Dichroism Signal Research Articles

Intercalator-Induced DNA Superstructure Formation: Doxorubicin and a Synthetic Quinoxaline Derivative.

Small molecules that intercalate DNA have tremendous therapeutic potential. Typically, DNA intercalators do not alter the overall DNA double-helical structure, except locally at the intercalation sites. In a previous report, we showed that a quinoxaline-based intercalator with a mandatory benzyl substitution (1d) induced an unusually large circular dichroism signal upon DNA binding, suggesting the formation of intercalated DNA superstructures. However, no detailed structural studies have been reported. Using atomic force microscopy, we have probed the nature of the superstructure and report the formation of a plectonemically oversupercoiled structure of pBR322 plasmid DNA by 1d, where close association of distant DNA double-helical stretches is the predominant motif. Without the benzyl moiety (1a), no such DNA superstructure was observed. Similar superstructures were also observed with doxorubicin (dox), a therapeutically important DNA intercalator, suggesting that the superstructure is common to some intercalators. The superstructure formation, for both intercalators, was observed to be GC-specific. Interestingly, at higher concentrations (1d and dox), the DNA superstructure led to DNA condensation, a phenomenon typically associated with polyamines but not intercalators. The superstructure may have important biological relevance in connection to a recent study in which dox was shown to evict histone at micromolar concentrations.

Chiroptical Activity from an Achiral Biological Metal-Organic Framework.

Chiroptical activity is observed from an achiral adenine-containing metal-organic framework (MOF) named ZnFDCA. Such a seemingly counterintuitive phenomenon can, in fact, be predicted by the intrinsic crystal symmetry of 4̅2 m point group. Although theoretically allowed, examples of optically active achiral crystals are extremely rare. ZnFDCA is the first reported achiral MOF showing optical activity, as demonstrated by a pair of circular dichroism signals with opposite signs and enhanced intensity. Moreover, simply through adding an amino substituent to adenine, the chiroptical activity, as well as nonlinear optical activity, of the analogous MOF, namely ZnFDCA-NH2, disappears due to diverse packing pattern giving rise to centrosymmetric crystal symmetry.

Preparation and Characterization of Chiral Transition-Metal Dichalcogenide Quantum Dots and Their Enantioselective Catalysis.

Two-dimensional transition-metal dichalcogenides (TMDs) had attracted enormous interests owing to their extraordinary optical, physical, and chemical properties. Herein, we prepared for the first time a series of chiral TMD quantum dots (QDs) from MoS2 and WS2 bulk crystals by covalent modification with chiral ligands cysteine and penicillamine. The chiral TMD QDs were carefully investigated by spectroscopic and microscopic techniques. Their chiral optical activity was confirmed by distinct circular dichroism signals different to those of the chiral ligands. Interestingly, with the assistance of copper ions, the chiral QDs displayed strong and chiral selective peroxidase-like activity. Up to now, inorganic nanomaterials with peroxidase-like activity were tremendous but seldom examples with enantioselectivity. The enantioselectivity of our chiral TMD QDs toward chiral substrates d- and l-tyrosinol was highly up to 6.77, which was almost the best performance ever reported. The mechanisms of enantioselectivity was further investigated by quartz crystal microbalance assays. We believed that because of the extraordinary electronic and optical properties, the chiral TMD QDs should be useful for nonlinear optical materials, asymmetric catalysis, chiral and biological sensors, and so on.

Chiral thiophene derivatives with optimal two‐photon absorption in near‐infrared window I and II

AbstractThiophene derivatives are outstanding organic materials due to their wide spectral response, superior optoelectronic properties, and excellent environmental stability, which have attracted widespread attention in both theory and applications. However, their chiral analogues and corresponding chiroptical behaviors have been rarely investigated. Herein, a series of chiral thiophene derivatives are firstly designed by taking both optical chirality and two‐photon absorption (TPA) response into consideration, and are then investigated by modern analytical response theory. The calculated results demonstrate that these novel chiral thiophene derivatives show optimal TPA in the near‐infrared (NIR) window I and II, indicating that they are promising for biological applications. More importantly, they exhibit reasonable two‐photon circular dichroism (TPCD) signals, which are desirable candidates for chiral recognition regions. Furthermore, the calculations of orbital transitions shed light on that the intramolecular charge transfer plays an important role in their excellent TPA and TPCD behaviors in NIR regions.

X-ray magnetic circular dichroism and near-edge X-ray absorption fine structure of buried interfacial magnetism measured by using a scanning tunneling microscope tip

Magnetism at buried interfaces plays a crucial role in many emerging phenomena, but detection of interfacial magnetism in close proximity to a surface with elemental and chemical sensitivity is a challenging task. Here, we use low temperature synchrotron x-ray scanning tunneling microscopy to investigate x-ray magnetic circular dichroism and the near edge x-ray absorption fine structure of La0.67Sr0.33MnO3-LaNiO3 superlattices. In stark contrast to the weak magnetic signal of Mn when the La0.67Sr0.33MnO3 layers are located on top, a robust x-ray magnetic circular dichroism signal is detected when they are buried underneath the LaNiO3 layers. The near edge x-ray absorption fine structure reveals the valence states of manganese, while the oxygen K-edge x-ray absorption spectra show an increase in hole formation, indicating a cogent charge transfer at the LaNiO3/La0.67Sr0.33MnO3 interface. This work demonstrates that scanning tunneling microscopy can be extended to the synchrotron X-ray study of buried interfaces by controlling the tip-sample separation in the nanometer regime.

Probing the Proximity of Magnetic Dichroic Signal in Electron Magnetics Circular Dichroism by Atomic Sized Electron Vortex Beam and Four Fold Astigmatic Beams.

Probing the Proximity of Magnetic Dichroic Signal in Electron Magnetics Circular Dichroism by Atomic Sized Electron Vortex Beam and Four Fold Astigmatic Beams.

Synthesis and Plasmonic Chiroptical Studies of Sodium Deoxycholate Modified Silver Nanoparticles

Sodium deoxycholate modified silver nanoparticles prepared in the presence of sodium deoxycholate as a chiral inducer exhibit plasmonic circular dichroism (CD) signals. The plasmon-induced chirality arises from the presence of chiral molecules (sodium deoxycholate) on the surface of Ag nanoparticles, which transfer their chiral properties to the visible wavelength range due to the Coulomb interactions between the chiral molecules and plasmonic nanoparticles. The prepared Ag nanoparticles (NPs) exhibit distinct line shapes of plasmonic CD, which can be tailored by varying the pH values of the solutions. A mechanism was proposed to explain the generation of the distinct plasmonic CD shapes, which indicated that the arrangements of chiral molecules in the plasmonic hot spots between Ag NPs are crucial for the induced plasmonic CD.

Emergence of Chiroptical Properties in Molecular Assemblies of Phenyleneethynylenes: The Role of Quasi-degenerate Excitations.

Chiroptical properties of supramolecular assemblies originate through the asymmetric coupling of molecular transition dipole moments. Herein, we report a joint experimental and theoretical investigation to understand the influence of intermolecular interactions on chiroptical properties, particularly during the early stages of self-assembly. In this regard, phenyleneethynylene-based molecular systems appended with d- and l-isomers of phenylalanine have been synthesized with one as well as two electronic transitions in the spectral region of interest. When self-assembled, these molecules show distinctly different chiroptical properties with the right- and left-handed organizations, guided by the chirality of phenylalanines. The standard exciton approach explains the observation of a bisignated electronic circular dichroism signal in systems with a single transition but fails when applied to systems with two nearby transitions. Here, we present a generalized exciton approach that addresses the unusual chiroptical properties of systems with multiple transitions.

Enantiomeric resolution of helicochiral paddlewheel complexes and their infrared, Raman, UV–vis and X-ray optical activity

Linear polynuclear paddlewheel complexes-extended atom chains or metal strings-have provided attractive models for the study of metal-metal bonding, magnetism and conductivity since their discovery in the 1990s [1]. Their helicoidal chirality, arising from mutual steric hindrance of the 3-pyridyl protons, resulting in the twisting of the equatorial ligand around the axis (see figure), has been less studied. Nonetheless, in one of the few examples of chiral resolution, the obtained enantiomers of a trinickel complex showed a remarkably high specific rotation of 5000 deg•mL•g −1 •dm −1 [2], motivating us to seek a general technique for the chiral resolution of such racemates. We have developed a procedure based on anion exchange for the chiral resolution of [M3(dpa)4] 2+ salts (M = Co(II) or Ni(II), Hdpa = 2,2'-dipyridylamine). Homochiral arsenyl tartrate (AsT) salts promoted the selective crystallization of [-M3(dpa)4(MeCN)2](NBu4)2[-AsT]2, or [-M3(dpa)4(MeCN)2](NBu4)2[-AsT]2 in the P4212 space group. The enantiopure compounds demonstrated surprisingly large optical activities using UV-vis, Raman and infrared spectroscopy in solution and, for the cobalt derivatives, in the X-ray range at the Co K-edge in single crystals. An intense X-ray linear dichroism was observed in the orthoaxial crystal orientation, whereas it vanished in the axial confirmation, while the angular dependence of the circular dichroism spectra followed the expected (3cos 2 − 1) function, thus spectroscopically confirming the D4 crystal symmetry. X-ray magnetic circular dichroism and X-ray magnetochiral dichroism signals at the Co K-edge were not detected, likely due to a strongly delocalized spin density on the metal-metal bonded tricobalt core. Nevertheless, these results establish that chiral polynuclear paddlewheel complexes can be cleanly resolved using selective crystallization and demonstrate considerable optical activity in the infrared, UV-vis and X-ray energy ranges, thus potentially offering future perspectives in non-linear optics and asymmetric synthesis [3].

Dynamic Covalent Chemistry within Biphenyl Scaffolds: Effects from Endocyclic to Exocyclic Sulfonamides

There is unabated interest in developing new strategies for the control of atropisomers despite the rich history of atropisomerism. We recently introduced dynamic covalent reactions (DCRs) within biphenyl skeletons for the incorporation and chirality recognition of multiple classes of mononucleophiles. To expand the scope of this strategy, the sulfonamide unit was switched from an endocyclic to an exocyclic position, and the influence of the resulting DCRs on chiral induction was investigated. The intramolecular equilibrium between the open aldehyde and its cyclic hemiaminal favored the ring form, and excellent chirality transfer from the hemiaminal stereocenter to the helical twist of the biphenyl was revealed. The modulation of unique dual reactivity then allowed the realization of DCRs of a diverse set of amines and alcohols. The degree of chirality induction was further explored by employing chiral substrates, affording significant circular dichroism signals.

Tunable Chiroptical Properties from the Plasmonic Band to Metal–Ligand Charge Transfer Band of Cysteine‐Capped Molybdenum Oxide Nanoparticles

AbstractUnderstanding the interactions between a semiconducting nanocrystal surface and chiral anchoring molecules could resolve the mechanism of chirality induction in nanoscale and facilitate the rational design of chiral semiconducting materials for chiroptics. Now, chiral molybdenum oxide nanoparticles are presented in which chirality is transferred via a bio‐to‐nano approach. With facile control of the amount of chiral cysteine molecules under redox treatment, circular dichroism (CD) signals are generated in the plasmon region and metal–ligand charge‐transfer band. The obtained enhanced CD signals with tunable lineshapes illustrate the possibility of using chiral molybdenum oxide nanoparticles as potentials for chiral semiconductor nanosensors, optoelectronics, and photocatalysts.

Tunable Chiroptical Properties from the Plasmonic Band to Metal-Ligand Charge Transfer Band of Cysteine-Capped Molybdenum Oxide Nanoparticles.

Understanding the interactions between a semiconducting nanocrystal surface and chiral anchoring molecules could resolve the mechanism of chirality induction in nanoscale and facilitate the rational design of chiral semiconducting materials for chiroptics. Now, chiral molybdenum oxide nanoparticles are presented in which chirality is transferred via a bio-to-nano approach. With facile control of the amount of chiral cysteine molecules under redox treatment, circular dichroism (CD) signals are generated in the plasmon region and metal-ligand charge-transfer band. The obtained enhanced CD signals with tunable lineshapes illustrate the possibility of using chiral molybdenum oxide nanoparticles as potentials for chiral semiconductor nanosensors, optoelectronics, and photocatalysts.

Solvent-dependent inversion of circular dichroism signal in naproxen: An unusual effect!

The electronic circular dichroism (ECD) spectra of naproxen enantiomers were studied as a function of solvents using experimental (circular dichroism) and theoretical (time-dependent density functional theory) approaches. The (R)- and (S)-naproxen enantiomers presented an unusual inversion in their ECD signals in the presence of ethanol and water when compared with polar aprotic solvents such as acetonitrile. From a practical point of view, these findings deserve great attention because these solvents are widely used for high-performance liquid chromatography analysis in quality control of chiral pharmaceutical drugs. This is particularly relevant to naproxen because the (S)-naproxen has anti-inflammatory properties, whereas (R)-naproxen is hepatotoxic. A time-dependent density functional theory computer simulation was conducted to investigate the signal inversion using the solvation model based on density, a reparameterization of polarized continuum model. Electronic circular dichroism signals of conformers were calculated by computer simulation and their contribution to the combined spectra obtained according to Boltzmann weighting. It was found that the experimentally observed ECD signal inversion can be associated with the minor or major contribution of different conformers of naproxen.

Surface- and pressure-induced bulk Kondo breakdown in SmB6

Motivated by the prediction of surface Kondo breakdown in topological Kondo insulators, we investigated the valence and magnetism of SmB6 with x-ray absorption and magnetic circular dichroism at the Sm M 4,5 and L 2 edges with surface and bulk sensitivity, respectively. A higher Sm valence state at the surface and in the bulk under pressure indicates the surface-and pressure-induced bulk Kondo breakdown. We confirmed the different magnetization origin from the surface (f electron) to the bulk (d electron) and ascertained the direct relationship between the disappearance of the Sm L 2-edge x-ray magnetic circular dichroism signal and the closure of the d-f hybridization gap in SmB6 bulk under pressure, paving the way for further investigations of the Kondo insulators. Above P c = 8.5 GPa, a more localized 4f state with higher valence and the disappearing of the 5d magnetism are observed, suggesting the closure of the hybridization gap in the bulk.

Responsive Self-Assembly of Supramolecular Hydrogel Based on Zwitterionic Liquid Asymmetric Gemini Guest.

A low-molecular-weight supramolecular hydrogel has been fabricated based on host-guest interactions between β-cyclodextrin (β-CD) and an asymmetric gemini zwitterionic liquid (ZIL) containing an azobenzene and bis(trifluoromethanesulfonyl)imide. Reversible sol-gel phase transitions were triggered by light and temperature. The binding stoichiometry, mainly noncovalent interactions in the hydrogel, photo- and thermoresponsive mechanisms, and mode of inclusion in the complex were studied in detail by NMR spectroscopy, UV/Vis spectroscopy, isothermal titration calorimetry, and control experiments. Interestingly, the β-CD in the complex can be photo-manipulated to shuttle along the guest molecule, accompanied by a change in the circular dichroism signals. Reversible switching of the conductivity accompanies the sol-gel phase transition, which demonstrates the stability of the supramolecular hydrogel and its potential application in multi-stimuli-responsive electric sensor materials.

Influence of thermal treatment on the characteristics of major oyster allergen Cra g 1 (tropomyosin).

Shellfish, including oysters, often cause allergic reactions in adults. Thermal treatment is one of the most common technologies for dealing with seafood, which may affect biological properties. The present study aimed to evaluate the impact of heating on the conformation and potential allergenicity of oyster-derived tropomyosin (Cra g 1). Sodium dodecylsulphate-polyacrylamide gel electrophoresis showed that there was an apparent band at 35 kDa of raw tropomyosin after purification and more significant polymers appeared in the heated protein. Interestingly, obvious changes in the intensity of the circular dichroism signal and 1-anilino-8-naphthalene sulfonate-binding fluorescence were observed especially in the case of the roasted form, which was associated with an increase in antibody reactivity. The degree of immunoglobulin (Ig)E binding of this treatment was demonstrated in the order roasted>boiled>raw. Furthermore, sequence alignment and amino acid composition revealed that Cra g 1 shared relatively high homology to tropomyosins from other shellfish and was also abundant in lysine that was apt to be modified by reducing sugars during heating. Heated Cra g 1 produces higher IgE reactivity than the raw form as a result of the denaturation and formation of polymers. These findings will benefit the diagnosis and management of potential allergenicity as a result of shellfish. © 2018 Society of Chemical Industry.

Robust numerical evaluation of circular dichroism from chiral medium/nanostructure coupled systems using the finite-element method

It has been demonstrated that circular dichroism (CD) signals from chiral molecules can be boosted by plasmonic nanostructures inducing strong local electromagnetic fields. To optimize nanostructures to improve CD enhancement, numerical simulations such as the finite element method (FEM) have been widely adopted. However, FEM calculations for CD have been frequently hampered by unwanted numerical artifacts due to improperly discretizing problem spaces. Here, we introduce a new meshing rule for FEM that provides CD simulations with superior numerical accuracy. We show that unwanted numerical artifacts can be suppressed by implementing the mirror-symmetric mesh configuration that generates identical numerical artifacts in the two-opposite circularly polarized waves, which cancel each other out in the final CD result. By applying our meshing scheme, we demonstrate a nanostructure/chiral molecule coupled system from which the CD signal is significantly enhanced. Since our meshing scheme addresses the previously unresolved issue of discriminating between very small CD signals and numerical errors, it can be directly applied to numerical simulations featuring natural chiral molecules which have intrinsically weak chiroptical responses.

Optically Active Semiconductor Nanosprings for Tunable Chiral Nanophotonics.

The search for the optimal geometry of optically active semiconductor nanostructures is making steady progress and has far-reaching benefits. Yet the helical springlike shape, which is very likely to provide a highly dissymmetric optical response, remains somewhat understudied theoretically. Here we comprehensively analyze the optical activity of semiconductor nanosprings using a fully quantum-mechanical model of their electronic subsystem and taking into account the anisotropy of their interaction with light. We show that the circular dichroism of semiconductor nanosprings can exceed that of ordinary semiconductor nanocrystals by a factor of 100 and be comparable to the circular dichroism of metallic nanosprings. It is also demonstrated that nanosprings can feature a total dissymmetry of optical response for certain ratios between their length and coil height. The magnitude and sign of the circular dichroism signal can be controlled by stretching or compressing the nanosprings, which makes them a promising material base for optomechanical sensors, polarization controllers, and other types of optically active nanophotonic devices.

A unified formulation of dichroic signals using the Borrmann effect and twisted photon beams

Dichroic X-ray signals derived from the Borrmann effect and a twisted photon beam with topological charge l = 1 are formulated with an effective wavevector. The unification applies for non-magnetic and magnetic materials. Electronic degrees of freedom associated with an ion are encapsulated in multipoles previously used to interpret conventional dichroism and Bragg diffraction enhanced by an atomic resonance. A dichroic signal exploiting the Borrmann effect with a linearly polarized beam presents charge-like multipoles that include a hexadecapole. A difference between dichroic signals obtained with a twisted beam carrying spin polarization (circular polarization) and opposite winding numbers presents charge-like atomic multipoles, whereas a twisted beam carrying linear polarization alone presents magnetic (time-odd) multipoles. Charge-like multipoles include a quadrupole, and magnetic multipoles include a dipole and an octupole. We discuss the practicalities and relative merits of spectroscopy exploiting the two remarkably closely-related processes. Signals using beams with topological charges l ≥ 2 present additional atomic multipoles.

Optical Activity of Semiconductor Gammadions beyond Planar Chirality.

We present rigorous analysis of optical activity of chiral semiconductor gammadions whose chirality in three dimensions is caused by the nonuniformity of thickness in the transverse plane. It is shown that such gammadions not only distinguish between the two circular polarizations upon scattering and reflection of light, like all two-dimensional semiconductor nanostructures with planar chirality do, but also exhibit circular dichroism and circularly polarized luminescence. Chiral semiconductor gammadions whose charge carriers are mostly confined to the arms are found to feature both high dissymmetry of optical response and a constant-sign circular dichroism signal over a wide frequency range. It is also shown that the strength of the gammadion's chiroptical response is determined solely by two geometric factors: the variation range of the gammadion's thickness and the arms' curvature. Our seminal theoretical study is intended to lay the foundation for future applications of semiconductor gammadions in chiral nanophotonics and nanotechnology.