Modification of hydrophilic channels in Nafion membranes by DMBA: Mechanism and effects on proton conductivity

Modification of proton conductive channels (PCCs) in Nafion has been achieved with the assistance of 3, 4‐dimethylbenzaldehyde (DMBA). During annealing, ionic clusters develop from small isolated spheres (1.72 nm) to wide continuous channels (5.15 nm), and the crystallinity of Nafion/DMBA membranes is also improved from 17% to 32% as shown by X‐ray diffraction. Molecular dynamic simulation reveals that hydrogen bonding and hydrophobic interaction between DMBA and Nafion work synergistically to achieve better phase separation. The morphology–property relationship shows that, versus various PCCs width, the corresponding proton conductivities vary greatly from 0.079 to 0.139 S/cm at 80 °C. By carefully tuning the width of PCCs, the proton conductivity shows an improvement of 22–34% as compared with pristine Nafion. A significant enhancement on the maximum power density is achieved for the membrane electrode assembly on Nafion/DMBA‐8h (as high as 1018 mW/cm^?2), yielding an enhancement of 39% on pristine Nafion‐8h (730 mW/cm^?2). © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014 52, 1107–1117     

Asymmetric synthesis of 1,3-oxathiolan-5-one derivatives through dynamic covalent kinetic resolution

The asymmetric synthesis of 1,3-oxathiolan-5-one derivatives through an enzyme-catalyzed, dynamic covalent kinetic resolution strategy is presented. Dynamic hemithioacetal formation combined with intramolecular, lipase-catalyzed lactonization resulted in good conversions with moderate to good enantiomeric excess (ee) for the final products. The process was evaluated for different lipase preparations, solvents, bases, and reaction temperatures, where lipase B from Candida antarctica (CAL-B) proved most efficient. The substrate scope was furthermore explored for a range of aldehyde structures, together with the potential access to nucleoside analog inhibitor core structures.     

Higher integrability for nonlinear elliptic equations with variable growth and discontinuous coefficients

In this paper, based on the theory of variable exponent spaces, we study the higher integrability for a class of nonlinear elliptic equations with variable growth and discontinuous coefficients. Under suitable assumptions, we obtain a local gradient estimate in Orlicz space for weak solution.     

Spatiotemporal Studies of the One-Dimensional Coordination Polymer [Fe(ebtz)2(C2H5CN)2](BF4)2: Tug of War between the Nitrile Reorientation Versus Crystal Lattice as a Tool for Tuning the Spin Crossover Properties**

Reaction of 1,2-di(tetrazol-2-yl)ethane (ebtz) with Fe(BF₄)₂⋅6 H₂O in different nitriles yields one-dimensional coordination polymers [Fe(ebtz)₂(RCN)₂](BF₄)₂⋅nRCN (n=2 for R=CH₃ ( 1 ) and n=0 for R=C₂H₅ ( 2 ) C₃H₇ ( 3 ), C₃H₅ ( 4 ), CH₂Cl ( 5 )) exhibiting spin crossover (SCO). SCO in 1 and 3 – 5 is complete and occurs above 160 K. In 2 , it is shifted to lower temperatures and is accompanied by wide hysteresis (T_1/2^↓=78 K, T_1/2^↑=123 K) and proceeds extremely slowly. Isothermal (80 K) time-resolved single-crystal X-ray diffraction studies revealed a complex nature for the HS→LS transition in 2 . An initial, slow stage is associated with shrinkage of polymeric chains and with reduction of volume at 77 % (in relation to the difference between cell volumes V_HS−V_LS) whereas only 16 % of iron(II) ions change spin state. In the second stage, an abrupt SCO occurs, associated with breathing of the crystal lattice along the direction of the Fe–nitrile bonds, while the nitriles reorient. HS→LS switching triggered by light (808 nm) reveals the coupling of spin state and nitrile orientation. The importance of this coupling was confirmed by studies of [Fe(ebtz)₂(C₂H₅CN/C₃H₇CN)₂](BF₄)₂ mixed crystals ( 2 a , 2 b ), showing a shift of T_1/2 to higher values and narrowing of the hysteresis loop concomitant with an increase of the fraction of butyronitrile. This increase reduces the capability of nitrile molecules to reorient. Density functional theory (DFT) studies of models of 1 – 5 suggest a particular possibility of 2 to adopt a low (140–145°) value of its Fe-N-C(propionitrile) angle.     

高效液相色谱手性固定相法拆分BETTI碱及其衍生物对映体

在纤维素三（3,5-二甲基苯基氨基甲酸酯）（Chiralcel OD-H）和Pirkle型(R, R)-Whelk-O1手性柱上对手性氨基酚1-(α-氨基苄基)-2-萘酚（Betti 碱）及其衍生物1-(α-苄氨基苄基)-2-萘酚和1-(α-哌啶基苄基)-2-萘酚对映体分离进行了研究，分别考察了在正己烷流动相中，碱性添加剂、醇类添加剂的种类和浓度对手性拆分的影响。结果表明：溶质在Chiralcel OD-H柱上的分离效果好，而在(R, R)-Whelk-O1手性柱上只有1-(α-苄氨基苄基)-2-萘酚部分分离。研究了空间立体结构因素对手性分离的影响，初步探讨和比较了溶质在这2种手性柱上的手性识别机理。发现对(R, R)-Whelk-O1柱，溶质与固定相之间的吸引作用很小，而对于Chiralcel OD-H柱，溶质在手性空腔中的空间适应性很可能是手性识别的关键。     

Ultra-broadband piezoelectric energy harvesting via bistable multi-hardening and multi-softening

Nonlinear Dynamics - An electromechanical coupled distributed parameter model is derived for a broadband piezoelectric energy harvester with nonlinear magnetic interaction and...     

纯奇点范畴中的Buchweitz定理

我们定义纯奇点范畴D_(psg)~b(R)为有界纯导出范畴D_(pur)~b(R)与纯投射模构成的有界同伦范畴K~b(■)的Verdier商,得到了纯奇点范畴D_(psg)~b(R)三角等价于相对纯投射模的Gorenstein范畴的稳定范畴■的一个充分必要条件.同时,还给出三角等价D_(psg)~b(R)≌D_(psg)~b(S)的充分条件,这里R和S都是环.     

Heterointerface Engineering of ZnO/CdS Heterostructures through ZnS Layers for Photocatalytic Water Splitting

Solar-driven water splitting to produce clean and renewable hydrogen offers a green strategy to address the energy crisis and environmental pollution. Heterostructure catalysts are receiving increasing attention for photocatalytic hydrogen generation. ZnO/ZnS/CdS and ZnO/CdS heterostructures have been successfully designed and prepared according to two different strategies. By introducing a heterointerface layer of ZnS between ZnO and CdS, a Z scheme charge-transfer channel was promoted and achieved superior photocatalytic performance. A highest hydrogen generation rate of 156.7 μmol g⁻¹ h⁻¹ was achieved by precise control of the thickness of the heterointerface layer and of the CdS shell. These findings demonstrated that heterostructures are promising catalysts for solar-driven water splitting, and that heterointerface engineering is an effective way to improve the photocatalytic properties of heterostructures.     

Inverse spectral problems for non-self-adjoint Sturm–Liouville operators with discontinuous boundary conditions

This paper deals with the inverse spectral problem for a non-self-adjoint Sturm–Liouville operator with discontinuous conditions inside the interval. We obtain that if the potential q is known a priori on a subinterval $$ \left[ b,\pi \right] $$ with $$b\in \left( d,\pi \right] $$ or $$b=d$$, then $$h,\,\beta ,\,\gamma $$ and q on $$\left[ 0,\pi \right] $$ can be uniquely determined by partial spectral data consisting of a sequence of eigenvalues and a subsequence of the corresponding generalized normalizing constants or a subsequence of the pairs of eigenvalues and the corresponding generalized ratios. For the case $$b\in \left( 0,d\right) $$, a similar statement holds if $$\beta ,\,\gamma $$ are also known a priori. Moreover, if q satisfies a local smoothness condition, we provide an alternative approach instead of using the high-energy asymptotic expansion of the Weyl m-function to solve the problem of missing eigenvalues and norming constants.