Ludan Zhao

Analysis of binding properties and interaction of thiabendazole and its metabolite with human serum albumin via multiple spectroscopic methods

Thiabendazole (TBZ), which is oxidized into 5-hydroxythiabendazole (5-OH-TBZ) in vivo, is a commonly used food preservative. Interactions of TBZ and 5-OH-TBZ with human serum albumin (HSA) were comprehensively studied via multiple spectroscopic methods and molecular docking. This study focussed on the mechanistic and structural information on binding of TBZ and 5-OH-TBZ to HSA to evaluate the impact of the food additive on HSA. 1H NMR spectra of the two ligands showed the binding exists. ITC and fluorescence spectroscopy results revealed that TBZ was a stronger ligand, with a binding constant of 105l/mol and formed a more stable complex with HSA than did 5-OH-TBZ via electrostatic interaction. Spectroscopic results (UV-vis, FT-IR, and CD) showed that TBZ and 5-OH-TBZ caused conformational changes in HSA, in which α-helix and β-turn transformed into β-sheet, causing HSA structure to loosen. Docking programs showed that both TBZ and 5-OH-TBZ bound to HSA via IB.

Investigating the interaction mechanism of fluorescent whitening agents to human serum albumin using saturation transfer difference-NMR, multi-spectroscopy, and docking studies

In this study, 2,2′-(4,4′-biphenylylenebisvinylene)bisbenzenesulfonicacid (CBS-X) and its disodiumsalt (CBS) were used as model compounds to investigate the interaction mechanism between 4,4′-distyrylbiphenyl based fluorescent whitening agents (DSBP-FWAs) and human serum albumin (HSA) through various techniques, including 1H saturation transfer difference nuclear magnetic resonance (1H STD-NMR), fluorescence studies, UV-vis absorption, Fourier transform infrared (FT-IR) spectroscopy, circular dichroism (CD) spectroscopy, and molecular docking. The 1H STD-NMR analyses indicated that CBS and CBS-X can bind to HSA at the favored Sudlows sites II and I, respectively. Fluorescence emission spectra showed that CBS and CBS-X quenches HSA fluorescence through a dynamic mechanism, and this was further verified by fluorescence lifetime experiments and UV-vis absorption. Moreover, the effective binding constant values of the two compounds at the same temperature decreased in the order CBS > CBS-X. Furthermore, the energy transfer efficiency for CBS and CBS-X were 50.5% and 40.6%, respectively. Thermodynamic analyses indicated that the binding of CBS and CBS-X with HSA are both primarily controlled by hydrophobic forces. FT-IR and CD spectroscopy provided complementary information on the micro-environmental and conformational changes of HSA with the additions of CBS and CBS-X. Molecular docking further confirmed the NMR and spectroscopic results. Overall, the comparative studies on the interaction mechanism of CBS and CBS-X when binding to HSA may provide useful information for evaluating their effects on the human body.

Binding behavior of trelagliptin and human serum albumin: Molecular docking, dynamical simulation, and multi-spectroscopy

This study aims to investigate the interaction mechanism of a hypoglycemic agent, trelagliptin (TLP), and human serum albumin (HSA) through computer simulation and assisted spectroscopy methods. Computer simulation including molecular docking and molecular dynamics analysis was conducted under physiological conditions. Molecular docking results indicate that TLP bound to HSA at site I, and the binding behavior was mainly governed by hydrophobic force. Competitive experiments further verified the theoretical conclusion from molecular docking. Molecular dynamics simulation revealed that TLP indeed stably bound to site I of HSA in the hydrophobic subdomain IIA. Moreover, TLP presented a certain effect on the structural compactness of HSA. In molecular dynamics simulation, hydrogen bonds appeared, which suggested the reliability and stability of the combination. The binding energy of the stable phase is around -250 kJ/mol. Fluorescence quenching studies and time-resolved fluorescence analysis indicated that the evident fluorescence quenching phenomenon of HSA could be due to TLP binding initiated by static quenching mechanism. The binding constants (Ka) of the complex were found to be around 104 via fluorescence data, and the calculated thermodynamic parameters indicated that hydrophobic force played major role in the binding of TLP to HSA. Synchronous fluorescence and three-dimensional fluorescence results demonstrated that TLP slightly disturbed the microenvironment of amino residues. Circular dichroism spectra showed that TLP affected the secondary structure of HSA. The theoretical and experimental results showed excellent agreement.

Interaction between azo dye Acid Red 14 and pepsin by multispectral methods and docking studies

The interaction of synthetic azo dye Acid Red 14 with pepsin was studied by fluorescence spectroscopy, UV-vis spectroscopy, circular dichroism and molecular docking. Results from the fluorescence spectroscopy show that Acid Red 14 has a strong capability to quench the intrinsic fluorescence of pepsin with static quenching. Binding constant, number of the binding sites and thermodynamic parameters were measured at different temperatures. The result indicates that Acid Red 14 interact with pepsin spontaneously by hydrogen bonding and van der Waals interactions. Three-dimensional fluorescence spectra and circular dichroism spectra reveal that Acid Red 14 could slightly change the structure of pepsin. The hydrogen bond is formed between Acid Red 14 and Tyr-189 and Thr-218 residues of pepsin. Furthermore, the binding between Acid Red 14 and pepsin inhibits pepsin activity. The study can provide a way to analyze the biological safety of Acid Red 14 on digestive proteases or other proteins.

Preparation and characterization of lotus fibers from lotus stems

Abstract Lotus stems were treated with sodium hydroxide followed by sodium chlorite to prepare lotus fibers. The lotus fibers were characterized by scanning electron microscopy (SEM), Fourier transform infrared spectrometry (FTIR), X-ray diffraction (XRD), and thermogravimetric (TG) analysis. The crystallinity and crystallinity index of lotus fibers are 62.11 and 62.29%, respectively. The content of cellulose in lotus fibers after being purified with sodium chlorite is improved and reaches 69.74%. The moisture regain of lotus fibers was studied and the results show that moisture regain of purified lotus fibers is 6.87%. The influences of concentration of sodium chlorite on tensile strength and breaking elongation of lotus fibers were investigated. The tensile strength and breaking elongation of lotus fibers both decrease as the concentration of sodium chlorite increases. The results are expected to provide valuable guidance for preparing lotus fibers from lotus stems through chemical treatment.

Photodegradation of organic dyes by Bi2WO6 coated cotton fabric modified with poly(diallyldimethylammoniumchloride) under visible light irradiation

In this study, a visible-light-driven photocatalyst Bi2WO6 was assembled on fibers by linking of poly(diallyldimethylammonium chloride) (PDDA) at room temperature. The samples were characterized by scanning electron microscopy, energy-dispersive spectroscopy and X-ray diffraction. Photocatalytic activity was evaluated by degradation of Rhodamine B (RhB) and Acid orange 7 (AO7) under visible light irradiation. Effects of concentration of PDDA in the pretreatment solution on degradation efficiency of RhB and AO7 in the presence of Bi2WO6 coated cotton fabrics were investigated. In addition, washing durability and breaking strength of Bi2WO6 coated cotton fabrics modified with PDDA were examined. The results revealed that Bi2WO6 with irregular shape were successfully coated on the cotton fabric modified with PDDA. Bi2WO6 coated cotton fabric modified with PDDA exhibited excellent photocatalytic activity with degradation efficiency of 97.4% of RhB and 94.5% of AO7, respectively. In addition, Bi2WO6 coating on the cotton fabrics modified with PDDA not only improved washing durability but also enhanced breaking strength of the fabric.

Capecitabine as a minor groove binder of DNA: molecular docking, molecular dynamics, and multi-spectroscopic studies

The interaction mechanism and binding mode of capecitabine with ctDNA was extensively investigated using docking and molecular dynamics simulations, fluorescence and circular dichroism (CD) spectroscopy, DNA thermal denaturation studies, and viscosity measurements. The possible binding mode and acting forces on the combination between capecitabine and DNA had been predicted through molecular simulation. Results indicated that capecitabine could relatively locate stably in the G-C base-pairs-rich DNA minor groove by hydrogen bond and several weaker nonbonding forces. Fluorescence spectroscopy and fluorescence lifetime measurements confirmed that the quenching was static caused by ground state complex formation. This phenomenon indicated the formation of a complex between capecitabine and ctDNA. Fluorescence data showed that the binding constants of the complex were approximately 2 × 104 M−1. Calculated thermodynamic parameters suggested that hydrogen bond was the main force during binding, which were consistent with theoretical results. Moreover, CD spectroscopy, DNA melting studies, and viscosity measurements corroborated a groove binding mode of capecitabine with ctDNA. This binding had no effect on B-DNA conformation.

Insights into the interaction of ulipristal acetate and human serum albumin using multi-spectroscopic methods, molecular docking, and dynamic simulation

Abstract Interaction between ulipristal acetate (UPA) and human serum albumin (HSA) was investigated in simulated physiological environment using multi-spectroscopic and computational methods. Fluorescence experiments showed that the quenching mechanism was static quenching, which was confirmed by the time-resolved fluorescence. Binding constants (Ka) were found to be 1 × 105 L mol−1, and fluorescence data showed one binding site. Thermodynamic constants suggested the binding process was mainly controlled by electrostatic interactions. Results from the competition experiments indicated that UPA bound to site I of HSA. Fourier transform infrared spectra, circular dichroism spectra, synchronous fluorescence spectra, and 3D fluorescence indicated that UPA can induce conformation change in the HSA. The content of α-helix and β-sheet increased, while β-turn decreased. Hydrophobicity around the tryptophan residues declined, whereas its polarity increased. Molecular docking results were consistent with the experimental results. Results suggested that UPA located at the hydrophobic cavity site I of HSA, and hydrophobic force played the key role in the binding process. Moreover, molecular dynamics simulation was performed to determine the stability of free HSA and HSA-UPA system. Results indicated that UPA can stabilize HSA to a certain degree and enhance the flexibility of residues around site I. Communicated by Ramaswamy H. Sarma GRAPHICAL ABSTRACT Communicated by Ramaswamy H. Sarma

Characterization and antioxidant activity of the complexes of tertiary butylhydroquinone with β-cyclodextrin and its derivatives

Tertiary butylhydroquinone (TBHQ) is a water-insoluble antioxidant. In this study, three cyclodextrin inclusion complexes were prepared to improve the water solubility of TBHQ and expand its range of application. Analysis of phase solubility indicated that TBHQ can form 1:1 inclusion complex with hydroxypropyl-beta-cyclodextrin (HP-β-CD) and dimethyl-beta-cyclodextrin (DM-β-CD) and 1:2 inclusion complex with beta-cyclodextrin (β-CD). The possible inclusion configuration between TBHQ and CDs was determined through FT-IR, PXRD, DSC, NMR, and SEM analyses. Results were validated by theoretical study of AutoDock molecular docking. The scavenging effects of the inclusion complexes were not effective on DPPH radical but higher on hydroxyl, superoxide and ABTS+ radicals than that of TBHQ monomer. Moreover, the water solubility of TBHQ increased after complexation with HP-β-CD and DM-β-CD. The stability of TBHQ is related to the type of storage materials used, and the stability can be improved by complexation with CDs.

Mechanism and structure studies of cinnamaldehyde/cyclodextrins inclusions by computer simulation and NMR technology

This work aims to explore the inclusion mechanism and structure of cinnamaldehyde (CNMA) and cyclodextrins (CDs), and to provide some theoretical information for the application of CNMA and its inclusion. In this study, we prepared three kinds of inclusion and investigated the mechanism and structure by theory and experiment. Molecular docking and dynamical simulations presented a stable 1:1 inclusion complex and the visual structure model. The structural features indicated that the benzene ring of CNMA was enclosed in the hydrophobic cavity of CDs, which were consistent with the results of 1H NMR, 2D-ROESY, Fourier transform infrared spectroscopy. The inclusion mechanism studies showed that the inclusion process was driven mainly by enthalpy with the binding constant following the order of DM (dimethyl) > HP (hydroxypropyl) > β-CD. Moreover, the inclusion complex showed an advantageous water solubility and dissolution rate compared with CNMA.