Multispectroscopic and Computational Investigations on the Binding Mechanism of Dicaffeoylquinic Acids with Ovalbumin.

Recently, studies on the interactions between ovalbumin (OVA) and polyphenols have received a great deal of interest. This study explored the conformational changes and the interaction mechanism of the binding between OVA and chlorogenic acid (CGA) isomers such as 3,4-dicaffeoylquinic acids (3,4-diCQA), 4,5-dicaffeoylquinic acids (4,5-diCQA), and 3,5-dicaffeoylquinic acids (3,5-diCQA) using multispectroscopic and in silico analyses. The emission spectra show that the diCQAs caused strong quenching of OVA fluorescence under different temperatures through a static quenching mechanism with hydrogen bond (H-bond) and van der Waals (vdW) interactions. The values of binding constants (OVA-3,4-diCQA = 6.123 × 105, OVA-3,5-diCQA = 2.485 × 105, OVA-4,5-diCQA = 4.698 × 105 dm3 mol-1 at 298 K) suggested that diCQAs had a strong binding affinity toward OVA, among which OVA-3,4-diCQA exhibits higher binding constant. The results of UV-vis absorption and synchronous fluorescence indicated that the binding of all three diCQAs to OVA induced conformational and micro-environmental changes in the protein. The findings of molecular modeling further validate the significant role of vdW force and H-bond interactions in ensuring the stable binding of OVA-diCQA complexes. Temperature-dependent molecular dynamics simulation studies allow estimation of the individual components that contribute to the total bound free energy value, which allows evaluation of the nature of the interactions involved. This research can provide information for future investigations on food proteins' physicochemical stability and CGA bioavailability in vitro or in vivo.

Exploring the interaction of the photodynamic therapeutic agent thionine with bovine serum albumin: multispectroscopic and molecular docking studies.

This study explores the binding interaction of thionine (TH) with bovine serum albumin (BSA) under physiological conditions (pH 7.40) using absorption, emission, synchronous emission, circular dichroism (CD) and three-dimensional (3D) emission spectral studies. The results of emission titration experiments revealed that TH strongly quenches the intrinsic emission of BSA via a static quenching mechanism. The apparent binding constant (K) and number of binding sites (n) were calculated as 2.09 × 10(5) dm(3) /mol and n ~1, respectively. The negative free energy change value for the BSA-TH system suggested that the binding interaction was spontaneous and energetically favourable. The results from absorption, synchronous emission, CD and 3D emission spectral studies demonstrated that TH induces changes in the microenvironment and secondary structure in BSA. Site marker competitive binding experiments revealed that the binding site of TH was located in subdomain IIA (Sudlow site I) of BSA. The molecular docking study further substantiates Sudlow site I as the preferable binding site of TH in BSA.

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 (Kb) 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 (ΔGmmgbsa) estimation obtained at 298, 303, 308 and 313 K, were in good agreement with our experimental (ΔGbind) values.

Zinc oxide nanoparticles synthesized using coffee leaf extract assisted with ultrasound as nanocarriers for mangiferin.

Plant extracts have been widely used to green synthesize zinc oxide nanoparticles (ZnO NPs); however, how the combination of ultrasound and coffee leaf extract (CLE) affects the structure characteristics and the yield of ZnO NPs remains unknown. In this study, we used CLE to green synthesize ZnO NPs with the help of ultrasound. The highest yield (43.59 ± 0.13%) of ZnO NPs was obtained under the optimal processing conditions of pH = 8.0, mass ratio of coffee leaves to C4H6O4Zn•2H2O = 1.71, ultrasound time = 10 min, ultrasound frequency = 28/40 kHz, ultrasound power = 180 W, and synthesis temperature = 30 °C. The as-synthesized ZnO NPs were characterized by UV-Vis, SEM, EDX, TEM, FTIR, XRD, and zeta potential analyses. SEM and TEM analyses revealed that ZnO NPs synthesized using ultrasound-assisted method were spherical with an average particle size of 8.29 ± 1.38 nm, which was smaller than ZnO NPs synthesized without ultrasound treatment (10.48 ± 1.57 nm) and the chemically synthesized ZnO NPs (17.15 ± 2.84 nm). HPLC analysis showed that the phenolic compounds in coffee leaves, especially 5-CQA, were the main reductants and chelating agents for ZnO NPs synthesis. The synthesized ZnO NPs were used to load mangiferin, which was control released under pH 7.4 over 132 h. Our study provides an easy and eco-friendly method using CLE assisted with ultrasound for green synthesis of ZnO NPs which can be used as nanocarriers to control release of mangiferin.

Exploring the binding mechanism between methylene blue and ovalbumin using spectroscopic analyses and computational simulations.

The detailed investigation of methylene blue (MB) dye with ovalbumin (OVA) was examined by multispectroscopic and computational techniques. The experimental results of emission spectral studies displayed that the quenching behaviour of OVA with MB dye is due to static quenching mechanism. Isothermal titration calorimetry experimental results suggested that the binding of MB dye became favoured with the aid of a favourable entropy contribution and negative enthalpy. The absorption and circular dichroism spectral experiments showed that the binding of MB dye prompted conformational modifications to the secondary structure of OVA protein. The computational studies have been used to predict the binding region and the stability of MB in OVA protein.Communicated by Ramaswamy H. Sarma.

Improved electrocatalytic activity of Au@Fe3O4 magnetic nanoparticles for sensitive dopamine detection.

Substantially, noble metals are important for the development of low-cost, sensitive, selective, superior performance, and portable electrochemical sensors. Herein, we describe gold (Au) nanoparticles (NPs) systematically decorated with magnetic Fe3O4 nanocomposites on the fabrication of sensitive dopamine sensor is described. Magnetic Au@Fe3O4 nanocomposites were prepared by reducing HAuCl4 on the surfaces of Fe3O4 nanoparticles. The surface morphology of Au@Fe3O4 nanocomposites was characterized by scanning electron microscopy (SEM), X-ray powder diffraction (XRD) and transmission electron microscopy (TEM). The electrochemical behaviour of the modified electrode was investigated by cyclic voltammetry (CV), differential pulse voltammetry (DPV) and amperometric techniques, in which it was shown to be highly sensitive and selective towards DA. The amperometric detection of dopamine sensor, using this sensing element, exhibits a wide linear response of 0-0.8 µM with a low detection limit of 2.7 nM. In addition, the fabricated electrode showed an excellent stability and good reproducibility. The proposed analytical method was successfully applied to determine the concentration of dopamine in human urine samples and the unknown concentration of DA in human urine samples No. 1, 2 and 3 were determined as 0.056 ± 0.82 × 10-3, 0.037 ± 0.87 × 10-3 and 0.020 ± 0.94 × 10-3 µM, respectively, with recoveries ranging from 97.2% to 103.4%, suggesting that the fabricated electrode can effectively detect DA in human urine samples.

Ag x Cu y Ni z Trimetallic Alloy Catalysts for the Electrocatalytic Reduction of Benzyl Bromide in the Presence of Carbon Dioxide.

Different compositions of trimetallic alloy containing silver, copper, and nickel (Ag x Cu y Ni z ) were electrodecorated in a protic ionic liquid medium on glassy carbon electrodes in order to investigate the suitability of the materials as catalysts for electrochemical reduction of carbon dioxide (CO2). Surface characteristic morphology obtained by scanning electron microscopy shows cauliflower crystallites for the deposit of Ag, whereas materials of Cu and Ni exhibit cubic grains and fine particles, respectively. Deposits of trimetallic alloy containing Ag, Cu, and Ni exhibit the mixture of the three characteristic features. Further, trimetallic alloy containing a large amount of Ag provides high crystallinity, whereas predominance of Cu as well as Ni results in porous structures, as revealed by X-ray diffraction analysis. Atomic absorption spectroscopy () was used to determine the compositions of different alloy materials. The suitability of nanomaterials as cathodes for electroreduction of benzyl bromide in CO2 containing 0.1 M tetra-n-butylammonium tetrafluoroborate (DMF/TBABF4)/N,N-dimethylformamide medium was explored. The linear sweep voltammogram reveals that Ag46Cu40Ni14 shows higher cathodic peak current and lower cathodic peak potential than those of other deposited nanomaterials as well as alloys, indicating its higher catalytic activity for such an electroreduction process, whereas potentiostatic electrolysis confirms the abovementioned results.

Probing the interaction of thionine with human serum albumin by multispectroscopic studies and its in vitro cytotoxic activity toward MCF-7 breast cancer cells.

The studies on protein-dye interactions are important in biological process and it is regarded as vital step in rational drug design. The interaction of thionine (TH) with human serum albumin (HSA) was analyzed using isothermal titration calorimetry (ITC), spectroscopic, and molecular docking technique. The emission spectral titration of HSA with TH revealed the formation of HSA-TH complex via static quenching process. The results obtained from absorption, synchronous emission, circular dichroism, and three-dimensional (3D) emission spectral studies demonstrated that TH induces changes in the microenvironment and secondary structure of HSA. Results from ITC experiments suggested that the binding of TH dye was favored by negative enthalpy and a favorable entropy contribution. Site marker competitive binding experiments revealed that the binding site of TH was located in subdomain IIA (Sudlow site I) of HSA. Molecular docking study further substantiates that TH binds to the hydrophobic cavity of subdomain IIA (Sudlow site I) of HSA. Further, we have studied the cytotoxic activity of TH and TH-HSA complex on breast cancer cell lines (MCF-7) by MTT assay and LDH assay. These studies revealed that TH-HSA complex showed the higher level of cytotoxicity in cancer cells than TH dye-treated MCF-7 cells and the significant adverse effect did not found in the normal HBL-100 cells. Fluorescence microscopy analyses of nuclear fragmentation studies validate the significant reduction of viability of TH-HSA-treated human MCF-7 breast cancer cells through activation of apoptotic-mediated pathways.