Synthesis of star-shaped monodisperse oligo(9,9-di-n-octylfluorene-2,7-vinylene)s functionalized truxenes with two-photon absorption properties

A series of new star-shaped monodisperse conjugated truxene derivatives bearing oligo(fluorene-vinylene) arms (Tr-OFVn, n = 1, 2, 3, 4) have been synthesized. It is found that the conjugation of the oligomers can be extended with prolonging the arms. Notably, the branched oligomers Tr-OFVn without strong donor and acceptor units exhibit two-photon absorption properties, and the two-photon absorption cross sections (δ(max)) increase with increasing the number of fluorene-vinylene units in the arms. The maximum value of δ(max) reaches 8073 GM for compound Tr-OFV4, which made it one of the most competitive compounds with enhanced TPA cross section. It provides a new platform for exploiting strong TPA compounds, in which the extended π-conjugated systems are involved in the absence of strong donor and acceptor units.     

On inequalities of Lyapunov for linear Hamiltonian systems on time scales

In this paper, we establish several new Lyapunov type inequalities for linear Hamiltonian systems on an arbitrary time scale T when the end-points are not necessarily usual zeroes, but rather, generalized zeroes, which generalize and improve all related existing ones including the continuous and discrete cases.     

Density functional theory for rod-coil polymers with different size segments

A polymer density functional theory (PDFT) for rod-coil copolymers with different size segments is proposed, in which the PDFT approach combines a modified fundamental measure theory for the excluded-volume effects, Wertheim's first-order thermodynamics perturbation theory for the chain connectivity and the mean field approximation for van der Waals attraction. First, for testing the PDFT derived, we compare the density profiles from present theory to simulation data, and find that the present theory successfully reproduces the simulation data. Therefore, we use the PDFT to further investigate the local density and solvation forces of rod-coils with different size (A(5)D(3)) and the same size (A(5)B(3)) segments. Results indicate that the excluded volume effect from the coil part determines the solvation force profiles of two rod-coil brushes at strong surface energy. In addition, owing to the vacuum effect, the weak attraction around the classical contact of the rod-coil brushes is also observed. In short, the present theory can be easily applied to the other architecture polymers containing different size segments. It is expected that the calculation results in this work could provide useful reference to select the rod-coils as stabilizer for the protection of surfaces or the colloidal stabilization.     

Probing the role of the bridging C509 between the [Fe4S4] cubane and the [Ni(p)Ni(d)] centre in the A-cluster of acetyl-coenzyme A synthase

The A-cluster of acetyl-coenzyme A synthase consists of an [Fe(4)S(4)] cubane bridged to a [Ni(p)Ni(d)] centre via C509 cysteinate. The bridging cysteinate, which could be substituted by histidine imidazole, mediates "communication" between the [Fe(4)S(4)] cubane and the [Ni(p)Ni(d)] centre during the synthesis of acetyl-coenzyme A.     

Surface modification of polyoxometalate host-guest supramolecular architectures: from metal-organic pseudorotaxane framework to molecular box

Precise controlling of the pH value leads to the formation of a new type of metal-organic pseudorotaxane framework and supramolecular box within accommodating POMs guests.     

Solvent autoxidation, electrolyte decomposition, and performance deterioration of the aprotic Li-O2 battery

The electrolyte decomposition is widely recognized as the greatest challenge to the successful development of the aprotic Li-O₂ battery. The decomposition of the organic ethers, which are the commonly used electrolyte solvents in the current studies, can be chemical or electrochemical during discharge or charge. In this paper, the influence of oxygen on the decomposition of the ether-based electrolyte is discussed. Ether solvents are found to be oxidized in contact with oxygen whether the cells operate or not. The solvent autoxidation significantly promotes the electrolyte decomposition during the discharge process of the ether-based Li-O₂ battery. As a result, the oxygen exposure time before battery operation significantly affects the electrochemical performance of the ether-based Li-O₂ battery. After the prolonged exposure to oxygen, both the discharge capacity and the working potential of the battery decrease to some extent. More importantly, the recharge potential of the battery greatly increases with extending the previous oxygen exposure time.     

Encapsulation of tyrosinase within liposome bioreactors for developing an amperometric phenolic compounds biosensor

A novel tyrosinase (Tyr) biosensor based on liposome bioreactor and chitosan (CS) nano-composite has been developed for the detection of phenolic compounds. Liposome-based bioreactors were prepared by encapsulating the enzyme Tyr in l-α-phosphatidylcholine liposome resulting in spherical bioreactor with a mean diameter of 8.5?±?1.25 μm. The encapsulation efficiency and drug loading content of the Tyr-loaded liposome-based bioreactors were about 46.35?±?0.85 and 41.15?±?0.95 %, respectively. Porins were embedded into the lipid membrane, allowing for the free substrate transport, but not that of the enzyme due to size limitations. The glassy carbon electrode (GCE) was alternately immersed in CS and Tyr liposome bioreactor (TLB) to assemble bilayer films [(CS/TLB)/GCE]. The presence of Tyr in the biosensor was confirmed by scanning electron microscopy, cyclic voltammetry, and electrochemical measurements. The results indicated that the biosensor was applied to detect phenol with a broad linear range from 0.25 nM to 25 μM, the detection limit was brought down to 0.091 nM. The apparent Michaelis–Menten constant, K _m, for the enzymatic reaction was 34.78 μM. The novel biosensor exhibits good repeatability and stability. Such new biosensor based on encapsulation of Tyr within liposome bioreactors shows great promise for rapid, simple, and cost-effective analysis of phenolic contaminants in environmental samples. The proposed strategy can be extended for the development of other enzyme-based biosensors.     

Intermittent operation of the aprotic Li-O2 battery: the mass recovery process upon discharge interval

The intermittent operation of the aprotic Li-O₂ battery is systematically studied in this paper. A combined study of the battery charge retention and the electrolyte stability to O₂ suggests a low self-discharge rate of the Li-O₂ battery, which is a prerequisite to achieve desirable intermittent discharge performance. The battery under intermittent operation exhibits significantly improved discharge performance as compared to the continuously discharged one. It is found that the capacity output is directly associated with the time interval between two discharge steps and with the capacity limit for each discharge step. The open-circuit potential and linear scan voltammetry analyses confirm that a “mass recovery” process, corresponding to the concentration relaxation of the oxygen which is available at the cathode, proceed during the discharge intervals. In the “mass recovery” process, an increased amount of O₂ homogeneously redistributes at the electrolyte/carbon interface at both sides of the electrode, which relieves the O₂ transport limit, enhances the availability of O₂ and the utilization of carbon material for the cathode, and thus significantly improves the discharge performance of the aprotic Li-O₂ battery.     

Development and application of ultra performance liquid chromatography-electrospray ionization tandem triple quadrupole mass spectrometry for determination of seven microcystins in water samples

In the present work, an ultra performance liquid chromatography (UPLC)-electrospray ionization tandem triple quadrupole/mass spectrometry (ESI-MS/MS) method was developed in selected reaction monitoring (SRM) mode to determine the amounts of seven/microcystin variants (MCYST-RR, -YR, -LR, -LA, -LY, -LW, -LF) in water samples. Solid phase extraction (SPE) or porous filter was used for sample cleaning-up and analyte enrichment. A C18 column enabled separation of 7 microcystins within 10 min. Translation reaction ions including 995.6 > 134.9 (RR), 1045.8 > 135.1 (YR), 910.9 > 375.7 (LA), 1002.3 > 375.6 (LY), 520.1 > 135.0 (LR), 1025.8 > 891.7 (LW), 986.8 > 852.6 (LF) were set as quantitative ions and the enkephalin was the internal standard. Upon method validation, the limits of detection (LODs) and limits of quantification (LOQs) were found to be 0.06 μg L⁻¹ and 0.2 μg L⁻¹ (injection volume of 10 μL), respectively, for all seven microcystin variants. The correlation coefficients were larger than 0.994 in all linear ranges and recoveries were in the range of 66.24-99.22%. The developed approach was highly sensitive and easy to perform. It generated accurate quantitative results for the analysis of microcystins in environmental water samples with a wide concentration range. The results showed that MC-RR and MC-LR widely existed in polluted water, while MC-LA and MC-LY were detected sporadically.