%0 Journal Article
%A Brezesinski, G.
%A Rudert, R.
%A Vollhardt, D.
%T Lattice and thermodynamic characteristics of N -stearoyl-allo-threonine monolayers
%J Physical chemistry, chemical physics
%V 22
%N 5
%@ 1463-9084
%C Cambridge
%I RSC Publ.
%M PUBDB-2021-00208
%P 2783 - 2791
%D 2020
%X 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. The compression curves are always located above the corresponding decompression curves and the decompression curves can be used as equilibrium isotherms for both the enantiomeric and racemic N-stearoyl-allo-threonine. The absolute T<sub>0</sub>-values (disappearance of the LE/LC-transition) are 4–5 K larger compared with the corresponding N-stearoyl-threonines, but the ΔT<sub>0</sub> between the enantiomeric (D) and the racemic (DL) forms is only slightly larger than that of N-stearoyl-threonine. The difference in the critical temperatures T<sub>c</sub>, above which the monolayer cannot be compressed into the condensed state, between the enantiomeric and the racemic forms, is quite small (ΔT<sub>c</sub> = 0.8 K) and is smaller compared to that of the corresponding threonines (ΔT<sub>c</sub> = 1.8 K). This is consistent with the dominance of the van der Waals interactions between the alkyl chains reducing the influence of chirality on the thermodynamic parameters. GIXD studies of N-stearoyl-allo-threonine monolayers provide information about the lattice structure of condensed monolayer phases on the Angstrom scale and stipulate the homochiral or heterochiral preference in the condensed phases. Comparable to N-stearoyl-threonine, the enantiomers exhibit an oblique lattice structure, whereas the racemates form a NNN tilted orthorhombic structure demonstrating the dominance of heterochiral interactions in the racemates independent of the diasteomeric structure change of the polar head group. The A<sub>0</sub> values are characteristic for rotator phases. The smaller A<sub>0</sub> value obtained for the racemic monolayers indicates their tighter packing caused by heterochiral interactions. The program Hardpack was used to predict the geometric parameters of possible 2-dimensional packings. For comparison with the experimental GIXD data, the two-dimensional lattice parameters and characteristic features of the enantiomeric and racemic diastereomeric stearoyl-threonine monolayers were calculated and are in reasonable agreement with the experimental GIXD data.
%F PUB:(DE-HGF)16
%9 Journal Article
%$ pmid:31957777
%U <Go to ISI:>//WOS:000517561500015
%R 10.1039/C9CP06304H
%U https://bib-pubdb1.desy.de/record/453844