Enantiomer-Specific State Transfer of Chiral Molecules

Abstract

State-selective enantiomeric excess is realized using microwave-driven coherent population transfer. The method selectively promotes either R or S molecules to a higher rotational state by phasecontrolled microwave pulses that drive electric-dipole allowed rotational transitions. We demonstrate the enantiomer-specific state transfer method using enantiopure samples of 1,2-propanediol. This method of state-specific enantiomeric enrichment can be applied to a large class of asymmetric, chiral molecules that can be vaporized and cooled to the point where rotationally resolved spectroscopy is possible, including molecules that rapidly racemize. The rapid chiral switching demonstrated here allows for new approaches in high-precision spectroscopic searches for parity violation in chiral molecules.PACS numbers: 33.15.-e, 33., 07.57.-c, 82. Chirality plays a major role in many biological processes and chemical reactions. A large number of pharmaceutically and biologically relevant molecules are chiral and exist in one of two mirror images (enantiomers). Although different enantiomers share many physical and chemical properties, their handedness often determines their functionality. Despite the high abundance of chiral species in nature, detecting and quantifying the handedness of a sample remains challenging. The origin of the observed biomolecular homochirality on Earth is unknown. A proposed explanation of this is parity violation (PV) effects in chiral molecules, that are predicted to cause tiny energy differences between enantiomers [1-3]. These PV effects have yet to be experimentally measured.There are a number of established spectroscopic techniques for chiral molecules that measure enantiomeric excess, which is a measure for the purity of a chiral sample, defining the excess of one enantiomer over the other in a mixture. These techniques include circular dichroism, vibrational circular dichroism, Raman optical activity [4][5][6], and, most recently, enantiomer-specific microwave spectroscopy (EMS) [7,8]. EMS is inherently mixture compatible and can yield a large signal, although it requires the sample to be vaporized and cooled. A natural extension of measuring enantiomeric excess (EE) is the separation of enantiomers from a sample of mixed chirality -an important and challenging task. The most widely used separation techniques are chromatography and capillary electrophoresis [9-13], both of which require specific development and optimization of intricate processes for different molecular species. All current demonstrated enantiomer separation methods rely on chemical mechanisms and are based on enantiomerspecific interactions with auxiliary substances, for example in a solution or in an enantioselective chromatographic column. The required time for chiral separation in these techniques is significantly longer than seconds, making chiral separation of rapidly racemizing compounds out of reach.Here we report enhancement of enantiomeric excess in a specific rotational state using an approach solely based on mic...

Structure Determination, Conformational Flexibility, Internal Dynamics, and Chiral Analysis of Pulegone and Its Complex with Water

“…Very recently,i tw as demonstrated that this technique can also be extended to achieve enantiomer-selective population transfer. [24,25] Here, we report our resultso fahigh-resolution broadband rotational spectroscopy study on the monoterpene pulegone (2-isopropylidene-5-methylcyclohexanone, see Figure1 below) in the gas phase, which provides information on the isolated speciesf ree of solvent effects. Pulegone can be found in many plants.…”

“…The twist pulse durations should fulfill p pulse conditions. [47] The p twist pulse transfers coherence from the 5 24 ! 5 14 (induced by the p/2 drive pulse) to the 5 14 !…”

“…For optimizing the duration of the drive pulses, the transitions (cycle 1: c-type transition 5 24 ! 5 14 at 2620.09 MHz; cycle 2: b-type transition5 05 !…”

“…M3WM has been applied to a number of terpenes and alcohols, including those with several stereogenic centers, as well as for the analysis of chiral mixtures. Very recently, it was demonstrated that this technique can also be extended to achieve enantiomer‐selective population transfer …”

Tailoring the volatility and stability of oligopeptides

“…Since the early days of Otto Stern [1] and Immanuel Estermann, [2] neutral molecular beams have played a key role in fundamental studies of physics and physical chemistry. [3][4][5] Experiments with isolated molecules in the gas phase have laid the ground for highprecision spectroscopy, [6,7] molecule and cluster deflectometry [8][9][10] and for an improved understanding of chemical reactions with quantum state control. [11,12] Modern molecular beam experiments have allowed setting new bounds on the electric dipole moment of the electron [13,14] and enabled the observation of quantum interference with clusters and molecules, [15,16] even with masses exceeding 10 0 000 amu.…”