Jeanette C. Hernandez

A direct comparison of extraction and homogeneous binding constants as predictors of efficacy in alkali metal cation transport

Abstract A family of 16 new lipophilic 12-, 15-, and 18-membered ring, ester and amide-sidearmed lariat ethers has been prepared, characterized, and studied. It is found that alkali metal cation transport in a bulk CHCl 3 membrane correlates well with both log K s determined in CH 3 OH and with picrate extraction constants determined in the membrane solvent mixture.

The first evidence for aggregation behavior in a lipophilic [2.2.2]-cryptand and in 18-membered ring steroidal lariat ethers

2-n-Tetradecyl-[2.2.2]-cryptand aggregates in aqueous solution to give micelles either in the presence or absence of Li+, Na+, or K+ but N-(3-cholesteryloxycarbonylmethyl)-aza-18-crown-6 shows unusual behavior that is interpreted in terms of micelle formation in the absence of cations and vesicle formation in their presence.

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.

Aggregation of steroidal lariat ethers: the first example of nonionic liposomes (niosomes) formed from neutral crown ether compounds

N-(3-Dihydrocholesteryloxycarbonylmethyl)-(1) and N-(3-cholesteryloxycarbonylmethyl)-1-aza-4,7,10,13-tetraoxa-cyclopentadecane (2) aggregate in water to from the first examples of niosomes based on amphiphiles having an uncomplexed crown ether residue as the head group.

Hydrogen bonding in macrocyclic receptor systems

Abstract The interactions of macrocyclic polyethers with alkali and alkaline earth cations have been well studied and much about their chemistry is now well understood. Less well examined or comprehended are hydrogen bond interactions. A combination of ion selective electrode binding constant determination techniques and fast atom bombardment mass spectrometry are brought to bear on this problem. It is found that all-oxygen crown ethers and their derivatives exhibit quite different complexation behaviour with ammonium salts than do their various azacrown counterparts.

Steroidal Aza-Lariat Ethers: Syntheses and Aggregation Behavior

Abstract Ten steroid-substituted lariat ether compounds have been prepared including one- and two—armed derivatives of aza-15-crown-5 and aza- and diaza-18-crown-6. They include, N-(3-cholesteryloxycarbonyl-methyl)-aza-15-crown-5, 1, N-(3-dihydrocholesteryloxycarbonylmethyl)-aza-15-crown-5, 2, N-(3-cholesteryloxycarbonylmethyl)-aza-18-crown-6, 3, N-(3-dihydrocholesteryloxycarbonylmethyl)-aza-18-crown-6, 4, N-(3-dihydrocholesteryloxycarbonylpropyl)-aza-15-crown-5, 5, N-(3-dihydrocholesteryloxycarbonylpentyl)-aza-15-crown-5, 6, N-(3-dihydrocholesteryloxycarbonylheptyl)-aza-15-crown-5, 7, N-(3-dihydrocholesteryloxycarbonyldecyl)-aza-15-crown-5, 8, N,N′-bis(3-cholestanyloxycarbonyl-methyl)-4,13-diaza-18-crown-6, 9, and N,N′-bis(3-cholestanyloxycarbonyldecyl)-4,13-diaza-18-crown-6, 10. Aqueous suspensions of these monomers were sonicated. Laser light scattering experiments showed that stable, vesicular aggregates formed. Dye entrapment experiments confirmed the vesicular nature of these aggregates in selected ...

Studies Directed Toward the Fabrication of a Synthetic Cation-conducting Channel Based on Lariat Ethers: the Feeble Forces Concept for Self-assembly

The work described here derives from our observation that while Nature certainly utilizes covalent interactions and other forces of great strength in the construction of biomolecules, many ‘feeble forces’ are involved as well. We have used feeble forces in model studies directed eventually to the synthesis of a self-assembling, cation-conducting channel. Specifically, we have prepared three models for portions of such a cation-conducting channel. The first is based on the steroidal lariat ethers that clearly self-assemble. This process involvesinter alia entropy as a feeble force of cumulative importance. Second, we have prepared threetris(macrocyclic) systems that are simplified versions of the proposed channel-former. Third, we have demonstrated the strength of carefully-conceived hydrogen bonding interactions by constructing a molecular box based on the interaction between adenine and thymine.