Experimental and Theoretical Approaches in the Study of Phenanthroline-Tetrahydroquinolines for Alzheimer's Disease

The imino-Diels-Alder reaction is one of the most common strategies in organic chemistry and is an important tool for providing a broad spectrum of biologically active heterocyclic systems. A combined theoretical and experimental study of the imino-Diels-Alder reaction is described. The new phenanthroline-tetrahydroquinolines were evaluated as cholinesterase inhibitors. Their cytotoxicity in human neuroblastoma SH-SY5Y cells was also evaluated. The theoretical results suggest that compounds formation in stages can be explained by endo cycloadducts under the established reaction conditions, thereby confirming experimental results obtained for percentage yield. These results allowed us to establish that pyridine substituent remarkably influences activation energy and reaction yield, as well as in acetylcholinesterase (AChE) activity. Among these derivatives, compounds with 4-pyridyl and 4-nitrophenyl showed favorable AChE activity and proved to be non-cytotoxic.     

有机酸取代基和溶剂效应的静电模型

本文根据气相实验结果和以往的静电理论, 建立了一个描述有机酸电离取代基和溶剂效应的静电模型。该模型不仅满足气相边界条件, 而且其参数B具有较明确的物理意义, 即与酸官能团的溶剂化半径以及取代基与溶剂分子之间特殊相互作用有关, 因而是描述溶质-溶剂相互作用的重要参数。     

Structure and Substituent Effects on Retention and Chiral Resolution of Ketones and Alcohols on Microcrystalline Cellulose Triacetate Plates

This paper reports a number of original thin layer chromatography enantioseparations of closely related ketones and alcohols such as tetralones, indanones, and benzhydrols carried out by elution with aqueous-alcoholic mixtures at different ratios. In order to investigate the structural and substituent effects on chiral recognition of microcrystalline cellulose triacetate, the results were compared with those obtained in previous papers for analogous compounds in similar experimental conditions. Even though the inclusion model of retention of analytes on this chiral stationary phase is confirmed, different and unexpected results were obtained for compounds having very favourable characteristics for resolution.     

Theoretical studies about the influence of different ring substituents on the nucleophilic ring opening of three-membered heterocycles and possible implications for the mechanisms of cysteine protease inhibitors

Epoxides, aziridines, and thiiranes are electrophilic building blocks that are widely used in synthetic organic chemistry. As a result of their reactivity against nucleophiles they are also used as electrophilic "warheads" for irreversible peptidic or peptidomimetic cysteine protease inhibitors. A general feature of these inhibitors is the remarkable higher inhibition potency of derivatives containing a free carboxylic acid in comparison to corresponding esters. In contrast, experimental investigations about the reaction of methyl thiolate with substituted epoxides revealed a contrary reactivity pattern. These studies also gave information about the regioselectivity of such reactions; however, mechanistic studies were not performed. By analyzing the computed energy profiles of the corresponding reactions we investigate the substituent effects (H vs ester vs carboxylic acid) on the kinetics and thermodynamics of the ring opening by the nucleophile methyl thiolate. Our model computations nicely explain experimental results concerning variations in the reactivities and the regioselectivities and indicate different reasons for the increased inhibition potency of three-membered heterocycles containing an acidic substituent. For aziridines an intramolecular water-mediated acid catalysis seems to be the main reason for the high activity of these inhibitors in acidic media. For epoxides and thiiranes this catalysis is not found, confirming the hypothesis that an ionic interaction between negatively charged carboxylate and the histidinium ion of the active site of the proteases mainly causes the high inhibitory activity of the acids compared to the esters.     

2(1H)-吡啶酮互变异构体系取代效应的理论计算

取代的2（1H）-吡啶酮团类化合物常具有诱人的生物活性[1，2]．由于其酮式和醇式结构的互变异构化性质，确定互变异构平衡体系中的优势结构及研究取代基对平衡体系的影响，对阐明该类化合物的构效关系有着重要的意义．实验发现2（1H）-吡啶酮的6-位H被取代后对其互变异构平衡有     

Synthesis,acid-base properties,and interphase distribution of new aminoalkylphosphates and -phosphonates

Using the Todd-Atherton reaction, we synthesized new ω-aminoalkylphosphates differing by location of phosphate amino group in the molecule. For these compounds and for α-, β-, and γ-amino-phosphonates of similar structure ionization constants of phosphate and phosphonate groups were determined which turned out to be similar. In all the cases the increase in basicity of amine centers was shown with the growing distance between them and the phosphorus-containing substituent. By the method of two-phase potentiometric titration the constants of partition between water and a series of organic solvents were measured. The data obtained are interpreted in the framework of additive Leo-Hansch model that allows estimation of the increments of phosphate and amidophosphate groups. These data can be applied to the study of biological activity and extraction properties of the compound of such class.     

几种芴衍生物(有机材料增感剂)的13C核磁共振研究

利用FX-60Q脉冲付里叶变换核磁共振波谱仪(磁场强度为14093高斯,观察频率为15.04MH_z)测定了四种劳衍生物的非去偶谱、偏共振谱和质子完全去偶谱。借助于偏共振技术、质子噪声(宽带)去偶、取代基化学位移加合规则以及模式化合物比较,确定了各峰的化学位移和一键、二键及三键偶合常数。实验结果表明,用化学位移和偶合常数的值除帮助识别各峰的归属外,还能推断未知化合物的碳键状态及取代基电负性的大小,对鉴别化合物结构可提供有用的线索。     

EFFECT OF HYPERCROSSLINKED RESINS SURFACE CHEMISTRY ON THE ADSORPTION OF PHENOL FROM AQUEOUS SOLUTION

Two hypercrosslinked resins with similar physical characters but different surface chemistry were synthesized and used to remove phenol from aqueous solutions. The FTIR spectra, elemental analysis and the Boehm titration were used to characterize the chemical properties of the resins. The adsorption experiments were carried out using the bottle-point technique, and the effects of the surface chemistry on the adsorption were discussed. The adsorption data fit well with the Freundlich model, indicating the heterogeneity of the resins surface. It could be seen from the experimental results that the adsorption capacity increased with the increase in the total surface concentration of oxygen-containing groups. The pH dependence and the effects of ionic strength were also discussed. The kinetic adsorption data fit well with the pseudo-second order model, and the results showed that the surface oxygen-containing groups have little effect on the adsorption rate.     

Study of solvent and substituent effects on organic acids. Part I. Consistency of a thermodynamic and an electrostatic model with experimental results of m-benzoic acid derivatives

Thermodynamic and electrostatic models relating to substituent and solvent effects on organic acids were evaluated. The two models were verified by means of experimental results of m-benzoic acid derivatives in water-DMSO solutions. Both the models are consistent with the experimental results in some mole fraction intervals.     

On the Additivity of Molecular Fragment Dipole Moments of 5‐Substituted Indole Derivatives

The estimate of the magnitude and the orientation of molecular electric dipole moments from the vector sum of bond or fragment dipole moments is a widely used approach in chemistry. However, the limitations of this intuitive model have rarely been tested experimentally, particularly for electronically excited states. Herein, we find rules for a number of indole derivatives by using rotationally resolved electronic Stark spectroscopy and ab initio calculations. Based on a natural‐bond‐orbital analysis, we discuss whether the vector additivity rule can be applied in a given electronic state. From a comparison of the experimental data with ab initio calculations, we deduced that the additivity model does not apply when the flow of electron density from the substituent is opposed to that inside the chromophore.     

Substituent cross-interaction effects on the electronic character of the C=N bridging group in substituted benzylidene anilines--models for molecular cores of mesogenic compounds. A 13C NMR study and comparison with theoretical results

13C NMR chemical shifts delta(C)(C=N) were measured in CDCl3 for a wide set of mesogenic molecule model compounds, viz. the substituted benzylidene anilines p-X-C6H4CH=NC6H4-p-Y (X = NO2, CN, CF3, F, Cl, H, Me, MeO, or NMe2; Y = NO2, CN, F, Cl, H, Me, MeO, or NMe2). The substituent dependence of delta(C)(C=N) was used as a tool to study electronic substituent effects on the azomethine unit. The benzylidene substituents X have a reverse effect on delta(C)(C=N): electron-withdrawing substituents cause shielding, while electron-donating ones behave oppositely, the inductive effects clearly predominating over the resonance effects. In contrast, the aniline substituents Y exert normal effects: electron-withdrawing substituents cause deshielding, while electron-donating ones cause shielding of the C=N carbon, the strengths of the inductive and resonance effects being closely similar. Additionally, the presence of a specific cross-interaction between X and Y could be verified. The electronic effects of the neighboring aromatic ring substituents systematically modify the sensitivity of the C=N group to the electronic effects of the benzylidene or aniline ring substituents. Electron-withdrawing substituents on the aniline ring decrease the sensitivity of delta(C)(C=N) to the substitution on the benzylidine ring, while electron-donating substituents have the opposite effect. In contrast, electron-withdrawing substituents on the benzylidene ring increase the sensitivity of delta(C)(C=N) to the substituent on the aniline ring, while electron-donating substituents act in the opposite way. These results can be rationalized in terms of the substituent-sensitive balance of the electron delocalization (mesomeric effects). The present NMR characteristics are discussed as regards the computational literature data. Valuable information has been obtained on the effects of the substituents on the molecular core of the mesogenic model compounds.     

溶剂效应和取代基效应对2-(2-氨基苯基)苯并噻唑光谱性质及激发态分子内质子转移的影响

合成了多种2-(2-氨基苯基)苯并噻唑(APBT)氨基氢原子被供电子及吸电子基团取代的衍生物, 并用紫外光谱﹑荧光光谱等方法和密度泛函理论(DFT)计算研究了溶剂效应和取代基效应对衍生物的光谱性质及激发态分子内质子转移(ESIPT)的影响规律. 结果表明, 相比于非极性溶剂环己烷, 随溶剂极性的增加及APBT-溶剂分子间氢键的形成, APBT的紫外-可见最大吸收峰和荧光最大发射峰均发生了一定程度的红移, 并对APBT的ESIPT产生了影响. 在APBT分子的氨基氮原子上引入不同的吸电子或斥电子取代基, 对氮原子的电荷性质有较大的影响. 在环己烷溶剂中, 甲基取代后的APBT仅有单重荧光发射峰, 体系未发生ESIPT过程; 而COCH₂Cl等吸电子基团能促进APBT的ESIPT, 其荧光发射光谱出现了明显的双重峰, 表明体系发生了激发态分子内质子转移反应. 量子化学的理论计算较好地验证了光谱实验结果.     

取代基效应定量研究新进展

综述了最近20多年有机化学取代基效应定量研究所取得的诸多新进展.主要内容包括：（1）电负性均衡原理得到普遍认同并用于计算分子中电荷分布和基团的诱导效应,分子电负性计算方法在几何平均法、调和平均法、加权平均法的基础上又提出了价电子均衡方法,进一步扩展了电负性均衡原理的应用范围.（2）试剂亲电、亲核能力的实验测定,提出了以二苯甲基正离子和醌甲基化合物等作为参考化合物的标定方法,其研究范围被扩展到气相条件、有机金属反应和自由基体系,得到一系列试剂的亲核参数N和亲电参数E.理论上提出亲电性指数和亲核性指数的概念及其定量计算公式,并对实验测定参数和理论计算指数之间的关系进行了深入研究.（3）极化效应参数从最初的经验方法,进而采用量子化学方法计算,再用统计方法提出了烷基极化效应指数PEI和基团极化效应参数PEIX,被广泛用于解释和估算有机化合物的气相酸碱性、电离能、生成焓、键能、反应速率、水溶解性和色谱保留值.（4）直接由取代苯的紫外光谱吸收能量计算得到的取代基激发态参数exCC,不同于取代基在分子处于基态的极性参数和自由基状态下的自旋离域效应参数,该参数用于对位二取代苯、取代二苯乙烯、二取代氮苄叉苯胺等多类有机化合物紫外光谱的定量相关,结果良好.（5）立体屏蔽效应的提出区分了传统的三种立体效应.在羰基与亲核试剂加成反应立体选择性定量表示,提出了立体选择性指数Ci;在表示基团对反应中心表面积屏蔽的定量提出了屏蔽参数SR,进一步基于反应中心体积被屏蔽的角度提出了拓扑立体效应指数TSEI,这些参数在分子内二面角、反应的立体选择性、烯烃和烷基苯的生成焓、咪唑离子液体的酸性以及烷烃与羟基自由基的反应速率等方面得到良好的应用.此外,论文还对有机化学取代基效应定量研究中值得进一步深入探索的领域和问题提出了建议和展望.     

Linear Free‐Energy Correlations for the Vinylheptafulvene Ring Closure: A Probe for Hammett σ Values

Linear free‐energy relationships, like Hammett correlations, are fundamental in physical organic chemistry for the elucidation of reaction mechanisms. In this work, we show that Hammett correlations exist for the ring closure of six different model systems of vinylheptafulvenes (VHFs) to their corresponding dihydroazulenes (DHAs). These first‐order reactions were easily followed by UV/Vis absorption spectroscopy on account of the significantly different absorption characteristics between VHFs and DHAs. Opposing effects displayed by substituent groups at two different positions are conveniently accounted for by simply subtracting the two Hammett σ values of each group. The linear correlations readily allow us to obtain unknown and approximate Hammett σ values for previously uninvestigated substituents. We also show that they can provide alternative values to the standard ones. We present values for a variety of substituent groups ranging from alkynes, sulfones, sulfoxides, and different heteroaromatics. The electronic effects exerted by substituent groups on VHFs are also reflected in their absorption maxima. Thus, we have established an empirical relationship between the absorption maximum of the VHF and the Hammett σ values of its substituents. This fine‐tuning of electronic properties is particularly important for the ongoing efforts of using the DHA/VHF molecular switch in molecular electronics devices.     

A substituent effects study reveals the kinetic pathway for an interfacial reaction

This paper describes the use of a substituent effects study to understand the mechanistic basis for an interfacial Diels-Alder reaction that does not proceed with standard second-order kinetics. Cyclopentadiene (Cp) undergoes a Diels-Alder reaction with a chemisorbed mercaptobenzoquinone to yield an immobilized Diels-Alder adduct. The pseudo-first-order rate constants are not linearly related to the concentration of diene, but they reach a limiting value with increasing concentrations of diene. The results of a substituent effects study support a mechanism wherein the electrochemical oxidation of hydroquinone produces two states of quinone. The first form, Q*, either reacts with Cp or isomerizes to Q, a form that is significantly less reactive with the diene. The interfacial reaction reaches a maximum rate when the concentration of diene is sufficiently high so that Q* undergoes complete Diels-Alder reaction and does not isomerize to Q. This work provides an example of the use of physical organic chemistry to understand an interfacial reaction.     

Investigation of the chromatographic regulation properties of benzyl groups attached to bridging nitrogen atoms in a calixtriazine‐bonded stationary phase

Two reversed‐phase/anion‐exchange mixed‐mode stationary phases for high‐performance liquid chromatography using calixtriazines as chromatographic ligands were investigated with Tanaka test solutes, monosubstituted benzenes, aromatic positional isomers, and inorganic anions. Calixtriazine as a chromatographic ligand has been reported previously, but the benzylated nitrogen‐bridged calixtriazine‐bonded silica gel reported in this study is new. The experimental data showed that the calixtriazine platform is a unique chromatographic selector because its multiple active sites are available for different solutes and its chromatographic selectivity could be tuned by introducing substituent on the bridging nitrogen atoms present in the calixtriazine matrix. The synergistic effects of aromatic rings, nitrogen atoms, benzyl groups, and tunable cavity in the host molecule influenced the separation selectivity by multiple retention mechanisms. Such hybrid stationary phases provide more versatility and have great potential in the analysis of complex samples. Moreover, the synthetic protocols presented herein may provide an alternative understanding on macrocyclic host–guest chemistry, leading to new and selective separation media.     

基础有机化学实验教学内容的改革探索

对基础有机化学实验的教学内容进行了全方位、系统化的改革探索。对传统有机化学实验内容,增加了新的知识和实验技术。将有机人名反应、优秀的科研成果改编成新的实验教学项目,同时增设了新的微型实验、绿色实验、原子经济反应实验、全英实验。该实验内容新体系经过多年的教学实践,教学效果有显著提高。     

Selective insertions of unsaturated organic molecules into the Ln-N or N-H bonds of biscyclopentadienyl lanthanide complexes

In this Perspective, selective N-H bond transformations of lanthanocene complexes are discussed. Recent efforts in this area from our laboratory have been devoted to development of new insertions and cyclizations of the anionic and neutral NH moieties of lanthanocene complexes into unsaturated substrates beyond the realm of the Ln-N bond, wherein various reactivity patterns of the N-H bond and the functional substituent effects are observed. The results demonstrate that the N-H moiety of organolanthanide complexes is an excellent platform for the in situ construction of new organic N-containing ligands in organolanthanide chemistry.