A Nanoscale View of Supramolecular Stereochemistry in Self-Assembled Monolayers of Enantiomers and Racemates

Abstract

The effect that molecular chirality has on the formation of monolayer structures by pure enantiomers and their racemates at the liquid/solid interface has been investigated for two chiral compounds (1 and 2) which differ from each other by the presence or absence of an ester function in their respective molecular structures. 1 shows pseudoracemate formation when the achiral graphite support is exposed to a solution containing a racemate while 2 shows racemic conglomerate formation. This difference is rationalized in terms of the orientation of the pure enantiomers with respect to the graphite substrate and highlights the importance of molecular structure and its influence on balancing the interplay between molecular conformation and molecular packing on the surface. For 1, nonstoichiometric mixtures of both enantiomers have been investigated, and the results are discussed in the framework of the sergeant and soldiers principle. These results are important for the understanding and prediction of spontaneous resolution in monolayer systems.

Tracking the chemical surface properties of racemic thalidomide and its enantiomers using a biomimetic functional surface on a quartz crystal microbalance

“…The utilization of quantum mechanical control of small aggregates is well known as it was this that established the chirality on the macromolecular assemblies, e.g., DNA. 39 The surface energy data were calculated using the frequency response for both the analytes. 38 In Figure 5(c), a BET isotherm for the (rac)-thalidomide was bound onto the respective imprinted layers that provided for the observable difference between the numbers of binding sites and the binding affinity value, K a of the two imprints with a highly satisfactory correlation coefficient (R 2 > 0.96) of the data.…”

Preferred Formation of Minority Concomitant Polymorphs in 2D Self‐Assembly under Lateral Nanoconfinement

“…Upon drop-casting a10mm solution of enantiopure 4-[(S/R-1methylheptyl)oxy]-4'-biphenylformamide (S/R-BFA) [20] in 1phenyloctane (PO) onto pristine HOPG,the molecules form an SAMN,a ppearing as ar ow-like structure in large-scale STM images (see the Supporting Information, Section S1 for experimental details) with two different orientations,t aking into account the threefold symmetry of the surface (Figure 2a). Upon drop-casting a10mm solution of enantiopure 4-[(S/R-1methylheptyl)oxy]-4'-biphenylformamide (S/R-BFA) [20] in 1phenyloctane (PO) onto pristine HOPG,the molecules form an SAMN,a ppearing as ar ow-like structure in large-scale STM images (see the Supporting Information, Section S1 for experimental details) with two different orientations,t aking into account the threefold symmetry of the surface (Figure 2a).…”

“…Thes econd molecule studied, enantiopure 4-[(S/R-1methylheptyl)oxy]phenyl-4'-formamidobenzoate (S/R-PFB, Figure 1b), [20,21] also forms row-like structures upon dropcasting a5.5 mm solution in PO onto pristine HOPG with two different orientations (Figure 3a Figure S1). Interestingly,a djacent polymorphs can merge without showing ac lear domain boundary (Figure 3b).…”

Discrimination between Conglomerates and Pseudoracemates Using Surface Coverage Plots in 2D Self‐Assemblies at the Liquid–Graphite Interface

“…Note that histogram of the rotation angle showed only two peaks centered at y =AE 78 8,s uggesting that there is no other polymorphs of 2D ordering for 1 in the tested conditions (Supporting Information, Figure S7). [24][25][26] These results plausibly suggest that the racemic mixture of (R,R)-1 and (S,S)-1 spatially separates into two enantiomerically enriched phases at the liquid-graphite interface through 2D crystallization.…”