Conclusions
We have demonstrated that formally achiral glycine can be made chiral by the application of an electric (E )-field that induces the formation of Sa and Ra stereoisomers. We furthermore demonstrated that the chirality Cσ can be controlled. Calculating the chirality in the form of the chiral discrimination Cσ also enables the determination of the bond-flexing Fσ and bond-anharmonicity Aσ for both formally achiral and chiral molecules. This investigation establishes and quantifies the robustness of theE -field-induced chirality Cσ of stereoisomers of glycine (Sa or Ra). We demonstrate that chirality increases with increase in the E -field, as indicated by the increase in the E -field amplification EAσ with the application of a non-structurally distorting E -field. The bond-anharmonicity Aσwas found to be rather invariant to the magnitude of the appliedE -field, as was the stereoisomeric excess Xσ. The magnitude of the bond-flexing Fσ, however, showed significant variations, both larger and smaller than in the absence of an applied E -field, with noticeable increases and decreases forE = -100×10-4 a.u. and E = +100×10-4 a.u., respectively. This finding indicates the role of monitoring the E -field direction to minimize the bond-strain, i.e. the magnitude of the bond-flexing Fσ, to achieve less destructive manipulation of the chirality Cσ.
The proportional response of the chirality Cσ,E -field amplification EAσ and the stereoisomeric excess, Xσ for modest E -field demonstrates their potential use as a molecular similarity measure. The ability to track and control chirality and associated properties could be used in asymmetric autocatalysis[61] or contribute to the design of enantioselective catalytic processes[62]. Another potential application would be in heterogeneous enantioselective catalysis. This is normally achieved through adsorbing chiral molecules on a surface. Using molecules that are chiral only in the presence of anE -field allows the use of a much wider range of molecules and allows changing the chirality of the product by changing the direction of the E -field. Besides catalysis, E -field or laser-field induced chirality could be used to grow chiral MOFs (metal organic frameworks) or other self-assembled structures on a surface.
Future avenues of investigation could also follow on from the recent work of Ayuso et al., generating synthetic controllable chiral light for ultrafast imaging of chiral dynamics in gases, liquids and solids[63], which can also be used to imprint chirality on achiral matter efficiently[64] and may lead to insights into laser-driven achiral–chiral phase transitions in matter[65]. Our approach could be a powerful analytical method to open up a wide scientific field for chiral solid state and molecular systems to track and quantify the chirality for the first time, e.g. in a wide range of molecular devices including substituted dithienylethene photochromic switches[66], azobenzene chiroptical switches[67] and the design of chiral-optical molecular rotary motors[68].