Study on the mechanism of the interaction between acteoside and pepsin using spectroscopic techniques.

The interaction of acteoside with pepsin has been investigated using fluorescence spectra, UV/vis absorption spectra, three-dimensional (3D) fluorescence spectra and synchronous fluorescence spectra, along with a molecular docking method. The fluorescence experiments indicate that acteoside can quench the intrinsic fluorescence of pepsin through combined quenching at a low concentration of acteoside, and static quenching at high concentrations. Thermodynamic analysis suggests that hydrogen bonds and van der Waal's forces are the main forces between pepsin and acteoside. According to the theory of Förster's non-radiation energy transfer, the binding distance between pepsin and acteoside was calculated to be 2.018 nm, which implies that energy transfer occurs between acteoside and pepsin. In addition, experimental results from UV/vis absorption spectra, 3D fluorescence spectra and synchronous fluorescence spectra imply that pepsin undergoes a conformation change when it interacts with acteoside.

Constructing a tetraphenylethene (TPE) derivative-decorated polyvinyl alcohol (PVA)/lanthanide nanoparticle composite system for tunable luminescence.

A novel tetraphenylethene (TPE) derivative-decorated lanthanide nanomaterial NaLnF4 (denoted as TPEBA-Ln, Ln = Gd3+, Tb3+ and Eu3+) was hydrothermally synthesized using (4-(1,2,2-triphenylvinyl)phenyl) boronic acid (TPEBA)-modified polyvinyl alcohol (PVA) as a coating ligand. Interestingly, the aggregation-induced emission (AIE) of the TPE moiety was activated because the intramolecular rotation of TPEBA was restricted via the esterification of TPEBA with PVA. More excitingly, it was found for the first time that the TPEBA-based ligand could further act as a donor and transfer energy to the lanthanide nanoparticle (Ln = Eu3+ and Tb3+) acceptor in this TPEBA-Ln system. Encouragingly, TPEBA had advantageous effects on the emission of the composite material, in which a more effective energy transfer process from the ligand to lanthanide ions was observed when TPEBA tended to be isolated on the surface of the nanoparticles. Furthermore, the material combining different ratios of TPEBA, Tb3+ and Eu3+ displayed tunable luminescence properties covering the wavelength range from 400 nm to 700 nm in the visible region due to the established energy transfer path (tetraphenylethene derivative-Tb3+-Eu3+), which provided a facile and effective strategy to obtain potential full-color emitters. Strikingly, distinct luminescence properties were induced by adding different PVA samples. When PVA with a higher hydrodynamic radius (Rh) and more curly structure was added, it substituted some TPEBA molecules and then twined around the surface to lock and isolate the remaining TPEBA molecules, resulting in a blueshift in the peak together with increased intensity in the emission spectrum. However, only attenuated aggregate emission was observed upon the addition of PVA with a lower Rh and more stretched chains because the arrangement of the TPEBA left on the surface was not significantly affected by the displacement of this type of PVA. This discovery may provide a facile approach to design and prepare more promising candidates as tunable optical composite materials and TPE-based fluorescent sensors.

Controllable fluorescence via tuning the m-substituents of added aromatic molecules in a pyrene derivative-decorated porous skeleton.

A novel pyrene derivative based composite fluorescent material was developed by immobilizing the pyrene-1-carboxylic acid (PyCOOH) into the pores of porous polyurea microspheres (denoted as PyCOOH-decorated PPUM). Encouragingly, the fluorescence spectrum of this synthesized composite microsphere only exhibited monomer emission of guest PyCOOH, indicating that the porous skeleton PPUM has excellent isolation ability to separate the guest molecules from each other. This discovery will provide an effective strategy to design and synthesize pyrene based host-guest systems without excimer emission. Notably, the PyCOOH-decorated PPUM can keep good fluorescent stability when dispersed in many organic solvents. More excitingly, it was found for the first time that the fluorescence of such a material can be regulated by adding aromatic compounds containing different m-substituted groups. When m-cresol was added, the intensity of the monomer emission enhanced significantly due to the unusual dissolution of the host porous polyurea sphere. By adding the m-toluidine, the monomer emission without the fluorescence of unassociated PyCOOH increased owing to the connection of m-toluidine and PyCOOH which escaped from the pores. In the presence of m-methylacetophenone and m-toluic acid, the monomer emission showing different degrees of decline was observed respectively because of the different substitution process. This result will contribute to the exploration of more promising candidates for pyrene-based fluorescent sensors.

Dissection of binding of trypsin to its natural inhibitor Gensenoside-Rg1 using spectroscopic methods and molecular modeling.

The interaction of trypsin with Gensenoside-Rg1 (G-Rg1) was studied using fluorescence, ultraviolet-visible (UV-vis), and circular dichroism (CD) spectroscopies along with enzyme activity assay and molecular docking. The enzyme activity assays showed that G-Rg1 inhibited the activity of trypsin effectively. The fluorescence experiments indicated that a complex of G-Rg1-trypsin was formed and that the fluorescence of trypsin was quenched by G-Rg1 via a mixed-quenching mechanism (both static and dynamic quenching). The thermodynamic analysis suggested that hydrophobic interaction and hydrogen bond were the major forces between G-Rg1 and trypsin. According to the theory of Förster's non-radiation energy transfer, the binding distance between trypsin and G-Rg1 was calculated to be 2.01 nm, which implies that energy transfer occurred within the complex. The experimental results obtained from UV-vis absorption spectra, synchronous fluorescence spectra, and CD spectra indicated that G-Rg1 was mainly located on tryptophan moiety and that the interaction between G-Rg1 and trypsin led to conformational changes of trypsin with some α-helix and unordered coil structures being transformed into ß-sheet structures. In addition, docking results supported the above experimental findings and suggested the possible binding location of G-Rg1 on trypsin along with the possible hydrogen bonds and hydrophobic interactions between G-Rg1 and trypsin. The experimental results from this study should be useful to minimize the antinutritional effects and make full use of Genseng extracts in the food industry and also be helpful to the design of the drugs for the diseases related to overexpression of trypsin. Communicated by Ramaswamy H. Sarma.

Inducing the distinctly different fluorescence properties of a tetraphenylethene (TPE) derivative modified lanthanide nanowire upon the addition of a pair of cis- and trans-isomers of fatty acids.

A simple layer-by-layer approach has been developed to introduce a 3,5-dicarboxylphenoxy decorated tetraphenylethene derivative (denoted as TPE-2COOH) into a lanthanide nanowire. Interestingly, the aggregation-induced emission (AIE) was turned on by loading the negative TPE-2COOH on the positive surface of the nanowire via electrostatic interactions. More excitingly, these synthesized composite nanowires exhibit significantly different fluorescence properties in the presence of a pair of cis- and trans-isomers of fatty acids (oleic acid and elaidic acid). The obvious emission peak (382 nm) upon the addition of oleic acid (cis-configuration) was observed, which was consistent with that of the frozen diluted TPE-2COOH solution (1.95 × 10-10 mol L-1), demonstrating the occurrence of the monomer emission of TPE-2COOH. When the oleic acid with a special cis-configuration got close to the nanowire, it substituted some TPE-2COOH and arranged as cages on the surface to isolate the TPE-2COOH molecule, leading to the monomer emission. Different from such monomer emission induced by oleic acid, an attenuated aggregate emission was detected by the addition of its trans isomer elaidic acid, because it is almost impossible for the elaidic acid with a linear structure to form the cage-like shape on the surface during the substitution process. It was found for the first time that the fluorescence of such a TPE-based material can be controlled by the configuration of isomers. This discovery may provide a facile strategy to design and synthesize more promising candidates for TPE-based fluorescent sensors.