Studies on the Interaction of Tricyclazole with β-cyclodextrin and human Serum Albumin by Spectroscopy

The molecular mechanisms of TRβ receptor interaction with polychlorinated biphenyls: A multispectral and computational exploration

The thyroid hormone (TH) system is susceptible to the toxic effects of polychlorinated biphenyls (PCBs). Pollutants may disrupt the TH system by binding to serum TH transport proteins or interacting with thyroid hormone receptors (TRs) in target cells. However, the molecular mechanism of interaction with the Thyroid Hormone Receptor Beta (TRβ) is not fully understood. This study employed fluorescence, UV-visible absorption, three-dimensional fluorescence, and Fourier-transform infrared spectroscopy, along with molecular docking and molecular dynamics simulations, to investigate the interaction between TRβ and PCBs. Moreover, molecular docking and fluorescence resonance energy transfer (FRET) findings suggest that TRβ and PCBs underwent resonance energy transfer consistent with Förster's theory. The root mean square deviation (RMSD) and docking outcomes indicate that the TRβ-PCB29 complex exhibited optimal structural stability. Thus, the study concludes that integrating spectroscopic data with molecular docking is essential for a comprehensive analysis. Further analysis of intermolecular interactions using quantum chemistry and reduced density gradient analysis (RDG) analysis revealed that van der Waals forces are the primary drivers of PCBs to TRβ.

Fluorescence Studies on the Binding Affinity and Determination of Vitamin B12 in the Presence of Fibrinogen

The binding properties between vitamin B12 (vitB12, cyanocobalamin) and fibrinogen (Fib) were investigated by UV-vis absorption and steady-state/three-dimentional (3D) fluorescence spectra techniques as well as molecular docking. The experimental results showed that the intrinsic fluorescence of Fib quenched by vitB12 with static mechanism to form a non-fluorescent complex. The positive signs of thermodynamic parameters, ΔH (92.18 kJ/mol) and ΔS (433.5 J/molK), indicated that the hydrophobic forces were dominant in the binding mode. The molecular docking data were found to be in agreement with these experimental results and were confirmed by three hydrophobic interactions between the Trp430, Try390 residues of Fib and the vitamin. 3D spectra showed that fibrinogen undergoes a conformation change when it interacts with vitB12. Based on non-radiative energy transfer theory, binding distance was calculated to be 3.94 nm between donor (tryptophan residues of Fib) and acceptor (vitB12). The limit of detection (LOD) of vitB12 was calculated as 2.08 µM in the presence of fibrinogen. The relative standard deviation (RSD) of method was 4.28% for determinations (n = 7) of a vitB12 solution with the concentration of 7.80 µM.

Non-Steroidal Anti-Inflammatory Drug Effect on the Binding of Plasma Protein with Antibiotic Drug Ceftazidime: Spectroscopic and In Silico Investigation

The coexistence of ceftazidime, which is a popular third-generation of cephalosporin antibiotic, with ubiquitous paracetamol or acetaminophen, is very likely because the latter is given to the patients to reduce fever due to bacterial infection along with an antibiotic such as the former. Therefore, in this study, we investigated the detailed binding of ceftazidime with plasma protein, human serum albumin (HSA), in the absence and presence of paracetamol using spectroscopic techniques such as fluorescence, UV-visible, and circular dichroism, along with in silico methods such as molecular docking, molecular dynamics simulations, and MM/PBSA-based binding free energy analysis. The basic idea of the interaction was attained by using UV-visible spectroscopy. Further, fluorescence spectroscopy revealed that there was a fair interaction between ceftazidime and HSA, and the mechanism of the quenching was a dynamic one, i.e., the quenching constant increased with increasing temperature. The interaction was, primarily, reinforced by hydrophobic forces, which resulted in the partial unfolding of the protein. Low concentrations of paracetamol were ineffective in affecting the binding of ceftazidime with has; although, a decrease in the quenching and binding constants was observed in the presence of high concentrations of the former. Competitive binding site experiments using warfarin and ibuprofen as site markers revealed that ceftazidime neither binds at drug site 1 or at drug site 2, articulating another binding site, which was confirmed by molecular docking simulations.

Protocatechuic acid and gallic acid improve the emulsion and thermal stability of whey protein by covalent binding

This study aimed to explore the impacts of gallic acid (GA)/protocatechuic acid (PA) on the structural and functional characteristics of whey proteins (WP) through covalent binding. To this purpose, the covalent complexes of WP-PA and WP-GA at different concentration gradients were prepared by the alkaline method. SDS-PAGE indicated that PA/GA was cross-linked by covalent bonds. The decreased contents of free amino and sulfhydryl groups suggested that WP formed covalent bonds with PA/GA by amino and sulfhydryl groups, and the structure of WP became slightly looser after covalent modification by PA/GA. When the concentration of GA was added up to 10 mM, the structure of WP was slightly loosened with a reduction of α-helix content by 2.3% and an increase in random coil content by 3.0%. The emulsion stability index of WP increased by 14.9 min after interaction with GA. Moreover, the binding of WP and 2-10 mM PA/GA increased the denaturation temperature by 1.95 to 19.87 °C, indicating the improved thermal stability of the PA/GA-WP covalent complex. Additionally, the antioxidant capacity of WP was increased with increasing GA/PA concentration. This work may offer worthful information for enhancing the functional properties of WP and the application of the PA/GA-WP covalent complexes in food emulsifiers.

Deciphering the binding site and mechanism of new methylene blue with serum albumins: A multispectroscopic and computational investigation

Herein, the interaction mechanism of new methylene blue (NMB) with human serum albumin (HSA) and bovine serum albumin (BSA) was carefully investigated both experimentally and conceptually, employing experimental and insilico analysis. The steady-state emission spectral studies showed that the emission intensity of HSA and BSA was quenched significantly by NMB. The findings of the Stern-Volmer and double logarithmic plot revealed that the observed emission quenching process was through a static quenching mechanism and the measured binding constant values (K_b) for HSA-NMB and BSA-NMB are 2.766 and 1.187 × 10⁵ dm³ mol^-1 respectively. The time-resolved fluorescence lifetime measurement and UV-vis absorption investigation further verify the complex formation between NMB and HSA/BSA. The assessment of thermodynamic parameters disclosed the binding process was spontaneous driven by hydrogen bonds (H-bond) and van der Waals interactions, which contributed a significant role in the complexation. Moreover, the secondary structural conformation and microenvironment of HSA/BSA were modified in the presence of NMB, as evidenced by circular dichroism and synchronous fluorescence data. Molecular docking study predicted a plausible binding mode of NMB inside the binding pocket of HSA and BSA. These results demonstrated that the stabilized NMB is found at the Subdomain IIA (site I) of both the proteins and the results were correlated well with the competitive binding assay. Additionally, the principal components analysis revealed less variation of docked poses for HSA, while, more dispersed docked poses were observed for the BSA model. This also highlights the effects of docking towards a modeled protein (BSA). Molecular dynamic (MD) simulation based binding free energy (ΔG_mmgbsa) estimation obtained at 298, 303, 308 and 313 K, were in good agreement with our experimental (ΔG_bind) values.

Highly efficient ferric ion sensing and high resolution latent fingerprint imaging based on fluorescent silicon quantum dots

Expanding the application of silicon based luminescent materials is a fast-growing interdisciplinary field. Herein, a novel fluorescent bifunctional probe based on silicon quantum dots (SiQDs) for highly sensitive Fe³⁺ sensing and high-resolution latent fingerprint (LFP) imaging was subtly devised. The SiQD solution was mildly prepared using 3-aminopropyl trimethoxysilane as the silicon source and sodium ascorbate as the reductant, showing green emission at 515 nm under UV irradiation with a quantum yield of 19.8%. As a highly sensitive fluorescent sensor, the SiQD was demonstrated to have a highly selective quenching with Fe³⁺ in the concentration range of 2-1000 μM with the LOD of 0.086 μM in water. The quenching rate constant and association constant of the SiQDs-Fe³⁺ complex was calculated to be 1.05 × 10¹² mol/s and 6.8 × 10³ L/mol, respectively, suggesting a static quenching effect between them. Moreover, to achieve high-resolution LFP imaging, a novel SiO₂@SiQDs composite powder was further fabricated. The SiQDs were covalently anchored on the surface of silica nanospheres to conquer aggregation-caused quenching for the high-solid fluorescence. In the demonstration of LFP imaging, this silicon based luminescent composite exhibited high developing sensitivity, high selectivity and high contrast, indicating its practical value as a fingerprint developer at crime scenes.

Investigation of the separate and simultaneous bindings of warfarin and fenofibrate to bovine serum albumin

Lipid-lowering drugs are often taken with anticoagulant drugs in hyperlipidemia patients. Fenofibrate (FNBT) and warfarin (WAR) are common clinical lipid-lowering drugs and anticoagulant drugs, respectively. A study of binding affinity, binding force, binding distance, and binding sites was performed to determine the interaction mechanism between drugs and carrier proteins (bovine serum albumin, BSA), as well as their effects on BSA conformation. Both FNBT and WAR can form complexes with BSA by van der Waals force and hydrogen bonds. WAR had a stronger fluorescence quenching effect on BSA, a stronger binding affinity, and greater effects on BSA conformation than FNBT. According to fluorescence spectroscopy and cyclic voltammetry, co-administration of drugs decreased one drug's binding constant to BSA and increased its binding distance. This suggested that each drug's binding to BSA was disturbed by each other, as well as each drug's binding ability to BSA was altered by the other. It was demonstrated that co-administration of drugs had greater effects on the secondary structure of BSA and microenvironment polarity surrounding amino acid residues, using multiple spectroscopy techniques, such as ultraviolet spectroscopy, Fourier transform infrared spectroscopy, and synchronous fluorescence spectroscopy.

A supramolecular cucurbit[8]uril-based rotaxane chemosensor for the optical tryptophan detection in human serum and urine

Sensing small biomolecules in biofluids remains challenging for many optical chemosensors based on supramolecular host-guest interactions due to adverse interplays with salts, proteins, and other biofluid components. Instead of following the established strategy of developing alternative synthetic binders with improved affinities and selectivity, we report a molecular engineering approach that addresses this biofluid challenge. Here we introduce a cucurbit[8]uril-based rotaxane chemosensor feasible for sensing the health-relevant biomarker tryptophan at physiologically relevant concentrations, even in protein- and lipid-containing human blood serum and urine. Moreover, this chemosensor enables emission-based high-throughput screening in a microwell plate format and can be used for label-free enzymatic reaction monitoring and chirality sensing. Printed sensor chips with surface-immobilized rotaxane-microarrays are used for fluorescence microscopy imaging of tryptophan. Our system overcomes the limitations of current supramolecular host-guest chemosensors and will foster future applications of supramolecular sensors for molecular diagnostics.

Study of fluorescence spectroscopy and molecular mechanisms for the interaction of Hg2+ ions and R-phycoerythrin from marine algae (Porphyra yezoensis)

Heavy metal is a worldwide hazardous material, and many efforts were made to detect them sensitively and selectively. R-phycoerythrin (R-PE), a marine fluorescent protein, is abundant in red algae and participates in photosynthesis. In this work, the fluorescence spectroscopy and molecular mechanism of Hg2+ ions and R-PE were further explored through fluorescence spectrum measurements, time-resolved fluorescence lifetimes, peak fitting of Fourier transform infrared spectroscopy, and molecular docking simulation in this study. It was proved by fluorescent spectrum measurements that Hg2+ ions could lead to static fluorescence quenching. Besides, the interaction was a spontaneous and exothermic process driven by hydrogen bond and Van der Waals (VDW) force. Importantly, Hg2+ ions bound to 78LYS and 82CYS on the α chain and 73CYS and 82CYS on the β chain, which resulted in the structural changes of the peptide chain and affected the secondary structure contents of R-PE. This study further explained the effect of Hg2+ ions on marine fluorescent protein R-PE.

Effect of enzymatic hydrolysis conditions on structure of soy protein isolate/gum arabic complex and stability of oil-in-water emulsion

BACKGROUND

The emulsifying, antioxidant and foaming properties of soy protein isolate hydrolysates (SPH) can be improved by the addition of gum arabic (GA). We investigated the effects of different hydrolysis conditions on the complexation of SPH and GA, and the effects of the complex on the properties of emulsions.

RESULTS

Fluorescence spectroscopy showed that the addition of GA had a stronger effect on bromelain and pepsin hydrolysates than trypsin hydrolysate, and therefore had a higher binding constant (K_A ) and a larger number of binding sites (n). The addition of GA could also improve protein solubility and emulsifying ability. The emulsions prepared with complexes, especially the complex of GA and SPH obtained by pepsin hydrolysis for 3 h, had a high absolute charge value, uniform particle size distribution, stable morphology, and good storage stability. After storage, the emulsification index (CI) of the emulsion only increased to 23.08%; its 1,1-diphenyl-2-picrylhydrazyl (DPPH) free radical scavenging activity was 24.37 ± 1.22% and its 2,2'-Azinobis-(3-ethylbenzthiazoline-6-sulphonate) (ABTS⁺ ) free radical scavenging activity was largely retained.

CONCLUSION

During long-term storage, pepsin-treated protein (especially protein treated for 3 h) and GA can form a stable emulsion with antioxidant properties. This work provides new ideas for the development of natural and safe emulsifiers that have antioxidant properties and can be stored long-term and used in the food industry. © 2022 Society of Chemical Industry.

Spectroscopic and Molecular Docking Investigation on the Interaction of Cumin Components with Plasma Protein: Assessment of the Comparative Interactions of Aldehyde and Alcohol with Human Serum Albumin

The interaction of the important plasma protein, human serum albumin (HSA), with two monoterpenes found in cumin oil, i.e., cuminaldehyde (4-isopropylbenzaldehyde) and cuminol (4-isopropylbenzyl alcohol), was studied in this paper. Both experimental and computational methods were utilized to understand the mechanism of binding. The UV absorption profile of HSA changes in the presence of both cuminaldehyde and cuminol, due to the interaction between HSA with both monoterpenes. The intrinsic fluorescence intensity of HSA was also quenched on the sequential addition of both ligands, due to change in the microenvironment of the fluorophore present in the former. Quenching of HSA by cuminaldehyde was much higher in comparison to that in the presence of cuminol. Fluorescence quenching data were analyzed using modified Stern-Volmer and Lineweaver-Burk methods, which suggested that the binding mechanism was of a static type for both ligands. In both cases, the binding was favored by the domination of hydrophobic as well as hydrogen bonding/Van der Waals forces. Both ligands partially unfolded the secondary structure of HSA, although the effect of cuminaldehyde was more pronounced, as compared to cuminol. The preferred binding site of cuminaldehyde and cuminol inside HSA was also the same; namely, drug binding site 1, located in subdomain IIA. The study showed that cuminaldehyde binds strongly with albumin as compared to its alcohol counterpart, which is due to the more hydrophobic nature of the former.

Nitrogen-doped fluorescence carbon dots as multi-mechanism detection for iodide and curcumin in biological and food samples

Iodine ion is one of the most indispensable anions in living organisms, particularly being an important substance for the synthesis of thyroid hormones. Curcumin is a yellow-orange polyphenol compound derived from the rhizome of Curcuma longa L., which has been commonly used as a spice and natural coloring agent, food additives, cosmetics as well as Chinese medicine. However, excess curcumin may cause DNA inactivation, lead to a decrease in intracellular ATP levels, and trigger the tissue necrosis. Therefore, quantitative detection of iodine and curcumin is of great significance in the fields of food and life sciences. Herein, we develop nitrogen-doped fluorescent carbon dots (NCDs) as a multi-mechanism detection for iodide and curcumin in actual complex biological and food samples, which was prepared by a one-step solid-phase synthesis using tartaric acid and urea as precursors without adding any other reagents. An assembled NCDs-Hg2+ fluorescence-enhanced sensor for the quantitative detection of I- was established based on a fluorescence "turn-off-on" mechanism in a linear range of 0.3-15 μM with a detection limit of 69.4 nM and successfully quantified trace amounts of I- in water samples and urine sample. Meanwhile, the as-synthesized NCDs also can be used as a fluorescent quenched sensor for curcumin detection based on the synergistic internal filtration effect (IFE) and static quenching, achieving a good linear range of 0.1-20 μM with a satisfactory detection limit of 29.8 nM. These results indicate that carbon dots are potential sensing materials for iodine and curcumin detection for the good of our health.

An exploration of the interaction mechanism of Direct Red 80 with α-Amylase at the molecular level

The use and production of Direct Red 80 (DR80) dye are growing rapidly, and a large amount of dye wastewater is discharged into the soil without treatment. DR80 accumulated in soil or sludge can lead to enzyme poisoning, inhibit microbial activity, and affect the transformation of substances in the soil. In this research, the interaction mechanism between DR80 and α-Amylase (a typical enzyme in soil and sludge) was investigated by multi-spectra, molecular docking, thermodynamics analysis and enzyme activity experiment. The results of UV-visible and resonance light scattering (RLS) spectra showed that the skeleton of α-Amylase became loosened and unfolded under the exposure of Direct Red. The size of α-Amylase was smaller and α-Amylase became dispersed under high concentration of DR80. Molecular docking and thermodynamic analysis showed that DR80 bound to the surface of domain A rather than the active site of α-Amylase in the form of hydrogen bonds, and the binding process was an exothermic reaction. In addition, the inhibition of α-Amylase activity by DR80 was verified by enzyme activity experiment. These results indicate that DR80 has an effect on the structure and function of α-Amylase at molecular level, which means that the toxicity of DR80 should receive more attention.

The interaction of sodium dodecyl sulfate with trypsin: Multi-spectroscopic analysis, molecular docking, and molecular dynamics simulation

The bioactivity of enzymes is sensitive to certain factors in their application environment, such as the pH, temperature, ionic strength, and additives, which can alter the native conformation of enzymes. To determine the mechanism by which the interaction of SDS influences the structure and activity of trypsin, molecular docking, molecular dynamics simulations, DSC, and multi-spectroscopic measures including UV absorption, fluorescence, and circular dichroism were used. The results show that the hydrolytic activity towards casein could be dramatically restrained by SDS. UV absorption, CD, and fluorescence spectra demonstrated the formation of a trypsin-SDS complex. Thermodynamic parameters and molecular docking data revealed that the binding process was spontaneous, and that the main binding forces between SDS and trypsin were hydrogen bonds and van der Waals forces. In addition, molecular docking predicted that the binding site of SDS on trypsin was located at the active center. Molecular dynamic simulations showed that treatment with SDS resulted in the structure of trypsin becoming unstable and unfolded near its active center. This work provides insights into the interaction of SDS with trypsin on the molecular level and is beneficial to understanding of how SDS affects the conformation and activity of trypsin in application processes.

Tailor-Made Polymer Nano-Assembly with Switchable Function and Amplified Anti-Tumor Therapy

The difficulty in killing tumor cells due to the tendency to metastasis and drug resistance are outstanding and urgent problems for the treatment of cancer. It is imperative to figure out an effective therapy strategy to break the treatment dilemmas. Nano self-assembly has the characteristics of flexible regulation, biological compatibility, and easy access. Herein, an albumin-polymer nano-assembly with switchable cytotoxicity and reactive oxygen species (ROS) amplification capability is developed for anti-tumor therapy. The nano-assembly (PFFBT@HSA) is comprised of conjugated polymer PFFBT and natural protein human serum albumin (HSA) via the hydrophobic and electrostatic interactions. The innovative switchable strategy is proposed and realized by HSA turning off the cytotoxicity of PFFBT and then turning on and enhancing the cytotoxicity by generating massive ROS upon light irradiation. The combination of HSA provides more stable microenvironment to benefit the generation of highly effective anti-tumor model of "0+1>1". These results display that the nanostructured self-assembly and the proposed anti-tumor regulation strategy are effective, which will contribute to the diversified treatment of cancer.

The effect of heparan sulfate on promoting amyloid fibril formation by β-casein and their binding research with multi-spectroscopic approaches

As a molecular chaperone, β-casein is difficult to form amyloid fibrils under physiological conditions due to its chaperone activity. Heparan sulfate (HS) has drawn attention of technologists all over the word because of its relation to amyloid deposits in some amyloidosis diseases. For better understanding the relationship between the β-casein and HS, the multi-spectroscopic studies were employed. The data of thioflavin T (ThT) binding assay, transmission electron microscopy (TEM) and circular dichroism (CD) demonstrated that HS promoted fibril formation by β-casein in the amount and the growth speed. The results of steady-state UV-vis absorption spectra, fluorescence spectroscopy and fluorescence lifetime revealed that the β-casein-HS complexes were formed and HS quenched the fluorescence of β-casein by a static quenching mechanism. On the basis of fluorescence analysis, the value of binding constant was equal to 1.17 × 10⁷ L mol^-1 at 338.15 K and there was about one binding site between them. According to thermodynamic parameters obtained, it was deduced that a spontaneous reaction happened, and protein-ligand complex was stabilized by hydrogen bonds and hydrophobic interaction. Furthermore, using fluorescence resonance energy transfer (FRET) assay, the value of binding distance between HS and Trp143 of β-casein was calculated to be 0.93 nm. Finally, on the basis of synchronous fluorescence experiment, the polarity increasing and hydrophobicity decreasing around Trp143 occurred during the period of fibril formation by β-casein.

Spectroscopic and cytotoxicity studies on the combined interaction of (-)-epigallocatechin-3-gallate and anthracycline drugs with human serum albumin

The interactions of (-)-epigallocatechin-3-Gallate (EGCG) and anthracycline drugs (doxorubicin, DOX and epirubicin, EPI) alone or in combination with human serum albumin (HSA) under physiological condition were studied by fluorescence spectroscopy, UV-vis absorption spectroscopy, circular dichroism (CD) spectroscopy, and dynamic light scattering (DLS). The cytotoxic activity of the single drug, combined drugs, and their complexes with HSA against human cervical cancer HeLa cell line was determined by MTT assay. Fluorescence quenching result and difference spectra of UV absorption revealed the formation of static complex between EGCG, DOX, or EPI and HSA. The binding of EGCG with HSA was driven by both enthalpy and entropy while the binding of DOX or EPI was mainly entropy driven. The nature of binding was expounded based on the effect of sodium chloride, tetrabutylammonium bromide, and sucrose which interfere in electrostatic, hydrophobic, and hydrogen bonding interactions, respectively. Site marker competitive experiments combined with synchronous fluorescence spectra showed that these three ligands mainly bound to subdomain IIA of HSA and were closer to tryptophan residues. In EGCG + DOX/EPI + HSA ternary system, the effect of one drug on the binding ability of another drug was discussed. The influences of the individual and combined binding of EGCG and DOX/EPI on the secondary structure and particle size of HSA were investigated by CD spectroscopy and DLS, respectively. Moreover, the synergistic cytotoxicity of EGCG and DOX/EPI as well as their complexes with HSA were discussed. Obtained results would provide beneficial information on the combination of EGCG and anthracyclines in clinic.

Spectroscopic and computational exploration of hypoxanthine riboside interacting with plasma albumin

Hypoxanthine riboside (HXR) is a nucleoside essential for wobble base pairs to translate the genetic code. In this work, an absorption and luminescence study showed that HXR and human serum albumin (HSA) formed a new complex through hydrogen bonds and van der Waals forces at ground state. Fluorescence probe experiments indicated that HXR entered the first subdomain of domain II in HSA and was fixed by amino acid residues in site I defined by Sudlow, and after competing with a known site marker. The recognition interaction featured negative ΔH^ϴ , ΔS^ϴ and ΔG^ϴ thermodynamic parameters. Fluorescence and circular dichroism spectra described the polarity of residues and α-helix and β-strand content changed because of HXR binding. The most rational structure for the HXR-HSA complex was recommended by the molecular docking method, in which the binding location, molecular orientation, adjacent amino acid residues, and hydrogen bonds were included. In addition, the influence of β-cyclodextrin and some essential metal ions on the balance of the HSA-HXR system interaction was measured. The study gained comprehensive information on the transportation mechanism for HXR in blood, and was of great significance in understanding the theory of HXR biotransformation and in discussing its clinical in vivo half-life.

Identification of Ellagitannins in the Unripe Fruit of Rubus Chingii Hu and Evaluation of its Potential Antidiabetic Activity

As a functional food, the unripe fruits of Rubus chingii Hu have been widely used in China for thousands of years. Twenty-five major ellagitannins (ETs) were identified from the unripe fruits, and a novel ellagitannin, chingiitannin A (1), together with four other known ETs (2-5) were isolated and identified by HPLC-QTOF-MS/MS and 2D-NMR. Chingiitannin A showed the highest α-glucosidase and α-amylase inhibitory activities (IC₅₀ 2.89 and 4.52 μM, respectively), which occurred in a reversible and noncompetitive manner. Static quenching was indicated in a fluorescence quenching assay. Molecular docking results revealed that chingiitannin A interacted with the enzymes mainly by hydrogen bonding and was bound in the allosteric site. Chingiitannin A was nontoxic, and it increased the glucose uptake in L6 myotubes. The results suggested that the unripe fruits of Rubus chingii Hu are rich sources of ETs, and chingiitannin A might be a good candidate for functional foods or antidiabetic drugs.

Interaction Mechanism of Different Surfactants with Casein: A Perspective on Bulk and Interfacial Phase Behavior

Understanding the interaction mechanism between proteins and surfactants is conducive to the application of protein/surfactant mixtures in the food industry. The present study investigated the interaction mechanism of casein with cationic Gemini surfactant (BQAS), anionic Gemini surfactant (SGS), anionic single-chain surfactant (sodium dodecyl sulfate [SDS]), and two biosurfactants (rhamnolipid [RL] and lactone sophorolipid [SL]) at the interface and in bulk phase. BQAS/casein and SDS/casein mixtures exhibit a strong synergistic effect on the surface activity. For SGS, RL, and SL, the formation of surfactant/casein complexes caused no improvement in surface activity. Dilational elasticity results indicate the displacement of casein by SGS, RL, and SL at the surface. However, the BQAS/casein complexes manifested varying dilational properties from pure casein surface. The strong electrostatic interaction between BQAS and casein produced large-size precipitate particles. For other surfactants, no precipitate particles formed. Determination of ζ-potential, UV-vis absorption spectra, and fluorescence spectra demonstrated the stronger interaction of BQAS and SDS with casein than that of SGS, RL, and SL. Addition of BQAS initially increased and then decreased the α-helix structure of casein. For SGS, RL, and SL, no noticeable change occurred in the casein structure. However, the formation of SDS/casein complexes was conducive to the casein structure. In conclusion, the interaction between BQAS and casein is similar to that of cationic single-chain surfactant. Furthermore, SGS exhibits a significantly different interaction mechanism from the corresponding monomer (SDS), possibly resulting from its excellent interfacial activity, low critical micelle concentration values, and strong self-assembly capability. For RL and SL, the weak interaction is attributed to the relatively complicated structure and less charged degree of hydrophilic headgroups.

Binding of triclosan and triclocarban to pepsin: DFT, spectroscopic and dynamic simulation studies

The use of antibacterial agents, triclosan (TCS) and triclocarban (TCC), in personal care products can result in direct human exposure. Density Functional Theory (DFT) was utilized to evaluate the electronic properties of TCS and TCC, and the determined energetically accessible transitions across the HOMO-LUMO gap. Choosing pepsin as a model protein, we explored the binding effects of TCS or TCC on pepsin by molecular docking and dynamic simulations. Titration of pepsin with TCS or TCC at pH 2.2 led to quenching of the pepsin intrinsic fluorescence via formation of a ground-state complex. The binding constants of the TCS/TCC-pepsin complexes, determined at 296 K, were (7.053 ± 0.030) × 10⁴ M^-1 and (6.233 ± 0.060) × 10⁴ M^-1, respectively. Analysis of the thermodynamic properties of each system at various temperatures demonstrated that the binding reaction is a spontaneous process driven by hydrophobic interactions. The spectroscopic results revealed that changes in the secondary structure of pepsin are induced by TCS or TCC. The thermal stability of pepsin was evaluated, and no change in thermal stability was observed upon substrate binding. However, the binding of either TCS or TCC to pepsin effectively reduced the activity.

The interaction of silver nanoparticles with papain and bromelain

These fundamental studies will provide some new insights into the safe and effective application of AgNPs in biological and medical areas.

A simple fluorescent assay for cyromazine detection in raw milk by using CYR-stabilized G-quadruplex formation

A rapid biosensor for the detection of cyromazine in milk is reported based on a fluorescence quenching result. When an FAM labelled G-rich ssDNA Tcy2 is treated with cyromazine, it can form a G-quadruplex-CYR complex and cause a change in fluorescence. As a result, the presence of cyromazine can be determined by fluorescence quenching. This sensor is selective for the detection of cyromazine in raw milk and has a limit of detection of 0.68 ppb and a detection range from 0 to 200 ppb.

A rapid biosensor for the detection of cyromazine in milk is reported based on a fluorescence quenching result.

Functional and conformational changes to soy proteins accompanying anthocyanins: Focus on covalent and non-covalent interactions

The present study was aimed to evaluate the interaction between anthocyanins from black rice and soybean protein isolate (SPI) via non-covalent and covalent bindings and the impact of these interactions on the functional and conformational changes of soybean protein. The conformational changes of the protein structure with different concentrations of anthocyanins (0.05, 0.1%, and 0.2%) were analyzed using three-dimensional fluorescence and Fourier transform infrared spectroscopy. The anthocyanins were more likely to form covalent interactions with SPI instead of non-covalent interactions. The addition of anthocyanins changed the secondary structure of SPI with a decrease in β-sheets and an increase in β-turns and random coils. The emulsifying and foaming properties of SPI were improved after complexation with anthocyanins. This study might be useful for elucidating the mechanisms behind the binding of anthocyanins with SPI and the possible uses of SPI-anthocyanin complexes in food formulations.

Impact of multiple quaternary ammonium salts on dynamic properties of BSA adsorption layer at different pH values

The interaction mechanism of multiple quaternary ammonium salts (MQAS) with bovine serum albumin (BSA) was examined by the fluorescence quenching method and circular dichroism (CD) spectra. Moreover, the effects of MQAS on the dynamic properties of BSA adsorption layers at different pH values were investigated using dilational interfacial rheology. Results show that the quenching constants increase with an increase in pH values and decrease with an increase in the experiment temperature at pH 5.3. The quenching mechanism is static quenching, and the electrostatic force dominates the interaction between MQAS and BSA at pH 5.3. Due to three positive head groups, MQAS can significantly affect the dynamic interfacial activity of BSA molecules at a relatively low concentration. At pH 4.3, the electrostatic repulsion is unfavorable for the formation of MQAS/BSA complexes. Consequently, MQAS molecules will replace BSA molecules from the interface by competitive adsorption. At the pH value above the isoelectric point of BSA, the electrostatic attraction is better for the formation of MQAS/BSA complexes, which exhibit a rapid adsorption rate and an enhanced interfacial activity. Moreover, the kinetic dependencies of interfacial dilational elasticity for the MQAS/BSA mixtures become nonmonotonous. The appearance of the maximum interfacial elasticity values can be attributed to the formation of tails and loops, which suggests that the addition of MQAS destroys the secondary and tertiary structure of protein in the bulk phase. In addition, the effects of MQAS on the secondary structure of protein were demonstrated by CD spectra.

Investigation of the binding affinity in vitamin B12-Bovine serum albumin system using various spectroscopic methods

The binding affinity between vitamin B12 (VitB12) and bovine serum albumin (BSA) has been investigated in aqueous solution at pH=7.4, employing UV-vis absorption and steady-state, synchronous and three-dimensional fluorescence spectra techniques. Representative effects noted for BSA intrinsic fluorescence resulting from the interactions with VitB12 confirm the formation of π-π stacked non-covalent and non-fluorescent complexes in the system VitB12-BSA. All the determined parameters, the binding, fluorescence quenching and bimolecular quenching rate constants (of the order of 10⁴Lmol^-1, 10³Lmol^-1 and 10¹¹Lmol^-1s^-1, respectively), as well as Förster resonance energy transfer parameters validate the mechanism of static quenching. The interaction with VitB12 induces folding of the polypeptide chains around Trp residues of BSA, resulting in a more hydrophobic surrounding. Presented outcomes suggest that the addition of VitB12 can lead to the more organized BSA conformation and its more folded tertiary structure, what could influence the physiological functions of bovine serum albumin, notably in case of its overuse or abnormal metabolism.

Studies on the mechanism of action of antitumor bis(aminophenolate) ruthenium(III) complexes

Two recently published Ru(III) complexes bearing (N₂O₂) tetradentate bis(aminophenolate) ligands, formulated as [Ru(III)(salan)(PPh₃)Cl] (salan is the tetradentate ligand 6,6'-(1S,2S)-cyclohexane-1,2-diylbis(azanediyl)bis(methylene)bis(3-methoxyphenol) in complex 1, or 2,2'-(1S,2S)-cyclohexane-1,2-diylbis(azanediyl)bis(methylene)bis(4-methoxyphenol) in complex 2; PPh₃ is triphenylphosphane) and found very active against ovarian and breast adenocarcinoma human cells were studied to outline their antitumor mode of action. The human cisplatin-sensitive ovarian adenocarcinoma line A2780 was used herein as the cell model. At a 24h challenge (similarly as found before for 72h) both complexes are active, their cytotoxicity being comparable to that of cisplatin in the same conditions. As a possible target in the cell for their action, the interaction of 1 and 2 with DNA was assessed through displacement of well-established DNA fluorescent probes (ethidium bromide, EB, and 4',6-diamidino-2-phenylindole, DAPI) through steady-state and time-resolved fluorescence spectroscopy. The whole emission spectra were analyzed globally for the binary DNA-probe and ternary DNA-probe-Ru(III) complex systems. Both Ru(III) complexes can displace EB and bind to DNA with similar and moderate strong affinity with conditional stability constants of logK'=(5.05±0.01) for 1 and logK'=(4.79±0.01) for 2. The analysis of time-domain fluorescence intensity decays confirmed both qualitatively and quantitatively the model used to describe the binding and competition processes. Cell studies indicated that apoptosis is the major mechanism of cell death for both complexes, with 2 (the more active complex) promoting that process more efficiently than 1. Transmission electron micrographs revealed clear alterations on intracellular organization consistent with the induction of programmed cell death processes.

Responses of soluble microbial products and extracellular polymeric substances to the presence of toxic 2,6-dichlorophenol in aerobic granular sludge system

The objective of this study was to evaluate the responses of soluble microbial products (SMP) and extracellular polymeric substances (EPS) to the presence of toxic 2,6-dichlorophenol (2,6-DCP) in aerobic granular sludge (AGS) system. Batch experiment showed that NH₄⁺-N removal efficiency significantly decreased from 99.6% to 47.2% in the toxic 2,6-DCP of 20 mg/L. Moreover, the inhibition degrees of 2,6-DCP on (SOUR)_H, [Formula: see text] and [Formula: see text] were 7.8%, 32.1% and 9.5%, respectively. The main components of SMP, including protein (PN) and polysaccharide (PS) increased from 2.3 ± 0.74 and 16.8 ± 0.12 mg/L to 66.4 ± 0.56 and 18.0 ± 0.19 mg/L in the presence of 2,6-DCP. Three-dimensional excitation-emission matrix (3D-EEM) spectroscopy identified tryptophan PN-like, humic acid-like and fulvic acid-like substances in the control SMP, and their fluorescence intensities increased after exposure to 2,6-DCP. Synchronous fluorescence spectra suggested that the fluorescence quenching between EPS and 2,6-DCP was a static quenching process. The obtained results could provide insightful information on the responses of microbial products to AGS in the presence of toxic chlorophenols.

Plasma Protein Binding of Anisomelic Acid: Spectroscopy and Molecular Dynamic Simulations

Anisomelic acid (AA) is a macrocyclic cembranolide compound extracted from Anisomeles herbal species. Recently, we have shown that AA possesses both anticancer and antiviral activity. However, to date, the plasma protein binding properties of AA are unknown. Here, we describe the molecular interactions of AA with two serum proteins, human serum albumin (HSA) and bovine serum albumin (BSA), adopting multiple physicochemical methods. Besides, molecular docking and dynamics simulations were performed to predict the interaction mode and the dynamic behavior of AA with HSA and BSA. The experimental results revealed that hydrophobic forces play a significant part in the interaction of AA to HSA and BSA. The outcomes of the principal components analysis (PCA) of the poses based on root-mean-squared distances showed less variation in AA-HSA, opposed to what is seen for BSA-AA. Furthermore, binding free energies estimated for AA-HSA and AA-BSA complexes at different temperatures (298, 303, 308, and 313 K) based on molecular mechanics-generalized Born surface area (MMGBSA) approaches were well correlated with our experimental results.

Introduction of an α,β-unsaturated carbonyl conjugated pyrene–lactose hybrid as a fluorescent molecular probe for micro-scale anisotropic media

A new fluorescent lactose molecule (pyd-lact) (E)-1-(galactose-β-(1→4)-β-d-glucopyranosyl)-4-(1-pyrene)-but-3-en-2-one, has been synthesized by attaching 1-pyrene-but-3-ene-2-one to lactose.

Non-enzymatic glycation mediated structure–function changes in proteins: case of serum albumin

Albumin, a major plasma protein with extraordinary ligand binding properties, transports various ligands ranging from drugs, hormones, fatty acids, and toxins to different tissues and organs in the body.