Optical Rotatory Dispersion Research Articles

Bi-Chiral Nanostructures Featuring Dynamic Optical Rotatory Dispersion for Polychromatic Light Multiplexing.

Chiral nanostructures featuring the unique optical activity have attracted broad interests from scientists. The typical polarization rotation of transmitted light is usually wavelength dependent, namely the optical rotatory dispersion. However, its dynamic tunability and intriguing collaboration with other optical degrees of freedom, especially the highly desired spatial phase, remain elusive. Herein, a bi-chiral liquid crystalline nanostructure is proposed to induce an effect called reflective optical rotatory dispersion. Thanks to the independent manipulation of opposite-handed self-assembled helices, spin-decoupled geometric phases are induced simultaneously. These naturally unite multi-dimensions of light and versatile stimuli-responsiveness of soft matter. Dynamic holography driven by heat and electric field is demonstrated with a fast response. For polychromatic light, the hybrid multiplexed holographic painting is exhibited with fruitful tunable colors. This study extends the ingenious construction of soft chiral superstructures, presents an open-ended strategy for on-demand light control, and enlightens advanced applications of display, optical computing, and communication.

Isolated and solvated chiroptical behavior in conformationally flexible butanamines.

The nonresonant optical activity of two highly flexible aliphatic amines, (2R)-3-methyl-2-butanamine (R-MBA) and (2R)-(3,3)-dimethyl-2-butanamine (R-DMBA), has been probed under isolated and solvated conditions to examine the roles of conformational isomerism and to explore the influence of extrinsic perturbations. The optical rotatory dispersion (ORD) measured in six solvents presented uniformly negative rotatory powers over the 320-590 nm region, with the long-wavelength magnitude of chiroptical response growing nearly monotonically as the dielectric constant of the surroundings diminished. The intrinsic specific optical rotation, (in deg dm-1 [g/mL]-1 ), extracted for ambient vapor-phase samples of R-MBA [-11.031(98) and -2.29 (11)] and R-DMBA [-9.434 (72) and -1.350 (48)] at 355 and 633 nm were best reproduced by counterintuitive solvents of high polarity (yet low polarizability) like acetonitrile and methanol. Attempts to interpret observed spectral signatures quantitatively relied on the linear-response frameworks of density-functional theory (B3LYP, cam-B3LYP, and dispersion-corrected analogs) and coupled-cluster theory (CCSD), with variants of the polarizable continuum model (PCM) deployed to account for the effects of implicit solvation. Building on the identification of several low-lying equilibrium geometries (nine for R-MBA and three for R-DMBA), ensemble-averaged ORD profiles were calculated at T = 300K by means of the independent-conformer ansatz, which enabled response properties predicted for the optimized structure of each isomer to be combined through Boltzmann-weighted population fractions derived from corresponding relative internal-energy or free-energy values, the latter of which stemmed from composite CBS-APNO and G4 analyses. Although reasonable accord between theory and experiment was realized for the isolated (vapor-phase) species, the solution-phase results were less satisfactory and tended to degrade progressively as the solvent polarity increased. These trends were attributed to solvent-mediated changes in structural parameters and energy metrics for the transition states that separate and putatively isolate the equilibrium conformations supported by the ground electronic potential-energy surface, with the resulting displacement of barrier locations and/or decrease of barrier heights compromising the underlying premise of the independent-conformer ansatz.

Monomer blended electrochemical polymerization in chiral liquid crystals to produce electro-optically active copolymer

Electro-optically active low-bandgap conjugated copolymers were obtained by electrochemical polymerization (EP) in cholesteric liquid crystal (CLC). We prepared CLC electrolyte mixture blends of monomers, and electrochemically polymerized for obtaining conjugated copolymer with optical activity, in which the structure of the CLC is transferred, from achiral monomers on a CLC template. In addition, this copolymer showed a narrow bandgap and a significant red shift of the absorption band compared to the homopolymer. The optical rotatory dispersion (ORD) indicates that the polymer is chiroptically active and that the optical rotation can be tuned via redox. The guest monomers used for the EP in liquid crystal (LC) require solubility in the host LC and a rod-like structure, limiting their structural design. This technique has the advantage that complex synthesis of monomers is no required, and simple composition of monomers can be used to prepare copolymer films in a convenient manner by blending various monomers. This method expands the design range of optically active electrochromic devices based on conjugated polymers with pleochroic properties.

Imaging-based intelligent spectrometer on a plasmonic rainbow chip

Compact, lightweight, and on-chip spectrometers are required to develop portable and handheld sensing and analysis applications. However, the performance of these miniaturized systems is usually much lower than their benchtop laboratory counterparts due to oversimplified optical architectures. Here, we develop a compact plasmonic “rainbow” chip for rapid, accurate dual-functional spectroscopic sensing that can surpass conventional portable spectrometers under selected conditions. The nanostructure consists of one-dimensional or two-dimensional graded metallic gratings. By using a single image obtained by an ordinary camera, this compact system can accurately and precisely determine the spectroscopic and polarimetric information of the illumination spectrum. Assisted by suitably trained deep learning algorithms, we demonstrate the characterization of optical rotatory dispersion of glucose solutions at two-peak and three-peak narrowband illumination across the visible spectrum using just a single image. This system holds the potential for integration with smartphones and lab-on-a-chip systems to develop applications for in situ analysis.

Measurements of large optical rotary dispersion in the adipose eyelid of Atlantic mackerel (Scomber scombrus).

Collagen is the most prevalent of Nature's structural proteins, and is found in the extracellular matrices of animals. The structures of collagen molecules and aggregates are chiral, which leads to the rotation of transmitted, plane-polarized light. Here, it is shown that the concentrations of chiral molecules and aggregates in the optically transparent, adipose eyelid of Atlantic mackerel (Scomber scombrus) can be so high, that plane-polarized light in the visible spectrum is rotated by tens to hundreds of degrees, depending on wavelength (the optical rotatory dispersion (ORD)). This gives rise to intensely coloured images of eyelid samples when illuminated with white light and viewed between crossed polarizers. The ORD in the visible spectrum is measured with monochromatic light sources, and using this dispersion, the variation of optical thickness within a sample (proportional to collagen concentration and path length) is determined. The agreement between observed and simulated white-light images is almost perfect. While collagen provides vital mechanical rigidity to animal tissue, it might also possess optical properties that are useful for vision and camouflage.

Lignan glycosides from the stems of Stephania cepharantha

Four new lignan glycosides (LGs) and four known analogues were isolated from the stems of Stephania cepharantha Hayata. Extensive spectroscopic analysis was used to study their structures, and electronic circular dichroism and optical rotatory dispersion data were used to establish their absolute configurations. These LG types were identified in Stephania cepharantha Hayata for the first time. Compounds 1 and 2 exhibited moderate inhibitory activity against nitric oxide production. Herein, we have also discussed their preliminary structure-activity relationship.

Chiral explosives: A theoretical investigation of structure and chiroptical properties of triacetone triperoxide and hexamethylene triperoxide diamine.

Triacetone triperoxide (TATP) and hexamethylene triperoxide diamine (HMTD) are cyclic peroxides that exhibit atropisomerism resulting from restricted rotation around three peroxide bonds. As a result, one pair of enantiomers with D3 symmetry and another pair of enantiomers with C2 symmetry can be identified. Previous studies, based on mass spectrometry data and computational results, have shown that conformations of TATP with D3 and C2 symmetry can be isolated. Assuming that enantiomer samples of TATP and HMTD can be obtained with sufficient enantiopurity, we investigated their chiroptical properties, namely, optical rotatory dispersion (ORD), vibrational circular dichroism (VCD), and Raman optical activity (VROA). ORD curves and VCD spectra are seen to be very similar for D3 - and C2 -symmetric atropisomers with the same overall helicity. Predicted VROA results, however, show significant differences between D3 - and C2 -symmetric atropisomers with the same overall helicity. The D3 -symmetric atropisomer is predicted to exhibit considerably larger magnitude vibrational optical activity signals than the C2 -symmetric atropisomer.

Computational methods and points for attention in absolute configuration determination

With the rapid development of high performance computers and computational methods, including software, an increasing number of experimental chemists have tried to use computational methods such as optical rotation (OR, including the matrix model), optical rotatory dispersion (ORD), electronic circular dichroism (ECD or CD), vibrational circular dichroism (VCD), and magnetic shielding constants—nuclear magnetic resonance (NMR)—to explain and/or assign absolute configuration (AC) for various compounds. Such reports in the field of natural products have increased dramatically. However, every method has its range of application. This leads, in some cases, to incorrect conclusions by researchers who are not familiar with these methods. In this review, we provide experimental chemists and researchers with more computational details and suitable suggestions, and especially hope that this experience may help readers avoid computational pitfalls. Finally, we discuss the use of simplified models to replace original complex structures with a long side chain. The fundamental basis for using models to represent complex chiral compounds, such as in OR calculations, is the existence of conformation pairs with near canceling conformer contributions that justify the use of models rather than the original compounds. Using examples, we here introduce the transition state (TS) calculation, which may benefit readers in this area for use and mastery for their AC study. This review will summarize the general concepts involved in the study of AC determinations.

Natural Antioxidants, Tyrosinase and Acetylcholinesterase Inhibitors from Cercis glabra Leaves.

Cercis glabra is a plant belonging to the legume family, whose flowers and barks are commonly used as food and traditional Chinese medicines. However, its leaves are usually disposed of as wastes. This research comprehensively investigated the bioactive constituents of C. glabra leaves, and two new phenolic, ceroffesters A-B (1-2) and thirteen known compounds (3-15) were isolated. Their structures were elucidated by spectroscopic methods such as nuclear magnetic resonance (1D NMR and 2D NMR), high-resolution electrospray ionization mass spectra (HR-ESI-MS), optical rotatory dispersion (ORD) and electronic circular dichroism (ECD). All of them were assessed for their antioxidant activities through ABTS, DPPH and PTIO methodologies, and evaluated for inhibitory activities against two enzymes (mushroom tyrosinase and acetylcholinesterase). As a result, compounds 3-6, 10 and 13 exhibited evident antioxidant activities. Meanwhile, compounds 5, 10 and 13 showed the most potent tyrosinase inhibitory activities, with IC50 of 0.64, 0.65 and 0.59 mM, and compared with the positive control of 0.63 mM (kojic acid). In the initial concentration of 1 mg/mL, compounds 3, 5 and 6 demonstrated moderate inhibitory activities against acetylcholinesterase with 85.27 ± 0.06%, 83.65 ± 0.48% and 82.21 ± 0.09%, respectively, compared with the positive control of 91.17 ± 0.23% (donepezil). These bioactive components could be promising antioxidants, tyrosinase and acetylcholinesterase inhibitors.

From Relative to Absolute Stereochemistry of Secondary Metabolites: Applications in Plant Chemistry

Structural elucidation of specialized metabolites or natural plant products, especially the stereochemical features of chiral bioactive metabolites, is the most important stage for all investigations in pharmacognosy and phytochemistry. Numerous methods have been established to solve the absolute configuration of natural products, including direct methods such as X-ray diffraction, chiroptical spectroscopy, stereo-controlled partial or total organic synthesis, and chemical correlation by simple organic reactions for derivatization, as well as indirect methods using a standard chiral compound or a derivatizing agent with known absolute configuration, for example, nuclear magnetic resonance by utilization of anisotropic effects of chiral agents. Once the relative configuration of a natural product is resolved, the absolute stereochemistry can be determined with the assistance of chiroptical spectroscopies supported by quantum mechanical-NMR prediction of chemical shifts, scalar coupling constants and simulation of optical rotatory dispersion, in addition to electronic and vibrational circular dichroism spectra. This review summarizes the most practical methods employed in the assignment of absolute stereochemistry of natural plant products with selected examples focused on multichiral center bioactive small molecules from the mega-diverse Brazilian and Mexican flora.

Bioactive Cembranoids from the Coral Sarcophyton trocheliophorum of Ximao Island.

Eight new cembranoids (sarcophytembranoids A-H, 1-8) and 10 known terpenoids (9-18) were obtained from the soft coral Sarcophyton trocheliophorum of Ximao Island. Notably, 11, 15, and 16 were obtained from a natural source for the first time. The structures of the new isolates were elucidated by extensive spectroscopic analysis, optical rotatory dispersion, and X-ray diffraction experiments. Although the isolated compounds did not show significant activity against the tested tumor cell lines, compounds 3, 7, 8, and 10-15 exhibited anti-inflammatory activities at 10 μM, and compounds 17 and 18 showed moderate protein tyrosine phosphatase 1B inhibition activities with the minimum inhibitory concentrations of 22.19 and 11.26 μM, respectively.

Chiroptical spectroscopic studies for the absolute configuration determination of hexahydrocurcumin and octahydrocurcumin.

Hexahydrocurcumin (HHC) and octahydrocurcumin (OHC) were synthesized, and their enantiomers were separated using supercritical fluid chromatography. The absolute configurations (ACs) of HHC and OHC were independently determined using experimental measurements and quantum theoretical predictions of vibrational circular dichroism, electronic circular dichroism, and optical rotatory dispersion. These studies lead to AC assignments of (-)-(R)-HHC and (+)-(R,R)-OHC. The AC of OHC is further confirmed by its structure determined from single crystal x-ray diffraction.

Modulating the Chiroptical Response of Chiral Polymers with Extended Conjugation within the Structural Building Blocks.

Advancing the emerging area of chiral photonics requires modeling-guided concepts of chiral material design to enhance optical activity and associated optical rotatory dispersion. Herein, we introduce conformational engineering achieved by tuning polymer backbone conjugation through introduction of thiophene structural units in a chiral fluorene polymer backbone. Our theoretical calculations reveal a relationship between the structural conformation and the resultant rotational strength. We further synthesize a series of chiral fluorene-based polymers copolymerized with thiophene whose optical chirality trend is in qualitative agreement with predictions of our quantum chemical calculations. Varying the number of thiophene units in the monomer building block allows us to modulate the rotational strength by tuning the intrafibril helicity of single-stranded polymer chains, whereby the monomer conjugation is retained throughout the whole length of the polymer backbone. Our design concept delineates an underexamined approach: the concept of tuning backbone conjugation and helicity within the main chain to enhance the optical activity of chiral polymer systems.

(Digital Presentation) Synthesis of Conjugated Polymer Alloy Prepared By Electrochemical Polymerization in Chiral Liquid Crystal

In this research, we synthesized polymer alloy by electrochemical polymerization in chiral liquid crystal. Homopolymers and the copolymer can be synthesized when electrochemical polymerization was conducted in the presence of several types of monomers. The polymer alloy thus prepared contains both blend of homopolymers and copolymers. The polymer alloy shows optical activity. The chirality derived from transcription of liquid crystal during the polymerization reaction results to show optical activity. The polymer alloy can show optical activity with no asymmetric centers. The optical activity is due to existence of charge carriers (polarons) in the main chain as a form of conjugated polymers. This is called chiral charge carrier “chiralions”. This research found that the chiral polymer alloy has chiralions.Polymer alloys have been prepared by blending several kinds of polymers in the reaction. Polymer alloys also can be prepared by melt method. Unsubstituted conjugated polymers have poor solubility and fusibility because of the rigid π-bonds in the skeleton, which is drawback for preparation of π-conjugated polymer-based alloys. We have studied on preparation of chiral conjugated polymer alloys with combination of achiral polymers and chiral polymers.In the present study, conjugated polymer alloys were synthesized with the method described in Figure 1a. Cholesteryl acetate (chiral inducer), 2,7-di(2-thienyl)fluorene (mono1), N-methyl-3,6-di(2-thienyl)carbazole (mono2) and TBAP (supporting salt) were dissolved in 4-cyano-4'-pentylbiphenyl (5CB) as a host liquid crystal to prepare a chiral liquid crystal electrolyte. The electrolyte exhibited a fingerprint structure under observation of polarizing optical microscopy. For the electrochemical polymerization reaction, the electrolyte solution is charged in the cell consisted of two indium-tin-oxide (ITO) glass plates as electrodes and a poly(tetrafluoroethylene) spacer (200 μm thickness). Next, dc voltage of 3.0 V was applied to the ITO glass cell for 30 min for electrochemical polymerization. The polymer was deposited on the anode electrode as a thin film form. After polymerization, the remaining electrolyte solution on the ITO glass electrode was carefully washed with a large amount of hexane, yielding dark blue film. This film is abbreviated as Alloy1. The molecular structure was confirmed by infrared spectroscopy with the KBr method. Alloy1 shows a fingerprint structure under POM observations (Figure 1b). The macroscopic structure of cholesteric liquid crystal was transcribed from the liquid crystal electrolyte solution to Alloy1. Synchrotron XRD measurement was carried out. The peak at 10.3 Å is derived from monomer repeat units. The XRD signal at 5.1 Å and 3.4 Å can be derived from π-stacking of Alloy1. Alloy1 shows UV-vis absorption due to the three signals derived from π-π* transition of the main chain, polarons (radical cations) and bipolarons (radical dications). Electrochemical properties of Alloy1 were evaluated by the cyclic voltammetry (CV). Alloy1 film deposited on the ITO glass was used as a working electrode. An Ag/Ag+ electrode and a platinum wire served as the reference and counter electrodes, respectively. A propylene carbonate solution with 0.1 M of TBAP was employed as an electrolyte solution for the CV measurements. Cyclic voltammograms of Alloy1 shows the oxidation peak and reduction trough (Figure 1c). Plots of the oxidation peak current (I pa) and the reduction peak current (I pc) as a function of the square root of the scan rate show a linear shape of the anodic and cathodic peak current values when scan rates from 10 to 100 mV/s with intervals of 10 mV/s. This result indicated that the redox reaction of Alloy1 was reversible and controlled by electron transfer processes. In-situ circular dichromism (CD) and in-situ optical rotatory dispersion (ORD) spectra of Alloy1 with application of voltages were examined in a propylene carbonate solution with 0.1 M of TBAP. The application voltages were between 0-1.2 V (vs. Ag/Ag+) with intervals of 0.1 V. A negative Cotton effect was observed from the in-situ CD, indicating Alloy1 has left-handed helical structure. The ORD shows negative signals, and changes with applied voltage. The ellipticity signal in the CD and optical rotation in the ORD could control in the electrochemical method, accompanied by electrochemical redox process.We synthesized the polymer alloy by electrochemical polymerization in chiral liquid crystal. The conjugated polymer alloy showed chirality with no chiral centers in the main chain. The CD and ORD bands at NIR range are assigned to doping band as a form of polarons (radical cations). This research evaluated electrochemical control of “chiralions”. Figure 1

A comparison study of the born-kuhn model and the finite-difference-time-domain calculations on stacked plasmonic nanorods

A detailed analysis of the Born-Kuhn (BK) model for two coupled oscillators and comparison to the chiral optical properties of the corner-stacked plasmonic nanorods (CSPNs) have been investigated. Based on the normalized coupling constant c (= coupling frequency /resonance frequency ) and the damping constant g (= dissipation γ/), the chiral optical response of the BK model could be significantly different, and the c-g space can be divided into two phase regions, a weak coupling and a strong coupling region. Once the c and g parameters are extracted from CSPN structures based on finite-difference time domain (FDTD) calculations, the BK model can be directly applied to predict the chiral plasmonic response of the CSPNs. In particularly, at , the BK model suggests the strongest optical rotation dispersion while stronger circular dichroism occurs with a small g and a large c. These predictions have been confirmed by the FDTD calculations of CSPN structures. The detailed analysis of the BK model and the use of the model to direct fit the optical property of CSPNs demonstrate that the BK model is a very versatile class model to predict the chiral response of a chiral plasmonic structure or help to design and optimize a specific chiral plasmonic structure for a specific application.

Reaction field induction self-amplification optical activity during polymerization in liquid crystal

A monomer having both chiral induction from nematic liquid crystal (LC) to cholesteric LC and polymerization activity was prepared. Addition of the compound to nematic LC induced the formation of a cholesteric liquid crystal in its chiral form. Subsequent electrochemical polymerization of the monomer produced an optically active polymer with a helical structure as confirmed by circular dichroism (CD) and optical rotatory dispersion measurements. While, the addition of the chiral monomer to an isotropic non-LC solution, and subsequent polymerization resulted a product with no clear optical activity. These results suggest that polymerization of the monomer in a cholesteric environment allows the formation of a polymer with high optical activity. Morphological imprinting from the matrix LC was confirmed by surface observation through polarizing optical microscopy. The chiral monomer changes the surrounding environment to grow into a more highly ordered helical structure. The matrix LC as the environment amplifies the optical activity with helical growth of the monomer during polymerization.

Natural tyrosinase inhibitors from Betula platyphylla barks

Abstract During the process of searching for tyrosinase inhibitors from natural medicines, one new monoterpene rhamnoside (1) and 13 known compounds (2–14) were isolated from the ethanolic extract of Betula platyphylla barks by repeated column chromatography. These structures were identified by comprehensive spectroscopic data analysis such as high-resolution electrospray ionization mass spectra (HR-ESI-MS), nuclear magnetic resonance (NMR), optical rotatory dispersion (ORD) and acid hydrolysis. In vitro assay revealed that compounds 6, 7 and 14 showed obvious inhibitory activity against tyrosinase.

Sinuhirtone A, An Uncommon 17,19-Dinorxeniaphyllanoid, and Nine Related New Terpenoids from the Hainan Soft Coral Sinularia hirta.

Chemical investigation of the Hainan soft coral Sinularia hirta resulted in the isolation and identification of a library of sixteen structurally diverse terpenoids, including a dinorditerpenoid with an uncommon 17,19-dinorxeniaphyllane skeleton, namely sinuhirtone A (7), six new xeniaphyllane-type diterpenoids (1–6), one new norxeniaphyllanoid (8), two new norcaryophyllene-type sesquiterpenoids (9 and 10), together with six known related compounds (11–16). Compounds 1–3 are three new furanone-containing xeniaphyllane-type diterpenoids. The structures of the new compounds, including their absolute configurations, were determined by extensive spectroscopic analysis and a series of quantum chemical calculations, including quantum mechanical-nuclear magnetic resonance (QM–NMR), time-dependent density functional theory–electronic circular dichroism (TDDFT–ECD), and optical rotatory dispersion (ORD) methods. A plausible biosynthetic connection between new compounds 1–9 was also proposed. New compounds 2–4, 7, and 8 were evaluated for in vitro cytotoxicity against four cancer cell lines.

Method for determination of optical rotatory dispersion curve by using a polarization axis finder

We report a new, to the best of our knowledge, measurement method of optical rotatory dispersion (ORD) based on a polarization axis finder (PAF) and digital image processing. The collimated quasi-monochromatic light is output by a monochromator and passes through a polarizer and the chiral samples, and a PAF is employed to modulate the light beam spatially to form an "hourglass" intensity pattern, which is utilized to determine the polarization direction of linearly polarized light. After being recorded by a digital camera, the modulated patterns with and without samples are analyzed by our specially designed digital image processing program to calculate the optical rotation (OR) angle of the chiral substance at a certain wavelength, and the ORD curve can be obtained by fitting a series of OR angles with different wavelengths. The ORD curves of two standard quartz plates with opposite chirality and a glucose solution with different concentrations are measured experimentally, and the fitted coefficients and measurement results agree well with their theoretical values, which indicates that the presented method is an effective and accurate way to determine the ORD of chiral substances conveniently.

Isolation and characterization of antioxidative monoterpenes from Cynanchum atratum roots.

One novel monoterpene rhamnoside (1) and 7 known monoterpenes (2-8) were isolated from the ethanol extract of Cynanchum atratum for the first time. Their structures were identified by comprehensive spectroscopic data analysis such as nuclear magnetic resonance, high-resolution electrospray ionization mass spectra, optical rotatory dispersion, and acid hydrolysis. In the subsequent antioxidant assay, compound 8 exhibited obvious 2,2-diphenyl-2-picrylhydrazyl hydrate radical scavenging activity.