Direct Determination of Absolute Molecular Stereochemistry in Gas Phase by Coulomb Explosion Imaging
06 Sep 2013-Science (American Association for the Advancement of Science)-Vol. 341, Iss: 6150, pp 1096-1100
TL;DR: A mass spectrometry approach is demonstrated that directly images the absolute configuration of individual molecules in the gas phase by cold target recoil ion momentum spectroscopy after laser ionization–induced Coulomb explosion.
Abstract: Bijvoet's method, which makes use of anomalous x-ray diffraction or dispersion, is the standard means of directly determining the absolute (stereochemical) configuration of molecules, but it requires crystalline samples and often proves challenging in structures exclusively comprising light atoms. Herein, we demonstrate a mass spectrometry approach that directly images the absolute configuration of individual molecules in the gas phase by cold target recoil ion momentum spectroscopy after laser ionization-induced Coulomb explosion. This technique is applied to the prototypical chiral molecule bromochlorofluoromethane and the isotopically chiral methane derivative bromodichloromethane.
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TL;DR: In this paper, the authors used high-harmonic generation from a randomly oriented gas of molecules subjected to an intense laser field, to probe chiral interactions on these sub-femtosecond timescales.
Abstract: Molecules that are mirror images of each other usually behave identically, unless they are interacting with other chiral objects. High-harmonic generation can provide access to the dynamics of chiral interactions on ultrafast timescales. Chiral molecules that are non-superimposable mirror images of each other, known as enantiomers, have identical chemical and physical properties unless they interact with another chiral entity, such as chiral light. Chiroptical1 effects arising from such interactions are used to detect enantiomers in mixtures and to induce enantioselective synthesis and catalysis. Chiroptical effects often arise from the interplay between light-induced electric- and magnetic-dipole transitions in a molecule and evolve on ultrafast electronic timescales. Here we use high-harmonic generation2,3 from a randomly oriented gas of molecules subjected to an intense laser field, to probe chiral interactions on these sub-femtosecond timescales. We show that a slight disparity in the laser-driven electron dynamics in the two enantiomers is recorded and amplified by several orders of magnitude in the harmonic spectra. Our work shows that chiroptical detection can go beyond detecting chiral structure4,5,6,7 to resolving and controlling chiral dynamics on electronic timescales.
246 citations
TL;DR: In this article, a resonant high-order harmonic generation of an elliptical laser pulse was proposed to measure photoelectron circular dichroism on chiral molecules, opening the route to table-top time-resolved femtosecond and attosecond chiroptical experiments.
Abstract: Circular dichroism in the extreme ultraviolet range is broadly used as a sensitive structural probe of matter, from the molecular photoionization of chiral species1, 2, 3 to the magnetic properties of solids4. Extending such techniques to the dynamical regime has been a long-standing quest of solid-state physics and physical chemistry, and was only achieved very recently5 thanks to the development of femtosecond circular extreme ultraviolet sources. Only a few large facilities, such as femtosliced synchrotrons6, 7 or free-electron lasers8, are currently able to produce such pulses. Here, we propose a new compact and accessible alternative solution: resonant high-order harmonic generation of an elliptical laser pulse. We show that this process, based on a simple optical set-up, delivers bright, coherent, ultrashort, quasi-circular pulses in the extreme ultraviolet. We use this source to measure photoelectron circular dichroism on chiral molecules, opening the route to table-top time-resolved femtosecond and attosecond chiroptical experiments.
221 citations
TL;DR: The capabilities and the potential of PECD are illustrated with various experimental examples and computational methods that are able to model quantitatively experimental PECD results are introduced, focusing on velocity map coincidence imaging where the momentum distribution of both the electron and the coincident ion is measured.
Abstract: In this Perspective we discuss photoelectron circular dichroism (PECD), a relatively novel technique that can detect chiral molecules with high sensitivity. PECD has an enantiomeric sensitivity of typically 1–10%, which is two to three orders of magnitude larger than that of the widely employed technique of circular dichroism (CD). In PECD a chiral molecule is photoionized with circular polarized light, and the photoelectron angular scattering distribution is detected using particle imaging techniques. We present the general physical principles of photoelectron circular dichroism and we address both single- and multiphoton excitation. PECD has been measured with synchrotron radiation in single-photon ionization as well as, very recently, with femtosecond laser radiation in multiphoton ionization. We discuss the experimental implementation of PECD, focusing on velocity map coincidence imaging where the momentum distribution of both the electron and the coincident ion is measured. The coincident detection of the mass and momentum of the ion adds very powerful mass-correlated information to the PECD measurement of the chiral molecule. We illustrate the capabilities and the potential of PECD with various experimental examples and introduce computational methods that are able to model quantitatively experimental PECD results. We conclude with an outlook on novel developments and (analytical) implementations of PECD that may further broaden the application of PECD for the sensitive detection of chirality in molecules.
159 citations
TL;DR: In this article, photoexcitation circular dichroism was proposed and demonstrated to be an order of magnitude more sensitive than photoabsorption circular dichromychroism in neutral molecules, taking advantage of the coherent helical motion of bound electrons excited by ultrashort circularly polarized light.
Abstract: Chiral effects appear in a wide variety of natural phenomena and are of fundamental importance in science, from particle physics to metamaterials. The standard technique of chiral discrimination—photoabsorption circular dichroism—relies on the magnetic properties of a chiral medium and yields an extremely weak chiral response. Here, we propose and demonstrate an orders of magnitude more sensitive type of circular dichroism in neutral molecules: photoexcitation circular dichroism. This technique does not rely on weak magnetic effects, but takes advantage of the coherent helical motion of bound electrons excited by ultrashort circularly polarized light. It results in an ultrafast chiral response and the efficient excitation of a macroscopic chiral density in an initially isotropic ensemble of randomly oriented chiral molecules. We probe this excitation using linearly polarized laser pulses, without the aid of further chiral interactions. Our time-resolved study of vibronic chiral dynamics opens a way to the efficient initiation, control and monitoring of chiral chemical change in neutral molecules at the level of electrons.
141 citations
TL;DR: In this article, isolated circularly polarized attosecond pulses were developed at National Tsing Hua University, Institute of Photonics Technologies, supported by the Ministry of Science and Technology, Taiwan.
Abstract: The experimental work was carried out at National Tsing Hua University, Institute of Photonics Technologies, supported by the Ministry of Science and Technology, Taiwan (grants 105-2112-M-007-030-MY3, 105-2112-M-001-030 and 104-2112-M-007-012-MY3). The concept of isolated circularly polarized attosecond pulses was developed by C.H.-G., D.D.H., M.M.M., C.G.D., H.C.K., A.B. and A.J.-B.. C.H.-G. acknowledges support from the Marie Curie International Outgoing Fellowship within the EU Seventh Framework Programme for Research and Technological Development (2007–2013), under Research Executive Agency grant agreement no. 328334. C.H.-G. and L.P. acknowledge support from Junta de Castilla y Leon (SA046U16) and the Ministerio de Economia y Competitividad (FIS2013-44174-P, FIS2016-75652-P). C.H.-G. acknowledges support from a 2017 Leonardo Grant for Researchers and Cultural Creators (BBVA Foundation). M.M.M. and H.C.K. acknowledge support from the Department of Energy Basic Energy Sciences (award no. DE-FG02-99ER14982) for the concepts and experimental set-up. For part of the theory, A.B., A.J.-B., C.G.D., M.M.M. and H.C.K. acknowledge support from a Multidisciplinary University Research Initiatives grant from the Air Force Office of Scientific Research (award no. FA9550-16-1-0121). A.J.-B. also acknowledges support from the US National Science Foundation (grant no. PHY-1734006). This work utilized the Janus supercomputer, which is supported by the US National Science Foundation (grant no. CNS-0821794) and the University of Colorado, Boulder. This research made use of the high-performance computing resources of the Castilla y Leon Supercomputing Center (SCAYLE, www.scayle.es), financed by the European Regional Development Fund (ERDF). J.L.E. acknowledges support from the National Science Foundation Graduate Research Fellowship (DGE-1144083). L.R. acknowledges support from the Ministerio de Educacion, Cultura y Deporte (FPU16/02591).
120 citations
References
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TL;DR: In this article, the topological analysis of chiral molecular models has been extended to deal with organic-chemical conformations, and, on the other hand, with inorganic-chemical configurations to ligancy six.
Abstract: The topological analysis of chiral molecular models has provided the framework of a general system for the specification of their chirality. The application, made in and before 1956, of this system to organic-chemical configurations is generally retained, but is redefined with respect to certain types of structure, largely in the light of experience gained since 1956 in the Beilstein Institute and elsewhere. The system is now extended to deal, on the one hand, with organic-chemical conformations, and, on the other, with inorganic-chemical configurations to ligancy six. Matters arising in connexion with the transference of chiral specifications from model to name are considered, notably that of the symbiosis in nomenclature of expressions of the general system and of systems of confined scope.
For corrigendum see DOI:10.1002/anie.196605111
1,538 citations
TL;DR: In this article, the authors present a comprehensive set of FDCSs for single ionization of atoms by ion-impact, the most basic atomic fragmentation reaction, brought new insight, a couple of surprises and unexpected challenges to theory at keV to GeV collision energies.
Abstract: Recoil-ion and electron momentum spectroscopy is a rapidly developing technique that allows one to measure the vector momenta of several ions and electrons resulting from atomic or molecular fragmentation. In a unique combination, large solid angles close to 4π and superior momentum resolutions around a few per cent of an atomic unit (a.u.) are typically reached in state-of-the art machines, so-called reaction-microscopes. Evolving from recoil-ion and cold target recoil-ion momentum spectroscopy (COLTRIMS), reaction-microscopes—the `bubble chambers of atomic physics'—mark the decisive step forward to investigate many-particle quantum-dynamics occurring when atomic and molecular systems or even surfaces and solids are exposed to time-dependent external electromagnetic fields. This paper concentrates on just these latest technical developments and on at least four new classes of fragmentation experiments that have emerged within about the last five years. First, multi-dimensional images in momentum space brought unprecedented information on the dynamics of single-photon induced fragmentation of fixed-in-space molecules and on their structure. Second, a break-through in the investigation of high-intensity short-pulse laser induced fragmentation of atoms and molecules has been achieved by using reaction-microscopes. Third, for electron and ion-impact, the investigation of two-electron reactions has matured to a state such that the first fully differential cross sections (FDCSs) are reported. Fourth, comprehensive sets of FDCSs for single ionization of atoms by ion-impact, the most basic atomic fragmentation reaction, brought new insight, a couple of surprises and unexpected challenges to theory at keV to GeV collision energies. In addition, a brief summary on the kinematics is provided at the beginning. Finally, the rich future potential of the method is briefly envisaged.
1,375 citations
TL;DR: A protocol for SCD analysis that does not require the crystallization of the sample is reported, which allows the direct characterization of multiple fractions and unambiguously determined the structure of a scarce marine natural product using only 5 micrograms of the compound.
Abstract: X-ray single-crystal diffraction (SCD) analysis has the intrinsic limitation that the target molecules must be obtained as single crystals. Here we report a protocol for SCD analysis that does not require the crystallization of the sample. In our method, tiny crystals of porous complexes are soaked in a solution of the target, such that the complexes can absorb the target molecules. Crystallographic analysis clearly determines the absorbed guest structures along with the host frameworks. Because the SCD analysis is carried out on only one tiny crystal of the complex, the required sample mass is of the nanogram–microgram order. We demonstrate that as little as about 80 nanograms of a sample is enough for the SCD analysis. In combination with high-performance liquid chromatography, our protocol allows the direct characterization of multiple fractions, establishing a prototypical means of liquid chromatography SCD analysis. Furthermore, we unambiguously determined the structure of a scarce marine natural product using only 5 micrograms of the compound. Chemists need reliable methods to analyse and determine molecular structures. Nuclear magnetic resonance (NMR) and mass spectrometry are indispensable tools in daily chemical research for rapidly analysing molecular structures, but, strictly speaking, they provide only speculative molecular structures that are sometimes assigned incorrectly. However, X-ray SCD provides direct structural information at the atomic level and is recognized as the most reliable structure determination method 1–3 . Unfortunately, X-ray SCD has some critical limitations. First, the crystallization of samples before measurement can not be automated and usually requires a time-consuming trial-and-error procedure. Second, the method is in principle not applicable to non-crystalline molecules. In this Article, we describe an advance in crystallographic analysis based on a new X-ray analysis protocol that does not require the crystallization of the sample molecules themselves. Our idea is to use networked porous metal complexes 4–7 as ‘crystalline sponges’ 8 . Owing to the high molecular-recognition ability of the pores, the crystalline sponges can absorb target sample molecules from their solution into the pores, rendering the incoming molecules regularly ordered in the crystal. Accordingly, the molecular structure of the absorbed guest will be displayed, along with the host framework, by the crystallographic analysis of the networked porous complexes. We emphasize that even trace amounts of samples (,0.1mg) can be analysed by this method because the experiment can be performed with only one tiny crystal (,0.1 mm to a side). In the following discussion, we thus describe the crystallographic analysis of non-crystalline compounds and nanogram–microgram-scale X-ray crystallography based on our method. The great advantage of trace-amount X-ray analysis is particularly emphasized by its application to liquid chromatography SCD analysis (see below), where high-performance liquid chromatography (HPLC) fractions are directly collected by the crystalline sponge and analysed by X-ray crystallography. Furthermore, we successfully determine the structure of a scarce marine natural product, miyakosyne A, including the absolute configuration of its chiral centre, which could not be determined by conventional chemical and spectroscopic methods. X-ray crystallography of liquid samples
641 citations
"Direct Determination of Absolute Mo..." refers methods in this paper
...A promising new approach using x-ray diffraction has recently been presented by Inokuma et al. (13)....
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TL;DR: In this article, the absolute configuration of Optically Active Compounds by means of X-Rays was determined by determination of the absolute position of the X-ray reflectors of the active compounds.
Abstract: Determination of the Absolute Configuration of Optically Active Compounds by Means of X-Rays
595 citations
TL;DR: This work uses nonlinear resonant phase-sensitive microwave spectroscopy of gas phase samples in the presence of an adiabatically switched non-resonant orthogonal electric field to map the enantiomer-dependent sign of an electric dipole Rabi frequency onto the phase of emitted microwave radiation.
Abstract: Chirality plays a fundamental part in the activity of biological molecules and broad classes of chemical reactions, but detecting and quantifying it remains challenging. The spectroscopic methods of choice are usually circular dichroism and vibrational circular dichroism, methods that are forbidden in the electric dipole approximation. The resultant weak effects produce weak signals, and thus require high sample densities. In contrast, nonlinear techniques probing electric-dipole-allowed effects have been used for sensitive chiral analyses of liquid samples. Here we extend this class of approaches by carrying out nonlinear resonant phase-sensitive microwave spectroscopy of gas phase samples in the presence of an adiabatically switched non-resonant orthogonal electric field; we use this technique to map the enantiomer-dependent sign of an electric dipole Rabi frequency onto the phase of emitted microwave radiation. We outline theoretically how this results in a sensitive and species-selective method for determining the chirality of cold gas-phase molecules, and implement it experimentally to distinguish between the S and R enantiomers of 1,2-propanediol and their racemic mixture. This technique produces a large and definitive signature of chirality, and has the potential to determine the chirality of multiple species in a mixture.
415 citations