Chiral aggregation phenomena. 2. Evidence for partial "two-dimensional resolution" in a chiral monolayer

Aspects of spontaneous separation of enantiomers in two- and three-dimensional crystals

“…Early surface pressure-area isotherm measurements on racemic and chiral Langmuir monolayers by Lundquist led her to the conclusion that certain racemates undergo spontaneous resolution in two dimensions. 33 Similar studies by Arnett and colleagues suggested that racemic mixtures of myristoyl alanine C 17 H 35 CONH(CHOH)COOH, separate into islands of opposite chirality, 11,34 as was recently established by grazing incidence X-ray diffraction and epifluorescence microscopy. 35 Separation of enantiomers in racemic Langmuir films was demonstrated recently by SFM and STM.…”

“…The question whether racemates of amphiphilic molecules will separate into two-dimensional crystallites of opposite handedness has long been a puzzle. 11 Only recently with the application of grazing incidence X-ray diffraction (GID), scanning tunneling microscopy (STM), and scanning force microscopy (SFM) for probing surfaces at the subnanometer level, has it become possible to distinguish the molecular packing arrangement of conglomerates and racemic compounds of two-dimensional assemblies.…”

Chiral Recognition in Biomembrane Models: What is behind a ‘Simple Model’

“…7 Note that it was proposed that the spontaneous segregation of enantiomers from a racemic mixture in monolayer aggregates might have played an important role in the transformation from racemic chemistry to chiral biology. 7,8 This hypothesis was supported by the generation of oligopeptides with homochiral sequences in the polymerization of racemic mixtures of monomers segregated into two-dimensional enantiomorphous domains at the air-water interface. 9 Chiral monolayers are able to discriminate the enantiomers of cholesterol, though this capability strongly depends on the nature of the lipid.…”

“…A number of investigations have focused on this facet of biological membranes and have pointed out, through different models, some consequences of lipid chirality. [4][5][6][7][8][9][10][11][12][13][14][15][16] It was found that the chiral information embedded in the molecular structure of monomers affects the organization of amphiphile aggregates. In fact, the transition temperature (T c ) of homochiral vesicles of 2-methyldodecanoic acid was found to be lower compared with the T c of the racemic vesicles; therefore, at 10 °C, racemic vesicles destabilized causing phase separation, whereas homochiral vesicles remained stable.…”

Thermodynamics and X-ray studies of 2-alcohol monolayers: Two-dimensional phase diagrams

“…Another example is the dipeptide Aspartame which is classically used as a sugar substitute, its natural form SS tastes sweet while the artificial RR seems bitter. In order to enhance molecular interactions, Arnett proposed to investigate molecules confined on a surface [4]. The surface potential forces molecules to be nearly vertical, with the chiral part of molecules next to one another, thus chiral interactions should probably be enhanced.…”