The homochirality of biomolecules is a signature of life on Earth and has significant implications in, for example, the production of pharmaceutical compounds. It has been suggested that biomolecular homochirality may have arisen from the amplification of a spontaneously formed small enantiomeric excess (e.e.). Many minerals exhibit naturally chiral surfaces and so adsorption has been proposed as one possible mechanism for such an amplification of e.e. Here we show that when gas-phase mixtures of D- and L-aspartic acid are exposed to an achiral Cu(111) surface, a small e.e. in the gas phase, e.e.g, leads to an amplification of the e.e. on the surface, e.e.s, under equilibrium conditions. Adsorption-induced amplification of e.e. does not require a chiral surface. The dependence of e.e.s on e.e.g has been modelled successfully using a Langmuir-like adsorption isotherm that incorporates the formation of homochiral adsorbate clusters on the surface.
Unequivocal evidence of enantioselective, equilibrium separation of a racemic mixture on a naturally chiral metal surface is presented for the first time. The enantioselectivity is much higher than that of chiral molecules on mineral surfaces. Furthermore, the quantitative nature of the 13C labeling method provides the first direct measure of an enantiospecific adsorption energy difference on a chiral metal surface.
A Z‐scheme heterojunction with spatially separated cocatalysts is proposed for overcoming fundamental issues in photocatalytic water splitting, such as inefficient light absorption, charge recombination, and sluggish reaction kinetics. For efficient light absorption and interfacial charge separation, Z‐scheme organic/inorganic heterojunction photocatalysts are synthesized by firmly immobilizing ultrathin g‐C3N4 on the surface of TiO2 hollow spheres via electrostatic interactions. Additionally, two cocatalysts, Pt and IrOx, are spatially separated along the Z‐scheme charge‐transfer pathway to enhance surface charge separation and reaction kinetics. The as‐prepared Pt/g‐C3N4/TiO2/IrOx (PCTI) hollow sphere photocatalyst exhibits an exceptional H2 evolution rate of 8.15 mmol h−1 g−1 and a remarkable apparent quantum yield of 24.3% at 330 nm in the presence of 0.5 wt% Pt and 1.2 wt% IrOx cocatalysts on g‐C3N4 and TiO2, respectively. Photoassisted Kelvin probe force microscopy is used to systematically analyze the Z‐scheme charge‐transfer mechanism within PCTI. Furthermore, the benefits of spatially separating cocatalysts in the PCTI system are methodically investigated in comparison to randomly depositing them. This work adequately demonstrates that the combination of a Z‐scheme heterojunction and spatially separated cocatalysts can be a promising strategy for designing high‐performance photocatalytic platforms for solar fuel production.
Equilibrium adsorption of gas phase mixtures of D-and Lalanine (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 (HO 2 13 CCH(NH 2 )CH 3 ) 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.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.