Optical Rotatory Dispersion Spectra Research Articles

Terahertz SWNT-based fluidic chip for sensing enantioselectivity

Enantioselectivity sensing is crucial in biological systems due to the impact of the selective behaviors of chiral compounds on their targets. Conventional approaches for detecting enantioselectivity are restricted by the presence of high phonon energy, complex device manufacturing processes, low sensitivity, and the need for large sample sizes. Here, we propose a single-walled carbon nanotube (SWNT)-based fluidic chip that uses terahertz (THz) optical rotatory dispersion (ORD) spectroscopy to detect tartaric acids with high selectivity in very small amounts of liquid. The chip is composed of tailored U-shaped metasurfaces that show significant amplification of the near-field around the typical peaks of tartaric acids in the ORD spectrum. Additionally, it includes subwavelength gratings made of SWNTs, allowing for accurate detection of polarization angles. The limit of detection (LOD) for d-tartaric acid and l-tartaric acid are 17.9 mg/L and 11.0 mg/L, respectively. The sensitivities are superior to those of UV ORD or CD spectrometers. Furthermore, the presence of tartaric acid in wine is effectively identified, with a LOD of 25.60 mg/L. This technological development provides a significant improvement in chiral analysis by allowing for quick, highly sensitive, and precise detection of enantiomers.

(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

Broadband Optical Activity Spectroscopy with Interferometric Fourier-Transform Balanced Detection.

Spectrally resolved measurements of optical activity, such as circular dichroism (CD) and optical rotatory dispersion (ORD), are powerful tools to study chiroptical properties of (bio)molecular and nanoplasmonic systems. The wider utilization of these techniques, however, has been impeded by the bulky and slow design of conventional spectropolarimeters, which have been limited to a narrowband scanning approach for more than 50 years. In this work, we demonstrate broadband measurements of optical activity by combining a balanced detection scheme with interferometric Fourier-transform spectroscopy. The setup utilizes a linearly polarized light field that creates an orthogonally polarized weak chiral free-induction-decay field, along with a phase-locked achiral transmitted signal, which serves as the local oscillator for heterodyne amplification. By scanning the delay between the two fields with a birefringent common-path interferometer and recording their interferogram with a balanced detector that measures polarization rotation, broadband CD and ORD spectra are retrieved simultaneously with a Fourier transform. Using an incoherent thermal light source, we achieve state-of-the-art sensitivity for CD and ORD across a broad wavelength range in a remarkably simple setup. We further demonstrate the potential of our technique for highly sensitive measurements of glucose concentration and the real-time monitoring of ground-state chemical reactions. The setup also accepts broadband pulses and will be suitable for broadband transient optical activity spectroscopy and broadband optical activity imaging.

Chiral Charge Carriers Chiralions for Polyaniline Examined with Optical Rotation Spectroelectrochemistry

In this study, the optical active polyaniline film was examined with optical rotatory dispersion (ORD) through change in potential with spectroelectrochemical method. Polyaniline is one of the representative conducting polymers. Preparation of polyaniline is convenient because synthesis of polyaniline can perform in water medium. Conducting polymers shows electrochromism via change in the electronic state upon electrochemical redox process. Polyaniline forms various electronic states such as emeraldine base, emeraldine salt, and pernigraniline. This change allows to color tuning through electrochemical method. Further, optically active polyanilines have been synthesized in the presence of (+) or (-)-camphorsulfonic acid (CSA) by electrochemical polymerization or chemical polymerization with ammonium persulfate (oxidizing agent). Both electrochemical method and chemical method produce polyaniline through radical polymerization process. Polyaniline emeraldine salt as prepared form of polyaniline is doped with CSA, showing optical activity in the circular dichroism. In this research, we carried out to synthesis of polyaniline in the presence of optically active CSA, according to previously reported method (by Wallace et al). Here, we have found that the polyaniline thus prepared showed optically active electrochromism via electrochemical redox process in circular dichroism spectroscopy measurements. In our previous study, we calculated the ORD spectra for the polymer by Kramars - Kronich (K-K) conversion from circular dichromism. In the present research, we successfully obtained experimental data of optical rotation-spectroelectrochemical result, as a first example of optical rotation control of natural optical activity for conjugated polymers based on electrochemical method. In the case of low potential for the polymer in the electrochemical redox process, the polymer shows intense optical rotation at visible wavelength range. On the other hands, higher potential at around 1 V affords to give doping process for the polymer, resulting generation of polaron as charge carrier, which shows optical activity at near infrared region. We referred this optical charge carrier as “chiral charge carrier chiralions”. The electrochemical oxidation equivalents to electrochemical doping from the polymer. In other words, electrochemical oxidation gives electrochemical doping which results change in degree of optical rotation for the polymer. The control of optical ration for materials can be driven by magnetic field (Faraday rotation), and electric field (Kerr rotation). We propose a new phenomenon as ‘‘electrochemical optical rotation’’. The electro-conductivity of the polymer is measured with four-probe method. The polymer which is electronic doped state with (+)-CSA as electric dopant for production of radical cation (polarons) or dication (bipolarons) as charge carriers and chiral inducer for twisting main-chain. The polymer film was synthesized as followed. First, electrochemical polymerization of aniline as a monomer was carried out in excessive optically active (+)-CSA with three electrode system consisting of working electrode (indium-tin oxide coated glass), counter electrode (platinum wire), and reference electrode (SCE) in water. The polymerization reaction is rapidly progressed with formation of polymer thin film onto the counter electrode. The polymer was washed with excess amount of water, acetone. The electroactive polymer film was thus deposited on the electrode was used for optical activity measurements. Cyclic voltammetry (CV) measurements were carried out for the resultant polymer (monomer free) deposited on to the ITO coated glass electrode. The CV results with change in scan rate from 10-100 mV/s indicates electroactive. Increase of scan rate increases current density for the polymer due to increase of diffusion of ion in the electrolyte solution. Oxidation signals of the polymer are observed due to change in electronic state of the polymer. Corresponding reduction signals against oxidation process are observed, indicating reversible redox activity for the polymer. ORD measurement reveled that the polymer film thus obtained is optically active. The polyaniline can be formed helical structure due to doping of optically active CSA. We carried out in-situ ORD measurement with potential change, evaluating electrochemical driven change in optical rotation. Chemical structure of the double layer polymer is examined with Fourie transform infrared optical absorption spectroscopy measurements which reveled this polymer is polyaniline, and CSA as a dopant. Ultra-violet optical absorption measurements for the polymer film indicates intense and wide range absorptions from invisible to infrared range as charge carriers the delocalized along the main-chain, indicating the polymers are conductive materials. The advantages of the polymer film are formation of self-standing redox activity, tuning of optical activity and color coordination. This paper reports novel function of control optical rotation with electrochemical method examined with spectroelectrochemistry. This concept can be a first example as optical rotation effect of electro-optically active conducting polymers. This paper reports the charge carries of helical polyaniline as chiralions can tune via electrochemical method.

Simultaneous measurement of optical rotation dispersion and absorption spectra for chiral substances.

We present a new method based on optical null methods for simultaneously measuring the optical rotatory dispersion (ORD) and absorption spectra of chiral substances. The optical rotation angle at a specific wavelength can be obtained from the optical nulls of the Malus curves with and without the sample. We use the optical nulls of the two curves as benchmark points and the readings to the right of the benchmark points by a certain angular offset to eliminate the influence of the analyzer on the light intensity and obtain the absorbance of the chiral substance at a specific wavelength. The 4096 pixels of the line scan CCD can measure multiple wavelengths simultaneously so that continuous ORD and absorption spectra can be obtained. The experimental results show that the standard deviation of the specific optical rotation is 0.11 deg mL g-1 dm-1 , the standard deviation of the maximum absorption wavelength is 0.45 nm, and that absorbance of the sample varies linearly with the concentration. This method is helpful for simplifying the experiment and has a profound influence on the analysis of the contents and molecular configurations of chiral substances in the future.

Formation and decomposition of Poly(l-lactic acid) charge-transfer complex with iodine: A new molecular switch

PLLA forms a charge-transfer (CT) complex with iodine in trichloromethane solution with Keq = 24.8 ± 1.8 M-1, much higher than the Keq = 0.75 M-1 measured with the model compound ethyl lactate-iodine in CHCl3. The higher equilibrium constant of the PLLA-I2 complex suggests a special polymer-iodine interaction which was confirmed by optical rotatory dispersion (ORD) measurements, taking advantage of the fact that PLLA is an optically active polymer. In fact, ORD measurement shows an induced Cotton effect at 500 nm giving further support to the model of iodine accommodated inside the helical coils of PLLA chains in solution. The PLLA-I2 complex was found very stable if stored in the dark and in the cold (i.e. +10 °C). The PLLA-I2 complex shows both the growth of the CT bands in the electronic spectrum and the induced Cotton effect in the ORD spectrum after prolonged storage. However, the PLLA-I2 complex is sensitive to visible light and it dissociates upon irradiation, but in the dark the complex is restored again, so that the complex could be defined as “photoreversible”. Furthermore, the PLLA-I2 complex is thermoreversible as it dissociates when heated at +50 °C but the complex is restored in full when cooled down to +10 °C in the dark. With these quite unique photoreversible and thermoreversible properties the PLLA-I2 complex behaves as a molecular switch i.e. a molecular system that can be reversibly interconverted between two states A and B by an external action or stimulus. Molecular switches are of key importance in nanotechnological applications.

Relativistic four-component linear damped response TDDFT for electronic absorption and circular dichroism calculations.

We present a detailed theory, implementation, and a benchmark study of a linear damped response time-dependent density functional theory (TDDFT) based on the relativistic four-component (4c) Dirac-Kohn-Sham formalism using the restricted kinetic balance condition for the small-component basis and a noncollinear exchange-correlation kernel. The damped response equations are solved by means of a multifrequency iterative subspace solver utilizing decomposition of the equations according to Hermitian and time-reversal symmetry. This partitioning leads to robust convergence, and the detailed algorithm of the solver for relativistic multicomponent wavefunctions is also presented. The solutions are then used to calculate the linear electric- and magnetic-dipole responses of molecular systems to an electric perturbation, leading to frequency-dependent dipole polarizabilities, electronic absorption, circular dichroism (ECD), and optical rotatory dispersion (ORD) spectra. The methodology has been implemented in the relativistic spectroscopy DFT program ReSpect, and its performance was assessed on a model series of dimethylchalcogeniranes, C4H8X (X = O, S, Se, Te, Po, Lv), and on larger transition metal complexes that had been studied experimentally, [M(phen)3]3+ (M = Fe, Ru, Os). These are the first 4c damped linear response TDDFT calculations of ECD and ORD presented in the literature.

Synthesis, structural characterization and photophysical properties of 7-cyanohexahelicene

7-Cyanoexahelicene has been prepared in racemic form through a short photochemical synthetic approach and its enantiomeric separation was studied and allowed to obtain (P)- and (M)-enantiomers in 100% ee and >98.5% ee, respectively. The optical rotatory dispersion and electronic circular dichroism (ECD) spectra of the resolved ones were measured. Other optical properties such as UV and photoluminescence as well as the electrochemical behavior were also examined in solutions.

Resolution-of-identity accelerated relativistic two- and four-component electron dynamics approach to chiroptical spectroscopies.

We present an implementation and application of electron dynamics based on real-time time-dependent density functional theory (RT-TDDFT) and relativistic 2-component X2C and 4-component Dirac-Coulomb (4c) Hamiltonians to the calculation of electron circular dichroism and optical rotatory dispersion spectra. In addition, the resolution-of-identity approximation for the Coulomb term (RI-J) is introduced into RT-TDDFT and formulated entirely in terms of complex quaternion algebra. The proposed methodology was assessed on the dimethylchalcogenirane series, C4H8X (X = O, S, Se, Te, Po, Lv), and the spectra obtained by non-relativistic and relativistic methods start to disagree for Se and Te, while dramatic differences are observed for Po and Lv. The X2C approach, even in its simplest one-particle form, reproduces the reference 4c results surprisingly well across the entire series while offering an 8-fold speed-up of the simulations. An overall acceleration of RT-TDDFT by means of X2C and RI-J increases with system size and approaches a factor of almost 25 when compared to the full 4c treatment, without compromising the accuracy of the final spectra. These results suggest that one-particle X2C electron dynamics with RI-J acceleration is an attractive method for the calculation of chiroptical spectra in the valence region.

Morphology and Magnetic Structure of the Ferritin Core during Iron Loading and Release by Magnetooptical and NMR Methods.

Ferritins are proteins, which serve as a storage and transportation capsule for iron inside living organisms. Continuously charging the proteins with iron and releasing it from the ferritin is necessary to assure proper management of these important ions within the organism. On the other hand, synthetic ferritins have great potential for biomedical and technological applications. In this work, the behavior of ferritin during the processes of iron loading and release was examined using multiplicity of the experimental technique. The quality of the protein's shell was monitored using circular dichroism, whereas the average size and its distribution were estimated from dynamic light scattering and transmission electron microscopy images, respectively. Because of the magnetic behavior of the iron mineral, a number of magnetooptical methods were used to gain information on the iron core of the ferritin. Faraday rotation and magnetic linear birefringence studies provide evidence that the iron loading and the iron-release processes are not symmetrical. The spatial organization of the mineral within the protein's core changes depending on whether the iron was incorporated into or removed from the ferritin's shell. Magnetic optical rotatory dispersion spectra exclude the contribution of the Fe(II)-composed mineral, whereas joined magnetooptical and nuclear magnetic resonance results indicate that no mineral with high magnetization appear at any stage of the loading/release process. These findings suggest that the iron core of loaded/released ferritin consists of single-phase, that is, ferrihydrite. The presented results demonstrate the usefulness of emerging magnetooptical methods in biomedical research and applications.

Computational Spectroscopic Characterization of a Bistable Binuclear Complex [(CO)2(benzoate)FeII/III(terephthalate)CoIII/II(benzoate)(CO)2

Electric dipole moments, polarizabilities, and IR, Raman, optical rotatory dispersion, and electronic and vibrational circular dichroism spectra of the four cis–trans isomers of the proposed [(CO)2(benzoate)FeII/III(terephthalate)CoIII/II(benzoate)(CO)2]+ binuclear complex, having bistablity due to intramolecular charge transfer (IMCT), is investigated using the time-dependent density functional theory ((TD)DFT) B3LYP/6–31G(d,p)[LanL2DZ] method. Results show that the two FeII–CoIII and FeIII–CoII IMCT states of this binuclear complex have distinctly different spectroscopic, optical, and electric response properties, and are sensitive to the cis–trans arrangement of the ligands around the two metallic centres. Furthermore, intrinsic reaction coordinates inter-connecting the two IMCT states are identified using the Duschinsky matrix method. Only one or two of the normal coordinates remain almost (above 80 %) intact during the IMCT reaction which denotes global changes in the bonding strengths and potential energy hypersurface of this bistable binuclear complex. Analysis of the calculated spin densities characterizes the IMCT transition state structures of the trans–trans, cis–cis, and trans–cis isomers as early, early, and late transition states, respectively.

Importance and Difficulties in the Use of Chiroptical Methods to Assign the Absolute Configuration of Natural Products: The Case of Phytotoxic Pyrones and Furanones Produced by Diplodia corticola.

α-Pyrones and furanones are metabolites produced by Diplodia corticola, a pathogen of cork oak. Previously, the absolute configuration (AC) of diplopyrone was defined by chiroptical methods and Mosher's method. Using X-ray and chiroptical methods, the AC of sapinofuranone C was assigned, while that of the (4S,5S)-enantiomer of sapinofuranone B was established by enantioselective total synthesis. Diplofuranone A and diplobifuranylones A-C ACs are still unassigned. Here electronic and vibrational circular dichroism (ECD and VCD) and optical rotatory dispersion (ORD) spectra are reported and compared with density functional theory computations. The AC of the (4S,5S)-enantiomer of sapinofuranone B and sapinofuranone C is checked for completeness. The AC of diplobifuranylones A-C is assigned as (2S,2'S,5'S,6'S), (2S,2'R,5'S,6'R), and (2S,2'S,5'R,6'R), respectively, with the Mosher's method applied to define the absolute configuration of the carbinol stereogenic carbon. The AC assignment of sapinofuranones is problematic: while diplofuranone A is (4S,9R), sapinofuranones B and C are (4S,5S) according to ORD and VCD, but not to ECD. To eliminate these ambiguities, ECD and VCD spectra of a di-p-bromobenzoate derivative of sapinofuranone C are measured and calculated. For phytotoxicity studies, it is relevant that all six compounds share the S configuration for the stereogenic carbon atom of the lactone moiety.

Pseudo Jahn-Teller effects and optical activities of negatively curved hydrocarbons

As a fundamental study on energetics of negatively curved structures, puckering energetics of [n]circulene is studied in view of vibronic interactions. In [7]circulene, the D7h geometry is subject to pseudo Jahn-Teller effect (PJT) and unstable with respect to the E1″, E2″, and E3″ vibrational modes. It is distorted into Cs or C2 geometries to form valleys of the potential surface ca. 9 kcal/mol below the D7h geometry. The C2 structure is slightly stable than Cs one, which is consistent with experiments. The resultant C2 geometry is optically active, and the CD (circular dichroism) and ORD (optical rotatory dispersion) spectra are well simulated. This type of optical activities is interesting in that they should be proportional to the PJT-distortion. PJT-induced optical activity in [2m+1]circulenes should be mainly originated from vibronic coupling constants in the initial and final states, which leads to helical rule characteristic of C2 molecules.

Novel method for determination of optical rotatory dispersion spectrum by using line scan CCD.

A novel method is presented for rapid measurement of optical rotatory dispersion (ORD). Light passes through a polarizer, sample and analyzer, to a transmission grating that disperses the collimated light beam. A step-motor rotating stage controlled by a digital signal processor changes the analyzer orientation. The light power is measured by a charge-coupled device (CCD) after each rotating-stage step. The optical rotation angle for each wavelength is determined from the shift between two Malus curves obtained from each CCD pixel. The ORD spectrum is obtained by transforming the optical rotation angle into specific rotation. The ORD spectrum for a standard quartz tube demonstrates good continuity and agreement with reference data.

Solvent, temperature and concentration effects on the optical rotatory dispersion of (R)-3-methylcyclohexanone

Optical rotatory dispersion (ORD) spectra are reported for isolated and solvated (R)-3-methylcyclohexanone (R-3MCH) in 10 solvents, of wide polarity range, and over the spectral range 350–650 nm. Sample concentration effects on ORD spectra of R-3MCH were also recorded and investigated over widely varying concentrations from 2.5 × 10−3 to 2.5 × 10−1 g/mL where an observed sensitivity of optical rotation (OR) to incident light wavelength at low concentrations is correlated to solvent effects. Temperature effects were also studied by recording ORD spectra over the temperature range 0–65 °C in toluene. Recorded specific OR was plotted against various solvent parameters, namely, dipole moment, polarity, refractive index and polarizability to probe solvent effects. Furthermore, solvent effects were studied by incorporating Kamlet's and Taft's solvent parameters in the multi-parametric linear fitting. Theoretically, ORD spectra and populations of optimized geometries of equatorial and axial conformers of R-3MCH were calculated in the gas and solvated phases. All theoretical calculations were performed employing the polarizable continuum model using density functional theoretical and composite scheme (G4) methods with aug-cc-pVTZ and aug-cc-pVDZ basis sets. Net ORD spectra of R-3MCH were generated by the Boltzmann-weighted sum of the contributions of the dominant conformers. Upon comparing theoretical and experimental ORD spectra, a very good agreement is observed for the ORD spectra in the gas phase and high polarity solvents compared to relatively lesser agreement in low polarity solvents.

Absolute configurations of phytotoxic inuloxins B and C based on experimental and computational analysis of chiroptical properties

The absolute configuration of phytotoxins inuloxins B and C, produced by Inula viscosa, and with potential herbicidal activity for the management of parasitic plants, has been determined by Time-dependent density functional theory computational prediction of electronic circular dichroism and optical rotatory dispersion spectra. The inuloxin B has been converted to its 5-O-acetyl derivative, which due to its more constrained conformational features facilitated the computational analysis of its chiroptical properties. The analysis based on experimental and computed data led to assignment of absolute configuration to naturally occurring (+)-inuloxin B and (−)-inuloxin C as (7R,8R,10S,11S) and (5S,7S,8S,10S), respectively.

The Clusters-in-a-Liquid Approach for Solvation: New Insights from the Conformer Specific Gas Phase Spectroscopy and Vibrational Optical Activity Spectroscopy.

Vibrational optical activity spectroscopies, namely vibrational circular dichroism (VCD) and Raman optical activity (ROA), have been emerged in the past decade as powerful spectroscopic tools for stereochemical information of a wide range of chiral compounds in solution directly. More recently, their applications in unveiling solvent effects, especially those associated with water solvent, have been explored. In this review article, we first select a few examples to demonstrate the unique sensitivity of VCD spectral signatures to both bulk solvent effects and explicit hydrogen-bonding interactions in solution. Second, we discuss the induced solvent chirality, or chiral transfer, VCD spectral features observed in the water bending band region in detail. From these chirality transfer spectral data, the related conformer specific gas phase spectroscopic studies of small chiral hydration clusters, and the associated matrix isolation VCD experiments of hydrogen-bonded complexes in cold rare gas matrices, a general picture of solvation in aqueous solution emerges. In such an aqueous solution, some small chiral hydration clusters, rather than the chiral solutes themselves, are the dominant species and are the ones that contribute mainly to the experimentally observed VCD features. We then review a series of VCD studies of amino acids and their derivatives in aqueous solution under different pHs to emphasize the importance of the inclusion of the bulk solvent effects. These experimental data and the associated theoretical analyses are the foundation for the proposed “clusters-in-a-liquid” approach to account for solvent effects effectively. We present several approaches to identify and build such representative chiral hydration clusters. Recent studies which applied molecular dynamics simulations and the subsequent snapshot averaging approach to generate the ROA, VCD, electronic CD, and optical rotatory dispersion spectra are also reviewed. Challenges associated with the molecular dynamics snapshot approach are discussed and the successes of the seemingly random “ad hoc explicit solvation” reported before are also explained. To further test and improve the “clusters-in-a-liquid” model in practice, future work in terms of conformer specific gas phase spectroscopy of sequential solvation of a chiral solute, matrix isolation VCD measurements of small chiral hydration clusters, and more sophisticated models for the bulk solvent effects would be highly valuable.

Disposable Plasmonics: Plastic Templated Plasmonic Metamaterials with Tunable Chirality.

Development of low-cost disposable plasmonic substrates is vital for the applicability of plasmonic sensing. Such devices can be made using injection-molded templates to create plasmonic films. The elements of these plasmonic films are hybrid nanostructures composed of inverse and solid structures. Tuning the modal coupling between the two allows optimization of the optical properties for nanophotonic applications.

Absolute configurations of phytotoxins seiricardine A and inuloxin A obtained by chiroptical studies

The absolute configuration (AC) of the plant phytotoxin inuloxin A, produced by Inula viscosa, and of the fungal phytotoxin seiricardine A, obtained from Seiridium fungi, pathogen for cypress, has been determined by experimental measurements and theoretical simulations of chiroptical properties of three related methods, namely, Optical Rotatory Dispersion (ORD), Electronic Circular Dichroism (ECD), and Vibrational Circular Dichroism (VCD). Computational prediction by Density Functional Theory (DFT) of VCD spectra and by Time-dependent DFT (TDDFT) of ORD and ECD spectra allowed to assign (7R,8R,10S) AC to naturally occurring (+)-inuloxin A. In the case of compound (−)-seiricardine A, which lacks useful for the analysis UV–Vis absorption, and thus provides a hardly detectable ECD spectrum and quite low ORD values, an introduction of a suitable chromophore by chemical derivatization was performed. The corresponding derivative, 2-O-p-bromobenzoate ester, gave rise to an intense ECD spectrum and higher ORD and VCD values. The comparison of computed spectra with the experimental ones allowed to assign (1S,2R,3aS,4S,5R,7aS) AC to (−)-2-O-p-bromobenzoate ester of seiricardine A and then to (−)-seiricardine A. This study further supports a recent trend of concerted application of more than a single chiroptical technique toward an unambiguous assignment of AC of flexible and complex natural products. Moreover, the use of chemical derivatization, with insertion of suitable chromophoric moieties has allowed to treat also UV–Vis transparent molecules by ECD and ORD spectroscopies.

Asymmetric electrochemical polymerization in cholesteric liquid crystalline media: Effect of isomeric structures of chiral inducers containing bornyl group

Five chiral inducers were synthesized with l-borneol and benzenecarboxylic acids. These chiral inducers have the same substituent (bornyl ester) but different geometries. Para-substituted chiral inducer (I-p) shows relatively high macroscopic helical twisting power (βM), while ortho-substituted chiral inducer (I-o) shows lower. This difference is related with the geometric similarity between the chiral inducers and the host liquid crystals. The result also suggested that distortion of π system induced by polar solvents causes low βM of the I-o. Optically active poly(3,4-ethylenedioxythiophene) (PEDOT) films were chemically prepared in cholesteric liquid crystal (CLC) electrolyte solution induced by the chiral inducers. Circular dichroism (CD) intensities of the resultant polymer films are almost proportional to helical twisting power (HTP) of the chiral inducers. Optical rotatory dispersion (ORD) spectra of the polymer film prepared in the CLC electrolyte induced by I-p (PF-para) shows isosbestic point during the oxidation. This indicates that electro-chiroptically active polymer film was obtained through chiral induction of the bornyl chiral inducer.