Monolayers of amino acid-type amphiphiles.

The monolayer characteristics of selected N-alkanoyl substituted α-amino acid are studied with the objective to demonstrate the specific effect of the chemical structure of the polar head group which is highlighted with the D- and L-enantiomers of the following selected examples: R-alanine, R-serine, R-threonine, R-allo-threonine, and R-aspartic acid (R = C, C). The thermodynamic effect of the head group variation is studied. Experimental π-A isotherms of the N-tetradecyl-L-alanine monolayers show similar behavior as those of usual amphiphiles.

Influence of Stereochemistry on the Monolayer Characteristics of -alkanoyl-Substituted Threonine and Serine Amphiphiles at the Air-Water Interface.

Thermodynamic and structural properties of the -alkanoyl-substituted α-amino acids threonine and serine, differing only by one CH group in the head group, are determined and compared. Detailed characterization of the influence of stereochemistry proves that all enantiomers form an oblique monolayer lattice structure whereas the corresponding racemates build orthorhombic lattice structures due to dominating heterochiral interactions, except -C16-dl-serine-ME as first example of dominating homochiral interactions in a racemic mixture of -alkanoyl-substituted α-amino acids. In all cases, the liquid expanded-liquid condensed (LE/LC) transition pressure of the racemic mixtures is above that of the corresponding enantiomers.

Lattice and thermodynamic characteristics of N-stearoyl-allo-threonine monolayers.

The effect of the second chiral center of diastereomeric N-alkanoyl-allo-threonine on the main monolayer characteristics has been investigated. The characteristic features of the enantiomeric and racemic forms of N-stearoyl-allo-threonine monolayers are studied on a thermodynamic basis and molecular scale. The π-A curves of the enantiomeric and racemic allo-forms show similar features to those of N-stearoyl-threonine.

Effect of the Alkanoyl Group Position at the Glycerol Backbone on the Monolayer Characteristics Demonstrated by 2-Monopalmitoyl-rac-glycerol.

The influence of the position of the aliphatic chain at the glycerol backbone has been basically unknown. Solely the results of 2-monopalmitoyl-rac-glycerol obtained at ≥13 °C indicated an essential influence of the position of the palmitoyl group at the glycerol backbone, substantiated by a disordered packing of the alkyl chains. Therefore, the present study extends the comprehensive characterization of 2-monopalmitoyl-rac-glycerol monolayers to the low-temperature range for highlighting the effect of the position of the aliphatic chain at the glycerol backbone of monoalkanoylglycerolester monolayers.

Temperature-dependent phase behavior and the crystal-forming nucleation process of ethyl 4-fluoro-2,3-dihydroxystearate monolayers.

The phase behavior of enantiomeric compounds as well as mixtures of enantiopure and racemic diastereomers of ethyl 4-fluoro-2,3-dihydroxystearates has been investigated using surface pressure-area isotherms and Brewster angle microscopy (BAM). All mixtures exhibit a small plateau region within the surface pressure-area isotherm at 20 degrees C, whereas the enantiopure compound shows an isotherm behavior similar to that of fatty acids. Corresponding to the film balance measurements, the BAM images demonstrate different shapes of the domains within the coexistence region of the liquid-condensed/liquid-expanded phase.