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].