Phosphine‐free direct arylation synthesis and self‐assembled nanostructure analysis of poly(3‐hexylselenophene)

Poly(3‐hexylselenophene)s (P3Hs) with high regioregularity (RR = 92–96%), that is, regioregular poly(3‐hexylselenophene)s (rr‐P3HSs), have been synthesized under the phosphine‐free direct arylation conditions in the presence of PdCl₂ as a precatalyst. rr‐P3HS with the high molecular weight (M_n ～ 10,000) was obtained as a result of screening of direct arylation conditions. Subsequently, the influences of primary structure, molecular weight (M_n = 3900–10,000) and regioregularity (RR = 57–96%), on optical properties and self‐assembled nanostructure of P3HS were investigated. X‐ray diffraction demonstrated that molecular weight, regioregularity, and preparation method of films dominate the crystallization behavior of P3HS. Among these parameters, it was evident that a high degree of regioregularity was the most fundamental contributor to achieve pure crystalline nanostructure. Furthermore, nanoassembly based on pure crystalline nanostructure, such as non‐woven fibrous and bundle‐like spherulitic self‐assembled nanostructures, was successfully prepared in rr‐P3HS, respectively, by appropriate modulation of the aforementioned parameters. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 2749–2755     

Highly sulfonated multiblock copoly(ether sulfone)s for fuel cell membranes

Highly sulfonated multiblock copoly(ether sulfone)s applicable to proton electrolyte fuel cells (PEFCs) were synthesized by the coupling reaction of corresponding hydroxyl‐ terminated oligomers in the presence of highly reactive decafluorobiphenyl (DFB) as a chain extender, followed by postsulfonation with concentrated sulfuric acid. Their molecular weights were reasonably high as determined by viscosity measurement (η_inh = 0.72–1.58 dL/g). It was also confirmed that postsulfonation selectively took place in hydrophilic segments to yield highly sulfonated multiblock copolymers (IEC = 1.90–2.75 mequiv/g). The resulting polymers gave transparent, flexible, and tough membranes by solution casting. The 4b membrane, as a representative sample, demonstrated good mechanical strength in the dry state regardless of high IEC value (2.75 mequiv/g). The 4a–c membranes with higher IEC values (IEC = 2.75–2.79 mequiv/g) maintained high water uptake (13.7–17.7 wt %) at 50% RH and it was still high (7.4–8.5 wt %) at 30% RH. Proton conductivity of all membranes at 80 °C and 95% RH was higher than that of Nafion 117. Furthermore, the 4a membrane showed high proton conductivity, comparable with Nafion 117 in the range of 50–95% RH, and maintained high proton conductivity (2.3 × 10^?3 S/cm) even at 30% RH. Finally, the surface morphology of the membrane was investigated by tapping mode atomic force microscopy, which showed well‐connected hydrophilic domains that could work as proton transportation channel. This phase separation and the high water uptake behavior probably contributed to high and effective proton conduction in a wide range of relative humidity. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 2757–2764, 2010     

Large time behaviors of hot spots for the heat equation with a potential

We consider the Cauchy problem of the heat equation with a potential which behaves like the inverse square at infinity. In this paper we study the large time behavior of hot spots of the solutions for the Cauchy problem, by using the asymptotic behavior of the potential at the space infinity.     

Phase-transfer-mediated electrochemical reaction: anodic disulfide bond formation under biphasic condition

The use of bromide ion as a redox mediator promotes electrochemical reactions in the non-conductive cyclohexane phase. Anodically oxidized species of bromide ion in the conductive methanol phase can bring oxidizing power across phases to induce oxidative disulfide bond formation of a hydrophobically-tagged tripeptide, which is located predominantly in the cyclohexane phase. In addition to commonly used tetraalkylammonium salts, inorganic sodium salt can also be effective alternatives for the bromide source.     

Host–Guest Complexation Behavior of Resorcinarenes with Tetraalkylammonium Ions and N-Methylpyridinium Ions in Methanol: The Effect of Bulky Hydrophobic Substituents at the Extra-Annular Positions

The host–guest interaction of C-methylresorcin[4]arene and its derivative having four tert-butylsulfanylmethyl groups at the extra-annular positions was studied by ¹ H NMR spectroscopy in CD₃OD. Based on the association constants (Ka) and the complexation-induced NMR shifts (CIS), it was concluded that the bulky substituents create a deep cavity with a narrow entrance and improve the size and shape selectivity.     

Metal-free catalytic reduction of aldehydes,ketones,aldimines,and ketimines

<正>The metal-free combination of catalytic amounts of PPh_3,B(C_6F_5)_3,and PhSiH_3 can efficiently hydrosilylate aldehydes, ketones,aldimines and ketimines to afford the corresponding reduction products in good yields.     

Improved catalytic performance of nitrided Co–Ti and Fe–Ti catalysts for oxygen reduction as non-noble metal cathodes in acidic media

M–Ti/carbon black electrocatalysts (M: Mn, Fe, Co, Ni, Cu, Mo) were prepared by the polymerized complex (PC) method and subsequent nitridation under ammonia flow, and were investigated as cathodes for the oxygen reduction reaction (ORR) in 0.1 M H₂SO₄ aq. Among the metals investigated, Co and Fe gave high onset potentials of 0.86 and 0.87 V vs. RHE, respectively. In comparison with the Co-only catalyst, the Co–Ti catalyst showed higher current, reflecting high density of Co-related active sites. The presence of Ti was also essential for the electrode stability under severe acidic and oxidizing conditions.     

Synthesis of Azanucleosides by Anodic Oxidation in a Lithium Perchlorate–Nitroalkane Medium and Diversification at the 4′‐Nitrogen Position

Azanucleosides, in which the 4′‐oxygen atom has been replaced with a nitrogen atom, have drawn much attention owing to their anticancer and antivirus activity, and tolerance towards nucleases. However, the traditional synthetic strategy requires multiple steps and harsh conditions, thereby limiting the structural and functional diversity of the products. Herein we describe the synthesis of azanucleosides by an electrochemical reaction in a lithium perchlorate–nitroethane medium, followed by postmodification at the 4′‐N position. N ‐Acryloyl prolinol derivatives were converted into azanucleosides by anodic activation of the N ‐α‐C−H bond. Moreover, the use of nitroethane instead of nitromethane lowered the oxidation potential of the N ‐acryloyl prolinols and increased the Faradic yield. The prepared azanucleosides were efficiently functionalized at the 4′‐N ‐acryloyl group with a lipophilic alkanethiol and a fluorescent dye by conjugate addition and olefin cross‐metathesis, respectively.