Lock‐and‐Key Principle on a Microscopic Scale: The Case of the Propylene Oxide⋅⋅⋅Ethanol Complex

Abstract

Molecular recognition: The binding between propylene oxide (PO) and ethanol resembles the lock‐and‐key principle, with (R)‐PO as a rigid lock and G−, G+, and T conformers of EtOH as different keys (see picture; C yellow, O red). Six hydrogen‐bonded PO⋅⋅⋅EtOH conformers were studied using rotational spectroscopy and ab initio calculations, revealing which EtOH key fits best into the PO lock.

Chirality Recognition between Neutral Molecules in the Gas Phase

“…[160] The methyl oxirane case is more complex because of the different faces or hydrogen-bond topologies, but the most stable dimer between methyl oxirane and ethanol corresponds to the preferred local environment in the complex of 2,3-dimethyl oxirane with ethanol. [94] An earlier example involves the complex of 2-naphtyl-1-ethanol with 1-propanol, [66] where a splitting in the fluorescence excitation spectrum has been attributed, on the basis of UV-UV double resonance experiments, to the two enantiomeric gt-1-propanol conformations binding differently to the chiral chromophore. Because monomer racemization involves heavy-atom motion in this case, the conformational lifetime could be in the ms range or longer.…”

“…It is crucial that the method used allows a complete exploration of complex potential energy surfaces (PES) of molecules with high conformational flexibility. Correlated methods are mostly applied to smaller systems such as those studied by microwave or FTIR spectroscopy, [93,94] for which the use of a large basis set is often necessary to reproduce the experimental spectra. For these small systems, a crude exploration of the surface is regularly made at the Hartree-Fock (HF) level, while a full optimization is performed with a correlated method.…”

Chirality effects in gas-phase spectroscopy and photophysics of molecular and ionic complexes: contribution of low and room temperature studies

“…Despite being limited to small and relatively rigid systems, microwave spectroscopy brings invaluable information as the size of the studied systems makes them amenable to high-level calculations and allows precise determination of their conformational landscape, as does high-resolution fluorescence spectroscopy [108][109][110][111]. Vibrational spectroscopy is of frequent use as it provides important structural information, directly comparable to calculations and therefore used as benchmark for the latter.…”

Infrared diode laser spectroscopic investigation of four C–H stretching vibrational modes of propylene oxide

“…It is both rigid and stable, and has one stereogenic center, namely the center carbon atom bonded with the methyl group. PO has been a valuable prototype molecule for theoretical and rotational spectroscopic studies of chiral recognition effects [16,17] and chiroptical activities [18][19][20][21]. A series of rotational spectroscopic studies of PO in its ground vibrational and excited internal rotational states were published [22][23][24][25].…”