Kristin A. Arnold

Novel synthetic access to 15- and 18-membered ring diaza-bibracchial lariat ethers (BiBLEs) and a study of sidearm-macroring cooperativity in cation binding

An extremely practical synthesis of 4,10-diaza-15-crown-5, 4,13-diaza-18-crown-6, and symmetrically N,N′-disubstituted derivatives thereof, is presented along with the first survey of cation binding data for the 15-membered ring systems.

Analysis of sodium, potassium, calcium, and ammonium cation binding and selectivity in one- and two-armed nitrogenpivot lariat ethers

Abstract Complexation of sodium, potassium, calcium, and ammonium cations by one- and two-armed (bibracchial) lariat ethers is surveyed and analyzed. A comprehensive list of binding data determined at 25.0±0.1 °C in anhydrous methanol is presented. More than 100 new, experimentally determined (K s ) and calculated (selectivity) values especially for calcium and ammonium are presented. Both cation binding strength and selectivity are evaluated in terms of ring size, sidearm length, number and type of donor groups and other factors. Hitherto unreported divalent calcium cation binding selectivities for bibracchial lariat ethers in aqueous solution rival the cation selectivities of some cryptands. N,N′-bis(Ethoxycarbonylmethyl)-4,13-diaza-18-crown-6 exhibits a Ca2+/K+ selectivity equal to that of [2.2.1]-cryptand and a Ca2+/Na+ selectivity better than that of any cryptand. Two bibracchial systems having >NCH2CONHCHRCOOCH2CH3 sidearms (R=H, s-butyl), have shown Ca2+ over Na+ selectivity in water of ≥103. Catio...

Lariat ethers: from cation complexation to supramolecular assemblies

Lariat ethers are now well-known as macrocycles having one or more sidearms that contain donor groups and can interact with ring bound cations. Variations in structure and donor group arrangements lead to variation in cation binding strengths and selectivities. Such systems exhibit enhanced cation complexation and generally high complexation dynamics. The binding dynamics and strength may readily be altered by reductive switching. This process has been accomplished using both reducing metals and electrochemical techniques. Cyclic voltammetry and EPR techniques confirm the redox switching and the formation of intramolecular ion pairs. Redox-switched lariats have been utilized in cation transport through bulk liquid membranes. When the sidearms are highly lipophilic systems such as cholesteryl, they readily form completely synthetic lipid bilayers or micelles and can assemble into vesicle systems of considerable size and stability.

One- and two-armed lariat ether peptide derivatives: syntheses and cation binding properties

Abstract Series of peptide-based lariat ethers derived from aza-18-crown-6 and bibracchial lariat ethers (BiBLEs) based on 4,13-diaza-18-crown-6 have been prepared. Sidearms incorporate inter alia the amino acids glycine, alanine, phenylalanine, leucine, isoleucine, and valine. Cation binding affinities for Na + and K + are reported.

Complexation by N-(3,6,9-trioxadecyl)monoaza-12-crown-4 lariat ether: a “calabash” complex of a potassium cation by a synthetic macrocycle containing a total of only seven donor atoms

Abstract Structural and cation binding data for the title compound demonstrate that the large value of Ks results from complete K+ cation encapsulation by one nitrogen and six oxygen atoms despite the presence of a twelve-membered macroring.

The remarkable indifference of alkali metal cation binding constants to sidearm thioether and sulfoxide donors in azalariat ethers

The first example of a lariat ether containing a sulfur sidearm donor is reported here along with a comparison of cation binding strengths to Na+ and K+. The binding strength differs remarkably little from analogs completely lacking a sidearm donor group and similar results are observed for the novel sulfoxide analog.