Hydraphile Channels: Structural and Fluorescent Probes of Position and Function in a Phospholipid Bilayer

Citations Over TimeTop 11% of 1999 papers

Abstract

Three novel tris(macrocycle)s having fluorescent residues at their distal termini have been prepared and studied. The compounds are of the form R〈N18N〉C12〈N18N〉C12〈N18N〉R in which R is 2-(3-indolyl)ethyl (1), 2-(3-(N-methylindolyl))ethyl (2), and dansyl (3). Compounds 2 and 3 were found to transport Na+ at rates similar to those of other tris(macrocyclic)s but 1 was not an ionophore in the bilayer as assessed by 23Na NMR analysis. The latter failure may be due to a hydrogen-bond blockade leading to a globular conformation adopted by the hydraphile. The fluorescence maximum of 3 was determined in a variety of solvents and in a phospholipid bilayer. The polarity experienced by the dansyl group in the bilayer was intermediate between that observed in methanol and ethanol. Fluorescence depth quenching using doxyl-substituted lipids showed that the dansyl headgroups of 3 were 14 Å from the bilayer's midplane or separated by about 28 Å. Fluorescence energy transfer between 2 and 3 showed that these two hydraphiles were not appreciably aggregated in the bilayer.

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