Supermolecular periodic structures (such as that shown in the Figure) have been obtained by preparing Langmuir–Blodgett films of amphiphilic molecules with two vicinal hydroxyl groups attached to the hydrophobic chain. The periodicity is adjustable, and the ordered region can be extended to over one hundred micrometers. The undulations are suggested to be due to structural changes in defect arrays upon compression.

Several enantioenriched methyl vic -dihydroxystearates 4 have been synthesized from methyl octadecenoates by enantioselective dihydroxylation in good yields (85-97%) and with satisfactory enantiomeric excess (ee 80-97%). The enantioenriched anti -9,10-dihydroxystearates ( anti -4c ) were prepared by HPLC separation of the corresponding dicamphanyl esters anti -6 . Their ee was determined by HPLC of the corresponding diastereoisomeric carbamates 7 , and their configuration was assigned by relation to a described compound or by applying the mnemonic device of Sharpless.Monolayers of chiral amphiphiles can spontaneously separate into chiral domains. 1 Most of the amphiphiles, studied so far bear chiral polar head groups. We wanted to explore how the monolayer behavior of methyl stearates is influenced by stereogenic centers located at different positions in the alkyl chain. For this purpose enantioenriched methyl vic -dihydroxystearates were prepared using the Sharpless 2 method for the enantioselective dihydroxylation of olefins. The corresponding methyl octadecenoates were synthesized by Kolbe electrolysis 3 or Wittig reaction. Methyl octadec-17-enoate (3a) has been obtained in 40% yield by coelectrolysis of one equivalent of undec-10-enoic acid (2) with four equivalents of methyl azelate (1) 4 (Scheme 1) at platinum electrodes in methanol in an undivided cell. 5 Ethyl trans -octadec-2-enoate (3b) was synthesized by a Wittig reaction from hexadecanal and (ethoxycarbonylmethylene)triphenylphosphorane in 74% yield.The synthesis of chiral vicinal diols by enantioselective dihydroxylation has been described for a variety of olefins; 2 however, to our knowledge this powerful conversion has not yet been applied to the synthesis of chiral vicdihydroxy fatty acid esters. The enantioselective dihydroxylation of 3a , b and of commercially available methyl trans -octadec-9-enoate (3c) led in excellent yield (85-97%) and satisfactory to high enantiomeric excess (ee 84-97%) to methyl vic -dihydroxystearates 4 (Scheme 2, Table 1). As reagents for the dihydroxylations commercially available AD-Mix-α and AD-Mix-β were used. 6In the case of methyl oleate (5) the enantiomeric excess of the dihydroxylation was very low, which has been reported before for the dihydroxylation of nearly symmetrical cisolefins. 7 The synthesis of enantioenriched methyl anti -9,10-dihydroxystearates was then achieved by HPLC separation of the corresponding diastereoisomeric dicamphanyl esters anti -6 (Scheme 3). For this purpose methyl oleate (5) was treated with OsO 4 to yield the methyl anti -9,10-dihydroxystearates ( anti -4c ). 8 The diastereoisomers anti -6 were obtained by diesterification of anti -4c with (-)-camphanic acid chloride, as described by Mohr and Rosini, 9 followed by HPLC separation and partial hydrolysis to the methyl anti -9,10-dihydroxystearates (-)-(9 S ,10 S )-4c and (+)-(9 R ,10 R )-4c (Scheme 3, Table 2).To determine their enantiomeric purity, the dihydroxy esters 4a , syn-4b and anti-4c were transformed into their diastereoiso...

Members of a new class of amphiphiles with two vicinal hydroxyl groups as a second polar moiety have been synthesized by dihydroxylation of trans-octadecenoates made of natural fatty acids or synthetic fatty acid esters. The phase behavior is studied by measuring surface pressure-area isotherms (π-A isotherms) and equilibrium spreading pressures (ESP) as well as Brewster angle microscopy (BAM) and fluorescence microscopy. Both, π-A isotherms and the micrographs of all compounds show a two-phase coexistence region, indicating a first-order phase transition from an expanded to a condensed phase. Depending on the position of the vicinal hydroxyl groups along the hydrophobic alkyl chain, the film pressure in the plateau region as well as the onset of the plateau region differ. Additionally, the position of the hydroxyl groups influences the formation of a stable condensed phase: only the methyl dihydroxyoctadecanoates with no or the largest distance between the two polar groups show an increase in surface pressure at small molecular areas. A molecular model for the processes during film compression is developed, where the two-phase coexistence region is interpreted as the continuous removal of one polar group from the water surface during compression.

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