Assembly of Lanthanide-Containing Tungstotellurates(VI): Syntheses, Structures, and Catalytic Properties.

Lanthanide (Ln)-containing polyoxometalates (POMs) have attracted particular attention owing to their structural diversity and potential applications in luminescence, magnetism, and catalysis. Herein three types of Ln-containing tungstotellurates(VI) (Ln = Dy3+, Ho3+, Er3+, Tm3+, Yb3+, and Lu3+), dimeric (DMAH) n [H22-n {Ln(H2O)3[TeW17O61]}2]·mH2O (abbreviated as {Ln2Te2W34}; DMAH+ = dimethylammonium), mono-substituted (DMAH)7Na2{H2Ln(H2O)4[TeW17O61]}·mH2O (abbreviated as {LnTeW17}), and three-dimensional (3D) inorganic frameworks (DMAH) n {H3-n Ln(H2O)4[TeW6O24]}·mH2O (abbreviated as {LnTeW6}), have been synthesized by using simple metal salts and characterized by single-crystal X-ray diffraction and other routine techniques. Interestingly, the assembly of these POMs is pH dependent. Using the same starting materials, {Ln2Te2W34} were obtained at pH 1.7, where two Dawson-like monovacant [TeW17O61]14- are linked by two Ln3+ ions; mono-substituted Dawson-like {LnTeW17} were isolated at pH 1.9, and 3D inorganic framework {LnTeW6} based on Anderson-type [TeW6O24]6- were formed at pH 2.3. It was also found that the assembly of Ln-containing POMs depends on the type of Ln3+ ions. The three types of POMs can be prepared by using Ln3+ ions with a relatively smaller ionic radius, such as Tb3+-Lu3+, while the use of Ln3+ ions (La3+-Eu3+) results in the formation of precipitation or {TeW18O62} clusters. Furthermore, three {LnTeW6} (Ln = Tb3+, Er3+, Lu3+) were used as Lewis acid catalysts for the cyanosilylation of benzaldehydes, and their catalytic activity decreases with the decrease of Ln3+ ionic radius, giving the order: {TbTeW6} > {ErTeW6} > {LuTeW6}. Notably, {TbTeW6} is stable to leaching and can be reused for five cycles without a significant loss of its activity.

Investigation of ECD conformational transition mechanism of GLP-1R by molecular dynamics simulations and Markov state model.

As a member of the class B G protein-coupled receptors (GPCRs), the glucagon-like peptide-1 (GLP-1) can regulate the blood glucose level by binding to the glucagon-like peptide-1 receptor (GLP-1R). Since the extracellular domain (ECD) of GLP-1R is considered as one of the binding sites of GLP-1, the open and closed states of ECD play an important role in the binding process of GLP-1. To investigate the transition path of GLP-1R ECD, the crystal structures of GLP-1R in its bound and unbound states (apo-state) are chosen to perform a total of 1.6 µs of molecular dynamics simulations. The simulated results show that the ECD of GLP-1R closes in the GLP-1 bound state and opens in the GLP-1 unbound state. To determine the critical role that GLP-1 played in regulating the open and closed states of the ECD, we applied the independent gradient model (IGM) to the simulation trajectories. We found that the "hand-like" N-terminal of the GLP-1R ECD plays an important role in the GLP-1 binding. In contrast, the apo-state GLP-1R ECD opens and exposes the two ligand binding domains of GLP-1 after 200 ns of simulations. To elucidate the open and closed mechanisms of GLP-1R ECD in the apo-state and GLP-1 bound state, the Markov state model (MSM) is performed on the MD simulation trajectories. Our results provide possible transition pathways from the closed state to open state of the apo-state GLP-1R ECD. Each pathway contains several intermediate states that correspond to different local minima in deep wells. The dynamical relationships and the most possible conversion pathway between two states are detailed through the MSM analysis. Our results profile the conformation transition mechanism of the GLP-1R ECD and will help in hypoglycemic peptide design of GLP-1R.

Self-Assembly of Ln(III)-Containing Tungstotellurates(VI): Correlation of Structure and Photoluminescence.

The generation of five types of Ln(III)-containing tungstotellurates(VI), dimeric (DMAH)12Na2[H10(WO2){Ln(H2O)5(TeW18O65)}2]· nH2O (abbreviated as {Ln2Te2W37}; Ln = Eu, Gd, or Tb; DMAH = dimethylammonium), tetrameric (DMAH)21Na7[H16{Ln(H2O)5(TeW18O64)}4]· nH2O (abbreviated as {Ln4Te4W72}, Ln = Eu or Gd), 2:2 dimeric (DMAH)12[H6{Tb(H2O)3(TeW17O61)}2]·25H2O (abbreviated as {Tb2Te2W34}), 1:1 monosubstituted (DMAH)7Na2[H2Tb(H2O)4(TeW17O61)]·21H2O (abbreviated as {TbTeW17}), and three-dimensional polymer (DMAH)2[HTb(H2O)4{TeW6O24}]·14H2O (abbreviated as {TbTeW6} n), provides insight into the rich condensation chemistry of lacunary and other Dawson-type polyoxometalates. The pH and the type of Ln3+ source both dictate which of these new complexes form. To our knowledge, {Ln4Te4W72} is the highest-nuclearity tungstotellurate to date, and {Tb2Te2W34} and {TbTeW17} contain the first lacunary {TeW17O61}. Electrospray ionization mass spectra analyses indicate that the Dawson-like building blocks, {TeW18O65} and {TeW17O61}, found in solid structures are also present in solution. The intense photoluminescence (characteristic green emission) of {TbTeW6} n, 100× greater than those of {Tb2Te2W37}, {Tb2Te2W34}, and {TbTeW17}, is explained by analysis of all 4 X-ray structures and multiple structure-intensity correlations.