DFT studies of cobalt hydride intermediate on cobaloxime‐catalyzed H2 evolution pathways

Chemical, electrochemical, and photochemical methods all had been utilized to explore proton reduction catalysis by cobaloxime complexes. It was postulated in these studies that the initial step toward making H₂ was protonation of Co^I to form a Co^III hydride intermediate. However, in the following steps, different results from electrochemical studies had led to both monometallic and bimetallic pathways. In this article, theoretical computation method (BP86/6‐31G*) was firstly performed on possible cobalt hydride intermediates involved in the reactive pathway of cobaloxime‐catalyzed H₂ evolution. The monometallic pathway B was excluded, both monometallic pathway A and bimetallic pathway were the possible process. However, the Gibbs free energy change for generation of H₂ following monometallic pathway A was much more negative than that following bimetallic pathway. The calculation on monometallic pathway A indicated that the main driving force of the reaction (i) came from the step of the reduction of 11 . The proton transfer steps were also studied in detail. The protonation of cobalt hydride intermediates could directly happen on the dimethylglyoximate part. All the results refer to gas‐phase calculations, not considering the solution. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2011     

Sequential one-pot and three-component reactions of an N-heterocyclic carbene to form 4-(1,2,4-triazol-5-ylidene)pyrrolidine-2,5-diones: a tandem umpolung/annulation sequence via deoxy-Breslow intermediates

The tandem sequence of the umpolung of α,β-unsaturated esters by an N-heterocyclic carbene (NHC) followed by annulation is demonstrated. The deoxy-Breslow intermediates are selectively generated from the reaction of NHC with methyl methacrylate, dimethyl itaconate, or methyl crotonate. Subsequently, they undergo annulation with isocyanates to give 4-(1,2,4-triazol-5-ylidene)pyrrolidine-2,5-diones in good isolated yields. In addition, the stoichiometric three-component reaction of NHC, methyl methacrylate, and phenyl isocyanate proceeded, accompanied by the formation of the 1:2 adduct of NHC with phenyl isocyanate.     

Integro-local and integral theorems for sums of random variables with semiexponential distributions

We obtain some integro-local and integral limit theorems for the sums S(n) = ξ(1) + ? + ξ(n) of independent random variables with general semiexponential distribution (i.e., a distribution whose right tail has the form $P(\xi \ge t) = e^{ - t^\beta L(t)} $ , where β ∈ (0, 1) and L(t) is a slowly varying function with some smoothness properties). These theorems describe the asymptotic behavior as x → ∞ of the probabilities P(S(n) ∈ [x, x + Δ)) and P(S(n) ≥ x) in the zone of normal deviations and all zones of large deviations of x: in the Cramér and intermediate zones, and also in the “extreme” zone where the distribution of S(n) is approximated by that of the maximal summand.     

Synthesis of a functionalized furan via ozonolysis—further confirmation of the Criegee mechanism

A new method for the synthesis of a tetrahydrofuran ring is described which involves ozonolysis of a diene possessing a free hydroxy group in the γ-position. The reaction proceeds via ozone attack on the terminal double bond, cleavage, and intramolecular cyclization through the free hydroxy group. The cyclization event can be rationalized through formation of Criegee’s carbonyl oxide, but not through the ‘unified’ mechanism, thereby lending support to the Criegee mechanism as a method of producing oxygen-containing heterocycles.     

Theoretical Investigation on Electronic Transition of Tris(8-quinolinolate) Aluminum Grafted on Poly(p-phenylenevinylene) Units with the Localized-density-matrix Method

An unsystematic molecule PPV‐Alq₃ [3‐(4‐((E)‐2‐(8‐hydroxy‐3‐(4‐styrylstyryl)quinolin‐Alq₂‐6‐yl)vinyl)‐ styryl)‐6‐(4‐styrylstyryl)quinolin‐8‐olate‐Alq₂; q=8‐quinolinolate], which combines poly(p‐phenylenevinylene) with tris(8‐quinolinolate)aluminum, has been studied using a localized‐density‐matrix method. The absorption spectra and electronic transition properties were analyzed and compared with both intermediate neglect of the differential overlap method and the localized‐density‐matrix method. Great efforts have been made on investigating conjugated system on the absorption properties as these can be particularly important for many applications. Two different absorptions of the special molecule, tris(8‐quinolinolate)aluminum grafted on poly(p‐phenylenevinylene) units, were further discussed with density matrices. For the molecule, the first absorption peak is at 413 nm near the purple light. Two 8‐hydroxyquinolines have very slight electronic transition properties. Another absorption peak is at 237 nm. The second characteristic peak of molecule is completely different from that of the first one, which comes from contribution of 8‐hyroxyquinolines in the two different side chains. Our studies show that electronic transition properties of poly(p‐phenylenevinylene) can be effectively tuned by grafting tris(8‐quinolinolate)‐aluminum on poly(p‐phenylenevinylene) from the standpoint of transition energies, frontier molecular orbitals and density matrices.     

中频磁脉冲处理Fe52Co34HfTB6Cu1非晶合金的正电子湮没研究

对熔体急冷法制备的非晶合金Fe52Co34HfTB6Cu1进行了不同频率的中频磁脉冲处理,用透射电子显微镜、穆斯堡尔谱、正电子湮没寿命谱等方法研究了处理前后试样的微观结构及结构缺陷变化．结果表明,经中频磁脉冲处理后,样品发生了部分纳米晶化,晶化量随磁脉冲频率增加而增加,当磁脉冲频率为2000Hz时,晶化量达33．1％：在淬态非晶样品中,正电子在类单空位中的湮没寿命t1为150．5ps,强度,1为77．7％,在微孔洞中的湮没寿命仡为349．7ps,强度I2为22．3％;随磁脉冲频率的增加,t1,t2值呈现减小的变化趋势,与淬态非晶相比,I1有所增加,如下降,t1,t2的平均值亍大幅降低．     

Normalized Excited Squeezed Vacuum State and Its Applications

By using the intermediate coordinate-momentum representation in quantum optics and generating function for the normalization of the excited squeezed vacuum state （ESVS）, the normalized ESVS is obtained. We find that its normalization constants obtained via two new methods are uniform and a new form which is different from the result obtained by Zhang and Fan [Phys. Lett. A 165 （1992） 14]. By virtue of the normalization constant of the ESVS and the intermediate coordinate-momentum representation, the tomogram of the normalized ESVS and some useful formulae are derived.     

近红外光谱与组合的间隔偏最小二乘法测定清开灵四混液中总氮和栀子苷的含量

应用近红外光谱分析技术结合化学计量学方法, 建立了中药清开灵注射液中间体总氮和栀子苷含量测定的新方法. 首先采用Kernard-Stone法对训练集样本和预测集样品进行分类, 然后应用组合的间隔偏最小二乘法(Synergy interval partial least squares, siPLS)对所得近红外透射光谱进行有效谱段范围的选择以及二者定量校正模型的建立, 并对光谱预处理方法进行了详细的讨论. 所建立的总氮和栀子苷校正模型的预测相关系数(R)分别为0.999和0.708; 交叉验证误差均方根(RMSECV)均为0.023; 预测误差均方根(RMSEP)分别为0.074和0.159; 预测结果表明, 本实验所建方法快速、无损且可靠, 可推广并应用于中药注射液中间体的在线质量控制.     

BHGAttN: A Feature-Enhanced Hierarchical Graph Attention Network for Sentiment Analysis

Recently, with the rise of deep learning, text classification techniques have developed rapidly. However, the existing work usually takes the entire text as the modeling object and pays less attention to the hierarchical structure within the text, ignoring the internal connection between the upper and lower sentences. To address these issues, this paper proposes a Bert-based hierarchical graph attention network model (BHGAttN) based on a large-scale pretrained model and graph attention network to model the hierarchical relationship of texts. During modeling, the semantic features are enhanced by the output of the intermediate layer of BERT, and the multilevel hierarchical graph network corresponding to each layer of BERT is constructed by using the dependencies between the whole sentence and the subsentence. This model pays attention to the layer-by-layer semantic information and the hierarchical relationship within the text. The experimental results show that the BHGAttN model exhibits significant competitive advantages compared with the current state-of-the-art baseline models.     

A Review on Generation and Reactivity of the N-Heterocyclic Carbene-Bound Alkynyl Acyl Azolium Intermediates

N-heterocyclic carbene (NHC) has been widely used as an organocatalyst for both umpolung and non-umpolung chemistry. Previous works mainly focus on species including Breslow intermediate, azolium enolate intermediate, homoenolate intermediate, alkenyl acyl azolium intermediate, etc. Notably, the NHC-bound alkynyl acyl azolium has emerged as an effective intermediate to access functionalized cyclic molecular skeleton until very recently. In this review, we summarized the generation and reactivity of the NHC-bound alkynyl acyl azolium intermediates, which covers the efforts and advances in the synthesis of achiral and axially chiral cyclic scaffolds via the NHC-bound alkynyl acyl azolium intermediates. In particular, the mechanism related to this intermediate is discussed in detail.