonmethylated species. The results are less consistent in the case of potassium cation which is larger than the 15-crown-5 compound's cation binding hole. The enhanced stability constant observed for sodium with the methyl lariats is attributed to reduced side-arm mobility or conformational changes in either the side arm or macroring.The class of molecules to which we have given the cognomen "lariat ethers"1 2is characterized by a macrocylic "crown" polyether ring and a donor group attached to the ring by a suitable, flexible side chain. The two principal groups of molecules thus far explored are the "carbonpivot" lariats which derive from a glycerol unit1,2 and the "nitrogen-pivot" molecules which derive from a diethanolamine unit.3 45"6 Of these two groups, the nitrogen-pivot molecules have proved to be quite flexible and strong cation binders while the carbon-pivot molecules have proved to be less flexible and to exhibit weaker cation binding strength.7 We now report that placement of a methyl group on the "pivot carbon atom" significantly influences cation-binding strength in carbon-pivot lariat ethers.8