物理化学课程内容的编排顺序是物理化学教学中的核心问题之一,教指委发布的《化学类专业化学理论教学建议内容》对其并未明文规定,经典教材对此处理各有不同.经过对比和分析不同经典教材的编排顺序差别,可以看出物理化学的学科思维和认知规律是决定编排顺序的两大原则.依据学科思维从空间、时间、体系等3个维度为物理化学课程的核心内容画出逻辑关系图,并结合认知规律提出了多种编排内容的方式.

The multiple free radical scavenging reactions of flavonoids have been studied considering the gas, benzene, and water phases by applying density functional theory (DFT). Intramolecular hydrogen-bonds are found in all the most stable geometries of flavonoids and can reduce the antioxidant activity of hydroxyl groups, acting as hydrogen-bond donors (5−OH, 3−OH and 3’−OH), while enhancing the antioxidant activity of hydroxyl groups, acting as hydrogen-bond acceptors (4’−OH). In the gas and benzene phases, all of the flavonoids first prefer performing continuous di-hydrogen atom transfer (HAT) reaction from the B ring OH groups to trap two free radicals with the formation of stable quinones for ampelopsin, taxifolin, dihydro orobol and eriodictyol and benzodioxole for hesperetin. They would trap the third free radical via the HAT in the gas phase. In the benzene phase, ampelopsin also favours to apply HAT to trap the third free radical, and the other flavonoids would use the sequential proton loss electron transfer (SPLET) mechanism. In the water phase, the investigated flavonoids would first perform consecutive proton loss (PL) reactions from all of the OH groups with the formation of polyanions. The multiple PL reactions begin from the 7−OH group. The second PL reaction prefers performing in the OH groups on the B benzene ring due to the better delocalization of the negative charge via conjugation over the entire skeleton. The polyanions of the investigated flavonoids scavenge three free radicals via three consecutive ET reactions.

锗元素1886年被发现于德国,随后其性质成为元素周期律的重要证据之一.经过早期开发之后,锗元素在半导体领域找到了它的主要应用方向,并且一度成为核心元素之一.但在上世纪中叶之后,由于半导体元件需求量的激增和锗元素自身储量的匮乏,锗逐渐让位于硅.锗的发现和利用史有助于深入理解化学元素开发和利用的一般规律.

Theoretical and computational chemistry aims to develop chemical theory and to apply numerical computation and simulation to reveal the mechanism behind complex chemical phenomena via quantum theory and statistical mechanics. Computation is the third pillar of scientific research together with theory and experiment. Computation enables scientists to test, discover, and build models/theories of the corresponding chemical phenomena. Theoretical and computational chemistry has been advanced to a new era due to the development of high-performance computational facilities and artificial intelligence approaches. The tendency to merge electronic structural theory with quantum chemical dynamics and statistical mechanics is of increasing interest because of the rapid development of on-the-fly dynamic simulations for complex systems plus low-scaling electronic structural theory. Another challenging issue lies in the transition from order to disorder, from thermodynamics to dynamics, and from equilibrium to non-equilibrium. Despite an increasingly rapid emergence of advances in computational power, detailed criteria for databases, effective data sharing strategies, and deep learning workflows have yet to be developed. Here, we outline some challenges and limitations of the current artificial intelligence approaches with an outlook on the potential future directions for chemistry in the big data era.

拉瓦锡在化学革命中的地位近年来经历了被反思和重新评价.他对化学发展的历史贡献主要包括定量方法的全面引入、破除化学元素的玄学概念和奠定现代化学实验规范的基础等.但拉瓦锡依然延续了旧时代的一些错误和局限,导致他的化学理论并未完成彻底的化学革命.化学革命的一般叙事过于理想,实际上它应当被视为旧有范式和新生范式之间进行长期博弈和选择的结果.上述历程对今天的化学研究和教学具有很强的启示意义.

Mixtures of ionic liquids (ILs) and molecular solvents can overcome the drawbacks (high viscosity, high polarity, and high cost) of pure ILs and extend their practical use. The structural and interaction properties of ILs form the bases for understanding their properties. In this work, the structural properties of the mixtures of an IL, 1-(2'-hydroxylethyl)-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([C2OHMIM][Tf2N]), with chloroform, a molecular solvent of weak polarity, in various concentrations were analysed using Fourier transform infrared spectroscopy and density functional theory calculations. Excess spectra were used to analyse the infrared spectra. The IL forms a stable ion cluster-CDCl3 complex with CDCl3 in the concentration range investigated. In the ion cluster-CDCl3 complex, the hydrogen atom of CDCl3 forms hydrogen-bonds with the fluorine atoms of the anion. In addition, the chlorine atom of CDCl3 forms a halogen-bond with the oxygen atom of the anion. All the hydrogen and halogen-bonds identified between the [C2OHMIM][Tf2N] ion cluster and CDCl3 exhibit low strength, closed shells, and electrostatically dominant interactions.

Caffeic acid ester derivatives have been widely found in propolis extract and plants. In this work, the effect of ester groups with different aromatic and alkyl chains on the antioxidant activity of caffeic acid was performed on the double H+/e- process using DFT calculations. We found that 1) O3-H3⋯O4 intramolecular hydrogen-bonds exist in the catechol moiety of the investigated compounds, which have the same strength and are closed shell interactions, weak-strength and electrostatic in nature, making the 4-OH more favourable than 3-OH to trap free radicals. 2) In weak polarity phases, caffeic acid and its derivatives prefer to perform the double H+/e- processes via the dHAT mechanism. In the polar phases, the SdPLdET mechanism is more favoured. The first step of these mechanisms is more possible in 4-OH groups. 3) The ester group with different aromatic and alkyl chains would enhance the antioxidant capacities of caffeic acid.

Mixing ionic liquids (ILs) with molecular solvents can extend the practical applications of ILs and overcome the drawbacks of neat ILs. Knowledge on the structure and hydrogen-bond interaction properties of IL-molecular solvent mixtures is essential for chemical applications. In this work, the structure and hydrogen-bond features of N-alkyl-N-methyl-pyrrolidinium bis(trifluoromethylsulfonyl)imide ([CnMPyr][Tf2N], n = 3, 4, 6 and 8) and DMSO mixtures were studied using Fourier transform infrared spectroscopy (FTIR) and density functional theory (DFT) calculations. Excess infrared absorption spectroscopy and two-dimensional correlation spectroscopy (2D-COS) were employed to extract structural information on the mixtures from the C-D systematic stretching vibrational (νs(C-D)) region of the methyl groups in DMSO-d6. It was found that the mixing process of [CnMPyr][Tf2N] and DMSO is non-ideal and interaction complexes form between [CnMPyr][Tf2N] and DMSO-d6. They are ion cluster-DMSO-d6 complexes and ion pair-DMSO-d6 complexes. In the mixing processes, the species present in pure DMSO gradually decrease from DMSO dimer to DMSO monomer with an increase in ILs. Besides, the ion cluster-DMSO complexes gradually increase, while the ion pair-DMSO complexes decrease due to the strong electrostatic interaction between the cation and anion. In the ion cluster-DMSO complexes and ion pair-DMSO complexes, the ring hydrogen atoms of the methylene group directly attached to the nitrogen atom are the preferred interaction sites of the [CnMPyr]+ cations. All the hydrogen bonds in the identified complexes are closed-shell, electrostatically dominant and weak.

The asymmetric distribution of lipids in plasma membranes is closely related to the physiological functions of cells. To improve our previous approach in fabricating asymmetric vesicles, we defined a parameter, asymmetric degree, in this work and investigated the effects of vesicle size, incubation temperature, and lipid composition on the formation process of asymmetric phosphatidylserine (PS)-containing lipid vesicles. The results indicate that all of the three factors have marked but different effects on the time-dependent asymmetric degree of the vesicles as well as the flip and flop rate constants of the PS lipids. However, only vesicle size and PS content show significant influence on the maximal asymmetric degree of the vesicles, while the incubation temperature exhibits negligible effect. This work not only deepens our understanding on the packing property of PS molecules in self-assembled membranes and the formation mechanism of asymmetric vesicles but also practically provides a solution to regulate the asymmetric degree of the PS-containing vesicles using the established kinetic equation. In addition, the method would facilitate researches related to asymmetric vesicles or reconstruction of biological membranes.

We propose the concept of local acidity in condensed-phase chemistry in this work. The feature is demonstrated in trifluoroethanol (TFE) by employing two Fourier-transform infrared spectroscopy (FTIR) nitrile probes, acetonitrile (CH3CN) and benzonitrile (PhCN). Specifically, three positive excess peaks were found in the binary systems composed of TFE and a probe using excess spectroscopy. To characterize the local acidity quantitatively, we have tried to correlate the wavenumbers of the positive excess peaks of the probes and the pKa values in water of a series of XH-containing compounds (X = O, N, and C). Good linear relationships were discovered. Accordingly, three different pKa values of TFE were determined based on the three positive excess infrared peaks, which are attributed to the monomer, dimer, and trimer of TFE with the help of quantum-chemical calculations. The concept of local acidity and its quantitative evaluation enrich our knowledge of acid-base chemistry and will shed light on a better understanding of microstructures of solutions.

The mixtures of ionic liquid (IL) and acetonitrile (CH3CN) can be used as reaction media, supercapacitors and thermally stable electrolytes. The macroscopic properties of ILs-CH3CN mixtures have been extensively studied. However, some fundamental questions regarding the microscopic properties of ILs-CH3CN mixtures still remain to be answered. In this work, the structure properties and hydrogen-bond interactions of two task-specific ILs, i.e., 1-propylnitrile-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([PCNMIM][Tf2N]) and 1-(2'-hydroxylethyl)-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([C2OHMIM][Tf2N]), and CH3CN were studied using the combination of Fourier transform infrared spectroscopy (FTIR) and density functional theory (DFT) calculations. The aromatic C‒H stretching vibration region of the cation was an area of special focus. Excess infrared spectroscopy with enhanced resolution was applied to analyse the original infrared spectra. It is found that: (1) The two ILs form stable hydrogen-bonds with CH3CN. (2) Ion cluster, ion cluster-acetonitrile, and ion pair-acetonitrile are identified in the mixture. Acetonitrile cannot break apart the strong electronic interaction between the cation and anion in the examined concentration range. (3) The hydrogen-bonds are weak strength, closed shell and electrostatic dominant interactions. (4) The preferred interaction site of [PCNMIM]+ cation is the hydrogen atom at the C2 site, while that of [C2OHMIM]+ cation is the hydrogen atom in the hydroxyl group.

The reaction energetics of the multiple free radical scavenging mechanisms of ellagic acid and its derivatives were studied by DFT method. Ellagic acid and its derivatives that bear catechol or guaiacyl moieties can proceed multiple free radical scavenging processes. Intramolecular hydrogen-bonds were found in the most stable geometries of the investigated compounds and can influence the antioxidant activity of the related groups and hydrogen atom/proton loss sequence. The stronger hydrogen-bond, the weaker antioxidant activity of the hydrogen atom/proton-donating group. The preferred mechanisms vary among different phases. All of the investigated compounds prefer to trap free radicals by multiple HAT mechanisms in gas and benzene phases. The second HAT reaction preferably occurs in the same catechol or guaiacyl unit of the first HAT group with the formation of stable quinone or benzodioxole. The catechol and guaiacyl moieties not only retain high free radical scavenging ability of the parent compounds but even show increased potency for the second and fourth H+/e‒ reactions. In water phase, ellagic acid and its derivatives would proceed consecutively PL reactions from the OH groups. The formed di/tri/tetra-anion would proceed one/four electron transfers following with single/double SPLET mechanism and electron donation reactions until forming the stable quinone or benzodioxole.

Rooperol and its derivatives, derived from the Hypoxis rooperi plant, are polyphenolic and norlignan compounds with excellent antioxidant activities. The reaction enthalpies for the free-radical scavenging by rooperol and its six derivatives were studied using density functional theory. We found that the C-H groups played a significant role in the antioxidant activities in non-polar phases. In the gas and benzene phases, rooperol and its derivatives preferentially underwent the free-radical scavenging process via the 3‒CH group by following the hydrogen atom transfer (HAT) mechanism. In polar phases, the sequential proton loss electron transfer (SPLET) was the most preferred mechanism, and the phenolic O‒H groups played a significant role. Additionally, we found that when the hydrogen atom in the OH group was replaced by a glucose moiety, the antioxidant activity of the adjacent OH group was reduced. ROP, DHROP-I, DHROP-II, ROP-4″-G and ROP-4'G have catechol moiety, they may proceed double step-wise mechanisms to trap free radicals. In the gas and benzene phases, the preferable mechanism is dHAT. In water phase, it is SPLHAT.

Mixing ionic liquids (ILs) with a molecular cosolvent can largely reduce the high viscosities, high polarities, and high costs of ILs. The macroscopic properties of IL-cosolvent mixtures have been studied extensively. However, some fundamental questions regarding the microscopic properties of the binary mixtures still remain to be answered. In this work, the structural and hydrogen-bond features of binary systems containing 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM][BF4]) and methanol/ethanol were studied by using the combination of Fourier-transform infrared spectroscopy (FTIR) and density functional theory (DFT) calculations. Excess infrared absorption spectroscopy with enhanced spectral resolution was used to analyse the original IR spectra. The alcohol tetramer/larger multimers, alcohol trimer, anion-alcohol, ion pair-alcohol, and ion cluster-alcohol complexes were identified in the excess spectra. With the increasing [BMIM][BF4], the alcohol multimers gradually broke out from the larger multimers into smaller multimers. The hydrogen-bonded complex related with anion [BF4]- and alcohol gradually changes from anion-alcohol complex to ion pair-alcohol complex. The ion cluster-alcohol appears when the x(alcohol) is <0.50. The most stable optimized geometries of anion-alcohol, ion pair-alcohol, and ion cluster-alcohol were carefully analysed, and the hydrogen-bonds were identified. All of the hydrogen-bonds in these studied complexes had weak strength, closed shells and electrostatically dominant interactions.

写作课是美国诸多一流高校的唯一必修课,是通识教育的重要组成部分.在前期广泛调研国外写作课的基础上,作者之一通过参加普林斯顿大学写作项目的新教师培训,深入了解典型美国大学写作课的建设情况.文章借鉴国外高校的写作课程建设经验,结合我国高校的实际情况,提出了建设符合国情、 校情的写作课建设的建议.

In this work, the structure and interaction properties of the mixtures of a task specific ionic liquid (TSIL) 1-propylnitrile-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([PCNMIM][Tf2N]) and chloroform (CDCl3) were elucidated by Fourier transform infrared spectroscopy (FTIR) and density functional theory (DFT) calculations. Excess infrared spectroscopy was applied to analyse the original infrared spectra. The main conclusions are: (1) stable hydrogen-bonding complexes are found in the mixtures, and they are the primary cause of the gradual shift of v(CH) of the [PCNMIM]+ cation. The hydrogen-bonds related to the aromatic CH are strengthened, while those related to the alkyl CH are weakened by the addition of CDCl3. (2) A number of species in the binary mixtures were identified, namely, ion cluster–CDCl3, ion pair–CDCl3, ion pair and ion cluster. CDCl3 cannot break apart the strong electronic interaction between [PCNMIM]+ and [Tf2N]− but can break apart the ion cluster into ion pair throughout the investigated concentration range. (3) Several hydrogen-bonds are identified in the ion cluster–CDCl3, ion pair–CDCl3, ion pair and ion cluster complexes. They are weak strength, closed shell and electrostatic dominant interactions. In addition, the hydrogen atom at the C2 site of the [PCNMIM]+ cation is the preferred interaction site.

The structure and hydrogen-bond interaction property of water and a model ionic liquid (IL): 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM][BF4]) were studied using the combination of Fourier transform infrared spectroscopy (FTIR) and density functional theory (DFT) calculations. The O-D stretching vibration region of the deuterated water was an area of special focus. Excess infrared spectroscopy with enhanced resolution was applied to analyse the original infrared spectra of nu(O-D). It is found that: (1) [BMIM][BF4] forms stable hydrogen-bonds with water in the mixture. (2) The hydrogen-bonds are weak strength, closed shell and electrostatic dominant interactions. The preferred interaction site of [BMIM](+) cation is the hydrogen atom at the C2. (3) Cage hexamer water, cyclic tetramer water, cyclic trimer water, ion cluster-water complex, ion pair-water, and anion-water complexes are identified in the mixture. When the mole fraction of D2O(x(D2O)) is larger than 0.9, ion cluster and ion pair were broken apart into individual cations and anions. The cage hexamer water, cyclic tetramer water, and cyclic trimer water disappear at x(D2O) < 0.8, 0.5, and 0.3, respectively. HDO formed by H/D isotope exchange was detected when x(D2O) is less than 0.3. (C) 2019 Elsevier B.V. All rights reserved.

Flavonoids widely found in natural foods are excellent free radical scavengers. The relationship between the substituent and antioxidative activity of flavonoids has not yet been completely elucidated. In this work, the antioxidative activity of apigenin derivatives with different substituents at the C3 position was determined by density functional theory (DFT) calculations. The bond dissociation enthalpy (BDE), ionization potential (IP), and proton affinity (PA) were calculated. Donator acceptor map (DAM) analysis illustrated that the studied compounds are worse electron acceptors than F and also are not better electron donors than Na. The strongest antioxidative group of apigenin derivatives was the same as apigenin. Excellent correlations were found between the BDE/IP/PA and Hammett sigma constants. Therefore, Hammett sigma constants can be used to predict the antioxidative activity of substituted apigenin and to design new antioxidants based on flavonoids. In non-polar phases, the antioxidative activity of apigenin was increased by the electron-withdrawing groups, while it was reduced by the electron-donating groups. Contrary results occurred in the polar phase. The electronic effect of the substituents on BDE(4′-OH), BDE(5-OH), PA(4′-OH), and IP is mainly controlled by the resonance effect, while that on BDE(7-OH), PA(5-OH), and PA(7-OH) is governed by the field/inductive effect.

Only a small amount of peptide bonds exists in the cis conformation, however, they play an important role in the functioning of proteins. Herein, 2-pyrrolidinone (C4H7NO) was used as a cis-proline analog to study the hydrogen bonds between cis-proline and different solvents (CCl4, DMSO, and H2O). Interestingly, with the addition of solvents, the hydrogen-bonding interactions that involved NH in the C4H7NO–CCl4 system are strengthened, while those in the C4H7NO–DMSO system are weakened, which is beyond our imagination. Combined with quantum chemical calculation and excess spectra, we find that it is due to the existence of the C4H7NO doubly hydrogen-bonded dimer, which is the most stable structure in the self-aggregation. During the dilution process, CCl4 hardly breaks double hydrogen bonds, DMSO only weakens the strong hydrogen bonds, and water thoroughly breaks the double hydrogen bonds. Several complexes, such as, doubly/singly hydrogen-bonded dimers, oligomers, monomers and their complexes with solvents, are identified in those three systems, which allow the dynamic changes in the solution structures of mixtures can be obtained. In addition, the band of singly hydrogen-bonded dimers is observed for the first time, thus reflecting the superiority of the excess spectra in improving the resolution. The findings of this work provide precious structural information on C4H7NO–solvents systems, reveal the effects of the solvents on cis-proline, and may inspire the understanding of the cis-proline and some biochemical processes.

Flavonoids widely found in natural foods are characterized by acting as antioxidants compounds. There are close relationship between the antiradical activities and structural properties of flavonoids. In this work, density functional theory (DFT) methods were applied to investigate the influence of the H5⋯OC4 intramolecular hydrogen-bond (IHB) on the antiradical activity of flavonoid based on three prevalently accepted radical scavenging mechanisms: hydrogen atom transfer (HAT), single electron transfer-proton transfer (SET-PT) and sequential proton-loss electron-transfer (SPLET). The thermodynamic properties: bond dissociation enthalpy (BDE), ionization potential (IP), proton dissociation enthalpy (PDE), proton affinity (PA) and electron transfer enthalpy (ETE) related with these mechanisms were calculated to elucidate the antiradical activity. The results showed that the 5−OH group is most influenced and its antiradical capacity was weakened by the H5⋯OC4 IHB. In the gas, benzene and chloroform phases, H5⋯OC4 IHB would reduce the antiradical activity of flavonoid via increasing the bond dissociation enthalpy. While, in the DMSO and H2O phases, the opposite result occurs by lowering the proton affinity.