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Search Results (603)

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Keywords = circular dichroism (CD)

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20 pages, 3157 KiB  
Article
Enhancement of Foaming Performance of Oat Globulin by Limited Enzymatic Hydrolysis: A Study from the Viewpoint of the Structural and Functional Properties
by Yahui Zhu, Junlong Zhang, Xuedong Gu, Pengjie Wang, Yang Liu, Yingze Jiao, Lin Yang and Han Chen
Gels 2025, 11(8), 615; https://doi.org/10.3390/gels11080615 - 6 Aug 2025
Abstract
This study identified the optimal enzymatic treatment for improving the foaming characteristics of oat globulin, and alkaline protease was found to be the most effective enzyme. The impact of alkaline protease on the foaming properties and structural changes in oat globulin was explored. [...] Read more.
This study identified the optimal enzymatic treatment for improving the foaming characteristics of oat globulin, and alkaline protease was found to be the most effective enzyme. The impact of alkaline protease on the foaming properties and structural changes in oat globulin was explored. The results show that the foaming capacity of oat globulin hydrolysates is negatively correlated with surface hydrophobicity and positively correlated with the degree of hydrolysis. The results of circular dichroism (CD) and size-exclusion chromatography (SEC) indicate that hydrolysis generated smaller, disordered peptides. Under equilibrium conditions at a 2% concentration, a reduction of 1.62 mN/m in surface tension and an increase of 3.82 μm in foam film thickness were observed. These peptides reduce surface tension between air and water, forming larger, thicker, and more stable foams. Compared to untreated oat globulin, the foaming capacity of hydrolyzed ones increased by 87.17%. Under comparable conditions, these findings demonstrate that limited hydrolyzed oat globulin exhibits potential as an effective plant-based foaming agent up to a degree of hydrolysis of 15.06%. Full article
(This article belongs to the Special Issue Gels for Plant-Based Food Applications (2nd Edition))
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25 pages, 2451 KiB  
Article
Complexation and Thermal Stabilization of Protein–Polyelectrolyte Systems via Experiments and Molecular Simulations: The Poly(acrylic acid)/Lysozyme Case
by Sokratis N. Tegopoulos, Sisem Ektirici, Vagelis Harmandaris, Apostolos Kyritsis, Anastassia N. Rissanou and Aristeidis Papagiannopoulos
Polymers 2025, 17(15), 2125; https://doi.org/10.3390/polym17152125 - 1 Aug 2025
Viewed by 346
Abstract
Protein–polyelectrolyte nanostructures assembled via electrostatic interactions offer versatile applications in biomedicine, tissue engineering, and food science. However, several open questions remain regarding their intermolecular interactions and the influence of external conditions—such as temperature and pH—on their assembly, stability, and responsiveness. This study explores [...] Read more.
Protein–polyelectrolyte nanostructures assembled via electrostatic interactions offer versatile applications in biomedicine, tissue engineering, and food science. However, several open questions remain regarding their intermolecular interactions and the influence of external conditions—such as temperature and pH—on their assembly, stability, and responsiveness. This study explores the formation and stability of networks between poly(acrylic acid) (PAA) and lysozyme (LYZ) at the nanoscale upon thermal treatment, using a combination of experimental and simulation measures. Experimental techniques of static and dynamic light scattering (SLS and DLS), Fourier transform infrared spectroscopy (FTIR), and circular dichroism (CD) are combined with all-atom molecular dynamics simulations. Model systems consisting of multiple PAA and LYZ molecules explore collective assembly and complexation in aqueous solution. Experimental results indicate that electrostatic complexation occurs between PAA and LYZ at pH values below LYZ’s isoelectric point. This leads to the formation of nanoparticles (NPs) with radii ranging from 100 to 200 nm, most pronounced at a PAA/LYZ mass ratio of 0.1. These complexes disassemble at pH 12, where both LYZ and PAA are negatively charged. However, when complexes are thermally treated (TT), they remain stable, which is consistent with earlier findings. Atomistic simulations demonstrate that thermal treatment induces partially reversible structural changes, revealing key microscopic features involved in the stabilization of the formed network. Although electrostatic interactions dominate under all pH and temperature conditions, thermally induced conformational changes reorganize the binding pattern, resulting in an increased number of contacts between LYZ and PAA upon thermal treatment. The altered hydration associated with conformational rearrangements emerges as a key contributor to the stability of the thermally treated complexes, particularly under conditions of strong electrostatic repulsion at pH 12. Moreover, enhanced polymer chain associations within the network are observed, which play a crucial role in complex stabilization. These insights contribute to the rational design of protein–polyelectrolyte materials, revealing the origins of association under thermally induced structural rearrangements. Full article
(This article belongs to the Section Polymer Physics and Theory)
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12 pages, 2346 KiB  
Article
SERS and Chiral Properties of Cinnamic Acid Derivative Langmuir-Blodgett Films Complexed with Dyes
by Xingdi Zhao, Xinyu Li, Pengfei Bian, Qingrui Zhang, Yuqing Qiao, Mingli Wang and Tifeng Jiao
Coatings 2025, 15(8), 890; https://doi.org/10.3390/coatings15080890 (registering DOI) - 1 Aug 2025
Viewed by 178
Abstract
Chiral molecules are crucial in the field of optical devices, molecular recognition, and other novel functional materials due to their unique spatially asymmetric configuration and optical activity. In this study, a chiral molecule, Cholest-3-yl (E)-3-(4-carbamoylphenyl)acrylate (CCA), was combined with dyes containing large conjugated [...] Read more.
Chiral molecules are crucial in the field of optical devices, molecular recognition, and other novel functional materials due to their unique spatially asymmetric configuration and optical activity. In this study, a chiral molecule, Cholest-3-yl (E)-3-(4-carbamoylphenyl)acrylate (CCA), was combined with dyes containing large conjugated structures, tetramethylporphyrin tetrasulfonic acid (TPPS), and Nickel(II) phthalocyanine-tetrasulfonic acid tetrasodium salt (TsNiPc), and composite LB films of CCA/TPPS and CCA/TsNiPc were successfully prepared by using Langmuir-Blodgett (LB) technology. The circular dichroism (CD) test proved that the CCA/TPPS composite film had a strong CD signal at 300–400 nm, and the composite film showed chirality. This significant optical activity provides a new idea and option for the application of LB films in chiral sensors. In the Surface Enhanced Raman Spectroscopy (SERS) test, the CCA/TPPS composite film was sensitive to signal sensing, in which the enhancement factor EF = 2.28 × 105, indicating that a large number of effective signal response regions were formed on the surface of the film, and the relative standard deviation (RSD) = 12.08%, which demonstrated that the film had excellent uniformity and reproducibility. The high sensitivity and low signal fluctuation make the CCA/TPPS composite LB film a promising SERS substrate material. Full article
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11 pages, 944 KiB  
Article
Amesilide, a New Bicyclic Polyketide from the Marine Fungus Amesia nigricolor MUT6601
by Giang Nam Pham, Matteo Florio Furno, Juan A. Garcia-Sanchez, Patrick Munro, Fatouma Mohamed Abdoul-Latif, Laurent Boyer, Giovanna Cristina Varese and Mohamed Mehiri
Molecules 2025, 30(15), 3169; https://doi.org/10.3390/molecules30153169 - 29 Jul 2025
Viewed by 268
Abstract
A new bicyclic polyketide, amesilide (1), along with the previously reported metabolites, chamisides A (2), B (3), and E (4), chaetoconvosins B (5) and C (6), and chaetochromins A (7 [...] Read more.
A new bicyclic polyketide, amesilide (1), along with the previously reported metabolites, chamisides A (2), B (3), and E (4), chaetoconvosins B (5) and C (6), and chaetochromins A (7) and B (8), were isolated from the marine fungus Amesia nigricolor MUT6601. The structures of the compounds were determined by extensive spectrometric (HRMS) and spectroscopic (1D and 2D NMR) analyses, as well as specific rotation. Absolute configurations of the stereogenic centers of amesilide (1) were determined by a comparison of its experimental circular dichroism (CD) spectrum with its time-dependent density functional theory (TD-DFT) electronic circular dichroism (ECD) spectra. Among them, chaetochromins A (7) and B (8) showed strong antibacterial activity against Staphylococcus aureus S25 (MBC values of 12.50 µM and MIC values of 6.25 µM) and a moderate cytotoxicity against monocytes (THP-1) and peripheral blood cells (PBMC) (IC50 values of 33.65–40.01 µM). Full article
(This article belongs to the Section Natural Products Chemistry)
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25 pages, 2181 KiB  
Article
Discovery of a Potent Antimicrobial Peptide Through Rational Design: A New Frontier in Pathogen Control
by Bruna Agrillo, Monica Ambrosio, Rosa Luisa Ambrosio, Marta Gogliettino, Marco Balestrieri, Alessandra Porritiello, Maria Francesca Peruzy, Andrea Mancusi, Luigi Nicolais and Gianna Palmieri
Biomolecules 2025, 15(7), 989; https://doi.org/10.3390/biom15070989 - 11 Jul 2025
Viewed by 477
Abstract
The increasing circulation of multi-drug-resistant pathogens, coupled with the sluggish development of new antibiotics, is weakening our capacity to combat human infections, resulting in elevated death tolls. To address this worldwide crisis, antimicrobial peptides (AMPs) are viewed as promising substitutes or adjuvants for [...] Read more.
The increasing circulation of multi-drug-resistant pathogens, coupled with the sluggish development of new antibiotics, is weakening our capacity to combat human infections, resulting in elevated death tolls. To address this worldwide crisis, antimicrobial peptides (AMPs) are viewed as promising substitutes or adjuvants for combating bacterial infections caused by multidrug-resistant organisms. Here, the antimicrobial activity and structural characterization of a novel 13-amino acid cationic peptide named RKW (RKWILKWLRTWKK-NH2), designed based on known AMPs sequences and the identification of a key tryptophan-rich structural motif, were described. RKW displayed a broad-spectrum and potent antimicrobial and antibiofilm activity against Gram-positive and Gram-negative pathogens, including ESKAPE bacteria and fungi with minimal inhibitory concentrations (MBC) ranging from 5 µM to 20 μM. Structural results by fluorescence and Circular Dichroism (CD) spectroscopy revealed that the peptide was folded into a regular α-helical conformation in a membrane-like environment, remaining stable in a wide range of pH and temperature for at least 48 h of incubation. Furthermore, RKW showed low toxicity in vitro against mammalian fibroblast cells, indicating its potential as a promising candidate for the development of new antimicrobial or antiseptic strategies. Full article
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17 pages, 8301 KiB  
Article
Composites of Pea Protein Nanofibril and Epigallocatechin Gallate: Formation Mechanism, Structural Characterization, and Antioxidant Activity
by Hailing Zhang, Yangxuan Yang, Yuting Fan and Jiang Yi
Foods 2025, 14(14), 2418; https://doi.org/10.3390/foods14142418 - 9 Jul 2025
Viewed by 316
Abstract
The EGCG/PPN composite, prepared by combining pea protein nanofibrils (PPNs) with epigallocatechin gallate (EGCG), could be used as a multifunctional nanocarrier. Compared to pea protein isolate (PPI), EGCG/PPN composites exhibited remarkably higher turbidity and zeta potential, along with similar UV spectra. Intrinsic fluorescence [...] Read more.
The EGCG/PPN composite, prepared by combining pea protein nanofibrils (PPNs) with epigallocatechin gallate (EGCG), could be used as a multifunctional nanocarrier. Compared to pea protein isolate (PPI), EGCG/PPN composites exhibited remarkably higher turbidity and zeta potential, along with similar UV spectra. Intrinsic fluorescence spectroscopy, ThT fluorescence spectroscopy, and surface hydrophobicity analysis suggested that the interactions between EGCG and PPN were primarily driven by hydrophobic forces. UV spectra indicated that the microenvironment of amino acid residues in the tertiary structure of the protein changes upon complexation, and circular dichroism (CD) revealed that the incorporation of EGCG increases the β-sheet content in the protein’s secondary structure. Analyses of DPPH and ABTS radical scavenging activity, as well as reducing power, demonstrated that the synergistic effect between EGCG and PPN did not hinder the inherent antioxidant properties of EGCG but rather enhanced them significantly. Transmission electron microscopy (TEM) images showed that the addition of EGCG reconstructed the fibril morphology, thereby affecting the properties of PPNs. Overall, the composite fabricated through the interaction between PPN and EGCG shows great potential as a nanocarrier in the processing of functional foods. Full article
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22 pages, 5743 KiB  
Article
The Synthesis, Characterization, and Biological Evaluation of a Fluorenyl-Methoxycarbonyl-Containing Thioxo-Triazole-Bearing Dipeptide: Antioxidant, Antimicrobial, and BSA/DNA Binding Studies for Potential Therapeutic Applications in ROS Scavenging and Drug Transport
by Lala Stepanyan, Tatevik Sargsyan, Valentina Mittova, Zurab R. Tsetskhladze, Nino Motsonelidze, Ekaterine Gorgoshidze, Niccolò Nova, Monika Israyelyan, Hayarpi Simonyan, Franco Bisceglie, Lusine Sahakyan, Karapet Ghazaryan and Giovanni N. Roviello
Biomolecules 2025, 15(7), 933; https://doi.org/10.3390/biom15070933 - 26 Jun 2025
Viewed by 1343
Abstract
We report on the synthesis and characterization of a novel fluorenyl-methoxycarbonyl (Fmoc)-containing thioxo-triazole-bearing dipeptide 5, evaluated for potential therapeutic applications. The compound was tested for its antioxidant and antimicrobial properties, demonstrating significant effects in scavenging reactive oxygen species (ROS) and inhibiting microbial [...] Read more.
We report on the synthesis and characterization of a novel fluorenyl-methoxycarbonyl (Fmoc)-containing thioxo-triazole-bearing dipeptide 5, evaluated for potential therapeutic applications. The compound was tested for its antioxidant and antimicrobial properties, demonstrating significant effects in scavenging reactive oxygen species (ROS) and inhibiting microbial growth, particularly when combined with plant extracts from an endemic Peonia species from the Caucasus. Circular dichroism (CD) binding studies with bovine serum albumin (BSA) and calf thymus DNA revealed important interactions, suggesting the dipeptide’s potential in biomedically relevant conditions that involve DNA modulation. Molecular docking and CD spectra deconvolution provided additional insights into the binding mechanisms and structural characteristics of the formed complexes with the biomolecular targets. The Fmoc group enhances the dipeptide’s lipophilicity, which may facilitate its interaction with cellular membranes, supporting efficient drug delivery. A computational evaluation at the ωB97XD/aug-cc-pVDZ level of theory was carried out, confirming the experimental results and revealing a powerful potential of the peptide as an antioxidant, through FMOs, MEP analysis, and antioxidant mechanism assessments. Together, these findings suggest that this dipeptide could be valuable as an antimicrobial and antioxidant agent, with potential applications in pathologies involving oxidative stress, DNA modulation, and microbial infections. Full article
(This article belongs to the Special Issue State of the Art and Perspectives in Antimicrobial Peptides)
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24 pages, 6370 KiB  
Article
Influence of Peptide Conjugation Sites on Lunatin–Alumina Nanoparticles: Implications for Membrane Interaction and Antimicrobial Activity
by Carolina Silva Ferreira, Lívia Mara Fontes Costa, Lúcio Otávio Nunes, Kelton Rodrigues de Souza, Giovanna Paula Araújo, Evgeniy S. Salnikov, Kelly Cristina Kato, Helen Rodrigues Martins, Adriano Monteiro de Castro Pimenta, Jarbas Magalhães Resende, Burkhard Bechinger and Rodrigo Moreira Verly
Pharmaceuticals 2025, 18(7), 952; https://doi.org/10.3390/ph18070952 - 24 Jun 2025
Viewed by 511
Abstract
Background/Objectives: The increasing prevalence of multidrug-resistant bacteria presents a major global health challenge, prompting a search for innovative antimicrobial strategies. This study aimed to develop and evaluate a novel nanobiostructure combining alumina nanoparticles (NPs) with the antimicrobial peptide lunatin-1 (Lun-1), forming peptide-functionalized nanofilaments. [...] Read more.
Background/Objectives: The increasing prevalence of multidrug-resistant bacteria presents a major global health challenge, prompting a search for innovative antimicrobial strategies. This study aimed to develop and evaluate a novel nanobiostructure combining alumina nanoparticles (NPs) with the antimicrobial peptide lunatin-1 (Lun-1), forming peptide-functionalized nanofilaments. The main objective was to investigate how the site of peptide functionalization (C-terminal vs. N-terminal) affects membrane interactions and antibacterial activity. Methods: NP–peptide conjugates were synthesized via covalent bonding between lun-1 and alumina NP and characterized using transmission electron microscopy (TEM), X-ray diffraction (XRD), zeta potential analysis, dynamic light scattering (DLS), Fourier-transform infrared (FTIR), and solid-state 13C NMR. Antibacterial activities were assessed against different Gram-positive and Gram-negative strains. Biophysical analyses, including circular dichroism (CD), isothermal titration calorimetry (ITC), differential scanning calorimetry (DSC), and solid-state 2H NMR, were employed to evaluate peptide–membrane interactions in the presence of membrane-mimetic vesicles composed of POPC:POPG (3:1) and DMPC:DMPG (3:1). Results: Characterization confirmed the successful formation of NP–peptide nanofilaments. Functionalization at the N-terminal significantly influenced both antibacterial activity and peptide conformation compared to C-terminal attachment. Biophysical data demonstrated stronger membrane interaction and greater membrane disruption when lun-1 was conjugated at the N-terminal. Conclusions: The site of peptide conjugation plays a crucial role in modulating the biological and biophysical properties of NP–lunatin-1 conjugates. C-terminal attachment of lunatin-1 retains both membrane interaction and antibacterial efficacy, making it a promising strategy for the design of peptide-based nanotherapeutics targeting resistant pathogens. Full article
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15 pages, 2608 KiB  
Article
Effect of Sugarcane Polyphenol Extract on α-Amylase Inhibition and Mechanism Exploration
by Yumei Wang, Jiulong An, Shenghong Yao, Chengfeng Zhang, Yanv Zhou, Lu Li and He Li
Foods 2025, 14(13), 2174; https://doi.org/10.3390/foods14132174 - 21 Jun 2025
Viewed by 473
Abstract
Although α-amylase is crucial for postprandial glucose control, existing inhibitors present various side effects, necessitating the exploration of natural alternatives. The ability of sugarcane polyphenol (SP) to inhibit α-amylase remains unclear. This study assessed the inhibitory activity of SP via in vitro assays, [...] Read more.
Although α-amylase is crucial for postprandial glucose control, existing inhibitors present various side effects, necessitating the exploration of natural alternatives. The ability of sugarcane polyphenol (SP) to inhibit α-amylase remains unclear. This study assessed the inhibitory activity of SP via in vitro assays, circular dichroism (CD), fluorescence quenching, and stability analysis, while the mechanism of action was elucidated using molecular docking and molecular dynamics (MD). The results showed that the IC50 of the SP was 0.841 ± 0.029 mg/mL, with proanthocyanidin-B1 (PC-B1) presenting the most potent effect (IC50 = 0.504 ± 0.019 mg/mL). CD and barycentric mean (BCM) analysis indicated that the complexes might limit substrate binding. The mechanistic assessment showed that the polyphenols bonded to the active enzyme pockets to form stable complexes with reduced key residue fluctuations. In conclusion, SP, especially PC-B1, effectively inhibited α-amylase activity via structural regulation and molecular interactions, providing a theoretical basis for developing natural hypoglycemic agents. Full article
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9 pages, 1292 KiB  
Article
Exploring the Feasibility of a Microchip Laser Ablation Method for the Preparation of Biopolymer-Stabilized Gold Nanoparticles: Case Studies with Gelatin and Collagen
by Nazgul Assan, Tomoyuki Suezawa, Yuta Uetake, Yumi Yakiyama, Michiya Matsusaki and Hidehiro Sakurai
Colloids Interfaces 2025, 9(4), 42; https://doi.org/10.3390/colloids9040042 - 20 Jun 2025
Cited by 1 | Viewed by 602
Abstract
Introducing small-sized metal nanoparticles directly into biopolymers susceptible to thermal and chemical stimulations remains a significant challenge. Recently, we showed a novel approach to fabricating gold nanoparticles through pulsed laser ablation in liquid (PLAL) using a microchip laser (MCL). Despite its lower pulse [...] Read more.
Introducing small-sized metal nanoparticles directly into biopolymers susceptible to thermal and chemical stimulations remains a significant challenge. Recently, we showed a novel approach to fabricating gold nanoparticles through pulsed laser ablation in liquid (PLAL) using a microchip laser (MCL). Despite its lower pulse energy compared to conventional lasers, this technique demonstrates high ablation efficiency, offering the potential to produce composites without compromising the distinctive structure of biopolymers. As a proof of concept, we successfully generated gelatin-stabilized gold nanoparticles with a smaller size (average diameter of approximately 4 nm), while preserving the unchanged circular dichroism (CD) spectra, indicating the retention of gelatin’s unique structure. Extending this technique to the preparation of type I collagen-stabilized gold nanoparticles yielded non-aggregated nanoparticles, although challenges in yield still persist. These results highlight the potential of the microchip laser ablation technique for producing metal nanoparticles within a vulnerable matrix. Full article
(This article belongs to the Special Issue State of the Art of Colloid and Interface Science in Asia)
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22 pages, 4202 KiB  
Article
Donkey-Hide Gelatin Peptide-Iron Complexes: Structural Characterization, Enhanced Iron Solubility Under Simulated Digestion, and Dual Iron Chelation-Antioxidant Functions
by Lili Yang, Chenyan Lv, Xingfeng Guo and Rong Liang
Foods 2025, 14(12), 2117; https://doi.org/10.3390/foods14122117 - 17 Jun 2025
Viewed by 632
Abstract
Iron deficiency is a global health issue, making the development of novel iron supplements to enhance iron absorption critically important. In this study, low molecular weight donkey-hide gelatin peptides (LMW DHGP) were enzymatically hydrolyzed from donkey-hide gelatin. Experimental results demonstrated that the iron [...] Read more.
Iron deficiency is a global health issue, making the development of novel iron supplements to enhance iron absorption critically important. In this study, low molecular weight donkey-hide gelatin peptides (LMW DHGP) were enzymatically hydrolyzed from donkey-hide gelatin. Experimental results demonstrated that the iron chelating capacity of LMW DHGP reached 249.98 μg/mg. Key amino acids (Asn, Gly, Cys, Lys) may participate in chelation. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) analysis showed rough, porous amorphous structures of LMW DHGP-iron complexes. The results of circular dichroism spectroscopy (CD) indicated that the self-assembly of LMW DHGP-iron complexes appears to be primarily mediated by peptide α-helical structural conformations. Fourier transform infrared (FTIR) spectroscopy further indicated that the interaction between LWM DHGP and Fe2+ likely occurs through carboxyl and amino functional groups. In vitro digestion stability studies demonstrated that LMW DHGP-iron complexes exhibited superior iron ion solubility compared to FeSO4 in simulated gastrointestinal conditions. PGPAG-iron complexes exhibited the highest antioxidant activity, with scavenging rates of 71.64% (DPPH radical) and 88.79% (ABTS radical). These findings collectively suggest that LMW DHGP-iron complexes possess significant potential as a novel iron supplement in food applications, which provides valuable theoretical insights for the development of innovative iron supplementation strategies. Full article
(This article belongs to the Special Issue Bioactive Peptides and Probiotic Bacteria: Modulators of Human Health)
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12 pages, 2302 KiB  
Article
Synthesis Amphiphilic One-Handed Helical Ladder Polymers with Circularly Polarized Luminescence
by Ziheng Pan and Wei Zheng
Molecules 2025, 30(12), 2606; https://doi.org/10.3390/molecules30122606 - 16 Jun 2025
Viewed by 425
Abstract
Helical ladder polymers attract attention because of their well-defined, one-handed helical ladder structures and unique properties, which differ from precursor polymers that have random-coil conformations. However, the synthesis of helical ladder polymers is difficult and inhibits their functions and applications. In this study, [...] Read more.
Helical ladder polymers attract attention because of their well-defined, one-handed helical ladder structures and unique properties, which differ from precursor polymers that have random-coil conformations. However, the synthesis of helical ladder polymers is difficult and inhibits their functions and applications. In this study, we reported the synthesis of amphiphilic optically active 2,2′-tethered binaphthyl-embedded helical ladder polymers carrying hydrophilic oligo (ethylene glycol) (OEG) as side chains through quantitative and chemoselective acid-promoted intramolecular cyclization of random-coil precursor polymers. The obtained helical ladder polymers exhibited dramatic circular dichroism (CD) and circularly polarized luminescence (CPL) enhancement. Moreover, we further established a circularly polarized fluorescence-energy transfer (CPF-ET) strategy in which the helical ladder polymers work as a donor, emitting circularly polarized fluorescence to excite an achiral fluorophore (coumarin-6) as the acceptor, producing green CPL with luminescence dissymmetry factor (2.5 × 10−4). Full article
(This article belongs to the Section Materials Chemistry)
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13 pages, 12842 KiB  
Article
Strong Coupling Based on Quasibound States in the Continuum of Nanograting Metasurfaces in Near-Infrared Region
by Yulun Zhao, Junqiang Li, Yuchang Liu, Yadong Yue, Yongchuan Dang, Yilin Wang, Kun Liang and Li Yu
Photonics 2025, 12(5), 508; https://doi.org/10.3390/photonics12050508 - 19 May 2025
Viewed by 576
Abstract
Quasibound states in the continuum (qBICs) have aroused much attention as a feasible stage to investigate optical strong coupling due to their extremely high-quality factors (Q-factors) and extraordinary electromagnetic field enhancement. However, current demonstrations of strong coupling based on qBICs have primarily focused [...] Read more.
Quasibound states in the continuum (qBICs) have aroused much attention as a feasible stage to investigate optical strong coupling due to their extremely high-quality factors (Q-factors) and extraordinary electromagnetic field enhancement. However, current demonstrations of strong coupling based on qBICs have primarily focused on the visible spectral range, while research in the near-infrared (NIR) regime remains scarce. In this work, we design a nanograting metasurface supporting Friedrich–Wintgen bound states in the continuum (FW BICs). We demonstrate that FW BIC formation stems from destructive interference between Fabry–Pérot cavity modes and metal–dielectric hybrid guided-mode resonances. To investigate the qBIC–exciton coupling system, we simulated the interaction between MoTe2 excitons and nanograting metasurfaces. A Rabi splitting of 55.4 meV was observed, which satisfies the strong coupling criterion. Furthermore, a chiral medium layer is modeled inside the nanograting metasurface by rewriting the weak expression and boundary conditions. A mode splitting of the qBIC–chiral medium system in the circular dichroism (CD) spectrum demonstrates that the chiral response successfully transferred from the chiral medium layer to the exciton–polaritons systems through strong coupling. In comparison to the existing studies, our work demonstrates a significantly larger CD signal under the same Pascal parameters and with a thinner chiral dielectric layer. Our work provides a new ideal platform for investigating the strong coupling based on quasibound states in the continuum, which exhibits promising applications in near-infrared chiral biomedical detection. Full article
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22 pages, 9092 KiB  
Article
α-Glucosidase Inhibition Mechanism and Anti-Hyperglycemic Effects of Flavonoids from Astragali Radix and Their Mixture Effects
by Xing Han, Pengpu Wang, Jing Zhang, Yang Lv, Zhigao Zhao, Fengxian Zhang, Mingying Shang, Guangxue Liu, Xuan Wang, Shaoqing Cai and Feng Xu
Pharmaceuticals 2025, 18(5), 744; https://doi.org/10.3390/ph18050744 - 18 May 2025
Cited by 1 | Viewed by 1519
Abstract
Background: Inhibition of intestinal α-glucosidase is a key strategy for controlling postprandial hyperglycemia in diabetes. Astragali Radix (AR), a traditional medicinal and dietary herb widely consumed in China, is rich in flavonoids that are believed to exhibit hypoglycemic properties. Methods: A [...] Read more.
Background: Inhibition of intestinal α-glucosidase is a key strategy for controlling postprandial hyperglycemia in diabetes. Astragali Radix (AR), a traditional medicinal and dietary herb widely consumed in China, is rich in flavonoids that are believed to exhibit hypoglycemic properties. Methods: A total of 29 AR-related flavonoids, including both original constituents and metabolites, were screened for α-glucosidase inhibitory activity using in vitro enzymatic assays. Mechanistic investigations were conducted through enzyme kinetics, circular dichroism (CD) spectroscopy, surface plasmon resonance (SPR), and molecular docking. The in vivo hypoglycemic effects were assessed using a postprandial hyperglycemic mouse model. Additionally, potential mixture effects of flavonoid combinations were evaluated. Results: Of the 29 flavonoids, 16 demonstrated significant α-glucosidase inhibitory activity, with five (C3, C17, C19, C28, and C29) identified as novel inhibitors. Structure–activity relationship (SAR) analysis revealed that hydroxylation, particularly at the C-3 position, enhanced activity, while glycosylation and methoxylation reduced it. Mechanistic studies demonstrated that these compounds bind to distinct amino acid residues within the active site of α-glucosidase, inducing conformational changes and exerting different types of inhibition, leading to varying inhibitory mechanisms. Additionally, 15 compounds reduced postprandial blood glucose levels, with C3, C16, C17, C19, and C28 confirmed as novel in vivo inhibitors. Notably, two compositions of flavonoids combined at their individually ineffective concentrations exhibited significant inhibitory effects. Conclusions: This study provides a comprehensive evaluation of AR-related flavonoids as α-glucosidase inhibitors and offers valuable insights for the development of highly effective, low-toxicity, flavonoid-based, antidiabetic therapeutics and functional foods. Full article
(This article belongs to the Section Pharmacology)
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26 pages, 5961 KiB  
Article
Structural Features Underlying the Mismatch Between Catalytic and Cytostatic Properties in L-Asparaginase from Rhodospirillum rubrum
by Igor D. Zlotnikov, Anastasia N. Shishparyonok, Marina V. Pokrovskaya, Svetlana S. Alexandrova, Dmitry D. Zhdanov and Elena V. Kudryashova
Catalysts 2025, 15(5), 476; https://doi.org/10.3390/catal15050476 - 12 May 2025
Cited by 1 | Viewed by 526
Abstract
The underlying structural features of the mismatch between catalytic and cytostatic properties in L-asparaginase from Rhodospirillum rubrum (RrA) and three of its mutants were investigated. The rationale for selecting the specific mutations (RrAA64V, E67K; RrAR118H, G120R; RrAE149R, V150P, [...] Read more.
The underlying structural features of the mismatch between catalytic and cytostatic properties in L-asparaginase from Rhodospirillum rubrum (RrA) and three of its mutants were investigated. The rationale for selecting the specific mutations (RrAA64V, E67K; RrAR118H, G120R; RrAE149R, V150P, F151T) is to elucidate the role of inter-subunit interaction in RrA and its impact on catalytic efficiency and stability. Bioinformatic modeling revealed a predominantly negative surface charge on RrA with limited positive charge clusters in the vicinity of the interface region. Thus, some negatively charged groups were replaced with positively charged ones to enhance the electrostatic interactions and stabilize the enzyme quaternary structure. RrAA64V, E67K and RrAR118H, G120R additionally contained an N-terminal 17-amino acid capsid peptide derived from the bacteriophage T7 (MASMTGGQQMGRGSSRQ), which could potentially affect the conformational stability of theenzymes. Circular dichroism (CD) spectroscopy was applied to the kinetic parameters analysis of Asn hydrolysis and showed that native RrA displayed a Vmax of 30 U/mg and a KM of 4.5 ± 0.5 mM. RrAE149R, V150P, and F151T exhibited a substantially increased Vmax of 57 U/mg. The catalytic efficiency of Vmax/KM also improved compared to the native enzyme: the Vmax/KM increased from approximately 7 U/mg × mM−1 (for the native enzyme) to 9 U/mg × mM−1 for Mut3. Other mutants exhibited less pronounced changes. Thermo-denaturation studies allowed us to determine the phase transition parameters of the RrA variants in comparison with commercial reference sample EcA. RrAA64V, E67K and RrAR118H, G120R exhibited the most favorable phase transition parameters, with melting temperatures (Tm) of 60.3 °C and 59.4 °C, respectively, exceeding that of the wild-type RrA (54.6 °C) and RrAE149R, V150P, F151T (52 °C). The EcA demonstrated a slightly superior thermal stability, with a Tm of 62 °C. The mutations showed a significant effect on protein stability during trypsinolysis. Therefore, RrAE149R, V150P, F151T showed higher resistance (45% activity remaining after 30 min of trypsin exposure) compared to the native RrA retained 20% activity. EcA preparations exhibited lower stability to trypsinolysis (losing over 90% activity in 15 min). The cytostatic effects were evaluated using MTT assays against K562 (leukemic) and A549 (lung carcinoma) cell lines. The MTT assays with K562 cells revealed that RrAE149R, V150P, F151T (IC50 of 10 U/mL) and RrAR118H, G120R (IC50 of 11.5 U/mL) exhibited superior antiproliferative activity compared to native enzymes RrA (IC50 of 15 U/mL) and EcA (24 U/mL). RrAE149R, V150P, F151T showed the most significant improvement in cytostatic activity. The results obtained indicate that the substitutions in RrAE149R, V150P, F151T resulted in the improvement of the enzyme biocatalytic properties and an increase in the resistance to aggregation and trypsinolysis. This highlights the role of electrostatic interactions in stabilizing the oligomeric structure of the enzyme, which eventually translates into an improvement in cytostatic efficiency and antiproliferative forces. Full article
(This article belongs to the Section Biocatalysis)
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