Yuan Wang

Bottom-Up Construction of POM-Based Macrostructures: Coordination Assembled Paddle-Wheel Macroclusters and Their Vesicle-like Supramolecular Aggregation in Solution

A bottom-up approach to obtain nanoclusters and large, uniform vesicle-like structures containing organic functionalized hexamolybdates in solution state were developed. Hexamolybdate functionalized carboxylic acid coordinated with two copper ions to form paddle-wheel tetrapolyoxometalate clusters with the features of macro-ions, which can spontaneously assemble into large, stable blackberry-type structures in suitable solvents, completing a hierarchical organization from small POM molecules to nanoscale complexes and then to supramolecular structures.

Colloidal Nanoparticles of a Europium Complex with Enhanced Luminescent Properties

We report an alternative approach, that is, forming Eu(tta)3dpbt (dpbt = 2-( N, N-diethylanilin-4-yl)-4,6-bis(3,5-dimethylpyrazol-1-yl)-1,3,5-triazine, tta = thenoyltrifluoroacetonato) nanoparticles in water/methanol mixtures, to satisfy the combined requirements of good dispersibility in water solutions and efficient long-wavelength sensitization for Eu (III) complexes to be used in biological applications. The size of Eu(tta)3dpbt colloidal particles with very high luminescent capabilities can be modulated to some extent by changing the preparation conditions. The optical excitation window for the Eu (III) luminescence of Eu(tta)3dpbt nanoparticles, extending up to 475 nm, is wider than that of Eu(tta)3dpbt molecules dissolved in toluene. This is the first example for obviously extending the sensitization window of luminescent lanthanide materials to the long-wavelength region by forming nanoparticles of a lanthanide complex. Quantum yields of Eu (III) luminescence of the prepared Eu(tta)3dpbt colloidal particles, with an average diameter of 33.1 nm, are 0.27, 0.27, 0.24, 0.19, 0.14, and 0.01 upon excitation at 402, 420, 430, 440, 450, and 475 nm, respectively. The Eu(tta)3dpbt nanoparticles exhibited excellent two-photon sensitization performance with a highest delta Phi value of 3.2 x 10(5) GM (1 GM = 10(-50) cm4 s photo(-1) particle(-1)) at the excitation wavelength of 832 nm, which is about 7 times higher than the highest value reported for the CdSe/ZnS core-shell quantum dots. The favorable luminescent properties and the good dispersibility in water solutions of the Eu(tta)3dpbt nanoparticles are very promising for the development of new luminescent nanoprobes for bioanalysis.

Role of ligand-to-metal charge transfer state in nontriplet photosensitization of luminescent europium complex.

We have investigated, by means of steady-state and time-resolved optical spectroscopies, the excited-state dynamics of the luminescent europium complex Eu(III)(tta)(3)dpbt (tta = henoyltrifluoroacetonate; dbpt = 2-(N,N-diethylanilin-4-yl)-4,6-bis(3,5-dimethylpyrazol-1-yl)-1,3,5-triazine) with Gd(III)(tta)(3)dpbt and Tb(III)(tta)(3)dpbt as the reference complexes that cannot be photosensitized. In the Eu(III)(tta)(3)dpbt complex, the ligand dpbt exhibited biphasic fluorescence decay kinetics; the faster component (decay time constant, 8.5 ps) is ascribed to the rapid conversion of the lowest-lying singlet excited state of dpbt (S(1) or (1)dpbt*) to a ligand-to-metal charge transfer singlet state of the complex ((1)LMCT*), whereas the slower one (1.8 ns) is shown by temperature-dependent luminescence spectroscopy to be delayed fluorescence due to the LMCT-to-dpbt backward energy transfer and represents the time scale of efficient excitation energy flow from the (1)LMCT* state to the (5)D(1) state of Eu(III). On the basis of the spectroscopic results of the Ln(III)(tta)(3)dpbt complexes (Ln = Eu, Gd, and Tb), the crucial role of the (1)LMCT* state in photosensitization of the Eu(III)(tta)(3)dpbt complex is established, and a LMCT-mediated nontriplet sensitization mechanism is proposed, which is advantageous in high efficiency and low excitation photon energy as well as in low susceptibility against oxygen quenching.

Preparation of colloidal solutions of thin platinum nanowires

Colloidal solutions of thin platinum nanowires having lengths of 10 to 70 nm and diameters of 1.5–3 nm were prepared by reducing K2PtCl4 with hydrogen in a glycol solution containing K2C2O4 and preformed Pt seeds. TEM, HRTEM, XRD and UV-Vis absorption spectroscopy were used to study the structure of the obtained nanowires and the effect of preparation conditions, such as pH value, temperature, preformed Pt nanoseeds and stabilizing agents, on the morphology of the products. The mechanism for forming the thin Pt nanowires in the absence of a 1D structure template was discussed based on the experimental results. Stable colloidal solutions of mercaptan-modified Pt nanowires were prepared for the first time by transferring the prepared thin Pt nanowires into toluene containing octadecylmercaptan.

Bionanoprobes with Excellent Two‐Photon‐Sensitized Eu3+ Luminescence Properties for Live Cell Imaging

Bioimaging or bioanalysis based on nanoprobes encapsulating Eu 3 + complexes with excellent two-photon-sensitized (TPS) luminescence properties combines the advantages of deep penetration, high sensitivity, high signal-to-noise ratio, stable signals during long term observation, low photodamage to biological samples, and desirable target recognizability. The TPS luminescence of lanthanide complexes is produced through the two-photon excitation (TPE) of a lightharvesting antenna ligand and subsequent excitation energy transfer (EET) to the metal ions, which provides a promising manner for extending the excitation windows of lanthanide complexes to the near-infrared (NIR) light wavelength region. In the last two decades, remarkable progress has been achieved in the design and synthesis of two-photonsensitized luminescent lanthanide complexes. [1] Several lanthanide complexes have been applied to the multiphoton-excited bioimaging of cells. [2–4] Due to the characteristic luminescence properties of Eu 3 + complexes, such as the characteristic narrow-line emission in the red-light wavelength region with acceptable transparence for many biosamples, high luminescence quantum yields, large Stokes shifts, and long luminescence lifetime (millisecond order), the TPS Eu 3 + luminescence is of significance for developing bioanal

Solvent‐Stabilized Photoconductive Metal Phthalocyanine Nanoparticles: Preparation and Application in Single‐Layered Photoreceptors

This article features solvent-stabilized nanoparticles of photoconductive metal phthalocyanines (MPcs) with small particle sizes and narrow size distributions, which are tractable building blocks for photoelectric devices. The preparation and stabilization mechanism of 1,2-dichloroethane (DCE)-stabilized oxovanadium phthalocyanine (VOPc) and oxotitanium phthalocyanine (TiOPc) nanoparticles are discussed. It is found for the first time that the DCE-stabilized TiOPc and VOPc nanoparticles are positively charged with zeta potentials of about +66 mV, which is ascribed to the electron transfer from the nanoparticles to DCE molecules. The excellent xerographic properties of the single-layered photoreceptors based on TiOPc or VOPc nanoparticles and the charge transport mechanism of these photoreceptors are discussed. The strategy for further improving the xerographic properties of single-layered photoreceptors is proposed.

Catalytic Asymmetric Total Synthesis of (−)‐Galanthamine and (−)‐Lycoramine

The catalytic asymmetric total syntheses of (-)-galanthamine (1) and (-)-lycoramine (2) have been achieved by using a conceptually new strategy featuring two metal-catalyzed reactions as the key steps. A new method for the construction of 3,4-fused benzofurans has been developed through a palladium-catalyzed intramolecular Larock annulation reaction, which was successfully applied to the construction of the ABD tricyclic skeleton of 1 and 2. To achieve the asymmetric synthesis of 1 and 2, a Sc(III)/N,N-dioxide complex was used to catalyze the enantioselective conjugate addition of 3-alkyl-substituted benzofuranone to methyl vinyl ketone for the construction of a chiral quaternary carbon center.

An excellent single-layered photoreceptor composed of oxotitanium phthalocyanine nanoparticles and an insulating resin.

Photoconductive oxotitanium phthalocyanine (TiOPc) nanoparticles with an average diameter of 3.6 nm were successfully prepared. These nanoparticles could be well dispersed in organic solvents such as 1,2-dichloroethane to form a stable organic sol of solvent-stabilized TiOPc nanoparticles. An obvious size effect of TiOPc semiconductor was revealed by the UV-vis absorption spectroscopy measurements. Single-layered photoreceptors were prepared by coating colloidal solutions containing the C(2)H(4)Cl(2)-stabilized TiOPc nanoparticles and a polycarbonate (PC) resin onto aluminum plates. Optimum xerographic properties of the present photoreceptors were obtained on a photoreceptor containing 20 wt% of the TiOPc nanoparticles, which exhibited a photoconductive sensitivity (E(1/2)) of 0.54 microJ/cm(2) and could be positively charged to 596 V.

Synthesis of Site-Specifically Phosphate-Caged siRNAs and Evaluation of Their RNAi Activity and Stability

A complete set of new photolabile nucleoside phosphoramidites were synthesized, then site-specifically incorporated into sense or antisense strands of siRNA for phosphate caging. Single caging modification was made along siRNA strands and their photomodulation of gene silencing were examined by using the firefly luciferase reporter gene. Several key phosphate positions were then identified. Furthermore, multiple caging modifications at these key positions led to significantly enhanced photomodulation of gene silencing activity, suggesting a synergistic effect. The caging group on both the terminally phosphate-caged siRNA and the single-stranded caged RNA has comparatively high stability, whereas hydrolysis of the caged group from the internally caged siRNA was observed, irrespective of the presence of Mg(2+). Molecular dynamic simulations demonstrated that enhanced hydrolysis of the caging group on internally phosphate-caged siRNAs was due to easy fragmentation of the caging group upon formation of the pentavalent intermediate of the phosphotriester with attack by water. The caging group in the terminally phosphate-caged siRNA or single-stranded caged RNA prefers to form π-π stacks with nearby nucleobases. In addition to providing explanations for previous observations, this study sheds further light on the design of caged oligonucleotides and indicates the direction of future development of nucleic acid drugs with phosphate modifications.

Regioselective Direct C-4 Functionalization of Indole: Total Syntheses of (-)-Agroclavine and (-)-Elymoclavine

An efficient rhodium-catalyzed method for direct C-H functionalization at the C4 position of unprotected indoles has been developed. The utility of this method is demonstrated by the concise total syntheses of agroclavine and elymoclavine in a divergent manner. These syntheses feature a Pd-catalyzed asymmetric allylic alkylation reaction to assemble the triyclic indole moiety, and a ring-closing metathesis reaction to form the D ring.