纳米晶复合Nd2Fe14B/α-Fe合金制备与磁性能的研究

采用熔体快淬及晶化处理工艺制备Nd11Fe71Co8V1.5Cr1B7.5纳米晶合金。经21m·s-1快淬及640℃ 4min晶化处理后,制成的粘结磁体的磁性能最佳,为:Br=0.64T,JHc=903.5kA·m-1,(BH)max=71kJ·m-3。添加Cr元素可提高内禀矫顽力,从而提高最大磁能积。     

YPxV1—xO4（0≤x≤1）：Dy^3＋的合成及其光谱性质的研究

本文报道了不同组成的ＹＰｘＶ１－ｘＯ４（０≤ｘ≤１）：Ｄｙ＾３＋的合成和结构。ＹＰｘＶ１－ｘＯ４（０≤ｘ≤１）为四方晶系，晶胞参数随ｘ的增大呈线性减小。基质的Ｓｔｏｋｅｓ位移随ｘ的增大逐渐变大，而激发光谱峰值则向短波方向移动。在ＹＰｘＶ１－ｘＯ４：０．００６Ｄｙ＾３＋体系中，ｘ＞０．４时出现的基质发射是由ＰＯ＾３－４引起的。基质及Ｄｙ＾３＋的发光效率和Ｄｙ＾３＋的发光强度的黄蓝比均与ｘ有关。同时探     

Crystallization behavior and biodegradation of poly(3-hydroxybutyrate) and poly(ethylene glycol) multiblock copolymers

Block copolymerization by using isocyanates is an effective method for incorporating PHB and PEG because it can prepare copolymers with good properties, such as toughness, strength, and so on. In this study, we adopted soil suspension system to estimate the biodegradability of a series of PHB/PEG multiblock copolymers with different compositions and block lengths. In the degradation process, the changes in weight loss, molecular weight, and tensile strength were periodically measured to determine the biodegradability, and the surface morphology was also observed by SEM. In contrast to pure PHB, the weight loss of the copolymer was relatively lower. On the other hand, the tensile strength and molecular weight experienced apparent decrease, and for BHG1000-3-1, they reached 46.7% and 77.7% of the initial value, respectively. SEM observation showed that the surface was covered with numerous erosion pits. All these indicate that the degradation indeed took place and long-chain molecules have been hydrolyzed into shorter ones. The crystallization behavior was also investigated by DSC and WAXD. The results showed that both the segments, PEG and PHB, can form crystalline phases at lower PHB contents ranging from 29% to 44%, and when PHB component was more than 60%, only PHB phase can crystallize.     

Baeyer-Villiger oxidation of ketones with hydrogen peroxide catalyzed by Sn-aniline complex

Sn-aniline complex was prepared by a simple procedure.Cyclic and acyclic ketones were oxidized into lactones or esters with very high selectivity and yield with 30% hydrogen peroxide in the presence of Sn-aniline complex.     

3-Aminooxetanes: versatile 1,3-amphoteric molecules for intermolecular annulation reactions

Despite the versatility of amphoteric molecules, stable and easily accessible ones are still limitedly known. As a result, the discovery of new amphoteric reactivity remains highly desirable. Herein we introduce 3-aminooxetanes as a new family of stable and readily available 1,3-amphoteric molecules and systematically demonstrated their amphoteric reactivity toward polarized π-systems in a diverse range of intermolecular [3 + 2] annulations. These reactions not only enrich the reactivity of oxetanes, but also provide convergent access to valuable heterocycles.

Despite the versatility of amphoteric molecules, stable and easily accessible ones are still limitedly known.

Amphoteric molecules, which bear both nucleophilic and electrophilic sites with orthogonal reactivity, represent an attractive platform for the development of chemoselective transformations.¹ For example, isocyanides are well-established 1,1-amphoteric molecules, with the terminal carbon being both nucleophilic and electrophilic, and this feature has enabled their exceptional reactivity in numerous multi-component reactions.² In the past few decades, substantial effort has been devoted to the search for new amphoteric molecules.^1–5 Among them, 1,3-amphoteric molecules proved to be versatile. The Yudin and Beauchemin laboratories have independently developed two types of such molecules, α-aziridine aldehydes and amino isocyanates, respectively.^4,5 With an electrophilic carbon and a nucleophilic nitrogen in relative 1,3-positions, these molecules are particularly useful for the chemoselective synthesis of heterocycles with high bond-forming efficiency without protective groups (Fig. 1). However, such elegant amphoteric systems still remain scarce. Therefore, the development of new stable amphoteric molecules with easy access remains highly desirable.Open in a separate windowFig. 1Representative [1,3]-amphoteric molecules versus 3-aminooxetanes.In this context, herein we introduce 3-aminooxetanes as a new type of 1,3-amphoteric molecules and systematically demonstrate their reactivity in a range of [3 + 2] annulations, providing rapid access to diverse heterocycles. Notably, 3-aminooxetanes are bench-stable and either commercially available or easily accessible. However, their amphoteric reactivity has not been appreciated previously.Oxetane is a useful functional group in both drug discovery and organic synthesis.^6–9 Owing to the ring strain, it is prone to nucleophilic ring-opening, in which it serves as an electrophile (Scheme 1A).^6–8 We envisioned that, if a nucleophilic group is installed in the 3-position (e.g., amino group), such molecules should exhibit 1,3-amphoteric reactivity due to the presence of both nucleophilic and electrophilic sites (Scheme 1B). Importantly, the 1,3-relative position is crucial for inhibiting self-destructive intra- or intermolecular ring-opening (i.e. the 3-nucleophilic site attack on oxetane itself) due to high barriers. Thus, such orthogonality is beneficial to their stability. In contrast, the nucleophilic site is expected to react with an external polarized π bond (e.g., X = Y, Scheme 1B), which enables a better-positioned nucleophile (Y) to attack the oxetane and cyclize. Thus, a formal [3 + 2] annulation should be expected. Unlike the well-known S_N2 reactivity of oxetanes with simple bond formation, this amphoteric reactivity would greatly enrich the chemistry of oxetanes with multiple bond formations and provide expedient access to various heterocycles. In contrast to the conventional approaches that require presynthesis of advanced intermediates (e.g., intramolecular ring-opening),⁸ the exploitation of such amphoteric reactivity in an intermolecular convergent manner from simple substrates would be more practically useful. Moreover, more activation modes could be envisioned in addition to oxetane activation. In 2015, Kleij and coworkers reported an example of cyclization between 3-aminooxetane and CO₂ in 55% yield, which provided a pioneering precedent.¹⁰ However, a systematic study to fully reveal such amphoteric reactivity in a broad context remains unknown in the literature.Open in a separate windowScheme 1Typical oxetane reactivity and the new amphoteric reactivity.To test our hypothesis, we began with the commercially available 3-aminooxetanes 1a and 1b as the model substrates. Phenyl thioisocyanate 2a and CS₂ were initially employed as reaction partners, as they both have a polarized C S bond as well as a relatively strong sulfur nucleophilic motif. Moreover, the resulting desired products, iminothiazolidines and mercaptothiazolidines, are both heterocycles with important biological applications (Fig. 2).¹¹ To our delight, simple mixing these two types of reactants in DCM resulted in spontaneous reactions at room temperature without any catalyst. The corresponding [3 + 2] annulation products iminothiazolidine 3a and mercaptothiazolidine 4a were both formed with excellent efficiency (Scheme 2). It is worth mentioning that catalyst-free ring-opening of an oxetane ring is rarely known, particularly for intermolecular reactions.^6–9 In this case, the high efficiency is likely attributed to the suitable choice and perfect position of the in situ generated sulfur nucleophile.Open in a separate windowFig. 2Selected bioactive molecules containing iminothiazolidine and mercaptothiazolidine motifs.Open in a separate windowScheme 2Initial results between 3-aminooxetanes and thiocarbonyl compounds.The catalyst-free annulation protocol is general with respect to various 3-aminooxetanes and isothiocyanates. A range of iminothiazolidines and mercaptothiazolidines were synthesized with high efficiency under mild conditions (Scheme 3). Many of them were obtained in quantitative yield. Quaternary carbon centers could also be generated from 3-substituted 3-aminooxetanes (e.g., 3j). The structure of product 3b was unambiguously confirmed by X-ray crystallography.Open in a separate windowScheme 3Formal [3 + 2] annulation with isothiocyanates and CS₂. Reaction conditions: 1 (0.3–0.4 mmol), 2 (1.1 equiv.) or CS₂ (1.5 equiv.), DCM (2 mL), RT, 3 h for 3 and 36 h for 4. Yields are for the isolated products.With the initial success of thiocarbonyl partners, we next turned our attention to isocyanates, in which the carbonyl group serves as the [3 + 2] annulation motif. Compared with sulfur as the nucleophilic site in the above cases, the oxygen atom is less nucleophilic. As expected, initial tests of the reactivity by mixing 1b and 5a resulted in no desired annulation product 6a in the absence of a catalyst (Table 1, entry 1). Next, Brønsted acids, including TsOH and the super acid HNTf₂, were examined as catalysts, but with no success (entries 2 and 3). We then resorted to various Lewis acids, particularly those oxophilic ones, in hope of activating the oxetane unit. Unfortunately, many of them still remained ineffective (e.g., ZnCl₂, AuCl, and FeCl₃). However, to our delight, further screening of stronger Lewis acids helped identify Sc(OTf)₃, Zn(OTf)₂, and In(OTf)₃ to be effective at room temperature, leading to the desired iminooxazolidine product 6a in good yield (entries 7–9). Its structure was confirmed by X-ray crystallography. Nevertheless, aiming to search for a cheaper catalyst, we continued to optimize this reaction at a higher temperature using previous ineffective catalysts. Indeed, FeCl₃ was found to be effective at 80 °C (61% yield, entry 10), while Brønsted acid TsOH remained ineffective at this temperature (entry 11). Notably, decreasing the loading of FeCl₃ to 1 mol% led to a higher yield (89% yield, entry 12). However, further decreasing to 0.5 mol% resulted in slightly diminished efficiency (entry 13).Reaction conditions for annulation with isocyanates^a

(XN)4R4簇合物的结构与化学键

用密度泛函理论,在B3LYP/6-311G水平上,对(XN)4R4 (X=C,Si,Ge;R=H,CH3,NH2,OH)及合成的先驱化合物(XN)2R2进行几何构型、电子结构、振动频率和化学反应焓变等进行了研究.结果表明,(RCN)4比(CNR)4更稳定.所有簇合物的零点能EZP值,R=H时最小,R=CH3时最大,R配位原子依次为C、N和O时,EZP值逐渐减小.     

BaCe1—xRExO3—0.5x的溶胶—凝胶法合成及离子导电性

用溶胶－凝胶法合成了系列钙钛矿结构的ＢａＣｅ１－ｘＲＥｘＯ３－０．５ｘ（ＲＥ＝Ｌａ，Ｎｄ，Ｓｍ，Ｅｕ，Ｇｄ，Ｄｙ，Ｈｏ，Ｅｒ和Ｙ）复合氧化物，通过ＸＲＤ和热分析对样品结构及生成过程进行了研究．测定了不同温度下样品的交流阻抗谱，讨论了稀土离子掺杂对ＢａＣｅＯ３电性质的影响．溶胶－凝胶法比固相反应法合成温度降低了６００～８００℃，稀土掺杂使ＢａＣｅＯ３离子导电率提高了１０～４０倍．     

Cover Picture: A Stepwise Annulation for the Transformation of Cyclic Ketones to Fused 6 and 7‐Membered Cyclic Enimines and Enones (Chin. J. Chem. 4/2019)

The cover picture shows a typical building within the Campus of Xiamen University displaying Chen Jiageng (Tan Kah Kee)'s style. Just like many beautiful buildings designed and constructed by human, Nature “designs and constructs” a huge number of useful molecules with fascinating structures called natural products. Many natural products possess a fused six or seven‐membered carbocyclic unity. On page 315–322, the Huang's group disclosed a three‐step “[2+n]” annulation method for the construction of fused six and seven‐membered carbocyclic enimines and enones. The method starts from simple cyclic ketones and terminal olefinic amides, and relies on both the Suzuki coupling reaction and the olefin‐amide based Friedel‐Crafts type acylating reaction, a method developed by Huang and coworkers.

     

Maximum spectrum of continuous wavelet transform and its application in resolving an overlapped signal

To estimate the number of peaks and to find the individual peak positions in an overlapped signal, a new method called maximum spectrum of continuous wavelet transform (MSCWT) was developed by extracting the maximum coefficients of continuous wavelet transform (CWT). The peak position in MSCWT was the same as that in its original signal. In this process, CWT was performed not on a single dilation but on an appreciation dilation range. To obtain such a range, a new criterion was introduced to choose a center dilation, which was used to form the dilation range. If Cdilation denoted the center dilation, the proper dilation range was [Cdilation -6 +/- 2, Cdilation +1 +/- 1]. The Mexican Hat function was an analytical wavelet. Utilizing the information of the peak number and the position detected by MSCWT, a fitting route was performed to recover the original signal. One simulated and four true overlapped signals, including high performance liquid chromatography (HPLC), ultraviolet-visible (UV) spectrum, and differential pulse voltammetric (DPV), were processed, and the results indicated that MSCWT could detect an overlapped peak number and position, and the curve fitting based on information of MSCWT had a higher accuracy. The proposed method was an efficient one in resolving different types of overlapped signals.     

不依赖于统计模型的手性毛细管电泳分离多指标同时优化

考虑到手性毛细管电泳分离机理的复杂性，提出了不依赖于统计模型的二进制编码遗传算法多目标优化策略。根据实验参数的多少及其重要性，采用均匀设计安排完成初步实验。并用Derringer功效函数作为多指标同时优化的评价指标，以取得较高的分离度和较快分离速度；通过对实验参数给予编码，转化为二进制字符串，根据得到的总功效函数值大小进行遗传算法操作，产生新的一组实验条件。重复上述过程直到得到最佳分离条件为止。此方法成功地应用于华法令对映体的毛细管电泳分离条件优化。