Membrane activity of 3-hydroxyglutarate diesters

Abstract

The synthesis and characterisation of the transport activity and membrane localisation of three 3-hydroxyglutarate diesters containing saturated and diphenylacetylene-derived groups are described. In bilayer vesicles and planar bilayers, the two compounds bearing a terminal carboxylic acid form active ion channels; a related neutral compound is inactive. Nonlinear current-voltage behaviour is observed for the active diphenylacetylene-derived diester. The transport activity occurs at concentrations that are substantially below the level at which the compounds aggregate. Diphenylacetylene-derived fluorescence allows the partitioning and the aggregation states of the compounds to be probed. It is clear that the active compounds do not simply act as detergents, but form defined, if irregular, ion channels in the membrane.

Mechanism of Ion Transport by Fluorescent Oligoester Channels

“…Typically a constant transport rate constant at a given concentration is expected irrespective of the delay between mixing the compound with the vesicles and the initiation of transport with the addition of base. We have previously noted that some compounds partition rather slowly and longer delays are desirable . The compound HO 2 C-Hex-Dip-Hex-C6 is unusual in that it shows the opposite behavior; it has significant activity shortly after mixing, but longer delays result in a condition where the activity falls to an undetectable level.…”

“…We have previously noted that some compounds partition rather slowly and longer delays are desirable. 33 The compound HO 2 C-Hex-Dip-Hex-C6 is unusual in that it shows the opposite behavior; it has significant activity shortly after mixing, but longer delays result in a condition where the activity falls to an undetectable level. Figure 2B shows the observed rate constant as a function of the delay between mixing and the pH gradient being established.…”

A membrane-spanning macrocyclic bolaamphiphile lipid mimic of archaeal lipids

“…Our potentially membrane-spanning macrocyclic archaeal lipid mimic is given in Figure 1. The design is driven by a combination of practical considerations and experience derived from linear oligoester ion channels 19,20,[28][29][30][31] . Good phospholipid miscibility is associated with extended alkyl esters 32,33 and the use of glutarate diesters in place of glycerol diesters is both a reliable and simplifying synthetic strategy 28,34 .…”

“…The design is driven by a combination of practical considerations and experience derived from linear oligoester ion channels 19,20,[28][29][30][31] . Good phospholipid miscibility is associated with extended alkyl esters 32,33 and the use of glutarate diesters in place of glycerol diesters is both a reliable and simplifying synthetic strategy 28,34 . The 1,2,3-triazole produced via copper-catalyzed alkyneazide coupling (CuAAC) 35 also has good lipid miscibility in conjunction with esters elsewhere in D r a f t the structure 33 and has previously featured in single-chain archaeal lipid mimics designed to enhance membrane permeability via flip-flop which necessarily requires a U-shaped insertion 36,37 .…”

“…A procedure involving removal of excess 1 by low temperature crystallization proved effective. Purifications of previous glutarate monoesters of this type also relied on differential solubility, but of the product monoester not the anhydride 28,31 . The same procedure produced compound 2 from 1-dodecanol (n = 12) or 1-tetradecanol (n = 14) albeit in lower yields dues to different product solubility under the low-temperature crystallization conditions.…”