•We used the ultrasonic-assistant method to extract polysaccharide of Angelica sinensis.•Response surface methodology is used for optimizing the extraction conditions.•We confirm the optimal conditions for polysaccharide extraction of Angelica sinensis.•The polysaccharide had remarkably scavenging capability of hydroxyl radical.In this study, polysaccharides from Angelica sinensis were extracted using the ultrasound-assisted extraction method. Based on the results of single factor experiments and orthogonal tests, three independent variables—water/raw material ratio, ultrasound time, and ultrasound power—were selected for investigation. Then, we used response surface methodology to optimize the extraction conditions. The experimental data were fitted to a quadratic equation using multiple regression analysis, and the optimal conditions were as follows: water/raw material ratio, 43.31 mL/g; ultrasonic time, 28.06 minutes; power, 396.83 W. Under such conditions, the polysaccharide yield was 21.89 ± 0.21%, which was well matched with the predicted yield. In vitro assays, scavenging activity of superoxide anion radicals, hydroxyl radicals, and 2,2-diphenyl-1-picry-hydrazyl radical showed that polysaccharides had certain antioxidant activities and that hydroxyl radicals have a remarkable scavenging capability. Therefore, these studies provide reference for further research and rational development of A. sinensis polysaccharide.Download high-res image (240KB)Download full-size image

•The interaction of BSA with Fe3O4 NPs was studied using the fluorescence method.•Thermodynamic analysis was used to investigate the intermolecular forces.•Energy transfer between BSA and Fe3O4 NPs was investigated.•Synchronous fluorescence spectroscopy indicated the conformation change.Fluorescence quenching was used to study the potential interaction mechanism of Bovine serum albumin (BSA) with either hydrophilic ferroferric oxide (Fe3O4) nanoparticles (NPs) or hydrophobic Fe3O4 NPs. The experimental results indicated the mechanism between BSA and hydrophilic Fe3O4 NPs was static quenching and the one between BSA and hydrophobic Fe3O4 NPs was dynamic process that was drove by Förster's resonance energy transfer (FRET). And the binding parameters for the interaction of BSA with either hydrophilic or hydrophobic Fe3O4 NPs were calculated by using the fluorescence quenching measurement. The binding constant (KA) values of hydrophilic Fe3O4 NPs were 8518.73 ± 23.35 (at 298 K), 1190.31 ± 15.41 (at 306 K) and 321.97 ± 8.57 (at 313 K), respectively. The thermodynamic analysis implied that the intermolecular forces between BSA and hydrophilic Fe3O4 NPs were Van der Waals interaction or hydrogen bond, because the values of ΔH and ΔS between them were negative. While the one of BSA and hydrophobic Fe3O4 NPs involved hydrophobic forces, owing to the positive ΔH and ΔS between them. But they were all enthalpy-driven and exothermic, since their ΔG values were all negative. Synchronous fluorescence spectroscopy suggested that the conformation of tryptophan residue of BSA was changed in the presence of hydrophilic Fe3O4 NPs or hydrophobic Fe3O4 NPs, because the position of the maximum emission wavelength had a discernible red shift.The interaction between BSA and hydrophilic Fe3O4 NPs were Van der Waals interaction or hydrogen bond, and the quenching mechanism of them was static quenching. Instead the interaction between BSA and hydrophobic Fe3O4 NPs were hydrophobic forces, and the mechanism was dynamic quenching.Download high-res image (125KB)Download full-size image

•The interactions between MBP and DPPS, DPPG at the air/water interface were studied by thermodynamic method and AFM.•The quantitative analysis of the interaction of molecules.•MBP could penetrate into both DPPS and DPPG monolayers depending on the concentration of proteins.•These dates are meaningful to understand the myelination process.Myelin basic protein (MBP) relate to multiple sclerosis, experimental cerebral spinal cord inflammation and other diseases of the central nervous system. It has important biological significance for the study the diseases which related to the interaction between myelin basic proteins (MBP) and DPPS, DPPG. In this paper, we studied the interaction between molecules at the air/water interface by thermodynamic method and atomic force microscopy (AFM). Experiments show that the average molecular area increases when the protein is incorporated into lipid monolayer. By means of analyzing surface pressure-mean molecular area (π-A) curves, a linear mass conservation plot (i.e. protein amount vs. a matching amount of lipids) was obtained. In addition, the protein partition coefficient and the mixing ration between protein and lipid were calculated. When the surface pressure of the monolayer was 10 mN/m, one MBP molecule could be combined with (58 ± 4) DPPS and (37 ± 6) DPPG molecules. The interaction between MBP and DPPG (or DPPS) to determine the nervous system of the disease has a good biophysical significance and medical value.

The glycosylphosphatidyl inositol (GPI)-anchored proteins are localized on the outer of the plasma membrane and clustered in membrane microdomain known as lipid rafts. Among them, mammalian alkaline phosphatase (AP) is an enzyme widely distributed. So, it has important biological significance to study the combination of AP with lipid monolayer. In our work, the interaction between AP and sphingomyelin has been studied at the air-buffer interface as a biomimetic membrane system by the Langmuir film technique and atomic force microscopy. The surface pressure-area isotherm for the mixed alkaline phosphatase/sphingomyelin monolayer shown the presence of a transition from a liquid-expanded phase to the liquid-expanded/liquid-condensed coexist phase. And the surface compressional modulus suggested the mixed alkaline phosphatase/sphingomyelin monolayer has larger compressibility compared with the pure sphingomyelin monolayer. Besides, according to the micrographs, we inferred when combined with lipid monolayer at the air-buffer interface, the AP molecules formed polymer not multilayer or micelle. And, according to the limiting molecules area of AP, we inferred that 12 AP molecules formed a hexagon polymer unit.

•The interaction between DOPC and palmitic acid (PA) has been investigated at the air–water interface.•The interaction between DOPC and PA was repulsive in all case.•The strongest interaction between DOPC and PA occurred at 1:1 ratio.•FM and AFM allow observing the phase separation in the monolayer.The interactions between 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) and palmitic acid (PA) in mixed monolayers were investigated through surface pressure measurements, fluorescence microscopy (FM) and atomic force microscopy (AFM). The miscibility of two components and the interactions between DOPC and PA in the mixed monolayers were accessed by analyzing surface pressure (π)–area (A) isotherms. It was found that there were both positive deviations for excess molecular area and excess Gibbs energy, which suggests the interaction is repulsive in all case and the strongest repulsive occurs at XPA = 0.5 ratio. The FM and AFM images showed that there were discernible phase separations at selected surface pressures. The increase of surface pressure and the phenomenon that the PA-enriched domains have been connected to form much larger platforms are in agreement with the thermodynamic results.