Graphical abstract

Equilibrium adsorption of gas phase mixtures of d- and l-alanine (Ala) onto the naturally chiral Cu{3,1,17}^R&S surfaces has been studied by both experiment and DFT-based modeling. Isotopically labeled _*l-Ala (HO₂¹³CCH(NH₂)CH₃) and unlabeled _d-Ala allow mass spectrometric enantiodifferentiation of the adsorbed species during temperature-programmed decomposition, following equilibrium adsorption. Measurements of the relative equilibrium coverages of _d- and _*l-Ala on the Cu{3,1,17}^R&S surfaces, θ_D/R/θ_*L/R = θ*_L/S/θ_D/S, at gas phase partial pressure ratios of P_*L/P_D = 1/2, 1, and 2 indicate that the _d-Ala and _*l-Ala conglomerate phases are more energetically stable than a _d*l-Ala racemate phase, but that their adsorption energies are not measurably enantiospecific, ΔΔE_DL ≈ 0. Although the DFT simulations provide a self-consistent structure of Ala overlayers on Cu{3,1,17}^R&S they overestimate the enantiospecificity of the adsorption energetics.