Right-handed Enantiomers Research Articles

Broadband spectral analysis of chiral nanophotonic structures at circularly polarized incidence using DGTD solver

Abstract A transient circularly polarized excitation and its implementation in a generalized dispersive material model based discontinuous Galerkin time-domain solver are proposed for spectral analysis of chiral nanophotonic structures. The expression of a circularly polarized pulse with a certain bandwidth, which is real-valued and enables multi-physics and nonlinearity, is derived comprehensively. Numerical examples of nanophotonic structures are given in this paper. Such as reflection from metallic mirrors, transmission from S-shaped dielectric metasurfaces, and the spin response of C4 symmetrically arranged right-handed enantiomers. These examples demonstrate the accuracy and capability of the proposed method.

The Effect of Carbon Nanotube Enantiomers in Macrophages

The inherent asymmetry within our bodies enables remarkable selectivity to chiral molecules. This selectivity is crucial because one stereoisomer may induce undesired effects, remain inactive, or, in the worst case, exhibit toxicity. Even though the knowledge of the interactions of stereoisomer, including enantiomer, with biological systems has been accumulated to a certain extent, our understanding of the body's response to single-wall carbon nanotube (SWCNT) enantiomers is very limited. In this study, we aimed to provide evidence of how macrophages respond to (6,5) enantiomers, finding the importance of their helicity at the nanometer scale. To achieve this, we first separated the left-handed (M) and right-handed (P) enantiomers of (6,5) using aqueous two-phase extraction (ATPE) and conducted a surfactant displacement procedure to coat them with single-stranded DNA. Following the separation and displacement processes, we quantified reactive oxygen species (ROS) as a crucial criterion for assessing the potential influence of the (6,5) enantiomers on macrophages. Considering ROS's role as a signaling molecule at a physiological level, quantifying ROS allows us to determine which enantiomer is more related to oxidative stress and, subsequently, nanotoxicity. To corroborate our findings, we conducted parallel assessments of cells, focusing on metabolic activity, cellular uptake, and proliferation. However, the complexity of the SWCNTs including the coating and aggregation states makes the observed cellular behaviors difficult to explain, even though the SWCNTs have been purified to the enantiomer level. In this regard, we probed the fluorescence signal to evaluate the aggregation states of SWCNTs, hoping to extract the sole enantiomer effects within biological environments. Our results improve the overall comprehension of the relation between SWCNT enantiomeric properties and macrophage responses, emphasizing the distinction between the left and right forms of SWCNTs and providing valuable insights for future biomedical applications of SWCNTs.

Kinetic control over the chiral-selectivity in the formation of organometallic polymers on a Ag(110) surface

Methods to control chiral-selectivity in molecular reactions through external inputs are of importance, both from a fundamental and technological point of view. Here, the self-assembly of prochiral 6,12-dibromochrysene monomers on Ag(110) is studied using scanning tunneling microscopy. Deposition of the monomers on a substrate held at room temperature leads to the formation of 1D achiral organometallic polymers. When the monomers are instead deposited on a substrate held at 373 K, homochiral organometallic polymers consisting of either the left- or right-handed enantiomer are formed. Post-deposition annealing of room temperature deposited samples at >373 K does not transform the achiral 1D organometallic polymers into homochiral ones and thus, does not yield the same final structure as if depositing onto a substrate held at the same elevated temperature. Furthermore, annealing promotes neither the formation of 1D covalently-coupled polymers nor the formation of graphene nanoribbons. Our results identify substrate temperature as an important factor in on-surface chiral synthesis, thereby demonstrating the importance of considering kinetic effects and the decisive role they can play in structure formation.

Enantiomer detection via quantum Otto cycle.

Enantiomers are chiral molecules that exist in right-handed and left-handed conformations. Optical techniques of enantiomers' detection are widely employed to discriminate between left- and right-handed molecules. However, identical spectra of enantiomers make enantiomer detection a very challenging task. Here, we investigate the possibility of exploiting thermodynamic processes for enantiomer detection. In particular, we employ a quantum Otto cycle in which a chiral molecule described by a three-level system with cyclic optical transitions is considered a working medium. Each energy transition of the three-level system is coupled with an external laser drive. We find that the left- and right-handed enantiomers operate as a quantum heat engine and a thermal accelerator, respectively, when the overall phase is the control parameter. In addition, both enantiomers act as heat engines by keeping the overall phase constant and using the laser drives' detuning as the control parameter during the cycle. However, the molecules can still be distinguished because both cases' extracted work and efficiency are quantitatively very different. Accordingly, the left- and right-handed molecules can be distinguished by evaluating the work distribution in the Otto cycle.

Helical fused 1,2:8,9-dibenzozethrene oligomers with up to 201° end-to-end twist: "one-pot" synthesis and chiral resolution.

Twisted polyarenes with persistent chirality are desirable but their synthesis has remained a challenge. In this study, we present a "one-pot" synthesis of 1,2:8,9-dibenzozethrene (DBZ) and its vertically fused dimers and trimers using nickel-catalyzed cyclo-oligomerization reactions. X-ray crystallographic analysis confirmed highly twisted helical structures that consist of equal parts left- and right-handed enantiomers. Notably, the end-to-end twist between the terminal anthracene units measured 66°, 130°, and 201° for the DBZ monomer, dimer, and trimer, respectively, setting a new record among twisted polyarenes. Furthermore, the chiral resolution by HPLC yielded two enantiomers for the fused DBZ dimer and trimer, both of which maintained stable configurations and showed absorption dissymmetry factors of around 0.008-0.009. Additionally, their optical and electrochemical properties were investigated, which exhibited a chain-length dependence.

Long-range current-induced spin accumulation in chiral crystals

Chiral materials, similarly to human hands, have distinguishable right-handed and left-handed enantiomers which may behave differently in response to external stimuli. Here, we use for the first time an approach based on the density functional theory (DFT)+PAOFLOW calculations to quantitatively estimate the so-called collinear Rashba–Edelstein effect (REE) that generates spin accumulation parallel to charge current and can manifest as chirality-dependent charge-to-spin conversion in chiral crystals. Importantly, we reveal that the spin accumulation induced in the bulk by an electric current is intrinsically protected by the quasi-persistent spin helix arising from the crystal symmetries present in chiral systems with the Weyl spin–orbit coupling. In contrast to conventional REE, spin transport can be preserved over large distances, in agreement with the recent observations for some chiral materials. This allows, for example, the generation of spin currents from spin accumulation, opening novel routes for the design of solid-state spintronics devices.

(Invited) Hyperspectral Detection of the Fluorescence Shift between Enantiomers of Empty and Water-Filled Single-Wall Carbon Nanotubes

The unusually chiral-structure-dependent properties of single-wall carbon nanotubes (SWCNTs) are also strongly influenced by their internal and external environment, which can therefore be investigated through optical spectroscopy.[1,2] In order to study this influence in detail, we developed a hyperspectral IR fluorescence imaging setup based on a microscope with a liquid crystal tunable filter. By resolving the spectra of individual SWCNTs, and even along the length of SWCNTs, the effect of inhomogeneous broadening is largely eliminated, and spectral details can be resolved which are inaccessible in bulk spectroscopy. An automated image processing scheme is used to obtain statistics on large numbers of individual SWCNTs. In particular, we show that not only the spectral shift in emission between empty and water-filled[1] chirality sorted SWCNTs can be resolved, but even separate emission peaks are observed for the left- and right-handed enantiomers, which interact slightly differently with the chiral surfactant with which they are coated. The approach is particularly promising for the quantification of enantio-selective separation results.[1] W. Wenseleers et al., Adv. Mater. 19, 2274 (2007); S. Cambré and W. Wenseleers, Angew. Chem. 50, 2764 (2011); S. Cambré et al., ACS Nano 6, 2649 (2012). [2] J. Campo et al., ACS Nano 2021, 15, 2301−2317.

Enantiomer-discriminating sensing using optical cavities at exceptional points

We propose a method for the detection of the handedness of otherwise identical chiral molecules using the coupling to a high-$Q$ cavity at an exceptional point. In particular, we show that the rates of spontaneous emission for left- or right-handed enantiomers interacting with the cavity mode can be strongly enhanced or suppressed. This provides a strong spectroscopic signature to distinguish enantiomers. The enantioselectivity is shown to be robust against perturbations that move the cavity mode away from the exceptional point.

Chiral phonons in microcrystals and nanofibrils of biomolecules

Chiral phonons are concerted mirror-symmetric movements of atomic groups connected by covalent and intermolecular bonds. Such lattice vibrations in crystals of biomolecules should be highly specific to their short- and long-range organizations, but their chiroptical signatures and structure–property relationships remain uncertain. Here we show that terahertz chiroptical spectroscopy enables the registration and attribution of chiral phonons for microscale and nanoscale crystals of amino acids and peptides. Theoretical analysis and computer simulations indicate that sharp mirror-symmetric bands observed for left- and right-handed enantiomers originate from the collective vibrations of biomolecules interconnected by hydrogen bonds into helical chains. The sensitivity of chiral phonons to minute structural changes can be used to identify physical and chemical differences in seemingly identical formulations of dipeptides used in health supplements. The generality of these findings is demonstrated by chiral phonons observed for amyloid nanofibrils of insulin. Their spectral signatures and polarization rotation strongly depend on their maturation stage, which opens a new door for medical applications of terahertz photonics. Chiral phonons—long-range lattice vibrations with rotational motion of atoms—are observed by terahertz chiroptical spectroscopy in biocrystals. Terahertz circular dichroism peaks between 0.2 and 2.0 THz clearly identify the chirality of these phonons in various microcrystalline and nanofibrils of biomolecules.

(Invited) Determining Surfactant Concentrations for Separation of (n,m) Chirality Swcnts in ATPE via Fluorescence Detection

In this talk I will present a methodology for rapid and quantitative determination of surfactant concentrations that result in top or bottom-phase partitioning of individual (n,m) SWCNTs species in an aqueous two-polymer phase extraction using near-infrared fluorescence measurements. This methodology enables quantitative evaluation of parameters affecting ATPE such as temperature, polymer molecular weight and composition, and surfactant choice without conducting an actual separation. Additional advantages of the technique include a very low sample concentration for measurement, rapid measurement, and no mass transfer derived limitations in interpreting results. Using the technique, we have investigated different combinations of surfactants to explore the effects of surfactant chemistry. In most cases, two transitions in the NIR fluorescence are observed with co-surfactant concentration for each (n,m) species, which we identify as differential separation of left and right-handed SWCNT enantiomers. Specific trends with (n,m) diameter and with variation of surfactant chemistry will be discussed.

Efficient and robust chiral resolution by composite pulses

We introduce a method for the detection of chiral molecules using sequences of three pulses driving a closed-loop three-state quantum system. The left- and right-handed enantiomers have identical optical properties (transition frequencies and transition dipole moments) with the only difference being the sign of one of the couplings. We identify 12 different sequences of resonant pulses for which chiral resolution with perfect contrast occurs. In all of them, the first and third pulses are $\ensuremath{\pi}/2$ pulses and the middle pulse is a $\ensuremath{\pi}$ pulse. In addition, one of the three pulses must have a phase shift of $\ensuremath{\pi}/2$ with respect to the other two. The simplicity of the proposed chiral resolution technique allows for straightforward extensions to more efficient and more robust implementations by replacing the single $\ensuremath{\pi}/2$ and $\ensuremath{\pi}$ pulses by composite pulses. We present specific examples of chiral resolution by composite pulses which compensate errors in the pulse areas and the detuning of the driving fields.

Light-driven deracemization enabled by excited-state electron transfer.

Deracemization is an attractive strategy for asymmetric synthesis, but intrinsic energetic challenges have limited its development. Here, we report a deracemization method in which amine derivatives undergo spontaneous optical enrichment upon exposure to visible light in the presence of three distinct molecular catalysts. Initiated by an excited-state iridium chromophore, this reaction proceeds through a sequence of favorable electron, proton, and hydrogen-atom transfer steps that serve to break and reform a stereogenic C-H bond. The enantioselectivity in these reactions is jointly determined by two independent stereoselective steps that occur in sequence within the catalytic cycle, giving rise to a composite selectivity that is higher than that of either step individually. These reactions represent a distinct approach to creating out-of-equilibrium product distributions between substrate enantiomers using excited-state redox events.

Enantiomers of Single Chirality Nanotube as Chiral Recognition Interface for Enhanced Electrochemical Chiral Analysis.

Although separation of single-walled carbon nanotubes (SWCNTs) according to their helicity and handedness has been attracting tremendous interest recently, exploration of the left- and right-handed SWCNT enantiomers (defined as "M" and "P") to chiral sensing still remains in the early stage. Here we presented a new electrochemical sensor for chiral discrimination, which for the first time amplified the chiral selection on the electrode surface based on the left- or right-handed semiconducting SWCNT enantiomers with (6,5)-enriched chirality. The enantioselectivity was demonstrated by different peak current response to analyte enantiomers, observed in differential pulse voltammogram (DPV). Chiral distinguishing might be a result of the formation of an efficient chiral nanospace originating from the high purity of single enantiomer of (6,5) SWCNT. The obtained chiral electrodes were also applied to determine the enantiomeric excess (ee) of DOPA. There was a good linear relationship between DPV peak currents and % ee of l-DOPA. This study is the first example showing how the structure of chiral SWCNTs influences electrochemical chiral recognition.

Aggregation-Induced Emission (AIE) in Ag-Au Bimetallic Nanocluster.

Herein we report the synthesis and structure determination of a non-fluorescent Au4 Ag5 (dppm)2 (SAdm)6 (BPh4 ) (dppm=bis(diphenylphosphino)methane and HSAdm=1-adamantane mercaptan) nanocluster in methanol with extremely strong AIE when aggregating to the solid state (i.e., film or crystal). This phenomenon was rarely reported in structural determined noble metal nanoclusters. The extended X-ray absorption fine structure (EXAFS) measurement ruled out the hypothesis that the luminescence originated from the structure change in different states. Besides, the crystal structure (determined by X-ray diffraction) revealed that the tightly combined left- and right-handed enantiomers induced the strong restriction of intramolecular motions (RIM), which may have an impact on aggregation-induced emission.

Charging through the looking glass

Organic Chemistry Asymmetric catalysis is a commonly applied technique to prepare just one of two mirror-image products in a chemical reaction. But what if you already have the compound you want, stuck in a mixture of left- and right-handed enantiomers? Shin et al. now show that light-induced electron transfer can trigger a favorable succession of proton and hydrogen-atom transfer steps, both of which are susceptible to biasing by catalysts, to preferentially convert a mixture of cyclic urea enantiomers into just one (see the Perspective by Wendlandt). Science , this issue p. [364][1]; see also p. [304][2] [1]: /lookup/doi/10.1126/science.aay2204 [2]: /lookup/doi/10.1126/science.aay6919

Nanoscopic control and quantification of enantioselective optical forces

Circularly polarized light (CPL) exerts a force of different magnitude on left- and right-handed enantiomers, an effect that could be exploited for chiral resolution of chemical compounds as well as controlled assembly of chiral nanostructures. However, enantioselective optical forces are challenging to control and quantify because their magnitude is extremely small (sub-piconewton) and varies in space with sub-micrometre resolution. Here, we report a technique to both strengthen and visualize these forces, using a chiral atomic force microscope probe coupled to a plasmonic optical tweezer. Illumination of the plasmonic tweezer with CPL exerts a force on the microscope tip that depends on the handedness of the light and the tip. In particular, for a left-handed chiral tip, transverse forces are attractive with left-CPL and repulsive with right-CPL. Additionally, total force differences between opposite-handed specimens exceed 10 pN. The microscope tip can map chiral forces with 2 nm lateral resolution, revealing a distinct spatial distribution of forces for each handedness.

Size-dependent emission kinetics and sensing capabilities of CdSe quantum dots functionalized with penicillamine ligands

The ligand induced chirality in semiconducting nanoparticles has recently gained special attention, due to possible application of chiral nanoparticles as optically active probes in enantioselective bio-sensing. However, the exact mechanisms of chiral organic ligands interaction with quantum dots surfaces are still not fully described. We have performed ligand exchange procedure in order to obtain water soluble CdSe QDs functionalized with left- and right-handed enantiomers of penicillamine molecules and the influence of such post-synthetic surface treatment on the optical properties of CdSe QDs with respect to their size has been investigated. In particular, picosecond and nanosecond time scale kinetics revealed strong hole trapping at the thiol molecules near to the quantum dots surfaces. Additionally, possible applications of chiral drug discrimination are shown for L- and D-penicillamine functionalized CdSe quantum dots.

Application Of Systems With Total Internal Reflection At Novosibirsk Free Electron Laser For Spectroscopy In The Terahertz Range

Attenuated total reflection (ATR) spectroscopy is widely used in the visible and infrared spectral ranges. Progress in the development of laboratory scale monochromatic sources of terahertz radiation, such as quantum cascade lasers, suggests that in the near future this kind of spectrometers will be widely spread in the terahertz range. For this reason, the development of ATR based methods and devices is highly relevant. In this paper, we discuss the features of the use of ATR spectroscopy in the terahertz range, and describe some of the optical systems, designed for experiments at the Novosibirsk free electron laser (NovoFEL). We show that in the terahertz range the ATR spectroscopy has a number of significant advantages over the absorption spectroscopy. As an example, we are discussing the possibility of using terahertz polarimetry to develop a method for early diagnosis of cancer via the detection of left-handed to right-handed polysaccharide enantiomers ratio. Spectra of selected polysaccharides were recorded with a standard Fourier spectrometer using developed by us an ATR unit. The possibility of studying the polarization characteristics of polysaccharides in aqueous solutions using spectrally selective polarimeter with the NovoFEL as a tunable radiation source was demonstrated.

Сhiral recognition of cysteine molecules by chiral CdSe and CdS quantum dots

Here, we report the investigation of mechanism of chiral molecular recognition of cysteine biomolecules by chiral CdSe and CdS semiconductor nanocrystals. To observe chiral recognition process, we prepared enantioenriched ensembles of the nanocrystals capped with achiral ligand. The enantioenriched samples of intrinsically chiral CdSe quantum dots were prepared by separation of initial racemic mixture of the nanocrystals using chiral phase transfer from chloroform to water driven by L- and D-cysteine. Chiral molecules of cysteine and penicillamine were substituted for achiral molecules of dodecanethiol on the surfaces of CdSe and CdS samples, respectively, via reverse phase transfer from water to chloroform. We estimated an efficiency of the hetero- (d-L or l-D) and homocomplexes (l-L) formation by comparing the extents of corresponding complexing reactions. Using circular dichroism spectroscopy data we show an ability of nanocrystals enantiomers to discriminate between left-handed and right-handed enantiomers of biomolecules via preferential formation of heterocomplexes. Development of approaches for obtaining chiral nanocrystals via chiral phase transfer offers opportunities for investigation of molecular recognition at the nano/bio interfaces.

Dissipative vibrational model for chiral recognition in olfaction.

We examine the olfactory discrimination of left- and right-handed enantiomers of chiral odorants based on the odorant-mediated electron transport from a donor to an acceptor of the olfactory receptors embodied in a biological environment. The chiral odorant is effectively described by an asymmetric double-well potential whose minima are associated to the left- and right-handed enantiomers. The introduced asymmetry is considered an overall measure of chiral interactions. The biological environment is conveniently modeled as a bath of harmonic oscillators. The resulting spin-boson model is adapted by a polaron transformation to derive the corresponding Born-Markov master equation with which we obtain the elastic and inelastic electron tunneling rates. We show that the inelastic tunneling through left- and right-handed enantiomers occurs with different rates. The discrimination mechanism depends on the ratio of tunneling frequency to localization frequency.