Showing papers on "Circular dichroism published in 2017"

Chirality detection of enantiomers using twisted optical metamaterials

Abstract: Many naturally occurring biomolecules, such as amino acids, sugars and nucleotides, are inherently chiral. Enantiomers, a pair of chiral isomers with opposite handedness, often exhibit similar physical and chemical properties due to their identical functional groups and composition, yet show different toxicity to cells. Detecting enantiomers in small quantities has an essential role in drug development to eliminate their unwanted side effects. Here we exploit strong chiral interactions with plasmonic metamaterials with specifically designed optical response to sense chiral molecules down to zeptomole levels, several orders of magnitude smaller than what is typically detectable with conventional circular dichroism spectroscopy. In particular, the measured spectra reveal opposite signs in the spectral regime directly associated with different chiral responses, providing a way to univocally assess molecular chirality. Our work introduces an ultrathin, planarized nanophotonic interface to sense chiral molecules with inherently weak circular dichroism at visible and near-infrared frequencies.

A new class of chiral semiconductors: chiral-organic-molecule-incorporating organic–inorganic hybrid perovskites

Abstract: An organic–inorganic hybrid perovskite incorporating chiral organic molecules is demonstrated as a new class of chiral semiconductors Chiral perovskites exhibit oppositely-signed circular dichroism (CD) according to the S- and R-configurations of chiral organics The CD signals can be also varied by changing the crystalline orientation and thickness of the chiral perovskite films

Biophysical Study on the Interaction between Eperisone Hydrochloride and Human Serum Albumin Using Spectroscopic, Calorimetric, and Molecular Docking Analyses.

Abstract: Eperisone hydrochloride (EH) is widely used as a muscle relaxant for patients with muscular contracture, low back pain, or spasticity. Human serum albumin (HSA) is a highly soluble negatively charged, endogenous and abundant plasma protein ascribed with the ligand binding and transport properties. The current study was undertaken to explore the interaction between EH and the serum transport protein, HSA. Study of the interaction between HSA and EH was carried by UV−vis, fluorescence quenching, circular dichroism (CD), Fourier transform infrared (FTIR) spectroscopy, Forster’s resonance energy transfer, isothermal titration calorimetry and differential scanning calorimetry. Tryptophan fluorescence intensity of HSA was strongly quenched by EH. The binding constants (Kb) were obtained by fluorescence quenching, and results show that the HSA–EH interaction revealed a static mode of quenching with binding constant Kb ≈ 104 reflecting high affinity of EH for HSA. The negative ΔG° value for binding indicated that...

Induction of Strong and Tunable Circularly Polarized Luminescence of Nonchiral, Nonmetal, Low‐Molecular‐Weight Fluorophores Using Chiral Nanotemplates

Abstract: A new strategy is described for generating strong circularly polarized luminescence with highly tunable emission bands through chiral induction in nonchiral, totally organic, low-molecular-weight fluorescent dyes by chiral nanotemplate systems. Our approach allows the first systematic investigation to clarify the correlation between the circular dichroism and circularly polarized luminescence intensities. As a result, a dilute solution system with the highest circularly polarized luminescence intensity achieved to date and a dissymmetry factor of over 0.1 was identified.

Self-Assembly of Chiral Gold Clusters into Crystalline Nanocubes of Exceptional Optical Activity

Abstract: Self-assembly of inorganic nanoparticles into ordered structures is of interest in both science and technology because it is expected to generate new properties through collective behavior; however, such nanoparticle assemblies with characteristics distinct from those of individual building blocks are rare. Herein we use atomically precise Au clusters to make ordered assemblies with emerging optical activity. Chiral Au clusters with strong circular dichroism (CD) but free of circularly polarized luminescence (CPL) are synthesized and organized into uniform body-centered cubic (BCC) packing nanocubes. Once the ordered structure is formed, the CD intensity is significantly enhanced and a remarkable CPL response appears. Both experiment and theory calculation disclose that the CPL originates from restricted intramolecular rotation and the ordered stacking of the chiral stabilizers, which are fastened in the crystalline lattices.

Benzo-Fused Double [7]Carbohelicene: Synthesis, Structures, and Physicochemical Properties

Abstract: A benzo-fused double [7]carbohelicene (D7H) was synthesized through a regioselective cyclodehydrogenation of a tetranaphthyl-p-terphenyl-based precursor. The twisted (D7H-1) and anti-folded (D7H-2) conformers of D7H were separated by recrystallization, and their double helicene structures with overlapping terminal benzene rings were unambiguously elucidated by X-ray crystallography. A record-high isomerization barrier (46.0 kcal mol−1) in double helicenes was estimated based on density functional theory (DFT) calculation, which resulted in the excellent conformational stability of D7H. The physicochemical properties of D7H-1 and D7H-2 were investigated by UV/Vis absorption spectroscopy and cyclic voltammetry, displaying the variation of electronic structure upon conformational changes. The optical resolution of the racemic D7H-1 was carried out by chiral HPLC, offering enantiopure D7H-1-(P,P) and D7H-1-(M,M), which were further characterized by circular dichroism spectroscopy.

Circular Dichroism Studies on Plasmonic Nanostructures.

Abstract: In recent years, optical chirality of plasmonic nanostructures has aroused great interest because of innovative fundamental understanding as well as promising potential applications in optics, catalysis and sensing Herein, state-of-the-art studies on circular dichroism (CD) characteristics of plasmonic nanostructures are summarized The hybrid of achiral plasmonic nanoparticles (NPs) and chiral molecules is explored to generate a new CD response at the plasmon resonance as well as the enhanced CD intensity of chiral molecules in the UV region, owing to the Coulomb static and dynamic dipole interactions between plasmonic NPs and chiral molecules As for chiral assembly of plasmonic NPs, plasmon–plasmon interactions between the building blocks are found to induce generation of intense CD response at the plasmon resonance Three-dimensional periodical arrangement of plasmonic NPs into macroscale chiral metamaterials is further introduced from the perspective of negative refraction and photonic bandgap A strong CD signal is also discerned in achiral planar plasmonic nanostructures under illumination of circular polarized plane wave at oblique incidence or input vortex beam at normal incidence Finally perspectives, especially on future investigation of time-resolved CD responses, are presented

Supramolecular Photoactivatable Anticancer Hydrogels

Abstract: A photoactivatable dopamine-conjugated platinum(IV) anticancer complex (Pt-DA) has been incorporated into G-quadruplex G4K+ borate hydrogels by using borate ester linkages (Pt-G4K+B hydrogel). These were characterized by 11B NMR, attenuated total reflection Fourier transform infrared spectroscopy, circular dichroism, scanning electron microscopy and transmission electron microscopy. Microscopy investigations revealed the transformation of an extended fiber assembly into discrete flakes after incorporation of Pt-DA. Pt-DA showed photocytotoxicity against cisplatin-resistant A2780Cis human ovarian cancer cells (IC50 74 μM, blue light) with a photocytotoxic index 5. Most notably, Pt-DA and Pt-G4K+B hydrogels show selective phototoxicity for cancer cells versus normal fibroblast cells (MRC5).

All-dielectric metasurface circular dichroism waveplate.

Abstract: We propose and experimentally demonstrate a high efficient circularly polarizing dichroism waveplate (CPDW) using a Si-based all-dielectric 2Dchiral metasurface. We demonstrate that the CPDW exhibits a unique dichroism in that it functions as a transmissive quarter waveplate for one of either left-or right-handed circularly polarized incident lightand a reflective mirror for the opposite polarization. The circular polarization dichroism (CPD = IRCP − ILCP) in transmission at wavelength ~1.5 μm reaches 97% and the extinction ratio (ER = IRCP/ILCP) is as high as 345:1. Experimental fabrications and measurements of the proposed all-dielectric metasurface are implemented and found to be in excellent agreement with the simulations. The proposed all-dielectric chiral metasurface is of advantages of high-dichroism, easy-fabrication and standard semiconductor fabrication techniques compatible, which could lead to enhanced security in fiber and free-space communications, as well as imaging and sensing applications for circularly polarized light with a highly integrated photonic platform.

Chiral-Selective Plasmonic Metasurface Absorbers Operating at Visible Frequencies

Abstract: We demonstrate theoretically and experimentally a chiral-selective plasmonic absorber by utilizing n-shaped-resonators in the visible frequencies. Our metasurface design enables chiral-selective absorption bands, in which absorption peaks for left-handed circularly polarized and right-handed circularly polarized occur at different resonance wavelengths resulting in significant circular dichroism (CD). Both simulated and measured absorption spectra exhibit maximum absorptions exceeding 80% associated with a CD value of ~0.5. Such a chiral plasmonic metasurface absorber with high performance could find applications in optical filters, non-linear optics, thermal emitters, and hot-electron collection devices.

Circularly Polarized Phosphorescent Electroluminescence from Chiral Cationic Iridium(III) Isocyanide Complexes

Abstract: Circularly polarized organic light-emitting diodes (CP-OLEDs), which directly emit CP light from organic light-emitting diodes, have attracted considerable attention because of their wide applications in various photonic devices. In this work, a pair of chiral bis-cyclometalated phosphorescent iridium(III) isocyanide complexes is designed and synthesized, which exhibits almost the same photophysical properties and obvious mirror image in circular dichroism spectrum. These two complexes are used for fabricating CP-OLEDs, obtaining 4473 cd m−2, 7.50 cd A−1, and 2.55 lm W−1 for the maximum luminance and the maximum current and power efficiencies, respectively. In addition, the dissymmetry gEL factors of CP emission are in the order of 10−3, which is the highest value among the reported devices based on phosphorescent Ir(III) complexes. The results demonstrate that the chiral Ir(III) complexes are of great potential value for application in CP-OLEDs.

Excitonic Circular Dichroism of Chiral Quantum Rods.

Abstract: As an emerging type of optically active materials, chiral molecules-stabilized semiconductor quantum dots (QDs) have achieved extensive attention. Unfortunately, understanding of the optical characteristics of chiral QDs observed by circular dichroism (CD) spectroscopy remains a great challenge due to their rather weak signals. Herein, we successfully achieve much enhanced CD responses from l- or d-cysteine-stabilized wurtzite CdSe quantum rods (QRs) thanks to their unique optical anisotropy. Furthermore, the optical activity of CdSe QRs is explored to be improved and subsequently become stable with the geometrical aspect ratio (AR) increasing, and such change matches well with alternation of the polarization factor of CdSe QRs. A non-degenerate coupled-oscillator (NDCO) model is established to elucidate the optical activity of chiral QRs, and the positive and negative natures of the CD peaks appearing at the first exciton band are clearly assigned to different transition polarization along 4pz,Se → 5sCd ...

The Helix to Super-Helix Transition in the Self-Assembly of π-Systems: Superseding of Molecular Chirality at Hierarchical Level.

Abstract: Higher-order super-helical structures derived from biological molecules are known to evolve through opposite coiling of the initial helical fibers, as seen in collagen protein. A similar phenomenon is observed in a π-system self-assembly of chiral oligo(phenyleneethylene) derivatives (S)-1 and (R)-1 that explains the unequal formation of both left- and right-handed helices from molecule having a specific chiral center. Concentration- and temperature-dependent circular dichroism (CD) and UV/Vis spectroscopic studies revealed that the initial formation of helical aggregates is in accordance with the molecular chirality. At the next level of hierarchical self-assembly, coiling of the fibers occurs with opposite handedness, thereby superseding the command of the molecular chirality. This was confirmed by solvent-dependent decoiling of super-helical structures and concentration-dependent morphological analysis.

Chiral Peropyrene: Synthesis, Structure, and Properties

Abstract: Herein we describe the synthesis, structure, and properties of chiral peropyrenes. Using p-terphenyl-2,2″,6,6″-tetrayne derivatives as precursors, chiral peropyrenes were formed after a 4-fold alkyne cyclization reaction promoted by triflic acid. Due to the repulsion of the two aryl substituents within the same bay region, the chiral peropyrene adopts a twisted backbone with an end-to-end twist angle of 28° that was unambiguously confirmed by X-ray crystallographic analysis. The chiral peropyrene products absorb and emit in the green region of the UV–visible spectrum. Circular dichroism spectroscopy shows strong Cotton effects (Δe = ±100 M–1 cm–1 at 300 nm). The Raman data shows the expected D-band along with a split G-band that is due to longitudinal and transversal G modes. This data corresponds well with the simulated Raman spectra of chiral peropyrenes. The chiral peropyrene products also display circularly polarized luminescence. The cyclization reaction mechanism and the enantiomeric composition of ...

Homochiral MOF as Circular Dichroism Sensor for Enantioselective Recognition on Nature and Chirality of Unmodified Amino Acids

Abstract: Self-assembly of zinc salt with rationally designed chiral ligand, (1R,2R)-2-(pyridine-4-ylcarbamoyl) cyclohexanecarboxylic acid (RR-PCCHC) generated 2D homochiral metal-organic framework [Zn(RR-PCCHC)2] (HMOF-1) that is composed of DNA-like right-handed double-helix structure. HMOF-1 shows high solvent and thermal stability and is also stable in neutral, weak acidic and weak basic aqueous solution. Emulsified HMOF-1 shows strong inherent circular dichroism (CD) signal in aqueous solution, which can show regular intensity change by induction of amino acids. On the basis of the measuring of CD signal intensity, a chemosensor for unmodified amino acids is fabricated, which differ from reported those in which CD signal is amplified by a complicated chemical reaction of originally CD-silent molecule with probed amino acids. This chemosensor can be used for rapid, convenient and sensitive detection of micro amount of amino acids. Most remarkably, 3 × 10-8 mol of l-aspartic acid and 4 × 10-8 mol of d-aspartic acid in aqueous solution can completely quench CD signal of emulsified HMOF-1 in H2O. It is found that the difference of recognition ability between d- and l-proline is the largest in all probed amino acids. The LOD (limit of detection) of the proposed sensor for the determination of aspartic acid is 13.31 ppm. The recognition efficiency η = [Formula: see text] × 100% for l-aspartic acid is as high as 92.1%. The interacting mechanism of DNA-like HMOF-1 with probed amino acids is similar to that of groove binding of targeting drug with DNA.

Chiral-at-Metal Phosphorescent Square-Planar Pt(II)-Complexes from an Achiral Organometallic Ligand

Abstract: The synthesis and characterization of a new kind of cis- and trans-cyclometalated square-planar platinum(II) complexes is reported. Uncharged organometallic compounds carrying one or two of the C∧N-donor ligand LCN were prepared. Due to the heterobidentate coordination of the achiral chelate ligand, the formed [PtLCNCl(SEt2)], cis- and trans-[PtLCN2] complexes are chiral with the metal serving as the stereo center. The enantiomers of complex trans-[PtLCN2] could be separated and their absolute configuration was determined by anomalous X-ray diffraction, in accordance with CD spectroscopic results and TD-DFT calculations. All compounds were fully characterized by NMR spectroscopy, mass spectrometry and X-ray structure determination. The photophysical properties of trans-[PtLCN2] have been investigated showing phosphorescence in solution and in the solid state with a moderate quantum yield. For the enantiomers, strong circular dichroism (CD) and circularly polarized luminescence (CPL) effects were observed,...

Protein conformation in pure and hydrated deep eutectic solvents.

Abstract: Deep eutectic solvents (DES) have recently been postulated as possible environments where protein structure may be preserved in the absence of water. Here we present our results towards understanding protein conformation in choline chloride-based DES and mixtures with water. Lysozyme and bovine serum albumin have been investigated by means of circular dichroism and small-angle neutron scattering.

Chirality Control of Electron Transfer in Quantum Dot Assemblies.

Abstract: Electron spin and molecular chirality are emerging as factors that can be used effectively to direct charge flow at the molecular scale. We report order of magnitude effects of molecular chirality on electron-transfer rates between quantum dots (QDs) in chiral QD assemblies. Indeed, both the circular polarization of the light that excites the electron donor and the imprinted chirality of the acceptor QDs affect the dot-to-dot electron-transfer kinetics. We define a polarization for the electron-transfer rate constant and show that it correlates with the strength of the acceptor QD circular dichroism (CD) spectrum. These findings imply that the CD strength of the QD exciton transition(s) may be used as a predictor for the spin-dependent electron transfer, indicating that chiral imprinting of the dots may lie at the origin of this phenomenon.

Multi-spectroscopic and HPLC Studies of the Interaction Between Estradiol and Cyclophosphamide With Human Serum Albumin: Binary and Ternary Systems

Abstract: Drug resistance is a phenomenon that frequently impairs a proper treatment of infections and cancer with chemotherapy. Multidrug efflux transporters extrude structurally dissimilar organic compounds often providing resistance to multiple toxic chemotherapeutic agents. The quantitative analysis of drug efflux requires measuring the affinity of ligands. In this work, the interaction between cyclophosphamide (Cyc) and estradiol (ES) with human serum albumin (HSA) was studied by fluorescence polarization, circular dichroism and high-performance liquid chromatography (HPLC) under physiological conditions (pH = 7.4). Gradual addition of HSA led to a marked increase in fluorescence polarization. Our assays indicated that the protein was bound to these drugs with different K d. Also, the Hill coefficient showed a simple drug binding process with no cooperativity. Circular dichroism results revealed the occurrence of conformational changes in HSA molecules by the binding of Cyc and ES. The protein binding of the drug was studied by HPLC. Our results indicated that the drug was bound to the protein and that the presence of a second drug affected the interaction and resistance between the first drug and the protein.

Reversible Quadruple Switching with Optical, Chiroptical, Helicity, and Macropattern in Self-Assembled Spiropyran Gels

Abstract: Enantiomeric glutamate gelators containing a spiropyran moiety are designed and found to self-assemble into a nanohelix through gelation Upon alternating UV and visible light irradiation, the spiropyran experiences a reversible change between a blue zwitterionic merocyanine state and a colorless closed ring state spiropyran in supramolecular gels This photochromic switch causes a series of subsequent changes in the optical, chiroptical, morphological properties from supramolecular to macroscopic levels While the solution of the gelator molecules does not show any circular dichroism (CD) signal in the region of 250–700 nm due to the fact that the chromophore is far from the chiral center, the gel shows chiroptical signals such as CD and circularly polarized luminescence (CPL) because of the chirality transfer by the self-assembly These signals are reversible upon alternating UV/vis irradiation Therefore, a quadruple optical and chiroptical switch is developed successfully During such process, the self-assembled nanostructures from the enantiomeric supramolecular gels also undergo a reversible change between helices and fibers under the alternating UV and visible light trigger Furthermore, a rewritable material fabricated from their xerogels on a glass is developed Such rewritable material can be efficiently printed over 30 cycles without significant loss in contrast and resolution using UV and visible light

Anticancer Activity of Iridium(III) Complexes Based on a Pyrazole-Appended Quinoline-Based BODIPY

Abstract: A pyrazole-appended quinoline-based 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene (L1, BODIPY) has been synthesized and used as a ligand for the preparation of iridium(III) complexes [Ir(phpy)2(L1)]PF6 (1; phpy = 2-phenylpyridine) and [(η5-C5Me5)Ir(L1)Cl]PF6 (2). The ligand L1 and complexes 1 and 2 have been meticulously characterized by elemental analyses and spectral studies (IR, electrospray ionization mass spectrometry, 1H and 13C NMR, UV/vis, fluorescence) and their structures explicitly authenticated by single-crystal X-ray analyses. UV/vis, fluorescence, and circular dichroism studies showed that complexes strongly bind with calf-thymus DNA and bovine serum albumin. Molecular docking studies clearly illustrated binding through DNA minor grooves via van der Waals forces and their electrostatic interaction and occurrence in the hydrophobic cavity of protein (subdomain IIA). Cytotoxicity, morphological changes, and apoptosis have been explored by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromi...

Biomimetic Chirality Sensing with Pyridoxal-5′-phosphate

Abstract: Pyridoxal-5′-phosphate (PLP) is introduced to a biomimetic indicator displacement assay for simultaneous determination of the absolute configuration, enantiomeric composition and concentration of unprotected amino acids, amino alcohols and amines. The chiroptical assay is based on fast imine metathesis with a PLP aryl imine probe to capture the target compound for circular dichroism and fluorescence sensing analysis. The substrate binding yields characteristic Cotton effects that provide information about the target compound ee and the synchronous release of the indicator results in a nonenantioselective off-on fluorescence response that is independent of the enantiomeric sample composition and readily correlated to the total analyte concentration.