Handedness Of Molecules Research Articles

Far-Field Polarization Optics Control the Nanometer-Scale Pattern of High-Fluorescence Dissymmetry Emission from Achiral Molecules near Plasmonic Nanodimers

Chiroptical spectroscopies like circular dichroism report on the handedness of molecules but are often limited to the high-concentration regime because of the mismatch between the wavelength of propagating visible light and the size of molecules. Recent work has demonstrated that the electromagnetic fields generated near chiral plasmonic nanostructures can have high optical chirality that bridges these length scales and can induce high-fluorescence dissymmetry signals from achiral dyes by redirecting their emission. As a step toward single-molecule chiral sources, the induced fluorescence dissymmetry and apparent emission pattern near chiral plasmonic nanoparticles must be quantified. Here, we measure the induced fluorescence dissymmetry from the achiral dye Cy5.5 near a chiral gold nanodimer structure, and we map out the apparent emission pattern of the dyes using super-resolution single-molecule microscopy. Our high-sensitivity approach quantifies the fluorescence dissymmetry from sampling only ∼100 zeptomoles of Cy5.5 and measures from Cy5.5 near gold nanodimers median fluorescence dissymmetry factors that are 2 orders of magnitude greater than those of synthesized chiral fluorescent molecules. We observe a spatial correlation between the simulated optical chirality about a plasmonic gold nanodimer and experimentally obtained super-resolution apparent emission patterns, and we use the incident polarization to control our detection bias for the brightest molecules to sample nanometer-scale regions of high electric flux.

Absolute configuration assignment of a chiral molecule in the gas phase using foil-induced Coulomb explosion imaging

Chiral molecules exist in two configurations that are nonsuperposable mirror images of one another. The underlying molecular structure is referred to as the absolute configuration. In chiral environments, the handedness of molecules influences their chemical characteristics dramatically, and therefore the determination of absolute configurations is of fundamental interest in organic chemistry and biology. Commonly applied techniques to assign absolute configuration are anomalous single-crystal x-ray diffraction and vibrational circular dichroism. However, these techniques become increasingly more challenging when applied to molecules that are made out of light atoms exclusively. Furthermore, there is no established method to determine the absolute handedness of gas-phase molecules that are not optically active. In this work, we apply the foil-induced Coulomb explosion imaging technique to determine directly the absolute configuration of the chiral molecule trans-2,3-dideuterooxirane (${\mathrm{C}}_{2}{\mathrm{OD}}_{2}{\mathrm{H}}_{2}$) in the gas phase. The experiment leads to the definitive assignment of the ($R,R$) configuration to an enantio-selected dideuterooxirane sample with a statistical confidence of $5\ensuremath{\sigma}$. As the handedness of trans-2,3-dideuterooxirane is unambiguously linked by chemical synthesis to the stereochemical key reference glyceraldehyde, our results provide an independent verification of the absolute configuration of the stereochemical reference standard.

The Left–Right Polarity Puzzle: Determining Embryonic Handedness

Whenever symmetry is broken in nature to yield only one of two equally probable outcomes, whether in physics, chemistry, or biology, there is an intriguing problem to be solved. Physicists from M. and P. Curie to T.-S. Lee and C.-D. Yang puzzled over such phenomena at the atomic level. Organic chemists puzzled over the handedness of molecules for many years after Pasteur showed that grape juice contained only one of the possible right- and left-handed mirror-image forms (enantiomers) of tartaric acid (Figure 1; see Glossary [Box 1]). And biologists continue to puzzle over the handedness of organisms.