Preparation of isoquercitrin and rhamnose from readily accessible rutin by a highly specific recombinant α-L-rhamnosidase (r-Rha1).

Isoquercitrin has superior in vivo bioactivities with respect to its primary glycoside rutin. Its conventional preparation was ineffective, with large chemical consumption and many by-products. Rhamnose, a high value-added monosaccharide, is usually separated from acid hydrolytes of rutin. This study aimed to establish a novel enzymatic hydrolysis-based approach for their preparation. α-L-rhamnosidase was expressed in Pichia pastoris GS115 and applied to enzymolysis of rutin. Then, one-factor-at-a-time optimisation of hydrolysis conditions was performed. Two compounds were produced in 0.02 M HAc-NaAc buffer (pH4.50) containing α-L-rhamnosidase/rutin (1:4, w/w) at 60 °C. Consequently, 20.0 g/L rutin was completely hydrolysed in 2 hrs, and isoquercitrin was obtained after purification by HPD-100 resin. Additionally, rhamnose was enriched by decolorisation and crystallisation. MD simulation analysis suggested that rutin was catalysed on the hydrophobic surface of r-Rha1 with van-der-Waals force being main driving force. This strategy is an efficient approach for preparation of isoquercitrin and rhamnose.

Biotransformation of ginsenoside Rb1 and Rd to four rare ginsenosides and evaluation of their anti-melanogenic effects.

Improving physiological activity of primary ginsenosides through biotransformation is of great significance for food applications. In this study, gynostapenoside XVII, gynostapenoside LXXV, ginsenoside F2, and ginsenoside CK were obtained by enzymolysis of an accessible extract composed of ginsenoside Rb1 and Rd. Their effects on melanin content and tyrosinase activity were compared in vitro, and molecular docking simulation was employed to elucidate the interaction between tyrosinase and individual saponin. The results indicated that four rare ginsenosides decreased tyrosinase activity, melanin content and microphthalmia-associated transcription factor (MITF) expression level, more greatly than their primary ginsenosides, and they were more readily to bind with ASP10 and GLY68 at active site of tyrosinase to inhibit tyrosinase activity as well. These findings suggested that the rare ginsenosides obtained by enzymolysis had excellent anti-melanogenic effect, which could expand the application of ginsenosides in the field of functional foods and health supplements.

Up-conversion luminescence lifetime thermometry based on the 1G4 state of Tm3+ modulated by cross relaxation processes.

ß-PbF2:Tm3+/Yb3+ glass ceramics (GCs) with varied Tm3+ doped concentrations were synthesized by the conventional melting-quenching method and the subsequent glass crystallization route. For the first time, the lifetime-based thermometer based on up-conversion luminescence (UCL) originating from the 1G4 state excited upon a miniaturized 976 nm diode laser excitation in ß-PbF2:Tm3+/Yb3+ GCs is achieved. Furthermore, the thermosensitivity of the 1G4 state lifetime is realized by the phonon-assisted cross relaxation (CR) processes between Tm3+ which depopulate the 1G4 state and get severer with temperature. The relative sensitivity (SR) of the 1G4 state lifetime is promoted by intensifying CR processes via raising Tm3+ concentration in this work. The maximum values of SR of 1G4 state lifetime obtained in 0.0005Tm, 0.01Tm and 0.05Tm are 0.16%K-1, 0.26%K-1, and 0.46%K-1 at 488 K, respectively, which indicates the potential ability of Tm3+-doped nanoparticles to work as indicators for UCL lifetime-based thermometers.

Crystallographic and spectroscopic evidence for intrinsic distortion in the disordered crystal ß-NaGdF4.

ß-NaREF4 (RE: rare earth metals) is a peculiar crystal due to its intriguing disordered structure. This crystal is usually considered to have an average structure with a space group of P-6 (174). However, a long-term contradiction existing in this system is that the luminescence characteristics do not match the corresponding theoretical predictions based on the average structure. To resolve this contradiction, we proposed a reasonable local structure model clearly showing the local symmetry of the cations based on the measurement of the extended X-ray absorption fine structure of ß-NaGdF4. We also observed an intrinsic distortion in the disordered structure that resulted from the disordered arrangement of the Na+ and Gd3+ cations. Furthermore, using Eu3+ as a photoluminescence probe, we concluded that the breakdown in the crystallographic site symmetry originated from the intrinsic distortion of these crystals. This work provides a comprehensive explanation for the contradiction observed in this system and a foundation for further investigations to understand such disordered structures.

Five-fold twinned ß-PbF2 nanocrystals in oxyfluoride glass ceramics.

Oxyfluoride glass ceramics (GCs) doped with trivalent lanthanide ions (Ln3+) have been prepared using a conventional melting-quenching method and studied by X-ray diffraction (XRD). ß-PbF2 nanocrystals (NCs) doped with Ln3+ ions (ß-PbF2:Ln3+) in GCs were released from the GCs by etching off the glass matrix. ß-PbF2:Ln3+ NCs can be clearly observed by eliminating the influence of the glass matrix. The nanotwinned structures of ß-PbF2:Ln3+ NCs, including two-fold twinned NCs and five-fold twinned NCs, were examined using high-resolution transmission electron microscopy (HRTEM). The five-fold twinned phenomenon in metal fluorides with strong ionicity in oxyfluoride GCs is reported for the first time. Based on detailed analysis of the twinned NC structure, the twinning mechanism of ß-PbF2:Ln3+ NCs was proposed. Ln3+ ions and 'sublattice melting' of fluorine ions (F-) in ß-PbF2 play extremely important roles in the formation of five-fold twinned ß-PbF2:Ln3+ NCs. The nanotwinned structures reported here may have far-reaching significance with respect to the further application of oxyfluoride glass ceramics doped with rare-earth elements and NC fabrication.