Circular Dichroism Research Articles

Arrhythmogenic calmodulin variants D131E and Q135P disrupt interaction with the L-type voltage-gated Ca2+ channel (Cav1.2) and reduce Ca2+-dependent inactivation.

Long QT syndrome (LQTS) and catecholaminergic polymorphism ventricular tachycardia (CPVT) are inherited cardiac disorders often caused by mutations in ion channels. These arrhythmia syndromes have recently been associated with calmodulin (CaM) variants. Here, we investigate the impact of the arrhythmogenic variants D131E and Q135P on CaM's structure-function relationship. Our study focuses on the L-type calcium channel Cav1.2, a crucial component of the ventricular action potential and excitation-contraction coupling. We used circular dichroism (CD), 1H-15N HSQC NMR, and trypsin digestion to determine the structural and stability properties of CaM variants. The affinity of CaM for Ca2+ and interaction of Ca2+/CaM with Cav1.2 (IQ and NSCaTE domains) were investigated using intrinsic tyrosine fluorescence and isothermal titration calorimetry (ITC), respectively. The effect of CaM variants of Cav1.2 activity was determined using HEK293-Cav1.2 cells (B'SYS) and whole-cell patch-clamp electrophysiology. Using a combination of protein biophysics and structural biology, we show that the disease-associated mutations D131E and Q135P mutations alter apo/CaM structure and stability. In the Ca2+-bound state, D131E and Q135P exhibited reduced Ca2+ binding affinity, significant structural changes, and altered interaction with Cav1.2 domains (increased affinity for Cav1.2-IQ and decreased affinity for Cav1.2-NSCaTE). We show that the mutations dramatically impair Ca2+-dependent inactivation (CDI) of Cav1.2, which would contribute to abnormal Ca2+ influx, leading to disrupted Ca2+ handling, characteristic of cardiac arrhythmia syndromes. These findings provide insights into the molecular mechanisms behind arrhythmia caused by calmodulin mutations, contributing to our understanding of cardiac syndromes at a molecular and cellular level.

Ultrasensitive circular dichroism spectroscopy based on coupled quasi-bound states in the continuum

Ultrasensitive circular dichroism spectroscopy based on coupled quasi-bound states in the continuum

Physical properties of chlorophyll–quinone conjugates prepared via Friedel–Crafts reaction

Pheophytin-a derivatives possessing plastoquinone and phylloquinone analogs in the peripheral 3-substituent were prepared by Friedel–Crafts reactions of a 3-hydroxymethyl-chlorin as one of the chlorophyll-a derivatives with benzo- and naphthohydroquinones, respectively, and successive oxidation of the 1,4-dihydroxy-aryl groups in the resulting dehydration products. The 3-quinonylmethyl-chlorins exhibited ultraviolet–visible absorption and circular dichroism spectra in acetonitrile, which were composed of those of the starting 3-hydroxymethyl-chlorin and the corresponding methylated benzo- and naphthoquinones. No intramolecular interaction between the chlorin and quinone π-systems was observed in the solution owing to the methylene spacer. The first reduction potentials of the quinone moieties in the synthetic conjugates were determined by cyclic voltammetry and shifted positively from those of the reference quinones. The former quinonyl groups were reduced more readily by approximately 0.1 V than the latter quinones, which was ascribable to the stabilization of the quinonyl anion radical by the nearby macrocyclic chlorin π-chromophore. This observation implied that the reduction potentials of quinones were regulated by the close pheophytin-a derivative by through-space interaction. Considering the charge shift from pheophytin-a anion radical to plastoquinone and phylloquinone in reaction centers of photosystems II and I, respectively, the reduction potentials of these quinones as a determinant factor of the rapid electron transfer process would be dependent on the pheophytin-a in the photosynthetic reaction centers of oxygenic phototrophs as well as on the neighboring peptides.

Counterintuitive Reversal of Circular Dichroism via Controllable Plasmonic Guided Mode Resonance in Diatomic Metasurfaces

Counterintuitive Reversal of Circular Dichroism via Controllable Plasmonic Guided Mode Resonance in Diatomic Metasurfaces

Chemical Constituents of the Deep-Sea-Derived Penicillium citrinum W22 and Their Ferroptosis Inhibitory Activity.

One new monomeric citrinin analog (1) and 42 known compounds (2-43) were isolated from Penicillium citrinum W22. The structure of 1 was determined by detailed analysis of the 1D and 2D nuclear magnetic resonance (NMR), HRESIMS, and time-dependent density functional theory (TD-DFT)-based electronic circular dichroism (ECD) calculation. Penicitrinol A (2) and methyl 2-(2-acetyl-3,5-dihydroxy-4,6-dimethylphenyl) acetate (11) significantly inhibited renin-angiotensin system-selective lethal 3 (RSL3)-induced ferroptosis with half maximal effective concentration (EC50) values of 1.6 and 34.0µM, respectively.

An unusual chiral-at-metal mechanism for BINOL-metal asymmetric catalysis

Chiral binaphthols (BINOL)-metal combinations serve as powerful catalysts in asymmetric synthesis. Their chiral induction mode, however, typically relies on multifarious non-covalent interactions between the substrate and the BINOL ligand. In this work, we demonstrate that the chiral-at-metal stereoinduction mode could serve as an alternative mechanism for BINOL-metal catalysis, based on mechanistic studies of BINOL-aluminum-catalyzed asymmetric hydroboration of heteroaryl ketones. Theoretical calculations reveal that an octahedral stereogenic-at-metal aluminum alkoxide species is the most stable species within the reaction system, and also is the catalytic relevant intermediate, promoting the stereo-determining hydroboration reaction through a ligand-assisted hydride transfer mechanism rather than the conventional hydroalumination mechanism. These computations reproduce the experimental selectivities and also rationalize the stereoinduction mechanism, which arises from the aluminum-centered chirality induced by chiral BINOL ligands during diastereoselective assembly. The reliability of the proposed mechanism could be verified by the single-crystal X-ray diffraction characterization of the octahedral aluminum alkoxide complex. Additional NMR and Electronic Circular Dichroism (ECD) experiments elucidated the behavior of the hexacoordinated aluminum alkoxide in the solution phase. We anticipate that these findings will extend the applicability of BINOL-metal catalysis to a broader range of reactions.

Readily Accessible, Versatile, and Adaptive Biaxially Chiral Chromophores.

Precisely controlling quantum states is relevant in next-generation quantum computing, encryption, and sensing. Chiral organic chromophores host unique light-matter interactions, which allow them to manipulate the quantized circular polarization of photons. Axially chiral organic scaffolds, such as helicenes or twisted acenes, are powerful motifs in chiral light manipulation. However, these systems usually require complex syntheses and small-scale (10 mg) enantiomer separations, typically complicating systematic investigations of their structure-property relationships. We report here the straightforward synthesis of both enantiomers (R/S) of 10 different axially chiral chromophores. This protocol relies on a readily accessible, enantiomerically pure, and axially chiral contorting element, benzodinaptho[1,4]dioxicine-2,3-diamine (DODA), that we synthesize in two steps with high purity and good yield at gram scale. Subsequent derivation of DODA transfers the chirality from one axis to twist the dominant chromophore around a second, orthogonal axis. Using this biaxial contortion design element, we produce 10 enantiopure biaxial chromophores, without the need for chromatographic separations, and no observable compromise to chiroptical integrity. These chromophores exhibit broadband single-handed absorption without Cotton effects from 265 to 485 nm, indicating chiral excitonic character that forms between the DODA and twisted core chromophore. This platform is responsive to solvent polarity in the excited state, displaying >50 nm bathochromic shifts in the photoluminescence spectra. In addition, this scaffold intensely interacts with changes in pH, which allows us to ultimately access monosignate circular dichroism absorption over a 300 nm range.

Vibronic Coupling and Multiple Electronic States Effect in ABS and ECD Spectra: Three [7]Helicene Derivatives.

Vibronic coupling and multiple electronic states effect play a pivotal role in the molecular spectroscopy of large systems. Herein, we present a detailed theoretical study on the absorption (ABS) and electronic circular dichroism (ECD) spectra of three [7]helicene derivatives in chloroform, with a particular emphasis on the significance of vibronic coupling and the multiple electronic states effect in spectral simulations. The vertical gradient (VG) and vertical Hessian (VH) models, incorporating the Franck-Condon (FC) effect and Herzberg-Teller (HT) contribution, are considered in the vibronic calculations. The results indicate that the simulated vibrationally resolved spectra obtained by the VG model combined with the FC effect are more reliable, showing advantages in the rationality of spectral shapes, the accuracy of the relative heights of absorption peaks, and the correctness of positive and negative signals. Reliable predictions of the three [7]helicene derivatives allowed us to further explore the importance of the multiple electronic states effect in the vibrationally resolved spectra, demonstrating that the high-energy electronic excited states, particularly the fifth (S5) and sixth (S6) excited states, are essential for accurately capturing the fine structures observed in the experimental spectra. Our study predicts reliable theoretical reference spectra for the family of [7]helicene derivatives and provides a fundamental understanding of the vibronic coupling of chiral organic molecules with multiple electronic states.

Shear-Mediated Stabilization of Spin Spiral Order in Multiferroic NiI2.

Type-II multiferroicity from non-collinear spin order is recently explored in the van der Waals material NiI2. Despite the importance for improper ferroelectricity, the microscopic mechanism of the helimagnetic order remains poorly understood. Here, the magneto-structural phases of NiI2 are investigated using resonant magnetic X-ray scattering (RXS) and X-ray diffraction. Two competing magnetic phases are identified. Below 60 K, an incommensurate magnetic reflection (q≈[0.143,0,1.49] reciprocal lattice units) is observed which exhibits finite circular dichroism in RXS, signaling the inversion symmetry-breaking helimagnetic ground state. At elevated temperature, in the non-polar phase (60 K<T<75 K), a distinct q≈[0.087,0.087,1.5] magnetic order is observed, attributed to a collinear incommensurate (CI) state. The first-order CI-helix transition is concomitant with a structural transition characterized by a significant interlayer shear, which drives the helimagnetic ground state as evidenced by a mean-field Heisenberg model including interlayer exchange and its coupling to the structural distortion. These findings identify interlayer magneto-structural coupling as the key driver behind multiferroicity in NiI2.

Proximity-induced flipped spin state in synthetic ferrimagnetic Pt/Co/Gd heterolayers

To develop new devices based on synthetic ferrimagnetic heterostructures, understanding the material’s physical properties is pivotal. Here, the induced magnetic moment (IMM), magnetic exchange coupling, and spin textures are investigated in Pt(1 nm)/Co(1.5 nm)/Gd(1 nm) multilayers using a multiscale approach. The magnitude and direction of the IMM are interpreted in the framework of both X-ray magnetic circular dichroism and density functional theory. The IMM transferred by Co across the Gd paramagnetic thickness leads to a nontrivial flipped spin state (FSS) within the Gd layers, in which their magnetic moments couple antiparallel/parallel with the ferromagnetic Co near/far from the Co/Gd interface, respectively. The FSS depends on the magnetic field, which, on average, reduces the Gd magnetic moment as the field increases. For the Pt, in both Pt/Co and Gd/Pt interfaces, the IMM follows the same direction as the Co magnetic moment, with negligible IMM in the Gd/Pt interface. Additionally, zero-field spin spirals were imaged using scanning transmission X-ray microscopy, whereas micromagnetic simulations were employed to unfold the interactions, stabilizing the ferrimagnetic configurations, where the existence of a sizable Dzyaloshinskii-Moriya interaction is demonstrated to be crucial.

High-Coercivity Ferrimagnet Co₂FeO₂BO₃: XMCD Insights into Charge-Ordering and Cation Distribution

The multi-sublattice ferrimagnet Co2FeO2BO3, a prominent example of lanthanide-free magnets, was the subject of element-selective studies using X-ray magnetic circular dichroism (XMCD) observations at the L- and K- X-ray absorption edges. Research findings indicate that the distinct magnetic characteristics of Co2FeO2BO3, namely its remarkable high coercivity (which surpasses 7 Tesla at low temperatures), originate from an atypical arrangement of magnetic ions in the crystal structure (sp.gr. Pbam). The antiferromagnetic nature of the Co2+-O-Fe3+ exchange interaction was confirmed by identifying the spin and orbital contributions to the total magnetization from Co (mL = 0.27 ± 0.1 μB/ion and meffS = 0.53 ± 0.1 μB/ion) and Fe (mL = 0.05 ± 0.1 μB/ion and meffS = 0.80 ± 0.1 μB/ion) ions through element-selective XMCD analysis. Additionally, the research explicitly revealed that the strong magnetic anisotropy is a result of the significant unquenched orbital magnetic moment of Co, a feature that is also present in the related compound Co3O2BO3. A complex magnetic structure in Co2FeO2BO3, with infinite Co²⁺O6 layers in the bc-plane and strong antiferromagnetic coupling through Fe3⁺ ions, is suggested by element-selective hysteresis data, which revealed that Co²⁺ ions contribute both antiferromagnetic and ferromagnetic components to the total magnetization. The findings underline the suitability of Co2FeO2BO3 for applications in extreme environments, such as low temperatures and high magnetic fields, where its unique magnetic topology and anisotropy can be harnessed for advanced technologies, including materials for space exploration and quantum devices. This XMCD study opens the door to the production of novel high-coercivity, lanthanide-free magnetic materials by showing that targeted substitution at specific crystallographic sites can significantly enhance the magnetic properties of such materials.

Antimicrobial Potential of Secalonic Acids from Arctic-Derived Penicillium chrysogenum INA 01369

In this study, two compounds have been isolated from the Arctic-derived fungus Penicillium chrysogenum INA 13460. Structural elucidation, performed using 2D NMR and HR-ESIMS data, has identified the compounds as stereoisomers of secalonic acids, dimeric tetrahydroxanthones. The absolute configurations of these stereoisomers have been determined through conformational NMR analysis and circular dichroism spectroscopy. The antimicrobial activity of secalonic acids D and F has been evaluated against a diverse range of microorganisms, including Gram-positive multidrug-resistant Staphylococcus aureus, Gram-negative Escherichia coli ATCC 25922, Pseudomonas aeruginosa ATCC 27853, the phytopathogen Pectobacterium carotovorum VKM-B1247, and the fungi Fusarium oxysporum VKPM F 890, Aspergillus fumigatus VKM F-37, and A. niger ATCC 16404. Genomic and chemical analyses further support P. chrysogenum INA 13460 as a promising natural source for antimicrobial drug discovery and biological control applications.

The Influence of the Supporting Substrate on Single‐Particle Circular Differential Scattering of DNA Assembled Nanorod Dimers

AbstractSingle‐particle measurements of chiral nanostructures have the potential to offer more detailed insights compared to the ensemble‐averaged signals obtained in ensemble circular dichroism spectroscopy. For instance, single‐particle circular differential scattering (CDS) studies have revealed the effects of structural heterogeneity in chiral plasmonic nanostructures. However, differential light‐matter interactions of 3D chiral nanostructures caused by diverse orientations on the supporting substrate remain largely unexplored. Here, the CDS of DNA origami‐templated twisted gold nanorod (AuNR) dimers on a glass support is investigated. With the help of correlated scanning electron microscopy and electromagnetic simulations, it is demonstrated how the broad diversity of spectral lineshapes and signal intensities as well as sign of the CDS originates mainly from four different orientations of the chiral dimer once deposited from solution on the substrate and dried. Most surprisingly, it is found that even for the same enantiomer a sign reversal is possible depending solely on the dimer orientation when deposited on the support. These results are important for the correct interpretation of single‐particle chiroptical studies and furthermore provide valuable insights into the design of substrate‐supported chiral plasmonic metamaterials.

Flavonoids and Kavalactones Isolated from Seeds of Alpinia katsumadai Hayata. and Their Cytotoxic Activities.

An unrevealed dihydroflavone-monoterpene conjugate (1), two unrevealed kavalactones (2-3, including one with an uncommon side chain), and thirteen previously identified compounds (4-16) were extracted from Alpinia katsumadai Hayata. seeds. The two-dimension structures of the new compounds were authenticated utilizing HRESIMS as well as NMR spectral analysis, while their absolute chiral configurations were ascertained either by correlating the experimental and simulated values of electronic circular dichroism (ECD) patterns or conducting X-ray diffraction experiments. Compounds 2-5, 9, 11, and 14 were assessed for their capacity to impede the growth of cancer cells of A549, HepG2, SGC7901, and SW480 using the MTT assay. Compounds 3 and 4 demonstrated antiproliferative activity with IC50 ranges of 3.94-21.78 μM, whereas the other compounds exhibited no significant cytotoxicity.

Investigation of magnetic properties in Y3Fe5O12/Cr2O3/Pt tri-layers

Abstract Artificial multiferroics combining ferroelectric and magnetic materials exhibits a sizable magnetoelectric coupling and further shows a great potential for realizing low power consumption information processing. In this work, hybrid structures consisting of the ferrimagnetic yttrium iron garnet (Y3Fe5O12, (YIG)) layer and anti-ferromagnetic chromium oxide (Cr2O3) layer are deposited directly onto (110)-oriented single-crystal Pb(Mg1/3Nb2/3)0.7Ti0.3O3 (PMN-PT) ferroelectric substrates by means of radio frequency magnetron sputtering and post-annealing procedures. The dynamical properties of YIG films are investigated via ferromagnetic resonance measurements and a low damping constant of 0.00258 is obtained. Combining the element-specific soft x-ray absorption spectroscopy, x-ray magnetic circular dichroism and x-ray magnetic linear dichroism, the magnetic order in YIG film and the Néel order in Cr2O3 layers are further characterized. By capping a platinum (Pt) layer on PMN-PT/YIG/Cr2O3, a visible spin-charge converted signal has been obtained via both spin pumping and spin Seebeck measurements. These results indicate that the artificial multiferroic structures PMN-PT/YIG/Cr2O3/Pt serve as a promising material platform for realizing an efficient manipulation of magnetism via electrical means.

The Effect of Lipids on the Structure and Function of Egg Proteins in Response to Pasteurization

In recent years, the consumption of liquid eggs has failed to meet the expectations of the public due to growing concerns regarding food safety and health. It is well known that there are interactions between the components in liquid eggs, and the interaction effect on the structure and functional properties of the proteins and antigenicity remains unclear. To investigate egg component interactions, we focused on four major egg lipids, namely phosphatidylcholine, palmitic acid, oleic acid, and linoleic acid, as well as four major egg proteins, including ovalbumin, ovotransferrin, ovomucoid, and lysozyme. The protein structural changes were analyzed using polypropylene gel electrophoresis, circular dichroism, ultraviolet absorption spectra, and exogenous fluorescence spectra, and the functional properties were assessed through solubility measurements and particle size analysis, while protein antigenicity was evaluated using an enzyme-linked immunosorbent assay. All the results revealed that oleic acid had the most significant effect on proteins’ secondary and tertiary structures, particularly affecting ovalbumin and ovotransferrin. Linoleic acid substantially increased the solubility of ovalbumin and ovomucoid, while palmitic acid significantly influenced the particle size of ovalbumin and lysozyme. Thus, we found that different lipids exhibit distinct effects on egg protein properties during pasteurization conditions, with oleic acid showing the most substantial impact on protein structure and antigenicity.

RuIII-Morpholine-Derived Thiosemicarbazone-Based Metallodrugs: Lysosome-Targeted Anticancer Agents.

The idea of coordinating biologically active ligand systems to metal centers to exploit their synergistic effects has gained momentum. Therefore, in this report, three RuIII complexes 1-3 of morpholine-derived thiosemicarbazone ligands have been prepared and characterized by spectroscopy and HRMS along with the structure of 2 through a single-crystal X-ray diffraction study. The solution stability of 1-3 was tested using conventional techniques such as UV-vis and HRMS. Further, the anticancer activity of 1-3 was tested in HT-29 and HeLa cancer cell lines. To gain insight into their mechanism of action, the cytotoxicity, hydrophobicity, and the interaction of 1-3 with DNA and HSA were evaluated by different conventional methods such as absorption, fluorescence, and circular dichroism studies. Along with favorable biomolecule interaction, 1-3 revealed potent selectivity toward cancer cells, which is a prerequisite for the generation of an anticancer drug. According to cell viability results, 1 has the highest cytotoxicity among all in the group, against both cells, respectively. Additionally, the fluorescence-active ruthenium complexes selectively target lysosomes, which is evaluated by live-cell imaging. 1-3 disrupt the lysosome membrane potential by generating an excessive amount of reactive oxygen species, which results in an apoptotic mode of cell death.

Bioactive Steroids with Structural Diversity from the South China Sea Soft Coral Lobophytum sp. and Sponge Xestospongia sp.

A chemical investigation of the soft coral Lobophytum sp. and the sponge Xestospongia sp. from the South China Sea led to the isolation of five steroids, including two new compounds (1 and 4) and one known natural product (3). Compounds 1–3 were derived from the soft coral Lobophytum sp., while 4 and 5 were obtained from the sponge Xestospongia sp. The structures of these compounds were determined by extensive spectroscopic analysis, the time-dependent density functional theory–electronic circular dichroism (TDDFT-ECD) calculation method, and comparison with the spectral data previously reported in the literature. The antibacterial and anti-inflammatory activities of isolated compounds were evaluated in vitro. Compounds 1–3, 4, and 5 exhibited weak antibacterial activity against vancomycin-resistant Enterococcus faecium G1, Streptococcus parauberis KSP28, Photobacterium damselae FP2244, Lactococcus garvieae FP5245, and Pseudomonas aeruginosa ZJ028. Moreover, compound 3 showed significant anti-inflammatory activity by inhibiting lipopolysaccharide (LPS)-induced NO production in RAW 264.7 cells, with an IC50 value of 13.48 μM.

Current-induced circular dichroism on metallic surfaces: A first-principles study

Current-induced circular dichroism on metallic surfaces: A first-principles study

Dramatical enhancement of circular dichroism in chiral hybrid perovskites via carboxylic hydrogen bond engineering

Dramatical enhancement of circular dichroism in chiral hybrid perovskites via carboxylic hydrogen bond engineering