Chiral Templating of Surfaces:  Adsorption of (S)-2-Methylbutanoic Acid on Pt(111) Single-Crystal Surfaces

Abstract

The adsorption and thermal chemistry of (S)-(+)-2-methylbutanoic acid ((S)-2MBA) on Pt(111) single-crystal surfaces was characterized by using temperature programmed desorption (TPD) and reflection-adsorption infrared (RAIRS) spectroscopies. Particular emphasis was placed on the characterization of the chiral superstructures formed upon the deposition of the submonolayer coverages of enantiopure (S)-2-methylbutanoate species that are produced by thermal dehydrogenation of the (S)-2MBA. The enantioselectivity of the empty platinum sites left open on those structures were identified by their difference in behavior toward the adsorption of the two enantiomers of propylene oxide. It was found that a significant enhancement in adsorption is possible on surfaces with the same chirality of the probe molecule, specifically that the uptake of (S)-propylene oxide is larger than that of (R)-propylene oxide on (S)-2-methylbutanoate adsorbed layers. This contrasts with the lack of enantioselectivity previously reported for the same adsorbate on Pd(111). Detectable differences in adsorption energetics of (R)- vs (S)-propylene oxide on the (S)-2-methylbutanoate/Pt(111) overlayers were measured but deemed not to be the controlling factor in the enantioselectivity reported in this system.

Chirally-modified metal surfaces: energetics of interaction with chiral molecules

“…Instead, it is hypothesized that the adsorbed MBA molecules form supramolecular structures with a long-range order. 25 This overlayer can be considered as a proxy for a templating-type of chirality induction.…”

“…As mentioned above, both chirally-modified surfaces were previously reported to exhibit appreciable enantioselectivity in the adsorption of PO enantiomers, both in terms of the adsorption energies and of the amount of the adsorbed PO. 25,26 To verify these findings and to obtain accurate adsorption energies using a direct calorimetric measurement, we measured the PO adsorption energies as a detailed function of the PO coverage at a constant modifier coverage. Complementarily, we varied the surface coverages of the chiral modifiers to tune the properties of the chiral surface overlayers and determined the PO adsorption energies on these surfaces.…”

“…9 Molecular chirality has also attracted much interest in surface science research, 10,11 where adsorption of chiral molecules on welldefined single-crystal surfaces and their interaction with other adsorbates have been extensively studied using a variety of surface sensitive techniques. [12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27] A recent review by Gellman, Tysoe and Zaera summarizes the latest report on chiral surface chemistry performed on model single crystalline surfaces. 28 As one of the major results of these studies, the authors put forward the idea that enantioselectivity arises from the energetic differences in the interaction of two opposite enantiomers with a chiral surface.…”

Asymmetric Thioethers as Building Blocks for Chiral Monolayers

“…In the arena of chiral assembly, tartaric acid [2][3][4][5][6][7][8][9][10], cinchona alkaloids [11][12][13] and heptahelicene [14][15][16] are among the most commonly studied molecules. Several reports in the literature have revealed that chiral adlayers on achiral surfaces exhibit enantiospecific interactions with chiral probe molecules [17][18][19][20]. For example, (S)-propylene oxide exhibits a preference for adsorption on a Pt(111) surface modified with (S)-butoxide over an identical surface modified with (R)-butoxide, with the former system adsorbing 35% more of the probe molecule than the latter [18].…”

Effect of Interaction Energies on the Adsorption of Glycine onto a Cu(110) Surface: A Monte Carlo Simulation

“…In recent years, chiral heterogeneous catalysis has received special attention as a convenient technique for the manufacture of enantiomerically pure compounds (Lee and Zaera 2006). One promising route for achieving this is to use chiral modifiers to endow enantioselective properties onto a metallic surface (Baiker and Blaser 1997).…”