Ruthenium‐Catalyzed Metathesis Cascade Reactions in Natural Products Synthesis

In this account, we provide a brief summary of recent developments in ruthenium‐catalyzed metathesis cascade reactions towards the total synthesis of natural products. We also highlight recent progress from our own laboratory regarding the synthesis of securinega alkaloids and humulanolides, which has resulted in the development of novel ruthenium‐catalyzed metathesis cascade reactions. Inspired and guided by the pioneering and elegant research conducted in this area, we developed a regio‐controlled relay dienyne metathesis cascade reaction and a cyclobutene‐promoted RCM/ROM/RCM cascade reaction for the synthesis of securinega alkaloids and humulanolides, respectively.     

Thermal stresses in a viscoelastic three-phase composite cylinder

A thermoviscoelastic analysis of a three-phase composite cylinder is presented in this work. The solutions of the heat conduction and thermoelastic problem for three dissimilar media are derived based on the method of analytic continuation associated with the alternation technique. A rapidly convergent series solution for both the temperature and stress field, which is expressed in terms of an explicit general term of the corresponding homogeneous potential, is obtained in an elegant form. The hereditary integral in conjunction with the Kelvin–Maxwell model is applied to simulate the thermoviscoelastic properties while a thermorheologically simple material is considered. According to the correspondence principle, the Laplace transformed thermoviscoelastic solution is directly determined from the corresponding thermoelastic one. The real time solution can then be solved numerically by taking inverse Laplace transform. Finally, some typical examples of interfacial stresses are discussed.     

Optical and structural characteristics of yttrium doped ZnO films using sol–gel technology

Yttrium-doped ZnO gel was spin-coated on the SiO₂/Si substrate. The as-prepared ZnO:Y (YZO) thin films then underwent a rapid thermal annealing (RTA) process conducted at various temperatures. The structural and photoluminescence characteristics of the YZO films were discussed thereafter. Our results indicated that the grain size of YZO thin films being treated with various annealing temperatures became smaller as compared to the ones without being doped with yttrium. Furthermore, unlike other ZnO films, the grains of YZO thin films appeared to separate from one another rather than aggregating together as both types of the films were annealed under the same environment. The photoluminescence characteristic measured showed that the UV emission was the only radiation obtained. However, the UV emission intensity of YZO thin film was much stronger than that of the ZnO thin film after annealing them with the same condition. It was also found that the intensity increased with an increase in the annealing temperature, which was caused by the exciton generated and the texture surface of the YZO thin film.     

Visible and infrared luminescence properties of Er-doped Y2Ti2O7 nanocrystals

Er³⁺-doped Y₂Ti₂O₇ nanocrystals were fabricated by the sol-gel method. While the annealing temperature exceeds 757 °C, amorphous pyrochlore phase Er_xY_2−xTi₂O₇ transfers to well-crystallized nanocrystals, and the average crystal size increases from ∼70 to ∼180 nm under 800-1000 °C/1 h annealing. Er_xY_2−xTi₂O₇ nanocrystals absorbing 980 nm photons can produce the upconversion (526, 547, and 660 nm; ²H_11/2→⁴I_15/2, ⁴S_3/2→⁴I_15/2, and ⁴F_9/2→⁴I_15/2, respectively) and Stokes (1528 nm; ⁴I_13/2→⁴I_15/2) photoluminescence (PL). The infrared PL decay curve is single-exponential for Er³⁺ (5 mol%)-doped Y₂Ti₂O₇ nanocrystals but slightly nonexponential for Er³⁺ (10 mol%)-doped Y₂Ti₂O₇ nanocrystals. For 5 and 10 mol% doping concentrations, the mechanism of up-converted green light is the two-photon excited-state absorption. Much stronger intensity of red light relative to green light was observed for the sample with 10 mol% dopant. This phenomenon can be attributed to the reduced distance between Er³⁺-Er³⁺ ions, resulting in the enhancement of the energy-transfer upconversion and cross-relaxation mechanisms.     

In situ spectral imaging of marker proteins in gastric cancer with near-infrared and visible quantum dots probes

This study presents the investigation of bioconjugating ability of near-infrared (NIR) CdSeTe/ZnS quantum dots (QDs) (710 nm) and visible CdSe QDs (595 nm) in immunofluorescent staining for cancer biomarkers in gastric cancer tissues probed with the homemade Hadamard transform (HT) spectral imaging microscope and a commercial multispectral imaging system. The results show that imunostaining ability of NIR QDs probes is stronger than that of visible QDs when the two kinds of QDs are simultaneously used to probe the cancer biomarkers such as cytokeratin 20 (CK20) and proliferating cell nuclear antigen (PCNA) in gastric cancer tissues. Moreover, when the two QDs probes are used for immunostaining successively for the same target molecules, staining order has great influences on the final results due to their different conjugating ability to the marker proteins. The results imply that NIR QDs hold more promise for real-time imaging of tumor tissues due to its higher sensitivity and contrast. In addition, the results also demonstrate the potential of Hadamard transform spectral imaging as a useful tool in biomedical analysis and quantitative evaluation for tumor tissues.     

Synthesis and characterization of Cu(In(x)B(1-x))Se2 nanocrystals for low-cost thin film photovoltaics

Chalcopyrite quaternary semiconductor Cu(In(x)B(1-x))Se(2) nanocrystals have been successfully prepared via a relatively simple and convenient solvothermal route. The effect of different solvents on the formation of the product also indicates that diethylenetriamine is the optimal solvent for this reaction. The device parameters for a single junction Cu(In(x)B(1-x))Se(2) solar cell under AM1.5G are as follows: an open circuit voltage of 265 mV, a short-circuit current of 25.90 mA/cm(2), a fill factor of 34%, and a power conversion efficiency of 2.34%. Based on a series of comparative experiments under different reaction conditions, the probable formation mechanism of crystal Cu(In(x)B(1-x))Se(2) nanorods is proposed.     

Three-component and nonclassical reaction of phosphines with enynes and aldehydes: formation of γ-lactones featuring α-phosphorus ylides

Inverted carbenoid species, generated from attack of phosphines at the α(δ')-carbon of hex-2-en-4-ynedioic acid dialkyl esters, react with aldehydes to give γ-lactones possessing an α-phosphorus ylide moiety.     

Excited-state intramolecular proton transfer molecules bearing o-hydroxy analogues of green fluorescent protein chromophore

o-Hydroxy analogues, 1a-g, of the green fluorescent protein chromophore have been synthesized. Their structures and electronic properties were investigated by X-ray single-crystal analyses, electrochemistry, and luminescence properties. In solid and nonpolar solvents 1a-g exist mainly as Z conformers that possess a seven-membered-ring hydrogen bond and undergo excited-state intramolecular proton transfer (ESIPT) reactions, resulting in a proton-transfer tautomer emission. Fluorescence upconversion dynamics have revealed a coherent type of ESIPT, followed by a fast vibrational/solvent relaxation (<1 ps) to a twisted (regarding exo-C(5)-C(4)-C(3) bonds) conformation, from which a fast population decay of a few to several tens of picoseconds was resolved in cyclohexane. Accordingly, the proton-transfer tautomer emission intensity is moderate (0.08 in 1e) to weak (～10(-4) in 1a) in cyclohexane. The stronger intramolecular hydrogen bonding in 1g suppresses the rotation of the aryl-alkene bond, resulting in a high yield of tautomer emission (Φ(f) ≈ 0.2). In the solid state, due to the inhibition of exo-C(5)-C(4)-C(3) rotation, intense tautomer emission with a quantum yield of 0.1-0.9 was obtained for 1a-g. Depending on the electronic donor or acceptor strength of the substituent in either the HOMO or LUMO site, a broad tuning range of the emission from 560 (1g) to 670 nm (1a) has been achieved.     

CO2 emission free co-generation of energy and ethylene in hydrocarbon SOFC reactors with a dehydrogenation anode

A dehydrogenation anode is reported for hydrocarbon proton conducting solid oxide fuel cells (SOFCs). A Cu-Cr(2)O(3) nanocomposite is obtained from CuCrO(2) nanoparticles as an inexpensive, efficient, carbon deposition and sintering tolerant anode catalyst. A SOFC reactor is fabricated using a Cu-Cr(2)O(3) composite as a dehydrogenation anode and a doped barium cerate as a proton conducting electrolyte. The protonic membrane SOFC reactor can selectively convert ethane to valuable ethylene, and electricity is simultaneously generated in the electrochemical oxidative dehydrogenation process. While there are no CO(2) emissions, traces of CO are present in the anode exhaust when the SOFC reactor is operated at over 700 °C. A mechanism is proposed for ethane electro-catalytic dehydrogenation over the Cu-Cr(2)O(3) catalyst. The SOFC reactor also has good stability for co-generation of electricity and ethylene at 700 °C.     

Optical waveguides at micro/nanoscale based on functional small organic molecules

Optical waveguides synthesized at the micro/nanoscale have drawn great interest for their potential applications in high speed miniaturized photonic integrations. In this Perspective article, we mainly focus on the related works on active optical waveguides based on functional small organic molecules in micro/nano regime. We begin with a general overview of recent progress in sub-wavelength optical waveguides, including the development of waveguide materials of inorganic semiconductors, polymers, and small organic molecules. Then brief highlights are put on the recently reported organic optical waveguides with various unique optical properties induced by the ordered molecular aggregations in the micro/nano-sized solid-state structures, such as polarized emission, lasing, aggregation-induced enhanced emission, etc. This article concludes with a summary and our personal view about the direction of future development in organic opto-functional waveguides as photonic devices.