硝基苯在离子液体BMimBF4-H2O中的电还原

采用循环伏安法和恒电位电解法研究了离子液体BMimBF4-H2O 中硝基苯在微铂电极上的电还原特性. 实验表明, 在BMimBF4中, 随着硝基苯和水的浓度变化, 循环伏安曲线的峰电位和峰电流呈现复杂的变化规律; 硝基苯在铂电极上的电还原反应为双分子8 电子3 步骤电化学过程, 第一步反应为准可逆单分子单电子转移步骤, 产生阴离子自由基, 第二步为2 电子转移步骤, 并伴有随后的双分子不可逆自由基偶合化学反应, 主要产物为氧化偶氮苯, 第三步是2 电子转移产生偶氮苯的过程.     

支化高分子在溶液中的交叠与缠结

溶液中高分子的交叠和缠结与其链结构密切相关。支化聚苯乙烯的临界交叠浓度C和临界缠结浓度C_E比分子量相同的线型聚苯乙烯的大,说明交叠和缠结同分子在溶液中线团的体积有直接关系。     

KCl-LiCl-H2O体系热力学性质的研究

用K-ISE、Li-ISE和Cl-ISE测定了25 ℃时体系中KCl、LiCl的平均活度系数, 溶液的离子强度从0.1～4.0 mol·kg~(-1), 组成范围从纯的KCl到纯的LiCl。将Pitzer方程应用于测定结果, 用多元线性回归方法求出了Pitzer参数。     

Thin-layer chromatography combined with diode laser desorption/atmospheric pressure chemical ionization mass spectrometry

The desorption of an analyte by a continuous wave diode laser from a porous surface of a thin-layer plate covered with a graphite suspension is presented. The thermally desorbed analyte molecules are ionized in the gas phase by a corona discharge at atmospheric pressure. Therefore, both essential processes--the desorption and the ionization of analyte molecules, which are often performed in one step--are separated. The target preparation is easy and fast since no additional extraction process is required. The mass spectrometric background signal was mostly limited to the low mass range showing no interference with typical compounds of interest. In this study, the calmative and antihypertensive drug reserpine was chosen as model analyte, which is often used for specification of mass spectrometers. No fragmentation was observed because of efficient collisional cooling under atmospheric pressure. The influence of diode laser power and the composition of the graphite suspension were investigated, and a primary optimization was performed.     

Room‐Temperature Solution‐Processed PbS Quantum Dot Solar Cells

Colloidal quantum dots (CQDs) are attractive absorber materials for high‐efficiency photovoltaics because of their facile solution processing, bandgap tunability due to quantum confinement effect, and multi‐exciton generation. To date, all published performance records for PbS CQDs solar cells have been based on the conventional hot‐injection synthesis method. This method usually requires relatively strict conditions such as high temperature and the utility of expensive source material (pyrophoric bis(trimethylsilyl) sulfide (TMS‐S)), limiting the potential for large‐scale and low‐cost synthesis of PbS CQDs. Here we report a facile room‐temperature synthetic method to produce high‐quality PbS CQDs through inexpensive ionic source materials including Pb(NO₃)₂ and Na₂S in the presence of triethanolamine (TEA) as the stabilizing ligand. The PbS CQDs were successfully prepared with an average particle size of about 5 nm. Solar cells based on the as‐synthesized PbS CQDs show a preliminary power conversion efficiency of 1.82%. This room‐temperature and low‐cost synthesis of PbS CQDs will further benefit the development of solution‐processed CQD solar cells.     

Formyl-selective deuteration of aldehydes with D2O via synergistic organic and photoredox catalysis

Formyl-selective deuteration of aldehydes is of high interest for labeling purposes and for optimizing properties of drug candidates. Herein, we report a mild general method for formyl-selective deuterium labeling of aldehydes with D₂O, an inexpensive deuterium source, via a synergistic combination of light-driven, polyoxometalate-facilitated hydrogen atom transfer and thiol catalysis. This highly efficient, scalable reaction showed excellent deuterium incorporation, a broad substrate scope, and excellent functional group tolerance and selectivity and is therefore a practical method for late-stage modification of synthetic intermediates in medicinal chemistry and for generating libraries of deuterated compounds.

Formyl-selective deuteration of aldehydes with D₂O mediated by the synergistic combination of light-driven, polyoxometalate-facilitated HAT and thiol catalysis is reported.     

A mesoporous non-precious metal boride system: synthesis of mesoporous cobalt boride by strictly controlled chemical reduction

Generating high surface area mesoporous transition metal boride is interesting because the incorporation of boron atoms generates lattice distortions that lead to the formation of amorphous metal boride with unique properties in catalysis. Here we report the first synthesis of mesoporous cobalt boron amorphous alloy colloidal particles using a soft template-directed assembly approach. Dual reducing agents are used to precisely control the chemical reduction process of mesoporous cobalt boron nanospheres. The Earth-abundance of cobalt boride combined with the high surface area and mesoporous nanoarchitecture enables solar-energy efficient photothermal conversion of CO₂ into CO compared to non-porous cobalt boron alloys and commercial cobalt catalysts.

Generating high surface area mesoporous transition metal boride is challenging but interesting because incorporation of boron atoms can generate lattice distortion to form amorphous metal boride which has unique properties in catalysis.     

Reductive radical-initiated 1,2-C migration assisted by an azidyl group

We report here a novel reductive radical-polar crossover reaction that is a reductive radical-initiated 1,2-C migration of 2-azido allyl alcohols enabled by an azidyl group. The reaction tolerates diverse migrating groups, such as alkyl, alkenyl, and aryl groups, allowing access to n+1 ring expansion of small to large rings. The possibility of directly using propargyl alcohols in one-pot is also described. Mechanistic studies indicated that an azidyl group is a good leaving group and provides a driving force for the 1,2-C migration.

We report here a novel reductive radical-polar crossover reaction that is a reductive radical-initiated 1,2-C migration of 2-azido allyl alcohols enabled by an azidyl group.

Since the groups of Ryu and Sonoda described the reductive radical-polar crossover (RRPCO) concept in the 1990s,¹ it has attracted considerable attention in modern organic synthesis.² By using this concept, a variety of complex molecules could be assembled in a fast step-economic fashion which is not possible using either radical or polar chemistry alone. However, only two RRPCO reaction modes are known to date: nucleophilic addition and nucleophilic substitution (Fig. 1A). The first RRPCO reaction is the nucleophilic addition of organometallic species, which is generated in situ from the reduction of a strong reducing metal with a carbon-centered radical intermediate and cations (E⁺ = H⁺, I⁺, Br⁺, path 1).³ However, the necessity for a large amount of harmful and strong reducing metals has greatly limited the scope and functional group tolerance of the reaction. Recently, photoredox catalysis has not only successfully overcome the shortcomings of using toxic strong reducing metals in the RRPCO reaction,⁴ but also enabled the development of several new RRPCO reaction types, including the nucleophilic addition with carbonyl compounds or carbon dioxide (path 2),⁵ the cyclization of alkyl halides/tosylates (path 3),⁶ and β-fluorine elimination (path 4).⁷ Although the RRPCO reaction has been greatly advanced by photoredox catalysis, it is still in its infancy, and the development of a novel RRPCO reaction is of great importance.Open in a separate windowFig. 1(A) Reductive radical-polar crossover reactions; (B) this work: reductive radical-initiated 1,2-C migration assisted by an azidyl group.Herein, we wish to report a new type of reductive radical-polar crossover cascade reaction that is the reductive radical-initiated 1,2-C migration under metal-free conditions (Fig. 1B). The development of this approach is not only to further expand the application of the RRPCO reaction, but also to solve the problems associated with the oxidative radical-initiated 1,2-C migration, such as the necessity for an oxidant and/or transition metal for the oxidative termination of the radicals, and also required sufficient ring strain to avoid the generation of epoxy byproducts.⁸ To realize this reaction, a driving force is needed to drive the 1,2-C migration after reductive termination, to avoid the otherwise inevitable protonation of the generated anion.⁹ Inspired by the leaving group-induced semipinacol rearrangement,¹⁰ we envisaged that 2-azidoallyl alcohols¹¹ might be the ideal substrates for the reductive radical-initiated 1,2-C migration because these compounds contain both an allylic alcohol motif, which is vital for the radical-initiated 1,2-C migration, and an azidyl group, a good leaving group,¹² which may facilitate the 1,2-C migration after the reductive termination of the radicals.With the optimal conditions established (ESI, Table S1^†), we then explored the scope of this radical-initiated 1,2-migration. As shown in Table 1, a series of naphthenic allylic alcohols could undergo n+1 ring expansion with minimal impact on the product yield (Table 1, 3aa–aq). Notably, only the alkyl groups were migrated when using benzonaphthenic allylic alcohols in the reaction. These results might be attributed to the aryl group possessing greater steric resistance. The structure of 3an was further verified by single-crystal diffraction. Interestingly, the vinyl azide derived from a pharmaceutical ethisterone was also a viable substrate, affording the migration product 3aq in 57% yield, which highlighted the applicability of this strategy in the late-stage modification of pharmaceuticals. Moreover, the acyclic allylic alcohol with an alkyl chain also successfully delivered the migration product 3ar in 64% yield.Substrate scope of 2-azidoallyl alcohols^ab

Low-temperature growth and photoluminescence property of ZnS nanoribbons

At a low temperature of 450 degrees C, ZnS nanoribbons have been synthesized on Si and KCl substrates by a simple chemical vapor deposition (CVD) method with a two-temperature-zone furnace. Zinc and sulfur powders are used as sources in the different temperature zones. X-ray diffraction (XRD), selected area electron diffraction (SEAD), and transmission electron microscopy (TEM) analysis show that the ZnS nanoribbons are the wurtzite structure, and there are two types-single-crystal and bicrystal nanoribbons. Photoluminescence (PL) spectrum shows that the spectrum mainly includes two parts: a purple emission band centering at about 390 nm and a blue emission band centering at about 445 nm with a weak green shoulder around 510 nm.     

Effect of Ce<Superscript>3+</Superscript> on spectral characteristic of D1/D2/Cytb559 complex from spinach

It was studied by spectroscopy that PSII reaction center complex consisting of three polypeptides, D₁, D₂ and Cytb559, were purified from PSII particle of CeCl₃ treated spinach. The results of the experiment show that Ce³⁺ could improve the growth of spinach, and accelerate electron transport of PSII particles. Of chl-a of UV-Vis spectrum of D1/D2/Cytb559 complex, Soret band was blue-shifted by 3 nm and Q band by 2 nm, respectively, and the fluorescence emission peak was blue-shifted by 5 nm in CeCl₃-treated spinach compared with the one in control. By the extended X-ray absorption fine structure (EXAFS) spectroscopy methods, it has been found that Ce³⁺ is coordinated with 8 nitrogen atoms in the first coordination shell with Ce-N bond length of 0.253 nm, and Ce³⁺ with 6 oxygen atoms in the second coordination shell with Ce-O bond length of 0.32 nm. However, the secondary structure of D1/D2/Cytb559 complex by circular dichroism (CD) spectroscopy has no significant change after CeCl₃ treated. It might be that Ce³⁺ binds to porphyrin rings of chlorophyll and oxygen of amino acid residue of polypeptide in D1/D2/Cytb559 complex, and then accelerates the primary reaction of PSII, intensifies function of P680⁺ primary electron donor of D1/D2/Cytb559, but there is little change in conformation of PSII reaction center complex.