Search Results (95)

A novel ocellatin-P1 isoform was isolated and purified from the skin secretion of the pepper frog Leptodactylus labyrinthicus. The crude skin secretion was fractionated by reversed-phase high-performance liquid chromatography (RP-HPLC) using a C₈ column and the peptide was subsequently purified on a reversed-phase C₁₈ column. Ocellatin-LB3 (as this isoform was named) was chemically sequenced by Edman degradation. This peptide is a linear C-terminally amidated molecule composed of 25 amino acid residues: ¹GLLDTLKGAAKNVVGGLASKVMEKL²⁵-NH₂. Synthetic ocellatin-LB3 was active against Escherichia coli, Klebsiella pneumoniae and Pseudomonas aeruginosa and inactive against Staphylococcus aureus, Staphylococcus epidermidis and Enterococcus faecalis. In addition, the peptide reduced the Trypanosoma cruzi infection in L6 cells. At 64 µM it did not reduce erythrocytes or polymorphonuclear leukocytes, but did reduce mononuclear leukocyte counts, as detected by flow cytometry. No hemolytic activity was observed in red blood cells even at 128 µM. The peptide exhibited limited antiproliferative activity against MCF-7 and HeLa tumor cells at 128 µM. Pre-incubation with the peptide appeared to enhance N-formylmethionine-leucyl-phenylalanine (fMLP)-induced migration, indicating a potential additive or synergistic effect on human neutrophils. The three-dimensional structure of ocellatin-LB3 was investigated by circular dichroism (CD) and nuclear magnetic resonance (NMR). In the presence of sodium dodecyl sulfate (SDS), the peptide adopts an α-helical structure spanning residues Leu³–Lys²⁴, which remains largely preserved even at 95 °C. NMR Hydrogen/Deuterium (H/D) exchange experiments suggest that ocellatin-LB3 adopts a preferential orientation when interacting with SDS micelles. Based on the similarity among ocellatins, and on the physicochemical and structural properties of this peptide, a possible membrane-mediated mode of action is proposed, although this remains to be experimentally validated. Full article

Short linear maltodextrin (SLMD) mixtures, which are modified from starch, comprise approximately 10 linear glucose molecules. In this study, we explored the noncovalent molecular association of SLMD with ferulic acid (FA) in aqueous and solid systems, as well as its applicability to water-in-oil (W/O) emulsion systems. Results showed that SLMD interacts with FA at a 1:1 molar ratio with an average equilibrium constant of 13.3 M⁻¹ in pure water. Changes in ellipticity in the involved circular dichroism absorption spectrum and nuclear magnetic resonance spectroscopy revealed that multipoint direct interactions exist between SLMD and FA suggesting complex formation through inclusion. Complexation does not impede the radical scavenging ability of FA; instead, there is an additive effect with a slight contribution from SLMD. SLMD crystals with a high FA content were obtained for B-type amylose. However, no strong interaction between the solid forms of SLMD and FA was recognized. For both SLMD aq. and W/O emulsions with different FA concentrations, the UV protection effect increased due to the solubility enhancement of FA by SLMD. Overall, this study demonstrates the ability and potential importance of SLMD to associate with functional components in water and solid systems and the applicability to emulsified systems. Full article

Background: The Fc region of immunoglobulin G (IgG) is a key target in therapeutic and analytical applications, such as antibody purification and site-specific bioconjugation. Although Protein A exhibits strong Fc-binding affinity, its large molecular weight and limited chemical flexibility pose challenges for use in compact or chemically defined systems. To address these limitations, we designed two α-helical peptides, SpA h1 and SpA h2, based on the Fc-binding helices of the Z34C domain from Staphylococcus aureus Protein A. Method: To enhance the structural stability and Fc-binding capability of these peptides, a lactam-based stapling strategy was employed by introducing lysine and glutamic acid residues at positions i and i + 4. Result: The resulting stapled peptides, (s)SpA h1 and (s)SpA h2, exhibited significantly improved α-helical content and IgG-binding performance, as demonstrated by circular dichroism (CD) spectroscopy and fluorescence-based IgG capture assays. Surface plasmon resonance (SPR) analysis confirmed specific, concentration-dependent interactions with the Fc region of human IgG, with (s)SpA h1 consistently showing the binding affinity and stability. Proteolytic resistance assays using α-chymotrypsin revealed that (s)SpA h1 maintained its structural integrity over time, exhibiting markedly enhanced resistance to enzymatic degradation compared to its linear counterpart. Furthermore, (s)SpA h1 exhibited strong Fc selectivity with minimal Fab affinity, confirming its suitability as a compact and Fc-specific binding ligand. Conclusions: These results confirm the successful design and development of structurally reinforced Fc-binding peptides that overcome the inherent limitations of short linear sequences through both high-affinity sequence optimization and lactam-based stapling. Among them, (s)SpA h1 demonstrates the most promising characteristics as a compact yet stable Fc-binding ligand, suitable for applications such as antibody purification and site-specific bioconjugation. Full article

The performance of synchrotron beamlines critically depends on the optimal coupling between the undulator and the monochromator. This work presents the implementation and quantitative characterization of a synchronized scanning system for the elliptically polarizing undulator (EPU) and the variable-line-spacing plane-grating monochromator at the BL07U beamline of the Shanghai Synchrotron Radiation Facility (SSRF). The system ensures that the monochromator’s narrow bandwidth dynamically tracks the brilliant central cone of the undulator radiation. A linear correlation between the monochromator energy and the undulator gap, justified theoretically for small scan ranges and reinforced by a robust real-time calibration procedure, forms the control basis. The automation is built upon a standard software stack comprising EPICS for device control, the Bluesky Suite for experimental orchestration, and Phoebus for the human–machine interface. Through comparative X-ray absorption spectroscopy (XAS) measurements at the Fe L_2,3-edges, the synchronized mode is shown to enhance beam brilliance by 37% and stabilize the incident flux, reducing its variation from 4.2% to 1.8%. This directly results in absorption spectra with superior lineshape fidelity, a 40% reduction in noise, and the elimination of pre- and post-edge artifacts, unequivocally isolating the synchronization effect. This advancement provides a stable, high-brilliance photon source essential for high-quality XAS and X-ray magnetic circular/linear dichroism (XMCD/XMLD) studies. Full article

Background: Polybasic peptides are being developed as components of reagents for diagnosing and treating patients with systemic amyloidosis. In addition to fibrils, amyloid deposits ubiquitously contain heparan sulfate proteoglycans. We have hypothesized that pan amyloid-targeting peptides can specifically engage, in addition to fibrils, a subset of glycosaminoglycans (GAGs) with high negative charge density. In this study, we characterized the binding of peptides p5+14 (a PET imaging agent for amyloid [¹²⁴I-evuzamitide]) and p5R (a fusion protein used in the therapeutic AT-02) to GAGs. Methods: The peptide structure was evaluated in the presence of low molecular weight heparin using circular dichroism, and their interaction with synthetic GAGs of varying length and charge was interrogated. The binding patterns of p5+14 and p5R were compared using correlation analyses. Results: The peptides exist as mixed structural-fractions in solution but adopt an α-helical structure in the presence of heparin. Both peptides preferentially recognize heparin and heparan sulfate GAGs with a linear positive correlation between binding and the total charge and charge density. Conclusions: These peptides have previously been shown to specifically target amyloid deposits in vivo. A component of this specificity is their preferential interaction with a subset of heparan sulfate GAGs that have high charge density, potentially related to the degree of 6-O-sulfation. These data support the hypotheses that amyloid-associated GAGs have unique sulfation patterns, thereby explaining why these peptides do not bind GAGs found on the plasma membrane and extracellular matrix of healthy tissues. Full article

A novel and general approach to the practical ROMP polymerization of cinchona alkaloid derivatives providing novel hybrid materials having quinine attached on a poly(norbornene-5,6-dicarboxyimide) matrix is presented. The concept involves an easy modification of quinine (in general, any cinchona alkaloid) toward clickable 9-azide that reacts with N-propargyl-cis-5-norbornene-exo-2,3-dicarboxylic imide in Cu(I)-catalyzed Huisgen cycloaddition (click chemistry). The resulting monomers undergo a controllable ROMP reaction that leads to novel polymers of a desired length and solubility. This sequence allows for the facile preparation of a regularly decorated polymeric material having one quinine moiety per single mer of the polymer chain inaccessible using typical immobilization methods. A poly(norbornene-5,6-dicarboxyimide) type of polymeric matrix was selected due to the high reactivity of the exo-norbornene motif in Ru(II)-catalyzed ROMP and its chemical and thermal stability as well as convenient, scalable access from inexpensive cis-5-norbornene-exo-2,3-dicarboxylic anhydride (‘one-pot’ Diels–Alder reaction of dicyclopentadiene and maleic anhydride). An appropriate combination of a Grubbs catalyst, Ru(II) (G1, G2), and ROMP conditions allowed for the efficient synthesis of well-defined soluble polymers with mass parameters in the range Mn = 2.24 × 10⁴ – 2.26 × 10⁴ g/mol and Mw = 2.90 × 10⁴–3.05 × 10⁴ g/mol with good polydispersity, Đ_M = 1.32–1.35, and excellent thermal stability (up to 309°C T_d10). Spectroscopic studies (NMR and electronic circular dichroism (ECD)) of these products revealed a linear structure with the slight advantage of a trans-configuration of an olefinic double bond. The resulting short-chain polymer discriminates mandelic acid enantiomers with a preference for the (R)-stereoisomer in spectrofluorimetric assays. This concept seems to be rather general with respect to other molecules dedicated to incorporation into the poly(norbornene-5,6-dicarboxyimide) chain. Full article

MicroRNA-155-3p (miR-155-3p) is an important biomarker in various pathological conditions, including cancer, making the development of sensitive and specific detection methods crucial. Here, we present a molecular beacon (MB-G4) that underwent a conformational switch upon hybridization with miR-155-3p, enabling the formation of a G-quadruplex (G4) structure. This G4 was recognized by the fluorogenic ligand N-methyl mesoporphyrin IX (NMM), producing a fluorescence signal proportional to the target concentration, making it a new detection method. The conformational dynamics of MB-G4 were characterized through circular dichroism (CD) spectroscopy and native polyacrylamide gel electrophoresis (PAGE), confirming the transition from a hairpin structure to an RNA–DNA hybrid duplex that facilitated G4 formation. The optimization of the experimental conditions, including the potassium chloride (KCl) and NMM concentrations, ensured selective detection with minimal background signal. The detection limit (LOD) was determined to be 10.85 nM, using a linear fluorescence response curve, and the specificity studies demonstrated a clear distinction between miR-155-3p and miR-155-5p. Furthermore, MB-G4 was studied with total RNA extracted from the lung cancer cell line A549 to evaluate its detection in a more complex environment and was able to detect its target, validating its potential for biological sample analysis. Full article

Electropolymerization is a convenient way to obtain conducting polymers (CPs) directly adhered to an electrode surface. CPs are well-known for their various application fields in photovoltaic cells, chemical sensors, and electronics. By implementing chirality into a CP, the application possibilities will spread further onto chiral sensors or optoelectronics. In this work, we introduce a new inherently chiral polymer based on a macrocyclic 3,4-ethylenedioxythiophene-diketopyrrolopyrrole-3,4-ethylenedioxythiophene triad (EDOT-DPP-EDOT) fused by 1,4-phenylene groups, which was prepared via oxidative electropolymerization directly on the electrode surface. The investigation of the chiroptical properties was performed by circular dichroism spectroscopy in the solid state. The enantiomeric pure polymer films obtained showed dissymmetry factors of up to −2.71 × 10⁻⁴, whereby linear dichroism contributions can be widely excluded. Full article

A new technology to write and read covert information in authentication labels is described. This technology uses the phenomenon of photo-induced chirality in Ge₂Sb₂Te₅ thin films to encode the left- or right-circular or linear polarization of the laser beam used to write the label. The written polarization can be revealed by a simple reading device, which is demonstrated to provide the same qualitative information as reading based on cyclotron circular dichroism spectroscopy and imaging. The suggested method, while based on existing manufacturing approaches, offers a balance between technological complexity for writing and simplicity for reading, and may be advantageous as a new authentication technology. Full article

We present a method of laser frequency stabilization based on the linear dichroism signal in a transverse magnetic field. This method is similar to the DAVLL (Dichroic Atomic Vapor Laser Lock) method. It differs from DAVLL and from its existing modifications primarily by the fact that it uses signals of linearly polarized light caused by alignment, rather than circular refraction caused by orientation, and therefore allows us to obtain error signals at the magnetic field modulation frequency (or its second harmonic) by extremely simple means. The method allows the laser frequency to be stabilized in the vicinity of the low-frequency transition in the D1 line of Cs; it does not require strong magnetic fields or careful shielding of cells containing cesium atoms. Although the absorption line in a gas-filled cell is typically gigahertz wide, the achievable resolution, limited by the signal-to-noise ratio of photon shot noise, can reach units or tens of kilohertz in a one hertz bandwidth. Full article

Ultrathin titanium nitride (TiN) is a novel material platform for constructing active metasurfaces in the near-infrared region (NIR). Here, we realized tunable polarization-selective absorption by gating ultrathin TiN in an Ultrathin TiN Grating Metasurface (UTGM) and a gold resonator/TiN film Hybrid Metasurface (GTHM), respectively. The TM wave absorption (0.96) was much larger than that of the TE wave in the UTGM. When the carrier density decreased by 12%, the near-perfect TM absorption peak blue-shifted by 0.3 μm. Similarly, the linear dichroism (0.96) peak in GTHM blue-shifted by 0.12 μm when gating ultrathin TiN film. Active metasurfaces with tunable polarization-selective absorption have huge potential in dynamic integrated electro-optic devices in NIR. Full article

The effect of resveratrol (RESV) on α-lactalbumin (α-LA) thermal stability was evaluated using differential scanning calorimetry (DSC), circular dichroism (CD) and dynamic light scattering (DLS) measurements. Complementary information offered by molecular docking served to identify the binding site of the ligand on the native structure of protein and the type of interacting forces. DSC thermograms revealed a double-endotherm pattern with partial overlapping of the two components. The most relevant effect of RESV is manifested in the narrowing of the protein thermal fingerprint: the first process (peak temperature T₁) is shifted to higher temperatures while the second one (peak temperature T₂) to lower values. The CD data indicated partial conformational changes in the protein non-α-helix domain at T₁, resulting in a β-sheet richer intermediate (BSRI) with an unaffected, native-like α-helix backbone. The RESV influence on this process may be defined as slightly demoting, at least within DSC conditions (linear heating rate of 1 K min⁻¹). On further heating, unfolding of the α-helix domain takes place at T₂, with RESV acting as a promoter of the process. Long time incubation at 333 K produced the same type of BSRI: no significant effect of RESV on the secondary structure content was detected by CD spectroscopy. Nevertheless, the size distribution of the protein population obtained from DLS measurements revealed the free (non-bound) RESV action manifested in the developing of larger size aggregates. Full article

Following changes in chirality can give access to relevant information on the function or reactivity of molecular systems. Time-resolved circular dichroism (TRCD) spectroscopy proves to be a valid tool to achieve this goal. Depending on the class of molecules, different temporal ranges, spanning from seconds to femtoseconds, need to be investigated to observe such chiroptical changes. Therefore, over the years, several approaches have been adopted to cover the timescale of interest, especially based on pump–probe schemes. Moreover, various theoretical approaches have been proposed to simulate and explain TRCD spectra, including linear and non-linear response methods as well as non-adiabatic molecular dynamics. In this review, an overview on both experimental and theoretical advances in the TRCD field is provided, together with selected applications. A discussion on future theoretical developments for TRCD is also given. Full article

Recently, a technical modification of a Reflectance Anisotropy Spectroscopy (RAS) spectrometer has been proposed to investigate the circular dichroism (CD) of samples instead of the normally studied linear dichroism. CD-RAS measures the anisotropy of the optical properties of a sample under right-handed and left-handed circularly polarized light. Here, we present the application of CD-RAS to measure the circular dichroism of a twisted bilayer of graphene, purposely prepared as a possible substrate for the adsorption of thin molecular layers, in air, in liquid or in a vacuum. This result demonstrates the performance of the apparatus and shows interesting perspectives for the investigation of chiral organic assemblies deposited in solid film. Full article

We propose and analyze numerically new approaches to force the laser emission from VCSELs in a well-defined linear polarization independent of the existing phase and amplitude anisotropies by using dielectric columnar thin-film (CTF) layers in the distributed Bragg reflector (DBR). In one approach, we have demonstrated CTF-VCSELs with top DBR consisting of two alternating CTF layers grown in orthogonally oriented planes and with high and low refractive index for one linear polarization while having the same value of the refractive index value for the orthogonal linear polarization. Such CTF-VCSELs have large dichroism of the mirror losses for two orthogonal linear polarizations. We have also shown DBR designs with parallel columnar orientations of the two CTF dielectric materials. In a second approach, we implement only one CTF layer in the dielectric DBR chosen in such a way that only one linearly polarized longitudinal mode is resonant in the CTF-VCSEL while light with the orthogonally oriented linear polarization is out of resonance and thus cannot lase. Simple estimation of the polarization mode suppression ratio for the different exemplary designs of CTF-VCSELs based on $Ti{O}_2$ and $Ta{O}_2$ dielectric CTFs results in values as high as 80 dB, which compares favorably to the existing alternative approaches. Full article