Gemini-Tensides and Ion Channels from Fatty acids

Gemini-Tensides and Ion-channels from Fatty acids
M. Dierker, C. Rüdiger and Hans J. Schäfer,
Organisch-Chemisches Institut der Universität Münster, Correns-Str. 40, D 48149 Münster

Nature provides in fatty acids a raw material of high synthetic value. Fatty acids are even numbered carboxylic acid with 12 to 24 carbon atoms and an unbranched alkyl chain that bears one to several - mostly Z-configurated - double bonds and hydroxy groups in distinct positions.
A variety of efficient synthetic conversions has been reported for fatty acids [1]. These comprise C,C-bond formations and functional group interconversions. There are substitutions of CH-bonds in ω- and ω-1-position, in allylic position or adjacent to a carbonyl group. Described are furthermore electrophilic, radical, nucleophilic additions, cycloadditions, metathesis, formation of triple bonds and their conversion. Carbon atoms adjacent to the carboxyl group can be subjected to radical coupling and addition by way of electrochemical decarboxylation.
Higher value products have been obtained by us by combining the amphiphilic nature of the fatty acid with bioactive groups [2], carbohydrates [3], dyes [4], corrosion inhibitors [4], antioxidants [5] and as organogels [6] or ion channels [7].

Tensides are surface active compounds for which the amphiphilic nature of fatty acids contributes excellent preconditions. We report here on two types of Gemini-tensides. The first type is produced by attaching two polar groups to the double bond of the methyl esters of oleic acid, erucic acid and petroselinic acid [8]. The second type is prepared by oxidative coupling of enolates of fatty acid methyl esters and subsequent conversion of the carboxyl group [9]. Polar groups introduced into the first type are ethoxylates, carbohydrates, sulfates and phosphates. The polar groups introduced into the second type are hydroxy groups, oligoethylene glycols and their methyl ethers, sulfates and N-methylglucamides.
The tensidic properties of the compounds as water solubility, decrease of the surface tension, critical micelle concentration, some complexing properties, foaming and wetting behaviour are reported.
The monolayer behaviour at the air-water interface is characterized by pressure-area isotherms. The bis(methyloligoethyleneglyol)ethers of 2,2’-coupled fatty alcohols show pressure/area isotherms that are similar to those of the alveloar lung surfactant, which is essential to reduce the energy consumption for breathing.
The 9,10-bis(methylethyleneglycol) adduct to methyl oleate turns out to be an artificial ion channel. The activity was determined by measurements of fluorescence decay in vesicles and ion conductance of single channels in lipid membranes. The ion conductivity is comparable to this of the natural ion channel forming compound: gramicidine. As gramicidine the synthetic channels exhibit an antibiotic acitivtity against Gram-positive and Gram-negative microorganisms.

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[2] C. Kalk, Dissertation, Universität Münster 2001.
[3] A. Weiper, H.J. Schäfer, Angew. Chem. 1990, 29, 195
[4] G. Feldmann, H. J. Schäfer, Oleagineux Corps gras Lipides 2001, 8, 60.
[5] C. Kalk, H. J. Schäfer, Oleagineux Corps gras Lipides 2001, 8, 89.
[6] K. Dreger, Dissertation, Universität Münster, 2004.
[7] T. Renkes, H. J. Schäfer, P. M. Siemens, E. Neumann, Angew. Chem. 2000, 39, 2512.
[8] M. Dierker, Dissertation, Universität Münster 2000.
[9] C. Rüdiger, Dissertation, Universität Münster, 1999.