Initiation Kinetics in Free‐Radical Polymerization: Prediction of Thermodynamic and Kinetic Parameters Based on ab initio Calculations

Initiation kinetics in free radical polymerization is investigated using density functional theory. Thermodynamic and kinetic parameters of the initiation reactions are predicted, and the role of the initiators in the polymerization process is evaluated. Methyl acrylate, methyl methacrylate, acrylonitrile, and styrene homo‐polymerizations with different initiators are studied. Reaction enthalpy and activation energy for each reaction between monomer and the radical fragments arising from the initiators have been determined. The initiation kinetic constants for all of these initiation reactions are evaluated and compared with both computational and experimental propagation kinetic constants of each monomer.

     

白喉毒素活性中心的量子化学计算与149位突变体的酶学动力学

通过量子化学计算确定白喉毒素分子催化区活性中心的关键氨基酸残基, 评价其取代后的酶活性的改变, 为导向性抗癌药物研究提供高效杀伤细胞工具. 结合目前关于白喉毒素结构与功能的研究状况和量子化学计算结果, 将白喉毒素催化区的第149位酪氨酸突变为苯丙氨酸, 对其酶活性和与底物的结合能力进行评价. Y149位酪氨酸位于正电中心, 起受电子作用, 与野生白喉毒素相比, 苯丙氨酸突变体的酶催化活性增加约一倍, 而与底物结合能力没有变化. Y149是酶活性中心的关键氨基酸残基, 对其取代能够影响蛋白质的生物活性.     

分子磁性的量子化学研究进展

本文概述了研究分子磁性的量子化学方法和研究进展。首先介绍分子磁性研究中的量子化学原理和所使用计算方法,总结了有代表性的自由基、自由基-金属配合物、桥联多核过渡金属配合物等分子磁性的研究情况,并对今后研究分子磁性的量子化学方法作了展望。     

A Polymer Reaction Engineering Approach to Polynucleotide Replication

It is often interesting to look at specific scientific questions from the perspective of other, related technologies. The problem of nonenzymatic RNA replication can be viewed from the perspective of classical polymer science and with some interesting insights. This communication will show that current mechanism of stalling, which is used to account for the fact that the rate of insertion errors in nonenzymatic RNA replication are much lower than would be expected, can be modeled by using the Mayo–Lewis equation for calculating copolymer composition in copolymerizations of synthetic polymers. Using kinetic parameters from the literature, it is possible to independently predict the error threshold for RNA replication. Agreement with the accepted model for nonenzymatic replication is surprisingly good.

     

Quantum Chemistry Calculation of Quercetin-silver Complex

1 INTRODUCTION Quercetin(3,5,7,3?,4?-pentahydroxyflavone,see Fig. 1) is a kind of flavonol with many pharma-colo- gical actions, such as anti-flammatory, antiviral and antioxidation[1], but its antioxidation is weak. In re- cent years, it has been reported that quercetin can form metallic complexes by combining with some metal ions like copper ion, zinc ion, nickel and rare earth metals, and its antioxidative activity will be stronger than quercetin due to the existence of co- operative ef…     

Reaction Optimization for Greener Chemistry with a Comprehensive Spreadsheet Tool

Green chemistry places an emphasis on safer chemicals, waste reduction, and efficiency. Processes should be optimized with green chemistry at the forefront of decision making, embedded into research at the earliest stage. To assist in this endeavor, we present a spreadsheet that can be used to interpret reaction kinetics via Variable Time Normalization Analysis (VTNA), understand solvent effects with linear solvation energy relationships (LSER), and calculate solvent greenness. With this information, new reaction conditions can be explored in silico, calculating product conversions and green chemistry metrics prior to experiments. The application of this tool was validated with literature case studies. Reaction performance was predicted and then confirmed experimentally for examples of aza-Michael addition, Michael addition, and an amidation. The combined analytical package presented herein permits a thorough examination of chemical reactions, so that the variables that control reaction chemistry can be understood, optimized, and made greener for research and education purposes.     

三环己基锡吡啶-4-甲酸酯聚合物的合成、结构和量子化学研究

双齿配体吡啶-4-甲酸与三环己基氢氧化锡反应,合成了三环己基锡吡啶-4-甲酸酯聚合物[Cy3Sn(O2CC5H4N)]n(Cy为环己基)。经IR、1H NMR、元素分析和X射线衍射表征结构,晶体结构属单斜晶系,空间群P21/c,晶体学参数:a=1.222 4(4)nm,b=0.980 9(5)nm,c=2.089 9(9)nm,β=107.238(3)°,Z=4,V=2.393 6(4)nm3,Dc=1.360 g.cm-3,μ(Mo Kα)=1.085 mm-1,F(000)=1 016,R1=0.028 2,wR2=0.068 4。中心锡原子为五配位三角双锥构型,通过吡啶-4-甲酸的1个氧和吡啶氮原子配位成链。两条相邻的链之间经氢键(C-H…O)作用组成"双链"结构,"双链"之间通过环己基H与另链的吡啶环发生σ→π作用形成二维结构。利用量子化学G98W软件,在lan12dz基组对配合物的稳定性、前沿分子轨道组成及能量进行研究。     

Quantum Chemistry in Solution: Fiftieth Anniversary

In this perspective, we briefly present the historical context in which, fifty years ago, dielectric continuum models were developed to incorporate solvent effects into quantum mechanical calculations. Since the first self-consistent-field equations including the solvent electrostatic potential (or reaction field) were reported in 1973, continuum models have become extremely popular in the computational chemistry community and are routinely used in a very wide range of applications.     

Polyolefin Macroradical Properties: A Semiempirical Quantum Chemistry Study

Summary: Semiempirical quantum chemistry simulations have been used to estimate the properties of mid‐chain alkyl radicals of ethylene, propylene and styrene oligomers depending on the chain length. The values of spin density and charge on the radical site proved to be almost unchanged for oligomer radicals having from 2 to 11 repeated units. Bond strength parameters of bonds neighboring the radical site demonstrate stable values starting from pentamers. The reliable inference is that the electron structure of polyethylene, poly(propylene) and polystyrene (PS) macroradicals may be simulated by means of relatively short oligomers. The obtained data indicate clearly that the polystyrene tertiary alkyl radical has noticeably decreased values of both spin and charge onto the radical site as well as very decreased strength of β‐bonds. For that reason the PS tert‐alkyl radical is estimated as that having decreased activity and increased susceptibility to chain scission. The most probable cause is delocalization of the free electron onto the neighboring aromatic ring.

Spin density distribution in tertiary radical of polystyrene.     

Quantum Chemical Investigation of Secondary Reactions in Poly(vinyl chloride) Free‐Radical Polymerization

Free‐radical polymerization of vinyl chloride is investigated computationally with special attention to the secondary reactions involving mid‐chain radicals (MCRs). Namely, the rate constants of backbiting, chain scission, chain transfer, and propagation reactions are evaluated using a density functional theory method. The rate coefficients of such reactions are estimated taking into account the position of the radical along the chain as well as its distance from the chain‐end. In particular 1:5, 5:1, and 5:9 backbiting are the most relevant secondary reactions, followed by the slower propagation of MCRs. Finally, a kinetic model of suspension polymerization including the investigated reactions is developed, in order to determine their impact on the quality of the final polymer.

     

利用量子化学高斯软件辅助工科教学——以能源、环境、化工学科为例

介绍了量子化学高斯软件在能源、环境和化工等大学传统工科教学中的应用,并结合3个具体实例羟基自由基与臭氧的基元反应、一氧化氮与羟基自由基的基元反应和甲酸超临界水气化制氢的反应路径进行了详细说明。实践表明,采用该方法可以使工科生从微观层面去洞悉化学反应的内在规律和本质问题,从而加深学生对“微观化学知识”的理解,激发学生对深层次“微观化学知识”探求的积极性和热情,产生了良好的教学效果。     

量子化学的研究现状、发展趋势与展望*

"本文通过对最近三届量子化学Sanibel国际研讨会和全国量子化学第5届学术讨论会会议内容的对比,评述了当前国际、国内约量子化学研究现状与发展趋势,并粗浅地探讨了我国量子化学的发展战略。     

A Supramolecular Polymer Network of Graphene Quantum Dots

Graphene quantum dot (GQD)–organic hybrid compounds (GQD‐ 2 b – e ) were prepared by introducing 3,4,5‐tri(hexadecyloxy)benzyl groups (C16) and linear chains terminated with a 2‐ureido‐4‐[1H]‐pyrimidinone (UPy) moiety onto the periphery of GQD‐ 1 . GQD‐ 2 b – e formed supramolecular assemblies through hydrogen bonding between the UPy units. GPC analysis showed that GQDs with high loadings of the UPy group formed larger assemblies, and this trend was confirmed by DOSY and viscosity measurements. AFM images showed the polymeric network structures of GQD‐ 2 e on mica with flat structures (ca. 1.1 nm in height), but no such structures were observed in GQD‐ 2 a , which only carries the C16 group. GQD‐ 2 c and GQD‐ 2 d formed organogels in n‐decanol, and the gelation properties can be altered by replacing the alkyl chains in the UPy group with ethylene glycol chains (GQD‐ 3 ). GQD can thus be used as a platform for supramolecular polymers and organogelators by suitable chemical functionalization.     

超分子高分子化学进展

综述了超分子高分子化学近年来的进展,着重介绍固相聚合和毛杆高分子等方面的最新研究成果及应用展望,对超分子高分子化学的主要研究方法也作了扼要的介绍。     

A Missing Reaction Step in Dithiobenzoate-Mediated RAFT Polymerization

The debate on the mechanism of dithiobenzoate-mediated RAFT polymerization may be overcome by taking the so-called “missing step” reaction between a highly reactive propagating radical and the three-arm star-shaped product of the combination reaction of an intermediate RAFT radical and a propagating radical into account. The “missing step” reaction transforms a propagating radical and a not overly stable three-arm star species into a resonance-stabilized RAFT intermediate radical and a stable polymer molecule. The enormous driving force behind the “missing step” reaction is estimated via DFT calculations of reaction enthalpies and reaction free enthalpies.     

Simulation vs. Understanding: A Tension,in Quantum Chemistry and Beyond. Part A. Stage Setting

We begin our tripartite Essay with a triangle of understanding, theory and simulation. Sketching the intimate tie between explanation and teaching, we also point to the emotional impact of understanding. As we trace the development of theory in chemistry, Dirac's characterization of what is known and what is needed for theoretical chemistry comes up, as does the role of prediction, and Thom's phrase “To predict is not to explain.” We give a typology of models, and then describe, no doubt inadequately, machine learning and neural networks. In the second part, we leave philosophy, beginning by describing Roald's being beaten by simulation. This leads us to artificial intelligence (AI), Searle's Chinese room, and Strevens’ account of what a go-playing program knows. Back to our terrain—we ask “Quantum Chemistry, † ca. 2020?” Then move to examples of AI affecting social matters, ranging from trivial to scary. We argue that moral decisions are hardly to be left to a computer. At this point, we try to pull the reader up, giving the opposing view of an optimistic, limitless future a voice. But we don't do justice to that view—how could we? We return to questioning the ascetic dimension of scientists, their romance with black boxes. Onward: In the 3rd part of this Essay, we work our way up from pessimism. We trace (another triangle!) the special interests of experimentalists, who want the theory we love, and reliable numbers as well. We detail in our own science instances where theory gave us real joy. Two more examples-on magnetic coupling in inorganic diradicals, and the way to think about alkali metal halides, show us the way to integrate simulation with theory. Back and forth is how it should be—between painfully-obtained, intriguing numbers, begging for interpretation, in turn requiring new concepts, new models, new theoretically grounded tools of computation. Through such iterations understanding is formed. As our tripartite Essay ends, we outline a future of consilience, with a role both for fact-seekers, and searchers for understanding. Chemistry's streak of creation provides in that conjoined future a passage to art and to perceiving, as we argue we must, the sacred in science.     

分子团簇的量子化学研究

采用Hartree-Fock方法、密度泛函(DFT)方法(BLYP、B3LYP)和MP2方法对Se4分子团簇的各种可能构型进行了结构优化和频率分析, 结果表明有5种构型是势能面上的稳定驻点, 同时对上述4种量子化学方法计算结果的差异进行了分析。并对这5种构型的结构稳定性、几何构型、前线分子轨道、Mulliken布局分析和偶极矩进行了分析, 根据分析结果对Se4分子的某些物理和化学性质进行了预测。     

Simulation vs. Understanding: A Tension,in Quantum Chemistry and Beyond. Part A. Stage Setting

We begin our tripartite Essay with a triangle of understanding, theory and simulation. Sketching the intimate tie between explanation and teaching, we also point to the emotional impact of understanding. As we trace the development of theory in chemistry, Dirac's characterization of what is known and what is needed for theoretical chemistry comes up, as does the role of prediction, and Thom's phrase “To predict is not to explain.” We give a typology of models, and then describe, no doubt inadequately, machine learning and neural networks. In the second part, we leave philosophy, beginning by describing Roald's being beaten by simulation. This leads us to artificial intelligence (AI), Searle's Chinese room, and Strevens’ account of what a go‐playing program knows. Back to our terrain—we ask “Quantum Chemistry, ? ca. 2020?” Then move to examples of AI affecting social matters, ranging from trivial to scary. We argue that moral decisions are hardly to be left to a computer. At this point, we try to pull the reader up, giving the opposing view of an optimistic, limitless future a voice. But we don't do justice to that view—how could we? We return to questioning the ascetic dimension of scientists, their romance with black boxes. Onward: In the 3rd part of this Essay, we work our way up from pessimism. We trace (another triangle!) the special interests of experimentalists, who want the theory we love, and reliable numbers as well. We detail in our own science instances where theory gave us real joy. Two more examples‐on magnetic coupling in inorganic diradicals, and the way to think about alkali metal halides, show us the way to integrate simulation with theory. Back and forth is how it should be—between painfully‐obtained, intriguing numbers, begging for interpretation, in turn requiring new concepts, new models, new theoretically grounded tools of computation. Through such iterations understanding is formed. As our tripartite Essay ends, we outline a future of consilience, with a role both for fact‐seekers, and searchers for understanding. Chemistry's streak of creation provides in that conjoined future a passage to art and to perceiving, as we argue we must, the sacred in science.